Effects of halothane, enflurane, isoflurane, sevoflurane and desflurane on myocardial reperfusion injury in the isolated rat heart

Desflurane inhibits platelet function in vitro similar to halothane

BACKGROUND AND OBJECTIVE

The effects of the volatile anaesthetic desflurane on platelet activation in vitro were studied and compared to those of halothane.

METHODS

Platelet-rich plasma was exposed to 2 MAC of desflurane or halothane, or air only and stimulated by platelet agonists ADP (2.5, 5 and 10 micromol L(-10) and collagen (10 microg m(L-1)). Platelet response was measured by Born aggregometry (maximum aggregation response, area under the curve) and flow cytometry (mean channel fluorescence, percentage of CD62P-positive cells, index of platelet activation for positive platelets).

RESULTS

Aggregation response was significantly reduced in platelets exposed to desflurane or halothane; the inhibitory effect was more pronounced when the areas under the curve were analysed: values ranged from 37.5% to 73.3% of control samples for ADP stimulation and 77.1% to 79.8% for collagen stimulation. CD62P expression before and after stimulation with receptor agonists was not statistically different in platelets exposed to desflurane, halothane or air.

CONCLUSIONS

By impairing platelet aggregation while not affecting alpha-degranulation desflurane has a differential effect on various aspects of platelet activation similar to halothane. Our results are compatible with the hypothesis of an impairment of platelet thromboxane receptor signalling by halothane. We suggest a similar mechanism for desflurane.

Cardioprotective effects of desflurane: effect of timing and duration of administration in rat myocardium

BACKGROUND

We compared the cardioprotective effects of 1 minimum alveolar concentration (MAC) desflurane administered before, during or after ischaemia, or throughout the experiment (before, during and after ischaemia) on myocardial infarct size following 30 min occlusion of the left anterior descending coronary artery and 3 h reperfusion in adult rats.

METHODS

Fifty male Sprague-Dawley rats were anaesthetized with pentobarbital, intubated and mechanically ventilated. Blood gases, pH and body temperature (37.5-38 degrees C) were controlled. Heart rate and arterial pressure were measured continuously. Animals were randomly assigned to the following groups (n=10 in each group): pentobarbital only ("Pento"); 15 min desflurane administration followed by 10 min of washout before 30 min ischaemia and 3 h reperfusion ("Precond"); 30 min desflurane administration during ischaemia period ('Isch'); desflurane administration during the 15 first min of reperfusion ("Reperf") and desflurane administration throughout the experiment (before, during and after ischaemia; "Long"). Volumes at risk and infarct sizes were assessed by Indian ink and with 2,3,5-triphenyltetrazolium chloride staining, respectively.

RESULTS

Physiological parameters and volumes at risk were not significantly different between groups. In the Pento group, mean myocardial infarct size was 65 (sd 15)% of the volume at risk; myocardial infarct size was reduced to a significant and comparable extent in the desflurane-treated groups (Precond 42 (14)%; Isch 34 (11)%; Reperf 41 (15)%; Long 33 (10)%; P<0.0002 vs Pento group).

CONCLUSIONS

In rats, desflurane 1 MAC significantly decreased myocardial infarct size whatever the period and duration of administration.

Cardioprotection against reperfusion injury is maximal with only two minutes of sevoflurane administration in rats

PURPOSE

Volatile anesthetics can protect the heart against reperfusion injury. When sevoflurane is given for the first 15 min of reperfusion, a concentration corresponding to one minimum alveolar concentration (MAC) provides a maximum protective effect. The present study addresses the question of how long sevoflurane has to be administered to achieve the best cardioprotection.

METHODS

Chloralose anesthetized rats were subjected to a 25-min occlusion of a major coronary artery, followed by 90 min of reperfusion. During the initial phase of reperfusion, an end-tidal concentration of 2.4 vol.% of sevoflurane (1 MAC) was given for two (n = 8), five (n = 8) or ten minutes (n = 7). Seven rats served as untreated controls. We measured left ventricular (LV) pressure, mean aortic pressure and infarct size (triphenyltetrazolium staining).

RESULTS

Administration of sevoflurane for two minutes resulted in the greatest reduction of infarct size to 15% (8-22 [mean (95% confidence interval)] of the area at risk compared with controls [51 (47-55) %, P < 0.001]. Five or ten minutes of sevoflurane administration reduced infarct size to 26 (18-34) and 26 (18-35) % [P < 0.05], respectively. The cardiodepressant effect of sevoflurane varied with the duration of its administration: LV dP/dt was reduced from 6332 mmHg x sec(-1) (5771-6894) during baseline to 4211 mmHg x sec(-1) (3031-5391), 3811 mmHg x sec(-1) (2081-5540) and 3612 mmHg x sec(-1) (2864-4359) after two, five and ten minutes of reperfusion, respectively.

CONCLUSION

Administration of 1 MAC sevoflurane for the first two minutes of reperfusion effectively protects the heart against reperfusion injury in rats in vivo. A longer administration time had lesser cardioprotective effects in this experimental model.

Protection of the human heart with ischemic preconditioning during cardiac surgery: role of cardiopulmonary bypass

OBJECTIVE

Studies on the effects of ischemic preconditioning in the human heart have yielded conflicting results and therefore remain controversial. This study investigated whether ischemic preconditioning was able to protect against myocardial tissue damage in patients undergoing coronary artery surgery with cardiopulmonary bypass and on the beating heart.

METHODS

A total of 120 patients were studied and divided into 3 groups: group I: cardiopulmonary bypass with intermittent crossclamp fibrillation; group II: cardiopulmonary bypass with cardioplegic arrest using cold blood cardioplegia; group III: surgery on the beating heart. In each group (n = 40), patients were randomly subdivided (n = 20/subgroup) into control and preconditioning groups (1 cycle of 5 minutes of ischemia/5 minutes reperfusion before intervention). Ischemic preconditioning was induced by clamping the ascending aorta in groups I and II or by clamping the coronary artery in group III. Serial venous blood levels of troponin T were analyzed before surgery and at 1, 4, 8, 24, and 48 hours after termination of ischemia. In addition, in vitro studies using right atrial specimens obtained before the institution of cardiopulmonary bypass, and then again 10 minutes after initiation of bypass, were performed. The specimens were equilibrated for 30 minutes before being allocated to 1 of the following 2 groups (n = 6 per group): (1) ischemia alone (90 minutes of ischemia followed by 120 minutes of reoxygenation) or (2) preconditioning with 5 minutes of ischemia and 5 minutes of reoxygenation before the long ischemic insult. Creatine kinase leakage (U/g wet weight) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction (mmol/l per gram wet weight), an index of cell viability, were assessed at the end of the experiment.

RESULTS

There were no perioperative myocardial infarctions or deaths in any of the groups studied. The total release of troponin T was similar in groups I and II (patients undergoing surgery with cardiopulmonary bypass) and in the release profile; they were unaffected by ischemic preconditioning. In contrast, the total troponin T release for the first 48 hours was significantly reduced by ischemic preconditioning in group III (patients undergoing surgery without cardiopulmonary bypass) from 3.1 +/- 0.1 to 2.1 +/- 0.2 ng. h. mL. Furthermore, the release profile that peaked at 8 hours in the control group shifted to the left at 1 hour. In the in vitro studies, the atrial muscles obtained before cardiopulmonary bypass were protected by ischemic preconditioning (creatine kinase = 2.6 +/- 0.2 and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide reduction = 152 +/- 24 vs creatine kinase = 5.4 +/- 0.6 and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide reduction = 87 +/- 16 in controls; P <.05); however, the muscles obtained 10 minutes after initiation of cardiopulmonary bypass were already protected (creatine kinase = 0.8 +/- 0.1 and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide reduction = 316 +/- 38), and ischemic preconditioning did not result in further improvements.

CONCLUSIONS

Ischemic preconditioning is protective in patients undergoing coronary artery surgery on the beating heart without the use of cardiopulmonary bypass, but it offers no additional benefit when associated with bypass regardless of the mode of cardioprotection used, because cardiopulmonary bypass per se induces preconditioning.

Myocardial protection by anesthetic agents against ischemia-reperfusion injury: an update for anesthesiologists

PURPOSE

The aim of this review of the literature was to evaluate the effectiveness of anesthetics in protecting the heart against myocardial ischemia-reperfusion injury.

SOURCE

Articles were obtained from the Medline database (1980-, search terms included heart, myocardium, coronary, ischemia, reperfusion injury, infarction, stunning, halothane, enflurane, desflurane, isoflurane, sevoflurane, opioid, morphine, fentanyl, alfentanil sufentanil, pentazocine, buprenorphine, barbiturate, thiopental, ketamine, propofol, preconditioning, neutrophil adhesion, free radical, antioxidant and calcium).

PRINCIPAL FINDINGS

Protection by volatile anesthetics, morphine and propofol is relatively well investigated. It is generally agreed that these agents reduce the myocardial damage caused by ischemia and reperfusion. Other anesthetics which are often used in clinical practice, such as fentanyl, ketamine, barbiturates and benzodiazepines have been much less studied, and their potential as cardioprotectors is currently unknown. There are some proposed mechanisms for protection by anesthetic agents: ischemic preconditioning-like effect, interference in the neutrophil/platelet-endothelium interaction, blockade of Ca2+ overload to the cytosolic space and antioxidant-like effect. Different anesthetics appear to have different mechanisms by which protection is exerted. Clinical applicability of anesthetic agent-induced protection has yet to be explored.

CONCLUSION

There is increasing evidence of anesthetic agent-induced protection. At present, isoflurane, sevoflurane and morphine appear to be most promising as preconditioning-inducing agents. After the onset of ischemia, propofol could be selected to reduce ischemia-reperfusion injury. Future clinical application depends on the full elucidation of the underlying mechanisms and on clinical outcome trials.

Sevoflurane suppresses noxious stimulus-evoked expression of Fos-like immunoreactivity in the rat spinal cord via activation of endogenous opioid systems

We investigated the antagonism of sevoflurane antinociception by opioid antagonists in the rat formalin test. Formalin injection into the hindpaw of the rat induces the nocifensive flinching behavior and the expression of Fos-like immunoreactivity (Fos-LI) in the spinal cord. Sevoflurane significantly suppressed the flinching behavior and decreased the number of Fos-LI neurons in the dorsal horn of spinal cord compared with the control group. Moreover, pretreatment with intraperitoneal naloxone plus naltrexone antagonized the suppression of flinching behavior and the decrease of the number of Fos-LI neurons produced by 3% sevoflurane. Intraperitoneal opioid antagonists themselves had no effects on both the behavior response and the expression of Fos-LI induced by formalin injection. This study supports the hypothesis that sevoflurane suppresses the nociceptive response, at least in part, by activating endogenous opioid systems.

Cardioprotection by sevoflurane against reperfusion injury after cardioplegic arrest in the rat is independent of three types of cardioplegia

BACKGROUND

Sevoflurane protects the heart against reperfusion injury even after cardioplegic arrest. This protection may depend on the cardioplegic solution. Therefore, we investigated the effect of sevoflurane on myocardial reperfusion injury after cardioplegic arrest with University of Wisconsin solution (UW), Bretschneider's cardioplegia (HTK), and St Thomas' Hospital solution (STH).

METHODS

We used an isolated rat heart model where heart rate, ventricular volume, and perfusion pressure were constant. The hearts underwent 30 min of normothermic ischaemia followed by 60 min of reperfusion. Seven groups were studied (n = 9 each). Three groups received 7 degrees C cold cardioplegic solutions (UW, HTK, STH) during the first 2 min of ischaemia at a flow of 2 ml min-1. In three groups (UW + Sevo, HTK + Sevo, STH + Sevo), sevoflurane was additionally added to the perfusion medium (membrane oxygenator) at 3.8% (1.5 MAC) during the first 15 min of reperfusion after cardioplegic arrest. Nine hearts served as untreated control group (control). We measured left ventricular developed pressure (LVDP) and infarct size.

RESULTS

LVDP was similar in all groups during baseline (130 (SEM 2) mm Hg). HTK and STH improved recovery of LVDP during reperfusion from 5 (1) (control) to 67 (7) (HTK) and 52 (8) mm Hg (STH, both P < 0.05), while UW had no effect on myocardial function (7 (2) mm Hg). In the sevoflurane-treated groups, LVDP at the end of the experiments was not significantly different from the respective group without anaesthetic treatment (UW + Sevo 11 (2); HTK + Sevo 83 (8); STH + Sevo 64 (8) mm Hg; P = ns). Infarct size was reduced in the HTK and STH groups (HTK 20 (4); STH 17 (3)%; P < 0.05) compared with controls (39 (5)%; P < 0.05), but not in the UW group (52 (4)%). Compared with cardioplegia alone, sevoflurane treatment during reperfusion reduced infarct size (UW + Sevo 31 (4); HTK + Sevo 8 (1); STH + Sevo 4 (1)%; P < 0.05).

CONCLUSION

We conclude, that the protection against reperfusion injury offered by sevoflurane is independent of the three cardioplegic solutions used.

Isoflurane and coronary heart disease

Early studies indicated that isoflurane caused coronary steal and should therefore be avoided in patients with coronary heart disease. Subsequently, more detailed trials have disputed this and have shown that as long as coronary perfusion pressure is maintained, isoflurane does not cause coronary steal or myocardial ischaemia. There is now growing evidence, initially in animal work but more recently in human studies, that isoflurane has myocardial protective properties, limiting infarct size and improving functional recovery from myocardial ischaemia. The mechanism for this protection mimics ischaemic preconditioning and involves the opening of adenosine triphosphate-dependent potassium channels. The few studies comparing the myocardial protection offered by individual anaesthetic agents indicate that isoflurane represents the anaesthetic agent of choice for patients with coronary heart disease.

Is there a place for preconditioning during cardiac operations in humans?

BACKGROUND

Activation of the kinase cascade (protein kinase C (PKC), tyrosine kinase (TK), and mitogen-activated protein kinase (MAPK) is a key feature of the transduction pathway, elicited by preconditioning signals and mediating their cardioprotective effects. We assessed whether such an activation occurred during cardiac operations and could thus represent a target for cardioprotective strategies.

METHODS

A total of 20 patients undergoing coronary artery bypass grafting surgery were studied. During the first 10 minutes of cardiopulmonary bypass (CPB), 10 were treated with sevoflurane (2.5 minimum alveolar concentration), an inhalational anesthetic that mimics preconditioning through a similar activation of the kinase cascade. Ten case-matched patients undergoing 10 minutes of sevoflurane-free CPB served as controls. Right atrial biopsies were taken before and 10 minutes after CPB and were then processed for the measurement of PKC, TK, and p38 MAPK activities by enzyme assay techniques. Troponin I was also monitored over the first 2 postoperative days.

RESULTS

Compared with pre-CPB values, PKC and p38 MAPK activities (in nanomoles per milligram of protein per minute and arbitrary units, respectively) increased significantly and to the same extent in both groups: PKC, from 20.7+/-0.7 to 29.9+/-3.9 in controls (p = 0.037) and from 18.4+/-1.1 to 23.9+/-1.8 in sevoflurane (p = 0.016); p38 MAPK, from 88.6+/-8.5 to 312.9+/-66.2 in controls (p = 0.005) and from 114.6+/-14.7 to 213.4+/-51.8 in sevoflurane (p = 0.045). Conversely, sevoflurane triggered a significant increase in TK activity (from 68.5+/-1.4 to 83.7+/-2.9 picomoles per milligram of protein per minute p = 0.0015) which did not occur in controls (from 67.5+/-1.9 to 76.8+/-4.2 picomoles per milligram of protein per minute, p = 0.09). Likewise, the peak postoperative value of troponin I was not different between controls and sevoflurane-treated patients (3.4+/-0.6 vs 2.4+/-0.4, p = 0.21).

CONCLUSIONS

Cardiopulmonary bypass triggers an activation of the kinase cascade that is mechanistically linked to opening of potassium channels. The direct opening of these channels by the anesthetic sevoflurane does not increase kinase activation further, nor does it improve markers of cell necrosis, thus suggesting that pharmacologically targeting potassium channels may overlap the preconditioning-like effects of CPB alone.

One MAC of sevoflurane provides protection against reperfusion injury in the rat heart in vivo

Volatile anaesthetics protect the heart against reperfusion injury. We investigated whether the cardioprotection induced by sevoflurane against myocardial reperfusion injury was concentration-dependent. Fifty-eight alpha-chloralose anaesthetized rats were subjected to 25 min of coronary artery occlusion followed by 90 min of reperfusion. Sevoflurane was administered for the first 15 min of reperfusion at concentrations corresponding to 0.75 (n=11), 1.0 (n=11), 1.5 (n=13), or 2.0 MAC (n=12). Eleven rats served as untreated controls. Left ventricular peak systolic pressure (LVPSP, tipmanometer) and cardiac output (CO, flowprobe) was measured. Infarct size (IS, triphenyltetrazolium staining) was determined as percentage of the area at risk. Baseline LVPSP was 131 (126-135) mm Hg (mean (95% confidence interval)) and CO 33 (31-36) ml min(-1), similar in all groups. During early reperfusion, sevoflurane reduced LVPSP in a concentration-dependent manner to 78 (67-89)% of baseline at 0.75 MAC (not significant vs controls 99 (86-112)%), 71 (62-80)% at 1 MAC (P<0.05), 66 (49-83)% at 1.5 MAC (P<0.05) and 56 (47-65)% at 2 MAC (P<0.05). CO remained constant. While 0.75 MAC of sevoflurane had no effect on IS (34 (27-41)% of the area at risk) compared with controls (38 (31-45)%, P=0.83), 1.0 MAC reduced IS markedly to 23 (17-30)% (P<0.05). Increasing the concentration to 1.5 MAC (23 (17-30)%) and 2 MAC (23 (13-32)%, both P<0.05 vs controls) had no additional protective effect. One MAC sevoflurane protected against myocardial reperfusion injury. Increasing the sevoflurane concentration above 1 MAC resulted in no further protection.

The effects of propofol or halothane on free radical production after tourniquet induced ischaemia-reperfusion injury during knee arthroplasty

BACKGROUND

Ischaemia-reperfusion injury following tourniquet release is a good in vivo model for evaluating acute conditions. The aim of the study was to investigate the effects of propofol or halothane anaesthesia on oxidative stress by determining malondialdehyde (MDA) levels during knee arthroplasty.

METHODS

Thirty patients undergoing orthopaedic surgery were divided into two groups. Anaesthesia was induced with either fentanyl 100 microg and propofol 2 mg kg(-1) (Group 1) or fentanyl 100 microg and thiopentone 5 mg kg(-1) (Group 2) and maintained with infusion of propofol in Group 1 or inhalation of halothane in Group 2. ECG, SpO2, EtCO2, and mean arterial pressure (MAP) were monitored. Venous and arterial blood samples were obtained at different measurement times for MDA and blood gas analyses.

RESULTS

There was a significant decrease in MAP in the 1st and 5th minutes after tourniquet release (ATR) when compared with the 5th minute before tourniquet release (BTR) in both groups. Heart rate (HR) increased significantly in the 1st minute ATR in Group 1 only. EtCO2 increased significantly in the 1st and 5th minutes ATR, SpO2 decreased in the 1st minute ATR in both groups. There was a significant decrease in pH and increase in pCO2 at 1, 5 and 30 min ATR in both groups. pO2 values decreased in the 1st minute ATR in Group 1 only and returned to control values at 5 min ATR and decreased at 30 min ATR in the recovery room in both groups. The differences in SaO2 were similar to SpO2. MDA levels decreased before and after release of tourniquet when compared to baseline in both groups. However, there was a statistically significant decrease only in Group 1.

CONCLUSION

Propofol may be a good choice of anaesthetic when an ischaemia-reperfusion injury is anticipated as in orthopaedic surgery requiring a tourniquet, due to its antioxidant properties, but halothane needs further study.

Activation of the adenosine triphosphate sensitive mitochondrial potassium channel is involved in the cardioprotective effect of isoflurane

The adenosine triphosphate-dependent potassium (K(ATP)) channel has been proposed to play an important role in the cardioprotective effect of isoflurane (ISO). However, the question of whether the K(ATP) channel, sarcolemmal or mitochondrial is the main contributor to the effect has not been clarified. The major aim of the present study was to determine whether or not the mitochondrial potassium channel was a site of action for ISO. Whether there was an acute "memory phase", in which drugs were not detected in the tissues, but the protective effect still remained in the ischemic preconditioning (IP) -like effect of ISO was also investigated. Dangling participle isolated rat hearts, a 20-min normothermic nonperfused phase was maintained to produce a global ischemia. Under these ischemic conditions, the effects of ISO, sodium 5-hydroxydecanoate (5HD: a selective mitochondrial K(ATP) channel antagonist), and ISO combined with 5HD on cardiac performance were examined. To all these four groups, (non-treated group, ISO group, 5HD group and ISO plus 5HD group, n=6 each) drugs were given for 30 min. After 10 min of drug-free perfusion (pre-ischemia restabilization period), 20 min of ischemia followed. Then the cardiac performance and the creatine kinase (CK) release during the reperfusion period were tested. In the non treated group and 5HD group, cardiac performance was stable during the treated period and pre-ischemia the restabilization period. In the ISO group and ISO plus 5HD group, heart rate (HR), left ventricular (LV) systolic pressure, and LV maximum rate of development of tension (dP/dtMax) during the drug-treated period became gradually and linearly worse. However, these values were the same as in the non-treated group and 5HD group at the end of the pre-ischemia restabilization period. So 5HD itself had no hemodynamic effect; nor did it have any influence on the actions of ISO. At the end of the pre-ischemia restabilization period, the significant hemodynamic differences among the groups diminished and ISO was not detected in the solution. In the post-reperfusion period, except for the ISO group, (non treated group, 5HD group and ISO plus 5HD group) cardiac performances were drastically decreased. ISO significantly ameliorated the dysfunction of cardiac output, LV systolic pressure and LV+dP/dtMax. The CK level in the coronary effluent during reperfusion was also significantly reduced by ISO. 5HD completely inhibited these cardiac effects of ISO. Activation of the adenosine triphosphate sensitive mitochondrial potassium channel is involved in the cardioprotective effect of ISO, and the action of this agent has an acute"memory phase" like ischemic preconditioning.

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.

Desflurane pharmacokinetics during cardiopulmonary bypass

OBJECTIVE

To describe the washin and washout of desflurane when first administered during cardiopulmonary bypass (CPB) for cardiac surgery.

DESIGN

A single-arm prospective study.

SETTING

University-affiliated hospital operating room.

PARTICIPANTS

Ten adult patients presenting for cardiac surgery.

INTERVENTIONS

Consenting patients presenting for cardiac surgery received anesthesia with midazolam and fentanyl. Patients were cooled to 32 degrees C on CPB, then desflurane 6% was administered and blood samples drawn repeatedly from the arterial and venous bypass cannulae as well as from the membrane oxygenator inlet and exhaust from 2 to 32 minutes of desflurane administration. Just before rewarming, final (maximum) washin samples were taken. On rewarming, desflurane was discontinued, and blood and gas samples were taken 2 to 24 minutes thereafter.

MEASUREMENTS AND MAIN RESULTS

CPB time was 116 +/- 10 minutes, and ischemic time was 81 +/- 6 minutes. Mean pump flow was 4.49 +/- 0.03 L/min, and mean arterial pressure was 70.1 +/- 1 mmHg during the study period. Arterial washin of desflurane was initially rapid; arterial concentrations reached 50% of administered concentrations within 4 minutes, but then slowed, reaching 68% of inspired concentrations at 32 minutes (desflurane concentration 4.0% +/- 0.3%). Arterial washout of desflurane was more rapid; arterial concentrations fell to 18% of the maximum concentration reached within 4 minutes, and only 8% of the maximum arterial concentration was present in blood 20 minutes later.

CONCLUSION

Desflurane showed rapid initial washin and washout on CPB when administration was started at 32 degrees C and stopped at time of rewarming.

Can isoflurane mimic ischaemic preconditioning in isolated rat heart?

Ischaemic preconditioning can protect the myocardium against ischaemic injury by opening of the adenosine triphosphate (ATP)-sensitive potassium (K(ATP)) channel. Isoflurane is also thought to open this channel. The present investigation tested the hypothesis that pre-ischaemic treatment with isoflurane mimics ischaemic preconditioning (producing chemical preconditioning) and thereby protects the myocardium against ischaemic injury in an isolated rat heart model. Control hearts underwent 30 min of global no-flow ischaemia followed by 60 min of reperfusion. The hearts of the preconditioning group underwent two 5 min periods of no-flow ischaemia interspersed with 5 min of reperfusion before the sustained ischaemia. In three additional groups, hearts were subjected to 15 min of 1.5 minimal alveolar concentration (MAC) of isoflurane (ISO-1), 15 min 3 MAC (ISO-2) or 25 min 1.5 MAC (ISO-3) of isoflurane followed by 5 min washout before the global ischaemia. Left ventricular (LV) developed pressure and creatine kinase release were measured as variables of myocardial performance and cellular injury, respectively. Recovery of LV developed pressure was improved after ischaemic preconditioning [after 60 min reperfusion, mean 63 (SEM 6)% of baseline] compared with the control group [18 (4)% P<0.01] but not by isoflurane, independently of concentration or duration of administration [ISO-1, 17 (2)%, P=0.99 vs control; ISO-2, 12 (3)%, P=0.64; ISO-3, 4 (1)%, P=0.06]. Total creatine kinase release over 1 h of reperfusion was not significantly different between control [251 (36) U g(-1) dry weight] and all isoflurane groups [ISO-1, 346 (24) U g(-1), P=0.30; ISO-2, 313 (33) U g(-1), P=0.73; ISO-3, 407 (40) U g(-1), P=0.03]. These results indicate that pre-ischaemic administration of isoflurane does not cause anaesthetic-induced preconditioning in the isolated rat heart.

Xenon administration during early reperfusion reduces infarct size after regional ischemia in the rabbit heart in vivo

The noble gas xenon can be used as an anesthetic gas with many of the properties of the ideal anesthetic. Other volatile anesthetics protect myocardial tissue against reperfusion injury. We investigated the effects of xenon on reperfusion injury after regional myocardial ischemia in the rabbit. Chloralose-anesthetized rabbits were instrumented for measurement of aortic pressure, left ventricular pressure, and cardiac output. Twenty-eight rabbits were subjected to 30 min of occlusion of a major coronary artery followed by 120 min of reperfusion. During the first 15 min of reperfusion, 14 rabbits inhaled 70% xenon/30% oxygen (Xenon), and 14 rabbits inhaled air containing 30% oxygen (Control). Infarct size was determined at the end of the reperfusion period by using triphenyltetrazolium chloride staining. Xenon reduced infarct size from 51%+/-3% of the area at risk in controls to 39%+/-5% (P<0.05). Infarct size in relation to the area at risk size was smaller in the xenon-treated animals, indicated by a reduced slope of the regression line relating infarct size to the area at risk size (Control: 0.70+/-0.08, r = 0.93; Xenon: 0.19+/-0.09, r = 0.49, P<0.001). In conclusion, inhaled xenon during early reperfusion reduced infarct size after regional ischemia in the rabbit heart in vivo.

Reduction of postischemic contractile dysfunction of the isolated rat heart by sevoflurane: comparison with halothane

Our aims were to evaluate the effect of sevoflurane on postcardioplegic functional recovery of the isolated rat heart including the role of the adenosine triphosphate regulated potassium (K(ATP)) channels and to compare the cardioprotective effects of equipotent concentrations of halothane and sevoflurane. Isolated perfused rat hearts were subjected to 45 or 60 min normothermic cardioplegic arrest and 30 min reperfusion. Sevoflurane (0.9% and 1. 7%), halothane (0.4% and 0.8%), or sevoflurane (0.9%) plus glibenclamide (10 microM) (a K(ATP) channel blocker) were administered at different time intervals. Measurements of mechanical activity were made before and after arrest. Function during reperfusion after cardioplegic arrest was significantly depressed in both untreated and treated hearts. However, sevoflurane administered both before and after arrest, or before only, significantly improved functional recovery after 45 min of cardioplegia. This protective effect was abolished by simultaneous administration of glibenclamide, suggesting a role of the K(ATP) channel. Sevoflurane was as effective as halothane in improving postcardioplegic functional performance. After 45 min of arrest, hearts exposed to either anesthetic at both concentrations had a significantly higher work performance on discontinuation of their administration than untreated controls. After 60 min of arrest, neither anesthetic elicited protection.

Effect of dantrolene in an in vivo and in vitro model of myocardial reperfusion injury

BACKGROUND

In skeletal muscle, dantrolene reduces free cytosolic calcium by inhibiting calcium release from the sarcoplasmic reticulum. A similar effect in ischemic-reperfused heart cells would protect myocardial tissue against reperfusion injury. We tested the hypothesis that dantrolene infusion during reperfusion protects the heart against reperfusion injury.

METHODS

Isovolumetric beating rat hearts were subjected to 30 min of ischemia followed by 60 min of reperfusion. Left ventricular (LV) developed pressure (LVDP) and creatine kinase release (CKR) were determined as indices of myocardial performance and cellular injury, respectively. In the treatment groups, dantrolene (25 (DAN25) or 100 (DAN100) micromol l(-1)) was infused during the first 15 min of reperfusion; control hearts received the respective concentration of the vehicle (mannitol (CON25, CON100), each group n=7). To investigate the effects of dantrolene on reperfusion injury in vivo, 18 chloralose-anesthetized rabbits were subjected to 30 min occlusion and 180 min reperfusion of a major coronary artery. LV pressure (LVP), cardiac output (CO), and infarct size were determined. During the last 5 min of ischemia, nine rabbits received 10 mg kg(-1) dantrolene intravenously (DAN). Another nine rabbits received the vehicle (dimethylsulfoxide) and served as controls (CON).

RESULTS

In isolated rat hearts, there was no recovery of LVDP in any group. Total CKR during 1 h of reperfusion was 845+/-76 (CON100) and 550+/-81 U g(-1) dry mass (DAN100, P<0.05). In rabbits in vivo, hemodynamic baseline values were similar between groups (CON vs. DAN: LVP, 99+/-6 (mean+/-SEM) vs. 91+/-6mm Hg, P=0.29; CO, 252+/-26 vs. 275+/-23 ml min(-1), P= 0.53). During coronary artery occlusion, LVP and CO were reduced in both groups (CON: LVP, 89+/-3%; CO, 90+/-5% of baseline values) and LVP did not recover to baseline values during reperfusion (51+/-5% (CON) vs. 67+/-7% (DAN) of baseline, P=0.10). Infarct size was 41+/-4% of the area at risk in controls and 37+/-6% in dantrolene treated hearts (P=0.59).

CONCLUSIONS

Dantrolene reduced CKR, indicating an attenuation of lethal cellular reperfusion injury in isolated rat hearts. However, in the rabbit in vivo, there was no effect on the extent of reperfusion injury after regional myocardial ischemia.

Beneficial effects of sevoflurane and desflurane against myocardial reperfusion injury after cardioplegic arrest

PURPOSE

To determine whether sevoflurane or desflurane offer additional protective effects against myocardial reperfusion injury after protecting the heart against the ischemic injury by cardioplegic arrest.

METHODS

Isolated rat hearts in a Langendorff-preparation (n = 9) were arrested by infusion of HTK cardioplegic solution and subjected to 30 min global ischemia followed by 60 min reperfusion (controls). An additional 18 hearts were subjected to the same protocol, and sevoflurane (n = 9) or desflurane (n = 9) was added to the perfusion medium during the first 30 min of reperfusion in a concentration corresponding to 1.5 MAC in rats. Left ventricular (LV) developed pressure and creatine kinase (CK) release were determined as indices of myocardial performance and cellular injury, respectively.

RESULTS

The LV developed pressure recovered to 46+/-7% of baseline in controls. Functional recovery during reperfusion was improved by inhalational anesthetics to 67+/-3% (sevoflurane, P<0.05) and 61+/-5% of baseline (desflurane, P<0.05), respectively. Peak CK release during early reperfusion was reduced from 52+/-11 U x min(-1) x g(-1) in controls to 34+/-7 and 26+/-7 U x min(-1) x g(-1) in sevoflurane and desflurane treated hearts, respectively. The CK release during the first 30 min of reperfusion was reduced from 312+/-41 U x g(-1) in control hearts to 195+/-40 and 206+/-37 U x g(-1) in sevoflurane and desflurane treated hearts.

CONCLUSION

After ischemic protection by cardioplegia, sevoflurane and desflurane given during the early reperfusion period offer additional protection against myocardial reperfusion injury.

Enflurane and isoflurane, but not halothane, protect against myocardial reperfusion injury after cardioplegic arrest with HTK solution in the isolated rat heart

To investigate the effects of halothane, enflurane, and isoflurane on myocardial reperfusion injury after ischemic protection by cardioplegic arrest, isolated perfused rat hearts were arrested by infusion of cold HTK cardioplegic solution containing 0.015 mmol/L Ca2+ and underwent 30 min of ischemia and a subsequent 60 min of reperfusion. Left ventricular (LV) developed pressure and creatine kinase (CK) release were measured as variables of myocardial function and cellular injury, respectively. In the treatment groups (each n = 9), anesthetics were given during the first 30 min of reperfusion in a concentration equivalent to 1.5 minimum alveolar anesthetic concentration of the rat. Nine hearts underwent the protocol without anesthetics (controls). Seven hearts underwent ischemia and reperfusion without cardioplegia and anesthetics. In a second series of experiments, halothane was tested after cardioplegic arrest with a modified HTK solution containing 0.15 mmol/L Ca2+ to investigate the influence of calcium content on protective actions against reperfusion injury by halothane. LV developed pressure recovered to 59%+/-5% of baseline in controls. In the experiments with HTK solution, isoflurane and enflurane further improved functional recovery to 84% of baseline (P < 0.05), whereas halothane-treated hearts showed a functional recovery similar to that of controls. CK release was significantly reduced during early reperfusion by isoflurane and enflurane, but not by halothane. After cardioplegic arrest with the Ca2+-adjusted HTK solution, halothane significantly reduced CK release but did not further improve myocardial function. Isoflurane and enflurane given during the early reperfusion period after ischemic protection by cardioplegia offer additional protection against myocardial reperfusion injury. The protective actions of halothane depended on the calcium content of the cardioplegic solution.

IMPLICATIONS

Enflurane and isoflurane administered in concentrations equivalent to 1.5 minimum alveolar anesthetic concentration in rats during early reperfusion offer additional protection against myocardial reperfusion injury even after prior cardioplegic protection. Protective effects of halothane solely against cellular injury were observed only when cardioplegia contained a higher calcium concentration.