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Ann Thorac Surg 1998;65:28-31
© 1998 The Society of Thoracic Surgeons

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Original Articles: Cardiovascular

Topical Hypothermia: Ineffective and Deleterious as Adjunct to Cardioplegia for Myocardial Protection

Section of Cardiothoracic Surgery, University of South Alabama, Mobile, Alabama, USA

Accepted for publication October 9, 1997.

Dr Elefteriades, Section of Cardiothoracic Surgery, Yale University School of Medicine, 121 FMB, 333 Cedar St, New Haven, CT 06520.

	Abstract

Top Abstract Introduction Material and Methods Results Comment References

 
Background. Topical hypothermia, an early method developed for myocardial protection by virtue of its reduction of cardiac metabolic rate, is not without sequelae such as phrenic nerve paralysis and pulmonary complications.

Methods. The hospital records of 505 nonrandomized consecutive patients undergoing coronary artery bypass grafting between 1991 and 1995 at the University of South Alabama were reviewed to evaluate the effectiveness of topical hypothermia and its relationship to pulmonary complications. Group A included 191 patients between 1991 and 1992 who received systemic hypothermia and topical hypothermia with iced slush in addition to cold blood cardioplegia. Group B included 314 patients between 1993 and 1995 who received systemic hypothermia and intermittent cold blood cardioplegia without iced slush.

Results. Myocardial temperature mapping did not reveal any difference between the two groups. Postoperative cardiac morbidity, manifested as intraaortic balloon use, low cardiac output, inotrope use, and perioperative myocardial infarction, was decreased in group B, but the difference failed to achieve statistical significance. Mortality (group A, 3.14%; group B, 3.82%) and rates of significant morbidity such as sternal infection, stroke, reoperation for bleeding, renal failure, and prolonged ventilation were comparable between the two groups. However, there was a statistically significant difference in the incidence of diaphragmatic paralysis between group A and group B. Group A had a 25% incidence of diaphragmatic paralysis on the first postoperative day, 18% on the 15th postoperative day, and 8% at 6 months, as opposed to group B, which had incidences of 2% on the first postoperative day, 1% on the 15th postoperative day, and 1% at 6 months (p < 0.001). Also, there was a significant difference in incidence of pleural effusions (60% versus 25%) and rate of thoracentesis (25% versus 8%) between groups A and B (p < 0.0001).

Conclusions. We conclude that topical hypothermia did not offer any additional cardioprotective benefit above systemic hypothermia and cold blood cardioplegia alone in coronary bypass patients, but significantly increased the incidence of diaphragmatic paralysis and associated pulmonary complications.

	Introduction

Top Abstract Introduction Material and Methods Results Comment References

 
Cardiac hypothermia by means of total-body deep hypothermia was applied for performing heart operations in the 1950s [1][2][3][4]. Topical hypothermia, as a tool of deliberate myocardial protection, was used as an adjunct to cardiac arrest by Cross and associates [5] and was popularized as a sole means of myocardial preservation by Shumway and colleagues [6] in the decade of the 1960s. Although cardiac hypothermia by infusion of intermittent cold cardioplegia is unequivocally cardioprotective by virtue of reduction of cardiac metabolic rate, the benefits and risks of adjunctive topical hypothermia remain controversial [7]. The purpose of this study was to determine if topical cooling with iced-slush is effective as a cardioprotective agent and whether it results in an increased incidence of phrenic nerve paralysis and associated pulmonary complications.

	Material and Methods

Top Abstract Introduction Material and Methods Results Comment References

 
The hospital records of 505 nonrandomized consecutive patients undergoing coronary artery bypass grafting between 1991 and 1995 at the University of South Alabama Medical Center were reviewed. Between 1991 and 1992, in 191 patients (group A), myocardial protection was achieved using systemic hypothermia with intermittent cold blood cardioplegia and local hypothermia with iced slush. Between 1993 and 1995, in 342 patients (group B), myocardial protection was achieved only with systemic hypothermia and intermittent cold blood cardioplegia without topical hypothermia. Cold blood cardioplegia was delivered through the aortic root (antegrade), through the coronary sinus (retrograde), or through both routes to achieve diastolic arrest and septal myocardial temperatures less than 15°C. An additional dose of cardioplegia was given routinely through each graft after completion of the distal anastomosis, as well as through the aortic root or coronary sinus each time the septal temperature exceeded 15°C or resumption of electrical activity of the heart was noted. A combination of antegrade/retrograde cardioplegia was used in redo operations, left main disease or equivalent, and acute left anterior descending coronary artery occlusion with myocardial infarction in evolution. Surgical technique was identical in both groups, using a single two-stage venous cannula via the right atrium and arterial return through the ascending aorta with an 8-mm Sarns cannula (3M Health Care, Ann Arbor, MI). Systemic hypothermia to 28°C was used in both groups. All operations were performed by a single surgeon (D.J.N.). The only procedural difference in the conduct of the operation between the two groups was the application of iced slush in group A, repeated every 15 minutes. Redo procedures constituted 6% of the slush group and 7.2% of the nonslush group. The internal mammary artery was used in 93% of the slush group and 94% of the nonslush group. Postoperative care of the two groups was identical.

Chest roentgenograms were taken on the first postoperative day, the 15th postoperative day, and 6 months postoperatively. All the roentgenograms (preoperative and postoperative) were reviewed by two different radiologists, who were blinded to the patients’ experimental grouping. Specific criteria were applied for the definition and diagnosis of diaphragmatic elevation and pleural effusion. Diaphragmatic elevation was diagnosed if there was a difference compared with the preoperative film of one costal space (rib and space) for the left hemidiaphragm and two costal spaces for the right hemidiaphragm. Pleural effusion was defined as obliteration of the costophrenic angle on the upright chest roentgenogram.

The Society of Thoracic Surgeons National Database and its definitions were used for preoperative risk stratification and postoperative mortality and morbidity comparisons between the two groups. Statistical analysis was performed using ² testing, and differences were considered statistically significant if they achieved a p value less than 0.05.

	Results

Top Abstract Introduction Material and Methods Results Comment References

 
Preoperatively, the two groups were comparable in age, sex, and incidence of diabetes, renal failure, morbid obesity, hypertension, chronic obstructive pulmonary disease, and peripheral vascular disease (Table 1). Group A had a higher incidence of subendocardial myocardial infarctions and cardiomegaly. However, the ejection fraction was comparable between the two groups. Group B included patients with a higher incidence of left main disease and New York Heart Association class IV angina, emergent operations, prior cerebrovascular accident, and cerebrovascular disease. The two groups were also comparable in the number of bypass grafts performed and in cross-clamp time.

	Comment

Top Abstract Introduction Material and Methods Results Comment References

 
The fundamental components of myocardial protection are diastolic arrest and cardiac hypothermia. Both are commonly achieved with intermittent perfusion of cold cardioplegia supplemented with topical hypothermia using iced slush. However, the use of topical cooling with iced slush has recently been challenged [7].

This study demonstrates that local hypothermia not only does not offer any additional cardioprotective effect above systemic hypothermia and blood cardioplegia alone, but instead increases the incidence of diaphragmatic paralysis and associated pulmonary complications. This is in contrast to the data reported by Landymore and colleagues [8]. Of note, the use of topical hypothermia in the present study did not significantly alter observed myocardial temperature.

Cooling with iced slush can induce myocardial and epicardial injury in both humans and dogs, as has been demonstrated by Speicher and coworkers [9]. In addition, local myocardial applications of iced slush can result in unilateral or bilateral phrenic nerve paralysis and diaphragmatic elevation [10]. In the present study, the incidence of diaphragmatic elevation was 25% on the 1st postoperative day and dropped to 8% at 6 months postoperatively in group A with iced slush applied, in marked contrast to group B without iced slush, in which the incidence of diaphragmatic elevation was 2% and 1%, respectively. Our data are consistent with other reports in regard to the incidence of diaphragmatic elevation [7][11][12]. It appears that the mechanism of phrenic nerve paralysis is a cold-induced injury due to a demyelinization process [13][14][15], with a significant chance of recovery up to 1 year postoperatively [11][12]. In most series, the left phrenic nerve was the one affected in more than 90% of cases due to its closer proximity and greater contact with the iced slush [12], a finding consistent with our data. Bilateral phrenic nerve paralysis is very rare, but constitutes a recognized catastrophic complication [10]. Each diaphragm contributes 30% to 60% of the tidal volume in adults in the supine position [16]. Pulmonary complications, such as atelectasis, pneumonia, pleural effusions, and thoracentesis are greatly increased in patients with diaphragmatic paralysis [7][11][12][17], a finding also consistent with our data. The negative consequences of increased incidence of diaphragmatic paralysis and associated pulmonary complications are reflected in length of stay and hospital cost.

Application of protective cooling jackets or pads around the heart can reduce but not eliminate the incidence of pulmonary complications [18][19]. These complications can be avoided by eliminating the use of topical hypothermia altogether [20].

Our data show that mortality as well as significant morbidity were comparable between the two groups of patients, slush and no slush. In regard to cardiac morbidity, manifested as need for intraaortic balloon support, need for inotropic medications, and perioperative myocardial infarction, there was no increase in these phenomena in our series consequent upon elimination of topical hypothermia. In fact, cardiac outcome was improved, although not to a degree of statistical significance. These data are consistent with those reported by Allen and associates [7], although their study did not include myocardial temperature mapping data.

Weaknesses of the present study are that it is nonrandomized and that the two groups of patients were operated on sequentially rather than concurrently. Also, the deleterious effects of iced slush may not translate fully to use of noniced topical cold saline solution.

We believe that use of topical hypothermia is unnecessary and deleterious. This study has shown that topical hypothermia is associated with a statistically significant increase in diaphragmatic paralysis and associated pulmonary complications without offering any additional cardioprotective benefit beyond systemic hypothermia and cold cardioplegia in coronary artery bypass grafting.

	References

Top Abstract Introduction Material and Methods Results Comment References

 

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Dimitris J. Nikas John A. Elefteriades Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Nikas, D. J. Articles by Elefteriades, J. A. Search for Related Content PubMed PubMed Citation Articles by Nikas, D. J. Articles by Elefteriades, J. A.