Anesthesia for Subspecialties and Comorbid Disease
Key domains
Subspecialty questions test how comorbidity changes anaesthetic management. Cardiac: ischaemic heart disease (maintain coronary perfusion, avoid tachycardia), valvular disease (aortic stenosis - avoid hypotension and tachycardia; mitral stenosis - avoid tachycardia), and pulmonary hypertension (avoid hypoxia, hypercapnia, acidosis). Respiratory: COPD and asthma (avoid histamine-releasing drugs, optimise bronchodilation), obstructive sleep apnoea (postoperative monitoring). Endocrine: diabetes (glycaemic control, insulin), thyroid disease, phaeochromocytoma (alpha-blockade before beta). Renal and hepatic: drug choice by clearance. Obstetric: left uterine displacement, aspiration prophylaxis, altered MAC. Paediatric: weight-based dosing, different airway anatomy.
Traps
- Giving a beta-blocker before alpha-blockade in phaeochromocytoma - can precipitate hypertensive crisis.
- Assuming aortic stenosis tolerates vasodilation - it does not; maintain afterload and sinus rhythm.
- Forgetting that pregnancy reduces functional residual capacity and increases aspiration risk.
- Missing that hepatic failure reduces albumin and alters drug binding, increasing free drug.
Rule of thumb
For any comorbidity, ask: what does this disease need to stay stable (perfusion, rhythm, oxygenation, glucose), and which drug or manoeuvre threatens it?
Worked example
A patient with severe aortic stenosis becomes hypotensive after induction. Treat with a vasopressor to restore afterload and avoid tachycardia; vasodilation would worsen the gradient and coronary perfusion.