Specialty Anesthesia Populations and Procedures
Physiologic extremes
Neonates and infants: MAC is highest in this group (sevoflurane roughly 3.3% in neonates), the head is large and the larynx anterior and cephalad, the narrowest point is the cricoid, hepatic clearance and protein binding are immature (more free drug), heat loss is rapid, and fetal hemoglobin shifts the oxygen curve left.
Obstetrics: aspiration risk, aortocaval compression after about 20 weeks relieved by left uterine displacement, and neuraxial techniques preferred. Preeclampsia brings magnesium therapy that potentiates neuromuscular blockade, plus thrombocytopenia and pulmonary edema.
Geriatrics: MAC falls roughly 6% per decade after age 40, clearance declines, and postoperative delirium is common - avoid benzodiazepines and anticholinergics where possible.
Cardiac: fixed output demands avoidance of tachycardia and afterload reduction; intracardiac shunt worsens when hypoxic pulmonary vasoconstriction is inhibited.
Neuro: cerebral perfusion pressure = MAP minus ICP. Brief hyperventilation to PaCO2 30–35 mmHg lowers ICP through vasoconstriction, but sustained hypocapnia risks ischemia.
Traps: pediatric doses are weight-based but not linearly scaled; MAC does not predict hemodynamic tolerance; general anesthesia remains necessary for some obstetric emergencies.
Worked example: ICP 20 mmHg with a CPP target of 60 requires MAP of 80. A MAP of 65 produces CPP 45 - inadequate in head injury.