The influence of patient characteristics on the requirements for postoperative analgesia

The requirements for analgesia after upper abdominal surgery were evaluated in 100 patients who received morphine by way of a patient-controlled analgesia system. Hourly and cumulative 24-hour requirements were analysed for possible correlations with patient characteristics and for the patterns of consumption throughout the 24-hour study period. The level of pain relief was assessed by linear analogue pain scores at 4-6 hours and 24 hours. Male patients (n = 46) required significantly more morphine than female patients (n = 54) to achieve similar levels of pain relief (p less than 0.05). There was an inverse correlation between age and morphine consumption in both males and females (r = -0.684, p less than 0.00005 and r = -0.502, p less than 0.00005 respectively). No correlation was found between morphine consumption and patient weight. The pattern of hourly morphine consumption appeared to follow a diurnal rhythm, with peak times of demand at 0900 and 2000 hours. The variations in requirements for analgesia among patients and with time of day should be taken into account when a regimen for postoperative analgesia is prescribed.