Effects of sevoflurane on ischaemic myocardium in dogs

Comparison of effects of sevoflurane versus propofol on left ventricular longitudinal global and regional strain in patients undergoing on-pump coronary artery bypass grafting

Background:

Assessment of myocardial deformation by quantifying peak systolic longitudinal strain (PSLS) is a sensitive and robust index to detect subclinical myocardial dysfunction. We hypothesize that sevoflurane by virtue of anesthetic preconditioning preserves myocardial function better than propofol.

Aims:

The authors have assessed the effects of sevoflurane and propofol on global longitudinal strain (GLS) as a primary outcome in patients undergoing on-pump coronary artery bypass grafting. Our secondary aim was to assess the pattern of regional distribution of segmental PSLS between the groups.

Materials and Methods:

Fifty patients with normal left ventricular function undergoing coronary artery bypass grafting were analyzed in this prospective observational study. Consecutive patients received either propofol (P) or sevoflurane (S) anesthesia.

Measurements:

Trans-esophageal echocardiographic images (mid-esophageal four-chamber, two-chamber, and three-chamber (long-axis)) were recorded during the precardiopulmonary bypass (CPB) and post-CPB period. Strain analysis (GLS/segmental PSLS) was done offline by investigators blinded to the study. The inotropic score, duration of inotropic support, and mechanical ventilation required were recorded.

Results:

Following cardiopulmonary bypass and coronary revascularization, GLS reduced significantly in both the groups (P < 0.05). In the S-group, significant reduction in segmental strain was observed only in apical segments including apex, whereas in P-group significant reduction in segmental strain was seen in mid- and apical segments. The postoperative VIS, duration of inotropes/vasopressor required, and mechanical ventilation were similar in both the groups.

Conclusions:

There are no significant differences in global left ventricular function as assessed by GLS between patients anesthetized with sevoflurane or propofol. However, regional PSLS was better preserved in the S-group compared to P-group.

Cellular and molecular approaches to enhance myocardial recovery after myocardial infarction

Reperfusion therapy has resulted in significant improvement in post-myocardial infarction morbidity and mortality in over the last 4 decades. Nonetheless, it is well recognized that simply restoring patency of the epicardial artery may not stop or reverse damage at microvascular level, and myocardial salvage is often suboptimal. Numerous efforts have been undertaken to elucidate the mechanisms underlying extensive myonecrosis to facilitate the discovery of therapies to provide additional and incremental benefits over current therapeutic pathways. To date, conclusively effective strategies to promote myocardial recovery have not yet been established. Novel approaches are investigating the foundational cellular and molecular bases of myocardial ischemia and irreversible injury. Herein, we review the emerging concepts and proposed therapies that may improve myocardial protection and reduce infarct size. We examine the preclinical and clinical evidence for reduced infarct size with these strategies, including anti-inflammatory agents, intracellular ion channel modulators, agents affecting the reperfusion injury salvage kinase (RISK) and nitric oxide signaling pathways, modulators of mitochondrial function, anti-apoptotic agents, and stem cell and gene therapy. We review the potential reasons of failures to date and the potential for new strategies to further promote myocardial recovery and improve prognosis.

The role of Volatile Anesthetics in Cardioprotection: a systematic review

This review evaluates the mechanism of volatile anesthetics as cardioprotective agents in both clinical and laboratory research and furthermore assesses possible cardiac side effects upon usage. Cardiac as well as non-cardiac surgery may evoke perioperative adverse events including: ischemia, diverse arrhythmias and reperfusion injury. As volatile anesthetics have cardiovascular effects that can lead to hypotension, clinicians may choose to administer alternative anesthetics to patients with coronary artery disease, particularly if the patient has severe preoperative ischemia or cardiovascular instability. Increasing preclinical evidence demonstrated that administration of inhaled anesthetics - before and during surgery - reduces the degree of ischemia and reperfusion injury to the heart. Recently, this preclinical data has been implemented clinically, and beneficial effects have been found in some studies of patients undergoing coronary artery bypass graft surgery. Administration of volatile anesthetic gases was protective for patients undergoing cardiac surgery through manipulation of the potassium ATP (K_ATP) channel, mitochondrial permeability transition pore (mPTP), reactive oxygen species (ROS) production, as well as through cytoprotective Akt and extracellular-signal kinases (ERK) pathways. However, as not all studies have demonstrated improved outcomes, the risks for undesirable hemodynamic effects must be weighed against the possible benefits of using volatile anesthetics as a means to provide cardiac protection in patients with coronary artery disease who are undergoing surgery.

Halothane binding proteome in human brain cortex

Inhaled anesthetics bind specifically to a wide variety of proteins in the brain. This set of proteins must include those that contribute to the physiological and behavioral phenotypes of anesthesia and the related side effects. To identify the anesthetic-binding targets and functional pathways associated with these targets in human brain, halothane photolabeling and two-dimensional (2D) gel electrophoresis were used. Both membrane and soluble proteins from human temporal cortex were prepared. More than 300 membrane and 400 soluble protein spots were detected on the stained blots, of which 23 membrane and 34 soluble proteins were labeled by halothane and identified by mass spectroscopy. Their functional classification reveals five groups, including carbohydrate metabolism, protein folding, oxidative phosphorylation, nucleoside triphosphatase, and dimer/kinase activity with different correlative stringency. When network analysis of the interaction between these protein molecules is used, the weighted interaction accentuates the cellular protein components important in cell growth and proliferation, cell cycle and cell death, and cell-cell signaling and interactions, although no pathway was specific. This study provides evidence for multiple anesthetic binding targets and suggests potential pathways involved in their actions.

Myocardial protection with volatile anaesthetic agents during coronary artery bypass surgery: a meta-analysis

Previous studies have investigated the role of volatile anaesthetic agents in myocardial protection during coronary artery bypass graft (CABG) surgery, and some have identified beneficial effects. However, these studies have been too small to identify a significant effect on myocardial infarction (MI) or mortality. We undertook a systematic overview and meta-analysis of all randomized trials comparing volatile with non-volatile anaesthesia in CABG surgery. We identified 27 trials that included 2979 patients. There was no significant difference in myocardial ischaemia, MI, intensive care unit length of stay or hospital mortality between the groups (all P>0.05). Post-bypass, patients randomized to receive volatile anaesthetics had 20% higher cardiac indices (P=0.006), significantly lower troponin I serum concentrations (P=0.002) and lesser requirement for inotropic support (P=0.004) compared with those randomized to receive i.v. anaesthetics. Duration of mechanical ventilation was reduced by 2.7 h (P=0.04), and there was a 1 day decrease in hospital length of stay (P<0.001). Some of these outcomes were based on a smaller number of trials because of incomplete data, largely because the individual trials focused on one or more surrogate endpoints. We found some evidence that volatile anaesthetic agents provide myocardial protection in CABG surgery, but larger adequately powered trials with agreed, defined outcomes need to be done to fully assess a possible beneficial effect of volatile anaesthetic agents on the risk of MI and mortality.

The concept of anaesthetic-induced cardioprotection: mechanisms of action

The mechanisms by which ischaemia reperfusion injury can be influenced have been the subject of extensive research in the last decades. Early restoration of arterial blood flow and surgical measures to improve the ischaemic tolerance of the tissue are the main therapeutic options currently in clinical use. In experimental settings ischaemic preconditioning has been described as protecting the heart, but the practical relevance of interventions by ischaemic preconditioning is strongly limited to these experimental situations. However, ischaemia reperfusion of the heart routinely occurs in a variety of clinical situations, such as during transplantations, coronary artery bypass grafting or vascular surgery. Moreover, ischaemia reperfusion injury occurs without any surgical intervention as a transient myocardial ischaemia during a stressful anaesthetic induction. Besides ischaemic preconditioning, another form of preconditioning was discovered over 10 years ago: the anaesthetic-induced preconditioning. There is increasing evidence that anaesthetic agents can interact with the underlying pathomechanisms of ischaemia reperfusion injury and protect the myocardium by a preconditioning mechanism. Hence, the anaesthetist himself can substantially influence the critical situation of ischaemia reperfusion during the operation by choosing the right anaesthetic. A better understanding of the underlying mechanisms of anaesthetic-induced cardioprotection not only reflects an important increase in scientific knowledge but may also offer the new perspective of using different anaesthetics for targeted intraoperative myocardial protection. There are three time windows when a substance may interact with the ischaemia reperfusion injury process: (1) during ischaemia, (2) after ischaemia (i.e. during reperfusion), and (3) before ischaemia (preconditioning).

The effect of anaesthetics on the myocardium - new insights into myocardial protection

A variety of laboratory and clinical studies clearly indicate that exposure to anaesthetic agents can lead to a pronounced protection of the myocardium against ischaemia-reperfusion injury. Several changes in the protein structure of the myocardium that may mediate this cardioprotection have been identified. Ischaemia-reperfusion of the heart occurs in a variety of clinical situations including transplantations, coronary artery bypass grafting or vascular surgery. Ischaemia may also occur during a stressful anaesthetic induction. Early restoration of arterial blood flow and measures to improve the ischaemic tolerance of the tissue are the main therapeutic options (i.e. cardioplegia and betablockers). There exists increasing evidence that anaesthetic agents interact with the mechanisms of ischaemia-reperfusion injury and protect the myocardium by a 'preconditioning' and a 'postconditioning' mechanism. Hence, the anaesthesiologist may substantially influence the critical situation of ischaemia-reperfusion during surgery by choosing the appropriate anaesthetic agent. This review summarizes the current understanding of the mechanisms of anaesthetic-induced myocardial protection. In this context, three time windows of anaesthetic-induced cardioprotection are discussed: administration (1) during ischaemia, (2) after ischaemia-during reperfusion (postconditioning) and (3) before ischaemia (preconditioning). Possible clinical implications of these interventions will be reviewed.

Cardioprotection with volatile anesthetics: mechanisms and clinical implications

Cardiac surgery and some noncardiac procedures are associated with a significant risk of perioperative cardiac morbid events. Experimental data indicate that clinical concentrations of volatile general anesthetics protect the myocardium from ischemia and reperfusion injury, as shown by decreased infarct size and a more rapid recovery of contractile function on reperfusion. These anesthetics may also mediate protective effects in other organs, such as the brain and kidney. Recently, a number of reports have indicated that these experimentally observed protective effects may also have clinical implications in cardiac surgery. However, the impact of the use of volatile anesthetics on outcome measures, such as postoperative mortality and recovery in cardiac and noncardiac surgery, is yet to be determined.

Sevoflurane protects stunned myocardium through activation of mitochondrial ATP-sensitive potassium channels

We sought to determine the hemodynamic and cardioprotective effects of sevoflurane in canine stunned myocardium. Forty-nine dogs were allocated to one of seven groups (n = 7 for each). In six separate groups, dogs received vehicle, glibenclamide (a nonselective adenosine triphosphate-dependent potassium [K(ATP)] channel antagonist) (0.3 mg/kg IV) or 5-hydroxydecanoic acid (a mitochondrial K(ATP) channel antagonist) (5 mg/kg IV) in the presence or absence of 1 minimum alveolar concentration (1 MAC) sevoflurane. In an additional group, dogs received 1 MAC sevoflurane with hemodynamic correction. Regional myocardial contractility was evaluated with segment shortening. Measurements were made before and during 15-min ischemia and 90-min reperfusion. Recovery of segment shortening 90 min after reperfusion was significantly improved in the dogs anesthetized with sevoflurane either with or without hemodynamic correction (70.1 +/- 4.2 and 75.9 +/- 3.1% of baseline, respectively), whereas the recovery was poor in control and glibenclamide or 5-hydroxydecanoic acid pretreated dogs (33.3 +/- 4.3, 33.8 +/- 6.8, and 45.0 +/- 5.5% of baseline, respectively). Regional myocardial perfusion showed no significant difference among groups. The results indicate that sevoflurane has a cardioprotective effect mediated through activation of mitochondrial K(ATP) channels and independent of coronary blood flow or reduction in cardiac work.

IMPLICATIONS

Sevoflurane exerts a cardioprotective effect that is mediated via activation of adenosine triphosphate-sensitive potassium channels in ischemic canine hearts.

Vital capacity inhalation induction with sevoflurane: an alternative to standard intravenous induction for patients undergoing cardiac surgery

OBJECTIVE

To determine the respiratory and cardiovascular effects of a high concentration vital capacity induction with sevoflurane compared with an intravenous induction with etomidate in patients scheduled for elective coronary artery bypass graft (CABG) surgery.

DESIGN

Prospective, randomized, double-blind, controlled clinical trial.

SETTING

Cardiothoracic unit at a university hospital referral center.

PARTICIPANTS

Twenty-two patients undergoing elective CABG surgery.

INTERVENTIONS

The study group (group S) received a vital capacity gaseous induction with sevoflurane 8% (n = 12) and the control group (group E) were given etomidate, 0.2 to 0.3 mg/kg (n = 10). Anesthesia was supplemented with fentanyl, 8 microg/kg, and vecuronium, 0.1 mg/kg, in both groups.

MEASUREMENTS AND MAIN RESULTS

The speed of induction of anesthesia was comparable between the groups. There was a significant increase in minute ventilation after induction of anesthesia in both groups. This increase was associated with a small reduction in PaCO2. There were no clinically significant changes in pH and PaO(2). The incidence of breath-holding and the need for an oropharyngeal airway were similar between the groups. Both groups had similar reductions in mean arterial pressure and cardiac output during the study period; however, a downward trend in mean pulmonary artery pressure was noted in group S, whereas in group E it remained unchanged. Absolute plasma epinephrine and norepinephrine values were low during the precardiopulmonary bypass period in both groups.

CONCLUSIONS

The technique of vital capacity inhalation induction with 8% sevoflurane offers a rapid onset of anesthesia, satisfactory airway control, and a good hemodynamic profile. Consideration should be given to the benefits of single-agent anesthesia and lowered pulmonary artery pressure during the precardiopulmonary bypass period. In addition to CABG surgery, this technique could be considered in patients with coronary artery disease undergoing noncardiac surgery, particularly for procedures in which spontaneous ventilation is preferred.

Sevoflurane and isoflurane do not enhance the pre- and postischemic eicosanoid production in guinea pig hearts

Eicosanoids and volatile anesthetics can influence cardiac reperfusion injury. Accordingly, we analyzed the effects of sevoflurane and isoflurane applied in clinically relevant concentrations on the myocardial production of prostacyclin and thromboxane A2 (TxA2) and on heart function. Isolated guinea pig hearts, perfused with crystalloid buffer, performed pressure-volume work. Between two working phases, hearts were subjected to 15 min of global ischemia followed by reperfusion. The hearts received no anesthetic, 1 minimum alveolar anesthetic concentration (MAC) isoflurane (1.2 vol%), or 0.5 and 1 MAC sevoflurane (1 vol% and 2 vol%), either only preischemically or pre- and postischemically. In additional groups, cyclooxygenase function was examined by an infusion of 1 microM arachidonic acid (AA) in the absence and presence of sevoflurane. The variables measured included the myocardial production of prostacyclin, TxA2 and lactate, consumption of pyruvate, coronary perfusion pressure, and the tissue level of isoprostane 8-iso-PGF2alpha. External heart work, determined pre- and postischemically, served to assess recovery of heart function. Volatile anesthetics had no impact on postischemic recovery of myocardial function (50%-60% recovery), perfusion pressure, lactate production, or isoprostane content. Release of prostacyclin and TxA2 was increased in the early reperfusion phase 5-8- and 2-4-fold, respectively, indicating enhanced AA liberation. Isoflurane and sevoflurane did not augment the eicosanoid release. Only 2 vol% sevoflurane applied during reperfusion prevented the increased eicosanoid formation in this phase. Infusion of AA increased prostacyclin production approximately 200-fold under all conditions, decreased pyruvate consumption irreversibly, and markedly attenuated postischemic heart work (25% recovery). None of these effects were mitigated by 2 vol% sevoflurane. In conclusion, only sevoflurane at 2 vol% attenuated the increased liberation of AA during reperfusion. Decreased eicosanoid formation had no effect on myocardial recovery in our experimental setting while excess AA was deleterious. Because eicosanoids influence intravascular platelet and leukocyte adhesion and activation, sevoflurane may have effects in reperfused tissues beyond those of isoflurane.

IMPLICATIONS

In an isolated guinea pig heart model, myocardial eicosanoid release was not increased by isoflurane or sevoflurane, either before or after ischemia. Sevoflurane (2 vol%) but not isoflurane attenuated the increased release of eicosanoids during reperfusion.

Anesthetic modulation of myocardial ischemia and reperfusion injury in pigs: comparison between halothane and sevoflurane

PURPOSE

Halothane offers protection against the reperfusion injury of the myocardium. This study compared sevoflurane with halothane in its potential to modulate the effects of acute severe ischemia and reperfusion on the myocardium.

METHODS

Experiments were conducted on 25 pigs. Anesthesia consisted of thiopental, vecuronium and fentanyl. The lungs were mechanically ventilated with oxygen and nitrogen. Animals were randomly allocated to receive either I MAC halothane or sevoflurane. A control group received fentanyl and pentobarbital. Regional myocardial function was measured with sonomicrometers. The left anterior descending coronary artery was occluded for 15 min followed by 60 min reperfusion.

RESULTS

Neither halothane nor sevoflurane protected the heart against the effects of acute and severe regional myocardial ischemia. During reperfusion, 89% of the animals receiving sevoflurane suffered from ventricular fibrillation compared with 30% in the halothane group (P < 0.005). Five minutes into the reperfusion period the animals subjected to halothane anesthesia demonstrated an 88% recovery in regional myocardial systolic function while in the sevoflurane group the recovery was 40% of pre-ischemic control (P < 0.05).

CONCLUSION

Halothane is associated with less reperfusion arrhythmias and, in addition, recovery of regional myocardial function during reperfusion was more rapid in the presence of halothane than with sevoflurane.

Thoracic epidural anesthesia does not affect functional recovery from myocardial stunning in sevoflurane-anesthetized dogs

OBJECTIVE

A beneficial effect of thoracic epidural anesthesia (TEA) on recovery from myocardial stunning was previously shown in awake dogs. The aim of this study was to investigate the effects of TEA on recovery from myocardial stunning in sevoflurane-anesthetized dogs.

DESIGN

Randomized animal study.

SETTING

Animal laboratory of a university hospital.

PARTICIPANTS

Chronically instrumented mongrel dogs.

INTERVENTIONS

Six dogs were chronically instrumented for measurement of hemodynamics and myocardial wall thickening fraction (WTF). The following experiments were performed on separate days in a crossover fashion: (1) 10 minutes of ischemia of the left anterior descending (LAD) coronary artery during sevoflurane anesthesia without TEA and (2) 10 minutes of ischemia during sevoflurane anesthesia with TEA.

MEASUREMENTS AND MAIN RESULTS

WTF was measured awake (baseline) and at predetermined time points until complete recovery of myocardial function occurred. Induction of anesthesia led to a decrease of WTF compared with baseline. Induction of ischemia led to a further decrease of WTF to negative values, which returned to positive values within the first minute of reperfusion. There were no differences between the two experimental conditions at any of the time points measured. In awake dogs, TEA improved the recovery from myocardial stunning compared with the control experiment. There was no difference between conscious dogs with TEA or sevoflurane-anesthetized dogs with or without TEA.

CONCLUSION

TEA has no additional protective effect on the recovery of WTF during sevoflurane anesthesia.

Volatile anesthetic effects on ischemic myocardium

Volatile anesthetics, particularly the new generation of agents, have a very rapid onset and offset of action. These properties allow for quick recovery from clinical anesthesia. Because there is additional evidence that these agents have protective effects during myocardial ischemia, there may be advantages for 'fast tracking' patients undergoing coronary revascularization procedures.

Sevoflurane preserves endocardial blood flow during coronary ligation in dogs: comparison with adenosine

BACKGROUND

Sevoflurane has been reported to attenuate ischaemia-induced changes of myocardial metabolism, but the mechanism is still unclear. We examined the effect of sevoflurane on regional myocardial blood flow (RMBF) in the ischaemic area and compared the flow with that in the presence of adenosine.

METHOD

Twenty-seven mongrel dogs were anaesthetized with fentanyl infused at the rate of 1 microgram.kg-1.min-1 throughout the experiment. Then they were divided into 4 groups; 0, 1, 2 MAC sevoflurane groups and adenosine group. Adenosine was infused into the left ventricle at a rate of 14.5 mg.kg-1.h-1. The left anterior descending coronary artery (LAD) was ligated for 3 min. RMBF in the endo- and epicardial layers were measured using coloured microspheres.

RESULTS

Sevoflurane decreased both systolic and diastolic blood pressures and LV dp/dt max. Adenosine increased heart rate and coronary flow. The endocardial blood flow in 2 MAC sevoflurane was almost the same as that in the 0 MAC group. Adenosine significantly increased the myocardial blood flow. During 3-min ischaemia, endocardial blood flow in the ischaemic area under 2 MAC sevoflurane was essentially the same as those in 0 MAC and adenosine groups, though myocardial work in 2 MAC sevoflurane was lower compared with that of the other groups.

CONCLUSION

Preservation of endocardial blood flow related to the myocardial work during ischaemia occurred during 2 MAC sevoflurane. The decrease in LV dp/dt max induced by 2 MAC sevoflurane is one of the factors responsible for the preservation of the endocardial blood flow during ischaemia.

[Sevoflurane]

Sevoflurane, a methylethylether halogenated solely with fluorine, is characterized by a low blood/gas solubility (blood/gas partition coefficient = 0.65). This feature allows in a more rapid uptake and elimination than with more soluble agents. MAC is about 2 vol% in young adults and 2.5 vol% in children of more than 6 months of age. It undergoes degradation by soda lime in various components. Among them, compound A (an olefin) produces renal toxicity in rats. Total sevoflurane metabolism represents about 5% of inhaled dose and produces inorganic fluorides. However no renal toxic effects has been reported up to now in animals and in patients. The effects on central nervous and cardiovascular systems are close to those of isoflurane. It decreases cerebral vascular resistances and cerebral oxygen consumption, but does not cause convulsive activity. It decreases myocardial contractility, systolic arterial pressure and systemic vascular resistances, but heart rate remains basically unchanged up to 1 MAC. It does not sensitize the myocardium to catecholamines. It depresses ventilation in a dose-dependent fashion, this effect being more pronounced than that of halothane but less than that of both isoflurane and enflurane. It is not irritant for the airways and has some bronchodilatory effect. In adults, recovery is more rapid than with isoflurane. In children, sevoflurane seems a promising agent owing to its good acceptance for mask induction, as well as its favourable haemodynamic profile. However due to its rapid elimination, analgesic drugs should be administered early enough to decrease the incidence of postoperative pain.