Topical cooling for myocardial protection: the results of a prospective randomized study of the "shallow technique"

Respiratory distress following cardiac surgery is a troublesome complication. In several cases it is associated to cool-related phrenic nerve injury (PNI) after adoption of iced slush or hypothermic cardiopulmonary bypass. We compare two different strategies for myocardial protection: the "shallow technique" (ST) (dripping and prompt removal of cold saline solution from the epicardial surface) plus normothermic cardiopulmonary bypass, versus mild hypothermic cardiopulmonary bypass plus iced slush.

Two hundred forty-nine patients undergoing elective cardiac surgery were randomly assigned to receive either ST (Group A) or iced slush (Group B). Occurrence of postoperative PNI (abnormal diaphragmatic movement plus alteration of nerve conduction) was evaluated. Multivariate analysis was performed for identification of factors associated to PNI. Patients had a 6-month follow-up.

PNI and failure of extubation occurred more frequently in Group B (p = 0.009 and p = 0.034, respectively), but there was no statistically significant difference in mean intensive care unit stay. Diabetes and the use of iced slush were independent predictors of phrenic dysfunction, while internal thoracic artery (ITA) harvest was a significant risk factor only among Group B patients. Abnormal diaphragmatic movement was persistent at 6 months only in 30% of Group B individuals who suffered this complication in the early postoperative.

ST likely reduces the incidence of postoperative PNI and might be protective mainly in the event of ITA harvest. It should be considered as a valuable tool for myocardial protection protocols.