INTERACTION OF EXTRADURAL MORPHINE AND LIGNOCAINE ON VENTILATORY RESPONSE

We have evaluated the effects of lumbar extradural morphine and lignoc aine on the ventilatory response to carbon dioxide. Twenty-four female patients were allocated randomly to receive extradural morphine 2 mg (group M), 2% lignocaine 10 mi (group L) or a combination of morphine 2 mg and 2% lignocaine 10 mi (group ML). On the day before surgery, re sting ventilatory values including minute volume (VE) and tidal volume (VT), and ventilatory response to progressive hyperoxic hypercapnia ( VE/PE'(CO2)) were measured. On the day of surgery, the same measuremen ts were repeated 30 min after extradural injection. Ventilatory values at rest were not altered after extradural injection. Mean VE/PE'(CO2) decreased significantly after extradural morphine (P = 0.002) and inc reased (P = 0.011) after extradural lignocaine. Mean VE 7.3 (VE at PE' (CO2) 7.3 kPa) decreased significantly after extradural morphine (P < 0.001) and increased after extradural lignocaine (P = 0.047). Extradur al morphine and lignocaine did not significantly alter mean VE/PE'(CO2 ) and mean VE 7.3: 14.6 (95% confidence intervals 12.1-17.1) to 15.3 ( 13.1- 17.6) litre min(-1) kPa(-1) and 22.8 (18.1-27.5) to 22.8 (17.3-2 8.3) litre min(-1), respectively. We conclude that extradural co-admin istration of morphine and lignocaine did not increase the risk of resp iratory depression associated with morphine.