Respiratory Depression after Extradural Morphine

on ketamine requirement. Following atropine premedication ketamine 5 mg lb" was administered i.m. They found that i.v. supplementation was required to prevent limb movement before surgery in 70% of patients less than 1 year of age and showed that i.v. ketamine requirements for surgical anaesthesia were associated with age, weight and surface area, age being most significant: i.v. ketamine (ng lb-'min-) = 70.4 —11.5 x age (yr) Other authors have described an increased MAC value for halothane in this age group (Gregory, Egerand Munson, 1969; Nicodemus et al., 1969). Alternative possibilities for the greater ketamine requirement of younger children include differences in cerebral blood flow and neuronal density, incomplete myelinization with impaired transmission, differences in cardiac output and larger extracellular fluid volumes. Regardless of the possibility of abnormal neuronal pathways within the brain, the ketamine requirement of young children should be expected to exceed that of adults.