Time course of postoperative hypoxaemia.

OBJECTIVE: To study the time course of nocturnal episodic and constant hypoxaemia during the first five nights after a major abdominal operation in patients not given supplementary oxygen. DESIGN: Open study. SUBJECTS: 17 patients undergoing major elective operations and with no recognised risk factors. MAIN OUTCOME MEASURES: Arterial oxygen saturation measured by pulse oximetry. RESULTS: The level of constant hypoxaemia was lowest during night 2 (p < 0.01) as was the time spent below 90% saturation (p < 0.01) compared with the other four postoperative nights. Episodic hypoxaemia was most common during night 3 (p < 0.05). It was not possible to predict the postoperative occurrence of hypoxaemia from the preoperative spirometric measurements. Preoperative awake arterial oxygen saturation correlated significantly with mean constant hypoxaemia on postoperative nights 1, 3, 4, and 5, but not with episodes of sudden desaturation after operation. Preoperative overnight oximetry correlated significantly with constant hypoxaemia on all five postoperative nights and with episodic hypoxaemia on nights 3 and 4. CONCLUSION: In the light of these results which show the natural history of postoperative hypoxaemia without supplementary oxygen, and because postoperative hypoxaemia may be associated with dysfunction of organ systems after major operations, controlled studies of supplementary oxygen in the late postoperative period are warranted.

Buprenorphine antagonism of ventilatory depression following fentanyl anaesthesia.

In order to compare the effect of buprenorphine and naloxone on respiratory depression after fentanyl anaesthesia (25 micrograms/kg), 32 women scheduled for elective abdominal hysterectomy participated in a double-blind randomized investigation. At termination of anaesthesia, after antagonizing residual neuromuscular blockade, 20 normocapnic patients with a respiratory rate of 4 breaths/min or less entered the study, receiving either buprenorphine (0.6 mg in 20 ml NaCl) or naloxone (0.4 mg in 20 ml NaCl) 2 ml/min until 20 ml was given or until the respiratory rate exceeded 8 breaths/min. Respiratory rate, PaCO2, sedation score, and pain intensity were evaluated during a 3-h study period. Fifteen min after beginning the treatment, all the patients in both groups had their ventilatory depression antagonized. There were no statistically significant differences in respiratory rates between groups except at 15 min. On no occasion did either PaCO2 or a sedation score differ statistically significantly between the groups. At 15 min all patients in the buprenorphine group had no or mild pain, compared to the patients in the naloxone group, of whom 50% had moderate to severe pain (P less than 0.05). It seems as if buprenorphine is as effective as naloxone in antagonizing respiratory rate depression following fentanyl anaesthesia.