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Ann Thorac Surg 2003;75:1387-1391
© 2003 The Society of Thoracic Surgeons

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Original article: cardiovascular

Impact of single clamp versus double clamp technique on neurologic outcome

^a Division of Cardiac Surgery, Johns Hopkins Hospital, Baltimore, MD, USA
^b Zanvyl Krieger Mind Brain Institute, Johns Hopkins University, The Johns Hopkins Medical Institutions, Baltimore, Maryland, USA

Accepted for publication December 11, 2002.

^* Address reprint requests to Dr Baumgartner, Blalock 618 Cardiac Surgery, Johns Hopkins Hospital, 600 N. Wolfe St., Baltimore, MD21287-4618, USA
e-mail: wbaumgar{at}csurg.jhmi.jhu.edu

	Abstract

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BACKGROUND: Atherosclerotic disease of the aorta has been identified as a risk factor for neurologic complications following coronary artery bypass grafting (CABG) due to the use of aortic clamping and manipulation. We reviewed a change from double clamp to single clamp technique to determine its impact on neurologic outcomes.

METHODS: Patients undergoing isolated CABG by a single surgeon were identified as having double clamp technique (DCT) (aortic cross clamp + sidebiting clamp) or single clamp technique (SCT) (aortic cross clamp only). Data were collected by study personnel and clinicians to determine stroke and neurologic injury (confusion, delirium, seizure, altered mental status, and agitation) outcomes for 461 patients.

RESULTS: Two hundred seventy-two patients had DCT and 189 patients had SCT performed. There were no differences in mean age, previous stroke, hypertension, or diabetes. Intraoperatively, patients with SCT had shorter bypass times (115 minutes vs 128 minutes, p = 0.001), longer aortic cross clamp time (89 minutes vs 80 minutes, p = 0.001), fewer coronary grafts (2.8 vs 3.1, p = 0.001), and had higher mean arterial blood pressure on cardiopulmonary bypass (76 mm Hg vs 69 mm Hg, p = 0.001). Postoperatively, the SCT group had fewer strokes (1.1% vs 2.9%, NS), and neurologic injuries (3.2% vs 9.6%, p = 0.008). By multivariate analysis, the factors that were related to neurologic injury were DCT (p = 0.04), age (p = 0.001), and number of coronary grafts (p = 0.03).

CONCLUSIONS: This experience suggests that the use of the SCT may be important in reducing neurologic injury following CABG.

	Introduction

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Poor neurologic outcomes, specifically stroke, after coronary artery bypass grafting (CABG) have been extensively reported in the past. There have been many attempts to identify patients at higher risk, as well as to identify intraoperative variables that may contribute to poor outcomes. A number of preoperative factors contribute to placing patients at higher risk, not just increasing age. In two recent studies [1, 2], similar preexisting medical variables were found to be risk factors in the identification of high-risk patients, ie, past stroke, hypertension, increased age, and carotid artery disease. Such factors are also related to the development of atherosclerotic disease. These, as well as intraoperative factors, have been implicated in contributing to stroke risk, including hypoperfusion and embolic phenomena. For example, atherosclerotic disease involving the ascending aorta has been found to contribute to the release of multiple emboli during aortic manipulation and clamping during cardiac surgery operations [3, 4]. Among the strategies developed to minimize aortic clamping/aortic trauma, and thereby to prevent neurologic complications, is the use of a single clamp technique rather than a double clamp technique requiring use of both an aortic cross clamp and a side-biting clamp. This relatively simple and cost-effective strategy has been presented in two previous studies [5, 6], and has provided an impetus for this data analysis.

In this analysis, we examined a single surgeons’ experience and compared the use of single, versus multiple aortic clamp manipulations on the outcomes of stroke and neurologic injury.

	Material and methods

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Patients having isolated CABG (not in combination with other cardiac surgical procedures), by a single surgeon (WAB), were entered into the cardiac surgical database at the Johns Hopkins Hospital. Patients were identified in two consecutive groups: those undergoing double clamp technique (January 1994 to November 1997); and those undergoing single clamp technique (from November 1997 to June 2000). In 1992 a neurologic assessment/outcome database was initiated to monitor the neurologic progress of patients in multiple research studies as well as to systematically follow the clinical outcomes for all cardiac surgical patients. In this database, preoperative, intraoperative, and outcome data are prospectively collected.

Preoperative data collected included history of previous stroke, hypertension, diabetes mellitus, age, presence of carotid bruit, and stroke risk probability [7] (identified as low, medium, or high risk for stroke). Intraoperative data collection included cardiopulmonary bypass time (CPB), aortic cross-clamp time, number of coronary grafts completed, the lowest esophageal temperature, and the mean arterial blood pressure while on CPB. Outcome data were collected on a daily basis by two investigators (MAG, LMB). These data included postoperative length of stay, adverse myocardial event, death, stroke, and neurologic injury. This information was gathered from daily rounds with clinicians, ie, nurses and physicians who were directly caring for the patients both in the ICU and on the hospital ward.

The analysis, examining the outcomes of patients in two different groups (single clamp vs double clamp), was approved by the Institutional Review Board at Johns Hopkins. This review is based on the implementation of a change in clinical/operative practice that occurred on November 13, 1997 for this surgeon (WAB), and was based on results presented in the cardiac surgical literature. Patients were not randomized into treatment groups for this analysis.

Operative technique
All patients underwent median sternotomy. Anesthetic technique was standardized and consisted of low-intermediate dose narcotics, inhalation agents, and paralytics. Cardiopulmonary bypass was carried out using a Sarns roller head pump (Sarns, Inc, Ann Arbor, MI), nonpulsatile flow, -stat pH blood gas management, antegrade crystalloid cardioplegia and topical hypothermia, moderate systemic hypothermia (28 to 32°C), and pump flow rates to achieve a mean arterial pressure of 60 to 80 mm Hg. For patients in the DCT group, the aortic cross clamp was applied and distal anastomoses were made. The aortic cross clamp was then released and the sidebiting clamp was applied once or twice, after which the proximal anastamosis was made. For patients in the SCT group, the aortic cross clamp remained in place for both distal and proximal coronary anastomoses. During the period of evaluation, one other change in technique occurred. Patients in the later time periods (after 1996) were actively cooled to 30°C, whereas patients in the earlier time periods were cooled to 28°C.

Outcome definitions
The outcome of stroke was defined as the clinical diagnosis of stroke made by a staff neurologist independent of confirmation by brain imaging (head computed tomography, or magnetic resonance imaging [MRI]). Sixty percent of the strokes were confirmed by imaging (primarily head computed tomography) in this series. The etiology of these strokes cannot be confirmed using these imaging data. In addition, we know from previous experience [8] that the majority of head computed tomography scans done within 48 hours of surgery do not reveal the full extent of infarcts that can be seen with subsequent MRI.

Neurologic injury was defined as a dichotomous (yes or no) outcome to include any of the following abnormal neurologic conditions reported by clinicians to have occurred postoperatively: confusion, delirium, combativeness, agitation, seizures, prolonged altered mental status, or coma. The stroke and neurologic injury outcomes are mutually exclusive.

Mortality was any death occurring during the same hospital stay. Postoperative length of stay (LOS) is the number of days the patient remained in the hospital after surgery.

Statistical analysis
For the univariate analysis, data were compared between the DCT group and the SCT group. Preoperative, intraoperative, and postoperative outcome data were reviewed. Continuous variables were compared by the Student’s t-test, and ² was used for dichotomous variables (using SPSS statistical package; SPSS, Chicago, IL). The Mann Whitney U-test was used when continuous data were not normally distributed. Multivariate analysis was used to determine whether variables other than clamp type contributed to the outcomes of stroke or neurologic injury.

	Results

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Preoperative and intraoperative patient characteristics
During the time periods specified, 461 patients underwent CABG by this surgeon. Six patients (4 patients during the single clamp time period, and 2 patients during the double clamp time period) were excluded from this analysis because aortic cross clamping was not used. There were 272 patients with double clamp (DCT) and 189 patients with single clamp technique (SCT). Demographic and preoperative patient characteristics are compared in Table 1. There were no differences in the distribution of high-risk patients (for stroke) between the groups.

Multivariate analysis
Multivariate analysis was performed for the outcome of neurologic injury only. Use of double clamp technique, increasing age, and the number of coronary grafts were all significantly associated with poor neurologic outcome (Table 4). Differences in mean arterial pressure or esophageal temperature while on cardiopulmonary bypass, which could have explained the differences in neurologic outcome, were not significant in the multivariate model.

	Comment

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In one earlier study, Aranki and colleagues [5] also reported that SCT patients had more favorable outcomes, such as fewer strokes. These authors also used a risk severity stratification model to examine whether there were differences in outcomes for higher risk patients. They found that even in higher risk patients, they still had improved outcomes using SCT. However, they found no differences between their groups in the number of coronary grafts placed. Our study revealed a difference, which may be related to the longer time period in which patients underwent surgery. Although their data collection was retrospective, they provided strong evidence that the use of the partial occluding clamp was the important difference between their groups.

A more recent study by Dar and coworkers [6] reported that patients with single clamp technique had improved cerebral protection as measured by the release of S-100 protein. The limitations of this study, however, were a small sample size (n = 50) and a lack of description of the methods used to determine clinically evident cognitive dysfunction. In addition, the patients studied appeared to be at very low risk for stroke. Applying the criteria from other stroke risk models to this population, the expected stroke rate would be quite low, making it even more difficult to demonstrate any effect of a particular treatment. Hammon and colleagues [9] have indicated a significant difference in neuropsychologic outcomes in patients in whom a partial occluding clamp was not used. They believe that the patient’s outcomes were improved because fewer emboli were generated.

Controversy continues to exist regarding the efficacy of SCT. Musumeci and coworkers [10] reported that the single clamp technique was not as effective as intermittent ischemic arrest in the prevention of myocardial ischemia and neurologic problems. Kim and colleagues [11] concluded that use of a SCT does not prevent stroke, but their study also did not have an adequate sample size to detect a significant difference in stroke occurrence.

We emphasize that our analysis also was not statistically powered to detect a difference in stroke rate. However, in addition to an improved neurologic injury outcome with SCT, a trend toward improvement in stroke rate was observed. In order to demonstrate a statistically significant difference between stroke rates with such a low incidence, a sample size of at least 1000 patients would be needed for each treatment arm.

The assessment of neurologic injury (other than stroke) following cardiac surgery has not been extensively studied in the past, even though this type of problem is well known to cardiac surgeons and caregivers. Patients who are confused, delirious, or agitated present a complicated clinical scenario. Importantly, patients with a neurologic injury in this analysis have an increased mortality and hospital length of stay. In an in-depth examination of the outcome of delirium, Rolfson and coworkers [12] reported an incidence of 32% postoperatively in a sample of elderly CABG patients. This is a clinically important outcome that requires further examination and the development of methods for prevention.

In a study by the McSPI Group [13], the incidence of this type of neurologic injury was 7.3%, with proximal aortic arteriosclerosis being a risk factor. This is critical because by 75 to 80 years old the incidence of severe aortic arteriosclerosis in patients is almost 10% [14]. Studies where epiaortic ultrasound was used to examine the aorta for the presence of atherosclerotic disease [15] have demonstrated that aortic disease is correlated with stroke outcome both within 30 days [16] and up to 5 years postoperatively [17]. Our study has indicated a correlation with age and the higher incidence of neurologic injury.

A strength of this study was that the determination of neurologic injury was made in a prospective manner, which is critical in outcome research. Thus, we are confident that the majority of patients with poor neurologic outcome were represented in our data set. The study had a large proportion of patients (44%) who were considered at high risk for stroke, and the distribution of high-risk patients was similar between the two clamp groups. We believe that our sample is representative of patients having surgery at most large academic institutions. A weakness of this study was that the clamp groups were not randomized and that there were no ultrasound measures recording the degree of proximal aortic disease, which has been strongly demonstrated to be related to neurologic outcome [16]. Also, other explanations for the reduction in neurologic outcomes are possible and include the lower frequency of patients with previous stroke and carotid bruit. This may indicate a subtle change in the way patients are referred to surgery and how they are managed medically (before surgery) with regard to percutaneous transluminal coronary angioplasty and stent placement. We cannot rule out these as possible explanations.

In conclusion, we believe that identifying and understanding preoperative risk factors and comorbidities for neurologic complications is important. This study has identified clamp technique as an important operative risk factor and supports the significant benefits of the single clamp technique in the neurologic outcomes for patients undergoing coronary artery bypass surgery.

	Acknowledgments

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We would like to acknowledge the contribution to this study of the cardiac intensive care unit staff, who care for our patients daily. Also, we thank Richard Royall, PhD, for his assistance in the statistical preparation of this manuscript, and Sharon Owens and Catherine Cristinzio for assistance with data collection.

	References

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