Does halothane really preserve cardiac baroreflex better than sevoflurane? - A noninvasive study of spontaneous baroreflex in children anesthetized with sevoflurane versus halothane

Heart rate profiles during the induction of anesthesia differ markedly between the administration of sevoflurane and halothane. Previous investigations have shown that halothane preserves cardiac parasympathetic activity more than sevoflurane. Because vagal drive to the sinus node is the main effector of arterial baroreflex control of heart rate, halothane may preserve cardiac baroreflex better than sevoflurane. To investigate cardiac baroreflex in anesthetized children, we used two noninvasive methods providing different approaches to the arterial blood pressure (BP) and R-R interval (RRI) relationship: the sequence methods investigating beat-to-beat changes in BP and RRI (time domain) and the cross-spectral analysis investigating relationships between oscillations of BP and RRI (frequency domain). Children were randomly assigned to mask induction with sevoflurane in 100% oxygen, sevoflurane in 50% nitrous oxide/50% oxygen, or halothane in 50% nitrous oxide/50% oxygen. After tracheal intubation, the inspired fraction of volatile anesthetic was reduced to 1 minimum alveolar anesthetic concentration (MAC). The spontaneous baroreflex (SBR) sensitivity was calculated with the sequence method at baseline, during induction, and after intubation. The cardiac baroreflex was also estimated with cross-spectral analysis at baseline and at 1 MAC (stationary conditions). In the three groups, the induction of anesthesia was associated with a marked decrease of SBR sensitivity, which occurred earlier with sevoflurane than with halothane. Five minutes after intubation (1 MAC), the sequence method showed a similar decrease of the SBR sensitivity in the three groups. Similarly, the cross-spectral analysis between systolic blood pressure and RRI showed a decrease of the gain calculated in the low-frequency band, but the gain in the respiratory band was higher with halothane compared with sevoflurane. In children, the induction of anesthesia with halothane and sevoflurane is associated with a marked decrease of cardiac baroreflex activity. The persistence of respiratory RRI fluctuations under halothane might reflect reflex respiratory arrhythmia rather than efficient parasympathetic baroreflex activity.