Clinical pharmacokinetics of the inhalational anaesthetics

Influence of Minimum Alveolar Concentration and Inhalation Duration of Sevoflurane on Facial Nerve Electromyography in Hemifacial Spasm: A Randomized Controlled Trial

BACKGROUND

The lateral spread response (LSR) is an electromyography feature of hemifacial spasm; intraoperative reduction in the LSR is associated with positive surgical outcomes. This study examined the effects of different minimum alveolar concentrations (MACs) and durations of sevoflurane inhalation on the LSR.

METHODS

Eighty patients undergoing microvascular decompression surgery for hemifacial spasm were randomly allocated to receive propofol-remifentanil total intravenous anesthesia alone or in combination with sevoflurane at 0.5, 0.75, or 1 MAC. The LSR and orbicularis oculi muscle wave were recorded before and at 15 and 30 minutes after the start of sevoflurane administration.

RESULTS

Sevoflurane reduced the LSR amplitude in a dose-dependent and duration-dependent manner. The curve representing the LSR amplitude preservation ratio change according to sevoflurane concentration is best fitted by regression analysis using a cubic model, as the cubic equations had the largest coefficient of determination; at 15 minutes ( R2 =0.76, F =78.36, P <0.05) and at 30 minutes ( R2 =0.882, F =189.94, P <0.05). The inhibitory effect of sevoflurane on the LSR amplitude was greater in the first 15 minutes than in the second 15 minutes of sevoflurane administration. Sevoflurane at 1 MAC for 30 minutes mildly decreased the amplitude of the orbicularis oculi muscle wave. The latencies of the LSR and the orbicularis oculi muscle wave were not affected by sevoflurane at all MACs studied.

CONCLUSIONS

The combination of intravenous propofol-remifentanil anesthesia with 0.5 MAC sevoflurane allows reliable intraoperative LSR monitoring in hemifacial spasm patients. Our findings support the central rather than peripheral hypothesis of the LSR.

Pharmacokinetic profile and metabolite identification of bornyl caffeate and caffeic acid in rats by high performance liquid chromatography coupled with mass spectrometry

Bornyl caffeate was initially discovered as a bioactive compound in medicinal plants. Despite the promising pharmacological activities including anti-tumor and antibacterial activities, the pharmacokinetics of the compound remain open. This work developed a high performance liquid chromatography-tandem mass spectrometric method for the determination of bornyl caffeate and caffeic acid (major metabolite and a main unit of bornyl caffeate) in vivo. Successful application of the method included identification of its metabolites and investigation on the drug pharmacokinetics. A total of 30 compounds were identified as the metabolites of bornyl caffeate in rats. We attributed these metabolites to phase I metabolic routes of reduction, oxidation, hydrolysis and phase II metabolic reactions of glucuronidation, sulfation, O-methylation and glycine. Glucuronidation, sulfation, O-methylation and reduction were the main metabolic pathways of bornyl caffeate. The method presented a linear range of 1–4000 ng mL⁻¹. The pharmacokinetic profile of bornyl caffeate was found to be a three compartment open model, while caffeic acid fitted to a two compartment open model when it was administered alone or served as the main metabolite of bornyl caffeate. The time to peak concentration (T_max) and the maximum plasma concentration (C_max) of bornyl caffeate were 0.53 h and 409.33 ng mL⁻¹. Compared with original caffeic acid, the compound displayed an increased half-life of elimination (T_1/2β), area under the concentration time curve from 0 to t (AUC_0–t) and area under the concentration time curve from 0 to ∞ (AUC_0–∞), a decreased half-life of absorption (T_1/2α) and an identical C_max. Taking together, we concluded that bornyl caffeate is able to rapidly initiate therapeutic effect and last for a relatively long time in rats; metabolic pathways of O-methylation and reduction is key to interpret the mechanism and toxicity of bornyl caffeate.

We revealed the metabolic profile of bornyl caffeate by HPLC-Q-TOF/MS, and then simultaneously examined the pharmacokinetics of bornyl caffeate and CA after administration of a single dose of bornyl caffeate by HPLC ion trap MS.

Up: The rise of nitrous oxide abuse. An international survey of contemporary nitrous oxide use

In recent years the recreational use of inhaled nitrous oxide gas (N2O) is becoming increasingly popular, yet little is known about the characteristics of its users or the effects they experience. This paper presents original research from the 2014 Global Drug Survey (GDS) (n=74,864). GDS runs the largest survey of recreational drug use in the world. The findings confirm N2O as a very common drug of use, in particular in the UK and US (38.6% and 29.4% lifetime prevalence). In the UK N2O was reported to be the eighth most commonly used substance. N2O was generally consumed via gas-filled balloons, at festivals and clubs where use of other substances was common. The vast majority of users use infrequently, and their use is not associated with significant harm. However, there appears to be a subpopulation of heavy users who may be using in a dependent pattern. Analysis of last year N2O users (n=4883), confirms that N2O is associated with hallucinations and confusion (which may be the desired effects) and persistent numbness and accidental injury (27.8%, 23.9%, 4.3% and 1.2% of last year users, respectively). Accidental injury is associated with the highest number of 'hits' per session, suggesting a dose-response relationship. The presence of significant harm is discussed in the light of public education on the risks of N2O use and harm-reduction strategies appropriate to N2O use. Further work needs to be completed to confirm the presence of persistent neurological symptoms in recreational users.

Environmental implications of anesthetic gases

For several decades, anesthetic gases have greatly enhanced the comfort and outcome for patients during surgery. The benefits of these agents have heavily outweighed the risks. In recent years, the attention towards their overall contribution to global climate change and the environment has increased. Anesthesia providers have a responsibility to minimize unnecessary atmospheric pollution by utilizing techniques that can lessen any adverse effects of these gases on the environment. Moreover, health care facilities that use anesthetic gases are accountable for ensuring that all anesthesia equipment, including the scavenging system, is effective and routinely maintained. Implementing preventive practices and simple strategies can promote the safest and most healthy environment.

Analgesia effect of a fixed nitrous oxide/oxygen mixture on burn dressing pain: study protocol for a randomized controlled trial

Background

Procedural burn pain is the most intense acute pain and most likely type of burn injury pain to be undertreated due to the physician’s fear of the adverse effect of analgesia and lack of anesthetist present. At our institution, in most of the cases, local burn detersion and debridement were performed at the ward level without any analgesics. This article describes a study designed to test the analgesia effect of a fixed nitrous oxide/oxygen mixture on burn dressing pain.

Methods/design

The experiment was carried out in three centers. The patients were given a number from 1 to 240. A randomization list was produced by a statistician according to our preliminary study. Due to the severity of the pain suffered, ethically it was decided to help as many as possible, so patients given the letters A, B or C were treated using a canister with the appropriate letter containing preprepared nitrous oxide/oxygen mixture (NOOM). Those with D were given oxygen only, from an identical-looking canister labeled D. Neither patients, nor doctors, nor nurses, nor data collector knew what was in each canister, thus they were all blind. The nursing officer who implemented the intervention handed the doctors envelopes containing the patients’ name and allocation of A, B, C or D. Thus, patients receiving NOOM or oxygen were in the ratio 3:1. Parameters, including pain severity, blood pressure, heart rate, digital oxygen saturation and the Chinese version of the burn specific pain anxiety scale (C-BSPAS), were taken before, during and after dressing for each group. A video and audio record was taken individually for later communication coding and outcome analysis. Rescue analgesic was recorded.

Discussion

Based on the findings from our previous qualitative study that physician’s reluctance to order narcotic analgesia is due to its adverse effect and from our pilot experiment, this study aims to test the hypothesis that a fixed nitrous oxide/oxygen mixture will promote better burn dressing pain alleviation and outcomes. Analyses will focus on the effects of the experimental intervention on pain severity during dressing (primary outcomes); physiological parameters, C-BSPAS and acceptance of both health care professionals and patients (secondary outcomes). If this model of analgesia for burn pain management implemented by nurses proves successful, it could potentially be implemented widely in hospital and prehospital settings and improve patients’ satisfaction and quality of life.

Trial registration

(Clinical Trials Identifier: CHICTR-TRC11001690).

Intrathoracic fire during preparation of the left internal thoracic artery for coronary artery bypass grafting

A surgical fire is a serious complication not previously described in the literature with regard to the thoracic cavity. We report a case in which an intrathoracic fire developed following an air leak combined with high pressure oxygen ventilation in a patient with severe chronic obstructive pulmonary disease. The patient presented to our institution with diffuse coronary artery disease and angina pectoris. He was treated with coronary artery bypass graft surgery, including left internal thoracic artery harvesting. Additionally to this rare presentation of an intrathoracic fire, a brief review of surgical fires is included to this paper.

Blood Concentrations of Enflurane Before, During, and After Hypothermic Cardiopulmonary Bypass

OBJECTIVE

The purpose of this study was to determine blood concentrations of enflurane delivered via a membrane oxygenator during hypothermic cardiopulmonary bypass (CPB) with changes in the input enflurane concentration and temperature and to characterize the pharmacokinetics of enflurane washout during and after CPB.

DESIGN

Blood enflurane concentrations were measured by gas chromatography before, during, and after CPB by using mean delivered enflurane concentrations of 0.5% v/v (group 1, n = 5), 0.8% (group 2, n = 7), and 1% (group 3, n = 14).

SETTING

The investigation was performed in a teaching hospital setting.

PARTICIPANTS

Twenty-six patients undergoing cardiac surgery requiring hypothermic CPB.

INTERVENTIONS

Variations in input enflurane concentration in different patients plus blood sampling from the arterial side of the circuit for enflurane assay.

MEASUREMENTS AND MAIN RESULTS

Median (25th and 75th percentiles) pre-CPB blood enflurane concentrations were 48 (25-50) mg/L, 52 (47-56) mg/L, and 115 (90-143) mg/L in groups 1 (0.5% v/v), 2 (0.8% v/v), and 3 (1% v/v), respectively. During hypothermia (28 degrees C) corresponding enflurane concentrations were 44 (31-53) mg/L, 56 (45-62) mg/L, and 145 (109-203) mg/L, respectively. For groups 1 and 2, there were no significant changes in blood enflurane compared with the corresponding pre-CPB value. However, for group 3, cooling resulted in a significant increase (p = 0.006) in blood enflurane. In all groups, enflurane concentrations after rewarming were similar to those in the pre-CPB period.

CONCLUSIONS

It is concluded that exposure to enflurane concentrations greater than 0.8% during CPB can result in high blood concentrations.

Application of MVBC equation to predict mixed venous blood concentrations of sevoflurane in cardiac anaesthesia

We have proposed an equation for estimating the real-time mixed venous blood concentration (MVBC) of isoflurane in cardiac anaesthesia. However, information related to the application of our method to sevoflurane is lacking. We studied 12 patients undergoing cardiac surgery and anaesthetised with sevoflurane. At different time points, pulmonary arterial blood samples were collected for gas chromatography-mass spectrometry (GC-MS) to determine the real mixed venous concentrations of sevoflurane. The inspired and expired concentrations of sevoflurane, measured by a gas monitor, were used for the MVBC calculations. Using Bland-Altman analyses, we found that the calculated MVBCs accurately represent the actual concentrations of sevoflurane in pulmonary arterial blood, as shown by a near-zero percentage bias with a 0.14% precision between the two concentrations. The results demonstrated that our equation could be a useful method for estimating the pulmonary blood concentration of sevoflurane.

Investigation of the metabolic fate of 2-, 3- and 4-bromobenzoic acids in bile-duct-cannulated rats by inductively coupled plasma mass spectrometry and high-performance liquid chromatography/inductively coupled plasma mass spectrometry/electrospray mass spectrometry

Inductively coupled plasma mass spectrometry (ICPMS) has been used to determine the rate and routes of excretion of bromine following the intraperitoneal administration (50 mg kg(-1)) of 2-, 3- and 4-bromobenzoic acids to male bile-duct-cannulated rats. Analysis of urine and bile for (79/81)Br using ICPMS showed that all three bromobenzoic acids were rapidly excreted (82-98%) within 48 h of dosing, primarily via the urine. High-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC/ICPMS) was then used to obtain metabolite profiles for bile and urine. These profiles revealed that extensive metabolism had taken place, with the unchanged bromobenzoic acids forming a minor part of the total of compound-related material detected. Concomitant MS studies, supplemented by alkaline hydrolysis, enabled the identification of the major metabolite of all three of the bromobenzoic acids as a glycine conjugate. Ester glucuronide conjugates were also identified, but formed only a small proportion of total.

On the use of multivariable piecewise-linear models for predicting human response to anesthesia

The standard modeling paradigm used to describe the relationship between input anesthetic agents and output patient endpoint variables are single-input single-output pharmacokinetic-pharmacodynamic (PK-PD) compartment models. In this paper, we propose the use of multivariable piecewise-linear models to describe the relations between inputs that include anesthesia, surgical stimuli and disturbances to a variety of patient output variables. Subspace identification methods are applied to clinical data to construct the models. A comparison of predicted and measured responses is completed, which includes predictions from PK-PD models, and piecewise-linear time-invariant models.

Emprego do propofol, isofluorano e morfina para a anestesia geral de longa duração em bezerros

Foram estudadas características da bioquímica do sangue, da pressão arterial e da freqüência de pulso de 12 bezerros mantidos sob anestesia por 13 horas, utilizando-se propofol para a indução e isofluorano para manutenção, associados à administração de morfina intra-tecal. Os valores de freqüência de pulso, pressão arterial e glicemia apresentaram pequenas variações e se mantiveram próximos dos valores de referência para bezerros anestesiados. Ao longo do período de anestesia houve aumento significativo, mas discreto, do hematócrito, hemoglobina, pCO2, CO2 total, bicarbonato e potássio. O pH do sangue, pO2, Na+ e Ca++ apresentaram reduções significativas. Este protocolo anestésico foi seguro para a manutenção de bezerros anestesiados por período prolongado.

Inhaled nitrous oxide versus placebo as an analgesic and anxiolytic adjunct to peripheral intravenous cannulation

The objective was to determine whether an inhaled 50:50 mixture of nitrous oxide and oxygen (N(2)O/O(2)) provides significant pain and anxiety relief during intravenous cannulation in healthy adults. The study was conducted at the ED of a military teaching hospital. Participants included adult volunteers aged 18 to 50 years. Excluded were those with allergy to N(2)O, anemia, cardiac disease, pregnancy, asthma, or bone marrow disorder. A prospective, randomized, double-blind, placebo-controlled crossover design was used comparing a 50:50 mixture of N(2)O/O(2) versus O(2). After recording baseline nonhatched 100mm visual analog scales (VAS) for pain and anxiety, subjects inhaled gas 1 for 120 seconds, followed by antecubital intravenous cannulation, discontinuance of gas and VAS rating of procedural pain and anxiety. After 15 minutes, the experiment was repeated with gas 2. Ten subjects would detect a 12mm difference in pain or anxiety with a standard deviation of 10 mm, an alpha error under 0.05 and a power over 80%. Differences between VAS were compared by matched 2-tailed t-test. Eleven subjects were enrolled. One withdrew because of dizziness while inhaling gas (N(2)O). The 10 remaining subjects reported significantly less pain (N(2)O/O(2) 14.5mm, SD 18; O(2) 34.3mm, SD 23.4; P < .01) and anxiety (N(2)O/O(2) - 7.9mm, SD 7.8; O(2) 6.0mm, SD 11.6; P < .02) when inhaling N(2)O/O(2) than when inhaling O(2) alone. N(2)O/O(2) provided significant pain and anxiety reductions during intravenous cannulation. Some patients may experience adverse perceptions while using N(2)O, limiting its utility. Further studies defining the role of N(2)O as an anxiolytic agent, efficacy in actual patients, and cost comparisons with intravenous conscious analgesia/sedation, are warranted.

Hypertonic saline treatment of severe hyperkalemia in nonnephrectomized dogs

OBJECTIVES

To determine whether a hypertonic saline bolus improves cardiac conduction or plasma potassium levels more than normal saline infusion within 15 minutes of treatment for severe hyperkalemia. Previously with this model, 8.4% sodium chloride (NaCl) and 8.4% sodium bicarbonate (NaHCO(3)) lowered plasma potassium equally effectively.

METHODS

This was a crossover study using ten conditioned dogs (14-20 kg) that received, in random order, each of three intravenous (IV) treatments in separate experiments at least one week apart: 1) 2 mmol/kg of 8.4% NaCl over 5 minutes (bolus); 2) 2 mmol/kg of 0.9% NaCl over one hour (infusion); or 3) no treatment (control). Using isoflurane anesthesia and ventilation (pCO(2) = 35-40 torr), 2 mmol/kg/hr of IV potassium chloride (KCl) was infused until conduction delays (both absent p-waves and >/=20% decrease in ventricular rate in </=5 minutes) were sustained for 15 minutes. The KCl was then decreased to 1 mmol/kg/hr (maintenance) for 2 hours and 45 minutes. Treatment (0 minutes) began after 45 minutes of maintenance KCl.

RESULTS

From 0 to 15 minutes, mean heart rate increased 29.6 (95% CI = 12.2 to 46; p < 0.005) beats/min more with bolus than infusion and 23.4 (95% CI = 2.6 to 43.5; p < 0.03) beats/min more with bolus than control. No clinically or statistically significant difference was seen in heart rate changes from 0 to 30 minutes. Decreases in potassium from 0 to 15 minutes were similar with bolus, infusion, and control.

CONCLUSIONS

In this model, 8.4% NaCl bolus reversed cardiac conduction abnormalities within the first 15 minutes after treatment, more rapidly than did the 0.9% NaCl infusion or control. This reversal occurred despite similar reductions in potassium levels.

A Multicenter Study Evaluating the Effects of Sevoflurane on Renal Function in Patients With Renal Insufficiency

BACKGROUND: This multicenter study was undertaken to compare the effect of sevoflurane with that of isoflurane on renal function in 26 patients with pre-existing renal insufficiency. Sevoflurane undergoes hepatic metabolism, with release of inorganic fluoride. Elevated fluoride levels have been associated with renal impairment in patients undergoing methoxyflurane anesthesia raising concerns about the nephrotoxic potential of sevoflurane. METHODS: Patients were ASA II or III class, with renal insufficiency defined by a preoperative serum creatinine concentration of 1.5-3.0 mg/dl. A standardized anesthetic regimen was used consisting of intravenous induction with propofol, vecuronium for muscle relaxation, and fentanyl for analgesia. Patients were randomized to receive either isoflurane or sevoflurane with 100% oxygen. Blood samples were obtained preoperatively and at 24, 48, and 72 h postoperatively for renal/electrolyte determinations. Blood samples for plasma fluoride measurement were obtained preoperatively. RESULTS: Plasma fluoride levels were significantly higher in patients receiving sevoflurane at all measurement points from 0 to 72 h postanesthesia. Mean peak fluoride concentration was 33.4 µM. The maximum fluoride value measured was 51.2 µM. There were no significant differences in postoperative serum creatinine values at any time between patients receiving sevoflurane or isoflurane. CONCLUSIONS: Sevoflurane metabolism produces elevations in plasma fluoride concentrations relative to isoflurane. Despite the increase in plasma fluoride levels, the administration of sevoflurane to patients with renal insufficiency did not produce any adverse effects on renal function as measured by serum creatinine concentration when compared with isoflurane.

Sevoflurane versus halothane for general anesthesia in pediatric patients: a comparative study of vital signs, induction, and emergence

STUDY OBJECTIVE

To compare vital signs and the speed of induction and emergence with sevoflurane versus halothane in pediatric patients.

DESIGN

Prospective, randomized, open study.

SETTING

Thomas Jefferson University Hospital.

PATIENTS

40 unpremedicated ASA Physical Status I and II children age 9 months to 16 years undergoing elective inpatient otorhinolaryngologic or orthopedic surgery.

INTERVENTIONS

Standardized induction of anesthesia with sevoflurane (start: 1%, maximum: 7%) or halothane (start: 0.5%, maximum: 5%) in nitrous oxide/oxygen (N2O/O2). Intubation following vecuronium and 4 minutes of controlled ventilation with 2 minimum alveolar concentration (MAC) drug in O2; 1.5 MAC drug in N2O/O2 delivered for 20 minutes; then 0.75 MAC until the end of surgery. Fentanyl 1 mcg/kg was administered 15 minutes before the anticipated end of surgery, at which time anesthetics were stopped and mechanical ventilation continued until eye opening (emergence).

MEASUREMENTS AND MAIN RESULTS

Blood pressure, heart rate (HR), oxygen saturation, end-tidal gas concentrations, and temperature were recorded. Induction and emergence times were measured to the nearest second. Induction (loss of eyelash reflex) was faster with sevoflurane (97 +/- 31 sec) than halothane (120 +/- 36 sec; p < 0.05), despite a lower inspired sevoflurane MAC. Emergence was faster with sevoflurane (9.9 +/- 2.9 min vs. 12.5 +/- 4.7 min; p < 0.05), despite a higher MAC multiple of end-tidal sevoflurane concentration at the end of surgery. Following intubation, HR (compared with the preinduction value in the operating room) was significantly higher in the halothane group (136.8% +/- 16.3% vs. 115.0% +/- 25.6%), as was mean arterial pressure (113.2% +/- 25.5% vs. 87.8% +/- 22.6%). This finding corresponded with a higher MAC multiple of end-tidal concentration in the sevoflurane group than in the halothane group.

CONCLUSIONS

Induction of and emergence from anesthesia was faster with sevoflurane than halothane. Airway complications were low in both groups. Vital signs were more stable with sevoflurane during induction through intubation, and were comparable during maintenance. Sevoflurane is an excellent drug for inhalational induction in pediatric patients.

Effects of hypothermia on the elimination of ethanol, diazepam and oxazepam in rat liver slice incubations

The elimination of ethanol, diazepam and oxazepam which are metabolised by different enzymes, has been studied for 30, 60, 90 and 120 min at 37, 27, 17 and 7 degrees C in rat liver slice incubations. Ethanol elimination followed zero-order kinetics at all temperatures, while the benzodiazepines consistently displayed first-order kinetics. No sign of phase transition was observed in the respective Arrhenius-plots. Ethanol elimination was more temperature dependent than the elimination of diazepam, while the elimination of oxazepam was little influenced by temperature. This is shown by the temperature ratios (Q10) and energies of activation (Ea) of 1.76, 1.56, 1.24 and 40.5, 31.9, 15.2 for ethanol, diazepam and oxazepam, respectively. This means that ethanol, diazepam and oxazepam elimination was reduced by 25, 22 and 14%, respectively, for each 10 degrees C of temperature reduction, which is considerably lower than the commonly observed 50% reduction of enzyme activity. We conclude that observations made for one drug on temperature dependent elimination may not apply to other drugs.

Role of nucleotide pyrophosphatase in enflurane-induced reduction of UDP-glucuronic acid concentration in mouse liver

Because hepatic UDP-glucuronic acid levels decrease upon exposure to volatile anesthetics, the present study was designed to determine the mechanism by which enflurane decreases UDP-glucuronic acid in mice by measuring the concentrations of intermediates and the activities of enzymes in the UDP-glucuronic acid pathway. UDP-glucuronic acid concentrations were decreased by 40% in both male and female mice after 10 min of enflurane-induced narcosis. Concentration of UDP-glucose and the activities of diethylstilbestrol UDP-glucuronosyltransferase and UDP-glucose dehydrogenase were not affected by enflurane treatment. In contrast, nucleotide pyrophophatase activity was increased approximately 50% in both sexes. Thus, the decrease in hepatic UDP-glucuronic acid upon exposure of mice to enflurane is probably due to increased degradation by nucleotide pyrophosphatase.

Displacement of warfarin from human serum proteins by halothane anaesthesia

The in vitro effects of the halothane metabolite, trifluoroacetic acid, on the binding of warfarin to human serum proteins have been investigated. An increase in the percentage of free warfarin following incubation with different concentrations of trifluoroacetic acid (1 and 4 mmol/l) was observed. In addition, protein binding of warfarin was studied in serum from patients undergoing halothane anaesthesia (1-2.5%; 2.5 h). After 24 h from the end of the halothane anaesthesia, an increase in the percentage of free warfarin was also detected (0.92 +/- 0.06% at 24 h vs 0.60 +/- 0.02% before halothane administration; P less than 0.005). We conclude that halothane anaesthesia may temporarily potentiate the pharmacological effect of warfarin in the postoperative period following anaesthetic procedures.

Uptake of trihalomethanes by patients during hemodialysis

Trihalomethanes (THM) present in tap water were also found in dialysis fluid because they were not eliminated by water treatment. THM, absorbed through the dialyser membranes, increased considerably in blood and in expired air of patients on hemodialysis during the dialysis sessions. The uptake of THM during each dialysis session was about 1 mg.