Effects of desflurane and isoflurane on systemic vascular resistance during hypothermic cardiopulmonary bypass

Effect on thermoregulatory responses in patients undergoing a tympanoplasty in accordance to the anesthetic techniques during PEEP: a comparison between inhalation anesthesia with desflurane and TIVA

BACKGROUND

It has been known that positive end-expiratory pressure (PEEP) increases the vasoconstriction threshold by baroreceptor unloading. We compared the effect on the thermoregulatory responses according to anesthetic techniques between an inhalation anesthesia with desflurane and a total intravenous anesthesia (TIVA) with propofol and reminfentanil when PEEP was applied in patients undergoing tympanoplasty.

METHODS

Forty-six patients with a scheduled tympanoplasty were enrolled and the patients were divided in two study groups. Desflurane was used as an inhalation anesthetic in group 1 (n = 22), while TIVA with propofol and remifentanil was used in group 2 (n = 24). PEEP was applied by 5 cmH2O in both groups and an ambient temperature was maintained at 22-24℃ during surgery. The core temperature and the difference of skin temperature between forearm and fingertip were monitored for about 180 minutes before and after the induction of general anesthesia.

RESULTS

The final core temperature was significantly higher in group 2 (35.4 ± 0.7℃) than in group 1 (34.9 ± 0.5℃). Peripheral thermoregulatory vasoconstriction was found in 5 subjects (23%) in group 1 and in 21 subjects (88%) in group 2. The time taken for reaching the thermoregulatory vasoconstriction threshold was 151.4 ± 19.7 minutes in group 1 and 88.9 ± 14.4 minutes in group 2.

CONCLUSIONS

When PEEP will be applied, anesthesia with TIVA may have more advantages in core temperature preservation than an inhalation anesthesia with desflurane.

[Vasoreactivity changes during extracorporeal circulation: effects of halogenated agents]

During cardiopulmonary bypass (CPB), endothelium is exposed to multiple disturbances leading to significant vasomotor tone and vascular systemic resistances (VSR) level modifications. Properties of endothelial function on vascular tone were summarized herein. According bibliographic findings, physiological and clinical impacts of respectively halogenated agents and CPB concerning vasomotor tone were reported. Main effects of halogenated agents administered through oxygenator during CPB were also identified. Usually when administered above one MAC, halogenated agents decreased VSR during hypothermic bypass. Once those mechanisms summarized, increase of halogenated agent's effects on VSR during normothermic CPB was postulated. Assuming that decrease of VSR could be deleterious favoring severe vasoplegia event, clinical experience of administration of isoflurane during CPB among more 4000 patients was retrospectively reported. Incidence of severe vasoplegia was established to 9.5 % in the studied population and this result was similar as others. More over predicting factors of severe vasoplegia were the same as previously reported : severity of preoperative clinical status according Euroscore, hemodynamical instability before induction of anesthesia, surgical procedure complexity and CPB duration. Absence of deleterious effects in SVR decrease when administering isoflurane during normothermic CPB was assumed but prospective comparative studies comparing effects of halogenated agents and other anesthetic agents are needed in order to confirm these findings.

Isoflurane, 0.5 Minimum Alveolar Concentration Administered Through the Precardiopulmonary Bypass Period, Reduces Postoperative Dobutamine Requirements of Cardiac Surgery Patients: A Randomized Study

OBJECTIVE

Cardioprotective properties have been shown with halogenated volatile agents. It was hypothesized that low-dose isoflurane administered before aortic cross-clamping may reduce the amount of dobutamine required to improve impaired postoperative cardiac function after various types of cardiac surgery.

DESIGN

A prospective, randomized trial.

SETTING

An anesthesia and intensive care unit, university hospital.

PARTICIPANTS

Two hundred eighty cardiac surgery patients.

INTERVENTIONS

All patients allocated to either isoflurane treatment (T) or no treatment (control group [C]) received total intravenous anesthesia. In the treatment group, isoflurane was administered at a 0.5 minimum alveolar concentration (MAC) from tracheal intubation to initiation of cardiopulmonary bypass (CPB). During weaning from CPB, dobutamine was introduced by using a hemodynamically driven decision tree.

MEASUREMENTS AND MAIN RESULTS

The number of patients receiving dobutamine was comparable (66 v 78, p = 0.07, in T and C groups, respectively). The total amount of postoperative dobutamine indexed to patient weight, considered as the primary endpoint, was reduced in the isoflurane-treated group (4.2 +/- 8 v 7.2 +/- 15, p < 0.02, in T and C, respectively). Isoflurane was identified as an independent variable significantly (odds ratio [confidence interval]) influencing the total amount of postoperative dobutamine (0.53 [0.31-0.92], p < 0.02). Postoperative troponin I release at 20 hours was not affected by isoflurane treatment.

CONCLUSIONS

This study revealed that exposure to 0.5 MAC isoflurane before CPB reduced the total amount of dobutamine required to normalize postoperative cardiac dysfunction in various types of cardiac surgical patients.

Desflurane and Sevoflurane in Cardiac Surgery: A Meta-Analysis of Randomized Clinical Trials

OBJECTIVES

The authors performed a meta-analysis to investigate whether the cardioprotective effects of volatile anesthetics translate into decreased morbidity and mortality in patients undergoing cardiac surgery.

BACKGROUND

It is commonly believed that the choice of the primary anesthetic agent does not result in different outcomes after cardiac surgery. Recent evidence, however, has indicated that volatile anesthetics improve postischemic recovery at a cellular level, in isolated hearts, in animals, and in humans.

METHODS

Four investigators independently searched BioMedCentral and PubMed. Inclusion criteria were random allocation to treatment and comparison of a total intravenous anesthesia regimen versus an anesthesia plan including desflurane or sevoflurane performed on cardiosurgical patients. Exclusion criteria were duplicate publications, nonhuman experimental studies, and no outcome data. The endpoints were the rate of perioperative myocardial infarction and hospital mortality.

RESULTS

The search yielded 22 studies, involving 1,922 patients. Volatile anesthetics were associated with significant reductions of myocardial infarctions (24/979 [2.4%] in the volatile anesthetics group v 45/874 [5.1%] in the control arm, odds ratio [OR] = 0.51 [0.32-0.84], p for effect = 0.008, and p for heterogeneity = 0.77) and mortality (4/977 [0.4%] v 14/872 [1.6%], OR = 0.31 [0.12-0.80], p for effect = 0.02, and p for heterogeneity = 0.88).

CONCLUSIONS

Desflurane and sevoflurane have cardioprotective effects that result in decreased morbidity and mortality. The present data show for the first time that the choice of an anesthetic regimen based on administration of halogenated anesthetics is associated with a better outcome after cardiac surgery.

Blood Concentrations of Enflurane Before, During, and After Hypothermic Cardiopulmonary Bypass

OBJECTIVE

The purpose of this study was to determine blood concentrations of enflurane delivered via a membrane oxygenator during hypothermic cardiopulmonary bypass (CPB) with changes in the input enflurane concentration and temperature and to characterize the pharmacokinetics of enflurane washout during and after CPB.

DESIGN

Blood enflurane concentrations were measured by gas chromatography before, during, and after CPB by using mean delivered enflurane concentrations of 0.5% v/v (group 1, n = 5), 0.8% (group 2, n = 7), and 1% (group 3, n = 14).

SETTING

The investigation was performed in a teaching hospital setting.

PARTICIPANTS

Twenty-six patients undergoing cardiac surgery requiring hypothermic CPB.

INTERVENTIONS

Variations in input enflurane concentration in different patients plus blood sampling from the arterial side of the circuit for enflurane assay.

MEASUREMENTS AND MAIN RESULTS

Median (25th and 75th percentiles) pre-CPB blood enflurane concentrations were 48 (25-50) mg/L, 52 (47-56) mg/L, and 115 (90-143) mg/L in groups 1 (0.5% v/v), 2 (0.8% v/v), and 3 (1% v/v), respectively. During hypothermia (28 degrees C) corresponding enflurane concentrations were 44 (31-53) mg/L, 56 (45-62) mg/L, and 145 (109-203) mg/L, respectively. For groups 1 and 2, there were no significant changes in blood enflurane compared with the corresponding pre-CPB value. However, for group 3, cooling resulted in a significant increase (p = 0.006) in blood enflurane. In all groups, enflurane concentrations after rewarming were similar to those in the pre-CPB period.

CONCLUSIONS

It is concluded that exposure to enflurane concentrations greater than 0.8% during CPB can result in high blood concentrations.

Cardiac and thoracic vascular surgery

The number of aged individuals is growing, and consequently the demands on resources for cardiac surgery will increase in the elderly. Even in the absence of obvious coexisting diseases, advanced age is always accompanied by a general decline in organ functions, and specifically by changes in structure and function of the heart and vasculature that will ultimately affect cardiovascular performance (e.g. hypertension, ischaemic heart disease, etc.). These alterations have to be taken into account when older patients require anaesthesia for cardiac surgery. Pre-operative examination must be performed carefully to estimate cardiac function as well as dysfunction of other organ systems. Benzodiazepines as well as alpha2-adrenoceptor agonists can be used for pre-medication; induction and maintenance of anaesthesia can be performed as balanced anaesthesia or total intravenous anaesthesia. Essential monitoring should include pulmonary artery catheterization and/or transoesophageal echocardiography. During cardiac surgery the risk for elderly individuals is increased; in particular, the central nervous system is more often compromised in the elderly than in younger patients. However, elderly patients without significant co-morbidity have a mortality rate comparable to that of younger patients.

High risk of intraoperative awareness during cardiopulmonary bypass with isoflurane administration via diffusion membrane oxygenators

In cardiac surgery with the aid of extracorporeal circulation (ECC), inhalation anaesthetics can be administered via the oxygenator. Until the recent advent of a new type of diffusion membrane oxygenator, we routinely added the inhalation agent, isoflurane, to the gas flow of a microporous capillary membrane-type oxygenator. Applying this procedure to the diffusion-type oxygenators, the depth of anaesthesia appeared to be affected, which manifested itself through unusually high intraoperative perfusion pressures. This observation led to a prospective randomized study comprising 60 patients and two models of a microporous capillary membrane oxygenator, as well as two models of a diffusion membrane oxygenator. Simultaneous isoflurane concentration measurements at both the gas inlet and outlet ports of the oxygenators showed that, whereas in the microporous capillary-type oxygenators the isoflurane administered was reduced by about 50% during the passage of gas through the device, there was only a minimal transfer of isoflurane in the diffusion-type membrane oxygenators.

An in vitro study of the effects of isoflurane on oxygen transfer

A common anesthetic technique utilized during cardiopulmonary bypass (CPB) includes the use of various inhalation agents, such as isoflurane. The purpose of this study was to evaluate the effects of this agent on oxygen transfer during CPB. An in vitro model was designed using bovine blood. Blood flow was held constant at 2 l/min, while gas flow was manipulated at 1 and 3 l/min. The percentage of inspired oxygen (FiO2) was set at 50 and 100%, and isoflurane was manipulated to 1.0, 3.0 and 5.0%. Blood gas analysis, oxygen transfer, and inlet and outlet isoflurane concentrations were measured at each of the given conditions. A total of 12 trials with four oxygenators were conducted. In the four oxygenators used in our study, no significant differences in oxygenator performance were found. At conditions of 1 I/min gas flow, 50% FiO2 and 1% isoflurane, there were no significant changes in O2 transfer between baseline and measurements taken during isoflurane administration (100.18 +/- 12.49 vs 102.35 +/- 10.99 ml O2/min, p=0.8031). At 3 I/min gas flow, 100% FiO2 and 5% isoflurane, no significant differences were found (142.35 +/- 10.76 vs 154.04 +/- 8.95 ml O2/min, p=0.1459). The only significant differences found for oxygen transfer were between 50 and 100% FiO2, all other conditions being set equal (102.35 +/- 10.99 vs 137.68 +/- 8.62 ml O2/min, p=0.0023). In conclusion, increasing concentrations of isoflurane up to 5% does not affect the efficiency of oxygen transfer in an in vitro circuit. Further studies are necessary to evaluate the effects in an in vivo setting.