Anesthesia in Patients with Comorbid Disease and Special Populations
What the exam tests
Comorbid disease questions test altered pharmacokinetics, perioperative risk, and drug interactions in cardiac, pulmonary, renal, hepatic, obese, elderly, and pregnant patients.
Core rules
- Elderly: decreased MAC, reduced clearance, polypharmacy, frailty; titrate slowly.
- Obesity: dose induction on lean body weight for most drugs; succinylcholine and nondepolarizing blockers may need adjusted dosing; OSA risk.
- Renal failure: avoid meperidine, adjust renally cleared drugs, watch potassium and volume.
- Liver disease: coagulopathy is complex; avoid hypotension and hypoxia; reduced clearance.
- Diabetes: hold SGLT2 inhibitors 3-4 days; metformin is usually continued unless contrast or AKI.
- Pregnancy: increased minute ventilation, decreased FRC, rapid desaturation; left uterine displacement after 20 weeks.
- Pulmonary hypertension: avoid hypoxia, hypercapnia, acidosis, and hypotension.
Worked example
A patient with type 2 diabetes on empagliflozin is scheduled for colonoscopy. Hold it for 3-4 days preoperatively. Reasoning: SGLT2 inhibitors can cause euglycemic diabetic ketoacidosis under fasting and surgical stress. Check ketones if symptoms occur; do not rely on glucose alone.
Traps
Dosing propofol on total body weight in obesity; continuing SGLT2 inhibitors; ignoring frailty in the elderly; giving NSAIDs in CKD; assuming liver disease protects against thrombosis.