Hypoxaemia and myocardial ischaemia on the night before coronary bypass surgery

Using pulse oximetry and Holter ECG monitoring on the night before coronary bypass surgery, we studied 30 male patients with coronary artery disease to determine the relationship between nocturnal hypoxaemia and myocardial ischaemia. The patients received intensive anti-angina medication and were sedated with clorazepate. Ten patients developed a total of 42 ischaemic episodes, 24 of which occurred between 22:00 and 06:00. Mean heart rate was significantly higher in patients with ischaemia than in those without ischaemia. In 60% of all patients, heart rate increased > or = 20% at the onset of the ischaemic episode. The patients spent a median of 2 (range 0.02-40.6)% of the night with oxygen saturation (SpO2) < 90% (the minimum SpO2 value recorded was 84 (69-88) %). Only five ischaemic episodes were associated with respiratory events. These were not associated with either extraordinary oxygen desaturation or marked increases in heart rate. Comparing patients with and without ischaemia, there were no significant differences in the extent of nocturnal hypoxaemia or the pattern of desaturation episodes (cyclic variations in saturation characteristic of periodical breathing vs non-cyclic desaturation episodes). Despite marked nocturnal hypoxaemia, simultaneous occurrence of desaturation episodes and myocardial ischaemia was a rare event in our study.