HYPOXEMIA AND MYOCARDIAL-ISCHEMIA ON THE NIGHT BEFORE CORONARY-BYPASSSURGERY

Using pulse oximetry and Holter ECG monitoring on the night before cor onary bypass surgery, we studied 30 male patients with coronary artery disease to determine the relationship between nocturnal hypoxaemia an d myocardial ischaemia. The patients received intensive anti-angina me dication and were sedated with clorazepate. Ten patients developed a t otal of 42 ischaemic episodes, 24 of which occurred between 22.00 and 06.00. Mean heart rate was significantly higher in patients with ischa emia than in those without ischaemia. in 60% of all patients, heart ra te increased greater than or equal to 20% at the onset of the ischaemi c episode. The patients spent a median of 2 (range 0.02-40.6)% of the night with oxygen saturation (Sp(O2)) < 90% (the minimum Sp(O2) value recorded was 84 (69-88)%). Only five ischaemic episodes were associate d with respiratory events. These were not associated with either extra ordinary oxygen desaturation or marked increases in heart rate. Compar ing patients with and without ischaemia, there were no significant dif ferences in the extent of nocturnal hypoxaemia or the pattern of desat uration episodes (cyclic variations in saturation characteristic of pe riodical breathing vs non-cyclic desaturation episodes). Despite marke d nocturnal hypoxaemia, simultaneous occurrence of desaturation episod es and myocardial ischaemia was a rare event in our study.