Hypoxaemia and myocardial ischaemia during colonoscopy

Myocardial ischaemia (defined as ST-segment deviation on electrocardiogram (ECG)) may occur during colonoscopy, but the pathogenic mechanisms are unknown. We have evaluated the occurrence of arterial hypoxaemia, tachycardia, and myocardial ischaemia during routine colonoscopy.

Eighteen patients underwent colonoscopy under conscious sedation and without supplementary oxygen. Arterial oxygen saturation was measured by continuous pulse oximetry, and ECG was monitored continuously with a Holter tape recorder during the procedure.

Arterial oxygen desaturation and tachycardia were common during colonoscopy and occurred in 45% and 35% of patients, respectively. Two patients developed signs of myocardial ischaemia during the colonoscopy: one case of ST depression (1.7 mV) and one case of ST elevation (4.3 mV). In both patients the ST deviation disappeared when the colonoscope was retracted. Myocardial ischaemia occurred in both patients simultaneously with tachycardia, and in one of these arterial hypoxaemia was also present.

Myocardial ischaemia occurs during routine colonoscopy, but with a lower incidence than previously reported during upper endoscopy. Myocardial ischaemia during colonoscopy may be associated with tachycardia and/or hypoxaemia. Further studies should clarify the relative role of tachycardia, hypoxaemia, and viscerocardiac reflexes in the pathogenesis of myocardial ischaemia during colonoscopy.