Optimizing myocardial hypothermia: II. Cooling jacket modifications and clinical results

After induction of myocardial hypothermia by cold cardioplegic solution, myocardial rewarming occurs at 0.5 degrees to 1.0 degrees C/min. In addition to preventing myocardial rewarming from systemic and pulmonary venous return, continuous cooling of the myocardial surface must be provided. Modifications of a previously reported cooling jacket are described. These modifications include decreased width and thickness of the metal skeleton for easier application and increased malleability, respectively. Also, the double-row flow channel markedly minimizes obstruction of flow secondary to kinking and allows inlet and outlet lines to attach at adjacent points of the jacket thus minimizing obstruction of the operative field. The effectiveness of the jacket in 36 patients undergoing valve replacement and 19 patients having pulmonary thromboendarterectomy was evaluated by measurement of myocardial temperatures at multiple sites throughout aortic cross-clamping. Temperatures at all sites were maintained at 12 degrees C or less. Temperatures measured in phrenic nerve pedicles ranged from 25 degrees to 27 degrees C. During cooling, heat removal by the jacket was 330 calories/min. During maintenance of myocardial hypothermia, heat flow was 190 calories/min. Modifications of a cooling jacket facilitate usability and an array of sizes enhances applicability.