|Home | About | Journals | Submit | Contact Us | Français|
To the Editor:
Hypothermia has been used as a standard method of cardiac protection since the early days of cardiac surgery1 and can be achieved with the use of cardioplegic solution, with or without the addition of topical hypothermia. Topical hypothermia provides substantial cardiac protection in patients who have acute regional myocardial ischemia.2 However, the use of ice slush for achieving hypothermia can cause phrenic nerve injury and diaphragmatic palsy, which, in turn, may result in postoperative complications.3 We herein present our technique for the application of topical hypothermia with a recirculator device.4 We have used this method of myocardial protection in over 2,500 patients over a 20-year period without any complications related to the method.
We use median sternotomy, which is the standard approach for most cardiac operations. The pericardium is opened widely in an inverted T fashion to expose the heart. Cardiopulmonary bypass is established in the conventional way, with 1 or 2 venous cannulae. Cold blood cardioplegic solution at 8 to 10 °C is used, anterograde and retrograde, for myocardial protection. The inflow and outflow lines of a Fountain topical cooling set (Cellplex Pty Ltd.; Melbourne, Australia) are placed in the pericardial cavity to establish continuous irrigation with cold saline or Hartmann solution. The circuit consists of high-thermal-efficiency plastic tubing and a cooling coil that is immersed in a bucket of ice. The coil has 2 tubes. One of these, a catheter with multiple openings, is placed behind the heart and aspirates cold fluid. The other has multiple side-holes and is placed over the right or left ventricle to spray cold solution. A roller pump maintains the circulation of cold fluid (Fig. 1). The system can deliver the cold fluid at a rate of 1,500 mL/min. The temperature of the fluid is maintained at 10 °C. Myocardial temperature is measured with a Mon-a-therm® myocardial temperature probe (Mallinckrodt Medical, Inc.; St. Louis, Mo) and is maintained below 15 °C.
Systemic hypothermia and cardioplegia are conventionally used for myocardial protection in various cardiac surgical procedures. During the early development of cardiac surgery, Shumway and coworkers1 accomplished local hypothermia by filling the pericardial cavity with ice-cold saline solution. It has been found that, after the initial cooling is induced by cold cardioplegic solution, the myocardial temperature increases due to heat gain from the environment and the entry of warm blood into the cardiac chambers and the coronary circulation.5
Ice can be detrimental to myocardial protection, and the damage is liable to occur at temperatures below 10 °C.3 The recirculating cooler described herein was designed to furnish a continuous supply of cold saline to the pericardium without wastage of solution. In our 20-year experience with this system, we have not encountered any case of phrenic nerve injury. We think that this system should find wider application in the clinical practice of cardiac surgery.