Extrahepatic metabolism of propofol in man during the anhepatic phase of orthotopic liver transplantation

Quantitation of propofol metabolites by LC-MS/MS demonstrating long detection window for urine drug monitoring

Introduction

Chromatographic methods for analysis of propofol and its metabolites have been widely used in pharmacokinetic studies of propofol distribution, metabolism, and clearance. Application of chromatographic methods is also needed in clinical and forensic laboratories for detecting and monitoring propofol misuse.

Objective

We report a method for sensitive analysis of propofol, propofol 1-glucuronide (PG), 4-hydroxypropofol 1-glucuronide (1-QG), 4-hydroxypropofol 4-glucuronide (4-QG) and 4-hydroxypropofol 4-sulfate (4-QS) in urine by LC-MS/MS analysis. The method employs a simple dilute-and-analyze sample preparation with stable isotope internal standardization.

Results

Validation studies demonstrate a linear calibration model (100-10,000 ng/mL), with dilution integrity verified for the extended range of concentrations experienced in propofol use. Criteria-based validation was achieved, including an average coefficient of variation of 6.5 % and a percent bias of -4.2 ng/mL. The method was evaluated in 12 surgical patients, with monitoring periods lasting up to 30 days following intravenous propofol administrations of 100-3000 mg on the day of surgery. While the concentration ratio of PG to 4-hydroxy propofol metabolite decreased significantly in the days following surgery, PG maintained the highest concentration in all specimens. Both PG and 1-QG were detectable throughout the monitoring periods, including in a patient monitored for 30 days. Lower concentrations were determined for 4-QG and 4-QS, with evidence of detection up to 20 days. Propofol was not detectable in any urine specimens, thereby proving ineffective for identifying drug use.

Conclusion

The validated method for quantifying propofol metabolites demonstrates its applicability for the sensitive detection of propofol misuse over a long window of drug-use detection.

Paving the way to environment-friendly greener anesthesia

Health-care settings have an important responsibility toward environmental health and safety. The operating room is a major source of environmental pollution within a hospital. Inhalational agents and nitrous oxide are the commonly used gases during general anesthesia for surgeries, especially in the developing world. These greenhouse gases contribute adversely to the environmental health both inside the operating room and in the outside atmosphere. Impact of these anesthetic agents depends on the total consumption, characteristics of individual agents, and gas flows, with higher levels increasing the environmental adverse effects. The inimical impact of nitrous oxide is higher due to its longer atmospheric half-life and potential for destruction of the ozone layer. Anesthesiologist of today has a choice in the selection of anesthetic agents. Prudent decisions will help in mitigating environmental pollution and contributing positively to a greener planet. Therefore, a shift from inhalational to intravenous-based technique will reduce the carbon footprint of anesthetic agents and their impact on global climate. Propofol forms the mainstay of intravenous anesthesia technique and is a proven drug for anesthetic induction and maintenance. Anesthesiologists should appreciate growing concerns about the role of inhalational anesthetics on the environment and join the cause of environmental responsibility. In this narrative review, we revisit the pharmacological and pharmacokinetic considerations, clinical uses, and discuss the merits of propofol-based intravenous anesthesia over inhalational anesthesia in terms of environmental effects. Increased awareness about the environmental impact and adoption of newer, versatile, and user-friendly modalities of intravenous anesthesia administration will pave the way for greener anesthesia practice.

Efficacy and safety of ciprofol (HSK3486) for procedural sedation and anesthesia induction in surgical patients: A systematic review and meta-analysis

Background

Ciprofol (HSK3486) is a novel gamma-aminobutyric acid type A (GABAA) receptor agonist that has attracted wide attention because of its lower injection pain and fewer adverse events. We summarized all available evidence and analyzed the efficacy and safety of ciprofol during procedural sedation and anesthesia induction.

Methods

An electronic search of PubMed, Embase, Cochrane Library, Web of Science, Google Scholar, Science Direct, the Chinese National Knowledge Infrastructure, Wan Fang Data, and the VIP Chinese Journal Service platform was conducted from inception of databases to March 1, 2023. Risk ratio (RR) and mean difference (MD) with 95 % confidence interval (CI) were used separately for binary categorical and continuous variables. We performed trial sequential analysis and the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) methodology to judge the certainty of evidence.

Results

Fifteen randomized controlled trials with 2441 patients were included in this study. Ciprofol showed similar advantages to propofol in terms of induction success rate (RR = 1, 95 % CI = 0.99, 1.01, moderate certainty) and induction time (MD = 3.31, 95 % CI = -0.34, 6.95, low certainty), but did not increase the incidence of adverse events (RR = 0.88, 95 % CI = 0.78, 1.00, very low certainty), such as bradycardia (RR = 0.96, 95 % CI = 0.77, 1.21, high certainty), hypoxia (RR = 0.79, 95 % CI = 0.46, 1.37, p = 0.40, moderate certainty) and other adverse events. Although it may be associated with a longer time to be fully alert (MD = 1.22, 95 % CI = 0.32, 2.12, very low certainty), ciprofol significantly reduced injection pain (RR = 0.15, 95 % CI 0.09, 0.24, low certainty) and may have reduced the incidence of hypotension (RR = 0.77, 95 % CI = 0.63, 0.94, low certainty) and respiratory depression (RR = 0.29, 95 % CI = 0.15, 0.56, moderate certainty).

Conclusion

Ciprofol and propofol had similar effects on most outcomes. While the time to full alertness may be prolonged, injection pain was significantly reduced, and hypotension and respiratory depression may be reduced compared with propofol. We believe that ciprofol is an effective alternative to intravenous anesthetic agents.

Clinical Guideline on Perioperative Management of Patients with Advanced Chronic Liver Disease

(1) Background: Patients with advanced chronic liver disease (ACLD) are living longer with more comorbidities because of improved medical and surgical management. However, patients with ACLD are at increased risk of perioperative morbidity and mortality; (2) Methods: We conducted a comprehensive review of the literature to support a narrative clinical guideline about the assessment of mortality risk and management of perioperative morbidity in patients with ACLD undergoing surgical procedures; (3) Results: Slight data exist to guide the perioperative management of patients with ACLD, and most recommendations are based on case series and expert opinion. The severity of liver dysfunction, portal hypertension, cardiopulmonary and renal comorbidities, and complexity of surgery and type (elective versus emergent) are predictors of perioperative morbidity and mortality. Expert multidisciplinary teams are necessary to evaluate and manage ACLD before, during, and after surgical procedures; (4) Conclusions: This clinical practice document updates the available data and recommendations to optimize the management of patients with advanced chronic liver disease who undergo surgical procedures.

Efficacy and safety of ciprofol for the sedation/anesthesia in patients undergoing colonoscopy: Phase IIa and IIb multi-center clinical trials

OBJECTIVE

Ciprofol is a new intravenous anesthetic agent similar to propofol that has the pharmacodynamic characteristics of a rapid rate of onset and recovery in pre-clinical experiments. The aims of the present clinical trials were to compare the efficacy and safety of ciprofol emulsion for sedation or general anesthesia during colonoscopy and to define optimal doses for a subsequent phase III clinical trial.

METHODS

A phase IIa multi-center, open-label, non-randomized, positive control, dose-escalating study was performed to determine a recommended phase IIb dose (RP2D) of ciprofol to induce sedation or anesthesia in patients undergoing colonoscopy. Phase IIb was also a multi-center clinical trial, but the patients were randomized into 3 groups at a ratio of 1:1:1. It was a double-blinded, propofol controlled study that administered ciprofol 0.4 mg/kg (n = 31) and 0.5 mg/kg (n = 32) or propofol at 2.0 mg/kg (n = 31), with the aim of establishing the optimal dose of ciprofol. The primary endpoint was the colonoscopy success rate. Secondary endpoints were the duration of colonoscope insertion, recovery time, number of top-up doses needed, and the total dose of ciprofol or propofol required to maintain adequate sedation or anesthesia. In addition, we evaluated the satisfaction of sedation/anesthesia from the endoscopists, anesthetists and patients' points of view. Safety was assessed according to the incidence of AEs including serious AEs and drug related AEs and the assessment of vital signs, a 12-lead ECG and laboratory tests.

RESULTS

In the phase IIa trial, the colonoscopy success rates in the 0.2-0.5 mg/kg ciprofol and propofol 2.0 mg/kg groups were 100% and all doses were safe and well tolerated. Ciprofol doses of 0.4 mg/kg and 0.5 mg/kg are recommended for subsequent IIb phases. In the phase IIb trial, a 100% success rate was reconfirmed in all the dosage groups. The mean time of colonoscope insertion in the ciprofol 0.4 mg/kg, ciprofol 0.5 mg/kg and propofol 2.0 mg/kg groups were 1.9, 1.5 and 1.5 min, the mean recovery times from colonoscope withdrawal were 6.1, 5.1, and 4.3 min, and the times to discharge were 11.8, 11.2 and 10.6 min, respectively. The satisfaction ratings of anesthetists in the ciprofol 0.5 mg/kg group (9.5 ± 0.8) were higher than in the ciprofol 0.4 mg/kg (9.2 ± 1.0) and propofol 2.0 mg/kg (9.2 ± 0.9) groups. The incidence of sedation and anesthesia-related AEs was highest in the propofol 2.0 mg/kg group (25.8%), followed by the ciprofol 0.5 mg/kg group (21.9%), and was least in the ciprofol 0.4 mg/kg group (16.1%) (P = 0.750).

CONCLUSIONS

Ciprofol was safe and well tolerated at doses ranging from 0.1 mg/kg to 0.5 mg/kg. Ciprofol 0.4-0.5 mg/kg induced equivalent sedation/anesthesia and had a similar safety profile to propofol 2.0 mg/kg during colonoscopy without producing serious AEs.

Exhaled Propofol Concentrations Correlate With Plasma and Brain Tissue Concentrations in Rats

BACKGROUND

Propofol can be measured in exhaled gas. Exhaled and plasma propofol concentrations correlate well, but the relationship with tissue concentrations remains unknown. We thus evaluated the relationship between exhaled, plasma, and various tissue propofol concentrations. Because the drug acts in the brain, we focused on the relationship between exhaled and brain tissue propofol concentrations.

METHODS

Thirty-six male Sprague-Dawley rats were anesthetized with propofol, ketamine, and rocuronium for 6 hours. Animals were randomly assigned to propofol infusions at 20, 40, or 60 mg·kg·h (n = 12 per group). Exhaled propofol concentrations were measured at 15-minute intervals by multicapillary column-ion mobility spectrometry. Arterial blood samples, 110 µL each, were collected 15, 30, and 45 minutes, and 1, 2, 4, and 6 hours after the propofol infusion started. Propofol concentrations were measured in brain, lung, liver, kidney, muscle, and fat tissue after 6 hours. The last exhaled and plasma concentrations were used for linear regression analyses with tissue concentrations.

RESULTS

The correlation of exhaled versus plasma concentrations (R = 0.71) was comparable to the correlation of exhaled versus brain tissue concentrations (R = 0.75) at the end of the study. In contrast, correlations between plasma and lung and between lung and exhaled propofol concentrations were poor. Less than a part-per-thousand of propofol was exhaled over 6 hours.

CONCLUSIONS

Exhaled propofol concentrations correlate reasonably well with brain tissue and plasma concentrations in rats, and may thus be useful to estimate anesthetic drug effect. The equilibration between plasma propofol and exhaled gas is apparently independent of lung tissue concentration. Only a tiny fraction of administered propofol is eliminated via the lungs, and exhaled quantities thus have negligible influence on plasma concentrations.

The use of PBPK modeling across the pediatric age range using propofol as a case

The project SAFEPEDRUG aims to provide guidelines for drug research in children, based on bottom-up and top-down approaches. Propofol, one of the studied model compounds, was selected because it is extensively metabolized in liver and kidney, with an important role for the glucuronidation pathway. Besides, being a lipophilic molecule, it is distributed into fat tissues, from where it redistributes into the systemic circulation. In the past, both bottom-up (Physiologically based pharmacokinetic, PBPK) and top-down approaches (population pharmacokinetic, popPK) were applied to describe its pharmacokinetics (PK). In this work, a combination of the two was used to check their performance to describe PK in children and neonates (both term and preterm) using propofol as a case compound. First, in vitro data was generated in human liver microsomes and recombinant enzymes and used to develop an adult PBPK model in Simcyp^®. Activity adjustment factors (AAFs) were calculated to account for differences between in vitro and in vivo enzyme activity. Clinical data were analyzed using a 3-compartment model in NONMEM. These data were used to construct a retrograde PBPK model and for qualification of the PBPK models. Once an accurate in vivo clearance was obtained accounting for the contribution of the different metabolic pathways, the resulting PBPK models were challenged with new data for qualification. After that, the constructed adult PPBK model for propofol was extrapolated to the pediatric population. Both the default built-in and in vivo derived ontogeny functions were used to do so. The models were qualified by comparing their predicted PK parameters to published values, and by comparison of predicted concentration-time profiles to available clinical data. Clearance values were predicted well, especially when compared with values obtained from trials where long-term sampling was applied, whereas volume of distribution was lower compared to the most common popPK model predictions. Concentration-time profiles were predicted well up until and including the preterm neonatal population. In this work, it was thus shown that PBPK can be used to predict the PK up to and including the preterm neonatal population without the use of pediatric in vivo data. This work adds weight to the need for further development of PBPK models, especially regarding distribution modeling and the use of in vivo derived ontogeny functions.

Metabolic Profiles of Propofol and Fospropofol: Clinical and Forensic Interpretative Aspects

Propofol is an intravenous short-acting anesthetic widely used to induce and maintain general anesthesia and to provide procedural sedation. The potential for propofol dependency and abuse has been recognized, and several cases of accidental overdose and suicide have emerged, mostly among the health professionals. Different studies have demonstrated an unpredictable interindividual variability of propofol pharmacokinetics and pharmacodynamics with forensic and clinical adverse relevant outcomes (e.g., pronounced respiratory and cardiac depression), namely, due to polymorphisms in the UDP-glucuronosyltransferase and cytochrome P450 isoforms and drugs administered concurrently. In this work the pharmacokinetics of propofol and fospropofol with particular focus on metabolic pathways is fully reviewed. It is concluded that knowing the metabolism of propofol may lead to the development of new clues to help further toxicological and clinical interpretations and to reduce serious adverse reactions such as respiratory failure, metabolic acidosis, rhabdomyolysis, cardiac bradyarrhythmias, hypotension and myocardial failure, anaphylaxis, hypertriglyceridemia, renal failure, hepatomegaly, hepatic steatosis, acute pancreatitis, abuse, and death. Particularly, further studies aiming to characterize polymorphic enzymes involved in the metabolic pathway, the development of additional routine forensic toxicological analysis, and the relatively new field of ‘‘omics” technology, namely, metabolomics, can offer more in explaining the unpredictable interindividual variability.

Sedation and Analgesia

Patients in the cardiothoracic intensive care unit (CTICU) are subject to numerous physical and mental stresses. While most of these cannot be completely eliminated, intensivists have many tools in their armamentarium to alleviate patients' pain and suffering. This chapter will consider the importance of analgesia and sedation in the CTICU and the relevant consequences of over- or under-treatment. We will examine the tools available for monitoring and titrating analgesia and sedation in critically ill patients. The major classes of medications available will be reviewed, with particular attention to their clinical effects, metabolism and excretion, and hemodynamic characteristics. Lastly, experimental evidence will be assessed regarding the best strategies for treatment of pain and agitation in the CTICU, including use of non-pharmacologic adjuvants.

Key to Opening Kidney for In Vitro-In Vivo Extrapolation Entrance in Health and Disease: Part II: Mechanistic Models and In Vitro-In Vivo Extrapolation

It is envisaged that application of mechanistic models will improve prediction of changes in renal disposition due to drug-drug interactions, genetic polymorphism in enzymes and transporters and/or renal impairment. However, developing and validating mechanistic kidney models is challenging due to the number of processes that may occur (filtration, secretion, reabsorption and metabolism) in this complex organ. Prediction of human renal drug disposition from preclinical species may be hampered by species differences in the expression and activity of drug metabolising enzymes and transporters. A proposed solution is bottom-up prediction of pharmacokinetic parameters based on in vitro-in vivo extrapolation (IVIVE), mediated by recent advances in in vitro experimental techniques and application of relevant scaling factors. This review is a follow-up to the Part I of the report from the 2015 AAPS Annual Meeting and Exhibition (Orlando, FL; 25th-29th October 2015) which focuses on IVIVE and mechanistic prediction of renal drug disposition. It describes the various mechanistic kidney models that may be used to investigate renal drug disposition. Particular attention is given to efforts that have attempted to incorporate elements of IVIVE. In addition, the use of mechanistic models in prediction of renal drug-drug interactions and potential for application in determining suitable adjustment of dose in kidney disease are discussed. The need for suitable clinical pharmacokinetics data for the purposes of delineating mechanistic aspects of kidney models in various scenarios is highlighted.

Determination of total and unbound propofol in patients during intensive care sedation by ultrafiltration and LC-MS/MS

For the quantification of propofol total and unbound drug concentrations a sensitive and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated. To separate unbound propofol an ultrafiltration step before sample preparation was performed. Both the ultrafiltrate and plasma samples were extracted with solid-phase extraction and substituted with deuterated propofol as an internal standard. Separation was performed by gradient elution using UPLC-like system and analyzed by MS/MS consisting of an electrospray ionization source. To detect low and high concentration levels of propofol two calibration curves were identified and showed linearity within the range of 1-50ng/ml and 50-20000ng/ml. The lower limit of quantification was 1ng/ml. Intra- and interassay precision and accuracy did not exceed ±15%. The method was applied to a clinical study during intensive care treatment of patients after coronary artery bypass grafting.

Online breath analysis of propofol during anesthesia: clinical application of membrane inlet-ion mobility spectrometry

BACKGROUND

Breath analysis of propofol is a potential noninvasive method for approximating the plasma propofol concentration. There have been various reported techniques for measuring the exhaled propofol concentration at steady state; however, the propofol concentration undergoes marked changes during clinical anesthesia. Therefore, this study investigated the use of membrane inlet-ion mobility spectrometry (MI-IMS) to monitor exhaled propofol discontinuously and continuously during propofol anesthesia.

METHODS

The study included 19 patients of American Society of Anesthesiologists physical status I or II. In experiment I (discontinuous study), breath and blood samples were collected discontinuously, with stable target propofol concentrations of 2.8 μg/ml, 3.2 μg/ml, 3.5 μg/ml, and 3.8 μg/ml. In experiment II (continuous study), propofol concentration was maintained at 3.5 μg/ml after induction, and exhaled breath was collected continuously every 3 min during propofol infusion. Relationships of the exhaled propofol concentration with the plasma propofol concentration, measured by high-performance liquid chromatography and the continuously measured bispectral (BIS) index were investigated.

RESULTS

Comparison of the exhaled and plasma propofol concentrations revealed a bias ± precision of 2.1% ± 14.6% (95% limits of agreement: - 26.5-30.7%) in experiment I and - 10.4% ± 13.2 (- 36.3-15.4%) in experiment II. In both experiments, exhaled propofol concentrations measured by MI-IMS were consistent with, the propofol effect represented by the BIS index.

CONCLUSIONS

MI-IMS may be a suitable method to predict plasma propofol concentration online during propofol anesthesia. Monitoring exhaled propofol may improve the safety of propofol anesthesia.

Renal drug metabolism in humans: the potential for drug-endobiotic interactions involving cytochrome P450 (CYP) and UDP-glucuronosyltransferase (UGT)

Although knowledge of human renal cytochrome P450 (CYP) and UDP-glucuronosyltransferase (UGT) enzymes and their role in xenobiotic and endobiotic metabolism is limited compared with hepatic drug and chemical metabolism, accumulating evidence indicates that human kidney has significant metabolic capacity. Of the drug metabolizing P450s in families 1 to 3, there is definitive evidence for only CYP 2B6 and 3A5 expression in human kidney. CYP 1A1, 1A2, 1B1, 2A6, 2C19, 2D6 and 2E1 are not expressed in human kidney, while data for CYP 2C8, 2C9 and 3A4 expression are equivocal. It is further known that several P450 enzymes involved in the metabolism of arachidonic acid and eicosanoids are expressed in human kidney, CYP 4A11, 4F2, 4F8, 4F11 and 4F12. With the current limited evidence of drug substrates for human renal P450s drug-endobiotic interactions arising from inhibition of renal P450s, particularly effects on arachidonic acid metabolism, appear unlikely. With respect to the UGTs, 1A5, 1A6, 1A7, 1A9, 2B4, 2B7 and 2B17 are expressed in human kidney, whereas UGT 1A1, 1A3, 1A4, 1A8, 1A10, 2B10, 2B11 and 2B15 are not. The most abundantly expressed renal UGTs are 1A9 and 2B7, which play a significant role in the glucuronidation of drugs, arachidonic acid, prostaglandins, leukotrienes and P450 derived arachidonic acid metabolites. Modulation by drug substrates (e.g. NSAIDs) of the intrarenal activity of UGT1A9 and UGT2B7 has the potential to perturb the metabolism of renal mediators including aldosterone, prostaglandins and 20-hydroxyeicosatetraenoic acid, thus disrupting renal homeostasis.

Anesthetic management of an 8-month-old infant with osteogenesis imperfecta undergoing liver transplantation: a case report

Anesthetic management of pediatric liver transplantation in a patient with osteogenesis imperfecta (OI) requires tough decisions and comprehensive considerations of the cascade of effects that may arise and the required monitoring. Total intravenous anesthesia (TIVA) with propofol and remifentanil was chosen as the main anesthetic strategy. Malignant hyperthermia (MH), skeletal fragility, anhepatic phase during liver transplantation, uncertainties of TIVA in children, and propofol infusion syndrome were considered and monitored. There were no adverse events during the operation. Despite meticulous precautions with regard to the risk of MH, there was an episode of high fever (40℃) in the ICU a few hours after the operation, which was initially feared as MH. Fortunately, MH was ruled out as the fever subsided soon after hydration and antipyretics were given. Although the delivery of supportive care and the administration of dantrolene are the core principles in the management of MH, perioperative fever does not always mean a MH in patients at risk for MH, and other common causes of fever should also be considered.

Neurologic manifestations of acute liver failure

Fulminant hepatic failure presents with a hepatic encephalopathy and may progress to coma and often brain death from cerebral edema. This natural progression in severe cases contributes to early mortality, but outcome can be good if liver transplantation is appropriately timed and increased intracranial pressure (ICP) is managed. Neurologists and neurosurgeons have become more involved in these very challenging patients and are often asked to rapidly identify patients who are at risk of cerebral edema, to carefully select the patient population who will benefit from invasive ICP monitoring, to judge the correct time to start monitoring, to participate in treatment of cerebral edema, and to manage complications such as intracranial hemorrhage or seizures. This chapter summarizes the current multidisciplinary approach to fulminant hepatic failure and how to best bridge patients to emergency liver transplantation.

Application of a physiologically based pharmacokinetic model to assess propofol hepatic and renal glucuronidation in isolation: utility of in vitro and in vivo data

A physiologically based pharmacokinetic (PBPK) modeling approach was used to assess the prediction accuracy of propofol hepatic and extrahepatic metabolic clearance and to address previously reported underprediction of in vivo clearance based on static in vitro-in vivo extrapolation methods. The predictive capacity of propofol intrinsic clearance data (CLint) obtained in human hepatocytes and liver and kidney microsomes was assessed using the PBPK model developed in MATLAB software. Microsomal data obtained by both substrate depletion and metabolite formation methods and in the presence of 2% bovine serum albumin were considered in the analysis. Incorporation of hepatic and renal in vitro metabolic clearance in the PBPK model resulted in underprediction of propofol clearance regardless of the source of in vitro data; the predicted value did not exceed 35% of the observed clearance. Subsequently, propofol clinical data from three dose levels in intact patients and anhepatic subjects were used for the optimization of hepatic and renal CLint in a simultaneous fitting routine. Optimization process highlighted that renal glucuronidation clearance was underpredicted to a greater extent than liver clearance, requiring empirical scaling factors of 17 and 9, respectively. The use of optimized clearance parameters predicted hepatic and renal extraction ratios within 20% of the observed values, reported in an additional independent clinical study. This study highlights the complexity involved in assessing the contribution of extrahepatic clearance mechanisms and illustrates the application of PBPK modeling, in conjunction with clinical data, to assess prediction of clearance from in vitro data for each tissue individually.

A rare case of propofol-induced liver injury during modified electroconvulsive therapy in an elderly woman

A 75-year-old woman developed depression in 2010 and was treated with oral medications at our Department of Psychiatry. Since she showed no tendency toward improvement, she underwent modified electroconvulsive therapy (mECT). Later, she developed severe liver injury that was presumably induced by the propofol used for mECT. Propofol is an intravenous anesthetic agent that reportedly can be used relatively safely in the presence of liver dysfunction. We herein report the first case of propofol-induced liver injury definitively diagnosed based on positive drug lympocyte stimulation testing (DLST).

Sedation for critically ill or injured adults in the intensive care unit: a shifting paradigm

As most critically ill or injured patients will require some degree of sedation, the goal of this paper was to comprehensively review the literature associated with use of sedative agents in the intensive care unit (ICU). The first and selected latter portions of this article present a narrative overview of the shifting paradigm in ICU sedation practices, indications for uninterrupted or prolonged ICU sedation, and the pharmacology of sedative agents. In the second portion, we conducted a structured, although not entirely systematic, review of the available evidence associated with use of alternative sedative agents in critically ill or injured adults. Data sources for this review were derived by searching OVID MEDLINE and PubMed from their first available date until May 2012 for relevant randomized controlled trials (RCTs), systematic reviews and/or meta-analyses and economic evaluations. Advances in the technology of mechanical ventilation have permitted clinicians to limit the use of sedation among the critically ill through daily sedative interruptions or other means. These practices have been reported to result in improved mortality, a decreased length of ICU and hospital stay and a lower risk of drug-associated delirium. However, in some cases, prolonged or uninterrupted sedation may still be indicated, such as when patients develop intracranial hypertension following traumatic brain injury. The pharmacokinetics of sedative agents have clinical importance and may be altered by critical illness or injury, co-morbid conditions and/or drug-drug interactions. Although use of validated sedation scales to monitor depth of sedation is likely to reduce adverse events, they have no utility for patients receiving neuromuscular receptor blocking agents. Depth of sedation monitoring devices such as the Bispectral Index (BIS©) also have limitations. Among existing RCTs, no sedative agent has been reported to improve the risk of mortality among the critically ill or injured. Moreover, although propofol may be associated with a shorter time to tracheal extubation and recovery from sedation than midazolam, the risk of hypertriglyceridaemia and hypotension is higher with propofol. Despite dexmedetomidine being linked with a lower risk of drug-associated delirium than alternative sedative agents, this drug increases risk of bradycardia and hypotension. Among adults with severe traumatic brain injury, there are insufficient data to suggest that any single sedative agent decreases the risk of subsequent poor neurological outcomes or mortality. The lack of examination of confounders, including the type of healthcare system in which the investigation was conducted, is a major limitation of existing pharmacoeconomic analyses, which likely limits generalizability of their results.

ED50 and recovery times after propofol in rats with graded cirrhosis

BACKGROUND

Patients with end-stage liver disease have increased sensitivity to general anesthetics. In this study, we sought to quantify sensitivity to propofol as a function of the degree of liver disease, in a rat model of cirrhosis.

METHODS

Liver disease was induced by carbon tetrachloride (CCl(4)) injections for 6, 9, or 12 weeks in 3 study groups. Control rats received saline injections on the same schedule as CCl(4)-injected rats. A second control (comparison) group was treated with phenobarbital for a week followed by 9 weeks of phenobarbital and 10% ethanol in drinking water. Liver function was assessed by liver function tests and pathologic scoring of liver histology.

RESULTS

Progressively worse cirrhosis was associated with longer CCl(4) treatment by histologic criteria, by hypersplenism, liver to body weight ratios, and liver function tests. The major findings were that mild liver disease (either steatosis or fibrosis) was not associated with increased propofol sensitivity, but recovery times after propofol bolus and propofol infusion were significantly increased in rats with more severe liver fibrosis.

CONCLUSION

Propofol sensitivity is not significantly affected in the setting of mild liver disease, similar to clinical observations, but end-stage liver disease (fibrosis) is associated with significantly prolonged time to recovery after propofol infusion. The progressive liver disease model used in these studies is useful for rigorously studying anesthetic sensitivity as a function of degree of hepatocellular-fibrotic liver disease.

Recovery profile of patients undergoing nasal surgical procedures: a comparison between sevoflurane and propofol

OBJECTIVES

To compare the recovery profile of sevoflurane and propofol in nasal surgical procedures.

DESIGN

A prospective, double blind, randomized study

SETTING

King Abdul Aziz University Hospital, Riyadh, Saudi Arabia, a tertiary care teaching hospital, attached with King Saud University, Riyadh Saudi Arabia.

PATIENTS

60 ASA I-II patients age between 18-35 years, and weighing 50-80 kg, scheduled for nasal surgical procedures.

METHODS

Patients were assigned randomly to one of the two groups, the Sevoflurane Group-S (n = 30) & the Propofol Group-P (n = 30). Anesthetic induction was carried out using propofol 2.0mg/kg.in both the groups. Cis-atracurium 0.15mg/kg was given for intubation. Airway was protected with a throat pack around the endo-tracheal tube. Fentanyl 1microgram/kg was given as bolus followed by infusion at a rate of 1 microgram/kg/ hour. Anesthesia was maintained with sevoflurane 2% in Group-S, and propofol infusion at a rate of 200 microgram/kg/min. in Group-P. 50% oxygen in nitrous oxide was given in both the groups. At the end of surgery, patients were extubated after reversal of the neuromuscular block. Immediate recovery was assessed by recording the time to breathe spontaneously, time to extubation, and time of spontaneous eyes movements from the time of giving reversal. Ketoprofen 1.5mg/kg intramuscularly was given to all patients before transfer to (PACU). In PACU, sedation score was assessed for 45 min. Intermediate recovery was assessed by TDT and DSST at 15, 30 and 45 min. Time taken to state name and father's name was recorded.

RESULTS

Patients in Group-S breathed significantly earlier than those in Group-P. Group-P showed significantly better performance with TDT at 45 min and with DSST at 30 and 45 min.

CONCLUSIONS

We conclude that both sevoflurane and propofol provide early and comparable post anesthesia recovery for patients undergoing nasal surgical procedures.

Therapy of intracranial hypertension in patients with fulminant hepatic failure

Severe intracranial hypertension (IH) in the setting of fulminant hepatic failure (FHF) carries a high mortality and is a challenging disease for the critical care provider. Despite considerable improvements in the understanding of the pathophysiology of cerebral edema during liver failure, therapeutic maneuvers that are currently available to treat this disease are limited. Orthotopic liver transplantation is currently the only definitive therapeutic strategy that improves outcomes in patients with FHF. However, many patients die prior to the availability of donor organs, often because of cerebral herniation. Currently, two important theories prevail in the understanding of the pathophysiology of IH during FHF. Ammonia and glutamine causes cytotoxic cerebral injury while cerebral vasodilation caused by loss of autoregulation increases intracranial pressure (ICP) and predisposes to herniation. Although ammonia-reducing strategies are limited in humans, modulation of cerebral blood flow seems promising, at least during the early stages of hepatic encephalopathy. ICP monitoring, transcranial Doppler, and jugular venous oximetry offer valuable information regarding intracranial dynamics. Induced hypothermia, hypertonic saline, propofol sedation, and indomethacin are some of the newer therapies that have been shown to improve survival in patients with severe IH. In this article, we review the pathophysiology of IH in patients with FHF and outline various therapeutic strategies currently available in managing these patients in the critical care setting.

Prediction of total propofol clearance based on enzyme activities in microsomes from human kidney and liver

OBJECTIVE

Propofol is commonly used for anesthesia and sedation in intensive care units. Approximately 53% of injected propofol is excreted in the urine as the glucuronide and 38% as hydroxylated metabolites. Liver, kidneys and intestine are suspected as clearance tissues. We investigated the contribution of the liver and kidneys to propofol metabolism in humans using an in vitro-in vivo scale up approach.

METHODS

Renal tissue was obtained from five patients who received nephrectomies. Each renal hydroxylation and glucuronidation enzymatic activities in microsomal fractions from patients were performed discretely and their estimation based on the decrease of propofol concentration. Hepatic hydroxylation and glucuronidation activities were also performed separately using human liver microsomes. This estimation is based on the decrease of propofol concentration, assuming that the contribution of hydroxylation activity without NADPH-generating system and glucuronidation activity without UDPGA in each microsomal fraction are negligible. Both renal and hepatic clearances were estimated assuming a well-stirred model.

RESULTS

Enzymatic activity of propofol oxidation in renal microsomes was negligible. Although glucuronidation activity in microsomes from kidneys was comparable to that from liver, the hepatic intrinsic clearance predicted from in vitro study was higher than that in kidneys due to the larger tissue volume and higher protein concentration. However, glucuronidation clearance in kidney is relatively similar to that in liver because of blood flow limitation of clearance in both tissues.

CONCLUSION

The high degree of hydroxylation activity in liver microsomes is consistent with the blood flow-limited hepatic clearance of propofol. Although the activity of propofol glucuronidation in liver is higher, glucuronidation in kidney may be a substantial contributor.

Effect of continuous infusion of propofol on its concentration in blood with and without the liver in pigs

In living donor liver transplantation, propofol, an intravenous anesthetic drug, has recently been used in both donors and recipients. Propofol is known to have intra- and extrahepatic metabolic pathways, but the effect of its continuous infusion during a long-term anhepatic state is yet to be determined. Recently, we successfully established a simplified pig model of the complete anhepatic state. In this state, we first evaluated hemodynamic parameters relating to the pharmacokinetics of continuously infused propofol (6 mg.kg(-1) x h(-1)). No significant changes in the concentration of hemoglobin or in hemodynamic parameters other than the heart rate were observed during the anhepatic phase when porpofol was continuously infused at the rate that maintains the state. Blood propofol concentrations in the mixed vein, artery, and portal vein were stable during the anhepatic phase. Finally, we confirmed the pharmacokinetics of continuously infused propofol using orthotropic liver transplantation in miniature pigs. The propofol concentration did not change markedly during the transplant procedure. In conclusion, the pharmacokinetics of continuously infused propofol was almost stable with and without the liver in pigs. Extrahepatic metabolism of propofol might help prevent changes in propofol concentrations.

Kidneys contribute to the extrahepatic clearance of propofol in humans, but not lungs and brain

AIMS

The principal site for the metabolism of propofol is the liver. However, the total body clearance of propofol is greater than the generally accepted hepatic blood flow. In this study, we determined the elimination of propofol in the liver, lungs, brain and kidneys by measuring the arterial-venous blood concentration at steady state in patients undergoing cardiac surgery.

METHODS

After induction of anaesthesia, propofol was infused continuously during surgery. For measurement of propofol concentration, blood samples were collected from the radial and pulmonary artery at predetermined intervals. In addition, blood samples from hepatic and internal jugular vein were collected at the same times in 19 patients in whom a hepatic venous catheter was fitted and the other six in whom an internal jugular venous catheter was fitted, respectively. In six out of 19 patients fitted with a hepatic venous catheter, blood samples from the radial artery and the renal vein were also collected at the same time, when the catheter was inserted into the right renal vein before insertion into the hepatic vein.

RESULTS

Hepatic clearance of propofol was approximately 60% of total body clearance. The hepatic extraction ratio of propofol was 0.87 +/- 0.09. There was no significant difference in the concentration of propofol between the radial, pulmonary arteries and internal jugular vein. However, a high level of propofol extraction in the kidneys was observed--the renal extraction ratio being 0.70 +/- 0.13.

CONCLUSIONS

We have demonstrated substantial renal extraction of propofol in human. Metabolic clearance of propofol by the kidneys accounts for almost one-third of total body clearance and may be the major contributor to the extrahepatic elimination of this drug.

Plasma propofol concentrations during orthotopic liver transplantation

OBJECTIVE

The aim of this study was to investigate the changes in plasma concentrations of propofol in three phases (the paleohepatic, anhepatic, and neohepatic phases) during orthotopic liver transplantation (OLT) using target-controlled infusion (TCI).

METHODS

Ten patients undergoing OLT without venovenous bypass were studied (age 29-53 years, weight 56-79 kg). After intubation, a non-hypnotic target concentration of propofol 0.5 microg ml(-1) using a Diprifusor pump (Zeneca Pharmaceuticals, Macclesfield, UK) was administered as a supplement anesthesia throughout the procedure. Plasma samples were obtained in each phase for propofol assay, respectively. Performance parameters for the Diprifusor system in each phase, the percentage median performance error (MDPE), the percentage median absolute performance error (MDAPE), and the percentage median absolute constancy error (MDACE) were evaluated.

RESULTS

In all patients, measured plasma propofol concentrations were several times higher than Diprifusor values in each phase during the procedure. In nine patients, propofol concentrations in the anhepatic phase were higher than those in the paleohepatic or neohepatic phase (P < 0.05). There were no significant differences between the paleohepatic and neohepatic phases. Interindividual variation of the plasma propofol concentrations was significant (P < 0.05). Percentage median performance error of Diprifusor in each phase, as well as MDAPE, was large (>300%) and was significantly higher in the anhepatic phase (P < 0.01), whereas MDACE was relatively small and there was no significant difference between phases.

CONCLUSIONS

Models used by Diprifusor are not suitable for liver transplantation patients. A further study should be performed in order to determine all pharmacokinetic parameters of propofol in these patients.

Total intravenöse Anästhesie mit Propofol und Remifentanil

INTRODUCTION

The aim of this study was to investigate efficacy and tolerability of propofol, remifentanil and cisatracurium or mivacurium in routine anesthetic practice.

PATIENTS AND METHODS

A total of 6,161 patients scheduled for abdominal or orthopedic surgery were included in this open multicenter phase IV study. Perioperative hemodynamics as well as induction, recovery and discharge times, anesthetics, frequency of PONV and side-effects were studied.

RESULTS

Quality of induction and maintenance of anesthesia were evaluated by anesthesiologists to be good or very good in 88%. 86% of the patients assessed anesthesia as good or very good. Adverse events were reported for 28 patients (0.45%), with hypotension and bradycardia being most frequent. Recovery was evaluated by anesthesiologists to be good or very good in 88%, surgeons and nursing staff assessed the TIVA as good or very good in 90%. Most frequent postoperative complaints were pain (16.7%), nausea (6.1%), shivering (3.1%) and vomiting (0.7%).

CONCLUSIONS

The study showed that total intravenous anesthesia using propofol, remifentanil and cisatracurium or mivacurium is safe, tolerable and effective and has a high degree of acceptance.

Blood Concentration of Propofol in a Patient with Delayed Emergence from Propofol-nitrous Oxide Anesthesia

We measured the blood concentration of propofol in a patient with delayed emergence from propofol-nitrous oxide anesthesia. A 78-year-old man underwent subtotal gastrectomy under both epidural and propofol-nitrous oxide anesthesia and did not regain consciousness soon after termination of propofol infusion. Preoperative laboratory examination revealed anemia and a low blood total protein concentration, but there was no evidence of impaired liver function. While the anesthesiologists were waiting for the patient to regain consciousness, a surgeon mentioned that the common hepatic artery might have been occluded during surgical manipulation. Arterial blood samples were obtained 50 and 80 minutes after termination of propofol infusion, and the blood concentration of propofol was measured. We considered that clearance of propofol through the hepatic route may have been impaired; however, the actual blood concentrations of propofol were not significantly increased compared with the respective blood concentrations obtained in the simulation. Therefore, the acute liver damage did not significantly impair elimination of propofol. Because most propofol molecules in the blood bind to proteins and erythrocytes, it is suspected that the anemia and low blood total protein concentration led to an increase in the free fraction of propofol in the blood, thereby delaying emergence from anesthesia.

Influence of formulation on propofol pharmacokinetics and pharmacodynamics in anesthetized patients

BACKGROUND

In anesthesia with propofol, variability persists besides sophisticated effect targeting. Drug formulation may be another factor. We have analyzed, retrospectively, the pharmacokinetics (PK) and pharmacodynamics (PD) in monitored surgery patients anesthetized with one each of five formulations of propofol.

METHODS

Propofol 1% ('form' 1: Diprivan(Zeneca Limited, Macclesfield, UK), 2: Recofol(Schering Espana, Madrid, Spain), 3: Ivofol(Juste, Madrid, Spain), 4: Propofol Abbott (Abbott Laboratories, Madrid, Spain), 5: Fresenius (Fresenius Kabi Espana, Barcelona, Spain)) was administered to 77 ASA I-II patients of age [mean (range) 44 (18-65) years]. Induction of anesthesia was with varying propofol doses up to endpoints of either 60 on the Bispectral Index system (BIS) in group I (n = 48, model development) or standard clinical signs in group II (n = 29, validation). Maintenance was with three 10-min infusions of 10, 8 and 6 mg kg(-1) h(-1). Three blood samples were obtained from each subject, immediately after induction, and at 15 and 30 min on maintenance, with BIS and hemodynamic variables recorded at these times also. Total and free blood concentrations (Cb) of propofol were determined with HPLC. Pharmacokinetic and PD models with link equilibration rate ke0, were studied with a mixed-effects procedure (NONMEM).

RESULTS

The induction dose (group I) showed large interindividual variability [mean (range) 163 (90-290 mg)] that correlated significantly with age, basal systolic blood pressure and formulation. The PK of propofol (basic model) was described by a one-compartment model with (typical value [interindividual coefficient of variation percent (CV%)]) CL=2.30 l min(-1) (27%) and V=8.40 l (80%). Weight (WT) and formulation, within NONMEM, were found to be significant covariates for CL and V, reducing their CV% to 25% and 74%, respectively. The final PK/PD model, which includes formulation, showed a 50% reduction in the CV% for both the ke0 and the residual error. This PK/PD model was validated in group II with 33% precision and no bias.

CONCLUSION

The PK and PD are not equal for all formulations, which contributes to an increase in variability of the observed effect.

Relative antioxidant capacities of propofol and its main metabolites

The antioxidant activity of propofol, a widely used anesthetic, has previously been demonstrated, but no study has focused on propofol metabolites although propofol undergoes extensive metabolism. In the present study, the antioxidant properties of propofol and its metabolites were studied by measuring malondialdehyde (MDA) produced from lipid peroxidation by microsomes triggered with several free radical generating systems. True MDA determination was performed using a specific high performance liquid chromatography technique. Gas chromatography-isotope ratio mass spectrometry methodology was also used to assess the antioxidant action in a homogeneous aqueous environment. Propofol, 2,6-di-isopropyl-1,4-quinol (1,4-quinol) metabolite and 3,5-di- tert-butyl-4-hydroxytoluene markedly inhibit lipid peroxidation at concentrations lower than 5 microM. The binding of the glucuroconjugated moiety to either one of two hydroxyl groups of 1,4-quinol lowers the radical scavenging activity. Propofol glucuronide did not exert any radical scavenging activity except when peroxidation was induced with tert-butylhydroperoxide. Our data demonstrate that propofol and its metabolites inhibit lipid peroxidation at concentrations similar to those measured in human plasma during anesthesia. Their antioxidant efficiency is influenced by several factors, including the type of radical initiator involved and the site of radical production.

Dosage scheme for propofol in children under 3 years of age

BACKGROUND

Propofol is a well-known drug for adults for total intravenous anaesthesia. Since 1999, the use of propofol has been approved for children less than 3 years of age. However, a suitable dosage scheme for these age groups was not available. The purpose of this study was to describe our clinical experience with the use of a new dosage scheme for propofol in patients under 3 years of age, based on experimental data and known pharmacological principles in children.

METHODS

A pilot study of 50 patients undergoing TIVA was performed to adapt the existing adult dosage scheme to the requirements of the younger population. Total number and time of administration of boluses and time to awakening were registered and used as criteria to adjust the dosage scheme. The subsequent dosage scheme was then evaluated in 2271 children undergoing anaesthesia for various procedures. Usual anaesthetic parameters were measured to monitor the safety of the patient: ECG, O2 saturation, respiratory frequency and blood pressure. Most of the patients were mechanically ventilated; only 15% were breathing spontaneously.

RESULTS

Overall, few side effects were recorded [bradycardia (12%), blood pressure fall (8%), desaturation (1%)], which were easily countered by routine measures.

CONCLUSIONS

This dosage scheme provides safe and smooth anaesthesia in children less than 3 years of age and is therefore a useful tool for a TIVA technique in small children.

Criteria for immediate postoperative extubation in adult recipients following living-related liver transplantation with total intravenous anesthesia

STUDY OBJECTIVE

To evaluate whether our criteria for immediate postoperative extubation predicts successful extubation in living-related liver transplantation of the right lobe, and to test the effects of our standardized anesthetic technique on the success of immediate postoperative extubation.

DESIGN

Open-label, descriptive study.

SETTING

University hospital.

PATIENTS

6 ASA physical status III and IV patients with end-stage liver disease undergoing living-related liver transplantation of the right lobe.

INTERVENTIONS

Patients received a standardized anesthetic technique with propofol, remifentanil, and cisatracurium. They were extubated when they met our criteria for immediate postoperative extubation: good donor liver function, <10 U packed red blood cells administered, hemodynamic stability, and alveolar-arterial oxygen gradient <200 mmHg.

MEASUREMENTS AND MAIN RESULTS

At the end of surgery, four of the six patients fulfilled our criteria for immediate postoperative extubation. They were uneventfully extubated rapidly after surgery and soon arrived in the intensive care unit. Their postoperative stay in the operating room was only 36 minutes (range: 30 to 42 min). No patient required reintubation in the operating room or the intensive care unit. They had no recorded hemodynamic or respiratory problems postoperatively.

CONCLUSIONS

Immediate extubation of selected living-related liver transplant recipients can be a safe procedure. Anesthetic management to immediate extubation seems appropriate and the derived guidelines appear acceptable.

The role of hepatic and extrahepatic UDP-glucuronosyltransferases in human drug metabolism

At present, the methods and enzymology of the UDP-glucuronosyltransferases (UGTs) lag behind that of the cytochromes P450 (CYPs). About 15 human UGTs have been identified, and knowledge about their regulation, substrate selectivity, and tissue distribution has progressed recently. Alamethicin has been characterized as a treatment to remove the latency of microsomal glucuronidations. Most UGT isoforms appear to have a distinct hepatic and/or extrahepatic expression, resulting in significant expression in kidney, intestine, and steroid target tissues. The gastrointestinal tract possesses a complex expression pattern largely containing members of the UGT1A subfamily. Thus, these forms are poised to participate in the first pass metabolism of oral drugs. The authors and others have identified a significant expression of UGT1A1 in human small intestine, an enzyme possessing considerable allelic variability and a polymorphic expression pattern in intestine. Intestinal glucuronidation therefore plays a major role not only in first pass metabolism, but also in the degree of interindividual variation in overall oral bioavailability. Due to issues such as significant genetic variability and tissue localization in first-pass organs, clearance due to UGT1A1 should be minimized for new drugs.

Propofol inhibits renal cytochrome P450 activity and enflurane defluorination in vitro in hamsters

PURPOSE

To determine the effect of propofol on renal cytochrome P450 activity and defluorination of enflurane.

METHODS

Renal microsomes were prepared by homogenization and differential centrifugation from pooled hamster kidneys. Defluorination of enflurane was assessed by measuring free fluoride metabolites after reacting enflurane with renal microsomes incubated with various concentrations, 0.05 - 1.0 mmol x L(-1) propofol in the NADPH-generating system. Drug metabolizing activities of renal cytochrome P450 mono-oxygenase enzymes were evaluated within microsomes preincubated with propofol and reacted with the specific marker substrates, aniline, benzo(a)pyrene, erythromycin and pentoxyresorufin, for cytochrome P450 2E1, 1A1, 3A4 and 2B1, respectively.

RESULTS

Renal defluorination of enflurane was inhibited by clinical concentrations, 0.05 mmol x L(-1) of propofol (P < 0.05). Dose-dependent inhibition of defluorination, aniline and benzo(a)pyrene hydroxylase within kidney microsomes was related to propofol concentration. Propofol demonstrated a profound inhibition of renal pentoxyresorufin dealkylase activity even at low concentrations, 0.05 mmol x L(-1) (P < 0.01). Propofol did not exhibit inhibition of erythromycin N-demethylation of kidney microsomes except at high concentration, 1.0 mmol x L(-1). Spectral analyses of key coenzymes of renal cytochrome P450 monooxygenase, cytochrome b5 and cytochrome c reductase, demonstrated an inhibition when incubated with high concentrations of propofol (P < 0.05).

CONCLUSION

In an in vitro study in an NADPH-generating system of hamster kidney microsomes, propofol, in clinical concentrations, exhibited a broad-spectrum of inhibition to renal monooxygenase activities and enflurane defluorination.

High-performance liquid chromatographic assay to detect hydroxylate and conjugate metabolites of propofol in human urine

This paper describes a HPLC method for the simultaneous detection of phase I (2,6-diisopropyl-1-4-quinol and 2,6-diisopropyl-1-4-quinone) and phase II (4-(2,6-diisopropyl-1-4-quinol)-sulphate, 1-(2,6-diisopropyl-1-4-quinol)-glucuronide, 4-(2,6-diisopropyl-1-4-quinol)-glucuronide, and propofol-glucuronide) metabolites of propofol in human urine samples. Separation was based on a simple mobile phase and a reversed-phase chromatographic column. Metabolite identification was performed by UV spectrum on a diode-array detector and by LC-APCI-MS. The identification was also carried out using in vitro incubation mixtures (cytosol and microsomes prepared from liver) from several species: human, rat and rabbit. This assay was performed using UV, fluorescence and electrochemical detection modes. Each of these was analyzed and discussed.

The influence of hypoxia and hyperoxia on the kinetics of propofol emulsion

PURPOSE

To study the effect of hypoxia and hyperoxia on the pharmacokinetics of propofol emulsion, hepatic blood flow and arterial ketone body ratio in the rabbit.

METHODS

Twenty four male rabbits were anesthetized with isoflurane (1.5-2%) in oxygen. After the surgical procedure, isoflurane administration was discontinued and intravenous propofol infusion (30 mg x kg(-1) x hr(-1)) was started. The infusion rate of propofol was maintained throughout the study. After an initial 90 min period of propofol infusion, rabbits were randomly allocated to one of three groups: hypoxia (F(I)O2 = 0.1), normoxia (F(I)O2 = 0.21), and hyperoxia (F(I)O2 = 1.0). Propofol infusion was continued under the allocated F(I)O2 for 60 min. Propofol concentrations in arterial blood, total body clearance of propofol, hepatic blood flow and arterial ketone body ratio were measured.

RESULTS

The mean arterial propofol concentration at the end of infusion was higher in the hypoxia group (15.2 +/- 2.8 microg x mL(-1), mean +/- SD) than in the normoxia (7.4 +/- 1.7) and hyperoxia (8.0 +/- 1.9) groups (P < 0.05). Total body clearance of propofol, hepatic blood flow and arterial ketone body ratio were all reduced in the hypoxia group (P < 0.05). Total ketone body concentration in arterial blood increased in the hyperoxia group (P < 0.01).

CONCLUSION

Hypoxia produced an accumulation of propofol in blood and reduced propofol clearance. These changes could result from decreased hepatic blood flow and low cellular energy charge in the liver. Hyperoxia, on the other hand, increased total ketone body in arterial blood.

Pediatric sedation with analgesia

Sedation with analgesia is frequently required to perform painful or invasive procedures in children. The best medication combination for pediatric sedation with analgesia is yet to be identified. Sixty-four of 243 total sedation with analgesia procedures from January 1994 through August 1995 were randomly chosen for descriptive retrospective review and analysis. Four minor complications from the procedures were identified, and recovery was complete in all cases. One medication combination (fentanyl 1 microg/kg with propofol 1.5 to 2 mg/kg, followed by an infusion of 150 microg/kg/min) provided the shortest mean time to dismissal (17.8 minutes v 38 minutes) when compared with other combinations used. No episodes of respiratory depression, hypotension, or nausea and vomiting occurred in the fentanyl/propofol group. These results show that fentanyl/propofol was superior to other medications used during this study period for pediatric sedation with analgesia. Prospective comparison of this medication combination with other short-acting agents in patients undergoing both elective and emergency procedures is necessary.

Venovenous bypass in adult orthotopic liver transplantation: routine or selective use?

BACKGROUND

The role of venovenous bypass (VVB) during orthotopic liver transplantation (OLT) remains controversial. The aims of this study were to evaluate the current role of VVB at all major centers in North America, to examine the results of OLT and complications of VVB between two periods with a strict policy for routine versus selective use of VVB, and to review the literature.

STUDY DESIGN

A survey of 50 major liver transplant centers was conducted using mailed questionnaires. A retrospective chart review was performed for 547 OLT patients having transplantation during two distinct periods with a strict policy for routine versus selective use of VVB at the University of Toronto, Canada, and at Duke University Medical Center, Durham, North Carolina. The literature was reviewed with a focus on the benefits and indications for routine versus selective use of VVB.

RESULTS

Thirty-eight (76%) of 50 centers responded. Sixteen (42%) of them used VVB routinely, with a reported complication rate of 10-30%. Lymphocele and hematoma were the most common complications, but patients having major vascular injury, air embolism, and death were reported. A recent change to selective use of VVB was reported in 30% of the centers (11 of 38). In the Duke-Toronto series, the complication rates were similar between the two periods, at 13.4% and 18.8%, respectively. The outcome of OLT was not influenced by the policy of routine or selective use of VVB.

CONCLUSIONS

There is a trend away from the routine use of VVB during OLT. Intraoperative hemodynamic instability during the hepatectomy and a failed trial of hepatic venous occlusion were the most important criteria for using VVB. We conclude that VVB should be used selectively to avoid associated complications and to decrease operative time and costs.

Pharmacokinetics of drugs used in critically ill adults

Critically ill patients exhibit a range of organ dysfunctions and often require treatment with a variety of drugs including sedatives, analgesics, neuromuscular blockers, antimicrobials, inotropes and gastric acid suppressants. Understanding how organ dysfunction can alter the pharmacokinetics of drugs is a vital aspect of therapy in this patient group. Many drugs will need to be given intravenously because of gastrointestinal failure. For those occasions on which the oral route is possible, bioavailability may be altered by hypomotility, changes in gastrointestinal pH and enteral feeding. Hepatic and renal dysfunction are the primary determinants of drug clearance, and hence of steady-state drug concentrations, and of efficacy and toxicity in the individual patient. Oxidative metabolism is the main clearance mechanism for many drugs and there is increasing recognition of the importance of decreased activity of the hepatic cytochrome P450 system in critically ill patients. Renal failure is equally important with both filtration and secretion clearance mechanisms being required for the removal of parent drugs and their active metabolites. Changes in the steady-state volume of distribution are often secondary to renal failure and may lower the effective drug concentrations in the body. Failure of the central nervous system, muscle, the endothelial system and endocrine system may also affect the pharmacokinetics of specific drugs. Time-dependency of alterations in pharmacokinetic parameters is well documented for some drugs. Understanding the underlying pathophysiology in the critically ill and applying pharmacokinetic principles in selection of drug and dose regimen is, therefore, crucial to optimising the pharmacodynamic response and outcome.

In vivo assessment of intestinal, hepatic, and pulmonary first pass metabolism of propofol in the rat

PURPOSE

The relative contribution of the intestinal mucosa, liver and lung to the in vivo disposition of propofol in the rat was investigated.

METHODS

Propofol (4.9-5.1 mg.kg-1) was administered to groups of rats (n = 4) via the intra-arterial, intravenous, hepatic portal venous and oral routes. The AUC's of propofol were estimated and the fractions of the administered dose escaping first pass metabolism by the gut wall (fG), liver (fH) and lung (fL) were calculated. In addition, transport experiments were carried out using Caco-2 cell monolayers to rule out the possibility that intestinal permeability is limiting the oral absorption of propofol.

RESULTS

Values for fG, fH and fL were the following: 0.21 +/- 0.07, 0.61 +/- 0.13, and 0.82 +/- 0.09, respectively. The apparent permeability coefficient of propofol across Caco-2 cell monolayers was 24.2 +/- 0.3 x 10(-6) cm.sec-1, which is similar to the apparent permeability coefficient obtained for propranolol (30.7 +/- 1.7 x 10(-6) cm.sec-1), a compound known to easily cross the intestinal epithelial membranes. The formation of propofol glucuronide, a major metabolite of propofol, could not be demonstrated during the flux experiments across the Caco-2 cell monolayers.

CONCLUSIONS

The intestinal mucosa is the main site of first pass metabolism following oral administration of propofol in the rat. Intestinal metabolism could therefore also contribute to the systemic clearance of propofol.