Levels of consciousness and ventilatory parameters in young children during sedation with oral midazolam and nitrous oxide
R. S. Litman, R. J. Berkowitz and D. S. Ward
Department of Pediatrics, University of Rochester School of Medicine and Dentistry, NY, USA. Rlitman@ccmail.anes.rochester.edu
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
(PETCO2), 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; PETCO2 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 PETCO2 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.
