Argon pharmacokinetics: measurements in pigs and analysis in humans using a physiologically based pharmacokinetics model

The primary objective of this study was to investigate the pharmacokinetics of inhaled argon in young pigs using mechanical ventilation. Also a physiologically based model of argon pharmacokinetics (PBPK) is validated with human data for xenon from the literature and the new data from juvenile pigs. The inherent difficulty in performing pharmacokinetics studies of argon makes the use of the PBPK model especially relevant. The model is used to investigate argon pharmacokinetics for adult and neonate applications. Juvenile pigs (n = 4) were anesthetized, submitted to endotracheal intubation, and mechanical ventilation using a conventional ventilator. Argon inhalation was achieved by switching the animal from the first mechanical ventilator (with air/oxygen) to a second one that was supplied with 75% argon and 25% oxygen from premixed gas cylinders. This administration yielded blood samples that were analyzed using a quadrupole based technique for determining argon concentration. The range of blood:gas partition coefficient corresponding to the average measured Cmax of 190-872 μM is 0.005-0.022. Based on the average curve, T1/2= 75 seconds. The PBPK is shown to be in general agreement with the experimental data in pigs. Inhaled argon administration exhibited an on-off nature such that AUC was proportional to administration time. Confidence in the PBPK model and the remarkably robust and stable on-off nature of argon pharmacokinetics, notwithstanding intersubject variability and comorbidity, suggests that inhaled argon could readily be applied to any treatment regime.

Pharmacokinetics of desflurane uptake and disposition in piglets

Introduction

Many respiratory but few arterial blood pharmacokinetics of desflurane uptake and disposition have been investigated. We explored the pharmacokinetic parameters in piglets by comparing inspiratory, end-tidal, arterial blood, and mixed venous blood concentrations of desflurane.

Methods

Seven piglets were administered inspiratory 6% desflurane by inhalation over 2 h, followed by a 2-h disposition phase. Inspiratory and end-tidal concentrations were detected using an infrared analyzer. Femoral arterial blood and pulmonary artery mixed venous blood were sampled to determine desflurane concentrations by gas chromatography at 1, 3, 5, 10, 20, 30, 40, 50, 60, 80, 100, and 120 min during each uptake and disposition phase. Respiratory and hemodynamic parameters were measured simultaneously. Body uptake and disposition rates were calculated by multiplying the difference between the arterial and pulmonary artery blood concentrations by the cardiac output.

Results

The rates of desflurane body uptake increased considerably in the initial 5 min (79.8 ml.min-1) and then declined slowly until 120 min (27.0 ml.min-1). Similar characteristics of washout were noted during the subsequent disposition phase. Concentration-time curves of end-tidal, arterial, and pulmonary artery blood concentrations fitted well to zero-order input and first-order disposition kinetics. Arterial and pulmonary artery blood concentrations were best fitted using a two-compartment model. After 2 h, only 21.9% of the desflurane administered had been eliminated from the body.

Conclusion

Under a fixed inspiratory concentration, desflurane body uptake in piglets corresponded to constant zero-order infusion, and the 2-h disposition pattern followed first-order kinetics and best fitted to a two-compartment model.

Propofol-based total intravenous anesthesia is associated with better survival than desflurane anesthesia in limb-salvage surgery for osteosarcoma: A retrospective analysis

Previous studies have demonstrated that anesthetic techniques can affect the outcomes of cancer surgery. We investigated the association between anesthetic techniques and patient outcomes after elective limb-salvage surgery for osteosarcoma (OS). This was a retrospective cohort study of patients who underwent elective limb-salvage surgery for OS between January 2007 and December 2018. Patients were grouped according to the administration of propofol-based total intravenous anesthesia (TIVA) or desflurane (DES) anesthesia. Kaplan-Meier analysis was performed, and survival curves were constructed from the date of surgery to death. Univariate and multivariate Cox regression models were applied to compare the hazard ratios (HRs) for death after propensity matching. Subgroup analyses were done for postoperative recurrence, metastasis, and tumor-node-metastasis (TNM) staging. A total of 30 patients (17 deaths, 56.7%) who received DES anesthesia and 26 (4 deaths, 15.4%) who received TIVA were eligible for analysis. After propensity matching, 22 patients were included in each group. In the matched analysis, patients who received TIVA had better survival with a HR of 0.30 (95% confidence interval [CI], 0.11-0.81; P = .018). Subgroup analyses also showed significantly better survival in the presence of postoperative metastasis (HR, 0.24; 95% CI, 0.06-0.87; P = .030) and with TNM stage II to III (HR, 0.26; 95% CI, 0.09-0.73; P = .011) in the matched TIVA group. In addition, patients administered with TIVA had lower risks of postoperative recurrence and metastasis than those administered with DES anesthesia in the matched analyses. Propofol-based TIVA was associated with better survival in patients who underwent elective limb-salvage surgery for OS than DES anesthesia. Prospective studies are needed to assess the effects of TIVA on oncological outcomes in patients with OS.

Assessments of prolonged effects of desflurane and sevoflurane on motor learning deficits in aged AppNL-G-F/NL-G-F mice

As the proportion of elderly in society increases, so do the number of older patients undergoing surgical procedures. This is concerning as exposure to anesthesia has been identified as a risk factor for Alzheimer's disease (AD). However, the causal relationship between clinical AD development and anesthesia remains conjectural. Preclinical studies have demonstrated that anesthesia, such as halothane, isoflurane, and sevoflurane, induces AD-like pathophysiological changes and cognitive impairments in transgenic mouse models of AD. Desflurane does not have these effects and is expected to have more potential for use in elderly patients, yet little is known about its effects, especially on non-cognitive functions, such as motor and emotional functions. Thus, we examined the postanesthetic effects of desflurane and sevoflurane on motor and emotional function in aged App^{NL-G-F/NL-G-F} (App-KI) mice. This is a recently developed transgenic mouse model of AD exhibiting amyloid β peptide (Aβ) amyloidosis and a neuroinflammatory response in an age-dependent manner without non-physiological amyloid precursor protein (APP) overexpression. Mice were subjected to a short behavioral test battery consisting of an elevated plus maze, a balance beam test, and a tail suspension test seven days after exposure to 8.0% desflurane for 6 h or 2.8% sevoflurane for 2 h. App-KI mice showed significant increments in the percentage of entry and time spent in open arms in the elevated plus maze, increments in the number of slips and latency to traverse for the balance beam test, increments in the limb clasping score, increments in immobile duration, and decrements in latency to first immobile episode for the tail suspension test compared to age-matched wild type (WT) controls. Desflurane- and sevoflurane-exposed App-KI mice showed a delayed decrement in the number of slips for each trial in the balance beam test, while air-treated App-KI mice rapidly improved their performance, and increased their clasping behavior in the tail suspension test. Furthermore, App-KI inhibited the change in membrane GluA3 following exposure to anesthetics in the cerebellum. These results suggest high validity of App-KI mice as an animal model of AD.

Current perspective on veterinary drug and chemical residues in food of animal origin

The marked increase in the demand for animal protein of high quality necessitates protecting animals from infectious diseases. This requires increasing the use of veterinary therapeutics. The overuse and misuse of veterinary products can cause a risk to human health either as short-term or long-term health problems. However, the biggest problem is the emergence of resistant strains of bacteria or parasites. This is in addition to economic losses due to the discarding of polluted milk or condemnation of affected carcasses. This paper discusses three key points: possible sources of drug and chemical residues, human health problems, and the possible method of control and prevention of veterinary drug residues in animal products.

Propofol-Based Total Intravenous Anesthesia is Associated with Better Survival than Desflurane Anesthesia in Epithelial Ovarian Cancer Surgery: A Retrospective Cohort Study

Background: Previous studies have shown that anesthetic techniques can affect outcomes of cancer surgery. We investigated the association between anesthetic techniques and patient outcomes after elective epithelial ovarian cancer surgery.

Methods: This was a retrospective cohort study of patients who received elective open surgery for epithelial ovarian cancer between January 2009 and December 2014. Patients were grouped according to the administration of propofol or desflurane anesthesia. Kaplan–Meier analysis was performed, and survival curves were constructed from the date of surgery to death. Univariate and multivariate Cox regression models were used to compare hazard ratios for death after propensity matching. Subgroup analyses were performed for age, body mass index, preoperative carbohydrate antigen-125 level, International Federation of Gynecology and Obstetrics staging, and operation and anesthesia time.

Results: In total, 165 patients (76 deaths, 46.1%) who received desflurane anesthesia and 119 (30 deaths, 25.2%) who received propofol anesthesia were eligible for analysis. After propensity matching, 104 patients were included in each group. In the matched analysis, patients who received propofol anesthesia had better survival with a hazard ratio of 0.52 (95% confidence interval, 0.33–0.81; p = 0.005). Subgroup analyses also showed significantly better survival with old age, high body mass index, elevated carbohydrate antigen-125 level, advanced International Federation of Gynecology and Obstetrics stage, and prolonged operation and anesthesia time in the matched propofol group. In addition, patients administered with propofol anesthesia had less postoperative recurrence and metastasis than those administered with desflurane anesthesia in the matched analysis.

Conclusion: Propofol anesthesia was associated with better survival in patients who underwent elective epithelial ovarian cancer open surgery. Prospective studies are warranted to evaluate the effects of propofol anesthesia on oncological outcomes in patients with epithelial ovarian cancer.

Exploratory analyses of postanesthetic effects of desflurane using behavioral test battery of mice

Halogenated ethers, such as desflurane, sevoflurane, and isoflurane, are known to exert an array of effects besides sedation. However, the postanesthetic effects of desflurane remain undiscovered as no study has explored these effects systematically. Phenotypic screening using behavioral test batteries is a powerful method to identify such effects. In the present study, we behaviorally phenotyped desflurane-treated mice to investigate postanesthetic effects. We applied comprehensive behavioral test batteries measuring sensorimotor functions, anxiety, depression, sociability, attention, and learning abilities, starting 7 days after anesthesia performed with 8.0% desflurane for 6 h. Although our previous study revealed postanesthetic effects of isoflurane in adult mice, in the current study, desflurane-treated mice exhibited no such effects in any behavioral test. To further examine whether desflurane affect behavior in more early time point, we built up a new additional test battery, which carried out 1 day or 3 days after exposure to desflurane. Mice treated with desflurane 1 day before testing showed more slips than other two groups in the first trial, suggesting mild acute side effects of desflurane on motor coordination. These results suggest the safety of desflurane in clinical settings and imply that postanesthetic effects are unique to each halogenated ether.

Development of a hybrid CFD-PBPK model to predict the transport of xenon gas around a human respiratory system to systemic regions

Administering incorrect doses of conventional anesthetic agents through the pulmonary route can cause potential health risks such as blood coagulation, platelet dysfunction, and deteriorating organ function. As an alternative, xenon can minimize the impact on the cardiovascular system and provide the neuroprotective effect, hemodynamic stability, and fast recovery. However, the inhalation pattern still needs to be carefully monitored and controlled to avoid health risks caused by over administering xenon to patients during unconsciousness. Thus, high-resolution lung absorption and whole-body translocation data are critically needed to fully understand how to administer the gas and coordinate with the patient to accurately control the dose. Clinical studies are not able to provide accurate dosimetry data due to their limited operational flexibility and imaging resolution. Therefore, a computational fluid dynamics (CFD) model was employed in this study to simulate the transport and absorption of the inhaled xenon which is connected with a physiologically based pharmacokinetic (PBPK) model to predict the translocation into the systemic regions. To study the effects of different breathing patterns on xenon transport dynamics in the human body, a realistic breathing waveform and two steady-state flow rates with inhalation durations of 2 and 1.5 seconds were selected. For the realistic breathing cycle, the inhalation-exhalation periods are defined for a human at rest and the other two cases have a fixed volumetric flow rate of 15 L/min. As the two latter cases only simulate the inspiratory phase, a 1-second holding time was applied to represent the missing periods of the full breathing time. Simulations were performed in a subject-specific human upper airway configuration from mouth to G6. Numerical results show that with the accurate lung uptake predictions obtained from the CFD model, the hybrid CFD-PBPK model with TRANSIT compartments generates more precise and breath-specific trends compared to simple PBPK models. Numerical results demonstrate that breathing pattern can significantly influence the xenon uptake in the human body, which can be utilized as a critical factor to be coordinated by clinicians to achieve the optimized xenon dose. Furthermore, parametric analyses were performed for the influence of breathing patterns on local airflow distributions, gas species translocations, and lung elimination mechanisms followed by species diffusion into the systemic regions.

European Society of Anaesthesiology Task Force on Nitrous Oxide: a narrative review of its role in clinical practice

Nitrous oxide (N₂O) is one of the oldest drugs still in use in medicine. Despite its superior pharmacokinetic properties, controversy remains over its continued use in clinical practice, reflecting in part significant improvements in the pharmacology of other anaesthetic agents and developing awareness of its shortcomings. This narrative review describes current knowledge regarding the clinical use of N₂O based on a systematic and critical analysis of the available scientific literature. The pharmacological properties of N₂O are reviewed in detail along with current evidence for the indications and contraindications of this drug in specific settings, both in perioperative care and in procedural sedation. Novel potential applications for N₂O for the prevention or treatment of chronic pain and depression are also discussed. In view of the available evidence, we recommend that the supply of N₂O in hospitals be maintained while encouraging its economic delivery using modern low flow delivery systems. Future research into its potential novel applications in prevention or treatment of chronic conditions should be pursued to better identify its role place in the developing era of precision medicine.

A physiologically based model for denitrogenation kinetics

Under normal conditions we continuously breathe 78% nitrogen (N₂) such that the body tissues and fluids are saturated with dissolved N₂. For normobaric medical gas administration at high concentrations, the N₂ concentration must be less than that in the ambient atmosphere; therefore, nitrogen will begin to be released by the body tissues. There is a need to estimate the time needed for denitrogenation in the planning of surgical procedures. In this paper we will describe the application of a physiologically based pharmacokinetic model to denitrogenation kinetics. The results are compared to the data resulting from experiments in the literature that measured the end tidal N₂ concentration while breathing 100% oxygen in the form of moderately rapid and slow compartment time constants. It is shown that the model is in general agreement with published experimental data. Correlations for denitrogenation as a function of subject weight are provided.

TREK-1 pathway mediates isoflurane-induced memory impairment in middle-aged mice

Post-operative cognitive dysfunction (POCD) has been widely reported, especially in elderly patients. An association between POCD and inhalational anesthetics, such as isoflurane, has been suggested. The TWIK-related K⁺ channel-1 (TREK-1) controls several major cellular responses involved in memory formation and is believed to participate in the development of depression, cerebral ischemia and blood-brain barrier dysfunction. However, the specific role of TREK-1 in mediating anesthesia-induced POCD remains unknown. In the current study, we determined that exposure to isoflurane affected memory in middle-aged mice and altered TREK-1 expression. In addition, TREK-1 over-expression exacerbated isoflurane-induced memory impairment, while TREK-1 silence attenuated the impairment. Taken together, our data demonstrate that inhibition of TREK-1 protects mice from cognitive impairment induced by anesthesia and TREK-1 is a potential therapeutic target against memory impairment induced by volatile anesthetics.

Factors Affecting Postoperative Nausea and Vomiting in Surgical Patients

PURPOSE

This study was to identify factors affecting postoperative nausea and vomiting (PONV) and to investigate the incidence of PONV for the first 24 hours after operation.

DESIGN

The prospective research was performed in an 1,100-bed university hospital, from April to December, 2011. The sample consisted of 609 patients with elective surgery.

METHODS

Factors affecting PONV were identified by multiple logistic regression.

FINDINGS

Incidence of PONV was 27.1% for the first postoperative 24 hours. Insertion of nasogastric tube (OR, 4.54, P = .002), history of PONV (OR, 3.24, P < .001), general anesthesia (OR, 2.76, P = .002), history of motion sickness (OR, 2.33, P < .001), and female sex (OR, 2.05, P = .004) were high risk factors of PONV. The nonadministration of antiemetics during operation (OR, 1.70, P = .014) and nonuse of intravenous patient-controlled analgesia (OR, 1.54, P = .038) increased PONV during the first postoperative 24 hours.

CONCLUSIONS

Patients of female gender, history of motion sickness and PONV, general anesthesia, and nasogastric insertion are more likely to experience PONV.

Gas transport during in vitro and in vivo preclinical testing of inert gas therapies

New gas therapies using inert gases such as xenon and argon are being studied, which require in vitro and in vivo preclinical experiments. Examples of the kinetics of gas transport during such experiments are analyzed in this paper. Using analytical and numerical models, we analyze an in vitro experiment for gas transport to a 96 cell well plate and an in vivo delivery to a small animal chamber, where the key processes considered are the wash-in of test gas into an apparatus dead volume, the diffusion of test gas through the liquid media in a well of a cell test plate, and the pharmacokinetics in a rat. In the case of small animals in a chamber, the key variable controlling the kinetics is the chamber wash-in time constant that is a function of the chamber volume and the gas flow rate. For cells covered by a liquid media the diffusion of gas through the liquid media is the dominant mechanism, such that liquid depth and the gas diffusion constant are the key parameters. The key message from these analyses is that the transport of gas during preclinical experiments can be important in determining the true dose as experienced at the site of action in an animal or to a cell.

Effects of changing from sevoflurane to desflurane on the recovery profile after sevoflurane induction: a randomized controlled study

PURPOSE

Desflurane has the lowest solubility of currently available volatile anesthetics and may allow for more rapid emergence and recovery compared with sevoflurane. Nevertheless, after volatile induction with sevoflurane, it has not been determined whether the use of desflurane provides faster emergence and recovery. The present study aimed to elucidate the effects of changing from sevoflurane to desflurane during the early part of anesthesia.

METHODS

Fifty-two patients who were scheduled for vitreous surgery with general anesthesia were enrolled in this randomized controlled study. Anesthesia was induced with volatile induction consisting of 100% oxygen (6 L·min(-1)) and 5% sevoflurane. For anesthesia maintenance, patients were randomized to receive 1-2% sevoflurane or 3-6% desflurane. In the desflurane group, the anesthetic agent was changed from sevoflurane to desflurane within five minutes following endotracheal intubation. After surgery, we assessed the following endpoints: the times from discontinuing volatile anesthetics to eye opening, obeying the command to squeeze the investigator's hand, tracheal extubation, and orientation to the patients' full name, date, and place.

RESULTS

Emergence and recovery were significantly faster in the desflurane group than in the sevoflurane group in times to mean (SD) eye opening [6.5 (2.9) vs 10.1(3.0) min, respectively; mean difference, 3.6 min; 95% confidence interval (CI), 1.9 to 5.3; P < 0.001], obeying commands [6.6 (2.7) vs 10.1 (3.1) min, respectively; mean difference, 3.5 min; 95% CI, 1.9 to 5.2; P < 0.001], and tracheal extubation [7.0 (2.5) vs 10.6 (3.0) min, respectively; mean difference, 3.6 min; 95% CI, 1.9 to 5.1; P < 0.001]. Similarly, the times from discontinuation of volatile anesthetics to orientation to the patients' full name, date, and place were significantly shorter in the desflurane group compared with the sevoflurane group. There were no significant differences between groups on a 100-mm visual analogue scale assessing postoperative nausea and vomiting, eye pain, and patient satisfaction regarding anesthesia.

CONCLUSION

Changing the anesthetic agent from sevoflurane to desflurane after sevoflurane induction provides faster emergence and recovery compared with sevoflurane anesthesia. This study protocol was registered at http://www.umin.ac.jp/ctr/index.htm , (UMIN000009941).

Pharmacokinetic analysis of the chronic administration of the inert gases Xe and Ar using a physiological based model

Background

New gas therapies using inert gases such as xenon and argon are being studied, which would require chronically administered repeating doses. The pharmacokinetics of this type of administration has not been addressed in the literature.

Methods

A physiologically based pharmacokinetics (PBPK) model for humans, pigs, mice, and rats has been developed to investigate the unique aspects of the chronic administration of inert gas therapies. The absorption, distribution, metabolism and excretion (ADME) models are as follows: absorption in all compartments is assumed to be perfusion limited, no metabolism of the gases occurs, and excretion is only the reverse process of absorption through the lungs and exhaled.

Results

The model has shown that there can be a residual dose, equivalent to constant administration, for chronic repeated dosing of xenon in humans. However, this is not necessarily the case for small animals used in pre-clinical studies.

Conclusions

The use of standard pharmacokinetics parameters such as area under the curve would be more appropriate to assess the delivered dose of chronic gas administration than the gas concentration in the delivery system that is typically reported in the scientific literature because species and gas differences can result in very different delivered doses.

Anesthetic selection and disease-free survival following optimal primary cytoreductive surgery for stage III epithelial ovarian cancer

BACKGROUND

Previous studies have offered conflicting results regarding an association between perioperative epidural analgesia and disease-free survival (DFS) following optimal primary cytoreductive surgery for stage III epithelial ovarian cancer. A possible separate role for inhalational anesthetics has not been assessed.

METHODS

We conducted a historical cohort study of all women undergoing optimal primary cytoreduction (<1 cm residual disease) for Stage III epithelial ovarian cancer between January 1, 2007, and December 31, 2011, at Brigham and Women's Hospital. Cohorts were defined by exposure to perioperative epidural analgesia or exposure to specific volatile anesthetics. The primary outcome was DFS.

RESULTS

A total of 194 patients met study inclusion criteria. Addition of epidural analgesia was associated with a lower overall rate of ovarian cancer recurrence compared with general anesthesia alone (72 vs. 85 %, p = 0.028). Longer median DFS was associated with more than 48 h of epidural use (14.9 months) compared with fewer than 24 h (10.9 months) or 24-48 h of epidural use (10.0 months; p = 0.025). Use of desflurane was associated with a lower overall rate of ovarian cancer recurrence compared with sevoflurane (63 vs. 84 %, p = 0.01). In multivariate analysis, use of desflurane was independently associated with improved DFS (hazards ratio 0.563; 95% confidence interval 0.33-0.962).

CONCLUSIONS

For patients with Stage III ovarian cancer, use of desflurane is associated with improved DFS following primary cytoreductive surgery compared with other volatile anesthetics. If epidural analgesia offers additional benefit, this effect appears limited to patients with more than 48 h of postoperative epidural use.

[General anesthesia for ambulatory surgery : Clinical pharmacological considerations on the practical approach]

Due to modern surgical and anesthesia techniques, many patients undergoing small or even medium surgical procedures will recover within minutes and can then be discharged after a few hours of monitoring. Aside from an optimized surgical technique, a precise and differentiated anesthesia concept is needed to guarantee rapid recovery and home readiness. Nowadays, remifentanil-propofol represents the standard regime in ambulatory anesthesia. The use of alfentanil, desfluran or sevofluran is also possible whereas other intravenous or inhaled anesthetics or other opioids are rarely used. If endotracheal intubation is necessary, a reduced intubating dose of neuromuscular blockers (NMB), such as mivacurium, atracurium and rocuronium, i.e. 1-1.5-times the 95 % effective dose (ED95) is a good possibility to accelerate neuromuscular recovery while still having acceptable intubation conditions. Due to its limitations and contraindications, succinylcholine is not the first choice but may be used in non-fasting patients in need of urgent (ambulatory) surgery, e.g. in bleeding women undergoing dilation and curettage. Even with these reduced dosages monitoring of neuromuscular recovery is crucial and should be applied to all patients when NMBs are used. Furthermore, patients should receive a risk-adapted postoperative nausea and vomiting (PONV) prophylaxis, e.g. with 4 mg dexamethasone and 4 mg ondansetron. Postdischarge nausea and vomiting (PDNV) should be anticipated by a new risk score and prophylaxis or treatment should be initiated. For postoperative pain relief, local or regional anesthesia techniques, such as infiltration, field or nerve blocks should be applied where possible. In addition, non-opioid analgesics are the basic treatment while longer-lasting opioids are only necessary for some patients.

Volatile anaesthetic depression of the carotid body chemoreflex-mediated ventilatory response to hypoxia: directions for future research

In assessing whether volatile anaesthetics directly depress the carotid body response to hypoxia it is necessary to combine in meta-analysis studies of when it is "functionally isolated" (e.g., recordings are made from its afferent nerve). Key articles were retrieved (full papers in English) and subjected to quantitative analysis to yield an aggregate estimate of effect. Results from articles that did not use such methodology were assessed separately from this quantitative approach, to see what could be learned also from a nonquantitative overview. Just 7 articles met the inclusion criteria for hypoxia and just 6 articles for hypercapnia. Within these articles, the anaesthetic (mean dose 0.75, standard deviation (SD) 0.40 minimum alveolar concentration, MAC) statistically significantly depressed carotid body hypoxic response by 24% (P = 0.041), but a similar dose (mean 0.81 (0.42) MAC) did not affect the hypercapnic response. The articles not included in the quantitative analysis (31 articles), assessed qualitatively, also indicated that anaesthetics depress carotid body function. This conclusion helps direct future research on the anaesthetic effects on putative cellular/molecular processes that underlie the transduction of hypoxia in the carotid body.

Inhaled anesthetics in horses

Inhaled agents represent an important and useful class of drugs for equine anesthesia. This article reviews the ether-type anesthetics in contemporary use, their uptake and elimination, their mechanisms of action, and their desirable and undesirable effects in horses.

Prolonged attenuation of acetylcholine-induced phosphorylation of extracellular signal-regulated kinase 1/2 following sevoflurane exposure

BACKGROUND

Volatile anaesthetics are known to affect cholinergic receptors. Perturbation of cholinergic signalling can cause cognitive deficits. In this study, we wanted to evaluate acetylcholine-induced intracellular signalling following sevoflurane exposure.

METHODS

Pheochromocytoma12 PC12 cells were exposed to 4.6% sevoflurane for 2 h. Subsequently, Western blotting was used to measure acetylcholine-induced phosphorylation of extracellular signal-regulated kinase 1/2 (ERK) 1/2 and basal Protein kinase B (AKT) phosphorylation.

RESULTS

After exposure, acetylcholine-induced ERK 1/2 phosphorylation was reduced to 58 ± 8% [95% confidence interval (CI): 38-77%, P = 0.003] compared with non-exposed controls. At 30 min after the end of sevoflurane administration [at 0.7% sevoflurane (0.102 mM)], ERK 1/2 phosphorylation remained reduced to 57 ± 7% (95% CI: 39-74%, P = 0.001) and was at 120 min [0.02% (0.003 mM] still reduced to 63 ± 10% (95% CI: 37-88%, P = 0.01), compared with control. At 360 min after exposure, acetylcholine-induced ERK 1/2 phosphorylation had recovered to 98 ± 16% (95% CI: 45-152%, P = 0.98) compared with control. In contrast, immediately after sevoflurane exposure, basal AKT phosphorylation was increased by 228 ± 37% (95% CI: 133-324%, P = 0.02) but had returned to control levels at 30 min after exposure, 172 ± 67% (95% CI: 0-356%, P = 0.34).

CONCLUSION

Sevoflurane exposure has differential effects on different intracellular signalling pathways. On one hand, we observed a prolonged attenuation of acetylcholine-induced ERK 1/2 phosphorylation that persisted even when sevoflurane concentrations close to detection level. On the other hand, basal AKT phosphorylation was increased twofold during sevoflurane exposure, with a rapid return to baseline levels after exposure. We speculate that the effects on acetylcholine-induced intracellular signalling observed in our in vitro model could be of relevance also for cholinergic signalling in vivo following sevoflurane exposure.

Desflurane: a clinical update of a third-generation inhaled anaesthetic

Available volatile anaesthetics are safe and efficacious; however, their varying pharmacology provides small but potentially clinically important differences. Desflurane is one of the third-generation inhaled anaesthetics. It is the halogenated inhaled anaesthetic with the lowest blood and tissue solubilities, which promotes its rapid equilibration and its rapid elimination following cessation of administration at the end of anaesthesia. The low fat solubility of desflurane provides pharmacological benefits, especially in overweight patients and in longer procedures by reducing slow compartment accumulation. A decade of clinical use has provided evidence for desflurane's safe and efficacious use as a general anaesthetic. Its benefits include rapid and predictable emergence, and early recovery. In addition, the use of desflurane promotes early and predictable extubation, and the ability to rapidly transfer patients from the operating theatre to the recovery area, which has a positive impact on patient turnover. Desflurane also increases the likelihood of patients, including obese patients, recovering their protective airway reflexes and awakening to a degree sufficient to minimise the stay in the high dependency recovery area. The potential impact of the rapid early recovery from desflurane anaesthesia on intermediate and late recovery and resumption of activities of daily living requires further study.

Reduced respiratory neural activity elicits phrenic motor facilitation

We hypothesized that reduced respiratory neural activity elicits compensatory mechanisms of plasticity that enhance respiratory motor output. In urethane-anesthetized and ventilated rats, we reversibly reduced respiratory neural activity for 25-30 min using: hypocapnia (end tidal CO(2)=30 mmHg), isoflurane (~1%) or high frequency ventilation (HFV; ~100 breaths/min). In all cases, increased phrenic burst amplitude was observed following restoration of respiratory neural activity (hypocapnia: 92±22%; isoflurane: 65±22%; HFV: 54±13% baseline), which was significantly greater than time controls receiving the same surgery, but no interruptions in respiratory neural activity (3±5% baseline, p<0.05). Hypocapnia also elicited transient increases in respiratory burst frequency (9±2 versus 1±1bursts/min, p<0.05). Our results suggest that reduced respiratory neural activity elicits a unique form of plasticity in respiratory motor control which we refer to as inactivity-induced phrenic motor facilitation (iPMF). iPMF may prevent catastrophic decreases in respiratory motor output during ventilatory control disorders associated with abnormal respiratory activity.