Recirculatory pharmacokinetics and pharmacodynamics of rocuronium in patients: the influence of cardiac output

DETERMINATION OF INDUCTION TIME IN ADULT PATIENTS WITH VALVULAR HEART DISEASE

OBJECTIVE

Intravenous anaesthetics induce loss of consciousness in one arm-brain circulation time. As the circulatory transit time in patients with mitral stenosis (MS) and aortic stenosis (AS) is increased, the delivery of anaesthetics to the brain may be prolonged and consequently the onset of hypnosis. This study aimed to compare the induction time in patients with and without valvular heart disease (VHD).

DESIGN

Prospective, single-center, open-label analytical study.

SETTING

It was conducted in adult patients undergoing elective cardiac surgery.

PARTICIPANTS

The patients (n = 144) were segregated into three groups; Group 1 - Stenotic VHD (MS, AS), Group 2 - Regurgitant VHD (Mitral Regurgitation, Aortic Regurgitation), and Group 3 - Control (coronary artery disease).

METHOD

General anaesthesia was induced with intravenous thiopental 4mg kg-1 bolus over 20s. The time to induction was noted as loss of eyelash reflex. Bispectral Index (BIS) values were recorded over 2 minutes. Statistical analysis was performed using SPSS software version 25.0. A P value < 0.05 was considered significant.

MAIN RESULTS

Patients in Group 1 (n = 48) had significantly prolonged induction time (99.6 ± 12.9s; P < 0.001) compared to the other two groups (n = 48 each) (68.5 ± 9.6s in Group 2 and 70.4 ± 11.8s in Group 3). Time required for BIS to fall below 60 was significantly longer in Group 1 (139.4 ± 24.6s; P < 0.001) compared to Group 2 (90.4 ± 6.3s) and Group 3 (92.1 ± 12s).

CONCLUSION

The induction time was prolonged in patients with stenotic VHD compared to patients with regurgitant VHD or those without VHD.

The Relationship between the Measured Blood Concentration of Rocuronium in Stable Muscle Relaxation with a Closed-Loop Control and the Estimated Blood Concentration from a Pharmacokinetic Simulation

We developed a system to adjust the rate of a continuous rocuronium (Rb) infusion to achieve 3 ≤ %T1 ≤ 10 with a closed-loop control. Samples were collected from 15 patients, and Rb blood concentrations were measured at the following time points: (1) when %T1 recovered to 3% or more after the initial Rb infusion; (2) when %T1 stabilized within the target range; (3) at the cessation of the Rb infusion; (4) 5 min after the sugammadex administration. The predicted Rb blood concentration at each time point was calculated and recorded using the pharmacokinetic parameters of Wierda et al. At time points (1), (2), and (3), the predicted blood concentrations were in good agreement with the measured values, but after the administration of sugammadex, the blood concentrations were higher than the predicted values because the Rb distributed in the tissues migrated into the blood. From the above, it was confirmed that the predicted blood concentration of Rb can be a good indicator for the automatic Rb administration control.

Rocuronium ≤1.5 mg/kg versus >1.5 mg/kg and inadequate paralysis in prehospital and retrieval intubation: A retrospective study

OBJECTIVE

Greater Sydney Area Helicopter Emergency Medical Service encouraged an increased dose of rocuronium for rapid sequence intubations (RSIs) from 1.5 mg/kg to 2.0 mg/kg from the end of 2017 in response to a number of inadequately paralysed patients identified by our airway audit processes. Subsequent protocol change incorporated 2.0 mg/kg rocuronium. This retrospective observational study was undertaken to see if doses over 1.5 mg/kg rocuronium were associated with a reduction in the number of inadequately paralysed patients.

METHODS

Retrospective review of patient prehospital notes and airway database records from 2017 to 2018 for all cases using rocuronium for RSI. Primary outcome of interest was physician notes describing skeletal muscle activity at laryngoscopy. Patients with tissued vascular access were excluded. Dose of rocuronium, estimated patient actual weight and grade of laryngoscopy were recorded. Comparisons were made between rocuronium doses ≤1.5 mg/kg and >1.5 mg/kg by estimated weight.

RESULTS

From 211 patients receiving rocuronium ≤1.5 mg/kg, five cases were inadequately paralysed, compared with two cases from 384 patients receiving >1.5 mg/kg rocuronium.

CONCLUSIONS

Although there were fewer inadequately paralysed patients with rocuronium doses >1.5 mg/kg, this did not reach statistical significance, presumably because of the low event rate. Further investigation into rocuronium dose for RSI is warranted.

The association of rocuronium dosing and first-attempt intubation success in adult emergency department patients

BACKGROUND

The recommended rocuronium dose for rapid sequence intubation is 1.0 mg/kg; however, the optimal dose for emergency airway management is not clear. We assessed the relationship between rocuronium dose and first-attempt success among emergency department (ED) patients undergoing rapid sequence intubation.

METHODS

This is a secondary analysis of the National Emergency Airway Registry (NEAR), an observational 25-center registry of ED intubations. Ninety percent recording compliance was required from each site for data inclusion. We included all patients > 14 years of age who received rocuronium for rapid sequence intubation from 1 Jan 2016 to 31 Dec 2018. We compared first-attempt success between encounters using alternative rocuronium doses (< 1.0, 1.0-1.1, 1.2-1.3 and ≥1.4 mg/kg). We performed logistic regressions to control for predictors of difficult airways, indication, pre-intubation hemodynamics, operator, body habitus and device. We also performed subgroup analyses stratified by device (direct vs. video laryngoscopy). We calculated univariate descriptive statistics and odds ratios (OR) from multivariable logistic regressions with cluster-adjusted 95% confidence intervals (CI).

RESULTS

19,071 encounters were recorded during the 3-year period. Of these, 8,034 utilized rocuronium for rapid sequence intubation. Overall, first attempt success was 88.4% for < 1.0 mg/kg, 88.1% for 1.0-1.1 mg/kg, 89.7% for 1.2-1.3 mg/kg, and 92.2% for ≥1.4 mg/kg. Logistic regression demonstrated that when direct laryngoscopy was used and when compared to the standard dosing range of 1.0-1.1 mg/kg, the adjusted odds of a first attempt success was significantly higher in ≥1.4 mg/kg group at 1.9 (95% CI 1.3-2.7) relative to the other dosing ranges, OR 0.9 (95% CI 0.7-1.2) for < 1.0 mg/kg and OR 1.2 (95% CI 0.9-1.7) for the 1.2-1.3 mg/kg group. First-attempt success was similar across all rocuronium doses among patients utilizing video laryngoscopy. Patients who were hypotensive (SBP < 100 mmHg) prior to intubation had higher first-attempt success 94.9% versus 88.6% when higher doses of rocuronium were used. The rates of all peri-intubation adverse events and desaturation were similar between dosing groups, laryngoscope type utilized and varying pre-intubation hemodynamics.

CONCLUSIONS

Rocuronium dosed ≥1.4 mg/kg was associated with higher first attempt success when using direct laryngoscopy and among patients with pre-intubation hypotension with no increase in adverse events. We recommend further prospective evaluation of the dosing of rocuronium prior to offering definitive clinical guidance.

Effects of prophylactic atropine on the time to tracheal intubation with the pre-administration of remifentanil

BACKGROUND

Pre-administration of remifentanil in target-controlled propofol and remifentanil anaesthesia could prolong the time of onset of muscle relaxation owing to haemodynamic effects, thereby prolonging the time to tracheal intubation. Although the sympatholytic effects of remifentanil result in bradycardia and hypotension, these responses can be attenuated by the administration of atropine. Therefore, we investigated whether prophylactic administration of atropine could prevent the prolongation of the time to tracheal intubation.

METHODS

Sixty-four patients were included in this study. They were randomised into Group A (atropine 0.5 mg, n = 32) and Group S (saline 0.9%, n = 32), immediately before the pre-administration of remifentanil. The primary outcome was the time to tracheal intubation and the secondary outcomes were rocuronium onset time, time to loss of consciousness (LOC), time to reach a value of 60 on the bispectral index (BIS) and haemodynamic variables.

RESULTS

The median [Interquartile range] of the time to tracheal intubation was 240 [214, 288]s in Group S and 190 [176, 212]s in Group A(median difference: 50 s, 95% confidence interval: 27-80 s, P = .001). Rocuronium onset time was significantly decreased in Group A compared to that in Group S (129 [110, 156] vs 172 [154, 200], P = .001). The times to LOC and reach 60 on the BIS were not significantly different between the two groups. Cardiac output(CO) and heart rate were less decreased in Group A than in Group S (P = .02, P < .001, respectively).

CONCLUSIONS

Prophylactic administration of atropine could compensate for the reduction in CO in cases pre-administered with remifentanil in target-controlled propofol and remifentanil anaesthesia. This in turn prevented the prolongation of rocuronium onset time and reduced the time to tracheal intubation.

Onset and duration of cis-atracurium neuromuscular block during fentanyl and lidocaine infusions in isoflurane-anaesthetised dogs

BACKGROUND

This retrospective study assessed the onset and duration of the neuromuscular block (NMB) induced by cis-atracurium 0.15 mg/kg intravenously with and without fentanyl or lidocaine infusions in 45 isoflurane-anaesthetised dogs.

METHODS

Dogs with neuromuscular function assessed by a calibrated train-of-four (TOF) monitor with stimulation (every 13 s) of the peroneal nerve were included. The onset and duration of the NMB were defined as the time from cis-atracurium administration until TOF=0 and the time during TOF=0 display, respectively.

RESULTS

The NMB onset was shorter during fentanyl (mean±sd) (1.9±0.7 minutes; P=0.0042) and lidocaine (2.0±0.7 minutes; P=0.0154) compared with control (2.9±0.8 minutes). The NMB duration was shorter in the fentanyl (27.5±7.3 minutes; P=0.0491), but not in the lidocaine group (32.3±6.9 minutes; P=0.0790), compared with control (33.7±9.1 minutes). The NMB onset was poorly but significantly correlated with the dose of fentanyl and lidocaine administered before cis-atracurium (r=-0.3396; P=0.0225). The fentanyl and lidocaine groups received more crystalloid and colloid boluses than the control.

CONCLUSIONS

Fentanyl and lidocaine shortened the NMB onset and the former decreased the NMB duration. Further prospective studies are required to clarify whether this was associated with an indirect decrease in blood pressure or a direct interaction between cis-atracurium and fentanyl and lidocaine.

Pre-administration of remifentanil in target-controlled propofol and remifentanil anesthesia prolongs anesthesia induction in neurosurgical patients: A double-blind randomized controlled trial

BACKGROUND

Pre- and co-administration of remifentanil in target-controlled propofol and remifentanil anesthesia are the most common methods in clinical practice. However, anesthesia induction time by timing remifentanil administration was not identified. Therefore, we investigated the induction time of anesthesia based on type of remifentanil administration in target-controlled anesthesia.

METHODS

A total of 60 patients were randomly assigned to 1 of 2 groups: Pre-administered with remifentanil before propofol infusion (Group R, n = 30) and co-administered with remifentanil with propofol (Group N, n = 30). The primary outcome was total induction time based on the order of remifentanil administration. Secondary outcomes were from start of the propofol infusion time to loss of consciousness (LOC), rocuronium onset time, time to Bispectral index (BIS) 60, and hemodynamic variables.

RESULTS

The mean ± SD of total induction time was 180.5 ± 49.0 s in Group N and 246.3 ± 64.7 s in Group R (mean difference: 65.8 seconds; 95% CI: 35.0-96.5 s, P < .01). Time to BIS 60 and rocuronium onset time were longer in the Group R (P < .01 and P < .01, respectively). The Δheart rate and Δcardiac output values were lower in the Group R (P = .02 and P = .04, respectively). Injection pain was reported by 11 of 28 (39%) in the Group N and in 2 of 28 (7%) in the Group R (difference in proportion: 32%, 95% CI: 10-51%, P = .01).

CONCLUSION

Pre-administration of remifentanil in target-controlled propofol and remifentanil anesthesia prolongs total induction time about 35% compared to co-administration of remifentanil and propofol by decreased CO.

Combined Recirculatory-compartmental Population Pharmacokinetic Modeling of Arterial and Venous Plasma S(+) and R(–) Ketamine Concentrations

What We Already Know about This Topic

What This Article Tells Us That Is New

Background

The pharmacokinetics of infused drugs have been modeled without regard for recirculatory or mixing kinetics. We used a unique ketamine dataset with simultaneous arterial and venous blood sampling, during and after separate S(+) and R(–) ketamine infusions, to develop a simplified recirculatory model of arterial and venous plasma drug concentrations.

Methods

S(+) or R(–) ketamine was infused over 30 min on two occasions to 10 healthy male volunteers. Frequent, simultaneous arterial and forearm venous blood samples were obtained for up to 11 h. A multicompartmental pharmacokinetic model with front-end arterial mixing and venous blood components was developed using nonlinear mixed effects analyses.

Results

A three-compartment base pharmacokinetic model with additional arterial mixing and arm venous compartments and with shared S(+)/R(–) distribution kinetics proved superior to standard compartmental modeling approaches. Total pharmacokinetic flow was estimated to be 7.59 ± 0.36 l/min (mean ± standard error of the estimate), and S(+) and R(–) elimination clearances were 1.23 ± 0.04 and 1.06 ± 0.03 l/min, respectively. The arm-tissue link rate constant was 0.18 ± 0.01 min–1, and the fraction of arm blood flow estimated to exchange with arm tissue was 0.04 ± 0.01.

Conclusions

Arterial drug concentrations measured during drug infusion have two kinetically distinct components: partially or lung-mixed drug and fully mixed-recirculated drug. Front-end kinetics suggest the partially mixed concentration is proportional to the ratio of infusion rate and total pharmacokinetic flow. This simplified modeling approach could lead to more generalizable models for target-controlled infusions and improved methods for analyzing pharmacokinetic-pharmacodynamic data.

Optimal neuromuscular blocking effects of remifentanil during tracheal intubation under general anesthesia

Objective

This study was performed to determine the effect of the remifentanil dose on the onset time of rocuronium with electromyography.

Methods

This retrospective comparative study included 75 patients undergoing general anesthesia for elective surgery. Patients received lidocaine (40 mg) and propofol (2 mg/kg) followed by rocuronium (0.6 mg/kg) with either saline infusion (Group S), remifentanil at 0.5 µg/kg/minute (Group R 0.5), or remifentanil at 1.0 µg/kg/minute (Group R 1.0). Neuromuscular block was monitored by train-of-four (TOF) electromyography, and the times taken to reach TOF 0 and TOF ratio (TOFR) 25% were recorded.

Results

The times taken to reach TOF 0 and TOFR 25% were significantly higher in Groups R 0.5 and R 1.0 than in Group S. The time taken to reach TOF 0 was 130.0 ± 6.4 s in Group S, 142.6 ± 6.0 s in Group R 0.5, and 183.0 ± 11.6 s in Group R 1.0. The time taken to reach TOFR 25% was also higher in Groups R 0.5 and R 1.0 than in Group S.

Conclusions

As the remifentanil dose increases, the intubation time required to reach TOF 0 also increases. Remifentanil has an effect on the onset of rocuronium.

Altered pharmacodynamics and pharmacokinetics of cisatracurium in patients with severe mitral valve regurgitation during anaesthetic induction period

AIM

The aim of the current study was to characterize the pharmacokinetics (PK) and pharmacodynamics (PD) of cisatracurium in patients with severe mitral valve regurgitation (MR) during the anaesthetic induction period.

METHODS

Thirty patients in the clinical trial were divided into two groups: the MR group (n = 15) and the control group (n = 15). Arterial blood samples were obtained before (time 0) and at 1, 2, 4, 6, 8, 10, 15 and 20 min after intravenous injection of 0.15 mg kg^-1 cisatracurium. The degree of neuromuscular block was measured by train of four (TOF) testing. The concentration of cisatracurium in the plasma was determined by high-performance liquid chromatography. A conventional two-compartment model and integrated PK/PD model were applied to PK and PD data analysis, respectively.

RESULTS

The results of PK model fitting demonstrated that severe MR reduced the distribution rate of cisatracurium from the central to peripheral compartment, resulting in a higher concentration of the drug in the plasma. The time to the maximal neuromuscular blocking effect of cisatracurium was delayed in the MR group (2.08 min in the control group vs. 4.12 min in the MR group). The PK/PD model indicated that the distribution rate of cisatracurium from the blood to the effect compartment was decreased in the MR group.

CONCLUSIONS

The present study suggested that the PK and PD of cisatracurium were significantly altered in patients with severe MR. The study has the potential to improve the safety of anaesthetic induction in patients with severe MR through accurate prediction of the PD responses of cisatracurium using the established PK/PD model.

Rocuronium pharmacokinetics and pharmacodynamics in the adductor pollicis and masseter muscles

BACKGROUND

The aim of this study was to characterize the dose-effect relationship of rocuronium at the adductor pollicis and masseter muscles.

METHODS

Ten, ASA I, adult patients, received a bolus dose of rocuronium 0.3 mg/kg during propofol based anesthesia. Train-of-four (TOF) was simultaneously monitored at the masseter and the adductor pollicis muscles until recovery. Rocuronium arterial serum concentrations were measured during 120 min. The first twitch of the TOF response was used to characterize the time-effect profile of both muscles using pharmacokinetic-pharmacodynamic analysis in NONMEM. A decrease in NONMEM objective function (∆OFV) of 3.84 points for an added parameter was considered significant at the 0.05 level.

RESULTS

Onset time at the masseter (mean ± SD, 1.5 ± 0.9 min) was faster than at the adductor pollicis (2.7 ± 1.4 min, P < 0.05). Recovery, measured as the time to TOF ratio = 0.9 was similar between muscles 29.9 ± 6.7 (adductor pollicis) vs. 29.3 ± 8.1 (masseter). (P = 0.77). The estimated pharmacodynamic parameters [mean (95% CI)] of the adductor pollicis muscle and the masseter muscle were; plasma effect-site equilibration half-time (teq) 3.25 (2.34, 3.69) min vs. 2.86 (1.83, 3.29) min, (∆OFV 383.665); Ce50 of 1.24 (1.13, 1.56) mg/l vs. 1.19 (1.00, 1.21) mg/l, (∆OFV 184.284); Hill coefficient of 3.97 (3.82, 5.62) vs. 4.68 (3.83, 5.71), (∆OFV 78.906).

CONCLUSIONS

We found that the masseter muscle has faster onset of blockade and similar recovery profile than adductor pollicis muscle. These findings were best, explained by a faster plasma effect-site equilibration of the masseter muscle to rocuronium.

Rapid-sequence intubation and cricoid pressure

Airway management is the most important clinical skill for anesthesiologist, emergency physician, and other providers who are involved in oxygenation and ventilation of the lungs. Rapid-sequence intubation is the preferred method to secure airway in patients who are at risk for aspiration because it results in rapid unconsciousness (induction) and neuromuscular blockade (paralysis). Application of cricoid pressure (CP) for patients undergoing rapid-sequence intubation is controversial. Multiple specialty societies have recommended that CP is not effective in preventing aspiration; rather it may worsen laryngoscopic view and impair bag-valve mask ventilation. Some experts think that CP should be applied in trauma and patients at risk for aspiration; however CP, if necessary, should be altered or removed to facilitate intubation.

The determinants of propofol induction time in anesthesia

Background

The required dose of anesthetics is generally smaller in patients with low cardiac output (CO). A high CO decreases the blood concentration of anesthetics during induction and maintenance of anesthesia. However, a high CO may also shorten the delivery time of anesthetics to the effect site, e.g. the brain. We assessed the time required for induction of anesthesia with propofol administered by target-controlled infusion (TCI), and investigated factors that modify the pharmacodynamics of propofol.

Methods

After measuring CO and blood volume (BV) by dye densitometry, propofol was infused using TCI to simulate a plasma concentration of 3 µg/ml. After infusion, the time taken to achieve bispectral index (BIS) values of 80 and 60 was determined. Age, sex, lean body mass (LBM), and cardiovascular parameters were analyzed as independent variables. The dependent variables were the time taken to achieve each BIS value and the plasma concentration of propofol (Cp) 10 min after the commencement of infusion.

Results

Multiple regression analysis revealed that a high CO significantly reduced the time taken to reach the first end point (P = 0.020, R² = 0.076). Age and LBM significantly prolonged the time taken to reach the second end point (P = 0.001). Cp was negatively correlated with BV (P = 0.020, R² = 0.073).

Conclusions

Cardiac output was a statistically significant factor for predicting the time required for induction of anesthesia in the initial phase, whereas, age and LBM were significant variables in the late phase. The pharmacodynamics of propofol was intricately altered by CO, age, and LBM.

Influence of cardiac output on the pseudo-steady state remifentanil and propofol concentrations in swine

BACKGROUND

The propofol concentration during constant infusion is affected by a change in cardiac output, but the effect of this change on remifentanil, which is frequently used in combination with propofol, is unclear.

METHODS

Ten swine were anaesthetised through inhalation of isoflurane and maintained with 1.5% isoflurane. After infusion of remifentanil (0.5 μg/kg/min) and propofol (6 mg/kg/h after 2 mg/kg bolus infusion) for 60 min (baseline 1), cardiac output was increased by continuous infusion of dobutamine and termination of isoflurane (high cardiac output state). Dobutamine infusion was then stopped, 1.5% isoflurane was restarted, and cardiac output was allowed to return to baseline (baseline 2). Finally, cardiac output was decreased by administration of 3% isoflurane (low cardiac output state). Blood samples were collected from the femoral artery at 10, 30, and 60 min after the change to each haemodynamic state.

RESULTS

An inverse relationship was found between cardiac output and the plasma remifentanil and propofol concentrations. The plasma drug concentrations were given by the following equations: [remifentanil] (ng/ml) = 17.5/cardiac output (l/min) + 4.52; and [propofol] (μg/ml) = 3.34/cardiac output + 1.17. The influence of changes in cardiac output on remifentanil were similar to those for coadministered propofol and the influence on the concentration of each drug was greater with decreasing cardiac output.

CONCLUSIONS

The plasma remifentanil concentration is influenced by cardiac output in a similar manner to that of propofol during remifentanil and propofol anaesthesia, although the metabolic sites are different.

Drug-administration sequence of target-controlled propofol and remifentanil influences the onset of rocuronium. A double-blind, randomized trial

BACKGROUND

Remifentanil is known to cause bradycardia and hypotension, as well as the decreases of cardiac output (CO). We hypothesized that hemodynamic suppression by remifentanil would affect the onset time of rocuronium. This study investigated whether the onset of rocuronium was influenced by the drug-administration sequence during induction of anesthesia with target-controlled infusion of propofol and remifentanil.

METHODS

Healthy adult patients (n = 126) undergoing elective surgery under general anesthesia were randomized into two groups according to drug-administration sequence. In Remi-Pro-Rocu group (n = 62), remifentanil was infused first, followed by propofol. Then, rocuronium was administered lastly. In Pro-Rocu-Remi group (n = 64), propofol, rocuronium, and remifentanil were given in that order. As a primary outcome, the onset time of rocuronium was measured. Mean arterial pressure (MAP), heart rate (HR), CO, and stroke volume were recorded before anesthesia (T1), at injection of rocuronium (T2), immediately before and after intubation (T3 and T4).

RESULTS

In Remi-Pro-Roc group, the onset of rocuronium was delayed significantly compared with Pro-Rocu-Remi group [median (interquartile range); 130 (105-150) vs. 90 (71-100) s, P < 0.001]. At the time of rocuronium injection (T2), MAP, HR, and CO were significantly lower in Remi-Pro-Rocu group than Pro-Rocu-Remi group (P < 0.001).

CONCLUSION

The onset time of rocuronium is prolonged significantly by early administration of remifentanil during target-controlled infusion of propofol and remifentanil, and it may be due to the decreased CO caused by remifentanil.

Neuromuscular blockade by vecuronium during induction with 5% sevoflurane or propofol

This randomized trial investigated whether 5% sevoflurane potentiated neuromuscular blockade by vecuronium. General anaesthesia was induced with 5% sevoflurane in oxygen in 16 patients or with propofol in 16 patients. After loss of consciousness, vecuronium was administered to all participants at randomly assigned doses of 25, 30, 35 or 40 μg/kg. Neuromuscular blockade was assessed by use of acceleromyography to measure responses to train-of-four stimuli in the adductor pollicis and corrugator supercilii muscles. Maximum blockade was significantly more intense in the adductor pollicis among patients in the sevoflurane group than in the propofol group, whereas there was no significant between-group difference at the corrugator supercilii muscles. In both groups, maximum blockade at the corrugator supercilii was significantly less intense than that achieved at the adductor pollicis. In the dose-response analysis, the 50% and 95% effective doses were lower for sevoflurane than for propofol in both muscles, although this did not reach statistical significance. It is concluded that induction of general anaesthesia with sevoflurane might provide improved conditions for intubation and reduce airway problems.

Was a hypertensive crisis in a patient with pheochromocytoma caused by rocuronium?: A case report

Pheochromocytoma is an uncommon tumor that originates in the adrenal medulla or in other paraganglia of the sympathetic nervous system. If a hypertensive crisis occurs during general anesthesia in incidental or untreated pheochromocytoma, it is a life-threatening event with a mortality rate of about 80%. Anesthetic drugs such as pancuronium, atracurium, and metoclopromide can exacerbate the potentially lethal cardiovascular effects of catecholamines. We report a case of a patient with pheochromocytoma who display abrupt increases in systolic arterial pressure and plasma norepinephrine following rocuronium administration. This case indicates the possible involvement of elevated sympathetic nervous system to a catecholamine crisis triggered by rocuronium in pheochromocytoma.

Pharmacokinetic-pharmacodynamic modeling of the influence of chronic phenytoin therapy on the rocuronium bromide response in patients undergoing brain surgery

BACKGROUND

Antiepileptic drugs decrease the intensity of the effect of neuromuscular blocking agents. The objective of this study was to evaluate the influence of chronic phenytoin therapy (CPT) on the pharmacokinetics (PK) and pharmacodynamics (PD) of rocuronium.

METHODS

A total of 21 patients undergoing intracranial surgery were enrolled in the study. Ten of these were under CPT. Rocuronium was administered intravenously. Arterial blood samples were drawn, and the T1% (percentage change from the response to the supramaximal stimulus) derived from electromyogram was continuously recorded. NONMEM: software was used to construct, evaluate and validate the PKPD models.

RESULTS

The PKPD of rocuronium was described using a three-compartment PK model and effect compartment model. The CPT therapy was found to increase the total plasma clearance from 0.26 to 0.75 L min(-1). The PD model parameter estimates were k(e0)= 0.073 min(-1), IC(50) (the steady-state plasma concentration eliciting half of the maximum response) = 836 ng mL(-1) and gamma = 3.13.

CONCLUSIONS

Chronic phenytoin therapy increases the clearance of rocuronium from 0.26 to 0.75 L min(-1) but has no effect on the k(e0), IC(50) or gamma parameters.

Advanced pharmacokinetic models based on organ clearance, circulatory, and fractal concepts

Three advanced models of pharmacokinetics are described. In the first class are physiologically based pharmacokinetic models based on in vitro data on transport and metabolism. The information is translated as transporter and enzyme activities and their attendant heterogeneities into liver and intestine models. Second are circulatory models based on transit time distribution and plasma concentration time curves. The third are fractal models for nonhomogeneous systems and non-Fickian processes are presented. The usefulness of these pharmacokinetic models, with examples, is compared.

Circulatory transport and capillary-tissue exchange as determinants of the distribution kinetics of inulin and antipyrine in dog

A pharmacokinetic model was developed to estimate physiologically meaningful parameters of distribution kinetics from plasma concentration-time data. The model is based on simultaneously measured disposition curves of drug and vascular marker. Employing residence time distribution theory, a recirculatory model with two subsystems, the pulmonary and systemic circulation, was constructed. In addition to intravascular mixing, the axially distributed model of the systemic circulation accounts for transcapillary transport of solutes, quantified by permeability-surface area product (PS) and diffusional equilibration time. Parameters of ICG, inulin, and antipyrine were estimated from disposition data obtained in awake dogs under control conditions and during an isoproterenol infusion or moderate hypovolemia. Results suggest that distribution kinetics is (1) governed by extravascular diffusion and (2) its dependency on cardiac output decreases with increasing diffusional resistance. Hemorrhage decreased the effective PS of inulin. In conclusion, this novel mechanistic model effectively described both the permeability-limited distribution of inulin into interstitial fluid and the flow-limited distribution of antipyrine into total body water and might be useful for other drugs.

Population pharmacokinetics/pharmacodynamics of anesthetics

In this article we review how population pharmacokinetic/pharmacodynamic (PD) modeling has evolved in the specialty of anesthesiology, how anesthesiology benefited from the mixed-effects approach, and which features of modeling need careful attention. Key articles from the anesthesiology literature are selected to discuss the modeling of typical anesthesiological PD end points, such as level of consciousness and analgesia, interactions between hypnotics and analgesics, estimation with poor and sometimes rich data sets from populations of various sizes, covariate detection, covariances between random effects, and Bayesian forecasting.

Physicochemical properties of neuromuscular blocking agents and their impact on the pharmacokinetic-pharmacodynamic relationship

BACKGROUND

Among the factors influencing the onset of action of neuromuscular blocking agents (NMBA), the potency (EC50) and the rate of equilibration between blood and the effect compartment (k(e0)) have been highlighted. Although these descriptors are intrinsically influenced by the physicochemical characteristics of the drug, the impact of lipid solubility, molecular weight and protein binding on pharmacokinetic-pharmacodynamic (PK-PD) descriptors has not been established for most NMBA.

METHODS

The octanol/phosphate buffer distribution coefficients (logD) of various NMBA (vecuronium, rocuronium, mivacurium isomers (cis-cis, cis-trans and trans-trans), doxacurium, cisatracurium, atracurium, succinylcholine) were determined. The free fraction for each drug was measured using an ultrafiltration technique. PK-PD descriptors were obtained from selected clinical studies. Correlations between physicochemical parameters (including molecular weight) and PK-PD descriptors were assessed by linear or multiple linear regression.

RESULTS

A wide range of log D (-4.15 for succinylcholine to 0.75 for vecuronium) and free fraction (from 31% for vecuronium to 80% for succinylcholine) is observed for NMBA. Molecular weight combined with either lipid solubility (r2=0.70; P=0.001) or free fraction (r2=0.84; P<0.001) were highly correlated with potency, while for k(e0) a greater degree of correlation was obtained when both lipid solubility and free fraction (r2=0.74; P=0.002) were included.

CONCLUSIONS

The basic characteristics of NMBAs, namely, molecular weight, lipid solubility and protein binding, are strongly associated with the kinetics of the drug response.

Strategies to Optimise Propofol-Opioid Anaesthesia

Propofol-opioid combinations are widely used in today's anaesthetic practice. Over the past 20-30 years the pharmacology of these agents has been described in increasingly greater detail. Together with novel intravenous administration devices and improved anaesthetic depth monitoring, this has created a basis for the optimisation of the administration of propofol-opioid anaesthesia. This article describes the current strategies regarding the application of this type of anaesthesia, focusing on three strategic tools: (i) application of pharmacokinetic-pharmacodynamic knowledge of propofol and the opioids, with particular attention to pharmacodynamic interactions between them; (ii) the use of state-of-the-art administration techniques; and (iii) the application of bispectral index monitoring. Together, these techniques have improved the level of control, the flexibility and the safety of anaesthetic practice.