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Haemodynamic changes during minimally invasive coronary artery bypass surgery using high-dose esmolol
Cardiovascular Surgery, Vol. 8, No. 3, pp. 204–207, 2000 2000 The International Society for Cardiovascular Surgery. Published by Elsevier Science Ltd All rights reserved. Printed in Great Britain 0967–2109/00 $20.00
PII: S0967-2109(00)00005-3
www.elsevier.com/locate/cardiosur
Haemodynamic changes during minimally invasive coronary artery bypass surgery using high-dose esmolol Ivan Aleksic*, Wolfgang Buhre†, Mersa M. Baryalei*, Frank Reitmeier*, Theodor Tirilomis*, Andreas Weyland† and Harald Dalichau* *Department of Thoracic and Cardiovascular Surgery, Georg-August University, Go¨ttingen, Germany and †Department of Anaesthesiology, Georg-August University, Go¨ttingen, Germany We aimed to investigate the effects of high-dose esmolol on haemodynamics and oxygen extraction in minimally invasive direct coronary artery bypass (MIDCAB) surgery patients. Methods: In 18 patients, heart rate (HR), mean arterial (MAP), central venous (CVP), pulmonary capillary wedge pressure (PCWP), cardiac output (CO), and mixed venous oxygen saturation (Sv02) were prospectively measured after induction of anaesthesia (T1), start of surgery (T2), during bypass grafting with -blockade (T3), and at the end of surgery (T4). Results: Mean esmolol dose at T3 was 0.44 ⫾ 0.2 mg kg−1 min−1. HR was unchanged, whereas significant decreases in mean CO (3.1 ⫾ 0.8 vs 4.8 ⫾ 1.0 l min−1 m−2, pre-esmolol), MAP (53 ⫾ 10 vs 89 ⫾ 14 mmHg), and SvO2 (65 ⫾ 10 vs 81 ⫾ 4%) were observed during esmolol administration. All haemodynamic parameters normalized immediately after termination of esmolol (T4). Conclusions: Despite unchanged HR esmolol reduced CO and MAP suggesting a favorable reduction of myocardial oxygen consumption. Mean Sv02 during esmolol administration reflects an acceptable ratio of whole-body oxygen delivery and consumption. Haemodynamic changes with high-dose esmolol during MIDCAB surgery remain within safety margins. 2000 The International Society for Cardiovascular Surgery. Published by Elsevier Science Ltd. All rights reserved Keywords: -blocker, esmolol, MIDCAB, coronary bypass
Introduction A new surgical method for the treatment of left anterior descending (LAD) stenosis has emerged over the last several years. This method, minimally invasive direct coronary artery bypass (MIDCAB), aims to avoid the disadvantages of conventional coronary artery bypass grafting (CABG), i.e. midline sternotomy and use of cardiopulmonary bypass. It is also expected to reduce postoperative pain, length of hospital stay and thereby cost of medical care. How-
Correspondence to: Ivan Aleksic, Klinik fu¨r Thorax-, Herz und Gefa¨ßchirurgie, Georg-August Universita¨t Go¨ttingen, Robert Koch Str. 40, 37075 Go¨ttingen, Germany. E-mail: [email protected]
204
ever, concerns have been raised regarding incomplete revascularization, long-term outcome, patency and accuracy of the anastomosis in contrast to conventional CABG, and the difficulties to teach it to the cardiac surgical residents [1]. In particular, the accuracy and patency of the anastomosis are of pivotal importance for the widespread acceptance of MIDCAB surgery. Several pharmacological methods apart from mechanical stabilization have been described to facilitate the surgeon’s task by reducing cardiac wall motion and reduce myocardial oxygen consumption at the same time. While Benetti et al. [2] use oral atenolol or metoprolol before the operation, Buffolo and coworkers rely on 5 mg of verapamil [3]. Calafiore et al. [4] prefer diltiazem to reduce the patient’s CARDIOVASCULAR SURGERY
APRIL 2000 VOL 8 NO 3
Changes during MIDCAB surgery: I. Aleksic et al.
heart rate, an approach described by Acuff et al. [5] as well. Other investigators [6] use a short-acting blocker, esmolol, to achieve a reduction in heart rate. Apparently, there is no consensus as to which drug offers the best pharmacological stabilization of the operative field. In this study we investigated the effects of high-dose esmolol on haemodynamics and oxygen extraction.
Results
Methods After approval by our institutional review board written informed consent was obtained from all patients. Eighteen patients undergoing MIDCAB surgery participated in the study. The mean age of patients was 59 yr (range:43–72 yr), their mean body height and weight were 169 ⫾ 9 cm and 79 ⫾ 15 kg respectively (mean ⫾ SD). Premedication consisted of flunitrazepam 1 mg p.o. on the evening before and the morning of surgery. In addition to individual preoperative medication, clonidine 150 g p.o. was given at the morning of surgery. The dose of ACE-inhibitors, if they were part of the patients’ routine medication, was reduced to one half of the normal dose. Prior to induction of anaesthesia, routine haemodynamic monitoring was established including electrocardiography (leads II and V5) and arterial and venous lines. After induction of anaesthesia a 7.5 F pulmonary artery oxymetric catheter was inserted via the right internal jugular vein. Induction of anaesthesia was performed by i.v. administration of 3 g kg−1 sufentanil, tracheal intubation was facilitated by 0.1 mg kg−1 pancuronium bromide. Anaesthesia was maintained by intravenous infusions of 3 g kg−1 h−1 sufentanil and intermittent doses of midazolam as clinically deemed necessary. A double lumen tube was used in all patients. Haemodynamic measurements were performed after induction of anaesthesia (T1), after surgical stimulation (T2), during esmolol administration and bypass grafting (T3) and at the end of surgery (T4). At each measurement arterial, central venous, pulmonary arterial and pulmonary capillary wedge pressure were recorded on an eight channel chart recorder; thermodilution measurements of cardiac output were taken at three random times during the respiratory cycle (Polymed CO computer, System 1281, Siemens, Munich, Germany). In addition, blood samples for measurements of arterial and mixed venous oxygen saturation, haemoglobin concentration, oxygen and carbon dioxide partial pressure (OSM 3, ABL 3, Radiometer, Copenhagen, Denmark) were drawn at each measurement period. Statistical analysis: Results in tables and figures are expressed as mean ⫾ standard deviation. The effects of esmolol on haemodynamic parameters were tested by analysis of variance for repeated meaCARDIOVASCULAR SURGERY
sures (ANOVA). If the ANOVA revealed a significant influence of the repeated measures factor, subsequent paired t-tests were used for post-hoc comparison. A level of P ⱕ 0.05 was considered statistically significant. All statistical procedures were performed on a microcomputer with the SPSS/PC ⫹ statistical software package.
APRIL 2000 VOL 8 NO 3
There was no early mortality in the study group. In one patient, MIDCAB could not be performed due to technical reasons. Cardiopulmonary bypass had to be instituted for this patient. The administration of a mean dose of 0.4 ⫾ 0.2 mg kg−1 min−1 esmolol did not lead to a reduction in heart rate. However, a significant decrease in cardiac output and mean arterial pressure was observed during administration of esmolol and bypass grafting (Figure 1, Table 1) whereas no significant changes in PCWP and CVP occurred. Consequently, during administration of esmolol SvO2 significantly decreased. SvO2, CO and MAP all normalized immediately after termination of esmolol infusion at the end of surgery (Figure 2, Table 1).
Discussion Coronary artery bypass grafting without cardiopulmonary bypass is gaining widespread acceptance as an alternative technique of myocardial revascularization. It was first described by Kolessov in 1967 [7]. Buffolo et al. [3] found lower costs per patient and shorter hospitalization to be some of the advantages of coronary artery surgery without CPB. Mini-
Figure 1 Time course of heart rate (쎲) and mean arterial pressure (䊏) during MIDCAB surgery. A significant decrease in MAP was observed (#P ⱕ 0.05) during esmolol administration and bypass grafting (T3). Data are presented as mean ⫾ SD. T1, induction of anesthesia; T2, start of surgery; T3, -blockade during bypass grafting; T4, end of surgery
205
Changes during MIDCAB surgery: I. Aleksic et al. Table 1 Effect of esmolol on systemic hemodynamic variables and mixed venous oxygen saturation HR (min−1) T1 T2 T3 T4
61 66 66 75
⫾ ⫾ ⫾ ⫾
9 10 7 12
MAP (mmHg) 82 89 53 74
⫾ ⫾ ⫾ ⫾
6 14 10* 11
PCWP (mmHg) 11 12 14 14
⫾ ⫾ ⫾ ⫾
4 4 4 3
CVP (mmHg)
CO (l min−1)
9⫾3 10 ⫾ 4 11 ⫾ 5 11 ⫾ 3
4.5 4.8 3.1 5.6
⫾ ⫾ ⫾ ⫾
1.1 1.0 0.8* 1.5
Sv02 (%) 83 81 65 84
⫾ ⫾ ⫾ ⫾
7 4 10* 5
T1, induction of anesthesia; T2, start of surgery; T3, -blockade during bypass grafting; T4, end of surgery. HR, heart rate; MAP, mean arterial pressure; PCWP, pulmonary capillary wedge pressure; CVP, central venous pressure; CO, cardiac output; SvO2, mixed venous oxygen saturation. *P ⱕ 0.05 compared to T1, T2 and T4. Values are mean ⫾ SD.
Figure 2 Comparison of changes in cardiac output (䊏) and mixed venous oxygen saturation (쎲) in patients undergoing MIDCAB surgery. Both parameters significantly decreased during esmolol administration and bypass grafting (P ⬍ 0.05) Data are presented as mean ⫾ SD. T1, induction of anesthesia; T2, start of surgery; T3, ß-blockade during bypass grafting; T4, end of surgery
mally invasive bypass surgery for the LAD is particularly appealing to the cardiac surgeon, as excellent 10-yr patency results with the left internal mammary artery (LIMA) as a bypass graft to the LAD have been reported [8]. Nevertheless, coronary angioplasty has become the most widely applied treatment method for proximal LAD disease with restenosis rates from 33% to 60% at 6 months [9]. Recently, Mariani et al. [10]) published data on the comparison of 181 consecutive patients who underwent angioplasty or MIDCAB for isolated type C stenosis ([11]) of the LAD. The principal finding was that freedom from repeat revascularizations was higher for MIDCAB than for PTCA patients (96.9% ⫾ 0.2% vs 67.6% ⫾ 0.5%, P ⬍ 0.001). Survival was not different between the two groups. Undoubtedly, the excellent long-term results after LIMA-LAD bypass surgery depend on the accuracy of the anastomosis. The results described by Loop et al. [8] were achieved on a non-beating heart with 206
CPB. In order to achieve comparable results with MIDCAB surgery without CPB, surgeons and anaesthesiologists have devised mechanical and pharmacological ways to create a localized stable operative field. One class of drugs for providing such a stable field are -blockers. Both the negative inotropic and chronotropic effect of -blockers are useful in this setting. Furthermore, -blockers can reduce myocardial oxygen consumption and lower systemic arterial lactate and coronary sinus lactate concentrations after CPB compared to placebo [12]. In particular, an ultra-short acting ß-blocker is desirable for MIDCAB surgery as potential side effects are supposed to be relieved fast after discontinuation of the drug. Esmolol has a distribution half-life of 2 min and an elimination half-life of 9 min [13]. Adverse effects of esmolol include cardiac arrest [14] and sudden death [15]. Therefore, studies evaluating the safety of esmolol application in terms of haemodynamic compromise and myocardial oxygen consumption during MIDCAB surgery are very important. In addition, the proven ability of esmolol to reduce the size of myocardial infarction and to provide myocardial protection make it an important drug to study, because of regional ischaemia induced by snaring the LAD proximal and distal from the arteriotomy with 5-0 Prolene (Ethicon, Norderstedt, Germany) sutures. The observed drop of cardiac output and mean arterial pressure upon administration of esmolol indicate a favorable reduction in myocardial oxygen consumption. This was achieved although the mean esmolol dose of 0.4 ⫾ 0.2 mg kg−1 min−1 given in our study did not decrease heart rate. Matching the decrease in cardiac output and mean arterial pressure, mean mixed venous oxygen concentration (Sv02) dropped as well, reflecting a higher degree of oxygen extraction during esmolol application. Absolute values of Sv02 proved that the ratio of whole body oxygen delivery and consumption was acceptable during esmolol administration and did not drop to dangerous levels in our patients who did not show signs of pre-existent disorders of other organ systems. Our results demonstrate that safe pharmacological stabilization of the operative field CARDIOVASCULAR SURGERY
APRIL 2000 VOL 8 NO 3
Changes during MIDCAB surgery: I. Aleksic et al.
can be achieved with esmolol. The unique pharmacokinetic properties of the drug can be useful during MIDCAB surgery. The decrease in cardiac performance is acceptable and remains within margins of safety. Equally important is the fact that the effects of esmolol on cardiac output and arterial pressure are quickly reversible as proven by the normalization of these parameters at the end of surgery. Since no side effects such as bundle branch blocks or even cardiac arrests were observed, early extubation was possible in most patients a few hours postoperatively. In conclusion, esmolol is a safe drug for reduction of cardiac oxygen consumption during MIDCAB surgery. The observed decrease in cardiac output, mean arterial pressure and mixed venous oxygen saturation remain within safety margins for the patient. The rapid reversibility of the drug’s effects and the ability to titrate it to the desired level make it a useful part of the common armamentarium of surgeons and anaesthesiologists for MIDCAB surgery. Future studies will prospectively have to compare the haemodynamic effects of esmolol with those of calcium antagonists.
References
5. 6.
7. 8.
9. 10. 11. 12.
13.
1. Reardon, M. J., Espada, R., Letsou, G. V., Safi, H. J., McCollum, C. H. and Baldwin, J. C., Editorial: minimally invasive coronary artery surgery — a word of caution. Journal of Thoracic and Cardiovascular Surgery, 1997, 114, 419–420. 2. Benetti, F., Mariani, M. A., Sani, G. et al., Video-assisted minimally invasive coronary operations without cardiopulmonary bypass: a multicenter study. Journal of Thoracic and Cardiovascular Surgery, 1996, 112, 1478–1484. 3. Buffolo, E., Silva De Andrade, J. C., Branco, J. N. R., Teles, C. A., Aguiar, L. F. and Gomes, W. J., Coronary artery bypass
CARDIOVASCULAR SURGERY
4.
APRIL 2000 VOL 8 NO 3
14. 15.
grafting without cardiopulmonary bypass. Annals of Thoracic Surgery, 1996, 61, 63–66. Calafiore, A. M., Angelini, G. D., Bergsland, J. and Salerno, T. A., Minimally invasive coronary artery bypass grafting. Annals of Thoracic Surgery, 1996, 62, 1545–1548. Acuff, T. E., Landreneau, R. J., Griffith, B. P. and Mack, M. J., Minimally invasive coronary artery bypass grafting. Annals of Thoracic Surgery, 1996, 61, 135–137. Arom, K. V., Emery, R. W., Nicoloff, D. M., Flavin, T. F. F. and Emery, A. M., Minimally invasive direct coronary artery bypass grafting: experimental and clinical experiences. Annals of Thoracic Surgery, 1997, 63(Suppl.), 48–52. Kolessov, V. L., Mammary artery–coronary artery anastomosis as a method of treatment for angina pectoris. Journal of Thoracic and Cardiovascular Surgery, 1967, 54, 535–544. Loop, F. R., Lytle, B. W., Cosgrove, D. M., Stewart, R. W. et al., Influence of the internal mammary artery graft on 10 year survival and other cardiac events. New England Journal of Medicine, 1986, 314, 1–6. Landau, C., Lange, R. A. and Hillis, L. D., Percutaneous transluminal angioplasty. New England Journal of Medicine, 1994, 330, 981–993. Mariani, M. A., Boonstra, P. W., Grandjean, J. G. et al., . Journal of Thoracic and Cardiovasccular Surgery, 1997, 114, 434–439. Ryan, T. J., Bauman, W. B., Kennedy, J. W. et al., Buidelines for percutaneous transluminal coronary angioplasty. Circulation, 1988, 88, 2987–3003. Cork, R. C., Kramer, T. H., Dreischmeier, B., Behr, S. and DiNardo, J. A., The effect of esmolol given during cardiopulmonary bypass. Anesthesiology and Analgesics, 1995, 80, 28– 40. Ravussin, P., Characteristiques et utilisation clinique de l’esmolol (Characteristics and clinical use of esmolol). Minerva Anesthesiology, 1992, 58(Suppl. 1), 77–79. Litman, R. S. and Zerngast, B. A., Cardiac arrest after esmolol administration: a review of acute -blocker toxicity. Journal of the American Osteopathy Association, 1996, 96, 616–618. Herschman, Z., Dimich, I. and Singh, P. P., Sudden death in a young postoperative patient given esmolol. Critical Care Medicine, 1993, 21, 1975–1976.
Paper accepted 17 January 2000
207
PII: S0967-2109(00)00005-3
www.elsevier.com/locate/cardiosur
Haemodynamic changes during minimally invasive coronary artery bypass surgery using high-dose esmolol Ivan Aleksic*, Wolfgang Buhre†, Mersa M. Baryalei*, Frank Reitmeier*, Theodor Tirilomis*, Andreas Weyland† and Harald Dalichau* *Department of Thoracic and Cardiovascular Surgery, Georg-August University, Go¨ttingen, Germany and †Department of Anaesthesiology, Georg-August University, Go¨ttingen, Germany We aimed to investigate the effects of high-dose esmolol on haemodynamics and oxygen extraction in minimally invasive direct coronary artery bypass (MIDCAB) surgery patients. Methods: In 18 patients, heart rate (HR), mean arterial (MAP), central venous (CVP), pulmonary capillary wedge pressure (PCWP), cardiac output (CO), and mixed venous oxygen saturation (Sv02) were prospectively measured after induction of anaesthesia (T1), start of surgery (T2), during bypass grafting with -blockade (T3), and at the end of surgery (T4). Results: Mean esmolol dose at T3 was 0.44 ⫾ 0.2 mg kg−1 min−1. HR was unchanged, whereas significant decreases in mean CO (3.1 ⫾ 0.8 vs 4.8 ⫾ 1.0 l min−1 m−2, pre-esmolol), MAP (53 ⫾ 10 vs 89 ⫾ 14 mmHg), and SvO2 (65 ⫾ 10 vs 81 ⫾ 4%) were observed during esmolol administration. All haemodynamic parameters normalized immediately after termination of esmolol (T4). Conclusions: Despite unchanged HR esmolol reduced CO and MAP suggesting a favorable reduction of myocardial oxygen consumption. Mean Sv02 during esmolol administration reflects an acceptable ratio of whole-body oxygen delivery and consumption. Haemodynamic changes with high-dose esmolol during MIDCAB surgery remain within safety margins. 2000 The International Society for Cardiovascular Surgery. Published by Elsevier Science Ltd. All rights reserved Keywords: -blocker, esmolol, MIDCAB, coronary bypass
Introduction A new surgical method for the treatment of left anterior descending (LAD) stenosis has emerged over the last several years. This method, minimally invasive direct coronary artery bypass (MIDCAB), aims to avoid the disadvantages of conventional coronary artery bypass grafting (CABG), i.e. midline sternotomy and use of cardiopulmonary bypass. It is also expected to reduce postoperative pain, length of hospital stay and thereby cost of medical care. How-
Correspondence to: Ivan Aleksic, Klinik fu¨r Thorax-, Herz und Gefa¨ßchirurgie, Georg-August Universita¨t Go¨ttingen, Robert Koch Str. 40, 37075 Go¨ttingen, Germany. E-mail: [email protected]
204
ever, concerns have been raised regarding incomplete revascularization, long-term outcome, patency and accuracy of the anastomosis in contrast to conventional CABG, and the difficulties to teach it to the cardiac surgical residents [1]. In particular, the accuracy and patency of the anastomosis are of pivotal importance for the widespread acceptance of MIDCAB surgery. Several pharmacological methods apart from mechanical stabilization have been described to facilitate the surgeon’s task by reducing cardiac wall motion and reduce myocardial oxygen consumption at the same time. While Benetti et al. [2] use oral atenolol or metoprolol before the operation, Buffolo and coworkers rely on 5 mg of verapamil [3]. Calafiore et al. [4] prefer diltiazem to reduce the patient’s CARDIOVASCULAR SURGERY
APRIL 2000 VOL 8 NO 3
Changes during MIDCAB surgery: I. Aleksic et al.
heart rate, an approach described by Acuff et al. [5] as well. Other investigators [6] use a short-acting blocker, esmolol, to achieve a reduction in heart rate. Apparently, there is no consensus as to which drug offers the best pharmacological stabilization of the operative field. In this study we investigated the effects of high-dose esmolol on haemodynamics and oxygen extraction.
Results
Methods After approval by our institutional review board written informed consent was obtained from all patients. Eighteen patients undergoing MIDCAB surgery participated in the study. The mean age of patients was 59 yr (range:43–72 yr), their mean body height and weight were 169 ⫾ 9 cm and 79 ⫾ 15 kg respectively (mean ⫾ SD). Premedication consisted of flunitrazepam 1 mg p.o. on the evening before and the morning of surgery. In addition to individual preoperative medication, clonidine 150 g p.o. was given at the morning of surgery. The dose of ACE-inhibitors, if they were part of the patients’ routine medication, was reduced to one half of the normal dose. Prior to induction of anaesthesia, routine haemodynamic monitoring was established including electrocardiography (leads II and V5) and arterial and venous lines. After induction of anaesthesia a 7.5 F pulmonary artery oxymetric catheter was inserted via the right internal jugular vein. Induction of anaesthesia was performed by i.v. administration of 3 g kg−1 sufentanil, tracheal intubation was facilitated by 0.1 mg kg−1 pancuronium bromide. Anaesthesia was maintained by intravenous infusions of 3 g kg−1 h−1 sufentanil and intermittent doses of midazolam as clinically deemed necessary. A double lumen tube was used in all patients. Haemodynamic measurements were performed after induction of anaesthesia (T1), after surgical stimulation (T2), during esmolol administration and bypass grafting (T3) and at the end of surgery (T4). At each measurement arterial, central venous, pulmonary arterial and pulmonary capillary wedge pressure were recorded on an eight channel chart recorder; thermodilution measurements of cardiac output were taken at three random times during the respiratory cycle (Polymed CO computer, System 1281, Siemens, Munich, Germany). In addition, blood samples for measurements of arterial and mixed venous oxygen saturation, haemoglobin concentration, oxygen and carbon dioxide partial pressure (OSM 3, ABL 3, Radiometer, Copenhagen, Denmark) were drawn at each measurement period. Statistical analysis: Results in tables and figures are expressed as mean ⫾ standard deviation. The effects of esmolol on haemodynamic parameters were tested by analysis of variance for repeated meaCARDIOVASCULAR SURGERY
sures (ANOVA). If the ANOVA revealed a significant influence of the repeated measures factor, subsequent paired t-tests were used for post-hoc comparison. A level of P ⱕ 0.05 was considered statistically significant. All statistical procedures were performed on a microcomputer with the SPSS/PC ⫹ statistical software package.
APRIL 2000 VOL 8 NO 3
There was no early mortality in the study group. In one patient, MIDCAB could not be performed due to technical reasons. Cardiopulmonary bypass had to be instituted for this patient. The administration of a mean dose of 0.4 ⫾ 0.2 mg kg−1 min−1 esmolol did not lead to a reduction in heart rate. However, a significant decrease in cardiac output and mean arterial pressure was observed during administration of esmolol and bypass grafting (Figure 1, Table 1) whereas no significant changes in PCWP and CVP occurred. Consequently, during administration of esmolol SvO2 significantly decreased. SvO2, CO and MAP all normalized immediately after termination of esmolol infusion at the end of surgery (Figure 2, Table 1).
Discussion Coronary artery bypass grafting without cardiopulmonary bypass is gaining widespread acceptance as an alternative technique of myocardial revascularization. It was first described by Kolessov in 1967 [7]. Buffolo et al. [3] found lower costs per patient and shorter hospitalization to be some of the advantages of coronary artery surgery without CPB. Mini-
Figure 1 Time course of heart rate (쎲) and mean arterial pressure (䊏) during MIDCAB surgery. A significant decrease in MAP was observed (#P ⱕ 0.05) during esmolol administration and bypass grafting (T3). Data are presented as mean ⫾ SD. T1, induction of anesthesia; T2, start of surgery; T3, -blockade during bypass grafting; T4, end of surgery
205
Changes during MIDCAB surgery: I. Aleksic et al. Table 1 Effect of esmolol on systemic hemodynamic variables and mixed venous oxygen saturation HR (min−1) T1 T2 T3 T4
61 66 66 75
⫾ ⫾ ⫾ ⫾
9 10 7 12
MAP (mmHg) 82 89 53 74
⫾ ⫾ ⫾ ⫾
6 14 10* 11
PCWP (mmHg) 11 12 14 14
⫾ ⫾ ⫾ ⫾
4 4 4 3
CVP (mmHg)
CO (l min−1)
9⫾3 10 ⫾ 4 11 ⫾ 5 11 ⫾ 3
4.5 4.8 3.1 5.6
⫾ ⫾ ⫾ ⫾
1.1 1.0 0.8* 1.5
Sv02 (%) 83 81 65 84
⫾ ⫾ ⫾ ⫾
7 4 10* 5
T1, induction of anesthesia; T2, start of surgery; T3, -blockade during bypass grafting; T4, end of surgery. HR, heart rate; MAP, mean arterial pressure; PCWP, pulmonary capillary wedge pressure; CVP, central venous pressure; CO, cardiac output; SvO2, mixed venous oxygen saturation. *P ⱕ 0.05 compared to T1, T2 and T4. Values are mean ⫾ SD.
Figure 2 Comparison of changes in cardiac output (䊏) and mixed venous oxygen saturation (쎲) in patients undergoing MIDCAB surgery. Both parameters significantly decreased during esmolol administration and bypass grafting (P ⬍ 0.05) Data are presented as mean ⫾ SD. T1, induction of anesthesia; T2, start of surgery; T3, ß-blockade during bypass grafting; T4, end of surgery
mally invasive bypass surgery for the LAD is particularly appealing to the cardiac surgeon, as excellent 10-yr patency results with the left internal mammary artery (LIMA) as a bypass graft to the LAD have been reported [8]. Nevertheless, coronary angioplasty has become the most widely applied treatment method for proximal LAD disease with restenosis rates from 33% to 60% at 6 months [9]. Recently, Mariani et al. [10]) published data on the comparison of 181 consecutive patients who underwent angioplasty or MIDCAB for isolated type C stenosis ([11]) of the LAD. The principal finding was that freedom from repeat revascularizations was higher for MIDCAB than for PTCA patients (96.9% ⫾ 0.2% vs 67.6% ⫾ 0.5%, P ⬍ 0.001). Survival was not different between the two groups. Undoubtedly, the excellent long-term results after LIMA-LAD bypass surgery depend on the accuracy of the anastomosis. The results described by Loop et al. [8] were achieved on a non-beating heart with 206
CPB. In order to achieve comparable results with MIDCAB surgery without CPB, surgeons and anaesthesiologists have devised mechanical and pharmacological ways to create a localized stable operative field. One class of drugs for providing such a stable field are -blockers. Both the negative inotropic and chronotropic effect of -blockers are useful in this setting. Furthermore, -blockers can reduce myocardial oxygen consumption and lower systemic arterial lactate and coronary sinus lactate concentrations after CPB compared to placebo [12]. In particular, an ultra-short acting ß-blocker is desirable for MIDCAB surgery as potential side effects are supposed to be relieved fast after discontinuation of the drug. Esmolol has a distribution half-life of 2 min and an elimination half-life of 9 min [13]. Adverse effects of esmolol include cardiac arrest [14] and sudden death [15]. Therefore, studies evaluating the safety of esmolol application in terms of haemodynamic compromise and myocardial oxygen consumption during MIDCAB surgery are very important. In addition, the proven ability of esmolol to reduce the size of myocardial infarction and to provide myocardial protection make it an important drug to study, because of regional ischaemia induced by snaring the LAD proximal and distal from the arteriotomy with 5-0 Prolene (Ethicon, Norderstedt, Germany) sutures. The observed drop of cardiac output and mean arterial pressure upon administration of esmolol indicate a favorable reduction in myocardial oxygen consumption. This was achieved although the mean esmolol dose of 0.4 ⫾ 0.2 mg kg−1 min−1 given in our study did not decrease heart rate. Matching the decrease in cardiac output and mean arterial pressure, mean mixed venous oxygen concentration (Sv02) dropped as well, reflecting a higher degree of oxygen extraction during esmolol application. Absolute values of Sv02 proved that the ratio of whole body oxygen delivery and consumption was acceptable during esmolol administration and did not drop to dangerous levels in our patients who did not show signs of pre-existent disorders of other organ systems. Our results demonstrate that safe pharmacological stabilization of the operative field CARDIOVASCULAR SURGERY
APRIL 2000 VOL 8 NO 3
Changes during MIDCAB surgery: I. Aleksic et al.
can be achieved with esmolol. The unique pharmacokinetic properties of the drug can be useful during MIDCAB surgery. The decrease in cardiac performance is acceptable and remains within margins of safety. Equally important is the fact that the effects of esmolol on cardiac output and arterial pressure are quickly reversible as proven by the normalization of these parameters at the end of surgery. Since no side effects such as bundle branch blocks or even cardiac arrests were observed, early extubation was possible in most patients a few hours postoperatively. In conclusion, esmolol is a safe drug for reduction of cardiac oxygen consumption during MIDCAB surgery. The observed decrease in cardiac output, mean arterial pressure and mixed venous oxygen saturation remain within safety margins for the patient. The rapid reversibility of the drug’s effects and the ability to titrate it to the desired level make it a useful part of the common armamentarium of surgeons and anaesthesiologists for MIDCAB surgery. Future studies will prospectively have to compare the haemodynamic effects of esmolol with those of calcium antagonists.
References
5. 6.
7. 8.
9. 10. 11. 12.
13.
1. Reardon, M. J., Espada, R., Letsou, G. V., Safi, H. J., McCollum, C. H. and Baldwin, J. C., Editorial: minimally invasive coronary artery surgery — a word of caution. Journal of Thoracic and Cardiovascular Surgery, 1997, 114, 419–420. 2. Benetti, F., Mariani, M. A., Sani, G. et al., Video-assisted minimally invasive coronary operations without cardiopulmonary bypass: a multicenter study. Journal of Thoracic and Cardiovascular Surgery, 1996, 112, 1478–1484. 3. Buffolo, E., Silva De Andrade, J. C., Branco, J. N. R., Teles, C. A., Aguiar, L. F. and Gomes, W. J., Coronary artery bypass
CARDIOVASCULAR SURGERY
4.
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14. 15.
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