Pharmacokinetics of midazolam in total i.v. anaesthesia

Comparison of the negative effect of remimazolam and propofol on cardiac contractility: Analysis of a randomised parallel-group trial and a preclinical ex vivo study

Remimazolam is a newly developed ultra-short-acting benzodiazepine that exerts sedative effects. This study aimed to clarify the effects of remimazolam on cardiac contractility. In a randomised-parallel group trial, haemodynamic parameters were compared between propofol (n = 11) and remimazolam (n = 12) groups during the induction of general anaesthesia in patients undergoing non-cardiac surgery. In a preclinical study, the direct effects of remimazolam on cardiac contractility were also evaluated using isolated rat hearts. RNA sequence data obtained from rat and human hearts were analysed to assess the expression patterns of the cardiac γ-aminobutyric acid type A (GABAA ) receptor subunits. In a clinical study, the proportional change of the maximum rate of arterial pressure rise was milder during the study period in the remimazolam group (propofol: -52.6 [10.2] (mean [standard deviation])% vs. remimazolam: -39.7% [10.5%], p = 0.007). In a preclinical study, remimazolam did not exert a negative effect on left ventricle developed pressure, whereas propofol did exert a negative effect after bolus administration of a high dose (propofol: -26.9% [3.5%] vs. remimazolam: -1.1 [6.9%], p < 0.001). Analysis of the RNA sequence revealed a lack of γ subunits, which are part of the major benzodiazepine binding site of the GABAA receptor, in rat and human hearts. These results indicate that remimazolam does not have a direct negative effect on cardiac contractility, which might contribute to its milder effect on cardiac contractility during the induction of general anaesthesia. The expression patterns of cardiac GABAA receptor subunits might be associated with the unique pharmacokinetics of benzodiazepines in the heart.

Korean clinical practice guidelines for diagnostic and procedural sedation

Safe and effective sedation depends on various factors, such as the choice of sedatives, sedation techniques used, experience of the sedation provider, degree of sedation-related education and training, equipment and healthcare worker availability, the patient's underlying diseases, and the procedure being performed. The purpose of these evidence-based multidisciplinary clinical practice guidelines is to ensure the safety and efficacy of sedation, thereby contributing to patient safety and ultimately improving public health. These clinical practice guidelines comprise 15 key questions covering various topics related to the following: the sedation providers; medications and equipment available; appropriate patient selection; anesthesiologist referrals for high-risk patients; pre-sedation fasting; comparison of representative drugs used in adult and pediatric patients; respiratory system, cardiovascular system, and sedation depth monitoring during sedation; management of respiratory complications during pediatric sedation; and discharge criteria. The recommendations in these clinical practice guidelines were systematically developed to assist providers and patients in sedation-related decision making for diagnostic and therapeutic examinations or procedures. Depending on the characteristics of primary, secondary, and tertiary care institutions as well as the clinical needs and limitations, sedation providers at each medical institution may choose to apply the recommendations as they are, modify them appropriately, or reject them completely.

Predicting Volume of Distribution in Neonates: Performance of Physiologically Based Pharmacokinetic Modelling

The volume of distribution at steady state (Vss) in neonates is still often estimated through isometric scaling from adult values, disregarding developmental changes beyond body weight. This study aimed to compare the accuracy of two physiologically based pharmacokinetic (PBPK) Vss prediction methods in neonates (Poulin & Theil with Berezhkovskiy correction (P&T+) and Rodgers & Rowland (R&R)) with isometrical scaling. PBPK models were developed for 24 drugs using in-vitro and in-silico data. Simulations were done in Simcyp (V22) using predefined populations. Clinical data from 86 studies in neonates (including preterms) were used for comparison, and accuracy was assessed using (absolute) average fold errors ((A)AFEs). Isometric scaling resulted in underestimated Vss values in neonates (AFE: 0.61), and both PBPK methods reduced the magnitude of underprediction (AFE: 0.82-0.83). The P&T+ method demonstrated superior overall accuracy compared to isometric scaling (AAFE of 1.68 and 1.77, respectively), while the R&R method exhibited lower overall accuracy (AAFE: 2.03). Drug characteristics (LogP and ionization type) and inclusion of preterm neonates did not significantly impact the magnitude of error associated with isometric scaling or PBPK modeling. These results highlight both the limitations and the applicability of PBPK methods for the prediction of Vss in the absence of clinical data.

Analytical and Clinical Validation of Assays for Volumetric Absorptive Microsampling (VAMS) of Drugs in Different Blood Matrices: A Literature Review

Volumetric absorptive microsampling (VAMS) is the newest and most promising sample-collection technique for quantitatively analyzing drugs, especially for routine therapeutic drug monitoring (TDM) and pharmacokinetic studies. This technique uses an absorbent white tip to absorb a fixed volume of a sample (10-50 µL) within a few seconds (2-4 s), is more flexible, practical, and more straightforward to be applied in the field, and is probably more cost-effective than conventional venous sampling (CVS). After optimization and validation of an analytical method of a drug taken by VAMS, a clinical validation study is needed to show that the results by VAMS can substitute what is gained from CVS and to justify implementation in routine practice. This narrative review aimed to assess and present studies about optimization and analytical validation of assays for drugs taken by VAMS, considering their physicochemical drug properties, extraction conditions, validation results, and studies on clinical validation of VAMS compared to CVS. The review revealed that the bio-analysis of many drugs taken with the VAMS technique was optimized and validated. However, only a few clinical validation studies have been performed so far. All drugs that underwent a clinical validation study demonstrated good agreement between the two techniques (VAMS and CVS), but only by Bland-Altman analysis. Only for tacrolimus and mycophenolic acid were three measurements of agreement evaluated. Therefore, VAMS can be considered an alternative to CVS in routine practice, especially for tacrolimus and mycophenolic acid. Still, more extensive clinical validation studies need to be performed for other drugs.

Unravelling the pharmacokinetics of aflatoxin B1: In vitro determination of Michaelis–Menten constants, intrinsic clearance and the metabolic contribution of CYP1A2 and CYP3A4 in pooled human liver microsomes

Mycotoxins, fungal secondary metabolites, are ubiquitously present in food commodities. Acute exposure to high levels or chronic exposure to low levels has an impact on the human body. The phase I metabolism in the human liver, performed by cytochrome P450 (CYP450) enzymes, is accountable for more than 80% of the overall metabolism of exogenous and endogenous compounds. Mycotoxins are (partially) metabolized by CYP450 enzymes. In this study, in vitro research was performed on CYP450 probes and aflatoxin B1 (AFB1), a carcinogenic mycotoxin, to obtain pharmacokinetic data on AFB1, required for further experimental work. The CYP450 probes of choice were a CYP3A4 substrate, midazolam (MDZ) and a CYP1A2 substrate, phenacetin (PH) since these are the main metabolizing phase I enzymes of AFB1. Linearity experiments were performed on the three substrates indicating that linear conditions were achieved at a microsomal protein concentration and incubation time of 0.25 mg/ml and 5 min, 0.50 mg/ml and 20 min and 0.25 mg/ml and 5 min for MDZ, PH and AFB1, respectively. The K_m was determined in human liver microsomes and was estimated at 2.15 μM for MDZ, 40.0 μM for PH and 40.9 μM for AFB1. The associated V_max values were 956 pmol/(mg.min) (MDZ), 856 pmol/(mg.min) (PH) and 11,536 pmol/(mg.min) (AFB1). Recombinant CYP systems were used to determine CYP450-specific Michaelis–Menten values for AFB1, leading to a CYP3A4 K_m of 49.6 μM and an intersystem extrapolation factor (ISEF) corrected V_max of 43.6 pmol/min/pmol P450 and a CYP1A2 K_m of 58.2 μM and an ISEF corrected V_max of 283 pmol/min/pmol P450. An activity adjustment factor (AAF) was calculated to account for differences between microsome batches and was used as a correction factor in the determination of the human in vivo hepatic clearance for MDZ, PH and AFB1. The hepatic blood clearance corrected for the AAF CL_H,B,MDZ,AAF, CL_H,B,PH,AAF CL_{H,B,AFB1,AAF(CYP3A4)} and CL_{H,B,AFB1,AAF(CYP1A2)} were determined in HLM at 44.1 L/h, 21.7 L/h, 40.0 L/h and 38.5 L/h. Finally, inhibition assays in HLM showed that 45% of the AFB1 metabolism was performed by CYP3A4/3A5 enzymes and 49% by CYP1A2 enzymes.

Midazolam at low nanomolar concentrations affects long-term potentiation and synaptic transmission predominantly via the α1-GABAA receptor subunit in mice

BACKGROUND

Midazolam amplifies synaptic inhibition via different GABAA receptor subtypes defined by the presence of α1, α2, α3 or α5-subunits in the channel complex. Midazolam blocks long-term potentiation and produces postoperative amnesia. The aims of this study were to identify the GABAA receptor subtypes targeted by midazolam responsible for affecting CA1-long-term potentiation and synaptic inhibition in neocortical neurons.

METHODS

The effects of midazolam on hippocampal CA1-long-term potentiation were studied in acutely prepared brain slices of male and female mice. Positive allosteric modulation on GABAA receptor-mediated miniature inhibitory postsynaptic currents was investigated in organotypic slice cultures of the mouse neocortex. In both experiments, wild-type mice and GABAA receptor knock-in mouse lines were compared in which α1-, α5-, α1/2/3-, α1/3/5- and α2/3/5-GABAA receptor subtypes had been rendered benzodiazepine-insensitive.

RESULTS

Midazolam 10nM completely blocked long-term potentiation (midazolam mean±SD 98±11%, n=14/8 (slices/mice) vs. control 156±19%, n=20/12; p<0.001). Experiments in slices of α1-, α5-, α1/2/3-, α1/3/5- and α2/3/5-knock-in mice revealed a dominant role for the α1-GABAA receptor subtype in the long-term potentiation suppressing effect.In slices from wild-type mice, midazolam increased (mean±SD) charge transfer of miniature synaptic events concentration-dependently, 50nM: 172±71% (n=10/6) vs. 500nM: 236±54% (n=6/6), p=0.041. In α2/3/5-knock-in mice, charge transfer of miniature synaptic events did not further enhance when applying 500nM midazolam, 50nM: 171±62% (n=8/6) vs. 500nM: 175±62% (n=6/6), p=0.454) indicating two different binding affinities for midazolam to α2/3/5- and α1-subunits.

CONCLUSIONS

These results demonstrate a predominant role of α1-GABAA receptors in the actions of midazolam at low nanomolar concentrations. At higher concentrations, midazolam also enhances other GABAA receptor subtypes. α1-GABAA receptors may already contribute at sedative doses to the phenomenon of postoperative amnesia that has been reported after midazolam administration.

The role of loops B and C in determining the potentiation of GABAA receptors by midazolam

Many benzodiazepines are positive allosteric modulators (PAMs) of GABAA receptors that cause sedation, hypnosis, and anxiolysis. Benzodiazepines bind GABAA receptors at the extracellular interface of the α and γ subunits. Within the α subunit, the benzodiazepine binding site is defined by three highly conserved structural loops, loops A-C. Although previous mutagenesis studies have identified His102 in Loop A as important for benzodiazepine modulation of GABAA receptors, the functional roles of many of the other conserved residues in loops A-C remain incompletely understood. In this study, we made single mutations in loops A-C of the benzodiazepine binding-site across all six α subunits. We used whole-cell patch clamp recording to measure the functional effects of these mutations on midazolam potentiation. The results showed that mutating the threonine in loop B and serine in loop C (Thr163 and S206 in human α1) did not abolish the receptors' responsiveness to midazolam, as the α1(H102R) mutation did. The loop C mutations exhibited a novel array of α-isoform specific effects on midazolam potentiation. The α3(S230I) and α5(S209I) mutations had the largest effect on midazolam potentiation, increasing the efficacy of midazolam. Novel benzodiazepines targeting loop C may represent a future direction for designing new drugs that specifically alter the activity of α3- and α5-containing GABAA receptors.

Terminal Withdrawal of Mechanical Ventilation: A Hospice Perspective for the Intensivist

The intensive care unit (ICU) and hospice inpatient unit (IPU) environments differ in many ways. Although both endeavor to provide the best care possible for their patients, the day-to-day goals of these environments are almost antithetical. Similarly, the experiences and expertise of the staff differ. When performing a similar clinical task, it may be addressed in different ways because each group is engrained in their primary day-to-day focus. Terminal withdrawal of mechanical ventilation is a procedure that is performed in both ICUs and some hospice IPUs. Previous examinations of this subject have been based largely upon the correlative background, practices, and perceptions of the ICU prescriber. The purpose of this review is to examine how the manner in which this procedure is performed in the hospice environment may differ in ways that the intensivist can incorporate into their own plan of care, or better appreciate when making the decision to remove mechanical ventilation in the critical care unit or transfer the patient to a hospice environment for the procedure to be completed.

Scaling clearance in paediatric pharmacokinetics: All models are wrong, which are useful?

Linked Articles

This article is commented on in the editorial by Holford NHG and Anderson BJ. Why standards are useful for predicting doses. Br J Clin Pharmacol 2017; 83: 685–7. doi: 10.1111/bcp.13230

Aim

When different models for weight and age are used in paediatric pharmacokinetic studies it is difficult to compare parameters between studies or perform model‐based meta‐analyses. This study aimed to compare published models with the proposed standard model (allometric weight^0.75 and sigmoidal maturation function).

Methods

A systematic literature search was undertaken to identify published clearance (CL) reports for gentamicin and midazolam and all published models for scaling clearance in children. Each model was fitted to the CL values for gentamicin and midazolam, and the results compared with the standard model (allometric weight exponent of 0.75, along with a sigmoidal maturation function estimating the time in weeks of postmenstrual age to reach half the mature value and a shape parameter). For comparison, we also looked at allometric size models with no age effect, the influence of estimating the allometric exponent in the standard model and, for gentamicin, using a fixed allometric exponent of 0.632 as per a study on glomerular filtration rate maturation. Akaike information criteria (AIC) and visual predictive checks were used for evaluation.

Results

No model gave an improved AIC in all age groups, but one model for gentamicin and three models for midazolam gave slightly improved global AIC fits albeit using more parameters: AIC drop (number of parameters), –4.1 (5), –9.2 (4), –10.8 (5) and –10.1 (5), respectively. The 95% confidence interval of estimated CL for all top performing models overlapped.

Conclusion

No evidence to reject the standard model was found; given the benefits of standardised parameterisation, its use should therefore be recommended.

Considerations for submucosal midazolam administration in combination with oral and inhaled medications for sedation of pediatric dental patients

Sedation allows patients to maintain their airway independently and respond appropriately to physical stimulation and verbal command while maintaining a minimum depressed level of consciousness. Drugs commonly used for sedation of pediatric dental patients include a combination of chloral hydrate, hydroxyzine, and nitrous oxide-oxygen. Midazolam is a benzodiazepine and currently one of the most commonly used intravenous sedative agents. It can be easily titrated to provide a wide range of sedation, from conscious sedation to deep sedation, and exhibits a wide safety margin without severe respiratory and circulatory depression. At an appropriate dose, it also decreases patient anxiety and induces amnesia. We found that the submucosal administration of midazolam combined with chloral hydrate provided increased sedative effects and decreased the postoperative vomiting response compared with conventional chloral hydrate administration, with no significant difference in physiological responses. The depth of sedation can be titrated using this technique.

Prediction of drug concentration-time profiles in children from adults: an allometric approach

The main objective of this work was to evaluate 2 methods to predict concentration-time profiles of drugs in children (aged 5 years or older) from adult pharmacokinetic (PK) parameters. Five drugs from the literature were chosen for this study, and all these 5 drugs were described by a 2-compartment model in both adults and children. PK parameters (CL, Vc, Vss, and Vβ) were allometrically predicted in children from adults. PK constants such as A, B, α, and β were also predicted in children from adults as described in . Using predicted PK parameters and constants, concentration-time profiles of 5 drugs were predicted in children and compared with the observed profiles. Both methods of predictions provided fairly good prediction of concentration-time profiles in children. The predicted concentration-time profiles in children were comparable with the observed profiles and can be used to design first-in-children clinical trials.

Inhibition of cardiac Kv1.5 potassium current by the anesthetic midazolam: mode of action

Midazolam is a short-acting benzodiazepine that is widely used in anesthesia. Despite its widespread clinical use, detailed information about cardiac side effects of midazolam is largely lacking. Using the double-electrode voltage clamp technique, we studied pharmacological effects of midazolam on heterologously expressed Kv1.5 channels underlying atrial repolarizing current I(Kur). Midazolam dose-dependently inhibited Kv1.5 current, yielding an IC50 of 17 μM in an HEK cell line and an IC50 of 104 μM in Xenopus oocytes. We further showed that midazolam did not affect the half-maximal activation voltage of Kv1.5 channels. However, a small negative shift of the inactivation curve could be observed. Midazolam acted as a typical open-channel inhibitor with rapid onset of block and without frequency dependence of block. Taken together, midazolam is an open channel inhibitor of cardiac Kv1.5 channels. These data add to the current understanding of the pharmacological profile of midazolam.

A maturation model for midazolam clearance

BACKGROUND

Physiological-based pharmacokinetic models have been used to describe midazolam clearance (CL) maturation. There are no maturation descriptors of CL from neonate to adulthood based on reported estimates at different ages.

METHODS

Published CL estimates after intravenous administration from time-concentration profiles were used to construct a maturation model based on size and age. Curve fitting was performed using nonlinear mixed effects models.

RESULTS

There were 16 publications reporting an estimate of CL after intravenous administration in children, although few estimates were available from 44-80 weeks postmenstrual age (PMA). CL maturation, standardized to a 70 -kg person was described using the Hill equation. Mature CL was 523 (CV 32%, 95%CI 469, 597) ml·min(-1) ·70 kg(-1) . The maturation half-time was 73.6 (95%CI 59.4, 80.0) weeks PMA and the Hill coefficient 3 (95%CI 2.2, 4.1). Predicted CL changes with age based on this model were in close agreement with physiologically based pharmacokinetic (PBPK) models. A comparison with a published PBPK model predictions revealed a root mean squared prediction error (precision) of 4.0% (95%CI 1.1, 5.8) and bias was -0.9% (95%CI -4.3, 2.6).

CONCLUSIONS

Previously published pharmacokinetic parameters can be used to develop maturation models that address gaps in current knowledge regarding the influence of age on a drug's disposition. If a midazolam sedation target concentration of 0.1 mg·l(-1) , similar to that given to adults, is assumed, then we might anticipate steady-state infusion rates of 0.014 mg·kg(-1) ·h(-1) in neonates, 0.05 mg·kg(-1) ·h(-1) in a 1-year-old, 0.06 mg·kg(-1) ·h(-1) in a 5-year-old and 0.05 mg·kg(-1) ·h(-1) in a 12-year-old child. Age-related pharmacodynamic differences that will affect dose and the impact of active metabolites on response are not yet quantified.

Comparison of effects of propofol and midazolam at sedative concentrations on sympathetic tone generation in the isolated spinal cord of neonatal rats

BACKGROUND

Propofol and midazolam are common sedatives for critically ill patients. Little is known about the effects of propofol and midazolam on central sympathetic activity when drug concentrations in extracellular milieu are under precise control. Previous work using an in vitro neonatal rat splanchnic nerve-spinal cord preparation has demonstrated that tonic sympathetic activity is generated spontaneously in the thoracic spinal cord. The aim of this study was to investigate the concentration effects of propofol and midazolam on spinally generated sympathetic activity.

METHODS

Using an in vitro neonatal rat splanchnic nerve-spinal cord preparation that allows the precise control of drug concentrations, the central sympathetic effects elicited by the application of propofol (10-640 microM) and midazolam (10-640 microM) were compared.

RESULTS

There was a prompt decrease in sympathetic activity on application of propofol or midazolam in a concentration-dependent manner. A significant decrease in sympathetic activity was observed on application of propofol at 80-640 microM; however, the application of propofol at 10-40 microM caused only a slight alteration in activity. The sympathetic activity was not altered significantly by 10 microM of midazolam, but the application of midazolam at 20-640 microM caused a significant decrease in activity. Thus, in these experimental conditions, the minimum concentration of propofol causing a significant decrease in sympathetic activity was 80 microM and that of midazolam was 20 microM.

CONCLUSIONS

The current findings suggest that the administration of 9-19 microM of propofol or 0.7-0.9 microM of midazolam, the clinically relevant concentrations for sedation, does not alter central sympathetic outflow at the spinal cord level. However, propofol at a concentration of 86 microM, which could be achieved by a single-bolus loading dose to induce sedation, depresses central sympathetic activity.

Parameter identification and sedative sensitivity analysis of an agitation-sedation model

Sedation administration and agitation management are fundamental activities in any intensive care unit. A lack of objective measures of agitation and sedation, as well as poor understanding of the underlying dynamics, contribute to inefficient outcomes and expensive healthcare. Recent models of agitation-sedation dynamics have enhanced understanding of the underlying dynamics and enable development of advanced protocols for semi-automated sedation administration. In this research, the agitation-sedation model parameters are identified using an integral-based fitting method developed in this work. Parameter variance is then analysed over 37 intensive care unit patients. The parameter identification method is shown to be effective and computationally inexpensive, making it suited to real-time clinical control applications. Sedative sensitivity, an important model parameter, is found to be both patient-specific and time-varying. However, while the variation between patients is observed to be as large as a factor 10, the observed variation in time is smaller, and varies slowly over a period of days rather than hours. The high fitted model performance across all patients show that the agitation-sedation model presented captures the fundamental dynamics of the agitation-sedation system. Overall, these results provide additional insight into the system and clinical dynamics of sedation management.

Physiological modelling of agitation–sedation dynamics including endogenous agitation reduction

Sedation administration and agitation management are fundamental activities in any intensive care unit. A lack of objective measures of agitation and sedation, as well as poor understanding of the underlying dynamics, contribute to inefficient outcomes and expensive healthcare. Recent models of agitation-sedation pharmacodynamics have enhanced understanding of the underlying dynamics and enable development of advanced protocols for semi-automated sedation administration. However, these initial models do not capture all observed dynamics, particularly periods of low sedative infusion. A physiologically representative model that incorporates endogenous agitation reduction (EAR) dynamics is presented and validated using data from 37 critical care patients. High median relative average normalised density (RAND) values of 0.77 and 0.78 support and minimum RAND values of 0.51 and 0.55 for models without and with EAR dynamics respectively show that both models are valid representations of the fundamental agitation-sedation dynamics present in a broad spectrum of intensive care unit (ICU) patients. While the addition of the EAR dynamic increases the ability of the model to capture the observed dynamics of the agitation-sedation system, the improvement is relatively small and the sensitivity of the model to the EAR dynamic is low. Although this may represent a limitation of the model, the inclusion of EAR is shown to be important for accurately capturing periods of low, or no, sedative infusion, such as during weaning prior to extubation.

Physiological modelling of agitation–sedation dynamics

Agitation-sedation cycling in critically ill patients, characterized by oscillations between states of agitation and over-sedation, damages patient health and increases length of stay and cost. A model that captures the essential dynamics of the agitation-sedation system and is physiologically representative is developed, and validated using data from 37 critical care patients. It is more physiologically representative than a previously published agitation-sedation model, and captures more realistic and complex dynamics. The median time in the 90% probability band is 90%, and the total drug dose, relative to recorded drug dose data, is a near ideal 101%. These statistical model validation metrics are 5-13% better than a previously validated model. Hence, this research provides a platform to develop and test semi-automated sedation management controllers that offer the significant clinical potential of improved agitation management and reduced length of stay in critical care.

Conscious sedation with midazolam or propofol does not alter left ventricular diastolic performance in patients with preexisting diastolic dysfunction: a transmitral and tissue Doppler transthoracic echocardiography study

The effects of midazolam and propofol on left ventricular (LV) diastolic function have not been evaluated in humans. We tested the hypothesis that midazolam and propofol alter LV diastolic function evaluated with transmitral and tissue Doppler transthoracic echocardiography in patients with normal LV systolic function in the presence and absence of preexisting diastolic dysfunction. After IRB approval and informed consent, patients (n = 34) with normal or reversed transmitral blood flow velocity E-to-A ratios received 3 escalating doses of midazolam (0.025, 0.05, and 0.1 mg/kg) or propofol (0.25, 0.5, and 1.0 mg/kg) over 10 s at 5-min intervals. Hemodynamic variables and indices of diastolic function were recorded 3 min after each dose of midazolam and propofol. Patients with diastolic dysfunction demonstrated decreased ratios of peak transmitral E-to-A wave velocity and their corresponding time-velocity integrals as compared with normal patients. Reductions in anterior and posterior mitral annulus E/A ratios were also present. Midazolam and propofol did not further alter indices of LV diastolic function in patients with impaired early LV filling. The results indicate that sedation with midazolam or propofol does not affect indices of LV diastolic performance in healthy patients and those with preexisting diastolic dysfunction.

IMPLICATIONS

Sedation with midazolam or propofol does not alter indices of left ventricular diastolic function in healthy patients and those with preexisting left ventricular filling abnormalities as evaluated by transthoracic echocardiography.

Benzodiazepines in the intensive care unit

The effects of BZ drugs result from interaction at the GABAA receptor within the CNS, producing anxiolysis, hypnosis, and amnesia in a dose-dependent fashion. These sedative effects are best titrated to reproducible clinical endpoints, using scoring systems such as the Ramsay scale. All BZs exhibit similar pharmacologic effects, but the important differences in pharmacokinetics and pharmacodynamics should be recognized to use these drugs safely and effectively within the ICU. Diazepam is the classic anxiolytic, amnestic, and sedative agent, but the presence of long-acting active metabolites that depend on the kidneys for elimination limits its use in many ICU patients. Lorazepam is the most potent BZ used in the ICU; it has stable pharmacokinetics and relatively low cost. This drug is best reserved for situations in which rapid onset is not essential and long-term sedation is anticipated. Midazolam has the shortest t1/2 of the commonly used BZs, generates few active metabolites, and is water soluble at physiologic pH. Thus, it is well suited for continuous infusion in the ICU, and the recent introduction of generic formulations of midazolam has decreased the drug-acquisition cost for many hospitals. Optimal sedation for ICU patients often requires BZ and concomitant therapy with drugs such as haloperidol, dexmedetomidine, opioids, and so forth, to reduce untoward side effects and, perhaps, overall drug costs. Flumazenil, a specific BZ antagonist, can be used for diagnostic or therapeutic reversal of BZ agonists when appropriate. Most experienced intensivists recommend an individualized approach to sedation and titration of anxiolysis to maximize efficacy, minimize side effects, and optimize cost effectiveness in the ICU. New CNS monitors of the EEG, such as the BIS or entropy EEG monitors, may refine titration algorithms further in the near future.

Adverse sedation events in pediatrics: analysis of medications used for sedation

OBJECTIVES

To perform a systematic investigation of medications associated with adverse sedation events in pediatric patients using critical incident analysis of case reports.

METHODS

One hundred eighteen case reports from the adverse drug reporting system of the Food and Drug Administration, the US Pharmacopoeia, and the results of a survey of pediatric specialists were used. Outcome measures were death, permanent neurologic injury, prolonged hospitalization without injury, and no harm. The overall results of the critical incident analysis are reported elsewhere. The current investigation specifically examined the relationship between outcome and medications: individual and classes of drugs, routes of administration, drug combinations and interactions, medication errors and overdoses, patterns of drug use, practitioners, and venues of sedation.

RESULTS

Ninety-five incidents fulfilled study criteria and all 4 reviewers agreed on causation; 60 resulted in death or permanent neurologic injury. Review of adverse sedation events indicated that there was no relationship between outcome and drug class (opioids; benzodiazepines; barbiturates; sedatives; antihistamines; and local, intravenous, or inhalation anesthetics) or route of administration (oral, rectal, nasal, intramuscular, intravenous, local infiltration, and inhalation). Negative outcomes (death and permanent neurologic injury) were often associated with drug overdose (n = 28). Some drug overdoses were attributable to prescription/transcription errors, although none of 39 overdoses in 34 patients seemed to be a decimal point error. Negative outcomes were also associated with drug combinations and interactions. The use of 3 or more sedating medications compared with 1 or 2 medications was strongly associated with adverse outcomes (18/20 vs 7/70). Nitrous oxide in combination with any other class of sedating medication was frequently associated with adverse outcomes (9/10). Dental specialists had the greatest frequency of negative outcomes associated with the use of 3 or more sedating medications. Adverse events occurred despite drugs being administered within acceptable dosing limits. Negative outcomes were also associated with drugs administered by nonmedically trained personnel and drugs administered at home. Some injuries occurred on the way to a facility after administration of sedatives at home; some took place in automobiles or at home after discharge from medical supervision. Deaths and injuries after discharge from medical supervision were associated with the use of medications with long half-lives (chloral hydrate, pentobarbital, promazine, promethazine, and chlorpromazine).

CONCLUSIONS

Adverse sedation events were frequently associated with drug overdoses and drug interactions, particularly when 3 or more drugs were used. Adverse outcome was associated with all routes of drug administration and all classes of medication, even those (such as chloral hydrate) thought to have minimal effect on respiration. Patients receiving medications with long plasma half-lives may benefit from a prolonged period of postsedation observation. Adverse events occurred when sedative medications were administered outside the safety net of medical supervision. Uniform monitoring and training standards should be instituted regardless of the subspecialty or venue of practice. Standards of care, scope of practice, resource management, and reimbursement for sedation should be based on the depth of sedation achieved (ie, the degree of vigilance and resuscitation skills required) rather than on the drug class, route of drug administration, practitioner, or venue.

Sedation in the intensive care unit

OBJECTIVE

To describe the goals of sedative use in the intensive care unit and review the pharmacology of commonly used sedative drugs as well as to review pertinent publications in the literature concerning the comparative pharmacology of these drugs, with emphasis on outcomes related to sedation and comparative pharmacoeconomics.

DATA SOURCES

Publications in the scientific literature.

DATA EXTRACTION

Computer search of the literature with selection of representative articles.

SYNTHESIS

Proper choice and use of sedative drugs is based on knowledge of the pharmacology of commonly used agents and is an essential component of caring for patients in the intensive care unit. The large variability in pharmacokinetics and pharmacodynamics in the critically ill make it difficult to directly compare agents. Midazolam provides rapid and reliable amnesia, even when administered for low levels of sedation. Propofol may be useful when deeper levels of sedation and more rapid awakening are required. Lorazepam can be used for long-term sedation in more stable patients if rapidity of effect is not required. Further investigation in assessment of depth of sedation in the critically ill is needed. Continued study of costs, side effects, and appropriate dosing strategies of all sedative agents is needed to answer questions not sufficiently addressed in the current literature.

CONCLUSION

An individualized approach to sedation based on knowledge of drug pharmacology is needed because of confounding variables including concurrent patient illness, depth of sedation, and concomitant use of analgesic agents. (Crit Care Med 2000; 28:854-866)

The effects of cardiopulmonary bypass on total and unbound plasma concentrations of propofol and midazolam

OBJECTIVE

To examine the effects of cardiopulmonary bypass (CPB) on total and unbound plasma concentrations of propofol and midazolam when administered by continuous infusion during cardiac surgery.

DESIGN

Prospective clinical study.

SETTING

University hospital.

PARTICIPANTS

Twenty-four adult patients undergoing cardiac surgery.

INTERVENTIONS

Patients received either propofol or midazolam to supplement fentanyl anesthesia. Twelve patients received a propofol bolus (1 mg/kg) followed by an infusion of 3 mg/kg/hr. A second group received midazolam, 0.2 mg/kg bolus, followed by an infusion of 0.07 mg/kg/hr.

MEASUREMENTS AND MAIN RESULTS

Blood sample were collected from the radial artery cannula at 0, 2, 4, 8, 8, 10, 15, 20 minutes and then every 10 minutes before CPB, at 1, 2, 3, 4, 6, 10, 15, 20 minutes and then each 10 minutes during CPB. On weaning from CPB samples were collected at 0, 5, 10 and 20 minutes. Plasma binding, total and unbound propofol and midazolam concentrations were determined by ultrafiltration and high-pressure liquid chromatography (HPLC). CPB resulted in a fall in total propofol and midazolam plasma concentrations, but the unbound concentrations remained stable. The propofol unbound fraction increased from 0.22 +/- 0.06% to 0.41 +/- 0.17%. The midazolam unbound fraction increased from 5.6 +/- 1.0% to 11.2 +/- 2.1%.

CONCLUSIONS

Unbound concentrations of propofol and midazolam are not affected by cardiopulmonary bypass. Total intravenous anesthesia algorithms do not need to be changed to achieve stable unbound plasma concentrations when initiating CPB.

Comparison of high-performance liquid chromatography and polyclonal fluorescence polarization immunoassay for the monitoring of midazolam in the plasma of intensive care unit patients

Midazolam (M) is used as an induction agent for anesthesia. The main metabolite is alpha-hydroxymidazolam (OM), which is pharmacologically active. Use of M for sedation is a recent application, rapidly gaining favor. Monitoring of the level of sedation is fundamental in that an excessive and prolonged effect is associated with the risk of complications. Thus, it was felt both necessary and useful to measure circulating M levels. We compared a high-performance liquid chromatography (HPLC) assay with fluorescence polarization immunoassay (FPIA) for the measurement of M in the serum of 138 sedated patients in the intensive care unit (i.e., 179 samples). Response of the OM was also assessed. The degree of crossover of the metabolite was between 76.8 and 32.7%. The equation of the regression line for sigma HPLC (i.e., the sum M + OM) versus FPIA was TDx = 1.1585 sigma HPLC + 143.42 (R = 0.966). The 95% confidence interval for the slope was 1.1551, 1.1619. The regression slope differed significantly from 1 (p < 0.001) and shows that FPIA measurements overestimated concentrations obtained by HPLC on the order of 19%. The discrepancy between the two techniques was all the more notable when concentrations were > 1,000 ng/ml. The relative selectivity of Abbott industrial reagent in terms of benzodiazepines leads to the identification of what might be called a midazolam-like (M-like) activity covering both M and OM. The development of a global FPIA method for measurement of this M-like activity in sedated patients provides a satisfactory solution to the question raised.

Liver and renal functions following total intravenous anesthesia using midazolam and fentanyl-comparison with enflurane-nitrous oxide anesthesia

Thirty patients undergoing lower abdominal surgery were studied to compare liver and renal functions in total intravenous anesthesia (TIVA) using midazolam and fentanyl with those in enflurane-nitrous oxide anesthesia (GOE).Patients were randomly divided into two groups of 15. In the TIVA group, anesthesia was induced with 0.3 mg·kg(-1) midazolam and maintained with 0.68 mg·kg(-1)·h(-1) midazolam for 15 min followed by 0.125 mg·kg(-1)·h(-1) midazolam and fentanyl. In the GOE group, anesthesia was induced with 5 mg·kg(-1) thiamylal and maintained with enflurane-nitrous oxide in oxygen. Plasma levels of aspartate aminotransferase, alanine aminotransferase (ALT), lactate dehydrogenase, total bilirubin, alkaline phosphatase, γ-glutamyl transpeptidase (γ-GTP), blood urea nitrogen (BUN), and creatinine (Cr) were measured before and at 1, 7, and 30 days after surgery. There were transient increases beyond the normal range in ALT and γ-GTP in both groups. BUN and Cr were within the normal range. There were no differences between the two groups regarding these parameters and the numbers with abnormally high levels of each parameter. In conclusion, liver and renal functions following TIVA using midazolam and fentanyl were the same as those following enflurane-nitrous oxide anesthesia.

Sedative and ventilatory effects of midazolam infusion: effect of flumazenil reversal

The purpose of this study was to evaluate the effects of flumazenil (1 mg i.v.) on the ventilatory response of premedicated patients receiving a continuous infusion of midazolam for sedation. After assessing baseline ventilatory function using a modified Read rebreathing method for determining hypercapnic ventilatory drive, 16 healthy outpatients were administered fentanyl, 50 micrograms i.v., and midazolam 2 mg i.v., followed by a variable-rate midazolam infusion, 0.3-0.5 mg.min-1. Upon termination of the midazolam infusion, serum midazolam concentrations were measured and ventilatory function was reassessed. Then, 10 ml either saline or flumazenil (1 mg) were administered according to a randomized, double-blind protocol. Ventilatory function was subsequently measured at 5 min, 30 min and 60 min intervals after study drug. Compared with the baseline value, midazolam infusion reduced tidal volume and increased respiratory rate and alveolar dead space. However, midazolam did not decrease the slope of the CO2-response curve. Flumazenil reduced the degree of midazolam-induced sedation and the decrease in tidal volume (P < 0.05), but not the change in resting respiratory rate. In some patients, the ventilatory response to hypercarbia actually decreased after flumazenil administration compared with the immediate prereversal (sedated) values. It is concluded that midazolam infusion, 0.43 mg.min-1, did not impair CO2-responsiveness. Flumazenil's effect on central ventilatory drive was more variable than its reversal of midazolam-induced sedation.

Predictive accuracy of midazolam in adult patients scheduled for coronary surgery

STUDY OBJECTIVE

To evaluate the predictive accuracy of midazolam during cardiac anesthesia so as to orient the selection of the most appropriate pharmacokinetic model for use in a computer-assisted continuous-infusion system.

DESIGN

Retrospective analysis.

SETTING

Operating room at a university hospital.

PATIENTS

66 consecutive middle-aged and elderly coronary patients scheduled for coronary artery bypass graft (CABG) surgery.

INTERVENTIONS

Patients were anesthetized using a variable-rate infusion of alfentanil combined with midazolam in an attempt to achieve and maintain target concentrations of 100 ng/ml or 500 ng/ml.

MEASUREMENTS AND MAIN RESULTS

A total of 323 arterial blood samples were taken, and serum midazolam concentrations were measured by high-performance liquid chromatography. Predicted midazolam concentrations were calculated using 3 selected data sets. Their bias, inaccuracy, and dispersion were assessed by determining the median performance error, the median absolute performance error (MDAPE), and the 10th and 90th percentiles. Two of the selected data sets of midazolam, with a clearance lower than 5 ml/kg/min, were very accurate (MDAPE less than 20%) in predicting low or high prebypass concentrations of midazolam in adult patients with good left ventricular function.

CONCLUSIONS

Two of the 3 pharmacokinetic data sets of midazolam studied may be selected when using a computer-assisted infusion system in adult coronary patients.

Predictive accuracy of alfentanil infusion in coronary artery surgery: a prebypass study in middle-aged and elderly patients

Twenty-three informed and consenting patients scheduled for CABG were anesthetized using computer-controlled infusions of alfentanil, midazolam, and pancuronium. Thirteen middle-aged patients received a preprogrammed infusion scheme of alfentanil, simulated using the population pharmacokinetic set of Maitre et al (Group M), and 10 elderly patients received a preprogrammed infusion scheme simulated using the model of Helmers et al (Group H). The target alfentanil concentrations in groups M and H for tracheal intubation were: 300-500 ng/mL and for sternotomy: 500-700 ng/mL. Blood alfentanil concentrations were measured at tracheal intubation, skin incision, sternotomy, and aortic cannulation. The bias, inaccuracy, and precision of each pharmacokinetic set were assessed by the median performance error (MDPE), the median absolute performance error (MDAPE), and the 10th and 90th percentiles of the performance errors (P10, P90), respectively. The predictive accuracy of seven other alfentanil pharmacokinetic sets selected from the literature was also evaluated retrospectively. The measured alfentanil concentrations were underpredicted when using all the pharmacokinetic sets, except the set of Scott et al (MDPE: -15.9%). The sets of Maitre et al and Helmers et al were found not to be accurate (MDAPE > 40%) in both groups M and H. The set of Scott et al with the lowest clearance (2.4 mL/kg/min) shows the best accuracy (MDAPE: 19.5%) and precision (P10: -40%, P90: 16%). In conclusion, the set of Scott et al should preferably be selected to predict prebypass alfentanil infusion accurately in either middle aged or elderly patients who have normal myocardial function (LVEF > 50%) and are scheduled for CABG.

Effects of midazolam and flumazenil on ventilation during sustained hypoxia in humans

The purpose of this study was to investigate whether increases in gamma-aminobutyric acid (GABA) in the brain stem underlie the ventilatory decline observed during hypoxia in man. The ventilatory responses to sustained isocapnic hypoxia were studied in six adult male subjects on three separate days in three pharmacological conditions: (1) without any drug administration; (2) during infusion of midazolam (a drug which potentiates the effect of GABA); and (3) during infusion of flumazenil (a benzodiazepine antagonist). On each experimental day, the following protocol was repeated three times: end-tidal PO2 was held at 100 Torr for 10 min, then at 50 Torr for 20 min and finally at 100 Torr for 5 min. End-tidal PCO2 was held constant throughout. Responses in the three pharmacological conditions were similar. We conclude that neither potentiation of GABA transmission (midazolam) nor antagonism of this potentiation (flumazenil) greatly affect the decline in ventilation which occurs during extended exposure to hypoxia.

Pharmacokinetic model-controlled infusion of midazolam. A prospective evaluation during general anaesthesia

The accuracy of a computer-controlled infusion of midazolam, based on previously published pharmacokinetic parameters, was tested prospectively in 12 adult female patients undergoing general anaesthesia. Anaesthesia consisted of an initial bolus followed by an exponentially decreasing infusion of midazolam given according to body weight, fentanyl, nitrous oxide and vecuronium. Venous blood samples were taken at 15 min-intervals throughout the procedures and for 1-2 h postoperatively. The bias of the model was -5.1% (95% CI -11.3 to 1.2%) and precision 24.8% (95% CI 20.9 to 28.6%). Least squares regression analysis decreased the bias to -2.8% but did not alter precision. Retrospective fitting of an alternative set of published parameters for midazolam resulted in significant deterioration of the model. The precision was similar to that found in past studies of intravenous anaesthetic agents. Further improvement in the accuracy of midazolam infusion awaits improved understanding of the causes of pharmacokinetic variability.

The effects of midazolam on cerebral blood flow and oxygen consumption. Interaction with nitrous oxide in patients undergoing craniotomy for supratentorial cerebral tumours

Cerebral blood flow and the cerebral metabolic rate of oxygen were measured in 30 patients during craniotomy for supratentorial cerebral tumours by a modification of the Kety-Schmidt technique using Xenon 133 intravenously. Anaesthesia was induced with midazolam 0.3 mg/kg, fentanyl and pancuronium, and maintained with midazolam as a continuous infusion, fentanyl, pancuronium and nitrous oxide in oxygen or oxygen in air. The concentration of midazolam in the blood of 10 patients was about 300 ng/litre during two measurements; the patients' lungs were ventilated with N2O in oxygen. The concentration of midazolam in the blood of another 10 patients was doubled to about 600 ng/litre during the second flow measurement; the patients' lungs were ventilated with N2O/O2. The concentration of midazolam in the blood of the third group of 10 patients was doubled to 600 ng/litre during the second flow measurement; the patients' lungs were ventilated with oxygen in air. No relationship was found between the dose of midazolam and cerebral blood flow or oxygen consumption. Nitrous oxide in combination with midazolam also had no effect on these variables.

Recovery from total intravenous anaesthesia. Propofol versus midazolam-flumazenil

The aim of this study was to compare recovery assessed with the Newman, deletion af a's and postbox tests after total intravenous anaesthsia for procedures lasting more than 90 min, with either propofol (PPF) or midazolam (MDZ), reversed or not by flumazenil (FMZ). Thirty patients scheduled for peripheral surgery were randomly allocated to 3 groups of 10, receiving by continuous infusion until the end of surgery either PPF (n = 10) or MDZ (n = 20) combined with alfentanil. FMZ was administered thereafter to 10 patients receiving MDZ until they opened their eyes on command or to a maximum dose of 1 mg. Recovery tests were performed 45, 90 and 180 min after the end of anaesthesia. Results were analysed with non-parametric tests. Recovery scores were significantly better in the PPF group at all times, reaching control values at 180 min for the three first tests. FMZ reversal did not improve the scores compared to those resulting from MDZ alone. This study provides further data in favour of PPF as far as rapid and complete recovery is concerned. The efficiency of FMZ is incomplete and only transient when administered in a single dose.

Anaesthesia techniques for midazolam and flumazenil--an overview

Midazolam, the latest benzodiazepine agonist, may be used in doses of 0.15 to 0.2 mg.kg-1 for induction of anaesthesia. It provides good correlation between plasma concentration and anaesthetic effect with an interindividual variability of only 20-25%. On this basis, dosage recommendations for midazolam in total intravenous anaesthesia techniques are possible, aiming at hypnotic plasma concentrations of at least 250 ng.ml-1. Due to its biological half-life of 150-180 min and interindividual differences in drug susceptibility, prolonged recovery periods have been observed that can safely and reliably be antagonised by flumazenil, if necessary. It is recommended that flumazenil be administered carefully by titration in increments of 0.1 mg.min-1 to avoid emergence reactions by awakening too fast (tachycardia, hypertension). Usually a mean total dose of 0.4-0.5 mg will lead to prompt awakening.

Anesthesia and monitoring during whole body radiation in children

During whole body radiation therapy of children, treatment may be done in places not equipped with acceptable scavenging systems for anesthetic gases and where clinical observation of the patient may be impossible. In order to solve this problem, the authors have used a total intravenous (IV) anesthetic technique using midazolam, pancuronium, and fentanyl. With midazolam as the only hypnotic agent, the problem with scavenging is solved, and a computer simulation of the plasma concentration of midazolam is presented. A modified stethoscope for monitoring during radiation also has been developed. This anesthetic technique and the stethoscope have been used in seven children. The total IV anesthesia proved to be a useful method for children during whole body radiation. The modified stethoscope functioned very well and was a useful complement to the monitoring equipment.

Plasma level changes of fentanyl and midazolam after release of a prolonged thigh tourniquet

In 14 elderly orthopedic patients undergoing total knee joint replacement, the influence of complete arterial occlusion of the limb on the course of plasma levels of fentanyl and midazolam was examined. The patients were premedicated with midazolam intramuscularly (0.05 mg/kg) and were then given neurolept anesthesia in dosages of 0.1 mg/kg midazolam and 0.01 mg/kg fentanyl intravenously prior to the placement of the tourniquet. Up to 4 h after the tourniquet was released, plasma levels of fentanyl and midazolam as well as pH value, PaCO2 and plasma lactate levels were measured. In 12 patients there was an increase in fentanyl and in 10 patients an increase in midazolam plasma levels after tourniquet release. The maximum increase varied between 1 min and 2 h after release. The plasma levels of midazolam after removal of the tourniquet varied greatly between individuals. Especially patients older than 70 years showed excessively high concentrations of midazolam. These results would indicate that there can be a clinically significant increase of fentanyl and midazolam levels due to initial reperfusion of the lower extremity following prolonged ischemia. Therefore a correspondingly extended period of postoperative surveillance is advisable.

Pharmacokinetics of the newer benzodiazepines

The assay methods used to determine the concentrations of the newer benzodiazepines include electron-capture gas-liquid chromatography, high performance liquid chromatography with ultraviolet detection, gas chromatography-mass spectrometry, radioassay and radioreceptor assay. The method used frequently is the highly sensitive and specific electron-capture gas-liquid chromatography. Other methods are associated with limitations. The triazolo- and imidazolebenzodiazepines differ structurally from the 'classical' benzodiazepines such as diazepam, and offer distinct differences in pharmacological activity and in time-course of effect. Alprazolam and triazolam, both 1,4-triazolobenzodiazepines, have high affinities for the benzodiazepine receptor as do midazolam and loprazolam, which are 1,4-imidazolebenzodiazepines. Absorption is characteristically rapid, with peak alprazolam and triazolam concentrations occurring within 1 hour after oral administration. Sublingual administration results in peak alprazolam and triazolam concentrations that are higher and occur earlier than with the oral route. The volume of distribution of alprazolam and triazolam is approximately 1L. Alprazolam is 70% bound to plasma proteins and the extent of binding is independent of concentration. Similarly, triazolam is approximately 85% bound to plasma proteins, variability in binding being explained by variations in alpha 1-acid glycoprotein concentration. The 1,4-triazolo ring prevents the oxidative metabolism of the classical benzodiazepines which results in formation of active metabolites with long elimination half-lives. Alprazolam is extensively metabolised: 29 metabolites have been identified in the urine, and its major metabolite, alpha-hydroxyalprazolam, has pharmacological activity. alpha-Hydroxyalprazolam and 4-hydroxyalprazolam are detectable in plasma in amounts which account for less than 10% of the administered dose. Mean alprazolam elimination half-life in healthy adult subjects ranges from 9.5 to 12 hours; liver disease prolongs alprazolam elimination, but renal insufficiency does not. Triazolam also undergoes oxidation and subsequent glucuronidation. alpha-Hydroxytriazolam is the major metabolite, in addition to which 4-hydroxyalprazolam and alpha-4-hydroxytriazolam have been identified in plasma and urine. The elimination half-life of triazolam ranges between 1.8 and 5.9 hours, while that of the conjugated metabolites is short, approximately 3.8 hours. Accumulation of triazolam or its metabolites after multiple doses does not occur. Liver disease prolongs triazolam elimination from the body, but renal disease does not.(ABSTRACT TRUNCATED AT 400 WORDS)

Duration of amnesia associated with midazolam/fentanyl intravenous sedation

The purpose of this study was to determine the duration of amnesia associated with the intravenous usage of midazolam and fentanyl. The midazolam was administered in three different dosages based on the patient's weight in kilograms. Patients were shown a series of pen-and-ink drawings at various times throughout the procedure and tested the next day for memory of the drawings using both free recall and match-to-sample paradigms. The results indicate that the low-dosage group (0.07 mg/kg) had insufficient amnesia, whereas the medium (0.10 mg/kg) and high (0.13 mg/kg) groups displayed adequate amnesia in the intraoperative period.

The pharmacokinetics of midazolam in paediatric patients

A serum concentration profile study on midazolam in children was done. Fifty six children aged 3-10 years took part. The routes investigated were intravenous, intramuscular, rectal and oral at 0.15 mg.kg-1, and the oral at 0.45 mg.kg-1 and 1 mg.kg-1. Serum concentration levels for 5 h were studied using gas liquid chromatography. The volume of distribution, Vss, was 1.29 l.kg-1, the elimination half-life 1.17 h and the serum clearance 9.11 ml.kg-1.min-1. Peak serum concentrations for the intramuscular, rectal and oral routes were at 15 min, 30 min and 53 min respectively. Bioavailability was 87%, 18%, 27% respectively at a dose of 0.15 mg.kg-1. The oral route bioavailability halved to 15% at the two higher doses. Bioequivalence was present between the 0.15 mg.kg-1 intramuscular dose and the 0.45 mg.kg-1 oral dose from 45 to 120 min.

Cardiovascular effects of sedative infusions of propofol and midazolam after spinal anaesthesia

The cardiovascular effects of intravenous sedation were studied in fifty patients after spinal anaesthesia for lower limb or pelvic surgery. Twenty patients received propofol (mean dosage 74 (SD 4) micrograms/kg/min for 0-20 minutes and 51 (SD 7) micrograms/kg/min for 20-40 minutes), twenty received midazolam (35 micrograms/kg + 2.54 (SD 0.2) micrograms/kg/min for 0-20 minutes and 1.35 (SD 0.2) micrograms/kg/min for 20-40 minutes) and ten patients received saline infusion only. The forearm vasoconstriction in response to the spinal anaesthesia was measured by strain gauge plethysmography. Spinal anaesthesia lowered systolic and diastolic blood pressure by 18 (SED 4) mmHg and 9 (SED 2) mmHg respectively. (SED = standard error of the difference.) This was associated with a 32% decrease in mean forearm blood flow. Propofol and midazolam caused similar additional reductions in systolic and diastolic blood pressure (10 (SED 4) mmHg and 4 (SED 2) mmHg) and a decrease in heart rate (P less than 0.005), but forearm vasoconstriction was not altered. In the control group, however, forearm vasoconstriction increased during 40 minutes in theatre (P less than 0.05). Recovery from propofol was far more rapid than after midazolam and was virtually complete in ten minutes. This was reflected by an increase in blood pressure and in forearm vasoconstriction in the recovery period.

Effects of the benzodiazepine antagonist flumazenil on postoperative performance following total intravenous anaesthesia with midazolam and alfentanil

Postoperative performance following total intravenous anaesthesia (TIVA) using midazolam and alfentanil was studied with and without the administration of a single dose of a benzodiazepine antagonist, flumazenil (Ro 15-1788). Performance was compared with a reference group anaesthetized with thiopentone, alfentanil and nitrous oxide. All patients were assessed by use of a rating scale which took into account the degree of sedation, amnesia, comprehension and cooperation as well as temporal and spatial orientation. There was a slow recovery following TIVA with somnolence and amnesia lasting several hours. Administration of flumazenil 1.0 mg i.v. at extubation caused a significant reduction of sedation (P less than 0.001) during the first postoperative hour, with patients fully awake or only lightly sedated, but was later followed by resedation. The patients of the reference group were moderately sedated during the observation period. Five and six hours postoperatively there was no difference between the groups. Amnesia was more profound in the groups that received midazolam; the effect of the antagonist could only be seen for 15 min after its administration. Comprehension and cooperation, as well as orientation, were equally good in the antagonist and in the reference group during the immediate postoperative period, whereas in the TIVA group a gradual improvement over the first hours was seen. In the antagonist group there was no increase in the number of analgesic requirements, no anxiety attacks or other adverse effects. It is concluded that flumazenil offers an improvement in postoperative performance following TIVA induced by midazolam and alfentanil, but the effects are of short duration.

Prolonged elimination of midazolam after i.m. administration

The elimination pharmacokinetics of midazolam after i.m. administration was compared with combined i.m. and i.v. administration in a randomized study of 55 gynaecological patients in outpatient general anaesthesia. Group 1 (n = 40) received midazolam 0.1 mg/kg i.m. as premedication 45 min before induction of general anaesthesia with midazolam 0.3 mg/kg i.v. Group 2 (n = 15) received midazolam 0.1 mg/kg i.m. as premedication 45 min before induction of general anaesthesia with thiopentone 4 mg/kg. Serum midazolam concentration measurements were performed regularly post-induction for 7 h in each patient. The elimination half-life of midazolam after i.m. administration (Group 2) was 6.6 +/- 1.2 h (mean +/- s.e. mean), which was significantly longer (P less than 0.05) than the 3.9 +/- 0.3 h observed after the combined i.m. and i.v. administration of midazolam (Group 1), and significantly longer than 2.9 h obtained from a calculated i.v. administration curve. We postulate a slow i.m. depot release of midazolam, representing the rate-limiting step in the elimination of midazolam after i.m. administration.

Effect of total intravenous anaesthesia with midazolam/alfentanil on the adrenocortical and hyperglycaemic response to abdominal surgery

The effect of anaesthesia on the hyperglycaemic and adrenocortical response induced by surgery was studied in patients undergoing abdominal hysterectomy. The study group was anaesthetized with midazolam and alfentanil using a totally intravenous anaesthetic technique. A reference group received anaesthesia with thiopentone, alfentanil and nitrous oxide. Midazolam 0.42 mg.kg-1 was given as a loading infusion followed by a maintenance infusion of 0.125 mg.kg-1.h-1. Alfentanil was given as a bolus dose of 0.075 mg.kg-1 in both groups, followed by a loading infusion of 0.3 mg.kg-1.h-1 for 15 min and a maintenance infusion of 0.065 mg.kg-1.h-1. Increments of alfentanil were given whenever heart rate or systolic blood pressure exceeded pre-induction values by more than 10%. During anaesthesia mean arterial pressure and heart rate were similar in both groups and there was no difference in alfentanil requirement. An immediate increase in blood glucose concentrations was seen following incision, but maximum concentrations were measured in the early postoperative period. Serum cortisol concentrations decreased after induction of anaesthesia. During surgery they returned to pre-induction values, and in the postoperative period they increased to about twice the pre-induction values. It is concluded that midazolam/alfentanil anaesthesia is as effective as anaesthesia induced by thiopentone, alfentanil and nitrous oxide in suppressing the stress-response to surgery until the postoperative period. No signs of prolonged adrenocortical depression were observed.