Myocardial ischemia and weaning failure in patients with coronary artery disease: An update

Objective: To determine the frequency and effects of weaning-related myocar dial ischemia on weaning outcomes in patients with coronary artery disease. Design:Prospective cohort study. Setting: Medical and cardiac intensive care units of a 300-bed teaching com munity hospital, Measurements and Main Results: Three-lead ST segments, heart rate-systolic blood pressure products, and respiratory ratel tidal volume ratios were obt ained for patients with coronary artery disease just before and during thei r initial trials of weaning from mechanical ventilation. ST segments were i nterpreted by a blinded cardiologist. Eighty-three patients with a mean age of 72.4 +/- 1.1 years (mean +/- SEM), a mean Acute Physiology and Chronic Health Evaluation II score of 16.4 +/- 0.8, and a mean duration of mechanic al Ventilation of 4.6 +/- 0.9 days were studied. Eight patients showed elec trocardiographic evidence of ischemia during weaning, and seven of these pa tients failed to be liberated on their first day of weaning. The presence o f ischemia significantly increased the risk of weaning failure (risk ratio, 2.1; 95% confidence interval, 1.4-3.1), The rate-pressure product for the group as a whole increased significantly during weaning, from 11.9 +/- 0.4 to 13.5 +/- 0.5 mm Hg x beats/min x 10(3) (p < .01). The increase in rate-p ressure product tended to be greater in patients who became ischemic (12.8 +/- 0.9 to 17.3 +/- 2.0 mm Hg x beats/min x 10(3)) than in patients who wer e not ischemic during weaning (11.8 +/- 0.4 to 13.0 +/- 0.5 mm Hg x beats/m in x 10(3); p = .05), The rate/volume ratio did not change significantly du ring weaning, but the rate/volume ratios after both 1 min (65.6 +/- 4.6 vs. 98.0 +/- 9.4 breaths/min/L; p < .05) and 30 mins (68.6 +/- 4.3 vs. 91.1 +/ - 8.9 breaths/min/L; p < .05) of unassisted breathing were lower in success ful than in unsuccessful patients. Conclusion: Electrocardiographic evidence of myocardial ischemia occurs fre quently and is associated with significantly increased risk of first-day we aning failure in patients with coronary artery disease.