Elimination of drugs and toxins during cardiopulmonary bypass

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.

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.

Pharmacokinetics of tranexamic acid in neonates and infants undergoing cardiac surgery

AIM

Tranexamic acid (TXA) continues to be one of the antifibrinolytics of choice during paediatric cardiac surgery. However, in infants less than 1 year of age, the optimal dosing based on pharmacokinetic (PK) considerations is still under discussion.

METHODS

Forty-three children less than 1 year of age were enrolled, of whom 37 required the use of cardiopulmonary bypass (CPB) and six were operated on without CPB. Administration of 50 mg kg^-1 TXA intravenously at the induction of anaesthesia was followed by 50 mg kg^-1 into the CPB prime in the CPB group. Plasma concentrations of TXA were analysed by gas chromatography-mass spectrometry. PK data were investigated using nonlinear mixed-effect models.

RESULTS

A two-compartment model was fitted, with the main covariates being allometrically scaled bodyweight, CPB, postmenstrual age (PMA). Intercompartmental clearance (Q), peripheral volume (V2), systemic clearance, (CL) and the central volume (V1) were calculated. Typical values of the PK parameter estimates were as follows: CL = 3.78 [95 % confidence interval (CI) 2.52, 5.05] l h^-1 ; central volume of distribution = 13.6 (CI 11.7, 15.5) l; Q = 16.3 (CI 13.5, 19.2) l h^-1 ; V2 = 18.0 (CI 16.1, 19.9) l. Independently of age, 10 mg kg^-1 TXA as a bolus, a subsequent infusion of 10 mg kg^-1 h^-1 , then a 4 mg kg^-1 bolus into the prime and a reduced infusion of 4 mg kg^-1 h^-1 after the start of CPB are required to maintain TXA concentrations continuously above 20 μg ml^-1 , the threshold value for an effective inhibition of fibrinolysis and far lower than the usual peak concentrations (the '10-10-4-4 rule').

CONCLUSIONS

The introduction of a modified dosing regimen using a starting bolus followed by an infusion and a CPB prime bolus would prohibit the potential risk of seizures caused by high peak concentrations and also maintain therapeutic plasma concentration above 20 μg ml^-1 .

Propofol Is Cardioprotective in a Clinically Relevant Model of Normothermic Blood Cardioplegic Arrest and Cardiopulmonary Bypass

The general anesthetic propofol has been shown to be cardioprotective. However, its benefits when used in cardioplegia during cardiac surgery have not been demonstrated. In this study, we investigated the effects of propofol on metabolic stress, cardiac function, and injury in a clinically relevant model of normothermic cardioplegic arrest and cardiopulmonary bypass. Twenty anesthetized pigs, randomized to propofol treatment ( n = 8) and control ( n =12) groups, were surgically prepared for cardiopulmonary bypass (CPB) and cardioplegic arrest. Doses of warm blood cardioplegia were delivered at 15-min intervals during a 60-min aortic cross-clamped period. Propofol was continuously infused for the duration of CPB and was therefore present in blood cardioplegia. Myocardial biopsies were collected before, at the end of cardioplegic arrest, and 20 mins after the release of the aortic cross-clamp. Hemodynamic parameters were monitored and blood samples collected for cardiac troponin I measurements. Propofol infusion during CPB and before ischemia did not alter cardiac function or myocardial metabolism. Propofol treatment attenuated the changes in myocardial tissue levels of adenine nucleotides, lactate, and amino acids during ischemia and reduced cardiac troponin I release on reperfusion. Propofol treatment reduced measurable hemodynamic dysfunction after cardioplegic arrest when compared to untreated controls. In conclusion, propofol protects the heart from ischemia-reperfusion injury in a clinically relevant experimental model. Propofol may therefore be a useful adjunct to cardioplegic solutions as well as being an appropriate anesthetic for cardiac surgery.

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.

Determinants of drug absorption in different ECMO circuits

Purpose

The aim of this in vitro study was to evaluate potential determinants of drug loss in different ECMO circuits.

Methods

Midazolam, morphine, fentanyl, paracetamol, cefazolin, meropenem and vancomycin were injected into three neonatal roller pump, two paediatric roller pump and two clinically used neonatal roller pump circuits, all with a silicone membrane, and two neonatal centrifugal pump circuits with polypropylene hollow-fibre membranes. Serial blood samples were taken from a post-oxygenator site. Drug recovery was calculated as the ratio between the determined and the theoretical maximum concentration. The latter was obtained by dividing dose by theoretical circuit volume.

Results

Average drug recoveries at 180 min in three neonatal silicone membrane roller pump circuits were midazolam 0.62%, morphine 23.9%, fentanyl 0.35%, paracetamol 34.0%, cefazolin 84.3%, meropenem 82.9% and vancomycin 67.8%. There was a significant correlation between the lipophilicity of the drug expressed as log P and the extent of drug absorption, p < 0.001. The recovery of midazolam and fentanyl in centrifugal pump circuits with hollow-fibre membrane oxygenator was significantly higher compared to neonatal roller pump circuits with silicone membranes: midazolam 63.4 versus 0.62%, fentanyl 33.8 versus 0.35%, p < 0.001. Oxygenator size and used circuits do not significantly affect drug losses.

Conclusions

Significant absorption of drugs occurs in the ECMO circuit, correlating with increased lipophilicity of the drug. Centrifugal pump circuits with hollow-fibre membrane oxygenators show less absorption for all drugs, most pronounced for lipophilic drugs. These results suggest that pharmacokinetics and hence optimal doses of these drugs may be altered during ECMO.

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.

Nesiritide during extracorporeal membrane oxygenation

Nesiritide is a recombinant formulation of B-type natriuretic peptide (BNP). Preliminary experience in the adult population has shown nesiritide to be an effective agent in the treatment of decompensated congestive heart failure (CHF) in adults. Given its physiological effects, it may be an effective agent in other clinical scenarios. We report the use of nesiritide in two infants during extracorporeal membrane oxygenation (ECMO). In one patient, nesiritide in doses up to 0.09 microg.kg(-1).min(-1) were used to control mean arterial pressure while in the other patient, doses of 0.01-0.03 microg.kg(-1).min(-1) were used to augment urine output. The potential applications of nesiritide and dosing regimens for this agent in the ECMO population are discussed.

Vecuronium pharmacokinetics and pharmacodynamics during hypothermic cardiopulmonary bypass in infants and children

PURPOSE

To determine the effect of moderate and deep hypothermic cardiopulmonary bypass (CPB) on the pharmacokinetic and pharmacodynamic behaviour of vecuronium in infants and children.

METHODS

We studied 12 patients undergoing surgery for congenital heart disease under narcotic-nitrous oxide anesthesia. Neuromuscular blockade was maintained constant (TI 4-10% by Datex electromyograph) by adjusting a vecuronium infusion. Plasma vecuronium concentrations (Cpss) were analysed by HPLC to describe a pseudosteady-state during each of the pre-CPB, CPB and post-CPB phases. Paired arterial blood samples were taken 20 min apart after at least 20 min of constant infusion.

RESULTS

Nine cases were analysed, mean age 20 mo, mean weight 9 kg. Three patients had deep and six moderate hypothermia. In the pre-CPB phase Cpss fell into two groups (mean +/- SD: 330 +/- 42 ng x ml(-1); 127 +/- 27 ng x ml(-1); P < 0.001); similarly the clearances showed a bimodal distribution (mean +/- SD: 5.08 +/- 0.94; 11.51 +/- 0.2 ml x min(-1) x kg(-1) P < 0.001), although in different patients. During CPB this bimodal distribution disappeared. Vecuronium infusion rate (VIR) decreased by 84% and 92% from pre-CPB to CPB phase in deep and moderate hypothermia groups respectively (P < 0.05), paralleled by decreases in Cpss of 36% (P > 0.05) and 52% (P < 0.05).

CONCLUSION

Changes in vecuronium requirements and plasma concentrations during CPB demonstrate that vecuronium pharmacokinetics and pharmacodynamics are both affected by hypothermic CPB in infants. The finding of bimodal distributions for plasma vecuronium and vecuronium clearance highlights the need for individual monitoring of neuromuscular blockade in this age group.

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.

Normothermic cardiopulmonary bypass increases heparin requirements necessary to maintain anticoagulation

OBJECTIVE

With the practice of warm cardiopulmonary bypass (CPB) at our institution we have observed an apparent increase in heparin requirements. CPB temperature predictability affects pharmacokinetics and differences in drug metabolism can be expected. We hypothesized that heparin requirements would increase with increasing CPB temperature.

METHODS

Following Institutional Review Board approval, we reviewed the charts of 354 patients undergoing primary coronary artery bypass graft surgery. We recorded patient demographic data, CPB duration, heparin requirements, and temperature during CPB. CPB was conducted between 24 degrees C and 37 degrees C. The Spearman's correlation coefficient, Pearson chi-square, and rank-sum tests were used for data analysis.

RESULTS

Core temperature during CPB correlated with heparin requirements (r = 0.13, p < 0.02). However, CPB duration was shorter in warm patients than in cold patients (r = -0.455, p < 0.0001). Additional heparin requirements adjusted for duration of CPB (units/minute) were also significantly greater in the warm group (p = 0.018).

CONCLUSIONS

Maintenance of adequate heparin anticoagulation during CPB is clinically important. Warm CPB patients required more heparin per minute than those undergoing cold CPB. More frequent assessment of anticoagulation and administration of additional heparin should be considered in patients undergoing warm CPB.