Postoperative analgesia by nicomorphine intramuscularly versus high thoracic epidural administration: Effects on ventilatory and airway occlusion pressure responses to CO2

In this study the effects of nicomorphine, administered either intramuscularly or by high thoracic epidural route, on the ventilatory and airway occlusion pressure response to CO₂ were investigated and compared. Twenty-four patients scheduled for thoracic surgery were allocated randomly to postoperative pain relief by i.m. nicomorphine or by high thoracic epidural nicomorphine. The ventilatory response to 5% carbon dioxide was measured in all patients: first 1 day before operation, secondly on the first day after surgery immediately before nicomorphine administration and finally after the administration, at the moment when no further rise in end-tidal Pco₂ (P_etco₂) was measured. Respiratory response was assessed in two ways, by measuring minute ventilation (Ve) and mouth occlusion pressure (p_0.1). There was a significant depression in ventilatory response to CO₂ in the intramuscular group ( P = 0.03) due to nicomorphine as assessed by the slope of V_e vs P_etCO₂ No significant depression was found in the epidural group, irrespective of measurement of V_E, or P_0.1. No significant shift of apnoeie threshold-P_ETco₂ was observed in either group.