Levels of consciousness and ventilatory parameters in young children during sedation with oral midazolam and nitrous oxide

Objective: To determine the ventilatory effects and levels of consciousness achieved during sedation with the combination of oral midazolam and inhaled nitrous oxide. Design: Case series. Setting: Surgical suite. Patients: Twenty-two consecutive children, aged 1 to 3 years, were seen for elective, ambulatory surgery. Interventions: Patients were premedicated with oral midazolam hydrochloride, 0.5 mg/kg, and then breathed 4 concentrations of nitrous oxide (N2O) in oxygen (15%, 30%, 45%, and 60%) for 4 minutes at each concentration prior to induction of general anesthesia. Main Outcome Measures: Levels of consciousness (conscious vs deep sedation) and ventilatory parameters: respiratory rate, end-tidal carbon dioxide tension (PETCO(2)), and oxyhemoglobin saturation (SPO2). Upper airway obstruction was diagnosed by clinical assessment by an experienced pediatric anesthesiologist (R.S.L.) and respiratory impedance plethysmography. Results: During inhalation of N2O, 12 of the 20 children demonstrated a mild degree of ventilatory depression; PETCO(2) values were equal to or greater than 45 mm Hg during at least 2 concentrations of N2O studied. There were no significant changes in SPO2 or PETCO(2) with increasing concentrations of N2O (P>.05). Respiratory rates tended to be lower during inhalation of 15% N2O than at higher concentrations (P=.05). No child developed upper airway obstruction or hypoxemia (SPO2 <92%) at any level of N2O inhalation. Sedation scores were significantly higher at 60% N2O than at all other concentrations of N2O (P<.02). At 15% N2O, 12 children were not clinically sedated, 8 children met the American Academy of Pediatrics definition of conscious sedation, and no child met the definition of deep sedation. At 30% N2O, 10 children were not clinically sedated, 9 met the definition of conscious sedation, and 1 child met the definition of deep sedation. At 45% N2O, 9 children were not clinically sedated, 9 met the definition of conscious sedation, and 2 met the definition of deep sedation. At 60% N2O, 6 children were not clinically sedated, 6 met the definition of conscious sedation, 6 met the definition of deep sedation, and 1 child progressed to a deeper level of sedation in that there was no response to a painful stimulus. One child was withdrawn from the study during inhalation of 45% N2O because of emesis. Conclusions: The combination of oral midazolam, 0.5 mg/kg, and up to 60% inhaled N2O caused mild ventilatory depression in some children and resulted in a progression from conscious to deep sedation beginning at 30% N2O. When using this particular combination of sedatives, practitioners should monitor each child's mental status continuously and adhere to the appropriate published guidelines for the monitoring and management of such patients.