Effects of halothane and sevoflurane on the paediatric respiratory pattern

Using a respiratory inductive plethysmograph, we investigated the effects of halothane and sevoflurane on the paediatric respiratory pattern under spontaneous breathing. We measured tidal volume per weight, respiratory rate, partial pressure of end-expiratory carbon dioxide (Pet_CO2), rib cage contribution to ventilation (%RC) and phase shift between rib cage and abdominal movements at 0.5, 1.0 and 1.5 MAC of these inhalational anaesthetics in oxygen. Both of these anaesthetics increased Pet_CO2 significantly with increase in depth of anaesthesia; sevoflurane produced more profound respiratory depression than halothane at high MAC. Both agents decreased %RC significantly with increase in depth of anaesthesia; paradoxical respiration occurred in the halothane group at high MAC. The profound respiratory depression of sevoflurane is due to both decreased tidal volume and decreased respiratory rate. The paradoxical respiration under halothane may be attributed to the potent suppression of intercostal muscle function and may be partly due to compensatory sparing effect on respiratory rate, which leads to the increase in airway flow and airway resistance.