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ORIGINAL ARTICLE |
Department of Cardiothoracic Surgery
1 Department of Anesthesiology, Southampton University Hospital, Southampton, UK
Theodore Velissaris, FRCS (C-Th), Tel: +44 23 80796234, Fax: +44 23 80798508, Email: theovelissaris{at}googlemail.com, Department of Cardiothoracic Surgery, Southampton General Hospital, Tremona Road, Southampton SO16 6YD, UK.
ABSTRACT
Cardiac maneuvering during off-pump coronary artery bypass surgery can compress the right ventricle, causing temporary dysfunction and hemodynamic instability. The hemodynamic impact of a decompression technique comprising right pleurotomy and pericardial release was investigated during cardiac elevation. Intraoperative continuous real-time monitoring of cardiac index and stroke volume index was carried out using the PulseCO system in 12 consecutive patients with normal ventricular function who underwent off-pump coronary artery bypass by a single surgeon. A pulmonary artery catheter was used to monitor pulmonary artery pressure and systemic venous O2 saturation. Hemodynamic changes during vertical displacement of the heart were measured before and after performing a right pleurotomy and pericardial release. Following right heart decompression, stroke volume index, cardiac index, mean arterial pressure, and systemic venous O2 saturation were significantly better preserved during cardiac elevation. This demonstrates that right heart decompression via pleurotomy and pericardial release significantly improves hemodynamic stability during cardiac manipulation. We recommend the use of this procedure in off-pump coronary artery bypass when cardiac tilting is required.
Key Words: Coronary Artery Bypass • Off-Pump • Hemodynamics
INTRODUCTION
Exposure of the posterior or lateral coronary vessels during off-pump coronary artery bypass (OPCAB) surgery requires significant cardiac displacement that results in transient hemodynamic impairment. Hemodynamic instability occasionally requires conversion of the surgical approach to the use of cardiopulmonary bypass (CPB).1 Hemodynamic impairment during vertical cardiac displacement is primarily due to right ventricular (RV) dysfunction resulting from direct mechanical compression of the RV between the interventricular septum and the surrounding right fibrous pericardium and pleura.2,3 Therefore, some centers have explored the use of RV assist devices during OPCAB.3,4 The Trendelenburg position has been shown to partly restore RV dimensions during cardiac elevation, by augmenting the preload and filling pressures.5 We have described a decompression technique comprising a right pleurotomy and pericardial release.6 This aims to decompress the right cardiac chambers and improve hemodynamic stability during cardiac manipulation. This study evaluated the hemodynamic impact of this maneuver during cardiac elevation in patients with normal ventricular function undergoing OPCAB.
PATIENTS AND METHODS
Twelve consecutive patients awaiting primary elective OPCAB, who fulfilled the study criteria, were recruited after obtaining informed consent. We excluded patients over the age of 75 years, those with left ventricular ejection fraction <50%, recent myocardial infarction (<3 months), unstable angina, previous cerebrovascular accident, diabetes mellitus, renal or hepatic failure. The study was approved by the Southampton and South West Local Research Ethics Committee, and all patients were operated on by the same surgeon.
The heart was approached through a median sternotomy and pericardiotomy. Vertical displacement of the heart was facilitated by the single-suture technique.7 Trendelenburg posture was employed throughout construction of the distal anastomoses. The Octopus 3 suction-based mechanical stabilizer (Medtronic Ltd., Watford, UK) was used to immobilize the target coronary arteries prior to arteriotomy. An intraluminal coronary shunt (Flo-Thru, Biovascular, Inc., St. Paul, MN, USA) was employed to maintain distal myocardial perfusion during distal anastomoses. The right decompression maneuver comprises the application of no traction to the incised right pericardial edge as well as a right pleurotomy.6 The pleurotomy is performed by the surgeon’s assistant, using diathermy or scissors. The incision runs laterally to the incised right pericardial edge, starting at the level of the superior vena cava where it joins the right atrium, and continuing down to the level of the diaphragm, where it extends vertically towards the inferior vena cava in an L-shaped fashion. The incision stops just anterior to the inferior vena cava. Care is taken to avoid injury to the right phrenic nerve. During cardiac elevation, the lack of traction on the right pericardium combined with the right pleurotomy ensure that there is adequate space in the right hemithorax to accommodate the right cardiac chambers (Figure 1
), which would otherwise be compressed against the fibrous pericardium and pleura. A standard protocol was followed in which fentanyl-based anesthesia was used in combination with benzodiazepine and vecuronium as a muscle relaxant. Aspirin was discontinued 7 days prior to surgery. All other antianginal, antihypertensive, or antiarrhythmic medication was continued up to the morning of the operation. Hemodynamic stability (target mean arterial pressure>60 mm Hg and cardiac index>2 L·min–1·m–2) was achieved primarily by preload management (intravenous fluids and Trendelenburg posture) with temporary inotropic support if necessary.
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Revascularization of the left anterior descending coronary artery was performed first, using the left internal mammary artery. Baseline hemodynamic values were obtained with the heart in anatomical position (position 1). Using the single-suture technique, the heart was elevated to a position suitable for grafting the posterior descending coronary artery (position 2), and hemodynamic parameters were recorded. During this initial cardiac elevation, traction was applied to the incised right pericardial edge via 2 pericardial sutures. The heart was returned to anatomical position, the right pericardial traction was released, a right pleurotomy was performed, and hemodynamic values were recorded again (position 3). The heart was lifted vertically again to expose the posterior descending artery, and final hemodynamic recordings obtained (position 4). Changes in hemodynamic parameters during cardiac elevation were calculated as: change before decompression (%) =(value in position 2 – value in position 1)/value in position 1 x100%; change after decompression (%) =(value in position 4 –value in position 3)/value in position 3 x100%. During each study, no changes were made to the fluid volume or inotropic support, and Trendelenburg posture was employed throughout.
Results are expressed as mean ± standard deviation. Percentage changes before and after decompression were compared using the paired-samples t test. A paired t test was also used to compare percentage changes in hemodynamic parameters during cardiac elevation with the pleura either open or closed. Statistical significance was set at p <0.05. SPSS version 16.0 software (SPSS, Inc., Chicago, IL, USA) was used for analyses.
RESULTS
No patient was excluded from the study, and all completed the protocol; their characteristics are summarized in Table 1. No patient required conversion to CPB. The mean number of grafts per patient was 2.8 ± 0.9. During the cardiac manipulations required by the study protocol, one patient received an infusion of dopamine 4.45 µg·kg–1·min–1 for cardiac support; the infusion rate remained unchanged throughout. No other inotropic or chronotropic support was required during the study. The hemodynamic values recorded in the 4 study positions are summarized in Table 2. Baseline hemodynamics before and after pleuropericardial release were similar (positions 1 and 3). There were significant hemodynamic changes during cardiac elevation before and after pleuropericardial release. Before pleuropericardial release (positions 1 and 2), values of CI, SVI, MAP, and SVO2 decreased significantly during cardiac elevation. With right decompression (positions 3 and 4), there were less marked reductions in these parameters during cardiac elevation; only the fall in SVI was statistically significant. With the right pleura either open or closed, significant increases in central venous pressure were observed during cardiac elevation, while heart rate, mean pulmonary arterial pressure, and systemic vascular resistance index were not significantly altered. Table 3 summarizes the hemodynamic changes during cardiac elevation before and after right heart decompression. Following right decompression, CI, SVI, MAP, and SVO2 were significantly better preserved during cardiac elevation. There were no major perioperative complications, and no patient developed clinical or radiological signs of right phrenic nerve injury.
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OPCAB is becoming increasingly popular as stabilizing devices continue to evolve, and several advantages of OPCAB vs. surgery with CPB have been demonstrated.9,10 However, some studies have shown significant transient hemodynamic impairment during cardiac manipulation.2,3,11,12 Periods of hemodynamic instability may adversely affect the perfusion and function of end-organs such as the brain, kidney, and gut. Neurocognitive dysfunction after OPCAB was found to be comparable to that after surgery with CPB;13 and we demonstrated similar degrees of renal and gastric mucosal injury after surgery with and without CPB.14,15
Hemodynamic deterioration during OPCAB manifests mainly as a transient drop in CO despite relative preservation of arterial blood pressure. However, CO measurement by the thermodilution technique and Swan-Ganz catheters is not useful because hemodynamic changes in OPCAB are very rapid. Continuous CO Swan-Ganz catheters are also unsatisfactory because the displayed values lag 5 to 15 min behind the true CO, making the system too slow for detection of acute hemodynamic changes.16–18 Recently, several systems providing real-time continuous CO monitoring have become available. The Pulse CO system is a minimally invasive monitoring system that connects to the arterial line and calculates CO in a continuous real-time fashion, using analysis of the arterial blood pressure waveform.8 CO measurements using lithium dilution are at least as accurate as thermodilution techniques.19,20 Hemodynamic impairment during cardiac tilting is primarily due to reduced RV preload and mechanical RV dysfunction.2 An echocardiographic study demonstrated that the RV is compressed between the left ventricle and the surrounding tissues during cardiac elevation, so that part of the RV free wall is pressed against the interventricular septum during the entire cardiac cycle.3 Trendelenburg posture is an adjunct to hemodynamic stability during cardiac manipulation, by augmenting the preload and filling pressures and restoring RV dimensions.5 RV assist devices significantly enhance hemodynamic stability during cardiac manipulation, whereas left ventricular assistance has no benefit.4,5
Our technique aims to decompress the RV by allowing the retracted right cardiac chambers to herniate into the right hemithorax. Our results demonstrate the beneficial hemodynamic effects of this technique during cardiac elevation: CI, SVI, MAP, and SVO2 were significantly better preserved. Interestingly, we did not observe any significant changes in heart rate and systemic vascular resistance index during cardiac elevation, although other studies have reported a compensatory increase in these parameters during distal anastomoses in OPCAB, which results in relative preservation of MAP.11,12 This may be because we did not allow time for these compensatory changes to occur; we recorded hemodynamic changes immediately on elevating the heart for adequate exposure of the posterior descending coronary artery.
To avoid several confounding factors, we used each patient as their own control, and recorded hemodynamic changes during cardiac elevation before and after the decompressing maneuver. The availability of real-time hemodynamic monitoring allowed all manipulations to be performed in a short period of time, so that no changes in inotropic support or fluid status occurred during the study. Several factors might have influenced hemodynamic status during the study, the most important being left ventricular function, anesthetic management, revascularization sequence, and body position. All our patients had normal left ventricular function; whether right decompression has a similar effect in those with a poorly functioning or dilated left ventricle remains unknown. Our patients were in the Trendelenburg position throughout the study, and all had left anterior descending coronary artery revascularization first to improve myocardial perfusion prior to cardiac elevation. A limitation of this study is that we did not assess the hemodynamic impact of pleuropericardial release during distal anastomoses, when other factors, such as application of the mechanical stabilizer, temporary coronary occlusion, or administration of vasoconstrictors and inotropics, might affect hemodynamics. Our study was specifically designed to assess the effect of right pleuropericardial release on hemodynamic stability during cardiac elevation, and the benefit of this maneuver during distal anastomosis remains unknown. Nevertheless, this study provides evidence that in patients with normal ventricular function undergoing OPCAB, right pleuropericardial release maintains hemodynamic stability when vertical cardiac displacement is required to expose coronary targets. The technique is safe and easy to perform, and it can be used in conjunction with other maneuvers, such as the Trendelenburg position, to optimize hemodynamic stability during OPCAB.
ACKNOWLEDGMENTS
Dr. T Velissaris was supported by a research fellowship sponsored by Ethicon and awarded by the Royal College of Surgeons of Edinburgh.
REFERENCES
Asian Cardiovasc Thorac Ann 2010;
18:17-21
© 2010 by SAGE Publications
DOI: 10.1177/0218492309355493
This article has been cited by other articles:
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  B. Atasever, C. Boer, R. Speekenbrink, J. Seyffert, P. Goedhart, B. de Mol, and C. Ince Cardiac displacement during off-pump coronary artery bypass grafting surgery: effect on sublingual microcirculation and cerebral oxygenation Interact CardioVasc Thorac Surg, December 1, 2011; 13(6): 573 - 578. [Abstract] [Full Text] [PDF]
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