Figure 38-18 Waveforms of visual evoked responses from one patient were elicited when awake and anesthetized at three end-expired levels of halothane. Four separate tracings obtained during each condition have been superimposed. (From Uhl RR, Squires KC, Bruce DL, et al: Effect of halothane anesthesia on the human cortical visual evoked response. Anesthesiology 53:273, 1980.)