Abstract
Background
Coronary artery bypass surgery (CABG) may be life saving, but known side effects include neurological damage and cognitive impairment. The temperature used during cardiopulmonary bypass (CPB) may be important with regard to these adverse outcomes, where hypothermia is used as a means of neuroprotection.
Objectives
To assess the effectiveness of hypothermia during CABG in reducing neurological damage and subsequent cognitive deficits.
Search methods
The Cochrane Controlled Trials Register was searched for randomised controlled trials (RCT) and this was updated by searching MEDLINE and EMBASE to December 1999 using database specific RCT filters. Reference lists of retrieved articles were searched and experts in the field were contacted.
Selection criteria
Only RCTs were considered. All patients undergoing CABG, either first time or revisions, elective or emergency procedures, were included. Any hypothermia protocol was considered. Only trials reporting neurological outcomes were included.
Data collection and analysis
Studies were selected independently and data were extracted from the source papers independently by two reviewers. Authors were contacted for further information. Studies were combined with meta-analysis where appropriate, and meta-regression was used to explore heterogeneity.
Main results
There was a trend towards a reduction in the incidence of non fatal strokes in the hypothermic group (OR 0.68 (0.43, 1.05)). Conversely, there was a trend for the number of non stroke related perioperative deaths to be higher in the hypothermic group (OR 1.46 (0.9, 2.37)). There was no evidence to suggest that hypothermia had an effect on the incidence of non fatal myocardial infarction (OR 1.05 (0.81, 1.37)), but the incidence of another marker of myocardial damage, low output syndrome, was higher in the hypothermic group (OR 1.21 (0.99, 1.48). When pooling all “bad” outcomes (stroke, perioperative death, myocardial infarction, low output syndrome, intra aortic balloon pump use) there was no significant advantage of either hypothermia or normothermia (OR 1.07 (0.92, 1.24)). Only 4 of 17 trials reported neuropsychological function as an outcome.
Authors’ conclusions
This review could find no definite advantage of hypothermia over normothermia in the incidence of clinical events. Hypothermia was associated with a reduced stroke rate, but this is off set by a trend towards an increase in non stroke related perioperative mortality and myocardial damage. There is insufficient data to date to draw any conclusions about the use of mild hypothermia. Similarly, there is insufficient data to date to comment on the effect of temperature during CPB on subtle neurological deficits, and further trials are needed in these areas.
Plain language summary
There is not enough evidence to show that lowering body temperature can reduce nerve damage during coronary artery bypass surgery.
For people with severe coronary artery (heart) disease, bypass surgery can be life saving. However, bypass surgery is sometimes associated with neurological complications, where very occasionally patients may suffer a stroke, or more commonly memory or personality may be affected. The temperature used during bypass surgery may influence these adverse effects. Reducing the temperature during surgery (hypothermia) may protect the brain and reduce the risk of complications. The review of trials found that there was not enough evidence to show the protective effects of hypothermia. More research is needed.
