The influence of meperidine and nitrous oxide on respiratory depression in rats.

Narcotic sedation is commonly accomplished with nitrous oxide (N2O) coadministration. Concerns regarding respiratory morbidity and mortality with drug combinations have been reported in the literature, particularly in patients not receiving supplemental oxygen (O2). The purpose of this investigation was to determine the effect of meperidine alone and in combination with N2O on respiration in laboratory rats by evaluating cardiovascular and arterial blood gas data. Fifty-four Sprague-Dawley rats were assigned to one of six groups (nine per group). Groups were allocated based upon the dosage of meperidine administered (0, 4.0, or 8.0 mg/kg intraperitoneally [i.p.]) and exposure to N2O (50% with oxygen) or O2 (100%). Following meperidine administration, animals were placed into a sealed chamber through which flowed either N2O or O2. Arterial blood was obtained, at baseline and at 15-min intervals, from a femoral artery catheter and pH, O2, CO2 (mm Hg), and oxygen saturation (%) were determined. Plasma samples were analyzed using a System 1306 pH/blood gas analyzer. Group comparisons demonstrated that: (a) N2O coadministration, in animals pretreated with meperidine, did not result in increased arterial CO2 levels, and (b) as expected, arterial O2 levels in all groups increased significantly from preexposure baseline values (P < 0.05). This investigation demonstrated that the coadministration of N2O to meperidine-sedated animals did not enhance respiratory depression.