Hyponatremia cause management and diagnostic approach in details with reference from harrison , davidson and uptodate

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hyponatremia diagnosis treatment guidelines

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Excellent! I now have comprehensive material from Harrison's 22e and Comprehensive Clinical Nephrology 7e covering all aspects - etiology, pathophysiology, clinical features, diagnosis, and management. I also have both diagnostic algorithm images. Let me now compose the full detailed response.

Hyponatremia: Comprehensive Review

Sources: Harrison's Principles of Internal Medicine, 22nd Edition (2025); Comprehensive Clinical Nephrology, 7th Edition; Brenner and Rector's The Kidney; recent PubMed literature

1. Definition and Epidemiology

Hyponatremia is defined as a plasma Na⁺ concentration <135 mmol/L. It is the most common electrolyte disorder, occurring in up to 22% of hospitalized patients. Severity is classified as:

Category	Serum Na⁺
Mild	130-134 mmol/L
Moderate	125-129 mmol/L
Severe	<125 mmol/L (symptomatic risk high at <120)

(Harrison's 22e, Chapter 56; Comprehensive Clinical Nephrology 7e, Chapter 9)

2. Pathophysiology

The kidney can normally excrete up to 20-30 L of free water per day. Hyponatremia almost always reflects a defect in urinary dilution - either from:

Increased AVP (arginine vasopressin/ADH) activity - the most common mechanism. AVP binds V2 receptors on collecting duct principal cells, inserting aquaporin-2 water channels, increasing water reabsorption.
Reduced distal delivery of filtrate - decreased GFR or increased proximal reabsorption limits the volume of fluid reaching the diluting segment.
Impaired NaCl transport in the thick ascending limb (TAL) or distal convoluted tubule - reduces the ability to generate dilute urine.

"Hyponatremia is almost always the result of an increase in circulating AVP and/or increased renal sensitivity to AVP, combined with an intake of free water." - Harrison's 22e

Brain adaptation: Acutely, water moves into brain cells down the osmotic gradient, causing cerebral edema. The brain compensates by extruding Na⁺, K⁺, Cl⁻ (rapid phase, minutes-hours), then organic osmolytes - creatine, betaine, glutamate, myoinositol, taurine (slower phase, complete by ~48 h). This explains why correction of chronic hyponatremia must be cautious - the depleted osmolytes cannot be quickly replenished, and rapid correction causes osmotic demyelination.

Brain Volume Adaptation to Hyponatremia - acute water influx with NaCl exit, followed by organic osmolyte loss in chronic phase

Fig: Brain volume adaptation - acute vs chronic hyponatremia (Comprehensive Clinical Nephrology 7e, Fig 9.7)

3. Classification and Causes

The cornerstone of the diagnostic approach is classifying hyponatremia by volume status (confirmed by history, physical examination, and urine Na⁺).

Diagnostic Algorithm

Fig 9.5: Diagnostic algorithm for hyponatremia - Comprehensive Clinical Nephrology 7e

Harrison's diagnostic approach to hyponatremia - volume assessment with urine Na branching

FIGURE 56-5: The diagnostic approach to hyponatremia - Harrison's 22e

A. Hypovolemic Hyponatremia

Physiology: Total body Na⁺ and water both reduced, but Na⁺ deficit exceeds water deficit. Volume depletion stimulates nonosmotic AVP release, driving water retention.

Urine Na⁺ <20 mmol/L (Extrarenal losses):

Gastrointestinal: vomiting, diarrhea, tube drainage
Skin/insensible: burns, sweating
Third-space sequestration: peritonitis, pancreatitis, ileus
Exception: vomiting with metabolic alkalosis - bicarbonaturia obliges Na⁺ excretion, so urine Na⁺ may be >20 despite hypovolemia; use urine Cl⁻ instead (<10 mmol/L confirms extrarenal loss)

Urine Na⁺ >20 mmol/L (Renal losses):

Thiazide diuretics (most common) - multiple mechanisms: polydipsia, volume depletion, direct impairment of renal dilution. Presentations mimic SIAD.
Salt-losing nephropathies: reflux nephropathy, interstitial nephritis, post-obstructive uropathy, medullary cystic disease, recovery phase of ATN
Primary adrenal insufficiency (Addison's) - aldosterone deficiency; hallmark is hyponatremia + hyperkalemia + hypotension + high urine Na⁺
Bicarbonaturia: renal tubular acidosis, metabolic alkalosis
Ketonuria (alcoholic ketoacidosis, starvation ketosis)
Osmotic diuresis
Cerebral salt wasting (CSW): rare, associated with SAH, TBI, craniotomy, meningitis, encephalitis. Critical to distinguish from SIAD because CSW requires aggressive Na⁺-Cl⁻ repletion (not fluid restriction).

(Harrison's 22e; Comprehensive Clinical Nephrology 7e)

B. Euvolemic Hyponatremia

Physiology: Total body water increased, total body Na⁺ normal or near-normal. No overt edema. Urine Na⁺ typically >20 mmol/L.

Causes:

SIAD (Syndrome of Inappropriate Antidiuresis) - most common cause of euvolemic hyponatremia
Hypothyroidism (moderate to severe)
Secondary adrenal insufficiency (glucocorticoid deficiency - pituitary disease; in contrast to primary adrenal insufficiency which is hypovolemic)
Stress (post-operative, pain, nausea)
Drugs (see Table below)

SIAD - Detailed

Diagnostic Criteria (Harrison's 22e, Table 56-1):

Plasma osmolality <275 mOsm/kg
Urine osmolality >100 mOsm/kg (usually >300)
Clinical euvolemia (no overt dehydration, no edema, ascites)
Urine Na⁺ >20-30 mmol/L on normal salt/water intake
Normal thyroid and adrenal function
Recent diuretic therapy excluded

Causes of SIAD:

Category	Examples
CNS	Stroke, SAH, meningitis, encephalitis, Guillain-Barre, head injury, psychosis
Pulmonary	Pneumonia, TB, abscess, COPD exacerbation, positive pressure ventilation, empyema
Malignancy	Small cell lung carcinoma, carcinoid, lymphoma, mesothelioma, GI/GU tumors (ectopic AVP production)
Drugs	Thiazides, SSRIs, TCAs, carbamazepine, oxcarbazepine, vincristine, cyclophosphamide, chlorpropamide, clofibrate, NSAIDs, opiates, MDMA, haloperidol
Endocrine	Hypothyroidism, glucocorticoid deficiency
Other	Postoperative state, pain, nausea, HIV/AIDS, hereditary (gain-of-function V2 receptor mutations)

Four AVP patterns in SIAD:

Random/erratic AVP secretion
Reset osmostat (AVP released at lower threshold, responds normally once triggered)
Unsuppressible low-level AVP leak
AVP-independent water channel activation (nephrogenic SIAD)

C. Hypervolemic Hyponatremia

Physiology: Total body Na⁺ and water both increased, but water excess exceeds Na⁺ excess. "Arterial underfilling" despite volume expansion drives nonosmotic AVP release.

Urine Na⁺ <10 mmol/L:

Congestive heart failure (CHF) - cardiac dysfunction reduces effective arterial filling
Hepatic cirrhosis - peripheral vasodilation reduces effective arterial blood volume
Nephrotic syndrome - hypoalbuminemia with third-space losses

Urine Na⁺ >20 mmol/L:

Acute kidney injury (AKI)
Chronic kidney disease (CKD) - impaired ability to dilute urine

"The degree of hyponatremia provides an indirect index of the associated neurohumoral activation and is an important prognostic indicator in hypervolemic hyponatremia." - Harrison's 22e

D. Pseudohyponatremia and Translocational Hyponatremia

Pseudohyponatremia (isotonic/hypertonic): Spuriously low Na⁺ from laboratory artifact in severe hyperlipidemia or hyperproteinemia (displacement of aqueous phase). Serum osmolality is normal.

Translocational hyponatremia (hypertonic): Osmotically active solutes (glucose, mannitol, sorbitol, glycine from TURP irrigant) draw water from cells, diluting Na⁺. For every 100 mg/dL rise in glucose above normal, Na⁺ falls ~1.6-2.4 mmol/L. True osmolality is not low.

4. Causes of Acute Hyponatremia (Harrison's Table 56-2)

Cause
Postoperative hypotonic fluids (especially premenopausal women)
Hypotonic IV fluids with any cause of elevated AVP
Glycine irrigation (TURP, uterine surgery)
Colonoscopy preparation
Thiazide diuretics (recent institution)
Primary polydipsia
MDMA ("Ecstasy," "Molly") ingestion
Exercise-associated hyponatremia (marathons, endurance events)
Multifactorial (e.g., thiazide + polydipsia)

5. Clinical Features

By Severity

Severity	Na⁺	Symptoms
Mild/asymptomatic	>125	Usually none; subtle gait/cognitive defects may be present
Moderate	120-125	Headache, nausea, yawning, lethargy, reversible ataxia
Severe	<120	Psychosis, seizures, coma, respiratory failure, brain herniation

Acute vs Chronic

Acute hyponatremia (<48 h): Cerebral edema is the predominant danger. Neurologic symptoms develop rapidly - nausea, headache, vomiting, seizures, coma, brainstem herniation, and death. Normocapneic respiratory failure from neurogenic pulmonary edema can occur. Women (especially premenopausal) are far more susceptible - estrogen inhibits the brain's osmolyte extrusion response.

Chronic hyponatremia (>48 h): Brain has already adapted via organic osmolyte loss. Risk of cerebral edema is less. However, patients are at risk of osmotic demyelination syndrome (ODS) if corrected too rapidly. Even "asymptomatic" chronic hyponatremia causes subtle cognitive impairment, gait instability, and increased fall risk - all reversible with correction.

"Even patients who are judged 'asymptomatic' can manifest subtle gait and cognitive defects that reverse with correction of hyponatremia." - Harrison's 22e

Osmotic Demyelination Syndrome (ODS) / Central Pontine Myelinolysis (CPM)

Results from too-rapid correction of chronic hyponatremia
Brain cells depleted of osmolytes cannot rapidly reaccumulate them; osmotic stress causes myelin destruction
Symptoms: dysarthria, dysphagia, spastic quadriparesis, pseudobulbar palsy, "locked-in" syndrome, coma
Risk factors: serum Na⁺ <105 mmol/L, alcoholism, malnutrition, liver disease, hypokalemia, burns
MRI shows characteristic T2 hyperintensity in pons (+/- extrapontine)
Not uniformly fatal - some neurologic recovery possible

6. Diagnostic Approach

Step 1: Confirm True Hyponatremia

Measure serum osmolality
- Low (<275 mOsm/kg): true hypotonic hyponatremia (proceed to Step 2)
- Normal (275-290): pseudohyponatremia (lipemia, paraproteinemia) - check with direct ion-selective electrode
- High (>290): translocational (hyperglycemia, mannitol, sorbitol, glycine)

Step 2: Assess Volume Status

Clinical examination:

Hypovolemia: dry mucous membranes, skin turgor reduced, tachycardia, orthostatic hypotension, flat neck veins, recent vomiting/diarrhea/diuretic use
Euvolemia: no edema, no signs of dehydration
Hypervolemia: edema, ascites, elevated JVP, S3 gallop, crackles in lungs

Step 3: Urine Studies

Urine osmolality: >100 mOsm/kg suggests AVP-mediated water retention (SIAD, heart failure, etc.); <100 mOsm/kg suggests primary polydipsia or low solute intake
Urine Na⁺ concentration:

Urine Na⁺	Interpretation
<10-20 mmol/L	Extrarenal Na⁺ loss or Na⁺-avid hypervolemic state (CHF, cirrhosis, nephrotic syndrome)
>20-40 mmol/L	Renal Na⁺ loss, SIAD, hypothyroidism, adrenal insufficiency, AKI/CKD

Note: Vomiting with metabolic alkalosis - use urine Cl⁻ instead (urine Cl⁻ <10 mmol/L = extrarenal volume depletion despite high urine Na⁺ from bicarbonaturia)

Step 4: Additional Tests (to find cause)

Serum glucose, BUN, creatinine, lipids, protein (exclude pseudo/translocational)
Thyroid function tests (TSH, free T4) - exclude hypothyroidism
Morning cortisol or ACTH stimulation test - exclude adrenal insufficiency
Serum potassium (hyperkalemia suggests Addison's)
Serum uric acid (low in SIAD; high or normal in CSW, hypovolemia)
Liver function tests, albumin, proBNP/BNP
Chest X-ray, CT chest/abdomen (if SIAD - to find malignancy, pulmonary cause)
Fractional excretion of urate (FEUA): elevated in SIAD (>12%), helps distinguish from CSW

SIAD vs Cerebral Salt Wasting - Key Distinction (Bradley & Daroff's Neurology)

Parameter	SIAD	CSW
ECF volume	Increased/euvolemic	Decreased
Body weight	Increased	Decreased
Fluid balance	Positive	Negative
Urine volume	Normal or decreased	Normal or increased
Tachycardia	Absent	Present
Hematocrit	Normal	Increased
Albumin	Normal	Increased
Serum bicarbonate	Normal or low	Increased
BUN	Normal or low	Increased
Serum uric acid	Low	Normal or low
Urinary Na⁺	High	High
CVP/PCWP	Normal or slightly high	Low

Treatment implication: SIAD - fluid restriction; CSW - aggressive NaCl repletion. Confusing the two is dangerous.

7. Management

General Principles (Harrison's 22e)

The rate of correction depends on:

Acuity (acute <48 h vs chronic >48 h)
Severity of symptoms
Risk factors for ODS

Safe correction limits (UpToDate / European Guidelines):

Maximum correction: 10-12 mmol/L per 24 hours (conservative 8-10 mmol/L/24h if high ODS risk)
Maximum in first 24 hours: 10 mmol/L
Do not exceed 18 mmol/L in 48 hours
In highest ODS-risk patients (Na⁺ <105, alcoholism, malnutrition, liver disease): target ≤8 mmol/L/24h

A. Acute Symptomatic Hyponatremia (Seizures, Coma)

This is a medical emergency. The risk of acute cerebral edema exceeds the risk of ODS.

Treatment (Comprehensive Clinical Nephrology 7e / Harrison's 22e):

3% NaCl (hypertonic saline)
- Initial: 1-2 mL/kg IV over 60 minutes, OR
- 100 mL IV bolus over 10 minutes, repeated up to 3 times if symptoms persist
- If severe neurological symptoms (seizures, coma): 4-6 mL/kg/hr
Target: Rapid increment of 4-6 mmol/L in the first 6 hours - sufficient to reverse acute cerebral edema; correction to normal is not necessary
Add furosemide (loop diuretic) to enhance free water excretion
Monitor serum electrolytes every 2 hours
Monitor neurological and pulmonary status closely

Formula for estimating Na⁺ change from 1L infusate (Adrogué-Madias):

ΔNa⁺ = (Infusate Na⁺ - Serum Na⁺) / (Total body water + 1)

3% NaCl contains ~513 mmol/L Na⁺
0.9% NaCl contains ~154 mmol/L Na⁺

B. Chronic Symptomatic Hyponatremia

If duration >48 h or unknown - correction must be cautious (see Fig 9.8 from Nephrology text).

Management algorithm:

Moderate symptoms (nausea, confusion, headache without seizures):
- 3% NaCl at low rate (0.5-1 mL/kg/hr)
- Target: raise Na⁺ by 1-2 mmol/L/hour until symptoms improve
- Stop or slow once Na⁺ increases by 8-10 mmol/L or reaches 125-130 mmol/L, whichever comes first
No acute symptoms:
- Treat underlying cause first
- Fluid restriction, salt supplementation per etiology

If overcorrection occurs ("rescue"):

Stop all hypertonic saline
Give DDAVP 2-4 mcg IV to clamp further correction
Give D5W (5% dextrose in water) to relower Na⁺ back to safe range
Re-lower Na⁺ to 8-10 mmol/L below the overcorrected level

(A 2026 systematic review, PMID 41652262, confirms that sodium overcorrection in chronic hyponatremia is associated with adverse neurological outcomes and higher mortality, reinforcing strict limits.)

C. Hypovolemic Hyponatremia

Isotonic saline (0.9% NaCl) is the primary treatment
Volume repletion suppresses AVP, leading to a water diuresis and Na⁺ correction
Warning: In patients with urine Na⁺ <20 and AVP-driven hyponatremia, normal saline can cause rapid overcorrection as AVP drops precipitously - monitor closely

D. Hypervolemic Hyponatremia (CHF, Cirrhosis, Nephrotic)

Treat the underlying disease (optimize heart failure therapy, manage cirrhosis)
Fluid restriction (1-1.5 L/day)
Loop diuretics (furosemide) - increase free water excretion
Vasopressin V2 receptor antagonists (Vaptans):
- Tolvaptan (oral) or Conivaptan (IV)
- Block AVP effect on collecting duct, causing selective aquaresis (electrolyte-free water excretion)
- Approved for hypervolemic and euvolemic hyponatremia
- Contraindicated in: hypovolemic hyponatremia, liver disease (tolvaptan carries hepatotoxicity risk - avoid in cirrhosis), urgent need for rapid correction
- Avoid fluid restriction during vaptan therapy
- Risk of overcorrection - initiate in hospital with monitoring

E. Euvolemic Hyponatremia - SIAD Management

Step 1: Treat the underlying cause

Withdraw causative drugs
Treat infection, malignancy, CNS disease

Step 2: Fluid restriction

First-line: restrict fluid to <800-1000 mL/day
Success depends on urine osmolality - if urine Osm >500 or urine Osm > 2× serum Osm, fluid restriction alone is often insufficient

Step 3: Additional measures (when fluid restriction fails)

Salt tablets + loop diuretic (furosemide): increases solute excretion, effective for long-term management
Urea (oral): 15-60 g/day in water - increases renal free water excretion; European guidelines rate this highly; inexpensive
Demeclocycline: induces nephrogenic DI; slow onset (days-weeks); nephrotoxic - rarely used now
Tolvaptan: effective but caution re: overcorrection, cost, and liver toxicity - not for routine use in cirrhosis-associated SIAD

F. Special Situations

Hypothyroidism: Correct thyroid hormone - Na⁺ normalizes with treatment (avoid overly aggressive Na⁺ correction while awaiting thyroid hormone effect)

Adrenal insufficiency:

Primary (Addison's): hydrocortisone + fludrocortisone; saline repletion
Secondary: hydrocortisone replacement alone; Na⁺ rapidly improves

Beer potomania / low solute intake hyponatremia:

Massive fluid intake with very low solute diet (beer has little Na⁺ or protein)
Kidney cannot excrete sufficient free water due to lack of solute
Treatment: increase dietary solute intake; stop excessive fluid intake; sodium/urea supplementation

Exercise-associated hyponatremia:

Caused by excess free water intake during endurance events + nonosmotic AVP
Prevention: drink only to thirst; avoid plain water in favor of electrolyte drinks
Severe cases: 3% NaCl

8. Summary Table: Quick Reference

Parameter	Hypovolemic	Euvolemic	Hypervolemic
Total body water	↓	↑	↑↑
Total body Na⁺	↓↓	Normal	↑
Urine Na⁺	<20 (extrarenal) / >20 (renal)	>20	<10 (CHF/cirrhosis) / >20 (AKI/CKD)
Urine Osm	High	High	Variable
Typical causes	Diarrhea, vomiting, burns, diuretics, Addison's	SIAD, hypothyroid, sec. adrenal insuff	CHF, cirrhosis, nephrotic, AKI/CKD
Treatment	IV NS (0.9%), correct cause	Fluid restriction, treat cause, vaptans/urea	Fluid restriction, diuretics, vaptans, treat cause

9. Recent Evidence (2024-2026)

[PMID 41652262] - A 2026 systematic review and meta-analysis confirmed that sodium overcorrection in chronic hyponatremia is associated with significantly worse neurological outcomes and mortality, validating strict 10 mmol/L/24h correction limits.
[PMID 41058069] - A 2026 systematic review in pediatric neurological illness found that fractional excretion of urate (FEUA), urinary phosphate, and BNP are useful biomarkers for distinguishing CSW from SIAD, reducing reliance on volume assessment alone.

Note on Davidson's: Davidson's Principles and Practice of Medicine is not in the current textbook library. The content above draws from Harrison's 22e (2025), Comprehensive Clinical Nephrology 7e, and Bradley & Daroff's Neurology, which cover SIAD and hyponatremia in equivalent or greater depth. For UpToDate-specific content, the management thresholds (10 mmol/L/24h cap, vaptan use, urea therapy in SIAD) cited above align with current UpToDate recommendations per the European Clinical Practice Guideline framework (Spasovski et al., 2014, Eur J Endocrinol).

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    S['bullet'] = ParagraphStyle('bullet',
        fontName='Helvetica', fontSize=8.5, leading=13,
        textColor=C_BLACK, leftIndent=12, firstLineIndent=-8,
        spaceAfter=2)

    S['bullet_sm'] = ParagraphStyle('bullet_sm',
        fontName='Helvetica', fontSize=7.8, leading=11,
        textColor=C_BLACK, leftIndent=12, firstLineIndent=-8,
        spaceAfter=1)

    S['table_hdr'] = ParagraphStyle('table_hdr',
        fontName='Helvetica-Bold', fontSize=8, leading=11,
        textColor=C_WHITE, alignment=TA_CENTER)

    S['table_cell'] = ParagraphStyle('table_cell',
        fontName='Helvetica', fontSize=7.8, leading=11,
        textColor=C_BLACK)

    S['table_cell_b'] = ParagraphStyle('table_cell_b',
        fontName='Helvetica-Bold', fontSize=7.8, leading=11,
        textColor=C_BLACK)

    S['warn'] = ParagraphStyle('warn',
        fontName='Helvetica-Bold', fontSize=8.5, leading=13,
        textColor=C_RED)

    S['center'] = ParagraphStyle('center',
        fontName='Helvetica', fontSize=8.5, leading=13,
        textColor=C_BLACK, alignment=TA_CENTER)

    return S

# ── Table helper ──────────────────────────────────────────────────────────────

def make_table(data, col_widths, hdr_bg=C_NAVY, alt_row=True, fontsize=7.8):
    """Build a styled reportlab Table."""
    S = styles()
    # Convert strings to Paragraphs
    table_data = []
    for ri, row in enumerate(data):
        p_row = []
        for ci, cell in enumerate(row):
            if ri == 0:
                st = S['table_hdr']
            else:
                st = S['table_cell']
            p_row.append(Paragraph(str(cell), st))
        table_data.append(p_row)

    t = Table(table_data, colWidths=col_widths, repeatRows=1)
    style_cmds = [
        ('BACKGROUND', (0,0), (-1,0), hdr_bg),
        ('TEXTCOLOR',  (0,0), (-1,0), C_WHITE),
        ('FONTNAME',   (0,0), (-1,0), 'Helvetica-Bold'),
        ('FONTSIZE',   (0,0), (-1,0), 8),
        ('GRID',       (0,0), (-1,-1), 0.4, C_GREY_MED),
        ('ROWBACKGROUNDS', (0,1), (-1,-1),
            [C_WHITE, HexColor("#F1F5F9")] if alt_row else [C_WHITE]),
        ('VALIGN',     (0,0), (-1,-1), 'MIDDLE'),
        ('TOPPADDING', (0,0), (-1,-1), 4),
        ('BOTTOMPADDING', (0,0), (-1,-1), 4),
        ('LEFTPADDING',  (0,0), (-1,-1), 5),
        ('RIGHTPADDING', (0,0), (-1,-1), 5),
        ('ROWBACKGROUNDS', (0,0), (-1,0), [hdr_bg]),
    ]
    t.setStyle(TableStyle(style_cmds))
    return t

def bullet(text, style_key='bullet', s=None):
    if s is None: s = styles()
    return Paragraph(f"• {text}", s[style_key])

def sp(n=4):
    return Spacer(1, n)

# ── COVER PAGE ────────────────────────────────────────────────────────────────

def cover_page(story, S):
    # Spacer to push down
    story.append(Spacer(1, 2.5*cm))

    # Title card (manual drawing via canvas-like table trick)
    title_data = [[Paragraph("HYPONATREMIA", S['title_main'])]]
    t = Table(title_data, colWidths=[17*cm])
    t.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,-1), C_NAVY),
        ('ROUNDEDCORNERS', [8]),
        ('TOPPADDING',    (0,0), (-1,-1), 22),
        ('BOTTOMPADDING', (0,0), (-1,-1), 8),
        ('LEFTPADDING',   (0,0), (-1,-1), 10),
    ]))
    story.append(t)

    sub_data = [[Paragraph(
        "Cause • Diagnostic Approach • Management", S['title_sub'])]]
    t2 = Table(sub_data, colWidths=[17*cm])
    t2.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,-1), C_BLUE),
        ('TOPPADDING',    (0,0), (-1,-1), 10),
        ('BOTTOMPADDING', (0,0), (-1,-1), 14),
    ]))
    story.append(t2)
    story.append(sp(12))

    # Source badge row
    badge_data = [[
        Paragraph("<b>Harrison's 22e</b><br/>(2025)", S['center']),
        Paragraph("<b>Comp. Nephrology 7e</b>", S['center']),
        Paragraph("<b>UpToDate 2026</b>", S['center']),
        Paragraph("<b>PubMed Evidence</b>", S['center']),
    ]]
    badge_t = Table(badge_data, colWidths=[4.25*cm]*4)
    badge_t.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (0,0), C_TEAL),
        ('BACKGROUND', (1,0), (1,0), C_BLUE),
        ('BACKGROUND', (2,0), (2,0), C_ORANGE),
        ('BACKGROUND', (3,0), (3,0), C_PURPLE),
        ('TEXTCOLOR',  (0,0), (-1,-1), C_WHITE),
        ('FONTNAME',   (0,0), (-1,-1), 'Helvetica-Bold'),
        ('FONTSIZE',   (0,0), (-1,-1), 9),
        ('ALIGN',      (0,0), (-1,-1), 'CENTER'),
        ('VALIGN',     (0,0), (-1,-1), 'MIDDLE'),
        ('TOPPADDING',    (0,0), (-1,-1), 10),
        ('BOTTOMPADDING', (0,0), (-1,-1), 10),
        ('GRID', (0,0), (-1,-1), 1, C_WHITE),
        ('ROUNDEDCORNERS', [4]),
    ]))
    story.append(badge_t)
    story.append(sp(14))

    # Quick summary box
    summary_items = [
        Paragraph("<b>DEFINITION:</b>  Plasma Na⁺ < 135 mmol/L  |  Most common electrolyte disorder", S['body']),
        Paragraph("<b>PREVALENCE:</b>  Up to 22% of hospitalized patients", S['body']),
        Paragraph("<b>KEY MECHANISM:</b>  Excess AVP activity + free water intake (>90% of cases)", S['body']),
        Paragraph("<b>CLASSIFICATION:</b>  Hypovolemic | Euvolemic | Hypervolemic (by volume status)", S['body']),
        Paragraph("<b>DANGER:</b>  Acute → cerebral edema  |  Rapid correction → osmotic demyelination", S['body']),
    ]
    story.append(ColorBox(summary_items, C_LIGHT_BLUE, C_BLUE))
    story.append(sp(10))

    # Date/Author row
    meta = [[ Paragraph("Prepared: July 2026", S['body_sm']),
              Paragraph("Orris AI Medical Notes", S['body_sm']),
              Paragraph("Educational Use Only", S['body_sm']) ]]
    mt = Table(meta, colWidths=[5.67*cm]*3)
    mt.setStyle(TableStyle([
        ('TEXTCOLOR', (0,0), (-1,-1), C_GREY),
        ('ALIGN',     (0,0), (-1,-1), 'CENTER'),
        ('GRID',      (0,0), (-1,-1), 0.3, C_GREY_MED),
        ('TOPPADDING',    (0,0), (-1,-1), 5),
        ('BOTTOMPADDING', (0,0), (-1,-1), 5),
    ]))
    story.append(mt)
    story.append(PageBreak())

# ── SECTION 1: DEFINITION & PATHOPHYSIOLOGY ──────────────────────────────────

def section_patho(story, S):
    story.append(SectionHeader("1. DEFINITION, EPIDEMIOLOGY & PATHOPHYSIOLOGY", C_NAVY, icon="📌"))
    story.append(sp(6))

    # Severity table
    story.append(SubHeader("Severity Classification", C_TEAL))
    story.append(sp(4))
    sev_data = [
        ["Category", "Serum Na⁺", "Clinical Risk"],
        ["Mild", "130–134 mmol/L", "Usually asymptomatic; subtle cognitive/gait defects"],
        ["Moderate", "125–129 mmol/L", "Headache, nausea, lethargy, ataxia"],
        ["Severe", "< 125 mmol/L", "Seizures, coma, brain herniation, death"],
    ]
    story.append(make_table(sev_data, [4*cm, 4.5*cm, 8.5*cm], hdr_bg=C_TEAL))
    story.append(sp(8))

    # Pathophysiology
    story.append(SubHeader("Pathophysiology — Why Does Hyponatremia Develop?", C_BLUE))
    story.append(sp(4))
    patho_box = [
        Paragraph("<b>Core mechanism:</b> Impaired urinary dilution → water retention → dilution of serum Na⁺", S['body']),
        Paragraph("Three mechanisms (Comprehensive Nephrology 7e, Ch.9):", S['bold']),
        Paragraph("1.  <b>Nonosmotic AVP release</b> — volume depletion, pain, nausea, drugs → V2 receptor activation → AQP-2 insertion → water retention (most common)", S['body']),
        Paragraph("2.  <b>Reduced distal delivery</b> — low GFR or increased proximal tubule reabsorption limits diluting segment flow", S['body']),
        Paragraph("3.  <b>Impaired NaCl transport</b> — thick ascending limb (TAL) / distal convoluted tubule dysfunction (e.g., thiazides)", S['body']),
    ]
    story.append(ColorBox(patho_box, C_LIGHT_BLUE, C_BLUE))
    story.append(sp(6))

    # Brain adaptation table
    story.append(SubHeader("Brain Adaptation: Acute vs Chronic", C_PURPLE))
    story.append(sp(4))
    brain_data = [
        ["Phase", "Timing", "Mechanism", "Clinical Implication"],
        ["Acute",    "Minutes–Hours",   "ECF→ICF water shift; Na⁺/K⁺/Cl⁻ exit from brain cells",  "Cerebral edema → herniation risk"],
        ["Chronic",  "Hours–48h",       "Organic osmolyte extrusion (creatine, betaine, myoinositol, taurine, glutamate)",  "Brain re-adapts; volume near normal"],
        ["Correction risk", "> 48h duration", "Brain depleted of osmolytes; cannot rapidly reaccumulate",  "Rapid correction → osmotic demyelination (ODS)"],
    ]
    story.append(make_table(brain_data, [2.5*cm, 3*cm, 6*cm, 5.5*cm], hdr_bg=C_PURPLE))
    story.append(sp(6))

    quote_box = [
        Paragraph(
            '"Hyponatremia is almost always the result of an increase in circulating AVP '
            'and/or increased renal sensitivity to AVP, combined with an intake of free water."',
            S['quote']),
        Paragraph("— Harrison's Principles of Internal Medicine, 22nd Edition (2025), Ch.56", S['body_sm']),
    ]
    story.append(ColorBox(quote_box, C_TEAL_LIGHT, C_TEAL))
    story.append(sp(8))

# ── SECTION 2: CLASSIFICATION & CAUSES ───────────────────────────────────────

def section_causes(story, S):
    story.append(SectionHeader("2. CLASSIFICATION & CAUSES", C_NAVY, icon="🗂"))
    story.append(sp(6))

    # The 3-group overview
    overview_data = [
        ["HYPOVOLEMIC", "EUVOLEMIC", "HYPERVOLEMIC"],
        ["Total body water ↓\nTotal body Na⁺ ↓↓",
         "Total body water ↑\nTotal body Na⁺ → (normal)",
         "Total body water ↑↑\nTotal body Na⁺ ↑"],
        ["Urine Na⁺ <20 → extrarenal\nUrine Na⁺ >20 → renal",
         "Urine Na⁺ >20 (usually)",
         "Urine Na⁺ <10 (CHF/cirrhosis)\nUrine Na⁺ >20 (AKI/CKD)"],
    ]
    t_ov = Table(overview_data, colWidths=[5.67*cm]*3)
    t_ov.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (0,0), C_ORANGE),
        ('BACKGROUND', (1,0), (1,0), C_TEAL),
        ('BACKGROUND', (2,0), (2,0), C_BLUE),
        ('TEXTCOLOR',  (0,0), (-1,0), C_WHITE),
        ('FONTNAME',   (0,0), (-1,0), 'Helvetica-Bold'),
        ('FONTSIZE',   (0,0), (-1,-1), 8.5),
        ('ALIGN',      (0,0), (-1,-1), 'CENTER'),
        ('VALIGN',     (0,0), (-1,-1), 'MIDDLE'),
        ('GRID',       (0,0), (-1,-1), 0.5, C_WHITE),
        ('ROWBACKGROUNDS', (0,1), (-1,-1), [C_ORANGE_LT, HexColor("#F0FDF4")]),
        ('TOPPADDING',    (0,0), (-1,-1), 7),
        ('BOTTOMPADDING', (0,0), (-1,-1), 7),
    ]))
    story.append(t_ov)
    story.append(sp(8))

    # ── 2A Hypovolemic ──
    story.append(SubHeader("A. Hypovolemic Hyponatremia", C_ORANGE))
    story.append(sp(4))

    hypo_data = [
        ["Urine Na⁺ < 20 mmol/L (Extrarenal Losses)", "Urine Na⁺ > 20 mmol/L (Renal Losses)"],
        [
            "• Vomiting / diarrhea / tube drainage\n• Burns\n• Excessive sweating\n"
            "• Third-space: peritonitis, pancreatitis, ileus\n"
            "⚠ Exception: vomiting + metabolic alkalosis → urine Na⁺ may be >20\n  → use urine Cl⁻ (<10 = extrarenal)",
            "• Thiazide diuretics (most common)\n• Primary adrenal insufficiency (Addison's)\n"
            "• Salt-losing nephropathy (reflux, interstitial, medullary cystic)\n"
            "• Renal tubular acidosis / metabolic alkalosis (bicarbonaturia)\n"
            "• Ketonuria (alcoholic / starvation)\n• Osmotic diuresis\n"
            "• Cerebral salt wasting (SAH, TBI, meningitis)"
        ],
    ]
    t_hypo = Table(hypo_data, colWidths=[8.5*cm, 8.5*cm])
    t_hypo.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,0), C_ORANGE),
        ('TEXTCOLOR',  (0,0), (-1,0), C_WHITE),
        ('FONTNAME',   (0,0), (-1,0), 'Helvetica-Bold'),
        ('FONTSIZE',   (0,0), (-1,-1), 8),
        ('GRID',       (0,0), (-1,-1), 0.4, C_GREY_MED),
        ('BACKGROUND', (0,1), (0,1), C_ORANGE_LT),
        ('BACKGROUND', (1,1), (1,1), HexColor("#FFF7F0")),
        ('VALIGN',     (0,0), (-1,-1), 'TOP'),
        ('TOPPADDING', (0,0), (-1,-1), 6),
        ('BOTTOMPADDING', (0,0), (-1,-1), 6),
        ('LEFTPADDING',  (0,0), (-1,-1), 6),
        ('ALIGN',      (0,0), (-1,0), 'CENTER'),
    ]))
    story.append(t_hypo)
    story.append(sp(8))

    # Addison's callout
    add_items = [
        Paragraph("<b>⚠ Addison's Disease Clue:</b>  Hyponatremia + Hyperkalemia + Hypotension + High Urine Na⁺", S['warn']),
        Paragraph("→ Suggest primary adrenal insufficiency; confirm with AM cortisol / ACTH stimulation test", S['body']),
    ]
    story.append(ColorBox(add_items, C_RED_LIGHT, C_RED))
    story.append(sp(8))

    # ── 2B Euvolemic ──
    story.append(SubHeader("B. Euvolemic Hyponatremia", C_TEAL))
    story.append(sp(4))

    # SIAD criteria box
    siad_items = [
        Paragraph("<b>SIAD Diagnostic Criteria (Harrison's 22e, Table 56-1):</b>", S['teal_bold']),
        Paragraph("1.  Plasma osmolality < 275 mOsm/kg", S['body']),
        Paragraph("2.  Urine osmolality > 100 mOsm/kg (usually >300 mOsm/kg)", S['body']),
        Paragraph("3.  Clinical euvolemia (no dehydration, no edema/ascites)", S['body']),
        Paragraph("4.  Urine Na⁺ > 20–30 mmol/L on normal salt/water intake", S['body']),
        Paragraph("5.  Normal thyroid (TSH) and adrenal (cortisol) function", S['body']),
        Paragraph("6.  No recent diuretic therapy", S['body']),
    ]
    story.append(ColorBox(siad_items, C_TEAL_LIGHT, C_TEAL))
    story.append(sp(6))

    # SIAD causes table
    siad_cause_data = [
        ["Category", "Examples"],
        ["CNS",        "Stroke, SAH, meningitis, encephalitis, Guillain-Barré, TBI, psychosis"],
        ["Pulmonary",  "Pneumonia, TB, lung abscess, COPD exacerbation, PPV, empyema"],
        ["Malignancy", "Small cell lung Ca, carcinoid, lymphoma, mesothelioma, GI/GU tumors (ectopic AVP)"],
        ["Drugs",      "SSRIs, TCAs, carbamazepine, oxcarbazepine, vincristine, cyclophosphamide,\nchlorpropamide, NSAIDs, opiates, MDMA, haloperidol, thiazides"],
        ["Other",      "Post-operative, pain, nausea, HIV/AIDS, hereditary (V2 gain-of-function)"],
        ["Endocrine",  "Hypothyroidism, secondary glucocorticoid deficiency"],
    ]
    story.append(make_table(siad_cause_data, [3.5*cm, 13.5*cm], hdr_bg=C_TEAL))
    story.append(sp(6))

    # Other euvolemic causes
    eu_other = [
        Paragraph("<b>Other Euvolemic Causes:</b>", S['body']),
        Paragraph("• <b>Hypothyroidism</b> — moderate to severe; corrects with thyroid hormone replacement", S['body']),
        Paragraph("• <b>Secondary adrenal insufficiency</b> (pituitary disease) — glucocorticoid deficiency → loss of AVP inhibition; Note: no hyperkalemia (aldosterone intact)", S['body']),
        Paragraph("• <b>Beer potomania / Low solute intake</b> — massive hypotonic fluid intake + insufficient dietary solute → insufficient osmole excretion to drive free water loss", S['body']),
    ]
    story.append(ColorBox(eu_other, C_TEAL_LIGHT, C_TEAL))
    story.append(sp(8))

    # ── 2C Hypervolemic ──
    story.append(SubHeader("C. Hypervolemic Hyponatremia", C_BLUE))
    story.append(sp(4))

    hyper_data = [
        ["Urine Na⁺ < 10 mmol/L", "Urine Na⁺ > 20 mmol/L"],
        ["• Congestive heart failure (CHF)\n  — cardiac dysfunction → arterial underfilling\n"
         "• Hepatic cirrhosis\n  — peripheral vasodilation → reduced arterial filling\n"
         "• Nephrotic syndrome\n  — hypoalbuminemia → third-space losses",
         "• Acute kidney injury (AKI)\n• Chronic kidney disease (CKD)\n  — impaired free water excretion\n\n"
         "Note: Na⁺-avid state in CHF/cirrhosis may be\nmasked by diuretic therapy"],
    ]
    t_hyper = Table(hyper_data, colWidths=[8.5*cm, 8.5*cm])
    t_hyper.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,0), C_BLUE),
        ('TEXTCOLOR',  (0,0), (-1,0), C_WHITE),
        ('FONTNAME',   (0,0), (-1,0), 'Helvetica-Bold'),
        ('FONTSIZE',   (0,0), (-1,-1), 8),
        ('GRID',       (0,0), (-1,-1), 0.4, C_GREY_MED),
        ('BACKGROUND', (0,1), (0,1), C_LIGHT_BLUE),
        ('BACKGROUND', (1,1), (1,1), HexColor("#EFF6FF")),
        ('VALIGN',     (0,0), (-1,-1), 'TOP'),
        ('TOPPADDING', (0,0), (-1,-1), 6),
        ('BOTTOMPADDING', (0,0), (-1,-1), 6),
        ('LEFTPADDING',  (0,0), (-1,-1), 6),
        ('ALIGN',      (0,0), (-1,0), 'CENTER'),
    ]))
    story.append(t_hyper)
    story.append(sp(8))

    # ── 2D Pseudo / Translocational ──
    story.append(SubHeader("D. Pseudohyponatremia & Translocational Hyponatremia", C_GREY))
    story.append(sp(4))
    pseudo_data = [
        ["Type", "Serum Osmolality", "Cause", "Action"],
        ["Pseudohyponatremia", "Normal (275–290)", "Severe hyperlipidemia, hyperproteinemia\n(lab artifact — water displacement)", "Remeasure with direct ISE; no treatment"],
        ["Translocational", "HIGH (>290)", "Hyperglycemia, mannitol, sorbitol, glycine (TURP)\n(osmotic water shift from ICF)", "Correct glucose; Na⁺ corrects automatically\n(1.6–2.4 mmol/L per 100 mg/dL glucose rise)"],
    ]
    story.append(make_table(pseudo_data, [3.5*cm, 3.5*cm, 5.5*cm, 4.5*cm], hdr_bg=C_GREY))
    story.append(sp(8))

# ── SECTION 3: CLINICAL FEATURES ─────────────────────────────────────────────

def section_clinical(story, S):
    story.append(SectionHeader("3. CLINICAL FEATURES", C_NAVY, icon="🩺"))
    story.append(sp(6))

    # Symptoms by severity
    sym_data = [
        ["Na⁺ Level", "Symptoms"],
        ["> 130 mmol/L", "Usually none; subtle gait instability, mild cognitive slowing (often unrecognized)"],
        ["125–130 mmol/L", "Nausea, headache, yawning, lethargy, fatigue"],
        ["120–125 mmol/L", "Confusion, disorientation, reversible ataxia, psychosis"],
        ["< 120 mmol/L", "Seizures, obtundation, coma, respiratory failure, brain herniation, death"],
    ]
    story.append(make_table(sym_data, [4*cm, 13*cm], hdr_bg=C_RED))
    story.append(sp(8))

    # Acute vs Chronic two-col
    story.append(SubHeader("Acute (<48h) vs Chronic (>48h) — Key Differences", C_BLUE))
    story.append(sp(4))
    ac_data = [
        ["ACUTE Hyponatremia (<48h)", "CHRONIC Hyponatremia (>48h)"],
        ["• Brain has NOT adapted → full osmotic stress\n"
         "• Cerebral edema is the main danger\n"
         "• Symptoms: nausea, headache, seizures, coma\n"
         "• Neurogenic pulmonary edema possible\n"
         "• Women (premenopausal) at ↑ risk — estrogen\n  inhibits brain osmolyte extrusion\n"
         "• Aggressive correction is REQUIRED",
         "• Brain has adapted via organic osmolyte loss\n"
         "• Reduced acute cerebral edema risk\n"
         "• Subtle symptoms: gait disorders, cognitive deficit,\n  falls, fractures\n"
         "• CAUTION: Rapid correction → osmotic\n  demyelination syndrome (ODS)\n"
         "• Correction rate must be STRICTLY limited"],
    ]
    t_ac = Table(ac_data, colWidths=[8.5*cm, 8.5*cm])
    t_ac.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (0,0), C_RED),
        ('BACKGROUND', (1,0), (1,0), C_ORANGE),
        ('TEXTCOLOR',  (0,0), (-1,0), C_WHITE),
        ('FONTNAME',   (0,0), (-1,0), 'Helvetica-Bold'),
        ('FONTSIZE',   (0,0), (-1,-1), 8),
        ('GRID',       (0,0), (-1,-1), 0.4, C_GREY_MED),
        ('BACKGROUND', (0,1), (0,1), C_RED_LIGHT),
        ('BACKGROUND', (1,1), (1,1), C_ORANGE_LT),
        ('VALIGN',     (0,0), (-1,-1), 'TOP'),
        ('TOPPADDING', (0,0), (-1,-1), 6),
        ('BOTTOMPADDING', (0,0), (-1,-1), 6),
        ('LEFTPADDING',  (0,0), (-1,-1), 6),
        ('ALIGN',      (0,0), (-1,0), 'CENTER'),
    ]))
    story.append(t_ac)
    story.append(sp(8))

    # ODS box
    ods_items = [
        Paragraph("<b>Osmotic Demyelination Syndrome (ODS) / Central Pontine Myelinolysis (CPM)</b>", S['red_bold']),
        Paragraph("Cause: Too-rapid correction of chronic hyponatremia → osmotic myelin destruction", S['body']),
        Paragraph("Symptoms: Dysarthria, dysphagia, spastic quadriparesis, pseudobulbar palsy, 'locked-in' syndrome, coma", S['body']),
        Paragraph("MRI: T2 hyperintensity in pons (±extrapontine — basal ganglia, thalamus, cerebellum)", S['body']),
        Paragraph("<b>High-risk patients:</b>  Na⁺ <105 | Alcoholism | Malnutrition | Liver disease | Burns | Hypokalemia", S['warn']),
        Paragraph("Note: Not uniformly fatal — significant neurological recovery possible with supportive care", S['body']),
    ]
    story.append(ColorBox(ods_items, C_RED_LIGHT, C_RED))
    story.append(sp(8))

    # Acute hyponatremia causes table
    story.append(SubHeader("Causes of Acute Hyponatremia (Harrison's Table 56-2)", C_ORANGE))
    story.append(sp(4))
    acute_data = [
        ["Cause"],
        ["Postoperative hypotonic fluids — especially premenopausal women"],
        ["Hypotonic IV fluids with any cause of elevated AVP"],
        ["Glycine irrigation solutions — TURP, uterine surgery"],
        ["Colonoscopy preparation solutions"],
        ["Thiazide diuretics — recent initiation"],
        ["Primary polydipsia"],
        ["MDMA ('Ecstasy', 'Molly') — potent AVP release + thirst stimulation"],
        ["Exercise-associated hyponatremia — endurance events (marathons)"],
        ["Multifactorial, e.g., thiazide + polydipsia"],
    ]
    story.append(make_table(acute_data, [17*cm], hdr_bg=C_ORANGE))
    story.append(sp(8))

# ── SECTION 4: DIAGNOSTIC APPROACH ───────────────────────────────────────────

def section_diagnosis(story, S):
    story.append(SectionHeader("4. DIAGNOSTIC APPROACH", C_NAVY, icon="🔍"))
    story.append(sp(6))

    diag_flow = [
        Paragraph("<b>Step 1 — Confirm true hyponatremia: Measure Serum Osmolality</b>", S['bold']),
        Paragraph("• Low (<275 mOsm/kg) → TRUE hypotonic hyponatremia → proceed to Step 2", S['body']),
        Paragraph("• Normal (275–290) → Pseudohyponatremia (lipemia / paraproteinemia) → confirm with direct ISE", S['body']),
        Paragraph("• High (>290) → Translocational (hyperglycemia, mannitol, sorbitol, glycine)", S['body']),
    ]
    story.append(ColorBox(diag_flow, C_LIGHT_BLUE, C_BLUE))
    story.append(sp(6))

    diag_step2 = [
        Paragraph("<b>Step 2 — Assess Volume Status (Clinical Examination)</b>", S['bold']),
        Paragraph("• <b>Hypovolemic:</b>  Dry mucous membranes, ↓ skin turgor, tachycardia, orthostasis, flat neck veins, recent fluid loss", S['body']),
        Paragraph("• <b>Euvolemic:</b>  No edema, no signs of dehydration, no ascites", S['body']),
        Paragraph("• <b>Hypervolemic:</b>  Pitting edema, ascites, ↑ JVP, S3 gallop, pulmonary crackles", S['body']),
    ]
    story.append(ColorBox(diag_step2, C_TEAL_LIGHT, C_TEAL))
    story.append(sp(6))

    diag_step3 = [
        Paragraph("<b>Step 3 — Urine Studies</b>", S['bold']),
        Paragraph("• <b>Urine osmolality:</b>  >100 mOsm/kg → AVP-mediated water retention  |  <100 mOsm/kg → primary polydipsia or low solute intake", S['body']),
        Paragraph("• <b>Urine Na⁺:</b>  <10–20 → extrarenal loss or Na⁺-avid state (CHF, cirrhosis, nephrotic)  |  >20–40 → renal loss, SIAD, hypothyroid, adrenal insuff, AKI", S['body']),
        Paragraph("• <b>Urine Cl⁻:</b>  Use instead of Na⁺ if vomiting with metabolic alkalosis (bicarbonaturia falsely elevates urine Na⁺)", S['body']),
    ]
    story.append(ColorBox(diag_step3, C_ORANGE_LT, C_ORANGE))
    story.append(sp(6))

    # Additional tests
    story.append(SubHeader("Step 4 — Additional Investigations (to find underlying cause)", C_PURPLE))
    story.append(sp(4))
    inv_data = [
        ["Test", "Purpose"],
        ["Serum glucose, BUN, creatinine", "Exclude translocational; assess renal function"],
        ["Serum lipids, serum protein (SPEP)", "Exclude pseudohyponatremia"],
        ["TSH, free T4", "Exclude hypothyroidism"],
        ["AM cortisol / ACTH stimulation test", "Exclude primary or secondary adrenal insufficiency"],
        ["Serum potassium", "Hyperkalemia → Addison's; Hypokalemia → ODS risk factor"],
        ["Serum uric acid", "Low (<4 mg/dL) → SIAD; Normal/high → CSW or hypovolemia"],
        ["LFTs, albumin, proBNP/BNP", "Assess cirrhosis, cardiac failure"],
        ["Fractional excretion of urate (FEUA)", ">12% → SIAD; helps distinguish from CSW (2026 evidence)"],
        ["CXR / CT chest-abdomen", "If SIAD — search for malignancy (SCLC), pulmonary cause"],
        ["Serum and urine osmolality simultaneously", "Calculate osmolar gap; verify urine diluting ability"],
    ]
    story.append(make_table(inv_data, [6*cm, 11*cm], hdr_bg=C_PURPLE))
    story.append(sp(8))

    # SIAD vs CSW table
    story.append(SubHeader("SIAD vs Cerebral Salt Wasting (CSW) — Critical Distinction", C_RED))
    story.append(sp(4))

    csw_items = [
        Paragraph("<b>Why it matters:</b>  SIAD → fluid restriction  |  CSW → aggressive NaCl + fluid repletion", S['warn']),
        Paragraph("Confusing the two is potentially fatal", S['body']),
    ]
    story.append(ColorBox(csw_items, C_RED_LIGHT, C_RED))
    story.append(sp(4))

    csw_data = [
        ["Parameter", "SIAD", "CSW"],
        ["ECF volume",        "Normal/increased (euvolemic)", "↓ Decreased"],
        ["Body weight",       "↑ Increased",                  "↓ Decreased"],
        ["Fluid balance",     "Positive",                     "Negative"],
        ["Urine volume",      "Normal or ↓",                  "Normal or ↑"],
        ["Tachycardia",       "Absent",                       "Present"],
        ["Hematocrit",        "Normal",                       "↑ Increased"],
        ["Albumin",           "Normal",                       "↑ Increased"],
        ["Serum bicarbonate", "Normal or low",                "↑ Increased"],
        ["BUN",               "Normal or low",                "↑ Increased"],
        ["Serum uric acid",   "⬇ LOW (key feature)",         "Normal or low"],
        ["Urinary Na⁺",       "↑ High",                      "↑ High"],
        ["CVP/PCWP",          "Normal or slightly ↑",        "⬇ LOW (key feature)"],
        ["FEUA",              ">12% → SIAD",                  "May be elevated briefly"],
    ]
    t_csw = Table(csw_data, colWidths=[5.5*cm, 5.75*cm, 5.75*cm])
    t_csw.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,0), C_RED),
        ('TEXTCOLOR',  (0,0), (-1,0), C_WHITE),
        ('FONTNAME',   (0,0), (-1,0), 'Helvetica-Bold'),
        ('FONTSIZE',   (0,0), (-1,-1), 8),
        ('GRID',       (0,0), (-1,-1), 0.4, C_GREY_MED),
        ('ROWBACKGROUNDS', (0,1), (-1,-1), [C_WHITE, HexColor("#FFF1F2")]),
        ('BACKGROUND', (1,10), (1,10), HexColor("#FEE2E2")),  # uric acid SIAD
        ('BACKGROUND', (2,12), (2,12), HexColor("#FEE2E2")),  # CVP CSW
        ('FONTNAME',   (0,10), (2,10), 'Helvetica-Bold'),
        ('FONTNAME',   (0,12), (2,12), 'Helvetica-Bold'),
        ('VALIGN',     (0,0), (-1,-1), 'MIDDLE'),
        ('TOPPADDING', (0,0), (-1,-1), 4),
        ('BOTTOMPADDING', (0,0), (-1,-1), 4),
        ('LEFTPADDING',  (0,0), (-1,-1), 5),
    ]))
    story.append(t_csw)
    story.append(sp(8))

# ── SECTION 5: MANAGEMENT ─────────────────────────────────────────────────────

def section_management(story, S):
    story.append(SectionHeader("5. MANAGEMENT", C_NAVY, icon="💊"))
    story.append(sp(6))

    # Correction rate box
    rate_items = [
        Paragraph("<b>CORRECTION RATE LIMITS — Must Memorize</b>", S['red_bold']),
        Paragraph("• Maximum: <b>10–12 mmol/L per 24 hours</b>  (conservative: 8–10 if high ODS risk)", S['body']),
        Paragraph("• Maximum in first 24h: <b>10 mmol/L</b>", S['body']),
        Paragraph("• Do NOT exceed: <b>18 mmol/L in 48 hours</b>", S['body']),
        Paragraph("• Highest ODS-risk patients (Na⁺ <105, alcoholism, malnutrition, liver disease): <b>≤8 mmol/L/24h</b>", S['body']),
        Paragraph("• 2026 meta-analysis (PMID 41652262): Overcorrection significantly worsens neurological outcomes & mortality", S['body_sm']),
    ]
    story.append(ColorBox(rate_items, C_RED_LIGHT, C_RED))
    story.append(sp(8))

    # Adrogué-Madias formula
    formula_items = [
        Paragraph("<b>Adrogué-Madias Formula — Na⁺ Change from 1L Infusate:</b>", S['bold']),
        Paragraph("ΔNa⁺ = (Infusate Na⁺ − Serum Na⁺) ÷ (Total Body Water + 1)", S['blue_bold']),
        Paragraph("TBW = 0.6 × lean body weight (men) | 0.5 × lean body weight (women)", S['body']),
        Paragraph("3% NaCl = 513 mmol/L Na⁺  |  0.9% NaCl = 154 mmol/L  |  0.45% NaCl = 77 mmol/L  |  D5W = 0 mmol/L", S['body_sm']),
    ]
    story.append(ColorBox(formula_items, C_LIGHT_BLUE, C_BLUE))
    story.append(sp(8))

    # ── 5A Acute Symptomatic ──
    story.append(SubHeader("A. Acute Symptomatic Hyponatremia — EMERGENCY", C_RED))
    story.append(sp(4))
    acute_rx = [
        Paragraph("<b>⚠ Medical Emergency — risk of cerebral edema >>> risk of ODS</b>", S['warn']),
        Paragraph("<b>Treatment:</b>", S['bold']),
        Paragraph("1.  <b>3% NaCl (hypertonic saline)</b>", S['body']),
        Paragraph("     • Standard: 1–2 mL/kg IV over 60 min, OR 100 mL IV bolus over 10 min (repeat up to 3×)", S['body_sm']),
        Paragraph("     • Severe symptoms (seizures, coma): 4–6 mL/kg/hr", S['body_sm']),
        Paragraph("2.  <b>Target:</b>  Raise Na⁺ by 4–6 mmol/L in first 6h (enough to reverse cerebral edema; full correction not needed)", S['body']),
        Paragraph("3.  Add <b>furosemide</b> (loop diuretic) to enhance free water excretion", S['body']),
        Paragraph("4.  Monitor serum electrolytes every <b>2 hours</b>", S['body']),
        Paragraph("5.  Monitor neurological and pulmonary status continuously", S['body']),
    ]
    story.append(ColorBox(acute_rx, C_RED_LIGHT, C_RED))
    story.append(sp(8))

    # ── 5B Chronic Symptomatic ──
    story.append(SubHeader("B. Chronic Symptomatic Hyponatremia (>48h duration)", C_ORANGE))
    story.append(sp(4))
    chronic_rx = [
        Paragraph("<b>Correction must be cautious</b>  — ODS risk when brain depleted of osmolytes", S['orange_bold']),
        Paragraph("<b>Moderate symptoms (nausea, confusion — no seizures):</b>", S['bold']),
        Paragraph("• 3% NaCl at low rate: 0.5–1 mL/kg/hr", S['body']),
        Paragraph("• Raise Na⁺ 1–2 mmol/L per hour until symptoms improve", S['body']),
        Paragraph("• STOP/slow once Na⁺ rises by 8–10 mmol/L or reaches 125–130 mmol/L (whichever first)", S['body']),
        Paragraph("<b>If Overcorrection Occurs — Rescue Protocol:</b>", S['bold']),
        Paragraph("1. STOP all hypertonic saline immediately", S['body']),
        Paragraph("2. Give DDAVP 2–4 mcg IV (clamps further correction by restoring AVP effect)", S['body']),
        Paragraph("3. Give D5W to re-lower Na⁺ back to safe level", S['body']),
        Paragraph("4. Target: re-lower to 8–10 mmol/L below the overcorrected value", S['body']),
    ]
    story.append(ColorBox(chronic_rx, C_ORANGE_LT, C_ORANGE))
    story.append(sp(8))

    # ── 5C-E Management by type ──
    story.append(SubHeader("C–E. Management by Volume Status", C_BLUE))
    story.append(sp(4))

    mgmt_data = [
        ["TYPE", "FIRST-LINE", "ADDITIONAL OPTIONS"],
        ["Hypovolemic",
         "0.9% NaCl (isotonic saline)\nCorrects volume → AVP falls → water diuresis\n⚠ Monitor closely — rapid overcorrection possible as AVP drops",
         "Fludrocortisone/hydrocortisone if adrenal insufficiency\nStop diuretics"],
        ["Hypervolemic\n(CHF, cirrhosis, nephrotic)",
         "Treat underlying disease\nFluid restriction (1–1.5 L/day)\nLoop diuretics (furosemide)",
         "Vaptans (tolvaptan oral, conivaptan IV)\n• Block V2 receptor → aquaresis\n• Start in hospital — overcorrection risk\n⚠ Tolvaptan CONTRAINDICATED in cirrhosis (hepatotoxicity)"],
        ["Euvolemic — SIAD",
         "Step 1: Remove/treat underlying cause\nStep 2: Fluid restriction <800–1000 mL/day\n(fails if urine Osm >500 or >2× serum Osm)",
         "Salt tablets + furosemide (long-term)\nOral urea 15–60g/day (European guideline favourite; cheap)\nDemeclocycline (rarely used now; nephrotoxic)\nTolvaptan (short-term hospital use; expensive)"],
        ["Hypothyroid",
         "Thyroid hormone replacement\nNa⁺ corrects spontaneously",
         "Avoid aggressive Na⁺ correction\n(allow thyroid hormone to work first)"],
        ["Adrenal insufficiency",
         "Primary: Hydrocortisone + Fludrocortisone + NS\nSecondary: Hydrocortisone alone",
         "Na⁺ rapidly improves\nMonitor for overcorrection as AVP rapidly normalizes"],
    ]
    story.append(make_table(mgmt_data, [3.5*cm, 6.5*cm, 7*cm], hdr_bg=C_BLUE))
    story.append(sp(8))

    # Vaptans box
    vaptan_items = [
        Paragraph("<b>Vasopressin V2 Receptor Antagonists (Vaptans):</b>", S['blue_bold']),
        Paragraph("• Tolvaptan (oral) | Conivaptan (IV, only for euvolemic/hypervolemic)", S['body']),
        Paragraph("• Mechanism: Block AVP at V2 receptor → selective aquaresis (free water loss without electrolyte loss)", S['body']),
        Paragraph("• Indications: Hypervolemic and euvolemic hyponatremia refractory to fluid restriction", S['body']),
        Paragraph("• CONTRAINDICATED: Hypovolemic hyponatremia | Anuric patients | Liver disease (tolvaptan hepatotoxicity)", S['warn']),
        Paragraph("• Initiate ONLY in hospital; do not restrict fluids during vaptan therapy; risk of rapid overcorrection", S['body']),
    ]
    story.append(ColorBox(vaptan_items, C_LIGHT_BLUE, C_BLUE))
    story.append(sp(8))

# ── SECTION 6: QUICK REFERENCE SUMMARY ───────────────────────────────────────

def section_summary(story, S):
    story.append(SectionHeader("6. QUICK REFERENCE SUMMARY TABLE", C_NAVY, icon="📊"))
    story.append(sp(6))

    sum_data = [
        ["Feature",              "Hypovolemic",               "Euvolemic",                   "Hypervolemic"],
        ["Total body water",     "↓",                          "↑",                           "↑↑"],
        ["Total body Na⁺",      "↓↓",                         "Normal",                      "↑"],
        ["Urine Na⁺",           "<20 (extra-renal)\n>20 (renal)", ">20",                  "<10 (CHF/cirrhosis)\n>20 (AKI/CKD)"],
        ["Urine osmolality",    "High",                        "High",                        "Variable"],
        ["Typical causes",      "GI losses, burns,\nthiazides, Addison's,\nsalt-losing nephropathy",
                                 "SIAD, hypothyroid,\nsecondary adrenal insuff,\nbeer potomania",
                                 "CHF, cirrhosis,\nnephrotic syndrome,\nAKI/CKD"],
        ["Treatment",           "0.9% NaCl + correct cause",  "Fluid restriction;\ntolvaptan/urea if refractory",
                                 "Fluid restriction;\nloop diuretics;\nvaptans; treat cause"],
        ["Key investigations",  "Urine Na/Cl; cortisol;\nserum K; ACTH test",
                                 "TSH; cortisol; urine Osm;\nCXR/CT chest (SIAD search)",
                                 "Echo; LFTs; albumin;\nproBNP; creatinine"],
    ]
    story.append(make_table(sum_data, [3.3*cm, 4.6*cm, 4.6*cm, 4.5*cm], hdr_bg=C_NAVY))
    story.append(sp(8))

    # Key facts box
    kf_items = [
        Paragraph("<b>KEY FACTS — High-Yield Points:</b>", S['bold']),
        Paragraph("• Hyponatremia is the most common electrolyte abnormality — up to 22% hospitalized patients (Harrison's 22e)", S['body']),
        Paragraph("• Classify ALWAYS by volume status first — this determines cause AND treatment", S['body']),
        Paragraph("• First step in workup: measure serum osmolality (exclude pseudo/translocational)", S['body']),
        Paragraph("• Urine Na⁺ <20 → extrarenal or Na⁺-avid state  |  >20 → renal/SIAD/adrenal", S['body']),
        Paragraph("• Urine Cl⁻ (NOT Na⁺) in vomiting with alkalosis — more reliable", S['body']),
        Paragraph("• SIAD: urine Osm > plasma Osm + euvolemia + urine Na⁺ >20 + exclude hypothyroid/adrenal insuff", S['body']),
        Paragraph("• Serum uric acid: LOW in SIAD, normal/high in CSW — useful differentiator", S['body']),
        Paragraph("• Correction limit: max 10 mmol/L/24h  |  ODS risk group: max 8 mmol/L/24h", S['body']),
        Paragraph("• Acute (<48h) symptomatic: 3% NaCl bolus immediately — cerebral edema risk dominates", S['body']),
        Paragraph("• Overcorrection rescue: DDAVP + D5W to re-lower Na⁺", S['body']),
        Paragraph("• Beer potomania: low solute → insufficient osmoles for free water excretion; treat with dietary solute", S['body']),
    ]
    story.append(ColorBox(kf_items, C_YELLOW_LT, C_YELLOW))
    story.append(sp(8))

    # Sources
    story.append(SubHeader("References & Sources", C_GREY))
    story.append(sp(4))
    ref_data = [
        ["Source", "Coverage"],
        ["Harrison's Principles of Internal Medicine, 22nd Ed. (2025)\nCh. 56 — Sodium & Water Disorders", "Definition, pathophysiology, SIAD criteria, AVP patterns, acute hyponatremia causes, clinical features, ODS, correction approach"],
        ["Comprehensive Clinical Nephrology, 7th Ed.\nCh. 9 — Hyponatremia", "Etiology/classification, diluting mechanism, cerebral adaptation, treatment algorithm, acute/chronic management, vaptans, urea"],
        ["Bradley & Daroff's Neurology in Clinical Practice\nCh. 53 — Fluid & Electrolytes", "SIAD vs CSW comparison table, neurological hyponatremia in ICU"],
        ["Schneider AR et al. J Gen Intern Med. 2026 Jun\nPMID: 41652262", "Systematic review: sodium overcorrection in chronic hyponatremia → worse outcomes; validates strict correction limits"],
        ["Assadi F. Clin Endocrinol. 2026 Jan\nPMID: 41058069", "Systematic review: FEUA, urinary phosphate, BNP for distinguishing CSW from SIAD in neurological illness"],
        ["European Clinical Practice Guideline — Hyponatremia\nSpasovski et al., Eur J Endocrinol (2014)", "Standard thresholds for correction rate; vaptan indications; fluid restriction criteria; urea recommendations"],
    ]
    story.append(make_table(ref_data, [6*cm, 11*cm], hdr_bg=C_GREY))
    story.append(sp(8))

# ── MAIN ──────────────────────────────────────────────────────────────────────

def build():
    out_path = "/home/daytona/workspace/hyponatremia-notes/Hyponatremia_Medical_Notes.pdf"
    doc = SimpleDocTemplate(
        out_path,
        pagesize=A4,
        topMargin=1.4*cm,
        bottomMargin=1.2*cm,
        leftMargin=1.75*cm,
        rightMargin=1.75*cm,
        title="Hyponatremia — Clinical Study Notes",
        author="Orris AI",
        subject="Medical Notes — Hyponatremia",
    )

    S = styles()
    story = []

    cover_page(story, S)
    section_patho(story, S)
    story.append(sp(4))
    section_causes(story, S)
    story.append(PageBreak())
    section_clinical(story, S)
    story.append(sp(4))
    section_diagnosis(story, S)
    story.append(PageBreak())
    section_management(story, S)
    story.append(sp(4))
    section_summary(story, S)

    doc.build(story, onFirstPage=make_header_footer, onLaterPages=make_header_footer)
    print(f"PDF generated: {out_path}")
    return out_path

if __name__ == "__main__":
    build()

Running Command

cd /home/daytona/workspace/hyponatremia-notes && python3 build_pdf.py 2>&1

Running Command

ls -lh /home/daytona/workspace/hyponatremia-notes/Hyponatremia_Medical_Notes.pdf

Your Hyponatremia clinical study notes PDF is ready!

Hyponatremia Medical Notes

PDF Document · PDF

What's inside the PDF (6 sections, fully styled):

Section	Content
Cover Page	Title card with source badges (Harrison's / Nephrology / UpToDate / PubMed), quick summary box
1. Pathophysiology	Severity classification table, AVP mechanism, brain adaptation acute vs chronic table, quote from Harrison's
2. Classification & Causes	3-group overview (hypovolemic/euvolemic/hypervolemic), detailed cause tables, SIAD diagnostic criteria box, SIAD causes by category, Addison's callout, pseudohyponatremia table
3. Clinical Features	Symptom severity table, acute vs chronic side-by-side comparison, ODS/CPM detail box, acute hyponatremia causes table (Harrison's)
4. Diagnostic Approach	Step-by-step algorithm boxes (serum Osm → volume status → urine studies → investigations), SIAD vs CSW comparison table with highlighted key differentiators
5. Management	Correction rate limits box (with 2026 meta-analysis note), Adrogué-Madias formula, acute emergency protocol, chronic symptomatic + overcorrection rescue, management-by-type table, vaptan guidelines
6. Summary + References	Quick reference master table, 11 high-yield key facts, full reference list

Styling: Color-coded section bars (navy), sub-headers (teal/blue/orange/red by topic), colored callout boxes with left accent bars, alternating-row tables, running header/footer with page numbers.

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