Effects of midazolam on ventilatory response to carbon dioxide when used as sedative during epiduralblockade / 中华麻醉学杂志

ABSTRACT

Objective To investigate the effect of midazolam on ventilatory response to carbondioxide (CO2) when it is used as sedative supplement to epidural blockade(EB). Methods Fifteen ASAⅠ -Ⅱ patients [age (49±7) years , weight (56±13)kg] undergoing upper abdominal surgery were studied. Patients with respiratory disease were excluded. No patient was addicted to smoking, alcohol,received any sedatives or hypotics within one month before surgery. The patients were premedicated with intramuscular phenobarbital 0. 1g and atropine 0.5mg. Epidural catheter was inserted in a cephala direction for 4 cm into epidural space via the tuohy needle at T9.10. 1% lidocaine and 0.2% pontocaine solution was used for epidural block. The level of block was T3.5. When the level of block was fixed, midazolam 0.1mg/kg was given intravenously. Respiratory rate(RR), tidal volume (VT), end-tidal concentration of CO2 (PETCO2) and pulse oxygen saturation (SpO2) were measured before anesthesia (baseline values), before midazolam when the level of block was fixed and 5 min after midazolam. Measurement of ventilatory response to CO2 the patient was asked to breathe with a closed system without a CO2 absorber. PET CO2 increased to 55 mm Hg in 6-10 min. RR, VT and minute ventilation (MV) were measured at PETCO2 40, 45, 50, and 55 mm Hg. The patient then breathed fresh air and PETCO2 returned to normal. 5 min after midazolam the measurment was repeated. The CO2 ventilatory response curve was obtained by plotting MV against the corresponding PET CO2. Results PET CO2, RR and SpO2 did not change significantly after epidural block and midazolam. There was no significant change in VT after epidural block as compared with the baseline value but VT decreased significantly after midazolam (P<0.01).There was no significant change in the slope of CO2 ventilatory response curve before and after midazolam but MV at different PET CO2 decreased significantly 5 min after midazolam. Conclusions Midazolam 0. 1mg/kg given after epidural block decreases VT but depression of respiratory center is slight and lasts for only a short period of time.[Key Words] Midazolam; Anesthesia, epidural; Carbon dioxide