| ||||||||||||||
|
|
|||||||||||||
,
,
Departments of
*Anesthesiology and
Medical Physiology, University of Stellenbosch Faculty of Medicine; and
MRC Experimental Biology Programme, Tygerberg, Republic of South Africa
Address correspondence and reprint requests to Prof. J. F. Coetzee, Department Anesthesiology, Faculty of Medicine, University of Stellenbosch, PO Box 19063, Tygerberg 7505, Republic of South Africa.
| Abstract |
|---|
|
|
|---|
Implications: In view of the possible significance for volatile anesthetics in cardiac surgery, the effects of sevoflurane and halothane were compared on postcardioplegic recovery of rat hearts. Both anesthetics were equally effective in improving functional recovery after normothermic cardioplegic arrest. Sevofluranes beneficial effects were abolished by glibenclamide, suggesting a role for the adenosine triphosphate regulated potassium channel.
| Introduction |
|---|
|
|
|---|
Various studies have shown that anesthetics such as halothane and isoflurane exert protective effects during reperfusion after myocardial ischemia (5,6) or cardioplegic arrest (7,8). Likely mechanisms include prevention of the rise and oscillations in intracellular Ca2+ associated with ischemia and reperfusion (9) and/or activation of the adenosine triphosphate regulated potassium (KATP) channels (10).
In view of the observations that sevoflurane improved functional recovery (11) and reduced infarct size (12) during reperfusion after ischemia, we hypothesized that it also protects against ischemic damage during cardioplegic arrest. In view of the possible significance for sevoflurane in cardiac surgery, the aims of this study were to (i) optimize the time of administration of sevoflurane in perfused rat hearts subjected to 45 min of normothermic cardioplegic arrest; (ii) evaluate the role of the KATP channel in the cardiac effects of sevoflurane; and (iii) compare the effects of sevoflurane with equipotent concentrations of halothane.
| Methods |
|---|
|
|
|---|
After removal, the hearts were arrested in cold Krebs-Henseleit buffer (4°C), mounted (within 30 s) onto an aortic cannula and perfused retrogradely via the aorta with Krebs-Henseleit buffer for 10 min (composition in mmol/L: NaCl 124; KCl 4.93; CaCl2 1.25; MgCl2 1.62; Na2SO4 0.6; KH2PO4 1.23; NaHCO3 26; glucose 10). The perfusate buffer was oxygenated with 95% O2/5% CO2 at 37.5°C. During retrograde perfusion, the left atrium was cannulated to allow perfusion in the working mode. The atrial filling pressure (15 cm H2O) and afterload (100 cm H2O) were kept constant before and after cardioplegia (for detailed description of technique, see Ref. 13).
After 20 min of perfusion in the working mode, the hearts were arrested with St. Thomas solution (temperature: 37.5°C; composition in mmol/L: NaCl 110; KCl 16; CaCl2 · 2H2O 1.2; MgCl2 · 6H2O 16; NaHCO3 10). Initially, administration of the cardioplegic solution was maintained for 3 min (pressure 100 cm H2O) and repeated for 3 min at 30 min cardioplegic arrest. After arrest, the hearts were reperfused retrogradely with Krebs-Henseleit buffer for 10 min, followed by perfusion in the working mode for 20 min. Sevoflurane or halothane was administered before and after cardioplegia, before cardioplegia, or after cardioplegia (Fig. 1), but was not present during cardioplegic arrest. The anesthetics were introduced into the gas supply of the perfusate by using a calibrated vaporizer (Penlon InterMed; Penlon Ltd., Abington, Oxon, UK). The concentration of the anesthetic was monitored continuously by using a calibrated anesthetic monitor (Ohmeda model 5330; Ohmeda, Louisville, CO).
|
Aortic and coronary flows were collected manually, while the aortic pressure and heart rate were monitored by using a pressure transducer (Viggo-spectramed) connected to a computer. Measurements were made before and after arrest as shown in Figure 1. Total work performance (pressure power + kinetic power) developed by the heart was calculated as follows (14):
|
|
|
|
= density of perfusate, Te = ejection time. At the end of reperfusion, hearts were freeze-clamped with Wollenberger tongs and stored in liquid nitrogen for determination of high energy phosphates (15).
Controls
The hearts were perfused retrogradely for 10 min, followed by 20 min of perfusion in the working mode, subjected to 45 or 60 min of normothermic arrest, followed by 30 min of reperfusion (10 min retrogradely, 20 min working heart).
Sevoflurane
Before and After Arrest.
After 10 min of retrograde and 10 min of working heart perfusion, sevoflurane (0.9% or 1.7%, = 0.5 or 1.0 minimum alveolar anesthetic concentration [MAC]) was administered for 10 min. After 45 or 60 min of normothermic cardioplegic arrest, hearts were reperfused for 30 min (10 min retrogradely and 10 min working heart in the presence of sevoflurane, followed by 10 min perfusion in the working mode in the absence of the anesthetic).
Before Arrest Only.
The perfusion protocol was as described above, except that sevoflurane (0.9%) was only administered for 10 min during perfusion in the working mode before cardioplegia. Reperfusion was as described above, but in the absence of sevoflurane.
After Arrest Only.
The perfusion protocol was as described for "before and after arrest," except that sevoflurane (0.9%) was administered during the first 20 min of reperfusion only.
Sevoflurane and Glibenclamide
Controls.
The hearts were perfused retrogradely for 10 min, followed by 10 min of perfusion in the working mode. Glibenclamide (10 µM) or sevoflurane (0.9%) was administered retrogradely for either 10 min before and 20 min after 45 min of cardioplegic arrest or for 10 min before arrest only.
Before and After Arrest.
The hearts were perfused retrogradely for 10 min, followed by 10 min of working heart perfusion. Sevoflurane (0.9%) and glibenclamide (10 µM) were then administered simultaneously for 10 min during retrograde perfusion. After 45 min of normothermic arrest, the hearts were reperfused retrogradely for 20 min in the presence of sevoflurane and glibenclamide, followed by 10 min of working heart perfusion in the absence of drugs.
Before Arrest.
The perfusion protocol was as described above, except that sevoflurane (0.9%) and glibenclamide (10 µM) were present before cardioplegia only.
Halothane
Before and After Arrest.
The perfusion protocol was similar to that described for sevoflurane. Halothane (0.4% and 0.8%, = 0.5 or 1.0 MAC) was administered before and after 45 or 60 min of normothermic cardioplegia.
Data analysis was performed by using a computer software package (Sigmastat for DOS version 5.0; Jandel Scientific Software, San Rafael, CA). Within-group hemodynamic measurements were evaluated by using repeated measurements analysis of variance (ANOVA) and between-group comparisons were made by using one-way ANOVA. If the data were not normally distributed (Kolmogorov-Smirnov test) and did not have equal variances (Levene Median test), equivalent nonparametric tests were performed by using the Friedman repeated measures ANOVA on ranks and the Kruskal-Wallis ANOVA on ranks. post hoc multiple comparison procedures were performed by using the Student-Newman-Keuls test. An
value equal to or less than 0.05 was regarded as indicating a significant result.
| Results |
|---|
|
|
|---|
|
The Effects of Glibenclamide on Sevoflurane-induced Protection
In these experiments, mechanical activity was measured before the administration of glibenclamide (10 µM) or sevoflurane (0.9%) (20 min total perfusion time) and at the end of reperfusion (105 min total perfusion time) after 45 min of normothermic cardioplegic arrest (Fig. 3). The administration of glibenclamide alone either before and after or only before cardioplegic arrest had no effect on functional recovery, and values obtained were similar to those of untreated controls. Simultaneous administration of sevoflurane and glibenclamide either before and after arrest or only before arrest completely abolished sevofluranes protective effects: aortic output, peak systolic pressure, and total work performance were significantly less than with sevoflurane alone. Similar results (not shown) were obtained with a combination of 5 µM glibenclamide and 0.9% sevoflurane.
|
|
Except for a reduction in heart rate, sevoflurane (0.9%) had no effect on the mechanical performance of hearts before cardioplegia. After 10 min of reperfusion, all variables (except coronary flow with 1.7% sevoflurane) were significantly less than values before cardioplegia. Reperfusion for a further period of 10 min in the absence of sevoflurane, increased aortic output, peak systolic pressure, and total work significantly, compared with values during reperfusion in the presence of the anesthetic. Except for the coronary flow, the values obtained at the end of reperfusion were significantly lower than those observed before cardioplegia.
Between-Group Comparisons.
In contrast to the halothane (0.4%) and sevoflurane groups, halothane (0.8%) decreased aortic output before cardioplegic arrest.
Aortic output after 20 min of reperfusion in the presence of the anesthetic drugs was lowest in the case of 0.8% halothane, whereas sevoflurane (0.9%) had values significantly greater than the other groups.
After 30 min of reperfusion, all hearts previously exposed to either anesthetic at both concentrations exhibited higher aortic output and total work values than the controls. No differences were observed between the halothane and sevoflurane groups.
Tissue High Energy Phosphates
Reperfusion after 45 or 60 min of normothermic cardioplegic arrest was associated with a marked reduction in tissue adenosine triphosphate (ATP), adenosine diphosphate (ADP), and adenosine monophosphate (AMP), while creatine phosphate (CP) values remained unchanged (Table 2). At the end of reperfusion, no differences in tissue ATP, ADP, AMP or CP contents were detected among the five groups studied.
|
|
| Discussion |
|---|
|
|
|---|
Sevoflurane
The significant sevoflurane-induced improvement in functional recovery during reperfusion after cardioplegic arrest confirms the results obtained in ischemic rat hearts (11). The marked improvement in function on withdrawal of sevoflurane is difficult to explain in view of the observation that sevoflurane had no effect on myocardial function before arrest (Table 1). One possibility is that the arrested heart is more sensitive to sevofluranes cardiodepressant action. This improvement may be caused by a reduction in ischemic injury during cardioplegic arrest, amelioration of stunning, and/or a reduction in infarct size. Previous studies suggested that both halothane (7) and sevoflurane (12) exerted their beneficial effects during reperfusion only, and it was presumed that this might also occur in the present study. Because sevoflurane, when given only before cardioplegic arrest, improved functional recovery as efficiently as when given both before and after (Fig. 2), this suggests protection against ischemic damage per se but does not eliminate an effect during reperfusion. Because of its lipid solubility sevoflurane may still be present at the onset of reperfusion, causing amelioration of stunning. Although infarct size was not measured in our study, sevoflurane has been shown to limit infarct size (12). When administered during reperfusion only, sevoflurane caused complete mechanical failure; an explanation for this phenomenon is not readily available.
Sevoflurane Versus Halothane
For comparison purposes, hearts were exposed to equipotent partial pressures of halothane and sevoflurane, expressed as multiples of MAC in humans. The MAC in rats is slightly greater than in humans (16), but this is of no consequence because the potency ratios between the anesthetics are equivalent in humans (0.44) and rat (0.42).
Before Cardioplegia
The results confirm the negative inotropic actions of halothane, previously observed in both isolated hearts (7) and cultured neonatal rat ventricular myocytes (4). However, in the latter model, halothane also had the most significant negative chronotropic effect, in contrast to the perfused rat heart where halothane had no effect (Table 1). These conflicting results may indicate differing modes of action on the two experimental preparations. The coronary vasodilatory action of sevoflurane (17) demonstrated in dogs was absent in the isolated perfused rat hearts (Table 1).
During Reperfusion
In the comparative study (Tables 1 and 3), halothane or sevoflurane was administered both before and after cardioplegic arrest, a protocol which does not permit distinction between their effects on ischemic and reperfusion damage. The results obtained showed that both anesthetics caused a significant improvement in functional recovery after 45 minutes of cardioplegic arrest. Both anesthetics exerted maximal protection at 0.5 MAC, confirming previous observations that halothane, as well as possibly other inhaled anesthetics, was effective at small concentrations in this particular experimental model (7,8). The protective effects were time-dependent and absent after 60 minutes of normothermic cardioplegia (Table 3). These findings are probably observed because the myocardium is irreversibly injured at this stage, as reflected by the reduced levels of high energy phosphate in such hearts (Table 2).
In our previous studies, functional recovery was assessed by the response to epinephrine; hearts pretreated with halothane (7), enflurane, or isoflurane (8) produced greater outputs than control untreated hearts on stimulation with epinephrine. Because halothane and sevoflurane potentiate the positive inotropic effects of
- and ß-adrenergic stimulation by approximately 200% (18,19), it may be argued that the improved outputs previously observed, resulted from halothanes potentiation of adrenergic stimulation rather than protection against reperfusion injury. However, the improved recovery induced by halothane or sevoflurane in hearts allowed to recover spontaneously (Table 1) confirms that halothane protects against postischemic contractile dysfunction or stunning per se. This was not associated with an increase in tissue high energy phosphate contents, when measured at the end of reperfusion (Table 2). Failure to show an association between tissue high energy phosphate levels at the end of reperfusion and improvement in functional recovery was also observed in our studies with enflurane and isoflurane (8).
Mechanism of Protection
The negative inotropic and chronotropic effects of anesthetics may provide an ATP-sparing mechanism which protects against ischemia. This appears unlikely, because the protection afforded by halothane was not associated with improved high energy phosphate levels at the end of cardioplegia (7). Furthermore, halothane caused greater depression in myocardial function than sevoflurane while their cardioprotective effects were the same. It is more likely that protection results from limiting function as seen during early reperfusion in the presence of the anesthetics.
Should the volatile anesthetics act via ameriolation of stunning, their effects are likely to be mediated by an effect of intracellular Ca2+ and free radical generation (20). The protective effects of halothane have been shown to be associated with inhibition of Ca2+ accumulation after myocardial ischemia and reperfusion (9), possibly via prevention of Ca2+-influx through the voltage-dependent Ca2+ channels (21), which in turn, may result from opening of the KATP channels and shortening of the action potential (22).
The cardioprotective actions of potassium channel openers are well established (23), and these drugs have been shown to be involved in halothane-induced coronary vasodilation (24) as well as isoflurane-induced reduction in infarct size (10,25). The abolition of sevoflurane-induced protection by glibenclamide (Fig. 3) suggests a role for the KATP channels in protection during cardioplegic arrest. Whether this occurs via shortening of the action potential remains to be determined.
In summary, the results obtained show that halothane and sevoflurane are equally protective in the setting of cardioplegia and suggest an application during cardiac surgery, bearing in mind the care which should be exercised when extrapolating from experimental animals to humans.
| Acknowledgments |
|---|
| References |
|---|
|
|
|---|
This article has been cited by other articles:
![]() |
J. A. Symons and P. S. Myles Myocardial protection with volatile anaesthetic agents during coronary artery bypass surgery: a meta-analysis Br. J. Anaesth., August 1, 2006; 97(2): 127 - 136. [Abstract] [Full Text] [PDF] |
||||
![]() |
B. Bein, J. Renner, D. Caliebe, J. Scholz, A. Paris, S. Fraund, W. Zaehle, and P. H. Tonner Sevoflurane but Not Propofol Preserves Myocardial Function During Minimally Invasive Direct Coronary Artery Bypass Surgery Anesth. Analg., March 1, 2005; 100(3): 610 - 616. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. Rodriguez-Sinovas, D. Garcia-Dorado, M. Ruiz-Meana, and J. Soler-Soler Enhanced effect of gap junction uncouplers on macroscopic electrical properties of reperfused myocardium J. Physiol., August 15, 2004; 559(1): 245 - 257. [Abstract] [Full Text] [PDF] |
||||
![]() |
R. Serita, H. Morisaki, K. Ai, Y. Morita, Y. Innami, T. Satoh, S. Kosugi, Y. Kotake, and J. Takeda Sevoflurane preconditions stunned myocardium in septic but not healthy isolated rat hearts Br. J. Anaesth., December 1, 2002; 89(6): 896 - 903. [Abstract] [Full Text] [PDF] |
||||
![]() |
D. Ebel, B. Preckel, A. You, J. Mullenheim, W. Schlack, and V. Thamer Cardioprotection by sevoflurane against reperfusion injury after cardioplegic arrest in the rat is independent of three types of cardioplegia Br. J. Anaesth., June 1, 2002; 88(6): 828 - 835. [Abstract] [Full Text] [PDF] |
||||
![]() |
B. Pouzet, J.-B. Lecharny, M. Dehoux, S. Paquin, M. Kitakaze, J. Mantz, and P. Menasche Is there a place for preconditioning during cardiac operations in humans? Ann. Thorac. Surg., March 1, 2002; 73(3): 843 - 848. [Abstract] [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|