Subspecialty Anesthesia (Cardiothoracic, Neuro, Obstetric, Pediatric, Ambulatory)
What you must understand
Each subspecialty has distinct physiology. Cardiothoracic: one-lung ventilation, hypoxic pulmonary vasoconstriction, cardiac output and shunt, and post-thoracotomy pain. Neuro: cerebral perfusion pressure (CPP = MAP − ICP), autoregulation, CO2 reactivity, and positioning (sitting craniotomy and venous air embolism). Obstetric: physiologic changes of pregnancy (increased cardiac output, decreased functional residual capacity, rapid desaturation), aspiration risk, and fetal monitoring. Pediatric: differences in airway anatomy, temperature regulation, and drug dosing by weight. Ambulatory: patient selection, PONV prophylaxis, and discharge criteria (e.g., Aldrete).
Traps in questions
Common traps: assuming the pregnant patient desaturates like a non-pregnant adult (she desaturates faster due to reduced FRC); forgetting that hyperventilation lowers CO2 and can reduce cerebral blood flow; and assuming one-lung ventilation is safe without understanding HPV (which hypoxia and vasodilators blunt). Pediatric traps: the infant airway is more anterior and the epiglottis is floppy; uncuffed tubes and small margins for error. Ambulatory traps: assuming all patients are appropriate - OSA and poorly controlled comorbidity may warrant inpatient care.
Rule of thumb
For neuro, remember CPP = MAP − ICP and that CO2 is a potent cerebral vasodilator. For obstetric, preoxygenate early and treat aspiration risk seriously. For pediatric, dose by weight and keep the child warm.
Worked example: A pregnant patient at 34 weeks needs emergency surgery. She has reduced FRC and rapid desaturation; preoxygenate, use left uterine displacement, and prepare for difficult airway.