COMPARISON OF RESPIRATORY EFFECTS OF TRAMADOL AND PETHIDINE

Tramadol is a centrally acting opioid with a low affinity for mu-opioi d receptors, which has been claimed not to depress respiration as do t he classic opioids. The respiratory effects of intravenous (i.v.) peth idine (0.6 mg kg(-1)) and tramadol (0.6 mg kg(-1)) were com pared in 3 6 ASA Grade I-II patients in a placebo-controlled double-blind study. After induction of anaesthesia with propofol followed by suxamethonium -facilitated endotracheal intubation, the patients spontaneously breat hed halothane in 70% nitrous oxide and oxygen via a non-rebreathing va lve. Inspiratory and expiratory oxygen, and end-tidal carbon dioxide c oncentrations (PETCO2), tidal volume (V-T), minute volume of ventilati on (MV) and respiratory rate were monitored by a side-stream spirometr y at an end-tidal halothane of 0.3%. The recordings were collected bef ore surgery. Pethidine caused significant respiratory depression seen as an increase in fractional inspiratory-expiratory oxygen difference and PETCO2 and as a decrease in MV and respiratory rate. However, the effects of tramadol were similar to those of a placebo. Tidal volume w as not affected by any study drug. In conclusion, tramadol 0.6 mg kg(- 1) was shown not to be associated with respiratory depression, unlike equipotent dose of pethidine in this setting.