Effect of cardiopulmonary bypass on the pharmacokinetics of drugs

Population pharmacokinetic modeling of sufentanil in adult Korean patients undergoing cardiopulmonary bypass surgery

Sufentanil is frequently used as an anesthetic agent in cardiac surgery owing to its cardiovascular safety and favorable pharmacokinetics. However, the pharmacokinetics profiles of sufentanil in patients undergoing cardiopulmonary bypass (CPB) surgery remain less understood, which is crucial for achieving the desired level of anesthesia and mitigating surgical complications. Therefore, this study aimed to develop a population pharmacokinetic model of sufentanil in patients undergoing CPB surgery and elucidate the clinical factors affecting its pharmacokinetic profile. Adult patients who underwent cardiac surgery with CPB and were administered sufentanil for anesthesia were enrolled. Arterial blood samples were collected to quantify plasma concentrations of sufentanil and clinical laboratory parameters, including inflammatory cytokines. A population pharmacokinetic model was established using nonlinear mixed-effects modeling. Simulations were performed using the pharmacokinetic parameters of the final model. Overall, 20 patients were included in the final analysis. Sufentanil pharmacokinetics were modeled using a two-compartment model, accounting for CPB effects. Sufentanil clearance increased 2.80-fold during CPB and warming phases, while the central compartment volume increased 2.74-fold during CPB. CPB was a significant covariate affecting drug clearance and distribution volume. No other significant covariates were identified despite increased levels of the inflammatory cytokines, including IL-6, IL-8, and TNF-α during CPB. The simulation indicated a 30 μg loading dose and 40 μg/h maintenance infusion for target-controlled infusion. Additionally, a bolus dose of 60 μg was added at CPB initiation to adjust for exposure changes during this phase. Considering the target sufentanil concentrations, a uniform dosing regimen was acceptable for effective analgesia.

Population Pharmacokinetics and Target Attainment of Allopurinol and Oxypurinol Before, During, and After Cardiac Surgery with Cardiopulmonary Bypass in Neonates with Critical Congenital Heart Disease

BACKGROUND

The CRUCIAL trial (NCT04217421) is investigating the effect of postnatal and perioperative administration of allopurinol on postoperative brain injury in neonates with critical congenital heart disease (CCHD) undergoing cardiac surgery with cardiopulmonary bypass (CPB) shortly after birth.

OBJECTIVE

This study aimed to characterize the pharmacokinetics (PK) of allopurinol and oxypurinol during the preoperative, intraoperative, and postoperative phases in this population, and to evaluate target attainment of the current dosing strategy.

METHODS

Nonlinear mixed-effects modeling was used to develop population PK models in 14 neonates from the CRUCIAL trial who received up to five intravenous allopurinol administrations throughout the postnatal and perioperative periods. Target attainment was defined as achieving an allopurinol concentration >2 mg/L in at least two-thirds of the patients during the first 24 h after birth and between the start and 36 h after cardiac surgery with CPB.

RESULTS

A two-compartment model for allopurinol was connected to a one-compartment model for oxypurinol with an auto-inhibition effect on the conversion, which best described the PK. In a typical neonate weighing 3.5 kg who underwent cardiac surgery at a postnatal age (PNA) of 5.6 days, the clearance (CL) of allopurinol and oxypurinol at birth was 0.95 L/h (95% confidence interval 0.75-1.2) and 0.21 L/h (0.17-0.27), respectively, which subsequently increased with PNA to 2.97 L/h and 0.41 L/h, respectively, before CPB. During CPB, allopurinol and oxypurinol CL decreased to 1.38 L/h (0.9-1.87) and 0.12 L/h (0.05-0.22), respectively. Post-CPB, allopurinol CL increased to 2.21 L/h (1.74-2.83), while oxypurinol CL dropped to 0.05 L/h (0.01-0.1). Target attainment was 100%, 53.8%, and 100% at 24 h postnatally, 24 h after the start of CPB, and 36 h after the end of cardiac surgery, respectively. The combined concentrations of allopurinol and oxypurinol maintained ≥ 90% inhibition of xanthine oxidase (IC90XO) throughout the postnatal and perioperative period.

CONCLUSIONS

The minimal target concentration of allopurinol was not achieved at every predefined time interval in the CRUCIAL trial; however, the dosing strategy used was deemed adequate, since it yielded concentrations well exceeding the IC90XO. The decreased CL of both compounds during CPB suggests influence of the hypothermia, hemofiltration, and the potential sequestration of allopurinol in the circuit. The reduced CL of oxypurinol after CPB is likely attributable to impaired kidney function.

Population Pharmacokinetics of Caffeine in Neonates with Congenital Heart Disease and Associations with Acute Kidney Injury

Cardiac surgery-associated acute kidney injury (CS-AKI) occurs in approximately 65% of neonates undergoing cardiac surgery on cardiopulmonary bypass and contributes to morbidity and mortality. Caffeine may reduce CS-AKI by counteracting adenosine receptor upregulation after bypass, but pharmacokinetics (PK) in this population are unknown. The goal of our analysis is to address knowledge gaps in age-, disease-, and bypass-related effects on caffeine disposition and explore preliminary associations between caffeine exposure and CS-AKI using population PK modeling techniques and an opportunistic, electronic health record-integrated trial design. We prospectively enrolled neonates receiving preoperative caffeine per standard of care and collected PK samples. We retrospectively identified neonates without caffeine exposure undergoing surgery on bypass as a control cohort. We followed US Food and Drug Administration guidance for population PK model development using NONMEM. Effects of clinical covariates on PK parameters were evaluated. We simulated perioperative exposures and used multivariable logistic regression to evaluate the association between caffeine exposure and CS-AKI. Twenty-seven neonates were included in model development. A 1-compartment model with bypass time as a covariate on clearance and volume of distribution best fit the data. Twenty-three neonates with caffeine exposure and 109 controls were included in the exposure-response analysis. Over half of neonates developed CS-AKI. On multivariable analysis, there were no significant differences between CS-AKI with and without caffeine exposure. Neonates with single-ventricle heart disease without CS-AKI had consistently higher simulated caffeine exposures. Our results highlight areas for further study to better understand disease- and bypass-specific effects on drug disposition and identify populations where caffeine may be beneficial.

Dose optimization and target attainment of vancomycin in children

Vancomycin is a glycopeptide antibiotic that has been adopted in clinical practice to treat gram-positive infections for more than 70 years. Despite vancomycin's long history of therapeutic use, optimal dose adjustments and pharmacokinetic/pharmacodynamic (PK/PD) target attainment in children are still under debate. Therapeutic drug monitoring (TDM) has been widely integrated into pediatric clinical practice to maximize efficacy and safety of vancomycin treatment. Area under the curve (AUC)-guided TDM has been recently recommended instead of trough-only TDM to ensure PK/PD target attainment of AUC0-24h/minimal inhibitory concentration (MIC) > 400 to 600 and minimize acute kidney injury risk. Bayesian forecasting in pediatric patients allows estimation of population PK to accurately predict individual vancomycin concentrations over time, and consequently total vancomycin exposure. AUC-guided TDM for vancomycin, preferably with Bayesian forecasting, is therefore suggested for all pediatric age groups and special pediatric populations. In this review we aim to analyze the current literature on the pediatric use of vancomycin and summarize the current knowledge on dosing optimization for target attainment in special patient populations.

Pharmacokinetics of dexmedetomidine in pediatric patients undergoing cardiac surgery with cardiopulmonary bypass

BACKGROUND

Cardiopulmonary bypass can affect the pharmacokinetics of anesthetic agents.

AIMS

We aimed to evaluate the pharmacokinetics of dexmedetomidine for infants and small children undergoing cardiac surgery with cardiopulmonary bypass based on population pharmacokinetics.

METHODS

We enrolled 30 pediatric cardiac surgical patients in this study. After anesthetic induction with atropine (0.02 mg/kg), thiopental sodium (5 mg/kg), and fentanyl (2-3 μg/kg), we administered 1 μg/kg of dexmedetomidine for 10 min, followed by administration of 0.5 μg/kg of dexmedetomidine per hour during surgery. At the initiation of cardiopulmonary bypass, 1 μg/kg of dexmedetomidine was infused over 5 min. Arterial blood was obtained at predefined time points. A pharmacokinetic model was developed using NONMEM. Theory-based allometric scaling with fixed exponents was applied. Weight, age, post-menstrual age, fat-free mass, whether to implement cardiopulmonary bypass and temperature were explored as covariates.

RESULTS

A total of 376 blood samples were obtained from 29 children (age: 20.3 ± 19.3 months, weight: 9.7 ± 4.1 kg). A two-compartment mammillary model with third compartment associated cardiopulmonary bypass procedure best explained the pharmacokinetics of dexmedetomidine. The pharmacokinetic parameter estimates (95% CI) standardized to a 70-kg person were as follows: V₁ (L) = 31.6 (17.9-39.5), V₂ (L) = 90.1 (44.0-330), Cl (L/min) = 1.08 (0.70-1.25), Q (L/min) = 2.0 (1.05-3.46). Volume for third compartment associated cardiopulmonary bypass procedure (L) = 39.4 (19.3-50.9). Clearance was not influenced by the presence of cardiopulmonary bypass in this model.

CONCLUSION

When cardiopulmonary bypass is applied, the plasma concentration of dexmedetomidine decreases due to an increase in the volume of distribution, so a loading dose is required to maintain the previous concentration.

Interactions of fentanyl with blood platelets and plasma proteins: platelet sensitivity to prasugrel metabolite is not affected by fentanyl under in vitro conditions

BACKGROUND

Clinical trials indicate that fentanyl, like morphine, may impair intestinal absorption and thus decrease the efficacy of oral P2Y₁₂ inhibitors, such as clopidogrel, ticagrelor, and prasugrel. However, the ability of fentanyl to directly negate or reduce the inhibitory effect of P2Y₁₂ receptor antagonists on platelet function has not been established. A series of in vitro experiments was performed to investigate the ability of fentanyl to activate platelets, potentiate platelet response to ADP, and/or diminish platelet sensitivity to prasugrel metabolite (R-138727) in agonist-stimulated platelets. The selectivity and specificity of fentanyl toward major carrier proteins has been also studied.

METHODS

Blood was obtained from healthy volunteers (19 women and 12 men; mean age 40 ± 13 years). Platelet function was measured in whole blood, platelet-rich plasma and in suspensions of isolated platelets by flow cytometry, impedance and optical aggregometry. Surface plasmon resonance and molecular docking were employed to determine the binding kinetics of fentanyl to human albumin, α₁-acid glycoprotein, apolipoprotein A-1 and apolipoprotein B-100.

RESULTS

When applied at therapeutic and supratherapeutic concentrations under various experimental conditions, fentanyl had no potential to stimulate platelet activation and aggregation, or potentiate platelet response to ADP, nor did it affect platelet susceptibility to prasugrel metabolite in ADP-stimulated platelets. In addition, fentanyl was found to interact with all the examined carrier proteins with dissociation constants in the order of 10^-4 to 10^-9 M.

CONCLUSIONS

It does not seem that the delayed platelet responsiveness to oral P2Y₁₂ inhibitors, such as prasugrel, in patients undergoing percutaneous coronary intervention, results from direct interactions between fentanyl and blood platelets. Apolipoproteins, similarly to albumin and α₁-acid glycoprotein, appear to be important carriers of fentanyl in blood.

Mitochondrial Oxygenation During Cardiopulmonary Bypass: A Pilot Study

Objective

Adequate oxygenation is essential for the preservation of organ function during cardiac surgery and cardiopulmonary bypass (CPB). Both hypoxia and hyperoxia result in undesired outcomes, and a narrow window for optimal oxygenation exists. Current perioperative monitoring techniques are not always sufficient to monitor adequate oxygenation. The non-invasive COMET® monitor could be a tool to monitor oxygenation by measuring the cutaneous mitochondrial oxygen tension (mitoPO2). This pilot study examines the feasibility of cutaneous mitoPO2 measurements during cardiothoracic procedures. Cutaneous mitoPO2 will be compared to tissue oxygenation (StO2) as measured by near-infrared spectroscopy.

Design and Method

This single-center observational study examined 41 cardiac surgery patients requiring CPB. Preoperatively, patients received a 5-aminolevulinic acid plaster on the upper arm to enable mitoPO2 measurements. After induction of anesthesia, both cutaneous mitoPO2 and StO2 were measured throughout the procedure. The patients were observed until discharge for the development of acute kidney insufficiency (AKI).

Results

Cutaneous mitoPO2 was successfully measured in all patients and was 63.5 [40.0-74.8] mmHg at the surgery start and decreased significantly (p < 0.01) to 36.4 [18.4-56.0] mmHg by the end of the CPB run. StO2 at the surgery start was 80.5 [76.8-84.3]% and did not change significantly. Cross-clamping of the aorta and the switch to non-pulsatile flow resulted in a median cutaneous mitoPO2 decrease of 7 mmHg (p < 0.01). The cessation of the aortic cross-clamping period resulted in an increase of 4 mmHg (p < 0.01). Totally, four patients developed AKI and had a lower preoperative eGFR of 52 vs. 81 ml/min in the non-AKI group. The AKI group spent 32% of the operation time with a cutaneous mitoPO2 value under 20 mmHg as compared to 8% in the non-AKI group.

Conclusion

This pilot study illustrated the feasibility of measuring cutaneous mitoPO2 using the COMET® monitor during cardiothoracic procedures. Moreover, in contrast to StO2, mitoPO2 decreased significantly with the increasing CPB run time. Cutaneous mitoPO2 also significantly decreased during the aortic cross-clamping period and increased upon the release of the clamp, but StO2 did not. This emphasized the sensitivity of cutaneous mitoPO2 to detect circulatory and microvascular changes.

Population pharmacokinetics of three alternative prophylactic antibiotics during cardiac surgery with extracorporeal circulation

AIMS

The aim of this pharmacokinetic study was to describe and quantify population pharmacokinetics of three antibiotics, cefazolin, ampicillin, and ciprofloxacin, used as antibacterial prophylaxis during cardiovascular surgery with the use of extracorporeal circulation (ECC).

METHODS

Adult patients undergoing cardiac surgery with ECC were enrolled to this prospective, pharmacokinetic study. An intravenous bolus of 2 g of ampicillin, 2 g of cefazolin or 400 mg of ciprofloxacin was administered 60-30 min before surgery. Blood samples were collected at 15, 30, 45, 60, 120 and 180 min after the administration and at the end of the surgery. Plasma concentrations of the antibiotics were measured using HPLC methods. Serum concentration-time profiles were analyzed using nonlinear mixed-effects modeling approach.

RESULTS

A total of 54 patients were enrolled into the study, 20 with ampicillin, 25 cefazolin and 9 ciprofloxacin. For all antibiotics, population pharmacokinetic models have been successfully developed.

CONCLUSION

We identified estimated glomerular filtration rate (eGFR) as the main factor determining the achievement of the pharmacokinetic/pharmacodynamic (PK/PD) target in ampicillin or cefazolin and body weight in ciprofloxacin prophylaxis during cardiac surgery with ECC support.

Methylprednisolone Plasma Concentrations During Cardiac Surgery With Cardiopulmonary Bypass in Pediatric Patients

Introduction: To our knowledge, methylprednisolone pharmacokinetics and plasma concentrations have not been comprehensively investigated in children with congenital heart disease undergoing cardiac surgery with cardiopulmonary bypass. It is unknown whether there is a significant influence of cardiopulmonary bypass on the plasma concentrations of methylprednisolone and whether this may be an explanation for the limited reported efficacy of steroid administration in cardiac surgery with cardiopulmonary bypass.

Methods: The study was registered in the Dutch Trial Register (NTR3579; https://www.trialregister.nl/trial/3428). Methylprednisolone 30 mg/kg was administered as an intravenous bolus after induction of anesthesia. Methylprednisolone concentration was measured with liquid chromatography tandem mass spectrometry and analyzed using linear mixed-effects modeling.

Results: Thirty-nine patients were included in the study, of which three were excluded. There was an acute decrease in observed methylprednisolone plasma concentration on initiation of cardiopulmonary bypass (median = 26.8%, range = 13.9–48.14%, p < 0.001). We found a lower intercept (p = 0.02), as well as a less steep slope of the model predicted methylprednisolone concentration vs. time curve for neonates (p = 0.048). A lower intercept (p = 0.01) and a less steep slope (p = 0.0024) if the volume of cell saver blood processed was larger than 91 ml/kg were also found.

Discussion: We report similar methylprednisolone plasma concentrations as earlier studies performed in children undergoing cardiopulmonary bypass, and we confirmed the large interindividual variability in achieved methylprednisolone plasma concentrations with weight-based methylprednisolone administration. A larger volume of distribution and a lower clearance of methylprednisolone for neonates were suggested. The half-life of methylprednisolone in our study was calculated to be longer than 6 h for neonates, 4.7 h for infants, 3.6 h for preschool children and 4.7 h for school children. The possible influence of treatment of pulmonary hypertension with sildenafil and temperature needs to be investigated further.

Methylprednisolone Does Not Reduce Acute Postoperative Pain After Cardiac Surgery: Subanalysis of a Randomized Clinical Trial

BACKGROUND

Pain after cardiac surgery is largely treated with opioids, but their poor safety profile makes nonopioid medications attractive as part of multimodal pathways. Anti-inflammatory drugs reduce acute postoperative pain, but the role of steroids in reducing acute poststernotomy pain is unclear. We evaluated the association between the intraoperative administration of methylprednisolone and postoperative analgesia, defined as a composite of pain scores and opioid consumption, during the initial 24 hours after cardiac surgery.

METHODS

We conducted a post hoc retrospective analysis of a large clinical trial in which adults having cardiac surgery were randomized 1:1 to receive 2 intraoperative doses of 250 mg IV methylprednisolone or placebo. Pain scores and opioid consumption were collected during the initial 24 hours after surgery. Methylprednisolone was considered to be associated with better pain control than placebo if proven noninferior (not worse) on both pain scores (defined a priori with delta of 1 point) and opioid consumption (delta of 20%) and superior to placebo in at least 1 of the 2 outcomes. This test was repeated in the opposite direction (testing whether placebo is better than methylprednisolone on postoperative pain management).

RESULTS

Of 251 eligible patients, 127 received methylprednisolone and 124 received placebo. Methylprednisolone was noninferior to placebo on pain with difference in mean (CI) pain scores of -0.25 (-0.71 to 0.21); P < .001. However, methylprednisolone was not noninferior to placebo on opioid consumption (ratio of geometric means [CI]: 1.11 [0.64-1.91]; P = .37). Because methylprednisolone was not noninferior to placebo on both outcomes, we did not proceed to superiority testing based on the a priori stopping rules. Similar results were found when testing the opposite direction.

CONCLUSIONS

In this post hoc analysis, we could not identify a beneficial analgesic effect after cardiac surgery associated with methylprednisolone administration. There are currently no data to suggest that methylprednisolone has significant analgesic benefit in adults having cardiac surgery.

Effect of cardiopulmonary bypass on cytochrome P450 enzyme activity: implications for pharmacotherapy

For patients undergoing cardiopulmonary bypass (CPB) during cardiac surgery, there are well-documented changes in the pharmacokinetics (PK) of commonly administered drugs. Although multiple factors potentially underpin these changes, there has been scant research attention on the impact of CPB to alter the activities of cytochrome P450 (CYP) isoenzymes. PK changes during cardiac surgery with CPB have the potential to adversely affect the safety and efficacy of pharmacotherapy and increase the risk of drug-drug interactions. Clinically significant changes in drug PK during CPB are likely to be prominent for drugs where CYP metabolism is a major clearance (CL) mechanism. However, clinical data from patients undergoing CPB surgery in support of this hypothesis are lacking, leaving a significant knowledge gap. In this review, we address the effects of CPB on the release of pro-inflammatory cytokines, in surgeries with and without CPB, both pre and post initiation of surgery. We reviewed literature to explore the relationship between the release of pro-inflammatory cytokines, and the expression and activities of CYP enzymes. Through this approach, we provide new insight on the effects of CPB on the PK of drugs administered to patients in the clinical setting. Future research to address this knowledge gap will have considerable impact to assist clinicians with optimizing pharmacotherapy in this patient population.

Weight-based versus set dosing of vancomycin for coronary artery bypass grafting or aortic valve surgery

OBJECTIVES

This study was undertaken to identify a preferred dosing strategy for patients undergoing coronary artery bypass grafting or valve replacement procedures with cardiopulmonary bypass.

METHODS

Patients undergoing coronary artery bypass grafting, valve replacement surgery, or both were randomly assigned to receive either standard 1-g dosing with vancomycin before and after cardiopulmonary bypass or a single weight-based 20-mg/kg dose before surgery. The primary outcome was the percentage of time plasma concentrations were greater than 15 μg/mL during cardiopulmonary bypass and at surgical closure. Secondary outcomes included concentration of vancomycin in endothoracic tissue after vancomycin infusion, average time patients had vancomycin concentrations greater than 15 μg/mL, and vancomycin plasma and tissue pharmacokinetic parameters.

RESULTS

Baseline characteristics were similar between the study dosing group (n = 10) and the standard dosing group (n = 10). From postinfusion to end of bypass, the median percentage of time vancomycin concentrations remained greater than 15 μg/mL was 100% (interquartile range [IQR], 72.6%-100%) for weight-based dosing versus 43.7% (IQR, 28.7%-53.4%) for standard dosing (P = .0005). From postinfusion to surgical closure, the percentage of time vancomycin concentrations remained greater than 15 μg/mL was significantly higher in the weight-based group (100% [IQR, 58.3%-100%] vs 34.6% [IQR, 25.3%-41.6%]; P = .0005). Weight-based dosing increased calculated time with vancomycin concentrations greater than 15 μg/mL and resulted in higher endothoracic tissue vancomycin concentrations.

CONCLUSIONS

Weight-based vancomycin dosing before coronary artery bypass grafting or valve replacement results in vancomycin concentrations greater than 15 μg/mL consistently more than does standard 1-g dosing.

Extracorporeal circulation interference on emergence from anesthesia in patients submitted to myocardial revascularization

BACKGROUND AND OBJECTIVES

Extracorporeal circulation (ECC) may change drug pharmacokinetics as well as brain function. The objectives of this study are to compare emergence time and postoperative sedation intensity assessed by the bispectral index (BIS) and the Ramsay sedation scale in patients undergoing myocardial revascularization (MR) with or without ECC.

METHOD

Ten patients undergoing MR with ECC (ECC group) and 10 with no ECC (no-ECC group) were administered with sufentanyl, propofol 2.0 μg.mL(-1) and pancuronium target controlled infusion. After surgery, propofol infusion was reduced to 1 μg.mL(-1) and suspended when extubation was indicated. Patients BIS, Ramsay scale and time to wake up were assessed.

RESULTS

The ECC group showed lower BIS values beginning at 60 minutes after surgery (no-ECC = 66±13 and ECC = 53±14, p=0.01) until 120 minutes after infusion (no-ECC = 85±8 and ECC = 73±12, p=0.02). Sedation level measured by the Ramsay scale was higher in the ECC group at 30 minutes after the end of the surgery (no-ECC = 5±1 and ECC = 6±0, p=0.021), at the end of infusion (no-ECC = 5±1 and ECC = 6±1, p=0.012) and 5 minutes after the end of infusion (no-ECC = 4±1 and ECC = 5±0.42, p=0.039). Emergence from anesthesia time was higher in the ECC group (no-ECC = 217±81 and ECC = 319±118, p=0.038).

CONCLUSIONS

There was a higher intensity of sedation after the end of surgery and a longer wake up time in ECC group, suggesting changes in the pharmacokinetics of propofol or effects of ECC on central nervous system.

Prospective, open-label investigation of the pharmacokinetics of daptomycin during cardiopulmonary bypass surgery

As methicillin-resistant Staphylococcus aureus (MRSA) becomes more prevalent, vancomycin is becoming increasingly used as a prophylaxis against surgical-site infections for cardiothoracic surgeries. However, vancomycin administration can be challenging, and the pharmacokinetics of alternative antibiotics in this setting are poorly understood. The primary objective of this investigation was to describe the pharmacokinetics of daptomycin in patients undergoing coronary artery bypass graft surgery. We enrolled 15 patients undergoing coronary artery bypass surgery requiring cardiopulmonary bypass. Each subject was administered a single open-label dose of daptomycin (8 mg/kg of body weight) for surgical prophylaxis. Fourteen daptomycin plasma samples were collected. Safety outcomes between subjects who received daptomycin and 15 control subjects who received the standard-of-care antibiotic were compared. The mean maximal concentration of daptomycin (C(max)) was 84.4 ± 27.1 μg/ml; the mean daptomycin concentration during the cardiopulmonary bypass procedure was 33.2 ± 11.4 μg/ml and was 30.9 ± 12.7 μg/ml at sternum closure. Mean daptomycin concentrations at 12, 18, 24, and 48 h were 22.7 ± 9.7, 16.2 ± 8.2, 12.0 ± 4.7, and 3.5 ± 2.3 μg/ml, respectively. Mean daptomycin concentrations were consistently above the MIC at which 90% of the tested isolates are inhibited (MIC₉₀) for S. aureus and S. epidermidis during the cardiopulmonary bypass procedure. Daptomycin was not associated with surgical-site infections or differences in adverse events compared to findings for control subjects. We found that a single dose of daptomycin at 8 mg/kg was well tolerated and achieved adequate plasma concentrations against common pathogens associated with surgical-site infections after cardiothoracic surgery. Daptomycin may be considered an alternative surgical prophylaxis antibiotic for patients undergoing cardiothoracic bypass surgery who are unable to receive vancomycin.

Population pharmacokinetics of remifentanil in infants and children undergoing cardiac surgery

Background

The aim of this study was to provide a model-based analysis of the pharmacokinetics of remifentanil in infants and children undergoing cardiac surgery with cardiopulmonary bypass (CPB).

Methods

We studied nine patients aged 0.5 to 4 years who received a continuous remifentanil infusion via a computer-controlled infusion pump during cardiac surgery with mildly hypothermic CPB were studied. Arterial blood samples taken prior to, during and after CPB were analyzed for remifentanil concentrations using a validated gas-chromatographic mass-spectrophotometric assay. We used population mixed-effects modeling to characterize remifentanil pharmacokinetics. The final model was evaluated by its predictive performance.

Results

The pharmacokinetics of remifentanil was described by a 1-compartment model with adjustments for CPB. Population mean parameter estimates were 1.41 L for volume of distribution (V) and 0.244 L/min for clearance. V was increased during CPB and post-CPB to 2.41 times the pre-CPB value. The median prediction error and the median of individual median absolute prediction error were 2.44% and 21.6%, respectively.

Conclusion

Remifentanil dosage adjustments are required during and after CPB due to marked changes in the V of the drug. Simulations indicate that a targeted blood concentration of 14 ng/mL is achieved and maintained in 50% of typical patients by administration of an initial dose of 18 μg remifentanil followed by an infusion of 3.7 μg/min before, during and post-CPB, supplemented with a bolus dose of 25 μg given at the start of CPB.

Effects of cardiopulmonary bypass on propofol pharmacokinetics and bispectral index during coronary surgery

PURPOSE

Cardiopulmonary bypass is known to alter propofol pharmacokinetics in patients undergoing cardiac surgery. However, few studies have evaluated the impact of these alterations on postoperative pharmacodynamics. This study was designed to test the hypothesis that changes in propofol pharmacokinetics increase hypnotic effects after cardiopulmonary bypass.

METHODS

Twenty patients scheduled for on-pump coronary artery bypass graft (group, n=10) or off-pump coronary artery bypass graft (group, n=10) coronary artery bypass grafts were anesthetized with sufentanil and a propofol target controlled infusion (2.0 microg/mL). Depth of hypnosis was monitored using the bispectral index. Blood samples were collected from the induction of anesthesia up to 12 hours after the end of propofol infusion, at predetermined intervals. Plasma propofol concentrations were measured using high-performance liquid chromatography, followed by a non-compartmental propofol pharmacokinetic analysis. Data were analyzed using ANOVA, considering p<0.05 as significant.

RESULTS

After cardiopulmonary bypass, despite similar plasma propofol concentrations in both groups, bispectral index values were lower in the on-pump coronary artery bypass graft group. Time to extubation after the end of propofol infusion was greater in the on-pump coronary artery bypass graft group (334 +/- 117 vs. 216 +/- 85 min, p = 0.04). Patients undergoing cardiopulmonary bypass had shorter biological (1.82 +/- 0.5 vs. 3.67 +/- 1.15 h, p < 0.01) and terminal elimination (6.27 +/- 1.29 vs. 10.5h +/- 2.18, p < 0.01) half-life values, as well as higher total plasma clearance (28.36 +/- 11.40 vs.18.29 +/- 7.67 mL/kg/min, p = 0.03), compared to patients in the off-pump coronary artery bypass graft group.

CONCLUSION

Aside from the increased sensitivity of the brain to anesthetics after cardiopulmonary bypass, changes in propofol pharmacokinetics may contribute to its central nervous system effects.

The effects of cardiopulmonary bypass on plasma concentrations and protein binding of methohexital and thiopental

The effects of cardiopulmonary bypass (CPB) on plasma concentrations and protein binding of methohexital and thiopental were studied during continuous infusions in two groups of ten cardiac surgical patients. Patients were administered an infusion regimen designed to produce a stable total plasma concentration at 5 mg/L for methohexital and 10 mg/L for thiopental. Prior to the commencement of CPB the mean (+/-SD) total plasma methohexital concentration was 5.00 +/- 0.69 mg/L. This fell to 3.12 +/- 0.89 mg/L at two minutes after commencement of CPB, and rose to 4.67 +/- 1.11 mg/L by 75 minutes after commencement of CPB. The unbound fraction rose from 27.1 +/- 5.1% to 42.8 +/- 9.2% at five minutes after the start of CPB, and gradually decreased to 32.1 +/- 4.9% by 75 minutes. The unbound concentration (1.37 +/- 0.32 mg/L) was unaffected by the onset of CPB, being 1.51 +/- 0.49 mg/L at 75 minutes after the start of CPB. Thiopental followed a similar pattern to methohexital, with the total plasma thiopental concentration falling from 9.22 +/- 0.73 mg/L to 4.90 +/- 0.83 mg/L at two minutes after commencement of CPB, and rising again to 7.13 +/- 1.03 mg/L 75 minutes later. During the same period the unbound fraction of thiopental rose from 16.1 +/- 2.5% to 30.3 +/- 7.3% five minutes after the start of CPB, and fell gradually to 22.8 +/- 5.8% after 75 minutes. The unbound concentration (1.51 +/- 0.21 mg/L) was again unchanged by the onset of CPB, being 1.71 +/- 0.29 mg/L at 75 minutes. Plasma protein binding of both drugs correlated strongly with plasma albumin concentration, which decreased by 40% during CPB. It is concluded that hemodilution caused the reduction in total drug concentration and protein binding at the onset of CPB, but that the decrease in protein binding counteracted the dilution of unbound drug, resulting in a stable unbound concentration throughout CPB, and that this effect may be common for barbiturates.

Cardiopulmonary bypass alters the pharmacokinetics of propranolol in patients undergoing cardiac surgery

The pharmacokinetics of propranolol may be altered by hypothermic cardiopulmonary bypass (CPB), resulting in unpredictable postoperative hemodynamic responses to usual doses. The objective of the present study was to investigate the pharmacokinetics of propranolol in patients undergoing coronary artery bypass grafting (CABG) by CPB under moderate hypothermia. We evaluated 11 patients, 4 women and 7 men (mean age 57 +/- 8 years, mean weight 75.4 +/- 11.9 kg and mean body surface area 1.83 +/- 0.19 m(2)), receiving propranolol before surgery (80-240 mg a day) and postoperatively (10 mg a day). Plasma propranolol levels were measured before and after CPB by high-performance liquid chromatography. Pharmacokinetic Solutions 2.0 software was used to estimate the pharmacokinetic parameters after administration of the drug pre- and postoperatively. There was an increase of biological half-life from 4.5 (95% CI = 3.9-6.9) to 10.6 h (95% CI = 8.2-14.7; P < 0.01) and an increase in volume of distribution from 4.9 (95% CI = 3.2-14.3) to 8.3 l/kg (95% CI = 6.5-32.1; P < 0.05), while total clearance remained unchanged 9.2 (95% CI = 7.7-24.6) vs 10.7 ml min(-1) kg(-1) (95% CI = 7.7-26.6; NS) after surgery. In conclusion, increases in drug distribution could be explained in part by hemodilution during CPB. On the other hand, the increase of biological half-life can be attributed to changes in hepatic metabolism induced by CPB under moderate hypothermia. These alterations in the pharmacokinetics of propranolol after CABG with hypothermic CPB might induce a greater myocardial depression in response to propranolol than would be expected with an equivalent dose during the postoperative period.

Systemic availability of prophylactic cefuroxime in patients submitted to coronary artery bypass grafting with cardiopulmonary bypass

Cardiopulmonary bypass and hypothermia (HCPB) is a procedure commonly used during heart surgery, representing a risk factor for the patient by promoting extensive haemodilution and profound physiological changes. Cefuroxime is used for the prevention of infection following heart surgery, and several dose schemes have been suggested for prophylaxis with cefuroxime. The objective of the present study was to assess, in a comparative manner, the systemic availability of cefuroxime administered intravascularly as a bolus dose of 1.5 g to 17 patients having heart surgery with or without HCPB. Plasma cefuroxime concentrations were determined by high-pressure liquid chromatography-UV, and the following values, expressed as medians, were obtained for the study group compared with controls: 69.1 vs. 62.7 mg/L (1st h), 35.8 vs. 26.0mg/L (3rd h), 14.6 vs. 8.7 mg/L (6th h, P<0.05), 6.1 vs. 3.0mg/L (9th h, P<0.05) and 2.6 vs. 1.0mg/L (12th h, P<0.05). Despite the differences recorded during the study period as a consequence of HCPB, low antibiotic concentrations were found as early as 6h post dose for both groups investigated. Thus, the low systemic availability of cefuroxime after the administration of a 1.5-g dose may not protect against postoperative infections. The data obtained permit us to recommend a change in the dose scheme in order to maintain adequate plasma levels of cefuroxime.

Pharmacokinetics and a simulation model of colforsin daropate, new forskolin derivative inotropic vasodilator, in patients undergoing coronary artery bypass grafting

Colforsin daropate, a water-soluble forskolin derivative, is an adenyl cyclase activator with positive inotropic and vasodilatory effects that are useful in the treatment of ventricular dysfunction. We investigated the pharmacokinetics of colforsin daropate in cardiac surgery patients and performed simulations to determine the dosage necessary to maintain an effective plasma concentration following cardiopulmonary bypass. In six patients undergoing coronary artery bypass graft, colforsin daropate (0.01mgkg(-1)) was administered immediately after separation from cardiopulmonary bypass. Arterial blood was sampled over the next 16h and plasma concentrations of colforsin daropate and its initial active metabolite were determined by gas-chromatography. Extended nonlinear least-squares regression was used to fit a three-compartment model to each patient's data. Distribution half-life (t(1/2alpha)) was 3.9+/-1.1min, metabolic half-life (t(1/2beta)) was 1.9+/-0.7h, and elimination half-life (t(1/2gamma)) was 95.3+/-15.2h. Central-compartment volume was 591.0+/-42.8mlkg(-1), volume distribution was 2689.2+/-450.6mlkg(-1), and elimination clearance was 27.7+/-14.7mlkg(-1)min(-1). In the pharmacokinetic simulation model, 0.5, 0.75, and 1.0microgkg(-1)min(-1) continuous infusion of colforsin daropate produce effective concentration (5-10ngml(-1)) within 30, 20, and 10min, respectively following administration. An initial active metabolite of decreased rapidly to less than 1.0ngml(-1) within the first 10min.A colforsin daropate infusion of 0.7-1.0microgkg(-1)min(-1) for 10-20min followed by 0.5microgkg(-1)min(-1) continuous infusion is recommended to produce an effective concentration (5-10ngml(-1)) within 10-20min and to maintain a therapeutic concentration throughout the administration period after cardiopulmonary bypass.

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.

Intrathecal versus IV fentanyl in pediatric cardiac anesthesia

Systemic large-dose opioids are widely used in pediatric cardiac anesthesia, but there are no randomized, prospective studies regarding the use of intrathecal (IT) opioids for these procedures. In this randomized, prospective study, we compared cardiovascular and neurohumoral responses during IT or IV fentanyl anesthesia for pediatric cardiac surgery. Thirty children aged 6 mo to 6 yr were anesthetized with an IV fentanyl bolus of 10 micro g/kg. This was followed by a fentanyl infusion of 10 micro g. kg(-1). h(-1) (Group IV; n = 10), 2 micro g/kg of IT fentanyl (Group IT; n = 10), or combined IV and IT protocols (Group IV + IT; n = 10). Heart rate, mean arterial blood pressure, additional fentanyl doses, time to first analgesic requirement, COMFORT and Children's Hospital of Eastern Ontario Pain Scale scores, and extubation time were recorded. Blood cortisol, insulin, glucose, and lactate levels were measured presurgery, poststernotomy, during the rewarming phase of cardiopulmonary bypass (CPB), and 6 and 24 h after surgery. The patients' urinary cortisol excretion rates were also measured during the first postoperative day. The findings in all three groups were statistically similar, except for higher blood glucose levels during CPB in Group IT compared with Group IV (P < 0.004). Group IV + IT was the only group in which the increases in heart rate and mean arterial blood pressure from presurgery to poststernotomy were not significant. The 24-h urinary cortisol excretion rates ( micro g. kg(-1). d(-1)) were 61.51 +/- 39, 92.54 +/- 67.55, and 40.15 +/- 29.69 for Groups IV, IT, and IV + IT, respectively (P > 0.05). A single IT injection of fentanyl 2 micro g/kg offers no advantage over systemic fentanyl (10 micro g/kg bolus and 10 micro g. kg(-1). h(-1)) with regard to hemodynamic stability or suppression of stress response. The combination of these two regimens may provide better hemodynamic stability during the pre-CPB period and may be associated with a decreased 24-h urinary cortisol excretion rate.

IMPLICATIONS

In this prospective, randomized study, we investigated the adequacy of a single intrathecal injection of fentanyl for intraoperative analgesia, compared the effects of IT and IV fentanyl on stress response, and assessed for an additive effect of IT and IV fentanyl administration in pediatric cardiac anesthesia. The results with these three different anesthetic regimens were similar regarding anesthesia depth and level of stress response. However, the combination of IT and IV routes may provide better hemodynamic stability and a less pronounced stress response, as reflected by 24-h urinary cortisol excretion.

The pharmacokinetics of remifentanil in patients undergoing coronary artery bypass grafting with cardiopulmonary bypass

Remifentanil is a potent opioid with a short duration of action. It has the potential for large-dose opioid anesthesia without an obligatory prolonged period of mechanical ventilation. However, because of high clearance and rapid tissue distribution, cardiopulmonary bypass (CPB) may influence its pharmacokinetics and alter drug requirements. We administered remifentanil by continuous infusion to 68 patients having coronary artery bypass graft surgery during CPB with hypothermia to describe the effects of these interventions on its pharmacokinetics. Remifentanil concentrations were measured before, during, and after CPB. Disposition was best described by a two-compartment model. The volume of distribution increased by 86% with institution of CPB and remained increased after CPB. Elimination clearance decreased by 6.37% for each degree Celsius decrease from 37 degrees C.

IMPLICATIONS

Remifentanil concentrations decrease with the institution of cardiopulmonary bypass because of an increase in the volume of distribution. The decrease in elimination clearance with hypothermia results in increased total remifentanil concentrations during cardiopulmonary bypass if the infusion rate is not altered. More constant blood remifentanil levels may be obtained by reducing remifentanil infusion rate by 30% for each 5 degrees C decrease in temperature.

Pharmacokinetics of vancomycin administered as prophylaxis before cardiac surgery

Vancomycin concentrations in serum, tissues, and sternum, administered as prophylaxis to patients during coronary artery bypass surgery, were measured. Vancomycin (15 mg/kg) was administered to 15 patients 1 hour before skin incision. Blood, tissue, and sternum samples were collected before, during, and after bypass. The concentration in serum at the end of infusion was 55.1 +/- 22.8 microg/mL, the mean elimination half-life was 9 +/- 4 hours, the areas under the concentration-time curve (AUC) from 0 to 12 hours and from 0 to infinity were 90.6 +/- 25.1 and 289.7 +/- 86.5 microg/h per mL, respectively, the mean residence time (MRT) was 11.9 +/- 5.0 hours, the mean volume of distribution was 51.1 +/- 12.2 L, and the total clearance was 78.3 +/- 32.6 mL/min. Vancomycin concentrations in serum, tissues, and sternum during the operation were greater than the MIC90 for most staphylococci and ranged from 16 to 55 microg/mL in serum and from 4 to 39 microg/g in sternum and tissues.

The pharmacokinetics of anesthetic drugs and adjuvants during cardiopulmonary bypass

The institution of cardiopulmonary bypass during cardiac surgery has profound effects on the plasma concentration of drugs and thus their therapeutic effectiveness. These changes occur through acute hemodilution, altered plasma protein binding, hypotension, as well as the use of hypothermia and heparin administration. Isolation of the lungs from the circulation and the possible sequestration of drugs in the bypass circuit also affect drug plasma concentrations on bypass. The individual characteristics of the drug in question are also important in determining the final plasma concentration: Lipid soluble drugs with a high volume of distribution may be more readily taken up by bypass equipment, but the initial fall in concentration at the start of cardiopulmonary bypass may be more readily counteracted by back diffusion into plasma, if large tissue stores have accumulated. The extent of the drug's plasma protein binding is of importance as the effective free fraction in plasma for highly bound drugs will be sensitive to changes in plasma protein binding brought on by factors such as hemodilution, heparin administration as well as alpha, acid-glycoprotein binding. Clearly the fate of drugs administered before or on bypass is complex and can only be accurately determined by specific studies evaluating drug plasma concentrations. This review updates the available data on anesthetics and drugs used during cardiac surgery in order that anesthetists may predict better the likely effect of drugs administered before or during cardiopulmonary bypass.

The effects of cardiopulmonary bypass on remifentanil kinetics in children undergoing atrial septal defect repair

Cardiopulmonary bypass (CPB) can greatly influence the pharmacokinetics of opioids. This study investigated the pharmacokinetic profile of remifentanil in 12 pediatric patients undergoing CPB for repair of an atrial septal defect. All patients received remifentanil (5 microg/kg) over 1 min into a peripheral vein both before the onset of CPB and after the discontinuation of CPB. Arterial blood samples were obtained at defined time periods, and remifentanil concentration was determined using high-performance liquid chromatography ultraviolet detection. The pharmacokinetic profiles both before and after bypass were determined in all 12 patients. There was no change in the volume of distribution at steady state, the volume of the central compartment, or the alpha- and beta-elimination half-life. Although the clearance values increased 20% in the postbypass period (from 38.7 +/- 9.6 to 46.8 +/- 14 mL x kg(-1) x min(-1), there was no meaningful change in the coefficient of variation (from 25% to 30%).

IMPLICATIONS

After cardiopulmonary bypass the clearance of remifentanil increases in children. However, the relative lack of change in the coefficient of variation suggests that remifentanil should be a predictable drug in the postcardiopulmonary bypass period.

The pharmacokinetics of a single dose of gentamicin (4 mg/kg) as prophylaxis in cardiac surgery requiring cardiopulmonary bypass

BACKGROUND

Cardiopulmonary bypass has complex effects on drug pharmacokinetics, which is important when considering the use of once-daily aminoglycoside regimens during cardiac surgery.

AIM

To study the effects of cardiopulmonary bypass on the pharmacokinetics of a single dose of gentamicin (4 mg/kg).

PATIENTS AND METHODS

Nine patients undergoing valve replacement surgery were given a single dose of gentamicin (4 mg/kg) at induction of anaesthesia and blood was taken for assay at 0, O.5, 1, 1.5, 2, 2.5, 3, 4, 6, 10, 16, 22 and 24 h following administration. The mean (range) gentamicin Cmax was 18.7 (12.4-26.3) mg/litre. Three patients had concentrations of gentamicin after 24 h of > 1 mg/litre. During cardiopulmonary bypass, the mean (range) gentamicin half-life (t1/2) was 5.1 (2.0-15.1) h and post-bypass the t1/2 was 7.1 (3.0-13.9) h.

CONCLUSION

There is significant correlation between the elimination t1/2 and length of cardiopulmonary bypass (r = 0.89, P < 0.01). These results suggest that gentamicin excretion is delayed following cardiopulmonary bypass so that with dose regimens of > 4 mg/kg there is a risk of toxicity.

Pharmacokinetic alterations after severe head injury. Clinical relevance

Pharmacological therapy, present and future, will undoubtedly continue to play a large role within the overall management of patients with severe head injury. Nevertheless, limited clinical data are available to evaluate the effect of severe head injury on pharmacokinetics. The disruption of the blood-brain barrier secondary to trauma and/or subsequent hyperosmolar therapy can be expected to result in higher than expected brain drug concentrations. Aggressive dietary protein supplementation may result in increased oxidative drug metabolism. These effects may counterbalance inhibitory influences on drug metabolism secondary to cytokine release during the acute phase response. Alterations in protein binding can also be anticipated with the hypoalbuminaemia and increases in alpha 1-acid glycoprotein typically observed in these patients. Based on studies in other patient populations, moderate hypothermia, a treatment strategy in patients with head injury, can decrease drug metabolism. The pharmacokinetics of the following drugs in patients with severe head injury have been studied: phenytoin, pentobarbital (pentobarbitone), thiopental (thiopentone), tirilazad, and the agents used as marker substrates, antipyrine, lorazepam and indocynanine green (ICG). Several studies have documented increase in metabolism over time with phenytoin, pentobarbital, thiopental, antipyrine and lorazepam. Increases in tirilazad clearance were also observed but attributed to concurrent phenytoin therapy. No changes in the pharmacokinetics of ICG were apparent following head injury. With the frequent use of potent inhibitors of drug metabolism (e.g., cimetidine, ciprofloxacin) the potential for drug interaction is high in patients with severe head injury. Additional pharmacokinetic investigations are recommended to optimise pharmacological outcomes in patients with severe head injury.

Elimination of drugs and toxins during cardiopulmonary bypass

Cardiopulmonary bypass (CPB) creates a myriad of pharmacological and physiological changes. Some of these changes have been studied in isolated in vitro studies. Integrating an in vitro system into an in vivo process is so complicated that many pharmacological studies simply avoid the bypass period. For the most part, the studies that do examine the bypass period deal with a single drug, reporting how it does or does not produce a predicted concentration on initiation, maintenance and termination of CPB. Based on the isolated results of these studies, this review hypothesizes a model that explains how different substances interact with the CPB system. A summary of the review's findings include the following: 1) drugs with a smaller volume of distribution are more likely to be effected; 2) the pharmacokinetic effects of lipophilic drugs undergo more alterations than hydrophilic drugs; and 3) protein binding minimizes alterations of lipophilic drugs and increase alterations of hydrophilic drugs.

Diclofenac plasma protein binding: PK-PD modelling in cardiac patients submitted to cardiopulmonary bypass

Twenty-four surgical patients of both sexes without cardiac, hepatic, renal or endocrine dysfunctions were divided into two groups: 10 cardiac surgical patients submitted to myocardial revascularization and cardiopulmonary bypass (CPB), 3 females and 7 males aged 65 +/- 11 years, 74 +/- 16 kg body weight, 166 +/- 9 cm height and 1.80 +/- 0.21 m2 body surface area (BSA), and control, 14 surgical patients not submitted to CPB, 11 female and 3 males aged 41 +/- 14 years, 66 +/- 14 kg body weight, 159 +/- 9 cm height and 1.65 +/- 0.16 m2 BSA (mean +/- SD). Sodium diclofenac (1 mg/kg, im Voltaren 75 twice a day) was administered to patients in the Recovery Unit 48 h after surgery. Venous blood samples were collected during a period of 0-12 h and analgesia was measured by the visual analogue scale (VAS) during the same period. Plasma diclofenac levels were measured by high performance liquid chromatography. A two-compartment open model was applied to obtain the plasma decay curve and to estimate kinetic parameters. Plasma diclofenac protein binding decreased whereas free plasma diclofenac levels were increased five-fold in CPB patients. Data obtained for analgesia reported as the maximum effect (EMAX) were: 25% VAS (CPB) vs 10% VAS (control), P < 0.05, median measured by the visual analogue scale where 100% is equivalent to the highest level of pain. To correlate the effect versus plasma diclofenac levels, the EMAX sigmoid model was applied. A prolongation of the mean residence time for maximum effect (MRTEMAX) was observed without any change in lag-time in CPB in spite of the reduced analgesia reported for these patients, during the time-dose interval. In conclusion, the extent of plasma diclofenac protein binding was influenced by CPB with clinically relevant kinetic-dynamic consequences.

Maintenance of therapeutic plasma aprotinin levels during prolonged cardiopulmonary bypass using a large-dose regimen

Aprotinin concentrations in the range of 127-191 kallikrein inactivator units (KIU)/mL at the end of cardiopulmonary bypass (CPB) (< 2 h duration) reduce transfusion requirements. It has been suggested that prolonged CPB may require higher infusion rates which significantly increase cost. We tested the hypothesis that large-dose aprotinin maintains therapeutic plasma levels during prolonged periods of CPB (< 2 h). Aprotinin was administered as follows: 2 x 10(6) KIU upon skin incision; 0.5 x 10(6) KIU/h x 4-h infusion on initiation of CPB; and 2 x 10(6) KIU added to the CPB prime solution. Aprotinin activity was measured 1) 30 min after initiation of drug administration (Pre-CPB); 2) 30 min after initiation of CPB (CPB + 30); 3) 90 min after initiation of CPB (CPB + 90); and 4) at CPB termination (End CPB). CPB duration (mean +/- SD) was 158 +/- 51 min. Plasma aprotinin concentrations (KIU/mL, mean +/- SD) were: 234 +/- 30 at Pre-CPB; 229 +/- 35 at CPB + 30; 184 +/- 27 at CPB + 90; and 179 +/- 22 at End CPB. In all patients, aprotinin levels at the completion of CPB were in the range previously reported to be effective. The authors conclude that large-dose regimen limited to 6 x 10(6) KIU maintained therapeutic plasma aprotinin concentrations during prolonged CPB.

Clinical pharmacokinetics of alfentanil, fentanyl and sufentanil. An update

Alfentanil, fentanyl and sufentanil are synthetic opioid analgesics acting at specific opioid receptors. These opioids are widely used as analgesics to supplement general anaesthesia for various surgical procedures or as primary anaesthetic agents in very high doses during cardiac surgery. Fentanyl and sufentanil especially are administered via infusion for long term analgesia and sedation in intensive care patients. Opioid analgesics are mainly administered using the intravenous route. However, other techniques of administration, including epidural, intrathecal, transdermal and intranasal applications, have been demonstrated. Important pharmacokinetic differences between alfentanil, fentanyl and sufentanil have been shown in many reports. Alfentanil has the most rapid analgesic onset and time to peak effect as well as the shortest distribution and elimination half-lives. The volume of distribution and total body clearance of this agent are smaller when compared with those of fentanyl and sufentanil. The pharmacokinetics of the opioid analgesics can be affected by several factors including patient age, plasma protein content, acid-base status and cardiopulmonary bypass, but not significantly by renal insufficiency or compensated hepatic dysfunction. In addition, pharmacokinetic properties can be influenced by changes in hepatic blood flow and administration of drug combinations which compete for the same plasma protein carrier or metabolising pathway. Although comparing specific pharmacokinetic parameters such as half-lives is deeply entrenched in the literature and clinical practice, simply comparing half-lives is not a rational way to select an opioid for specific requirements. Using pharmacokinetic-pharmacodynamic models, computer simulations based on changes in the effect site opioid concentration or context-sensitive half-times seem to be extremely useful for selecting an opioid on a more rational basis.

Pharmacokinetics of vancomycin in critically ill infants undergoing extracorporeal membrane oxygenation

Extracorporeal membrane oxygenation (ECMO) is a widely used therapy for neonates with respiratory failure. Because of sepsis, many of these infants require antibiotics like vancomycin during ECMO treatment. ECMO transiently alters renal function and increases the circulating blood volume by 75%. Initial vancomycin pharmacokinetics were determined in 12 infants undergoing ECMO to determine an adequate drug administration regimen. Vancomycin dosage was based on current recommendations for weight and gestational age. Pharmacokinetic parameters were determined by fitting the data to a two compartment model. This study yielded a mean steady-state volume of distribution of 1.1 +/- 0.5 (range, 0.6 to 2.1) liters/kg and a mean vancomycin clearance of 0.78 +/- 0.19 (range, 0.49 to 1.07) ml/min/kg. The mean vancomycin half-life was 16.9 +/- 9.5 (range, 8.8 to 42.9) h. Nomogram-calculated creatinine clearance was a significant predictor of vancomycin terminal rate constant and clearance. These data suggest alterations in the pharmacokinetics of vancomycin in infants on ECMO. With the goal of achieving vancomycin concentrations in serum above the MIC for the offending pathogen while using the least amount of the drug necessary, new administration guidelines for term infants without renal impairment undergoing ECMO should be 20 mg of vancomycin per kg at an interval of 24 h. With significant renal impairment, the interval should be extended on the basis of concentrations in serum. In comparison with previously published data, the neonates undergoing ECMO in our study demonstrated a much larger volume of distribution, a lower clearance, and consequently a longer vancomycin half-life.

The effect of midazolam at two plasma concentrations of hemodynamics and sufentanil requirement in coronary artery surgery

OBJECTIVES

In this study, the hemodynamics and sufentanil requirement were compared at two midazolam target plasma concentrations in patients undergoing coronary artery bypass grafting (CABG).

DESIGN

Prospective, randomized study.

SETTING

University hospital, single institution.

PARTICIPANTS

Patients undergoing CABG.

INTERVENTIONS

Patients were randomly assigned to receive midazolam at a target plasma concentration of 150 ng/mL (group 1; n = 10) or 300 ng/mL (group 2; n = 10). Sufentanil infusion was titrated to maintain hemodynamic stability, defined as mean arterial pressure within 15% of baseline values. All patients received preoperative beta-blocking agents. Arterial blood samples of midazolam and sufentanil were analyzed by high-performance liquid chromatography and radioimmunoassay, respectively.

MEASUREMENTS AND MAIN RESULTS

The mean dose of sufentanil (7.5 +/- 1.7 microgram/kg in group 1 v 7.2 +/- 2.5 micrograms/kg in group 2) did not differ. There were no significant differences in hemodynamics between the groups in the period before or after cardiopulmonary bypass (CPB). Before CPB, in two patients in each group, hypertension was controlled with sufentanil only. One patient in group 1 required a vasodilator in addition to sufentanil. No ischemic events occurred before CPB. After CPB, one patient in group 2 required a vasodilator to control hypertension. Two patients in group 2 required treatment with nitroglycerin for myocardial ischemia. Stable plasma concentrations of sufentanil and midazolam were obtained during and after CPB. The midazolam infusion was continued in both groups at a rate of 1.25 micrograms/kg/min during the first 4 postoperative hours. The time to awakening did not differ between the groups (100 +/- 58 minutes in group 1 v 173 +/- 147 minutes in group 2) nor did the plasma concentrations of midazolam (96 +/- 28 ng/mL v 108 +/- 42 ng/mL) at the time of awakening. Intraoperative awareness was not reported.

CONCLUSION

In patients undergoing CABG, good hemodynamic control with a similar incidence of hemodynamic interventions was observed at midazolam target plasma concentrations of 150 and 300 ng/mL when coadministered with sufentanil. The sufentanil requirement was identical in both groups. This study suggests that a midazolam plasma concentration of 150 ng/mL is sufficient to provide satisfactory hemodynamic control and to avoid intraoperative awareness.

The pharmacokinetics of alfentanil after normothermic and hypothermic cardiopulmonary bypass

The pharmacokinetics of alfentanil were studied after two different methods of cardiopulmonary bypass (CPB) which used either a normothermic technique or a hypothermic technique with body temperatures below 30 degrees C. A group of surgical patients who did not undergo CPB were also studied. All patients (n = 36) received alfentanil 50 micrograms/kg as a rapid infusion over 10 min and plasma levels were measured for the following 8 h. The volume of distribution in steady state (Vdss) and the volume of central compartment (Vc) were significantly greater in the CPB groups (P = 0.009 and P = 0.04), compared to the nonbypass group. However, the elimination half-life of alfentanil (t1/2 beta) (mean, 95% confidence interval) did not differ significantly between the normothermic (134 min, range 104-172), hypothermic (143 min, range 111-184), and nonbypass (111 min, range 86-142) groups. Between the normothermic and hypothermic CPB groups no significant differences in Vdss, rate of clearance (Cl), or t1/2 beta were found. The pharmacokinetics of alfentanil showed fewer changes after CPB in this study than have been reported previously. Furthermore, different temperature management protocols during CPB did not influence alfentanil elimination.

Comparison of two different loading doses of milrinone for weaning from cardiopulmonary bypass

OBJECTIVE

To compare the hemodynamic effects, pharmacokinetic profiles, and the need for vasoactive agents between a low (20 micrograms/kg during 15 minutes [group 1; n = 10]) and a high (40 micrograms/kg during 15 minutes [group 2; n = 10]) loading dose of milrinone.

DESIGN

Prospective, randomized, double-blind.

SETTING

University hospital.

PARTICIPANTS

Twenty patients scheduled for elective coronary artery surgery.

INTERVENTIONS

Weaning from CPB was achieved using a strict protocol. After atrioventricular pacing at 90 beats per minute and preload optimalization, a first weaning attempt was started with only calcium and nitroglycerin as support. If this attempt was unsuccessful (cardiac index < 2L/min/m2), CPB was reinitiated and weaning level 2 was prepared, consisting of inotropic support with milrinone. Patients received either the low (group 1) or the high (group 2) loading dose of milrinone. After the end of the loading dose, a continuous infusion of milrinone of 0.5 micrograms/kg/min was started in both groups.

MEASUREMENTS AND MAIN RESULTS

Both groups were comparable regarding preoperative and intraoperative data. Hemodynamic data were comparable in both groups at each time of measurement (p = 0.941). The need for vasoactive medication (norepinephrine [NE]) in order to keep mean arterial pressure > or = 50 mm Hg was significantly higher in group 2 (p = 0.004). Need for NE during the loading infusion was 9.6 +/- 4.9 micrograms (mean +/- SEM) in group 1 and 41.6 +/- 7.6 micrograms in group 2 (p = 0.004). Need for NE during the immediate post-CPB period was also higher in group 2 (16.0 +/- 10.4 micrograms in group 1 and 232.5 +/- 82.8 micrograms in group 2 (p = 0.002)). Plasma clearance of milrinone after CPB was less in both groups than in healthy volunteers. However, clearance of milrinone was significantly higher in group 2 (p = 0.006), and consequently, half-life of milrinone was significantly less in group 2 (p = 0.007).

CONCLUSIONS

The present results demonstrate that when milrinone is used during weaning from CPB, a loading dose of 20 micrograms/kg provided to similar hemodynamic support a loading dose of 40 micrograms/kg. The need for vasoconstrictive medication was significantly less in the group with the low loading dose.

Pharmacokinetics of alcuronium in children with acyanotic and cyanotic cardiac disease undergoing cardiopulmonary bypass surgery

The aim of this study was to determine the pharmacokinetic parameters for alcuronium in children with cyanotic or acyanotic congenital cardiac disease undergoing cardiopulmonary bypass surgery and to compare these parameters with previously reported values in children and adults with normal cardiac function. Seven children with acyanotic disease and seven with cyanotic disease were studied. Alcuronium (base) was administered in an initial dosage of 0.25 mg.kg-1 with additional doses as needed to maintain paralysis. Using time averaged data, cyanotic children had lower mean clearance, elimination half-life and volume of distribution at steady state than the acyanotic children; none of these differences was, however, statistically significant. In this study, children with acyanotic and cyanotic cardiac disease undergoing bypass, had a diminished clearance (P < 0.05) and a smaller volume of distribution (P < 0.05) than normal children and a shorter elimination half-life (P < 0.05) than adults. Onset of cardiopulmonary bypass caused an immediate marked decrease in alcuronium plasma concentrations which remained low in the acyanotic children at the completion of bypass.