Advances in propofol pharmacokinetics and pharmacodynamics

Effect of Butorphanol-Medetomidine and Butorphanol-Dexmedetomidine on Echocardiographic Parameters during Propofol Anaesthesia in Dogs

This study compared the effects of butorphanol-medetomidine and butorphanol-dexmedetomidine combinations on echocardiographic parameters during propofol anaesthesia in dogs. The dogs were randomly divided into two groups. In the butorphanol-medetomidine (BM) group, butorphanol (0.2 mg/kg) and medetomidine (15 μg/kg) were intravenously administered; in the butorphanol-dexmedetomidine (BD) group, butorphanol (0.2 mg/kg) and dexmedetomidine (7.5 μg/kg) was used. Anaesthesia was induced with propofol and maintained with a constant-rate infusion of propofol (0.2 mg/kg/min). The echocardiographic parameters were assessed in conscious dogs (T0). Echocardiography was conducted again at 10 min post premedication (T1), followed by assessments at 30 (T2), 60 (T3), and 90 (T4) mins. The dogs were subjected to diagnostic procedures (radiography, computed tomography) under anaesthesia. A significant reduction in heart rate and cardiac output was noted in both groups at T1. There was no significant difference in the stroke volume between the BM and BD groups. The application of butorphanol-dexmedetomidine caused a significant increase in the left ventricular internal diameter in diastole and the diameter of the left atrium compared to that caused by butorphanol-medetomidine. This study documented that butorphanol-medetomidine and butorphanol-dexmedetomidine combinations caused similar reductions in heart rate and cardiac output in both groups. 'New´ valvular regurgitation occurred following their administration.

Heart rate, arterial pressure and propofol-sparing effects of guaifenesin in dogs

OBJECTIVE

To evaluate the heart rate (HR) and systemic arterial pressure (sAP) effects, and propofol induction dose requirements in healthy dogs administered propofol with or without guaifenesin for the induction of anesthesia.

STUDY DESIGN

Prospective blinded crossover experimental study.

ANIMALS

A total of 10 healthy adult female Beagle dogs.

METHODS

Dogs were premedicated with intravenous (IV) butorphanol (0.4 mg kg^-1) and administered guaifenesin 5% at 50 mg kg^-1 (treatment G50), 100 mg kg^-1 (treatment G100) or saline (treatment saline) IV prior to anesthetic induction with propofol. HR, invasive sAP and respiratory rate (f_R) were recorded after butorphanol administration, after guaifenesin administration and after propofol and endotracheal intubation. Propofol doses for intubation were recorded. Repeated measures analysis of variance (anova) was used to determine differences in propofol dose requirements among treatments, and differences in cardiopulmonary values over time and among treatments with p < 0.05 considered statistically significant.

RESULTS

Propofol doses (mean ± standard deviation) for treatments saline, G50 and G100 were 3.3 ± 1.0, 2.7 ± 0.7 and 2.1 ± 0.8 mg kg^-1, respectively. Propofol administered was significantly lower in treatment G100 than in treatment saline (p = 0.04). In treatments G50 and G100, HR increased following induction of anesthesia and intubation compared with baseline measurements. HR was higher in treatment G100 than in treatments G50 and saline following induction of anesthesia. In all treatments, sAP decreased following intubation compared with baseline values. There were no significant differences in sAP among treatments. f_R was lower following intubation than baseline and post co-induction values and did not differ significantly among treatments.

CONCLUSIONS AND CLINICAL RELEVANCE

When administered as a co-induction agent in dogs, guaifenesin reduced propofol requirements for tracheal intubation. HR increased and sAP and f_R decreased, but mean values remained clinically acceptable.

Disturbance of Key Cellular Subproteomes upon Propofol Treatment Is Associated with Increased Permeability of the Blood-Brain Barrier

Background: Propofol is a short-acting anesthetic, which is often used for induction and maintenance of general anesthesia, sedation for mechanically ventilated adults and procedural sedation. Several side effects of propofol are known and a substantial number of patients suffer from post-operative delirium after propofol application. In this study, we analyzed the effect of propofol on the function and protein expression profile on a proteome-wide scale. Methods: We cultured human brain microvascular endothelial cells in absence and presence of propofol and analyzed the permeability of the blood-brain barrier (BBB) by fluorescein passage and protein abundance on a proteome-wide scale by mass spectrometry. Results: Propofol interfered with the function of the blood-brain barrier. This was not due to decreased adhesion of propofol-treated human brain microvascular endothelial cells. The proteomic analysis revealed that some key pathways in these cells were disturbed, such as oxygen metabolism, DNA damage recognition and response to stress. Conclusions: Propofol has strong effects on protein expression which could explain several side effects of propofol.

The influence of cardiac output on propofol and fentanyl pharmacokinetics and pharmacodynamics in patients undergoing abdominal aortic surgery

Cardiac output (CO) is expected to affect elimination and distribution of highly extracted and perfusion rate-limited drugs. This work was undertaken to quantify the effect of CO measured by the pulse pressure method on pharmacokinetics and pharmacodynamics of propofol and fentanyl administrated during total intravenous anesthesia (TIVA). The data were obtained from 22 ASA III patients undergoing abdominal aortic surgery. Propofol was administered via target-controlled infusion system (Diprifusor) and fentanyl was administered at a dose of 2-3 µg/kg each time analgesia appeared to be inadequate. Hemodynamic measurements as well as bispectral index were monitored and recorded throughout the surgery. Data analysis was performed by using a non-linear mixed-effect population modeling (NONMEM 7.4 software). Three compartment models that incorporated blood flows as parameters were used to describe propofol and fentanyl pharmacokinetics. The delay of the anesthetic effect, with respect to plasma concentrations, was described using a biophase (effect) compartment. The bispectral index was linked to the propofol and fentanyl effect site concentrations through a synergistic Emax model. An empirical linear model was used to describe CO changes observed during the surgery. Cardiac output was identified as an important predictor of propofol and fentanyl pharmacokinetics. Consequently, it affected the depth of anesthesia and the recovery time after propofol-fentanyl TIVA infusion cessation. The model predicted (not observed) CO values correlated best with measured responses. Patients' age was identified as a covariate affecting the rate of CO changes during the anesthesia leading to age-related difference in individual patient's responses to both drugs.

Application of Intravenous Lidocaine in Obese Patients Undergoing Painless Colonoscopy: A Prospective, Randomized, Double-Blind, Controlled Study

OBJECTIVE

Propofol for procedural sedation and analgesia (PSA) for colonoscopy can result in a high prevalence of severe respiratory depression. Studies have shown that intravenous (IV) infusion of lidocaine can reduce propofol requirements significantly and increase the ventilatory response to carbon dioxide in humans. We tested the hypothesis that IV lidocaine could improve propofol-induced respiratory depression in obese patients during colonoscopy.

METHODS

Ninety obese patients scheduled for painless colonoscopy were randomized to receive lidocaine (1.5 mg/kg, then 2 mg/kg/h, IV) or the same volume of 0.9% saline. Intraoperative sedation was provided by propofol. The primary outcome was the number of oxygen-desaturation episodes. Secondary outcomes were: the number of apnea episodes; total propofol consumption; time to the first hypoxia episode; time to consciousness loss; intraoperative hemodynamic parameters; awakening time; adverse events; duration of post-anesthesia care unit (PACU) stay; satisfaction of endoscopists and patients.

RESULTS

Demographic characteristics between the two groups were comparable. The number of oxygen-desaturation episodes in group L (1.49±1.12) decreased by 0.622 (P=0.018) compared with that in group N (2.11±1.32), and the number of apnea episodes in group L decreased by 0.533 (P<0.001). Kaplan-Meier curves showed that the median time to the first hypoxia episode was longer in group L (86.78 s) than that in group N (63.83 s) (Log rank P=0.0008). The total propofol consumption, awakening time, and duration of PACU stay were reduced in group L. There was no significant difference in the prevalence of adverse events (P>0.05 for all). Satisfaction scores for endoscopists and patients in group L were higher than that in group N (P<0.001).

CONCLUSION

Intravenous infusion of lidocaine could significantly reduce the number of oxygen-desaturation and apnea episodes in obese patients during painless colonoscopy. This method is worthy of clinical promotion.

CLINICAL TRIALS REGISTRATION

ChiCTR2000028937.

[Drugs for intravenous induction of anesthesia: ketamine, midazolam and synopsis of current hypnotics]

Ketamine and midazolam form the endpoint of a series of articles about intravenous induction of anesthesia . Both substances can be used as single induction hypnotic drugs; however, in practice, this is unusual. Both substances, with the exception of a few very specific indications and clinical situations, are more frequently used in combination or with one of the more common alternatives propofol, barbiturates and etomidate. The reasons are the activity and side effects of both substances and their positive characteristics are used more as a supplement. In the concluding comparison the five discussed induction hypnotics are judged against each other. The use in certain clinical constellations and in special patient populations is evaluated individually for each substance. It is highlighted which drug appears most appropriate in which situation. As methohexital is nowadays only administered in very few clinical situations, this substance is not included in the comparative assessment.

Hemodynamic variables in piglets anesthetized with isoflurane or propofol, kept under spontaneous ventilation and FIO2 of 0.5

ABSTRACT This study aimed to evaluate comparatively the effects of propofol or isoflurane on hemodynamic variables in piglets that received inspired oxygen fraction (FIO2) of 0.5 under spontaneous ventilation. Therefore, sixteen piglets weighing 16±1.1kg, were randomly divided into two groups: GI (Isoflurane and FIO2 of 0.5) and GP (Propofol and FIO2 of 0.5). Heart rate (HR), systolic, diastolic and mean arterial pressure (SAP, DAP and MAP), central venous pressure (CVP), cardiac output (CO), mean pulmonary arterial pressure (mPAP) and mean capillary pulmonary pressure (mCPP) were assessed 40 minutes after anesthetic induction (T0), followed by 15 minutes intervals (from T15 to T60). The variables cardiac index (CI), stroke volume (SV), stroke index (SI), total peripheral resistance (TPR), total peripheral resistance index (TPRI), pulmonary vascular resistance (PVR), and pulmonary vascular resistance index (PVRI) were calculated. SAP and TPRI were significantly different between groups at T30 and T60 (P< 0.05) with higher GP values being recorded. There were no differences in the other variables, however, GP presented mean closer to normality on most of the analyzed variables. Therefore, we conclude that total intravenous anesthesia with propofol presented greater stability of the hemodynamic variables evaluated.

[Drugs for intravenous induction of anesthesia: propofol]

In a series of articles dealing with hypnotics for induction of anesthesia, this article describes the development and current value of propofol. Its significance far exceeds that of a pure induction hypnotic (sedation in diagnostic and therapeutic procedures and on the intensive care unit). Propofol is also used for sedation in diagnostic and therapeutic procedures and on the intensive care unit. In the field of induction of anesthesia, the alternatives are barely used. Some contraindications are still controversial whereas others are no longer sufficiently anchored in the users' awareness (widespread off-label use). Adverse effects, such as injection pain, infection risk and propofol-related infusion syndrome (PRIS) could be significantly reduced by pharmacovigilance. With appropriate caution nearly the whole spectrum of anesthesiology patients can be treated using propofol. The hemodynamic side effects and the rare but potentially fatal PRIS are limitations. Further developments address the water solubility and the solubilizing agents of propofol.

Propofol sedation in colonoscopy: from satisfied patients to improved quality indicators

Background

Propofol-mediated sedation is safe and clearly associated with increased patient satisfaction. However, whether it results in a favorable effect on colonoscopy outcomes and performance compared to standard sedation with benzodiazepines/opiates remains unclear.

Objectives

To determine the effect of propofol-mediated sedation on colonoscopy-quality measures compared to traditional sedation.

Methods

A large cohort of 44,794 patients who had undergone sedated colonoscopies were included. Colonoscopy-quality indicators were examined in benzodiazepine/opiate-sedated patients and compared with a propofol-mediated sedation group. Adjustment for potential confounders, such as age, sex, quality of bowel preparation, procedural setting, and indication was performed.

Results

Patients who received propofol-mediated sedation were more likely, and in a dose-dependent manner, to have an enhanced polyp-detection rate (22.8% vs 20.9%, P<0.001), cecal intubation rate (90.4% vs 87.3%, P<0.001), and terminal ileum-intubation rate (6.4% vs 1.6%, P<0.001). On multivariate analysis, these findings were maintained, as propofol-mediated sedation use was significantly associated with improved colonoscopy indicators.

Conclusion

Propofol-mediated sedation during colonoscopy is associated with better examination performance and improved outcomes. Further prospective or randomized trials to support these findings are warranted.

Comparison of bolus versus continuous infusion of propofol for procedural sedation: a meta-analysis

OBJECTIVE

To compare the efficacy and safety of bolus infusion versus continuous infusion for propofol sedation.

METHODS

We searched OVID-MEDLINE, Embase, Cochrane Central Register of Controlled Trials (CENTRAL), Google Scholar, Koreamed, and Kmbase databases to identify all randomized controlled trials that compared bolus infusion with continuous infusion for propofol sedation. We evaluated propofol dose used, procedure, sedation, and recovery time. The incidences of respiratory and cardiovascular complications were also evaluated.

RESULTS

A total of 12 studies of 963 patients were included. The required propofol dose was significantly higher in continuous infusion compared with bolus infusion (standardized mean difference [SMD]: -0.44; 95% confidence interval [CI]: -0.71 to -0.16; I² = 84%). Sedation time was significantly longer in continuous infusion compared with bolus infusion (mean difference [MD]: -8.58 min; 95% CI: -15.13 to -2.03; I² = 44%). The recovery time and incidences of desaturation, airway intervention, hypotension, and bradycardia were comparable between bolus and continuous infusion.

CONCLUSIONS

Propofol sedation by continuous infusion required a higher dose of propofol compared with bolus infusion, but the recovery time and frequency of complications were similar.

A Review of Agents for Palliative Sedation/Continuous Deep Sedation: Pharmacology and Practical Applications

Continuous deep sedation at the end of life is a specific form of palliative sedation requiring a care plan that essentially places and maintains the patient in an unresponsive state because their symptoms are refractory to any other interventions. Because this application is uncommon, many providers may lack practical experience in this specialized area and resources they can access are outdated, nonspecific, and/or not comprehensive. The purpose of this review is to provide an evidence- and experience-based reference that specifically addresses those medications and regimens and their practical applications for this very narrow, but vital, aspect of hospice care. Patient goals in a hospital and hospice environments are different, so the manner in which widely used sedatives are dosed and applied can differ greatly as well. Parameters applied in end-of-life care that are based on experience and a thorough understanding of the pharmacology of those medications will differ from those applied in an intensive care unit or other medical environments. By recognizing these different goals and applying well-founded regimens geared specifically for end-of-life sedation, we can address our patients' symptoms in a more timely and efficacious manner.

Intermittent Bolus versus Continuous Infusion of Propofol for Deep Sedation during ABR/Nuclear Medicine Studies

Objective  A comparison of intermittent bolus (IB) versus continuous infusion of propofol for deep sedation. Material and Methods  A retrospective review of patients sedated for Auditory Brainstem Response (ABR)/nuclear medicine studies between September 2008 and February 2015. A ketamine bolus (0.5 mg/kg < 20 kg, 0.25 mg/kg > 20 kg) followed by propofol bolus of 1 mg/kg over 2 minutes. In the IB group, maintenance of deep sedation was with incremental bolus of 10 to 20 mg of propofol. In continuous infusion group (CG), maintenance was with a continuous infusion of 83 mcg/kg/min of propofol. Results  Of the 326 cases completed, 181 were in CG group and 145 were in IB group. There were no statistical differences in patient's age, weight, and American Society of Anesthesiologist (ASA) classification. The cardiovascular and respiratory parameters in the two groups were not different statistically. Mean total propofol dose was higher in CG group versus IB group (CG 7.6 mg ± 3.6 mg, IB 6.5 mg ± 3.6 mg; p  = 0.008). Procedure time in CG group was longer by 8 minutes compared with IB group (CG 49.8 min ± 25.4 min versus 42.3 min ± 19.2 min; p  = .003). CG group has both shorter recovery time (CG 8.1 min ± 4.7 min versus IB 10.0 min ± 8.5 min; p  = 0.01) and discharge time. Conclusion  Satisfactory sedation and completion of the procedure was accomplished with both sedation protocols.

The Role of the α2-Adrenoceptor Agonist Dexmedetomidine in Postsurgical Sedation in the Intensive Care Unit

Dexmedetomidine was evaluated for sedation of 401 postsurgical patients in this double-blind, randomized, placebocontrolled, multicenter trial. Dexmedetomidine or saline was started on arrival in the intensive care unit (ICU) (1.0 mcg/kg for 10 minutes), then titrated at 0.2 to 0.7 mcg/kg/h to effect. Patients could be given propofol if necessary. Morphine was administered for pain. Sixty percent of the dexmedetomidine patients required no other sedative to maintain an RSS ≥ 3; 21% required < 50 mg propofol. In contrast, 76% of the control group received propofol; 59% required ≥ 50 mg. Dexmedetomidine patients required significantly less morphine for pain relief (P < .001). Continuously given throughout the ICU stay, dexmedetomidine had no effect on respiratory rate, oxygen saturation, duration of weaning, or times to extubation. Nurses judged the dexmedetomidine patients were easier to manage. Later, fewer dexmedetomidine patients remembered pain or discomfort. The majority of dexmedetomidine patients maintained blood pressures within normal range, without rebound. Hypertension, atelectasis, and rigors occurred more frequently in the control group, while hypotension and bradycardia occurred more frequently in the dexmedetomidine group. Preoperative cardiovascular conditions were not risk factors for dexmedetomidine patients.

Propofol Pharmacokinetics and Estimation of Fetal Propofol Exposure during Mid-Gestational Fetal Surgery: A Maternal-Fetal Sheep Model

BACKGROUND

Measuring fetal drug concentrations is extremely difficult in humans. We conducted a study in pregnant sheep to simultaneously describe maternal and fetal concentrations of propofol, a common intravenous anesthetic agent used in humans. Compared to inhalational anesthesia, propofol supplemented anesthesia lowered the dose of desflurane required to provide adequate uterine relaxation during open fetal surgery. This resulted in better intraoperative fetal cardiac outcome. This study describes maternal and fetal propofol pharmacokinetics (PK) using a chronically instrumented maternal-fetal sheep model.

METHODS

Fetal and maternal blood samples were simultaneously collected from eight mid-gestational pregnant ewes during general anesthesia with propofol, remifentanil and desflurane. Nonlinear mixed-effects modeling was performed by using NONMEM software. Total body weight, gestational age and hemodynamic parameters were tested in the covariate analysis. The final model was validated by bootstrapping and visual predictive check.

RESULTS

A total of 160 propofol samples were collected. A 2-compartment maternal PK model with a third fetal compartment appropriately described the data. Mean population parameter estimates for maternal propofol clearance and central volume of distribution were 4.17 L/min and 37.7 L, respectively, in a typical ewe with a median heart rate of 135 beats/min. Increase in maternal heart rate significantly correlated with increase in propofol clearance. The estimated population maternal-fetal inter-compartment clearance was 0.0138 L/min and the volume of distribution of propofol in the fetus was 0.144 L. Fetal propofol clearance was found to be almost negligible compared to maternal clearance and could not be robustly estimated.

CONCLUSIONS

For the first time, a maternal-fetal PK model of propofol in pregnant ewes was successfully developed. This study narrows the gap in our knowledge in maternal-fetal PK model in human. Our study confirms that maternal heart rate has an important influence on the pharmacokinetics of propofol during pregnancy. Much lower propofol concentration in the fetus compared to maternal concentrations explain limited placental transfer in in-vivo paired model, and less direct fetal cardiac depression we observed earlier with propofol supplemented inhalational anesthesia compared to higher dose inhalational anesthesia in humans and sheep.

Mechanical ventilation during pregnancy: sedation, analgesia, and paralysis

Pregnant women occasionally require mechanical ventilation. Ventilated patients commonly need some form of analgesia and/or sedation with or without paralytics. The use of these agents is common in the intensive care unit setting, but most maternal-fetal medicine specialists are unfamiliar with their use. In the vast majority of cases, guidelines and recommendations regarding the use of these agents should be followed as recommended for nonpregnant individuals. This article discusses the most relevant issues of sedatives, analgesics, and neuromuscular blockers used in modern critical care practice.

Pharmacokinetics and pharmacodynamics of propofol in cancer patients undergoing major lung surgery

Despite the growing number of cancer cases and cancer surgeries around the world, the pharmacokinetics (PK) and pharmacodynamics (PD) of anesthetics used in this population are poorly understood. Patients operated due to cancer are usually in severe state and often require chemotherapy. It might affect the PK/PD of drugs used in this population. Therefore, in this study we explored the PK/PD of propofol in cancer patients having a major lung surgery. 23 patients that underwent a propofol-fentanyl total intravenous anesthesia were included in the analysis. A large set of demographic, biochemical and hemodynamic parameters was collected for the purpose of covariate analysis. Nonlinear mixed effect modeling in NONMEM was used to analyze the collected data. A three-compartment model was sufficient to describe PK of propofol. The anesthetic effect (AAI index) was linked to the propofol effect site concentrations through a sigmoidal E max model. A slightly higher value of clearance, a lower value of distribution clearance, and a decreased volume of peripheral compartment were observed in our patients, as compared with the literature values reported for healthy volunteers by Schnider et al. and by Eleveld et al. Despite these differences, both models led to a clinically insignificant bias of -8 and -1 % in concentration predictions, as reflected by the median performance error. The C e50 and propofol biophase concentration at the time of postoperative orientation were low and equaled 1.40 and 1.13 mg/L. The population PK/PD model was proposed for cancer patients undergoing a major lung surgery. The large body of studied covariates did not affect PK/PD of propofol significantly. The modification of propofol dosage in the group of patients under study is not necessary when TCI-guided administration of propofol by means of the Schnider model is used.

Predictors of severe hypotension in neurocritical care patients sedated with propofol

INTRODUCTION

Propofol is used extensively in neurocritical care (NCC) due to its pharmacologic properties allowing for facilitation of serial neurologic examinations. Despite widespread use, few studies have identified risk factors for hypotension in these patients. We aimed to determine predictors of hypotension in NCC patients sedated with propofol.

METHODS

This retrospective, multicenter study evaluated 237 patients at two academic medical centers, both with dedicated NCC teams led by board-certified neurointensivists. Univariate analyses were performed to determine risk factors associated with severe hypotension during sedation with propofol. Multivariable analysis was performed to determine variables independently associated with hypotension, defined as a mean arterial pressure (MAP) less than 60 mmHg.

RESULTS

There was an average maximum reduction in MAP of 28.8 % after propofol initiation in the entire cohort. Severe hypotension developed in 62 (26.2 %) patients to a median nadir MAP of 56 mmHg. Those who developed severe hypotension had a longer median duration of mechanical ventilation (5.0 vs. 3.6 days; p = 0.01) and an increased in-hospital mortality (38.7 vs. 24.0 %; p = 0.03). Multivariable logistic regression analysis identified increasing number of changes to the propofol infusion rate, baseline MAP 60-70 mmHg, and need for renal replacement therapy (RRT) as factors independently associated with hypotension.

CONCLUSIONS

Multiple factors predicted hypotension in NCC patients receiving propofol. Clinicians should use propofol cautiously in patients with a lower baseline MAP or receiving RRT. Development of protocols related to the frequency of dose titrations is also recommended to prevent this avoidable complication.

Predictors of severe hypotension in neurocritical care patients sedated with propofol

INTRODUCTION

Propofol is used extensively in neurocritical care (NCC) due to its pharmacologic properties allowing for facilitation of serial neurologic examinations. Despite widespread use, few studies have identified risk factors for hypotension in these patients. We aimed to determine predictors of hypotension in NCC patients sedated with propofol.

METHODS

This retrospective, multicenter study evaluated 237 patients at two academic medical centers, both with dedicated NCC teams led by board-certified neurointensivists. Univariate analyses were performed to determine risk factors associated with severe hypotension during sedation with propofol. Multivariable analysis was performed to determine variables independently associated with hypotension, defined as a mean arterial pressure (MAP) less than 60 mmHg.

RESULTS

There was an average maximum reduction in MAP of 28.8 % after propofol initiation in the entire cohort. Severe hypotension developed in 62 (26.2 %) patients to a median nadir MAP of 56 mmHg. Those who developed severe hypotension had a longer median duration of mechanical ventilation (5.0 vs. 3.6 days; p = 0.01) and an increased in-hospital mortality (38.7 vs. 24.0 %; p = 0.03). Multivariable logistic regression analysis identified increasing number of changes to the propofol infusion rate, baseline MAP 60-70 mmHg, and need for renal replacement therapy (RRT) as factors independently associated with hypotension.

CONCLUSIONS

Multiple factors predicted hypotension in NCC patients receiving propofol. Clinicians should use propofol cautiously in patients with a lower baseline MAP or receiving RRT. Development of protocols related to the frequency of dose titrations is also recommended to prevent this avoidable complication.

Pharmacokinetics and pharmacodynamics of propofol in patients undergoing abdominal aortic surgery

Available propofol pharmacokinetic protocols for target-controlled infusion (TCI) were obtained from healthy individuals. However, the disposition as well as the response to a given drug may be altered in clinical conditions. The aim of the study was to examine population pharmacokinetics (PK) and pharmacodynamics (PD) of propofol during total intravenous anesthesia (propofol/fentanyl) monitored by bispectral index (BIS) in patients scheduled for abdominal aortic surgery. Population nonlinear mixed-effect modeling was done with Nonmem. Data were obtained from ten male patients. The TCI system (Diprifusor) was used to administer propofol. The BIS index served to monitor the depth of anesthesia. The propofol dosing was adjusted to keep BIS level between 40 and 60. A two-compartment model was used to describe propofol PK. The typical values of the central and peripheral volume of distribution, and the metabolic and inter-compartmental clearance were V(C) = 24.7 l, V(T) = 112 l, Cl = 2.64 l/min and Q = 0.989 l/min. Delay of the anesthetic effect, with respect to plasma concentrations, was described by the effect compartment with the rate constant for the distribution to the effector compartment equal to 0.240 min(-1). The BIS index was linked to the effect site concentrations through a sigmoidal E(max) model with EC(50) = 2.19 mg/l. The body weight, age, blood pressure and gender were not identified as statistically significant covariates for all PK/PD parameters. The population PK/PD model was successfully developed to describe the time course and variability of propofol concentration and BIS index in patients undergoing surgery.

Anesthetic implications of obesity in the surgical patient

The obese patient presents many challenges to both anesthesiologist and surgeon. A good understanding of the pathophysiologic effects of obesity and its anesthetic implications in the surgical setting is critical. The anesthesiologist must recognize increased risks and comorbidities inherent to the obese patient and manage accordingly, optimizing multisystem function in the perioperative period that leads to successful outcomes. Addressed from an organ systems approach, the purpose of this review is to provide surgical specialists with an overview of the anesthetic considerations of obesity. Minimally invasive surgery for the obese patient affords improved analgesia, postoperative pulmonary function, and shorter recovery times at the expense of a more challenging intraoperative anesthetic course. The physiologic effects of laparoscopy are discussed in detail. Although laparoscopy's physiologic effects on various organ systems are well recognized, techniques provide means for compensation and reversing such effects, thereby preserving good patient outcomes.

Real time monitoring of propofol blood concentration in ponies anaesthetized with propofol and ketamine

This study examined the pharmacokinetics of propofol by infusion in ponies using an analyser for the rapid measurement of propofol concentrations. The analyser (Pelorus 1000; Sphere Medical Ltd., Cambridge, UK) has a measurement cycle of approximately five minutes. Ten Welsh-cross ponies (weighing 135-300 kg) undergoing minor procedures were studied after premedication with acepromazine 0.03 mg/kg and detomidine 0.015 mg/kg. Anaesthesia was induced with ketamine 2 mg/kg and diazepam 0.03 mg/kg, and maintained with an infusion of propofol at an initial rate of 0.16 mg/kg/min for the first thirty minutes, after a bolus of 0.3 mg/kg; and ketamine by infusion (20-40 μg/kg/min). Blood samples (<2 mL) were collected prior to, during and after the infusion, and on assuming standing position. Anaesthesia was uneventful; with the duration of infusion 31-89 min. Blood propofol concentrations during the infusion ranged between 1.52 and 7.65 μg/mL; pseudo-steady state concentrations 3.64-6.78 μg/mL, and concentrations on assuming standing position 0.75-1.40 μg/mL. Propofol clearance and volume of distribution were 31.4 (SD 6.1) mL/min/kg and 220.7 (132.0) mL/kg, respectively. The propofol analyser allows titration of propofol to a given concentration; and may be useful for anaesthesia in animals where kinetics are unknown; in disease states; and where intercurrent therapies affect propofol disposition.

Pediatric palliative sedation therapy with propofol: recommendations based on experience in children with terminal cancer

BACKGROUND

The use of propofol for palliative sedation of children is not well documented.

OBJECTIVE

Here we describe our experience with the use of propofol palliative sedation therapy (PST) to alleviate intractable end-of-life suffering in three pediatric oncology patients, and propose an algorithm for the selection of such candidates for PST.

PATIENTS AND METHODS

We identified inpatients who had received propofol PST within 20 days of death at our institution between 2003 and 2010. Their medical records were reviewed for indicators of pain, suffering, and sedation from 48 hours before PST to the time of death. We also tabulated consumption of opioids and other symptom management medications, pain scores, and adverse events of propofol, and reviewed clinical notes for descriptors of suffering and/or palliation.

RESULTS

Three of 192 (1.6%) inpatients (aged 6-15 years) received propofol PST at the end of life. Consumption of opioids and other supportive medications decreased during PST in two cases. In the third case, pain scores remained high and sedation was the only effective comfort measure. Clinical notes suggested improved comfort and rest in all patients. Propofol infusions were continued until the time of death.

CONCLUSIONS

Our experience demonstrates that propofol PST is a useful palliative option for pediatric patients experiencing intractable suffering at the end of life. We describe an algorithm that can be used to identify such children who are candidates for PST.

The effects of intravenous anesthetics on mouse embryonic fibroblast viability and proliferation

PURPOSE

The aim of this study is to evaluate the cytotoxic and antiproliferating effects of intravenous anesthetics on an mouse fibroblast in vitro cell culture system.

METHODS

The cells were exposed to the usual clinical plasma concentration of intravenous anesthetics, i.e., midazolam (0.15 μg/ml), propofol (2 μg/ml), remifentanil (2 μg/ml), thiopental (10 μg/ml), for 4, 8, or 24 h. Cell proliferation (n = 6 for each) under intravenous anesthetics was analyzed using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. Cytotoxicity (n = 6 for each) of intravenous anesthetics was investigated using a LIVE/DEAD viability assay kit.

RESULTS

Intravenous anesthetic exposure time did not affect the proliferation rate of mouse fibroblasts. The cytotoxicity of intravenous anesthetics did not differ in accordance with exposure time.

CONCLUSION

Our results showed that intravenous anesthetics may not affect mouse fibroblast proliferation and viability.

Pharmacodynamic considerations for moderate and deep sedation

Moderate and deep sedation can be provided using various classes of drugs, each having unique mechanisms of action. While drugs within a given classification share similar mechanisms and effects, certain classes demonstrate superior efficacy but added concern regarding safety. This continuing education article will highlight essential principles of pharmacodynamics and apply these to drugs commonly used to produce moderate and deep sedation.

Remifentanil-propofol sedation as an ambulatory anesthesia for carpal tunnel release

OBJECTIVE

This prospective study evaluated the use of continuous sedation using propofol and remifentanil when carpal tunnel release (CTR) was performed under local anesthesia.

METHODS

We sedated 60 patients undergoing CTR using local anesthesia with remifentanil at loading and continuous doses of 0.5 µg kg(-1) and 0.05 µg kg(-1)min(-1), respectively, and propofol, using a target controlled infusion (TCI) pump set to a target of 2 µg mL(-1) (group A), or with the same drug doses except that the continuous remifentanil dose was 0.07 µg kg(-1)min(-1) (group B) or 0.1 µg kg(-1)min(-1) (group C).

RESULTS

In group B, the levels of pain when local anesthetics were administered (p = 0.001), intraoperative pain (p < 0.001) and anxiety (p = 0.001) were significantly lower than those of group A. Furthermore, the incidence of adverse events, including desaturation (p < 0.001) and vomiting (p = 0.043), was significantly lower in group B than in group C.

CONCLUSION

Continuous sedation using an appropriate dose of remifentanil and propofol can be used as safe, efficacious ambulatory anesthesia in cases of CTR under local anesthesia, performed using only 2 mL of local anesthetic, with a high degree of patient satisfaction.

Assessing circadian rhythms in propofol PK and PD during prolonged infusion in ICU patients

This study evaluates possible circadian rhythms during prolonged propofol infusion in patients in the intensive care unit. Eleven patients were sedated with a constant propofol infusion. The blood samples for the propofol assay were collected every hour during the second day, the third day, and after the termination of the propofol infusion. Values of electroencephalographic bispectral index (BIS), arterial blood pressure, heart rate, blood oxygen saturation and body temperature were recorded every hour at the blood collection time points. A two-compartment model was used to describe propofol pharmacokinetics. Typical values of the central and peripheral volume of distribution and inter-compartmental clearance were V_C = 27.7 l, V_T = 801 l, and CL_D = 2.73 l/min. The systolic blood pressure (SBP) was found to influence the propofol metabolic clearance according to Cl (l/min) = 2.65·(1 − 0.00714·(SBP − 135)). There was no significant circadian rhythm detected with respect to propofol pharmacokinetics. The BIS score was assessed as a direct effect model with EC₅₀ equal 1.98 mg/l. There was no significant circadian rhythm detected within the BIS scores. We concluded that the light–dark cycle did not influence propofol pharmacokinetics and pharmacodynamics in intensive care units patients. The lack of night–day differences was also noted for systolic blood pressure, diastolic blood pressure and blood oxygenation. Circadian rhythms were detected for heart rate and body temperature, however they were severely disturbed from the pattern of healthy patients.

Pain on injection from propofol may be avoided by changing its formulation

BACKGROUND

After using propofol for a decade, pain on injection had been considered routine by patients and medical personnel. When given propofol from a different manufacturer, patients did not complain. Two preparations of propofol were compared.

METHODS

A comparative, double-blind, randomized study was conducted in 22 adult patients undergoing pain relief procedures; they received sedation by an intravenous injection of 1.7 mg/kg of propofol and then were treated with paravertebral injections. Pain on injection was assessed by verbal complaint, movement of the extremity, of the whole body and recollection of pain at induction, when discharged. Propofol from Baxter Laboratories, mixed with either 5 ml of 2% lidocaine or 5 ml of NaCl 0.9%, was compared with propofol Laboratorios Gray, which was similarly mixed. Injections were randomly administered four times, blindly, to each of 22 patients. Statistical analysis was conducted using the analysis of variance method.

RESULTS

A total of 352 propofol injections were given. Each of the four propofol solutions was administered 88 times; of patients receiving Baxter propofol+saline, 74 (84%) had pain; when mixed with 2% lidocaine 45 (50.2%) complained. After propofol Gray with NaCl 0.9% was given, two patients (2.2%) experienced pain. Propofol Gray with 2% lidocaine produced no pain. None of the latter group remembered having pain, whereas, those given propofol Baxter 54 (61.3%) and 26 (29.5%) remembered experiencing pain at injection. Pain on injection was prevented and statistically reduced (<0.01) with the propofol from Laboratorios Gray.

CONCLUSIONS

By changing the formulation (size of molecules and their dispersion) of propofol, pain on injection was avoided.

Episodic Waveforms in the Electroencephalogram during General Anaesthesia: A Study of Patterns of Response to Noxious Stimuli

Previous studies of the electroencephalogram (EEG) during anaesthesia have identified two distinct patterns of change in response to a noxious stimulus, a classical arousal pattern and a paradoxical arousal pattern. We developed methods of EEG analysis to quantify episodic EEG patterns – namely sleep spindle-like (‘10 Hz-score’) and burst-suppression-like fluctuations in high frequencies (‘high frequency variation index’) – and used traditional power spectral quantification of non-episodic delta waves. We studied 30 healthy adult patients undergoing elective surgery under general anaesthesia with propofol, fentanyl (1.0, 2.5 or 4.0 μg/kg, n=10 for each group), muscle relaxant and sevoflurane. Prefrontal EEG data were recorded during the operation and analysed for changes in episodic patterns before and after noxious stimuli (intubation and incision). Before noxious stimuli, the EEG patterns varied markedly between patients and were not strongly correlated to calculated effect-site concentrations of fentanyl, propofol or sevoflurane. Noxious stimuli reduced the 10Hz-score from 0.25 to 0.20 (P=0.01) after intubation and from 0.33 to 0.27 (P=0.01) after incision; and high frequency variation index from 2.8 to 2.0 (P=0.02) after incision – the classical arousal pattern. The nociception-induced reduction in spindles was greater in the low-dose fentanyl group (P=0.01). There was less tachycardia in the high-dose fentanyl group (P=0.002). It is possible to quantify such episodic EEG patterns during general anaesthesia and in this study noxious stimulation tended to reduce the prevalence of these patterns.

Propofol and isoflurane enhancement of tonic gamma-aminobutyric acid type a current in cardiac vagal neurons in the nucleus ambiguus

BACKGROUND

General anesthesia with propofol and isoflurane induces alterations of the cardiovascular system, including hypotension and changes in heart rate. The preganglionic cardiac vagal neurons (CVNs) are one of the major central components controlling heart rate and autonomic regulation. In this study, we examined whether propofol and isoflurane act on phasic or tonic gamma-aminobutyric acid type A (GABA(A)) receptor-mediated inhibition in CVNs.

METHODS

CVNs were identified in vitro by retrograde fluorescent labeling. Phasic and tonic GABA currents in CVNs were examined using the whole cell patch-clamp technique.

RESULTS

Propofol (10 microM) increased the membrane holding currents by 63 +/- 13% and prolonged the decay time of GABAergic miniature inhibitory postsynaptic currents (mIPSCs) from 42.3 +/- 2.8 ms in control to 61.8 +/- 4.5 ms. Isoflurane, at concentrations of 100, 300, and 500 microM, decreased GABAergic mIPSCs frequency by 26.0 +/- 16%, 64.6 +/- 10.4%, and 70.5 +/- 9.8%, prolonged the decay time of GABAergic mIPSCs from 47.9 +/- 7.3 to 64.5 +/- 8.1 ms, 70.3 +/- 10.4 ms, and 66.8 +/- 8.1 ms, and increased the membrane holding currents by 32.8 +/- 12.8%, 42.7 +/- 10%, and 39.9 +/- 3%, respectively. The GABAergic antagonist gabazine (25 microM) blocked GABAergic mIPSCs, but failed to alter the enhanced holding potential induced by propofol and isoflurane. In contrast, the channel blocker of GABA(A) receptors, picrotoxin (100 microM), reversed the propofol and isoflurane-evoked increase in membrane holding current.

CONCLUSION

The results demonstrate that the general anesthetics propofol and isoflurane enhance both phasic and tonic GABA(A) receptor-mediated inhibition of CVNs.

Propofol-fentanyl anaesthesia at high altitude: anaesthetic requirements and haemodynamic variations when compared with anaesthesia at low altitude

BACKGROUND

There are few published accounts of anaesthesia delivery at high altitude. Natives at high altitude are known to have altered cardiorespiratory reserve. This study seeks to demonstrate the safety of propofol-fentanyl anaesthesia at high altitude titrated to the bispectral index (BIS) (3505 metres above sea level) in native highlanders. It also shows the differential effects of anaesthesia and surgery on the haemodynamics of such individuals as compared with individuals living at low altitude.

METHODS

Fifteen consenting adults scheduled to undergo general surgical/orthopaedic procedures under general anaesthesia using fentanyl, and propofol infusions titrated to the BIS along with nitrous oxide in oxygen after intubation, were recruited in the high-altitude arm. Their anaesthesia record was compared with retrospective data from low altitude with respect to anaesthetic requirements, recovery after anaesthesia and the haemodynamic responses to surgical stress.

RESULTS

The high-altitude dwellers required significantly larger doses of propofol at anaesthetic induction (2.31+/-0.64 vs. 1.41+/-0.24 mg/kg, P<0.0001) and thereafter to maintain designated BIS than their low-altitude counterparts (6.22+/-1.14 vs. 4.61+/-1.29 mg/kg/h, P<0.01). They, however, had uneventful and short recovery times. The high-altitude population also had significantly lower baseline heart rates (72+/-9.83 vs. 88+/-12.1, P<0.04) as also the heart rate responses to noxious stimulation such as direct laryngoscopy or skin incision (P<0.04, P<0.005, respectively).

CONCLUSIONS

High-altitude dwellers require significantly larger amounts of intravenous anaesthetic propofol. Heart rate at rest as also the heart rate responses to surgical stress were significantly attenuated at high altitude.

Clinical Practice Advisory: Emergency Department Procedural Sedation With Propofol

We present an evidence-based clinical practice advisory for the administration of propofol for emergency department procedural sedation. We critically discuss indications, contraindications, personnel and monitoring requirements, dosing, coadministered medications, and patient recovery from propofol. Future research questions are considered.

Sedation in the mechanically ventilated patient

OBJECTIVE

To discuss the approach to sedation of the mechanically ventilated patient.

DATA SYNTHESIS

Mechanically ventilated patients in the intensive care unit frequently require sedation and analgesia for anxiety and pain experienced during the time they are intubated. Multiple drugs are available for this purpose. Strategies that optimize comfort while minimizing the predilection for sedative and analgesic drug accumulation with prolongation of effect have been shown to improve outcomes. In particular, such strategies may decrease mechanical ventilation duration, intensive care unit length of stay, and complications associated with critical illness.

CONCLUSIONS

Sedation and analgesia are important in the management of patients who require mechanical ventilation. An evidence-based approach to administering sedatives and analgesics is necessary to optimize short- and long-term outcomes in mechanically ventilated patients.

Propofol attenuates lung endothelial injury induced by ischemia-reperfusion and oxidative stress

Lung dysfunction after cardiopulmonary bypass and lung transplantation results from oxidant-mediated cellular damage. Previously, we observed the shedding of angiotensin-converting enzyme (ACE) from the endothelial cell surface to be a more sensitive and earlier marker of oxidative lung endothelial injury than lung wet-to-dry weight ratio. The aim of this study was to evaluate the potential of the anesthetic propofol, which has antioxidant properties, to prevent oxidative lung injury by measuring ACE shedding. ACE release from isolated perfused rat lungs increased significantly after ischemia-reperfusion (I/R). Propofol significantly decreased I/R-induced ACE release by 23.4% (P < 0.05). Perfusion with 0.75 mM H(2)O(2) also caused ACE release from the lung microvasculature, which was similarly attenuated by propofol. The protective effect of propofol on H(2)O(2)-induced ACE shedding was confirmed in vitro using Chinese Hamster Ovary cells overexpressing human ACE. Thus, propofol can attenuate oxidative injury of the pulmonary endothelium as detected by ACE shedding in I/R and H(2)O(2) models of acute lung injury.

Propofol Inhibits Human Platelet Aggregation Induced by Proinflammatory Lipid Mediators

Lysophosphatidic acid (LPA), platelet-activating factor (PAF), and thromboxane A(2) are proinflammatory lipid mediators that activate surface receptors on platelets, producing increased intracellular calcium, which is necessary for aggregation. We investigated propofol's effect on platelet aggregation and intracellular calcium mobilization caused by these three agonists. Platelets from human volunteers were incubated in buffers containing LPA (1 microM), U46619 (thromboxane A(2) analog; 1 microM), or PAF (10 nM). Propofol emulsion or 2,6-diisopropylphenol (propofol without fat emulsion) dissolved in ethanol was added to achieve concentrations of propofol used clinically: 5 or 10 microg/mL. After 2 min, aggregation or intracellular calcium concentrations were measured with optical techniques. Propofol emulsion and propofol in ethanol produced similar inhibition of platelet aggregation induced by LPA, PAF, and U46619 in a dose-dependent fashion. LPA, PAF, and U46619 each caused significant increases in intracellular calcium that were not modified by propofol. Because propofol does not significantly alter intracellular calcium increases caused by receptor activation, inhibition appears to act distal to platelet receptors, inositol phosphate 3, and phospholipase C. Because the three lipid mediators play a key role in inflammation, their inhibition by propofol might be clinically important.

Comparative tolerability of sedative agents in head-injured adults

Sedative agents are widely used in the management of patients with head injury. These drugs can facilitate assisted ventilation and may provide useful reductions in cerebral oxygen demand. However, they may compromise cerebral oxygen delivery via their cardiovascular effects. In addition, individual sedative agents have specific and sometimes serious adverse effects. This review focuses on the different classes of sedative agents used in head injury, with a discussion of their role in the context of clinical pathophysiology. While there is no sedative that has all the desirable characteristics for an agent in this clinical setting, careful titration of dose, combination of agents, and a clear understanding of the pathophysiology and pharmacology of these agents will allow safe sedative administration in head injury.

Pharmacokinetics and anesthetic and cardiopulmonary effects of propofol in red-tailed hawks (Buteo jamaicensis) and great horned owls (Bubo virginianus)

OBJECTIVE

To determine induction doses, anesthetic constant rate infusions (CRI), and cardiopulmonary effects of propofol in red-tailed hawks and great horned owls and propofol pharmacokinetics in the owls during CRI.

ANIMALS

6 red-tailed hawks and 6 great horned owls.

PROCEDURE

The CRI dose necessary for a loss of withdrawal reflex was determined via specific stimuli. Anesthesia was induced by IV administration of propofol (1 mg/kg/min) and maintained by CRI at the predetermined dose for 30 minutes. Heart and respiratory rates, arterial blood pressures, and blood gas tensions were obtained in awake birds and at various times after induction. End-tidal CO2 (ETCO2) concentration and esophageal temperature were obtained after induction. Propofol plasma concentrations were obtained after induction and after completion of the CRI in the owls. Recovery times were recorded.

RESULTS

Mean +/- SD doses for induction and CRI were 4.48 +/- 1.09 mg/kg and 0.48 +/- 0.06 mg/kg/min, respectively, for hawks and 3.36 +/- 0.71 mg/kg and 0.56 +/- 0.15 mg/kg/min, respectively, for owls. Significant increases in PaCO2, HCO3, and ETCO2 in hawks and owls and significant decreases in arterial pH in hawks were detected. A 2-compartment model best described the owl pharmacodynamic data. Recovery times after infusion were prolonged and varied widely. Central nervous system excitatory signs were observed during recovery.

CONCLUSIONS AND CLINICAL RELEVANCE

Effects on blood pressure were minimal, but effective ventilation was reduced, suggesting the need for careful monitoring during anesthesia. Prolonged recovery periods with moderate-to-severe excitatory CNS signs may occur in these species at these doses.

Plasma propofol concentration and EEG burst suppression ratio during normothermic cardiopulmonary bypass

BACKGROUND

During cardiopulmonary bypass (CPB), several factors affect drug disposition and action. This topic has not been studied extensively during normothermic CPB. In this study, we related propofol dose to plasma propofol concentration and burst suppression of the EEG during normothermic bypass.

METHODS

After institutional approval and informed consent, 45 patients having cardiac surgery were assigned randomly to receive propofol infusions at 4 (Group A), 5 (Group B) and 6 (Group C) mg kg(-1) h(-1) during normothermic CPB. In all patients, small to moderate doses of fentanyl were also administered. Plasma propofol concentration and burst suppression ratio (BSR) were measured at the following times: (1) 10 min before CPB, (2) 10 min after the start of CPB, (3) 30 min after the start of the CPB, (4) just after aortic declamping, and (5) 60 min after CPB.

RESULTS

At baseline, plasma propofol concentrations were similar among the three groups. After the start of CPB, the concentrations of propofol decreased significantly by 41, 35, and 30% of control values in Groups A, B, and C, respectively. In Group A, the concentration of propofol during CPB remained unchanged at less than the concentration before bypass. In Groups B and C, plasma propofol concentrations gradually increased during CPB to the pre-bypass concentrations. In Group A, BSR values did not change significantly during CPB. In Groups B and C, BSR values gradually increased and became significantly greater than baseline values. No patient reported intraoperative awareness.

CONCLUSION

The pharmacokinetics and pharmacodynamics of propofol change during normothermic CPB. During normothermic CPB, the efficacy of propofol may be enhanced compared with before CPB.

Sedation in the intensive care unit

Although the administration of sedatives is a commonplace activity in the ICU, few guidelines are available to aid the clinician in this practice. The first principle of sedative administration is to define the specific problem requiring sedation and to rationally choose the drug and depth of sedation appropriate for the indication. Next, the clinician must recognize the diverse and often unpredictable effects of critical illness on drug pharmacokinetics and pharmacodynamics. Failure to recognize these effects may lead initially to inadequate sedation and subsequently to drug accumulation. Drug accumulation may result in prolonged encephalopathy and mechanical ventilation and may mask the development of neurologic or intra-abdominal complications. Daily interruption of continuous sedative infusions is a simple and effective way of addressing this problem. A glossary of sedative drugs commonly used in the ICU is included in this review.