Pulmonary Function Tests - MD Anesthesia Final Practical Viva Guide

SECTION 1 - LUNG VOLUMES AND CAPACITIES (The Foundation)

Key Definitions (rattle these off quickly)

Critical viva point: RV, FRC, and TLC cannot be measured by spirometry alone - you need nitrogen washout, helium dilution, or body plethysmography (Boyle's law).

SECTION 2 - SPIROMETRY GRAPHS

Graph 1: Volume-Time Curve (Spirogram)

• FVC = total volume forcefully exhaled
• FEV1 = volume exhaled in first 1 second
• FEV1/FVC ratio = the single most important ratio in PFT interpretation
• FEF25-75% = forced expiratory flow between 25-75% of FVC (sensitive marker for small-airway disease)
• Peak Flow = highest flow rate achieved during forced expiration

Graph 2: Flow-Volume Loops - Normal vs Pathological (Fishman's)

• Upper half (above zero) = expiration
• Lower half (below zero) = inspiration
• X-axis = lung volume (right = TLC, left = RV)
• Red solid = normal; Blue dashed = pathological

Graph 3: Upper Airway Obstruction - Fixed vs Variable (Miller's Anesthesia 10e)

• Variable extrathoracic obstruction (e.g., vocal cord paresis): During forced inspiration, intratracheal pressure drops below atmospheric, causing the extrathoracic trachea to collapse inward - so the inspiratory limb is flattened. During expiration, tracheal pressure exceeds atmospheric, so obstruction lessens.
• Variable intrathoracic obstruction (e.g., tracheomalacia): During forced expiration, pleural pressure exceeds intraluminal pressure, compressing the intrathoracic segment - so the expiratory limb is flattened. During inspiration, transmural pressure holds the airway open.
• Fixed obstruction (e.g., tracheal scar): The geometry doesn't change during the respiratory cycle - both limbs are truncated equally (the classic "box-shaped" loop).

SECTION 3 - INTERPRETATION FRAMEWORK

Step-by-Step Approach (Say this in the viva)

• YES → Obstructive pattern
• NO → go to Step 2

• YES, with normal FEV1/FVC → Restrictive pattern (confirm with TLC)
• Both FVC and FEV1/FVC low → Mixed pattern

The Master Comparison Table (Barash Clinical Anesthesia 9e)

COPD GOLD Staging (must know for viva)

SECTION 4 - SPECIFIC PFT PATTERNS AND THEIR CAUSES

Obstructive Pattern Diseases

Restrictive Pattern Diseases

• FVC ↓, FEV1 ↓, FEV1/FVC normal or increased, TLC ↓, DLCO ↓

• Chest wall: kyphoscoliosis, obesity, ankylosing spondylitis
• Pleural: effusion, fibrosis
• Neuromuscular: myasthenia gravis, Guillain-Barré, diaphragm palsy
• In neuromuscular disease: FVC ↓, but DLCO is preserved (key distinguishing feature)

DLCO Patterns (a favourite viva topic)

SECTION 5 - ANESTHESIA-SPECIFIC APPLICATIONS

Pre-operative Risk Stratification (Most Important for Anesthesia Viva)

Effect of Anesthesia on PFT Parameters

• FRC decreases by 400-500 mL on induction (supine position + loss of respiratory muscle tone)
• This FRC reduction causes airway closure and V/Q mismatch → hypoxemia
• FRC reduction is greater in: obesity, elderly, pregnancy, pulmonary disease
• SpO2 < 81% occurs in ~20% of patients for up to 5 minutes after induction

• 50% of anesthesia-related deaths relate to hypoxemia

Preoperative Optimization Based on PFT

SECTION 6 - POSSIBLE VIVA QUESTIONS & ANSWERS

Q1. What is FRC and why is it important for the anesthesiologist?

Q2. A patient with known COPD comes for elective laparotomy. How do you interpret his PFT and what anesthetic implications does it have?

• FEV1/FVC < 0.70 post-bronchodilator confirms COPD
• Severity graded by FEV1 % predicted (GOLD I-IV)
• FEV1 < 60% = high risk for postoperative pulmonary complications
• Air trapping: TLC ↑, RV ↑, FRC ↑
• DLCO reduced in emphysema (not in pure chronic bronchitis)
• Anesthetic implications: regional preferred, avoid prolonged positive pressure ventilation, risk of pneumothorax from high airway pressures, anticipate delayed extubation, postoperative respiratory failure risk

Q3. What is the difference between obstructive and restrictive PFT patterns?

Q4. How do you distinguish asthma from COPD on PFT?

• Positive reversibility = FEV1 increase ≥ 200 mL AND ≥ 12% from baseline → suggests asthma
• No significant reversibility → suggests COPD (fixed obstruction)

Q5. What does a flow-volume loop showing flattening of the inspiratory limb suggest?

Q6. What is DLCO and what does it measure?

Q7. What are the criteria for positive bronchodilator reversibility?

Q8. What is FEF25-75% and what is its clinical significance?

Q9. How do you assess a patient for lung resection surgery?

1. Spirometry: FEV1 > 2L (or > 60%) for pneumonectomy; > 1.5L for lobectomy
2. DLCO: Should be > 60% predicted
3. CPET (if FEV1 or DLCO are borderline): VO2 max > 15 mL/kg/min = acceptable risk; < 10 mL/kg/min = prohibitive risk

Q10. What body plethysmography measures and why is it preferred over nitrogen washout?

Q11. What is the significance of a "scooped-out" expiratory limb on the flow-volume loop?

Q12. What are acceptability criteria for a valid spirometry result?

1. Rapid, abrupt start with high peak expiratory flow
2. Duration ≥ 6 seconds in adults (or until plateau)
3. No cough, extra breaths, or artifacts
4. Maximum 8 attempts; best of at least 3 acceptable maneuvers; top 2 FVC values should be within 150 mL of each other

SECTION 7 - QUICK-FIRE MNEMONICS

SECTION 8 - RAPID REFERENCE NORMAL VALUES

Classification of Pulmonary Function Tests + Bedside PFTs

CLASSIFICATION OF PULMONARY FUNCTION TESTS

CLASS 1 - TESTS OF VENTILATORY MECHANICS (Spirometry)

A. Static Tests (no airflow - measures volumes at rest)

Note: RV, FRC, and TLC cannot be measured by spirometry - they need plethysmography, nitrogen washout, or helium dilution.

B. Dynamic Tests (during airflow - measures flow and timed volumes)

• Airway reactivity (bronchial provocation - methacholine, histamine)
• Small airway function (closing volume, closing capacity, nitrogen slope)

CLASS 2 - TESTS OF LUNG VOLUMES (Static Absolute Volumes)

Key exam point: In COPD, plethysmography gives a higher FRC/TLC than nitrogen washout or helium dilution because trapped gas is measured. The difference between the two estimates is a measure of gas trapping.

CLASS 3 - TESTS OF GAS TRANSFER / DIFFUSING CAPACITY

CLASS 4 - TESTS OF GAS EXCHANGE AND CONTROL OF BREATHING

CLASS 5 - EXERCISE TESTING (Cardiopulmonary Exercise Testing - CPET)

SUMMARY: COMPLETE CLASSIFICATION AT A GLANCE

PULMONARY FUNCTION TESTS
│
├── 1. SPIROMETRY (Ventilatory Mechanics)
│   ├── Static: VC, TV, IRV, ERV, IC
│   └── Dynamic: FVC, FEV1, FEV1/FVC, FEF25-75%, MVV, Flow-Volume Loops
│
├── 2. LUNG VOLUMES (Absolute)
│   ├── Body Plethysmography (Boyle's law)
│   ├── Nitrogen Washout
│   └── Helium Dilution
│       → Gives: FRC, RV, TLC
│
├── 3. GAS TRANSFER
│   └── DLCO (Single-breath CO method)
│       → DLCO/VA = KCO
│
├── 4. GAS EXCHANGE & VENTILATORY CONTROL
│   ├── ABG / A-a gradient
│   ├── Pulse oximetry
│   ├── Closing volume
│   └── Ventilatory response curves (CO2/O2 drives)
│
└── 5. EXERCISE TESTING (CPET)
    → VO2 max, Anaerobic threshold, VE/VCO2

BEDSIDE PULMONARY FUNCTION TESTS

Complete List of Bedside PFTs (with interpretations)

1. Snider's Match Blowing Test

• Patient mouth wide open, chin supported, no head tilt, no air movement in room
• Match held 6 inches (15 cm) from the mouth at the same level
• Patient blows the match out forcefully

Historical note: One of the earliest preoperative pulmonary tests described - BJA Education notes this "provides a simple measure of FEV1 or maximum breathing capacity." Some clinicians held the match at arm's length to correct for the subject's height.

2. Forced Expiratory Time (FET)

• Patient takes a deep breath → exhales maximally and forcefully
• Stethoscope placed over the trachea and listen to the duration of expiratory breath sounds

The FET correlates with FEV1/FVC ratio - a prolonged FET reliably predicts obstruction.

3. Seberese's (Sabrasez's) Single Breath Count Test

• Patient takes a deep breath (maximal inspiration)
• Counts aloud: 1, 2, 3 ... as fast as possible in a single breath until breath runs out

• Indicates vital capacity indirectly
• Useful for monitoring trends pre- and post-operatively
• Simple, repeatable, no equipment needed

4. Seberese's (Sabrasez's) Breath Holding Test

• Patient takes a normal tidal inspiration and holds it
• Time (in seconds) is recorded

Normal VC = 3100-4800 mL or 60-70 mL/kg

5. Cough Test

• Patient takes a deep breath, then coughs forcefully
• Assess: ability to cough, strength, effectiveness

• FVC < 20 mL/kg
• FEV1 < 15 mL/kg

• Inadequate cough = inability to clear secretions post-extubation
• Risk of aspiration, atelectasis, and postoperative pneumonia
• Guides decision on extubation readiness and postoperative physiotherapy need

6. Debono's Whistle Test

• Patient blows into a whistle-like device or pursed-lip breathing test
• Assesses expiratory reserve and expiratory flow rate
• Normal: able to produce a sustained whistle
• Reduced: indicates poor expiratory reserve

7. Wright's Peak Flow Meter

• Patient takes maximal inspiration → exhales forcefully and rapidly into the peak flow meter
• Reads Peak Expiratory Flow Rate (PEFR) in L/min

• Simple monitoring tool for asthma (diurnal variation > 20% = asthma)
• Pre- and post-bronchodilator comparison at bedside

8. Spirometry with a Pocket-Sized Spirometer

• Handheld devices (e.g., MicroSpiro, Vitalograph) can be used at bedside
• Gives FVC, FEV1, FEV1/FVC ratio
• Acceptable for screening; less accurate than laboratory spirometry

Additional Bedside Assessments (from BJA Education / Miller's)

QUICK COMPARISON TABLE: BEDSIDE PFTs

VIVA PEARLS ON CLASSIFICATION AND BEDSIDE PFTs

IV Fluids - MD Anesthesia Final Practical Viva Guide

HOW TO PRESENT AN IV FLUID IN VIVA

"Sir/Ma'am, this is a bag of [Name]. It is a [crystalloid/colloid], [isotonic/hypotonic/hypertonic] solution. Its composition is... Its osmolality is... Its pH is... It is used for... Key clinical considerations are..."

PART 1 - THE MASTER COMPOSITION TABLE

PART 2 - INDIVIDUAL FLUID PRESENTATIONS

1. Normal Saline (0.9% NaCl)

"This is 0.9% Normal Saline. It is an isotonic, unbalanced crystalloid. It contains Na⁺ 154 mEq/L and Cl⁻ 154 mEq/L. Osmolality is 308 mOsm/L, pH is 5.0. It distributes to the extracellular compartment - approximately 25% remains intravascular, 75% moves to the interstitium."

• Called "normal" but is not physiologically normal - plasma Cl⁻ is 97-107 mEq/L; NS has 154 mEq/L (supraphysiologic)
• The excess chloride reduces the Strong Ion Difference (SID) → causes hyperchloremic, non-anion gap metabolic acidosis with large volumes
• 1 L NS gives ~308 mOsm of solute - stays in ECF

• Hypovolemia, hemorrhage resuscitation
• Hypochloremic, hypokalemic metabolic alkalosis (vomiting, NGT suction)
• Blood transfusion diluent (compatible; RL causes Ca²⁺-mediated clotting)
• Drug dilution (many drugs incompatible with RL)
• Correction of hyponatremia (relative to hypotonic NS)

• Avoid large volumes in: renal failure, hyperchloremia, hypernatremia
• Avoid if at risk of hyperchloremic acidosis (trauma, massive resuscitation)
• Not ideal for maintenance - causes fluid retention (no buffer mechanism)

2. Ringer's Lactate (RL) / Hartmann's Solution

"This is Ringer's Lactate, also called Hartmann's solution. It is an isotonic, balanced crystalloid. Composition: Na⁺ 130, Cl⁻ 109, K⁺ 4, Ca²⁺ 3 mEq/L, with lactate 28 mEq/L as buffer. Osmolality 273-275 mOsm/L, pH 6.5. It most closely mimics plasma composition among commonly available fluids."

• Lactate metabolized primarily by hepatic oxidation or gluconeogenesis at up to 200 mmol/hour
• Contains racemic D- and L-lactate (D-lactate in trace amounts - concerns about encephalopathy not confirmed at clinical doses)
• Avoid in severe liver failure - lactate cannot be metabolized
• Slightly hypotonic (275 vs 285-295 mOsm/L of plasma) - minimal free water effect
• Does not cause hyperchloremic acidosis
• Contains Ca²⁺ - incompatible with blood transfusion (Ca²⁺ chelates citrate anticoagulant, can cause clotting in giving set)
• Contains K⁺ 4 mEq/L - use with caution in hyperkalemia (renal failure, burns)

• Fluid resuscitation (surgical losses, burns, trauma, diarrhea)
• Preferred intraoperative maintenance fluid
• Burns (Parkland formula: 4 mL/kg/% BSA burned in first 24h, half in first 8h)
• GI losses (closest match to intestinal fluid composition)
• Hypovolemia in most routine surgical cases

• Severe liver failure (cannot metabolize lactate)
• Hyperkalemia (contains K⁺ 4 mEq/L - though clinically minor)
• Blood transfusion via same IV line
• Head injury (slightly hypotonic - theoretical concern of cerebral edema; use NS instead)

3. D5W (5% Dextrose in Water)

"This is 5% Dextrose in Water - D5W. It contains 50 grams of glucose per litre in sterile water. Initial osmolality is 252 mOsm/L, but once glucose is metabolized, it becomes effectively free water. pH is 4.0. It is functionally hypotonic."

• 1 L D5W provides 200 kcal (not meaningful caloric support - maintenance glucose only)
• Once glucose is taken up by cells: distributes as free water → 1/12 remains intravascular, 8/12 goes intracellular, 3/12 to interstitium
• Glucose 5 g/dL = 278 mmol/L → same as glucose in plasma but as a bolus this rapidly equilibrates
• Do not use for resuscitation - minimal intravascular volume expansion

• Hypoglycemia
• Hypernatremia (provides free water to dilute Na⁺)
• DKA (after initial NS resuscitation, when glucose < 250 mg/dL - to prevent hypoglycemia while continuing insulin)
• Maintenance fluid to provide calories and prevent ketosis (often used as D5 in 0.45% NS or D5 in 0.225% NS for maintenance)
• Vehicle for IV medications (e.g., amiodarone infusion)

• Head injury (hypotonic → worsens cerebral edema)
• Acute stroke
• Trauma (free water worsens edema)
• Burns (hypovolemia worsens)
• Liver failure (impaired glucose metabolism)
• Never use for resuscitation - no oncotic/effective osmotic pressure

4. DNS (Dextrose Normal Saline = D5 + 0.9% NS)

"This is DNS - Dextrose Normal Saline, containing 5% dextrose in 0.9% normal saline. It is a hypertonic solution with osmolality approximately 560 mOsm/L. Na⁺ 154, Cl⁻ 154, glucose 50 g/L. pH ~4.5."

• The dextrose component adds 252 mOsm/L on top of NS's 308 mOsm/L → hypertonic initially
• Once glucose is metabolized → effectively becomes 0.9% NS
• Provides both sodium and calories - used when both fluid and limited energy are needed

• Maintenance fluid in paediatrics (classic: 4-2-1 rule maintenance often uses D5/0.45% NS)
• Post-operative maintenance when caloric support needed along with electrolyte replacement
• Hypoglycemia with mild hyponatremia
• Patients who are NPO for extended periods

• Same hyperchloremic acidosis risk as NS in large volumes
• Hyperglycemia risk (monitor glucose, especially diabetics and post-cardiac surgery)

5. Sterofundin ISO (Balanced Crystalloid)

"Sterofundin ISO is a balanced, isotonic crystalloid. Its composition closely mimics plasma: Na⁺ 140, Cl⁻ 127, K⁺ 4, Ca²⁺ 2.5 mEq/L, with acetate 24 and malate 5 mEq/L as buffers. Osmolality ~309 mOsm/L, pH 5.1-5.9. It is similar to PlasmaLyte."

• Chloride level (127) is much closer to plasma (97-107) - less risk of hyperchloremic acidosis
• Uses acetate and malate instead of lactate - metabolized by liver, muscle, heart
• Acetate has faster metabolism than lactate (300 mmol/h vs 200 mmol/h)
• Does not require hepatic metabolism predominantly - useful in liver failure
• Does not contain Ca²⁺ → compatible with blood transfusion (unlike RL)
• Near-physiologic SID → maintains acid-base balance

• General perioperative fluid replacement
• Preferred when large volumes needed - less acidosis risk than NS
• When hepatic lactate metabolism is impaired
• Increasingly replacing NS in ICU and OR

6. 3% NaCl (Hypertonic Saline)

"This is 3% Sodium Chloride, a hypertonic saline solution. It contains Na⁺ 513, Cl⁻ 513 mEq/L. Osmolality 1026 mOsm/L - approximately 3.5 times that of plasma. It is a highly concentrated hypertonic solution administered in small volumes via central venous access."

• Creates a strong osmotic gradient → draws free water from cells into the intravascular space
• Reduces intracellular volume → reduces cerebral edema
• Rapidly corrects hyponatremia

• Severe symptomatic hyponatremia (seizures, coma, Na⁺ < 120 mEq/L with symptoms)
• Raised intracranial pressure / cerebral edema (alternative to mannitol; preferred in some units)
• Neurosurgery (TBI, SAH)
• After cardiac surgery with hyponatremia

• Must be given via central venous catheter (peripheral extravasation → tissue necrosis)
• Rate of correction: max 8-10 mEq/L per 24 hours (risk of osmotic demyelination syndrome / central pontine myelinolysis if corrected too fast)
• Monitor serum Na⁺ every 2-4 hours during infusion
• Do not use in hypernatremia, heart failure, renal failure

PART 3 - COLLOIDS

Classification of Colloids

COLLOIDS
│
├── NATURAL
│   └── Albumin (4-5%, 20-25%)
│
└── SYNTHETIC
    ├── Gelatins (Gelofusine, Haemaccel)
    ├── Hydroxyethyl Starch (HES) - Voluven, Volulyte
    └── Dextrans (Dextran 40, Dextran 70)

Why Colloids Expand Plasma Volume Better Than Crystalloids

7. Albumin (5% and 25%)

"Albumin is a natural colloid derived from pooled human plasma. The 5% albumin solution is iso-oncotic, with osmolality ~309 mOsm/L. The 25% albumin is hyperoncotic and draws fluid from the interstitium into the intravascular space. Na⁺ 130-160 mEq/L."

• Spontaneous bacterial peritonitis (SBP) with cirrhosis
• Hepatorenal syndrome (HRS)
• Large volume paracentesis (>5L) - prevents paracentesis-induced circulatory dysfunction
• Burns (after first 24h, replacing colloid loss)
• Hypoalbuminemia when serum albumin < 2 g/dL with clinical manifestations
• SAFE trial: No harm vs NS in ICU; may benefit patients with TBI (trend toward harm with albumin in TBI)

• Expensive
• Risk of viral transmission (though heat-treated)
• Anaphylactoid reactions (rare)

8. Hydroxyethyl Starch (HES) - Voluven 6%, Volulyte

"Voluven is 6% Hydroxyethyl Starch in 0.9% NaCl. HES is a synthetic polysaccharide derived from waxy maize starch. It has a molecular weight of ~130 kDa. It is an isotonic colloid with good plasma expansion properties."

• Cleared by amylases (serum, tissue) → excreted renally
• C2:C6 ratio and degree of substitution determine half-life and renal clearance
• Voluven (130/0.4) has lower molecular weight and degree of substitution than older HES → less tissue accumulation

• Hypovolemia and plasma volume expansion
• Perioperative volume replacement

• Banned/severely restricted in: sepsis, renal impairment, ICU patients, intracranial surgery
• 6Cs/CHEST trial evidence: HES associated with increased AKI and need for renal replacement therapy, increased mortality in septic patients
• Do not use in: critical illness, sepsis, renal failure, liver failure, intracranial bleeding

9. Gelatin Solutions (Gelofusine, Haemaccel)

"Gelofusine is a 4% succinylated gelatin solution in 0.9% NaCl. Molecular weight ~30,000 Da. Na⁺ 154, Cl⁻ 125 mEq/L. Osmolality 308 mOsm/L, pH 7.4. Haemaccel is a 3.5% polygeline in electrolyte solution."

• Cheaper and more available than albumin
• Smaller molecules → leak across capillaries faster → shorter duration of effect
• Lower anaphylaxis risk than dextrans
• No effect on coagulation (unlike dextrans and HES)
• Not restricted like HES - can use in wider range of patients

10. Dextrans (Dextran 40, Dextran 70)

"Dextran is a synthetic polysaccharide colloid. Dextran 40 is a 10% solution in NS (MW ~40,000 Da); Dextran 70 is a 6% solution (MW ~70,000 Da). Both have osmolality ~310 mOsm/L."

• Anti-thrombotic / anti-sludging effects: Dextran 40 reduces red cell aggregation, improves microcirculation - used in peripheral vascular surgery, free flap surgery
• Coats platelets and vessel walls → inhibits coagulation - risk of bleeding
• Excreted renally - can cause tubular obstruction (dextran nephropathy)

• Anaphylaxis - highest risk among colloids (1:3000 to 1:50,000)
• Coagulopathy (max dose 1.5 g/kg/day for Dextran 70; 20 mL/kg for Dextran 40)
• Interfere with blood cross-matching (coat RBCs - blood bank must be aware)
• Dextran nephropathy with high doses
• Pulmonary edema

PART 4 - IV PARACETAMOL (PCM) INFUSION

How to Present:

"This is Perfalgan or IV Paracetamol - acetaminophen 10 mg/mL in 100 mL vial (i.e., 1 gram in 100 mL). It is an analgesic and antipyretic for IV use. It is given as a 15-minute infusion."

Composition:

• Paracetamol 10 mg/mL (1 g/100 mL)
• Mannitol as excipient (for solubility)
• pH: 5.5 (adjusted with hydrochloric acid/NaOH)
• Osmolality: ~290 mOsm/L

Dosing:

Mechanism of Action:

• Inhibits prostaglandin synthesis centrally (COX-1 and COX-2 in CNS - weak peripheral effect)
• Acts on endocannabinoid system (AM404 metabolite activates TRPV1 channels)
• May act on serotonergic descending pain pathways
• No peripheral anti-inflammatory action (unlike NSAIDs) - no COX inhibition in peripheral tissues at clinical doses

Advantages over oral PCM in perioperative setting:

• Faster Tmax (end of infusion vs 30-60 min for oral)
• Reliable absorption (no GI uncertainty in perioperative period)
• Can be given when patient is NPO
• Opioid-sparing effect: reduces morphine requirement by 20-30%
• No GI side effects, no platelet effects (unlike NSAIDs)
• Safe in renal impairment (unlike NSAIDs)

Indications (perioperative):

• Part of multimodal analgesia protocol
• Post-operative pain (mild-moderate)
• Antipyresis in ICU
• Opioid-sparing strategy (reduces PONV, respiratory depression risk)

Contraindications / Cautions:

• Hepatic impairment / active liver disease - reduce dose or avoid
• Alcoholism (increased NAPQI formation)
• G6PD deficiency (relative)
• Paracetamol poisoning: NAPQI accumulates → hepatic necrosis → treat with N-acetylcysteine (NAC)
• Drug interactions: warfarin (prolonged INR with chronic use), isoniazid (increases NAPQI)

Hepatotoxicity Mechanism (must know):

PART 5 - CRYSTALLOID vs COLLOID: THE KEY VIVA COMPARISON

PART 6 - POSSIBLE VIVA QUESTIONS & IDEAL ANSWERS

• First 10 kg: 4 mL/kg/hour
• Next 10 kg (10-20 kg): 2 mL/kg/hour
• Each kg above 20 kg: 1 mL/kg/hour Example: 25 kg child → (10×4) + (10×2) + (5×1) = 40 + 20 + 5 = 65 mL/hour

QUICK MEMORY AID

• Balanced = Sterofundin, PlasmaLyte
• Osmolality comparison: NS 308 > Sterofundin 309 > RL 275 > D5W 252
• RL = No blood transfusion (Ca²⁺ issue)
• NS = Hyperchloremic acidosis in large volumes
• Sodium 154 in NS; 130 in RL; 140 in Sterofundin; 513 in 3% NaCl
• Acidosis from NS - hyperchloremic, normal anion gap
• D5W = Free water once metabolized - avoid in head injury