Thirty postoperative patients were allocated randomly to receive oxygen by Hudson face mask at 4 litre min-1 (group I) or 2 litre min-1 (group II) via nasal cannulae. From 22:00 on the first night after operation, the position of the nasal cannula or face mask was observed for 8 h using video and oxyhaemoglobin saturation (SpO2) recorded simultaneously. In group I the mask remained on and positioned correctly in five patients. In the 10 other patients it was removed a total of 28 times, 17 for nursing tasks, for a median time of 2 min 39 s (range 30 s to 7 h 40 min 40 s). In group II the nasal cannula was removed once in one patient for 16 min 38 s and eight times in another for a total of 1 h 18 min 7 s. Average SpO2 with mask on was 98% (range 96.1-99.9%), with mask off 95% (range 89.8-98.8%) and with cannula 97% (range 90.8-99.3%). We conclude that nasal cannulae are more likely to remain in position than face masks and maintain an adequate saturation in most patients.

Summary Fourteen adults underwent cardiac surgery with a standard anaesthetic technique. Prior to surgery and the day after surgery, gastric emptying was determined using the paracetamol absorption technique. Resultsfrom 13patients were available for analysis.The mean time to reach the maximum plasma concentration was 14.1 min Key wordsGastrointestinal tract; stomach, emptying Pharmacology; stomach A decrease in gastric motility will adversely affect enteral nutrition and delay the absorption of most oral medication [I]. After uncomplicated cardiac surgery it is our practice to start oral medication and nutrition on the first postoperative day. Drugs prescribed include anti-arrhythmia and hypotensive agents and delayed absorption may have an important effect on cardiovascular stability. The major cause of impaired gastric motility in the postoperative period is opioid analgesia, although other drugs and physiological and pathological factors also have an effect [I, 21. We have therefore studied patients before and after elective cardiac surgery in order to determine the effect of anaesthesia and surgery on gastric motility. MethodsEthics committee approval and informed patient consent were obtained. Patients were studied 1 or 2 days before and the day after surgery, thereby acting as their own controls. All patients required cardiopulmonary bypass for coronary artery bypass grafting (10 patients), valve replacement (two patients), or both (two patients). Patients were studied in two equal groups; one group was cooled to a core temperature of 18 to 20°C and given 1-2 1 of ice-cold cardioplegia solution topically and as coronary artery perfusate. Core temperature in the other patients was maintained above 33°C and cardioplegia was not administered. In these patients surgery was performed after the aorta was crossclamped and the heart fibrillated.Routine cardiac medications were continued until the morning of surgery. Patients received a standard general anaesthetic consisting of premedication with oral lorazepam followed by intramuscular papaveretum and hyoscine. Induction of anaesthesia was with fentanyl, midazolam and thiopentone, and maintenance was with nitrous oxide, oxygen and enflurane with increments of fentanyl and midazolam as indicated. Pancuronium was used to produce neuromuscular blockade. Postoperative analgesia was with papaveretum given by infusion and, if additional sedation was required while the patient's trachea remained intubated, small bolus doses of midazolam were administered. Gastric emptying was measured using paracetamol absorption [ 11. In both pre-and postoperative studies, patients were given 1 g of paracetamol solution at approximately 0800 h after

Patients may not receive prescribed oxygen because the oxygen face mask becomes displaced. Using video, we have observed the position of the face mask in 20 postoperative patients and recorded the timing and the events associated with mask displacement. Correct placement of the mask was confirmed at the start of the 8-h study period from 22:00 on the first night after operation. The mask remained on continuously and positioned correctly in only one patient. In the other 19 patients, it was removed 64 times (range 1-10 times per patient). The mask was removed 45 times for nursing tasks such as mouth care and temperature measurement and these represented 70% of the total number of times that the mask was not in position. Other reasons for removal were vomiting, retching and removal by the patient. The mask remained off a median time of 6 min 55 s per episode (range 46 s to 7 h 46 min 57 s) and per patient a median of 1 h 6 min 48 s (range 1 min to 7 h 46 min 57 s). Mask removal resulted in an average decrease in oxygen saturation of 4%. Oxygen by mask at 4 litre min-1 maintained an average saturation > or = 95% in most, but not all, of the patients.