Treatment of SAIO (Small/Acute Intestinal Obstruction)

The Three Main Measures (Summary Box 78.11)

1. Gastrointestinal drainage via nasogastric (NG) tube
2. Fluid and electrolyte replacement
3. Relief of obstruction (surgical or conservative)

Surgical treatment is necessary for most cases, but should be delayed until resuscitation is complete, unless there are signs of strangulation or closed-loop obstruction.

1. Supportive / Resuscitative Management

Nasogastric Decompression

• Insert a non-vented (Ryle) or vented (Salem sump) tube
• Place on free drainage with 4-hourly aspiration, or continuous/intermittent suction
• Decompresses the bowel proximal to obstruction and reduces aspiration risk during anaesthesia

Fluid and Electrolyte Replacement

• The primary biochemical deficit is sodium and water loss
• Replace with Hartmann's solution or normal saline
• Volume guided by clinical, haematological, and biochemical parameters (urine output, serum electrolytes, haematocrit)

2. Indications for EARLY Surgical Intervention (Summary Box 78.13)

• Classic dictum: "The sun should not both rise and set on a case of unrelieved acute intestinal obstruction"
• If complete obstruction with no ischaemia: defer surgery until resuscitation is complete
• If obstruction is likely adhesive: conservative management for up to 72 hours is acceptable

3. Conservative (Non-operative) Management

• Obstruction is partial (gas present distal to obstruction)
• Likely adhesive cause in a patient with prior abdominal surgery
• No signs of strangulation

• NG tube decompression
• IV fluids and electrolytes
• Strict observation - any clinical deterioration mandates surgery
• Duration: should rarely exceed 72 hours

A relative contraindication to conservative management is complete SBO (dilated small intestine with no distal gas).

4. Surgical Treatment

Approach

• If the site of obstruction is unknown: midline laparotomy for best exposure
• Assess:
  1. Site of obstruction
  2. Nature of the obstruction
  3. Viability of the gut

Operative Decompression

• Insert a large-bore orogastric tube and milk small bowel contents retrogradely to the stomach
• Take care - bowel is distended and oedematous; avoid mesenteric tears
• Savage's decompressor through a seromuscular purse-string suture may be used (but carries septic/leak risk)

Procedures Depending on Cause

Assessing Bowel Viability

• Wrap doubtful bowel in hot moist packs for 10 minutes, then reassess
• Check: colour, sheen, peristalsis, and mesenteric pulsation
• If still in doubt - resect, unless the extent of resection risks short bowel syndrome
• Serosal tears should be repaired; areas of doubtful viability should be invaginated or resected

Laparoscopic Adhesiolysis

• Can be considered in highly selected cases of SBO due to adhesions
• Classed as an advanced laparoscopic procedure - only by surgeons with appropriate skills

5. Treatment of Adhesive Obstruction (Summary Box 78.14)

• Initially treat conservatively (no signs of strangulation)
• Conservative treatment should rarely exceed 72 hours
• At operation: divide only the causative adhesion(s) - limit dissection to minimise further adhesion formation
• Repair serosal tears; invaginate or resect areas of doubtful viability

6. Treatment of Recurrent Obstruction from Adhesions

• Repeat adhesiolysis (enterolysis) - the standard approach
• Noble's plication operation
• Childs-Phillips transmesenteric plication
• Intestinal intubation (long tube stenting)

The latter three are largely of historical interest and rarely required in modern practice.

7. Postoperative / Early Mechanical Obstruction

• Distinguish from paralytic ileus (which is more common early post-op)
• Mechanical obstruction is more likely if the patient regained bowel function and it subsequently stopped
• Most are incomplete and managed conservatively initially
• Requires surgical intervention if conservative management fails

Quick Summary Algorithm

SAIO diagnosed
     │
     ├── Signs of strangulation / closed loop / unoperated abdomen?
     │         YES → Resuscitate + URGENT SURGERY
     │
     └── No signs of strangulation + likely adhesive?
               │
               ├── Conservative (NG tube + IV fluids) up to 72 hours
               │
               └── No resolution at 72 hours / deterioration?
                         → SURGERY (enterolysis ± resection)

Drugs Used to Relieve SAIO (Small/Acute Intestinal Obstruction)

1. Gastrografin (Diatrizoate Meglumine - Water-Soluble Contrast)

Mechanism

• Gastrografin is hyperosmolar (1,900 mOsm/L)
• Draws fluid into the bowel lumen by osmosis
• This decreases bowel wall oedema at the obstruction point
• The resulting increase in intraluminal fluid may stimulate peristalsis and mechanically "break" the obstruction
• The exact mechanism is not completely understood

Evidence (Maingot's Abdominal Operations)

Dose & Administration

• Given orally (or via NG tube) - 100 mL diluted in water
• If contrast reaches the colon within 4-8 hours on follow-up X-ray → strongly predicts non-operative resolution
• If contrast does not reach colon → surgery more likely needed

Contraindications

• Suspected strangulation or perforation (absolute contraindication)
• Complete bowel obstruction with closed-loop features
• Aspiration risk - if aspirated, causes severe pneumonitis
• Rapidly becomes diluted in established distal SBO, reducing efficacy

Special Use: Meconium Ileus

• Gastrografin enema is both diagnostic AND therapeutic in meconium ileus in neonates
• Relieves the obstructing meconium plug by drawing water into the terminal ileum
• Failure of Gastrografin enema → surgical indication

2. IV Fluids - Resuscitative "Drugs"

• Volume guided by: urine output, serum electrolytes, haematocrit, clinical assessment
• Must be given before any surgical intervention

3. Antibiotics

• Broad-spectrum IV antibiotics covering gram-negative organisms and anaerobes (e.g., piperacillin-tazobactam, cefuroxime + metronidazole)
• Indicated perioperatively when bowel resection is performed or strangulation suspected
• Rationale: bacterial translocation occurs across ischaemic bowel wall; endotoxin release from gram-negative organisms contributes to sepsis

4. Corticosteroids (Crohn's Disease-related Obstruction)

• IV corticosteroids (e.g., hydrocortisone, methylprednisolone) reduce the inflammatory oedema component
• Combined with NG decompression and IV hydration
• Partial obstruction from Crohn's can resolve with this approach
• Does not help fibrotic/chronic strictures - those require surgery or endoscopic dilatation

5. Octreotide (Somatostatin Analogue)

• Reduces intestinal secretions (anti-secretory effect)
• Decreases splanchnic blood flow
• Reduces cramping abdominal pain
• Effective for palliation in prospective trials in malignant obstruction
• Not a standard drug for benign mechanical SBO
• Dose: 100-300 mcg SC/IV 8-hourly or by continuous infusion

6. Antiemetics

Caution: Prokinetics (metoclopramide, erythromycin) are contraindicated in complete mechanical obstruction - they increase peristaltic pressure against the obstruction and risk perforation. They are only acceptable in confirmed paralytic ileus (adynamic obstruction).

7. Analgesics / Opioids

• Opioids (morphine, fentanyl) for pain control
• In malignant obstruction: IV or subcutaneous opioids, transitioning to transdermal patches when stable
• Morphine also reduces intestinal secretions (useful in malignant obstruction)

Summary Table

Does Bisacodyl Help in Relieving SAIO?

Short Answer: No - Bisacodyl is Contraindicated in Mechanical SAIO

What Bisacodyl Actually Does

Mechanism of Action (Goodman & Gilman's Pharmacological Basis of Therapeutics)

• Acts on enterocytes, enteric neurons, and GI smooth muscle
• Requires hydrolysis by intestinal esterases for activation - meaning it can act in both the small and large intestine (unlike senna/sodium picosulfate which act only in the colon)
• Induces powerful propulsive peristaltic motor activity almost immediately when applied to the colonic mucosa
• Stimulates colonic secretion (net fluid accumulation in the lumen)
• Can cause apoptosis of colonic epithelial cells and has been shown to cause colonic ischaemia and inflammatory changes in the small bowel and colon

Onset of Action

• Oral (enteric-coated tablet): 6-10 hours
• Rectal suppository: 15-60 minutes

Why Bisacodyl is Harmful in Mechanical SAIO

The Key Pharmacological Principle

In mechanical obstruction, any agent that increases peristaltic drive (bisacodyl, metoclopramide, senna, castor oil) is contraindicated because it pushes intestinal contents against a fixed blockage, risking perforation and ischaemia.

What Bisacodyl IS Used For

• Chronic constipation (short-term, max 10 consecutive days)
• Bowel preparation before procedures
• Post-operative constipation once mechanical obstruction is excluded and bowel sounds are confirmed

What to Use Instead in SAIO

Bottom Line

Alprazolam (Xanax)

Classification

• Class: Benzodiazepine (high-potency, short-to-intermediate acting)
• Schedule: Schedule IV controlled substance (DEA)
• Trade names: Xanax, Xanax XR, Alprax, Restyl, Tafil, Niravam, Frontin, Alzolam, Ksalol, Onax, and many others

Mechanism of Action

• Enhancement of Cl⁻ ion influx into neurons
• Both pre- and post-synaptic inhibition throughout the CNS
• Net effect: sedation, anxiolysis, muscle relaxation, anticonvulsant activity

Pharmacokinetics

Because of its intermediate half-life, dosing less frequently than TID (e.g. every-other-day) is not recommended - it risks inter-dose withdrawal symptoms as plasma levels fluctuate.

Indications

Alprazolam has particularly well-established evidence for panic disorder - multicenter double-blind studies show it is effective, and in equivalent doses, other benzodiazepines are similarly effective (Kaplan & Sadock's).

Available Formulations & Doses

• Anxiety: 0.25-0.5 mg TDS, max 4 mg/day
• Panic disorder: 0.5-1 mg TDS, may need up to 6-10 mg/day in severe cases
• Elderly: start 0.25 mg BD-TDS (reduce initial dose)

Adverse Effects

Dependence, Withdrawal & Misuse

Dependence

• FDA boxed warning: physical dependence and withdrawal can occur within "several days to weeks, even as prescribed"
• Not everyone who stops will experience withdrawal - depends on dose, duration, and individual factors
• Abrupt cessation can cause life-threatening seizures

Alprazolam Withdrawal - Particularly Difficult (Kaplan & Sadock's)

• Inter-dose withdrawal symptoms are common if doses are spaced too far apart
• A paradoxical effect occurs as doses are reduced below ~1-1.5 mg/day: the GABA-A receptor undergoes paradoxical downregulation instead of upregulation, worsening withdrawal symptoms even with a slow taper
• Withdrawal symptoms include: worsening anxiety, insomnia, nightmares, irritability, hypervigilance, rage reactions, dissociation, suicidal/homicidal ideation (case series at high-dose long-term use)
• Symptoms can persist for "several weeks to more than 12 months" after stopping (FDA)

Management of Withdrawal

• Slow taper over 3-6 months or longer
• Switch to a longer-acting benzodiazepine (e.g. diazepam) before tapering - 1 mg alprazolam ≈ 20 mg diazepam equivalent
• Reinstate previous dose if withdrawal established, then taper more slowly
• Adjuncts: clonazepam (to facilitate the final taper), carbamazepine, pregabalin, melatonin, CBT

Misuse

• 17% of people taking benzodiazepines report misuse (2015-2016 national survey)
• Highest misuse rates: ages 18-25 years (51%)
• Most commonly misused in combination with opioids or stimulants (to augment the "high")
• Only 1% of substance abuse program patients identify benzodiazepines as their primary drug of abuse

Important Drug Interactions

Contraindications

• Myasthenia gravis
• Severe respiratory insufficiency
• Sleep apnoea syndrome
• Severe hepatic impairment
• Pregnancy (risk of neonatal withdrawal, floppy infant syndrome)
• Acute angle-closure glaucoma
• Known hypersensitivity to benzodiazepines

Key Clinical Points

1. Alprazolam is high-potency - small doses produce significant pharmacological effects
2. Its shorter half-life (vs. diazepam) makes it more prone to inter-dose withdrawal and rebound anxiety
3. Receptor occupancy is hyperbolic - to minimise withdrawal during tapering, dose reductions should also be hyperbolic (larger reductions early, smaller reductions later), not linear
4. For safe discontinuation: switch to diazepam equivalent and taper diazepam gradually
5. Despite widespread use, alprazolam should be used only short-term and not as a first-line long-term anxiolytic - SSRIs/SNRIs are preferred for chronic anxiety and panic disorder

Nicorandil

Classification

• Class: Antianginal agent - hybrid K_ATP channel opener + nitrate donor
• Chemical: Nicotinamide nitrate ester
• Availability: Approved in Europe, Japan, and many Asian countries - NOT approved in the USA
• Trade names: Ikorel (UK/Europe), Sigmart (Japan), Dancor

Mechanism of Action - Dual Action (Unique)

1. K_ATP Channel Opening (Potassium Channel Opener)

• Opens ATP-sensitive potassium (K_ATP) channels on vascular smooth muscle
• K⁺ efflux → membrane hyperpolarisation → closure of voltage-gated Ca²⁺ channels → smooth muscle relaxation
• Preferential action on arterial (resistance vessel) beds → reduces afterload
• This effect is partially blocked by glibenclamide (sulphonylurea - a K_ATP channel blocker), confirming K_ATP channel involvement

2. Nitrate-Like Action (cGMP-mediated)

• Acts as a nitric oxide (NO) donor via its nitrate ester component
• NO activates soluble guanylyl cyclase → ↑ cGMP → protein kinase G activation → vascular smooth muscle relaxation
• Preferential action on venous (capacitance vessel) beds → reduces preload
• Effect is potentiated by PDE5 inhibitors (e.g. sildenafil) - this is a key drug interaction

Combined Haemodynamic Effect

• Dilates both arterial and venous vascular beds
• Reduces preload (venodilation) AND afterload (arteriodilation)
• In the absence of direct negative inotropic effects, reduced afterload → cardiac output increases (stronger than seen with pure nitrovasodilators)
• Reflex tachycardia contributes to this
• Haemodynamic profile lies between nitrovasodilators and dihydropyridine CCBs

Additional Mechanism: Ischaemic Preconditioning

• Mimics ischaemic preconditioning - the protective phenomenon where brief ischaemia protects the myocardium from subsequent prolonged ischaemia
• Mediated via activation of mitochondrial K_ATP channels
• Reduces intracellular Ca²⁺ overload by activating Na⁺/Ca²⁺ exchanger
• Net effect: cardioprotection - reduces myocardial injury during ischaemia/MI

Pharmacokinetics (ADME)

The short half-life is a pharmacokinetic limitation - standard BD dosing does not maintain adequate trough plasma levels.

Indications

Clinical Evidence

IONA Trial (Impact Of Nicorandil in Angina)

• Large randomised controlled trial in patients with stable angina
• Nicorandil significantly reduced the relative risk of fatal and non-fatal coronary events
• One of the few antianginal drugs (beyond beta-blockers) to show a prognostic benefit
• Katzung's notes: "One large trial showed a significant reduction in relative risk of fatal and nonfatal coronary events in patients receiving the drug"

Tolerance

• Unlike organic nitrates, there is less tolerance development with nicorandil
• However, early studies (Meany et al. 1989; Rajaratanam et al. 1999) reported a clear decrease or loss of antianginal effect after 2 weeks of oral treatment - this remains an unresolved issue

Adverse Effects

Nicorandil-associated ulceration is a distinctive and serious adverse effect. It can affect the mouth, GI tract (oesophagus, stomach, small bowel, colon), perianal region, and skin. These ulcers are often large, painful, and non-healing - they resolve on stopping the drug. It should be listed on the drug history in any patient with unexplained GI or perianal ulceration.

Key Drug Interactions

Contraindications

• PDE5 inhibitor use (sildenafil, tadalafil, vardenafil)
• Cardiogenic shock or severe hypotension
• Left ventricular failure with low filling pressures
• Hypersensitivity to nicorandil
• Hypovolaemia

Comparison with Other Antianginals

Key Clinical Pearls

1. Nicorandil is the only antianginal with both K_ATP channel opening AND nitrate activity simultaneously
2. It reduces both preload and afterload without directly reducing contractility
3. The IONA trial demonstrated prognostic benefit - rare among antianginals
4. Tolerance is less of a problem than with organic nitrates, but loss of efficacy over 2 weeks has been reported
5. Nicorandil-associated ulcers are a serious, underrecognised complication - always consider stopping the drug in any patient with unexplained oral, GI, perianal, or cutaneous ulcers
6. The PDE5 inhibitor interaction is absolute - same principle as with organic nitrates (synergistic hypotension)
7. Glibenclamide may blunt its efficacy in diabetic patients on sulphonylureas

Hypothyroidism Management in a 50-Year-Old Male with HTN and CAD

Why This Patient is Complex

• Raises LDL cholesterol (decreases hepatic LDL receptor numbers + reduces cholesterol 7α-hydroxylase activity)
• Worsens hypertension (increases systemic vascular resistance)
• Causes endothelial dysfunction and elevated homocysteine
• Depresses myocardial contractility and cardiac output
• Causes diastolic dysfunction

Drug of Choice

Levothyroxine (L-T4, Synthetic T4)

• Only recommended thyroid replacement therapy in this patient
• Purified synthetic preparation of L-thyroxine (T4)
• Gradual peripheral conversion to active T3 provides a physiological, buffered response - safer than direct T3 (liothyronine), which acts too quickly and unpredictably in CAD

Do NOT use liothyronine (T3) or desiccated thyroid in CAD patients - their rapid action and direct cardiac stimulation carry significantly higher risk of precipitating ischaemia.

Dosing Protocol - CAD-Specific (Braunwald's Heart Disease)

Scenario A: Known Stable CAD, No Revascularisation Planned

Start very low and go very slow - the rationale is that even small increases in T4 can increase myocardial oxygen demand enough to precipitate angina in a patient with critical coronary stenoses.

Scenario B: Patient Has Unstable Angina / Left Main / 3-Vessel Disease

• CABG can and should be performed first, even in overt hypothyroidism
• Hypothyroid patients can undergo cardiac surgery safely
• (Note: severe hypothyroidism may prolong bleeding times/PTT - check clotting factors pre-op)
• Thyroid replacement is then started post-operatively at full or near-full doses (orally or parenterally), once the coronary circulation is revascularised and the patient is no longer at acute ischaemic risk

Scenario C: At-Risk but Asymptomatic (No Proven CAD, but Risk Factors)

For Reference: Healthy Patient < 50 with No Heart Disease

• Full replacement: 1.5 µg/kg/day from the start (no dose titration needed)
• This is NOT appropriate for this patient

Target TSH and Monitoring

Restoration of euthyroidism decreases systemic vascular resistance and reduces afterload - this actually tends to improve myocardial ischaemia over time once the patient has adapted to each dose increment.

Cardiovascular Benefits of Achieving Euthyroidism

• Reduce LDL cholesterol (reducing atherosclerosis progression)
• Lower BP (reduce SVR)
• Improve left ventricular contractility and diastolic function
• Resolve myocardial perfusion defects (scintigraphy studies show ischaemic perfusion defects resolve with T4 treatment)
• Reduce CV events risk - subclinical hypothyroidism with TSH >7 mIU/L is associated with significantly increased CV mortality

Key Drug Interactions Relevant to This Patient

Practical Administration of L-T4

• Take orally, fasting, 30-60 minutes before breakfast
• Consistent timing daily - absorption varies with food
• Avoid within 4 hours of: iron supplements, calcium, antacids, PPIs
• Store at room temperature, away from light and moisture

Summary Algorithm for This Patient

50M with HTN + CAD + Hypothyroidism
           │
           ├── Unstable angina / left main / 3-vessel disease?
           │         YES → Revascularise FIRST (CABG/PCI)
           │               Then start L-T4 post-op at standard doses
           │
           └── Stable CAD (no immediate revascularisation needed)?
                         │
                         ├── Start L-T4 at 12.5 µg/day
                         ├── Ensure beta-blocker is optimised
                         ├── Increase by 12.5-25 µg every 6-8 weeks
                         ├── Check TSH 6-8 weeks after each change
                         └── Target: TSH 0.4-4.0 mIU/L
                               Monitor: Lipids, BP, angina symptoms

Key Clinical Pearls

1. Never start full-dose L-T4 in a CAD patient - even a small dose increase in thyroid hormone can precipitate MI or unstable angina
2. Beta-blocker pre-treatment is protective - ensures the heart is rate-controlled before the metabolic demand of T4 kicks in
3. The benefit of achieving euthyroidism outweighs the risks of remaining hypothyroid - hypothyroidism itself is proatherogenic and worsens cardiac function
4. Myocardial perfusion defects seen on nuclear scans in hypothyroidism are functional, not structural - they resolve with T4 replacement (do not misinterpret as fixed CAD)
5. TSH > 7 mIU/L is a threshold above which treatment benefit is clear even for subclinical hypothyroidism in a cardiac patient
6. The combination of hypothyroidism + hypertension strongly suggests undertreated or undiagnosed hypothyroidism as a contributing cause of the HTN - correction of thyroid status may reduce antihypertensive drug requirements