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Ann Thorac Surg 1998;66:301-302
© 1998 The Society of Thoracic Surgeons
a Cardiothoracic & Vascular Surgical Associates, 4815 Liberty Ave, Suite GR-59, Pittsburgh, PA 15224, USA
To the Editor
The article by Nikas and associates [1] asserts that topical hypothermia is an ineffective and deleterious adjunct to cardioplegia for myocardial protection. They retrospectively reviewed the records of 505 patients undergoing coronary artery bypass. Of the 191 patients who had iced slush for topical hypothermia, 25% had diaphragmatic paralysis on the first day, with persistence of paralysis in 8% by 6 months. Hospital mortality was 3.14%. Of note is the fact that no protective pad was used.
Their experience is quite different from mine. I have used iced slush topical hypothermia with a protective pad for many years with quite different results: In the last 700 consecutive coronary artery bypass patients (including second- and third-time operations and acute emergency/salvage operations), the incidence of diaphragmatic paralysis was zero! The hospital mortality was 1.85% (1.38% for primary coronary artery bypass grafting, including emergency/salvage operations). The need for intraaortic balloon pump insertion in the operating room was 1.85% (0.43% to wean from cardiopulmonary bypass). In all cases, moderate systemic hypothermia (28°C) and intermittent, antegrade, cold, blood, potassium cardioplegia plus topical iced slush was the method of myocardial protection. I personally reviewed all postoperative chest roentgenograms, with special attention being paid to any evidence of diaphragmatic paralysis. Patient data, including all complications, were recorded in a computerized database.
Several technical points must be followed if topical hypothermia is to be used safely: First, a plastic foam insulating pad (DLP, Grand Rapids, MI) must be used and carefully positioned so that no ice comes into contact with the pericardium. Special attention must be paid to the cephalad portion of the pericardial sac near the pulmonary artery: any ice that lodges in this area will remain in close proximity to the phrenic nerve. The ice must also be placed in solution and allowed to equilibrate as slush (at 4°C), rather than removed directly from the slush-maker and placed on the heart (in which case the ice is the same subzero temperature as the slush-maker), to prevent injury to the epicardium.
The deleterious effects of placing iced slush in the pericardium without the use of an insulating pad are well-known, and the high incidence of phrenic nerve paralysis in the absence of protective pads [1, 2] is not surprising. The failure of protective pads, as reported by Esposito and Spencer [3], may be related to their use of a silicone sheet, which is far less effective for thermal insulation than plastic foam.
Any surgical technique, when improperly applied, can lead to complications. However, if properly used, topical hypothermia can be a safe and valuable adjunct to cold cardioplegia. Whether or not equally good results could have been obtained without the use of topical hypothermia cannot be answered without a randomized, prospective study.
If used properly, topical ice-slush is a safe and effective adjunct to hypothermic cardioplegia for myocardial protection. Diaphragmatic paralysis can be avoided if appropriate measures are taken.
References
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