Anesthetic Considerations: DNB Anesthesia Theory (5 Marks Each)

1. ANESTHETIC CONSIDERATIONS IN PEDIATRIC PATIENTS

A. Physiological Differences (Why children are NOT small adults)

• Relatively large head, short neck, large tongue, anterior larynx (C3-C4 vs C5-C6 in adults)
• Epiglottis is U-shaped, floppy, angled at 45 degrees - use straight blade (Miller)
• Narrowest part of airway is at cricoid ring (subglottic) - makes uncuffed tubes acceptable in children <8 years (though cuffed tubes now widely used)
• Obligate nasal breathers in neonates - nasal obstruction causes respiratory distress
• Formula for ETT size: (Age/4) + 4 (uncuffed); (Age/4) + 3.5 (cuffed)

• High oxygen consumption (~6-8 mL/kg/min vs 3-4 mL/kg/min in adults)
• Low FRC with high closing capacity - rapid desaturation during apnea
• Chest wall compliance is high; lung compliance is low - prone to atelectasis
• Diaphragmatic breathing; intercostal muscles relatively weak

• Heart rate dependent cardiac output (high resting HR: neonates 120-160 bpm)
• Decreased myocardial compliance - cannot increase stroke volume easily
• Bradycardia is poorly tolerated and is the most common cause of cardiac arrest
• Atropine premedication (0.02 mg/kg, minimum 0.1 mg) given to prevent vagally mediated bradycardia, especially with suxamethonium and laryngoscopy

• Large BSA:weight ratio - rapid heat loss
• Non-shivering thermogenesis (brown fat) in neonates
• OR temperature should be maintained at 26-28°C for neonates

B. Pharmacological Considerations

• MAC is higher in infants and children (peak MAC at 1-6 months), then decreases with age
• Inhalational induction is preferred - sevoflurane (non-pungent, low blood-gas solubility, fast onset/offset) is agent of choice
• IV access often obtained after inhalational induction
• Propofol: use with caution in children; PRIS (Propofol Infusion Syndrome) is a risk with prolonged infusions - avoid for PICU sedation
• Suxamethonium: dose is 2 mg/kg (higher than adults). Beware: can cause hyperkalemia in undiagnosed myopathies (Duchenne's) - routine use in children is controversial
• Opioids: neonates have increased BBB permeability, higher sensitivity; reduce doses
• Protein binding: lower albumin and alpha-1 acid glycoprotein in neonates - increased free drug fractions
• Volume of distribution: larger for water-soluble drugs in neonates (higher TBW)

C. Preoperative Considerations

• Fasting: 2-4-6-8 rule: clear fluids 2 hr, breast milk 4 hr, formula/light meal 6 hr, solid food 8 hr
• URTI: postpone elective surgery for 4-6 weeks if recent URTI (increased laryngospasm, bronchospasm risk)
• Premedication: midazolam 0.5 mg/kg oral (max 20 mg) 30 min before; reduces separation anxiety
• EMLA cream: for IV cannulation pain

D. Intraoperative Concerns

• Laryngospasm is the most common respiratory complication - treat with CPAP, jaw thrust, propofol (0.5 mg/kg IV), suxamethonium (1-2 mg/kg IV or 4 mg/kg IM)
• Fluid management: Hartmann's / PlasmaLyte preferred; avoid hypotonic fluids (hyponatremia risk). Maintenance: 4 mL/kg/hr for first 10 kg, 2 mL/kg/hr for next 10 kg, 1 mL/kg/hr thereafter (4-2-1 rule)
• Hypoglycemia monitoring is essential - neonates have limited glycogen stores
• Postoperative apnea: high risk in ex-premature infants (<60 weeks post-conceptual age) - monitor for 12-24 hrs post-op

E. Equipment

• Appropriate-sized mask, LMA, ETT, breathing circuits (Mapleson F/Jackson-Rees for <20 kg), heated humidifier, warming blanket

2. ANESTHETIC CONSIDERATIONS IN ELDERLY PATIENTS

A. Physiological Changes with Aging

• Decreased myocardial compliance and diastolic dysfunction (increased incidence of diastolic dysfunction even without overt disease)
• Reduced cardiac reserve and blunted heart rate response (decreased beta-adrenergic sensitivity)
• Increased vagal tone; decreased baroreceptor sensitivity - prone to orthostatic hypotension
• Prolonged circulation time - delays onset of IV drugs but speeds inhalational induction
• Atherosclerosis, hypertension, coronary artery disease are prevalent
• Exaggerated hypotension during induction

• Decreased lung elasticity - alveolar overdistension and small airway collapse
• Increased residual volume and functional residual capacity; decreased FEV1 and FVC
• Closing capacity exceeds FRC at age 45 years (supine) and 65 years (sitting) - ventilation-perfusion mismatch
• Decreased PaO2 with age: expected PaO2 = 102 - (0.33 × age) mmHg
• Impaired cough reflex and mucociliary clearance - increased aspiration risk
• Decreased response to hypoxia and hypercapnia

• Reduced GFR and renal blood flow (decreases ~1% per year after age 40)
• Serum creatinine may be normal despite reduced GFR (due to reduced muscle mass)
• Impaired Na handling, concentrating/diluting capacity - risk of both dehydration and fluid overload
• Decreased drug excretion - prolonged drug effect

• Liver mass and hepatic blood flow decline - reduced biotransformation
• Reduced albumin synthesis - higher free drug fractions
• Reduced plasma cholinesterase (prolonged suxamethonium effect)

• Brain mass decreases; neuronal loss in frontal cortex
• Reduced synthesis of serotonin, noradrenaline, GABA
• Increased risk of postoperative delirium (POD) and postoperative cognitive dysfunction (POCD)
• Decreased MAC requirement for volatile agents
• Lower dose requirements for propofol, opioids, benzodiazepines, barbiturates

• Reduced muscle mass, osteoporosis, kyphoscoliosis
• Risk of pressure injuries and nerve injuries from positioning

B. Pharmacological Considerations

• Reduced MAC: decrease volatile agent requirements by ~6% per decade after age 40
• Propofol: reduce induction dose by 30-50% (start 1-1.5 mg/kg vs 2-2.5 mg/kg); give slowly
• Opioids: increased brain sensitivity; reduce doses; prolonged effect due to reduced clearance
• Benzodiazepines: increased sensitivity, prolonged sedation, avoid if possible (risk of delirium - part of STOPP/START criteria)
• Muscle relaxants: vecuronium and rocuronium duration prolonged due to reduced hepatic/renal clearance; use neuromuscular monitoring
• Suxamethonium: reduced plasma cholinesterase may prolong block
• Beta-blockers: continue perioperatively to avoid rebound hypertension and tachycardia

C. Preoperative Assessment

• Comprehensive geriatric assessment including:
  • Cognitive status (Mini-Cog test)
  • Depression screening
  • Frailty scoring (Makary frailty index)
  • Functional status and fall history
  • Nutritional status (BMI <18.5, albumin <3 g/dL, weight loss >10% in 6 months = severe risk)
  • Medication reconciliation - polypharmacy common; stop SGLT-2 inhibitors 3-4 days pre-op
  • ACC/AHA cardiac evaluation algorithm for non-cardiac surgery

D. Intraoperative Considerations

• Positioning: pad all pressure points carefully; slow position changes to avoid hypotension
• Temperature: active warming mandatory - reduced thermogenesis, increased heat loss
• Monitoring: arterial line for major surgery; processed EEG (BIS) monitoring to avoid overdose and potentially reduce POD
• Airway: decreased jaw mobility, cervical spine arthritis - difficult intubation anticipated
• Fluid management: precise titration - prone to both under- and over-resuscitation
• Hypotension during induction: vasopressors (phenylephrine, ephedrine) ready; avoid large fluid boluses

E. Postoperative Concerns

• Postoperative Delirium (POD): most common complication; risk factors include age >70, pre-existing dementia, polypharmacy, sleep deprivation, immobility. Prevention: avoid anticholinergics and benzodiazepines, early mobilization, sleep hygiene
• POCD: subtle cognitive decline persisting weeks-months post-op; multifactorial
• Analgesia: multimodal analgesia preferred (paracetamol + NSAID + regional); minimize opioids
• Regional vs General: regional anesthesia associated with lower incidence of DVT/PE (peripheral vasodilation); may reduce POD risk

3. ANESTHETIC CONSIDERATIONS IN HYPERTENSIVE PATIENTS

A. Pathophysiology Relevant to Anesthesia

• Chronic hypertension causes increased systemic vascular resistance, left ventricular hypertrophy (LVH), diastolic dysfunction, and impaired autoregulation
• Target organ damage: brain (cerebrovascular disease), heart (CAD, LVH, CCF), kidneys (CKD), eyes (retinopathy)
• Antihypertensive medications affect anesthetic drug interactions

B. Preoperative Assessment

• Mild-moderate HTN (SBP <180, DBP <110 mmHg): generally safe to proceed
• Severe HTN (SBP ≥180 or DBP ≥110 mmHg): traditionally recommended to postpone elective surgery, optimize BP over weeks - though evidence for this is not strong
• Hypertensive urgency/emergency: postpone elective surgery; treat acutely

• ECG: LVH, ischemic changes, arrhythmias
• Echo: assess LV function, degree of hypertrophy
• RFT: renal involvement (serum creatinine, BUN, electrolytes)
• Urinalysis: proteinuria
• Fundoscopy: Keith-Wagener-Barker grading
• Chest X-ray: cardiomegaly, pulmonary edema

• Continue most antihypertensives on the morning of surgery with a sip of water
• ACE inhibitors/ARBs: controversial - some recommend holding on day of surgery (risk of refractory intraoperative hypotension); consensus now leans toward holding the morning dose
• Beta-blockers: MUST be continued - abrupt withdrawal causes rebound hypertension, tachycardia, myocardial ischemia
• Diuretics: may hold on day of surgery to avoid hypovolemia and electrolyte imbalance
• Calcium channel blockers: continue perioperatively
• Alpha-2 agonists (clonidine): continue; sudden discontinuation causes severe rebound hypertension

C. Intraoperative Considerations

• Greatest risk: exaggerated hypotension at induction and hypertension at laryngoscopy/intubation (hemodynamic instability)
• Hypertensive patients have a blunted/shifted autoregulation curve - tolerate hypo- and hypertension poorly
• Use smooth, slow induction; propofol (dose-titrated) or etomidate (more cardiovascular stable, preferred in compromised LV function)
• Attenuate laryngoscopy response:
  • Fentanyl 2-3 mcg/kg IV 3-5 min before laryngoscopy
  • Lidocaine 1.5 mg/kg IV 90 sec before intubation
  • Esmolol 0.5-1 mg/kg IV before laryngoscopy (short-acting beta-blocker)
  • Adequate depth before instrumentation
  • Minimize laryngoscopy time (<15 seconds)

• Volatile agents (isoflurane, sevoflurane, desflurane) cause dose-dependent vasodilation and BP reduction - useful for BP control
• Avoid desflurane for rapid inhalational inductions - sympathetic stimulation risk
• Maintain BP within 20% of preoperative baseline
• Avoid hypotension (risk of end-organ ischemia, particularly coronary and cerebral) and hypertension (risk of myocardial ischemia, stroke, aortic dissection)
• Arterial line mandatory for major surgery - beat-to-beat BP monitoring

• Deepen anesthesia first
• IV labetalol (5-10 mg boluses), esmolol, nitroglycerine, or hydralazine
• Sodium nitroprusside (SNP) for hypertensive emergencies: 0.5-10 mcg/kg/min (beware cyanide toxicity with prolonged use)

• Reduce volatile agent depth
• IV fluids if hypovolemic
• Vasopressors: phenylephrine (pure alpha-agonist, preferred if tachycardic), ephedrine (if bradycardic/young patient), noradrenaline infusion for resistant cases
• Treat bradycardia with atropine or glycopyrrolate

D. Specific Drug Interactions

E. Postoperative Considerations

• Postoperative hypertension: common cause is pain, bladder distension, hypoxia, hypercarbia - treat the cause first
• Resume antihypertensives as soon as oral intake is possible
• Continue BP monitoring in recovery room
• Increased risk of myocardial ischemia, arrhythmias, and stroke in the perioperative period
• If patient cannot take oral medications: IV labetalol, hydralazine, or nitroglycerine infusion
• Epidural/regional analgesia: reduces sympathoadrenal stress response, helps BP control postoperatively

• Pediatric: High HR, High O2 demand, Low FRC, Vagal dominant, MAC peaks at 1-6 months, Sevoflurane preferred, watch for laryngospasm and postop apnea in ex-prems
• Elderly: Reduced MAC, Reduced drug doses, Diastolic dysfunction, POCD/POD risk, Renal & hepatic decline, Frailty assessment, Careful positioning
• Hypertensive: Continue beta-blockers, Hold ACE-I/ARBs morning of surgery, Attenuate laryngoscopy response, Maintain BP within 20% baseline, Arterial line for major surgery, Treat both hypo- and hypertension promptly

Sources: Morgan & Mikhail's Clinical Anesthesiology 7e, Ch. 43 (Geriatric Anesthesia), Ch. 54 (Pediatric Anesthesia); Barash, Cullen & Stoelting's Clinical Anesthesia 9e, Ch. 43 (Pediatric Anesthesia)