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Respiratory effects of sevoflurane used in combination with nitrous oxide and surgical stimulation
1Department of Anesthesiology and Intensive Care, Hamamatsu University School of Medicine, Japan.
Study Objective:
To evaluate the respiratory effects of sevoflurane anesthesia with and without nitrous oxide (N2O) during surgical stimulation.
Design:
Randomized study.
Setting:
Operating theater at a university hospital.
Patients:
10 patients scheduled for minor head or neck surgery.
Interventions:
Sevoflurane anesthesia was administered alone or in combination with N2O. After basal measurements were recorded, the following end-tidal anesthetic concentrations were administered: Group 1 = 1.3 minimum alveolar concentration (MAC) sevoflurane alone; Group 2 = 0.9 MAC sevoflurane with 0.4 MAC N2O; Group 3 = 1.5 MAC sevoflurane alone; Group 4 = 1.1 MAC sevoflurane with 0.4 MAC N2O.
Measurements And Main Results:
PaCO2, minute volume (VE), respiratory rate, tidal volume (VT), percentage of rib cage contribution to tidal volume (%RC), rate of inspiratory time in a breath cycle (TI/Ttot, where TI = inspiratory time and Ttot = tidal respiratory time), and mean inspired flow (VT/TI) were measured. The substitution of 0.4 MAC N2O for sevoflurane decreased PaCO2 and increased VE, with a consequent increase in VT. At 1.3 MAC sevoflurane-N2O anesthesia, spontaneous respiration maintained PaCO2 at appropriate levels (42.7 +/- 3.6 mmHg). At 1.3 MAC sevoflurane alone and 1.5 MAC sevoflurane-N2O anesthesia, spontaneous respiration was moderately depressed. Sevoflurane and N2O combined did not change %RC or TI/Ttot.
Conclusion:
Sevoflurane administered at an appropriate anesthetic depth maintained spontaneous respiration at acceptable levels during surgical stimulation, especially when combined with N2O.