Desflurane pharmacokinetics during cardiopulmonary bypass

Pharmacokinetics of desflurane uptake and disposition in piglets

Introduction

Many respiratory but few arterial blood pharmacokinetics of desflurane uptake and disposition have been investigated. We explored the pharmacokinetic parameters in piglets by comparing inspiratory, end-tidal, arterial blood, and mixed venous blood concentrations of desflurane.

Methods

Seven piglets were administered inspiratory 6% desflurane by inhalation over 2 h, followed by a 2-h disposition phase. Inspiratory and end-tidal concentrations were detected using an infrared analyzer. Femoral arterial blood and pulmonary artery mixed venous blood were sampled to determine desflurane concentrations by gas chromatography at 1, 3, 5, 10, 20, 30, 40, 50, 60, 80, 100, and 120 min during each uptake and disposition phase. Respiratory and hemodynamic parameters were measured simultaneously. Body uptake and disposition rates were calculated by multiplying the difference between the arterial and pulmonary artery blood concentrations by the cardiac output.

Results

The rates of desflurane body uptake increased considerably in the initial 5 min (79.8 ml.min-1) and then declined slowly until 120 min (27.0 ml.min-1). Similar characteristics of washout were noted during the subsequent disposition phase. Concentration-time curves of end-tidal, arterial, and pulmonary artery blood concentrations fitted well to zero-order input and first-order disposition kinetics. Arterial and pulmonary artery blood concentrations were best fitted using a two-compartment model. After 2 h, only 21.9% of the desflurane administered had been eliminated from the body.

Conclusion

Under a fixed inspiratory concentration, desflurane body uptake in piglets corresponded to constant zero-order infusion, and the 2-h disposition pattern followed first-order kinetics and best fitted to a two-compartment model.

Inhalational or total intravenous anesthetic for cardiac surgery: does the debate even exist?

PURPOSE OF REVIEW

Perioperative myocardial injury related to cardiac surgery is associated with organ dysfunction and increased mortality. Volatile anesthetics (VA) have been used during cardiac surgery for decades because of their direct and indirect preconditioning and protection against ischemia-reperfusion injury. The current review provides a summary of the latest literature comparing pharmacological preconditioning and the potential benefits of using VA versus total intravenous anesthesia (TIVA) for general anesthesia to improve outcomes after cardiac surgery.

RECENT FINDINGS

Recent literature reports lower mortality and better outcomes when VA is used alone or in combination with remote ischemic preconditioning compared with groups receiving TIVA. However, inconsistent research findings over the years have led to continued debate regarding the anesthetic technique considered more favorable for cardiac surgery.

SUMMARY

Research findings regarding the use of volatile anesthetic versus TIVA for better outcomes after cardiac surgery are inconsistent. Variability in timing, duration, dosing, and type of VA as well as surgical and patient-related factors may have influenced these results. Therefore, either technique can reasonably be adopted depending on provider and institutional preference and used safely in patients undergoing cardiac surgery.

Volatile Anesthesia Versus Total Intravenous Anesthesia During Cardiopulmonary Bypass: A Narrative Review on the Technical Challenges and Considerations

The Mortality in Cardiac Surgery Randomized Controlled Trial of Volatile Anesthetics (MYRIAD) demonstrated that cardiac surgery with either volatile anesthesia or intravenous anesthesia techniques can be comparable with respect to morbidity and mortality. Maintaining anesthesia during cardiopulmonary bypass (CPB) with either approach requires appreciation of the nuances that are unique to each. This narrative review addresses these technical challenges and other considerations.

The depth of anaesthesia associated with the administration of isoflurane 2.5% during cardiopulmonary bypass

BACKGROUND

Administering isoflurane 2.5% into the oxygenator during cardiopulmonary bypass results in no patient movement. However, doing so may result in an excessive depth of anaesthesia particularly, when hypothermia is induced. Bispectral index and arterial blood and oxygenator exhaust concentrations of volatile anaesthetics should be related to depth of anaesthesia. The primary aim of this study was to measure the depth of anaesthesia using bispectral index, resulting from administering isoflurane 2.5% into the oxygenator during cardiopulmonary bypass, and secondary aims were to examine the relationships between blood and oxygenator exhaust isoflurane concentrations and bispectral index.

METHODS

Arterial and mixed-venous blood samples were aspirated at three time points during cardiopulmonary bypass and measured for isoflurane concentration using mass spectrometry. Simultaneously, oxygenator exhaust isoflurane concentration, nasopharyngeal temperature and bispectral index were recorded.

RESULTS

When averaged across the three time points, all patients had a bispectral index score below 40 (binomial test, p < 0.001). There were no significant correlations between bispectral index score and arterial or mixed-venous blood isoflurane concentrations (r = -0.082, p = 0.715; r = -0.036, p = 0.874) and oxygenator exhaust gas concentration of isoflurane (r = -0.369, p = 0.091).

CONCLUSION

When 2.5% isoflurane was administered into the sweep gas supply to the oxygenator during cardiopulmonary bypass, all patients experienced a bispectral index score less than 40 and no significant relationship was found between either arterial or mixed-venous blood or oxygenator exhaust concentrations of isoflurane and bispectral index.

Assessing the depth of isoflurane anaesthesia during cardiopulmonary bypass

INTRODUCTION

Bispectral index (BIS) and monitoring of end-tidal concentration may be associated with a reduction in the incidence of awareness during volatile-based general anaesthesia. An analogue of end-tidal concentration during cardiopulmonary bypass (CPB) is measuring exhausted isoflurane concentration from the oxygenator as an estimate to blood and, so, brain concentration. The aim of this study was to determine the relationships between oxygenator exhaust and blood concentrations of isoflurane and the BIS score during CPB when administering isoflurane into the sweep gas supply to the oxygenator.

METHODS

Seventeen patients undergoing elective cardiac surgery using CPB and isoflurane with BIS monitoring were recruited in a single-centre university hospital. Isoflurane gas was delivered via a calibrated vaporiser at the beginning of anaesthetic induction. Radial arterial blood samples were collected after the initiation of CPB and before aortic cross-clamping, which were analysed for isoflurane by gas chromatography and mass spectrometry. The BIS score and the concentration of exhausted isoflurane from the oxygenator membrane, as measured by an anaesthetic gas analyser, were recorded at the time of blood sampling.

RESULTS

The mean duration of anaesthetic induction to arterial blood sampling was 90 min (95%CI: 80,100). On CPB, the median BIS was 39 (range, 7-43) and the mean oxygenator exhaust isoflurane concentration was 1.24 ± 0.21%. No significant correlation was demonstrated between BIS with arterial isoflurane concentration (r=-0.19, p=0.47) or oxygenator exhaust isoflurane concentration (r=0.07, p=0.80). Mixed-venous blood temperature was moderately correlated to BIS (r=0.50, p=0.04). Oxygenator exhaust isoflurane concentration was moderately, positively correlated with its arterial concentration (r=0.64, p<0.01).

DISCUSSION

In conclusion, in patients undergoing heart surgery with CPB, the findings of this study indicate that, whilst oxygenator exhaust concentrations were significantly associated with arterial concentrations of isoflurane, neither had any association with the BIS scores, whereas body temperature has moderate positive correlation.

Coronary Sinus Isoflurane Concentration in Cardiac Surgery

OBJECTIVE

Volatile anesthetic agents such as isoflurane may be associated with fewer adverse myocardial events compared with total intravenous anesthesia in cardiac surgery. The authors aimed to determine whether reasonable isoflurane concentrations at tissue level were being achieved to protect the myocardium using this agent. The isoflurane concentration in myocardium has never been measured. The primary aim was to sample coronary sinus (CS) blood and measure its isoflurane concentration. Secondary aims were to determine whether the CS blood concentration would equilibrate with the arterial blood concentration and the relationship of CS blood concentration with oxygenator exhaust isoflurane concentrations during cardiopulmonary bypass (CPB).

DESIGN

Prospective, observational study.

SETTING

Single-center university hospital.

PARTICIPANTS

The study comprised 23 patients undergoing cardiac surgery using CPB and isoflurane.

MEASUREMENTS AND MAIN RESULTS

Shortly after initiation of CPB and insertion of a CS retrograde cardioplegia catheter but before aortic cross-clamping, CS blood was aspirated, followed by radial artery blood, which then were analyzed for isoflurane with gas chromatography and mass spectrometry. The oxygenator exhaust isoflurane level was measured with an anesthetic gas analyzer. The mean arterial and CS isoflurane concentrations were 87.7 ± 50.1 and 73.0 ± 42.9 μg/mL, respectively. There was a significant mean difference of 14.7 μg/mL (95% confidence interval 6.7-22.8) between CS and arterial isoflurane concentrations. Oxygenator exhaust isoflurane levels were correlated positively with those in the CS blood (r = 0.68, p < 0.001) and arterial blood (r = 0.72, p < 0.001).

CONCLUSIONS

This was the first study in which CS blood was sampled and measured for isoflurane concentration. The CS isoflurane concentration could be estimated from the isoflurane concentration in the oxygenator exhaust gas. However, the value of this relationship is limited because the CS isoflurane concentration does not accurately represent its myocardial levels during CPB.

Feasibility of Anesthesia Maintenance With Sevoflurane During Cardiopulmonary Bypass: A Pilot Pharmacokinetics Study

OBJECTIVE

Adequate maintenance of hypnosis during anesthesia throughout surgery using sevoflurane alone was investigated. In addition, sevoflurane pharmacokinetics during cardiopulmonary bypass were analyzed.

DESIGN

This was a pilot pharmacokinetic study.

SETTING

Tertiary care university hospital.

PARTICIPANTS

The study comprised 10 patients aged between 18 and 75 years who underwent elective mitral valve surgery.

INTERVENTIONS

The end-tidal and sevoflurane plasma concentrations were measured throughout cardiac surgery procedures involving cardiopulmonary bypass. The sevoflurane plasma concentration was measured using gas chromatography. In addition, the ratio between sevoflurane alveolar concentration and inspired concentration over time (F_A/F_I) was analyzed to describe wash-in and wash-out curves.

MEASUREMENTS AND MAIN RESULTS

Hypnosis was maintained adequately throughout surgery using sevoflurane alone. The bispectral index was maintained between 40 and 60 during cardiopulmonary bypass. The end-tidal sevoflurane was significantly different before and during cardiopulmonary bypass (1.86%±0.54% v 1.30%±0.58%, respectively; p<0.001). However, the sevoflurane plasma concentration was not significantly different before and after cardiopulmonary bypass start-up (40.55 µg/mL [76.62-125.33] before cardiopulmonary bypass and 36.24 µg/mL [56.49-81-42] during cardiopulmonary bypass). This mismatch possibly can be explained by changes that occured after cardiopulmonary bypass start-up, such as reductions of body temperature (36.33°C±0.46°C v 32.98°C±2.38°C, respectively; p<0.001) and hematocrit (35.62%±3.98% v 25.5%±3.08%, respectively; p<0.001). The sevoflurane alveolar concentration varied according to sevoflurane plasma concentration and bispectral index values. No adverse events regarding sevoflurane administration during cardiopulmonary bypass were observed.

CONCLUSIONS

Sevoflurane end-tidal values were reliable indicators of adequate anesthesia during all cardiac surgery procedures involving cardiopulmonary bypass.

Bispectral index guided titration of sevoflurane in on-pump cardiac surgery reduces plasma sevoflurane concentration and vasopressor requirements: a prospective, controlled, sequential two-arm clinical study

BACKGROUND

Electroencephalographic-based monitoring systems such as the bispectral index (BIS) may reduce anaesthetic overdose rates.

OBJECTIVE

We hypothesised that goal-directed sevoflurane administration (guided by BIS monitoring) could reduce the sevoflurane plasma concentration (SPC) and intraoperative vasopressor doses during on-pump cardiac surgery.

DESIGN

A prospective, controlled, sequential two-arm clinical study.

SETTING

German university medical centre with more than 2500 cardiac surgery interventions per year.

PATIENTS

Sixty elective on-pump cardiac surgery patients.

INTERVENTION

In group Sevo1.8% (n = 29), the sedation depth was maintained with a sustained inspired concentration of sevoflurane 1.8% before and during cardiopulmonary bypass (CPB). In group SevoBIS (n = 31), the inspired sevoflurane concentration was titrated to maintain a BIS target between 40 and 60.

OUTCOME MEASURES

SPC during CPB and the intraoperative administration of noradrenaline. Additional analyses were performed on intraoperative awareness, postoperative blood lactate concentration, duration of mechanical ventilation, intensive care unit length of stay and kidney injury.

RESULTS

Mean inspired sevoflurane concentration was 0.8% in group SevoBIS, representing a 57.1% reduction (P < 0.001) compared with group Sevo1.8%. The mean SPC was 42.3 μg ml(-1) [95% confidence interval (CI) 40.0 to 44.6] in group Sevo1.8% and 21.0 μg ml(-1) (95% CI 18.8 to 23.3) in group SevoBIS, representing a 50.2% reduction (P < 0.001). During CPB, the mean cumulative dose of noradrenaline administered was 13.48 μg kg(-1) (95% CI 10.52 to 17.19) in group Sevo1.8% and 4.06 μg kg(-1) (95% CI 2.67 to 5.97) in group SevoBIS (P < 0.001). Pearson's correlation coefficient (between the cumulative applied dosage of sevoflurane calculated from the area under the curve of the SPC over time and the administered cumulative noradrenaline dose) was 0.607 (P < 0.001). No intraoperative awareness signs were detected.

CONCLUSION

BIS-guided titration of sevoflurane reduces the SPC and decreases noradrenaline administration compared with routine care during on-pump cardiac surgery.

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.

A model for differential volatile anesthetic delivery to the upper and lower torso of the rabbit

INTRODUCTION

We have developed a model that permits differential delivery of volatile anesthetics to the upper and lower torso of the rabbit.

METHODS

Rabbits were anesthetized with isoflurane (n = 4) or halothane (n = 3), and blood was drained from a carotid cannula into a membrane oxygenator and reinfused via a renal artery cannula into the lower torso circulation using a roller pump. Bypass of the lower torso circulation was achieved by tightening a ligature around the aorta at the level of the renal arteries. Blood concentrations of anesthetic (assessed by gas chromatography) and cardiovascular responses to noxious stimulation were determined with and without anesthetic delivery to the membrane oxygenator.

RESULTS

When the anesthetic was removed from the oxygenator gas flow, the arterial concentration of isoflurane in the lower torso was 28 +/- 15 microg/ml, while it was 133 +/- 28 microg/ml in the upper torso circulation; the corresponding values for the halothane-anesthetized rabbits were 63 +/- 8 and 270 +/- 49 microg/ml. There was a significant correlation (r=.92-.99) between pump flow and lower torso pressure in each individual rabbit. When anesthetic was delivered to both upper and lower torso, noxious electrical stimulation of the tail or hindpaw did not affect lower torso pressures (52 +/- 10 to 54 +/- 12 mmHg). Decreasing the anesthetic concentration in the lower torso resulted in significant increases in lower torso blood pressure during noxious stimulation (82 +/- 19 to 131 +/- 35 mmHg, P < .05).

DISCUSSION

The results indicate that volatile anesthetics isoflurane and halothane can be differentially delivered to the upper and lower torso of the rabbit, with an approximate 75-80% reduction in the anesthetic concentration in the lower torso when the anesthetic is eliminated from the gas flow to the oxygenator. This preparation can be used to study the pharmacological properties of volatile anesthetics.

Parasternal Block and Local Anesthetic Infiltration with Levobupivacaine After Cardiac Surgery with Desflurane: The Effect on Postoperative Pain, Pulmonary Function, and Tracheal Extubation Times

Early tracheal extubation has become common after cardiac surgery. Anesthetic techniques designed to achieve this goal can make immediate postoperative analgesia challenging. We conducted this randomized, placebo-controlled, double-blind study to investigate the effect of a parasternal block on postoperative analgesia, respiratory function, and extubation times. We enrolled 20 patients having cardiac surgery via median sternotomy; 17 patients completed the study. A de-sflurane-based, small-dose opioid anesthetic was used. Before sternal wire placement, the surgeons performed the parasternal block and local anesthetic infiltration of sternotomy and tube sites with either 54 mL of saline placebo or 54 mL of 0.25% levobupivacaine with 1:400,000 epinephrine. Effects on pain and respiratory function were studied over 24 h. Patients in the levobupivacaine group used significantly less morphine in the first 4 h after surgery (20.8 +/- 6.2 mg versus 33.2 +/- 10.9 mg in the placebo group; P=0.013); they also had better oxygenation at the time of extubation. Four of nine in the placebo group needed rescue pain medication, versus none of eight in the levobupivacaine group (P=0.08). Peak serum levobupivacaine concentrations were below potentially toxic levels in all patients (0.64 +/- 0.43 microg/mL; range, 0.24-1.64 microg/mL). Parasternal block and local anesthetic infiltration of the sternotomy wound and mediastinal tube sites with levobupivacaine can be a useful analgesic adjunct for patients who are expected to undergo early tracheal extubation after cardiac surgery.

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.