Postoperative recovery of patients with differential requirements for sevoflurane after abdominal surgery: A prospective observational clinical study

An association between animals and volatile anaesthetic requirements has been shown; however, evidence related to the postoperative outcome of human patients is lacking. Our aim was to investigate whether there is a difference in the requirement for sevoflurane among people undergoing gastrointestinal surgery.We observed 390 adult patients who underwent gastrointestinal surgery with an American Society of Anesthesiologists physical status of I or II with an expected surgery duration of > 2 hours. We used the bispectral index (BIS) to guide the regulation of end-tidal sevoflurane concentration (ETsevo). The mean ETsevo from 20 minutes after endotracheal intubation to 2 hours after the start of surgery was calculated for all patients. Differential sevoflurane requirements were identified according to ETsevo. The BIS, ETsevo, heart rate, mean arterial pressure, dose of sufentanil and cisatracurium, tracheal extubation time, incidence of intraoperative awareness, and incidence of postoperative nausea and vomiting were compared between patients with a low requirement for sevoflurane (group L) and patients with a high requirement for sevoflurane (group H).The mean ETsevo of the 390 patients was 1.55% ± 0.26%. Based on our definition, patients with an ETsevo of < 1.29% were allocated to the low requirement group (group L; n = 69), while patients with an ETsevo of > 1.81% were allocated to the high requirement group (group H; n = 78). The ETsevo of group L was significantly lower than the ETsevo of group H (1.29% ± 0.014% vs 1.82% ± 0.017%, P < .001). There was no significant difference in the ETsevo, BIS, heart rate, mean arterial pressure, dose of sufentanil and cisatracurium, tracheal extubation time, incidence of intraoperative awareness, and incidence of postoperative nausea and vomiting. The tracheal extubation time in the L group was significantly shorter than that in the H group. No intraoperative awareness occurred.There was a significant difference in the requirement for sevoflurane in adult patients. The tracheal extubation time in group L was significantly shorter than that in group H.

Prediction of expiratory desflurane and sevoflurane concentrations in lung-healthy patients utilizing cardiac output and alveolar ventilation matched pharmacokinetic models: A comparative observational study

The Gas Man simulation software provides an opportunity to teach, understand and examine the pharmacokinetics of volatile anesthetics. The primary aim of this study was to investigate the accuracy of a cardiac output and alveolar ventilation matched Gas Man model and to compare its predictive performance with the standard pharmacokinetic model using patient data.Therefore, patient data from volatile anesthesia were successively compared to simulated administration of desflurane and sevoflurane for the standard and a parameter-matched simulation model with modified alveolar ventilation and cardiac output. We calculated the root-mean-square deviation (RMSD) between measured and calculated induction, maintenance and elimination and the expiratory decrement times during emergence and recovery for the standard and the parameter-matched model.During induction, RMSDs for the standard Gas Man simulation model were higher than for the parameter-matched Gas Man simulation model [induction (desflurane), standard: 1.8 (0.4) % Atm, parameter-matched: 0.9 (0.5) % Atm., P = .001; induction (sevoflurane), standard: 1.2 (0.9) % Atm, parameter-matched: 0.4 (0.4) % Atm, P = .029]. During elimination, RMSDs for the standard Gas Man simulation model were higher than for the parameter-matched Gas Man simulation model [elimination (desflurane), standard: 0.7 (0.6) % Atm, parameter-matched: 0.2 (0.2) % Atm, P = .001; elimination (sevoflurane), standard: 0.7 (0.5) % Atm, parameter-matched: 0.2 (0.2) % Atm, P = .008]. The RMSDs during the maintenance of anesthesia and the expiratory decrement times during emergence and recovery showed no significant differences between the patient and simulated data for both simulation models.Gas Man simulation software predicts expiratory concentrations of desflurane and sevoflurane in humans with good accuracy, especially when compared to models for intravenous anesthetics. Enhancing the standard model by ventilation and hemodynamic input variables increases the predictive performance of the simulation model. In most patients and clinical scenarios, the predictive performance of the standard Gas Man simulation model will be high enough to estimate pharmacokinetics of desflurane and sevoflurane with appropriate accuracy.

Effects of the reservoir bag disconnection on inspired gases during general anesthesia: a simulator-based study

BACKGROUND

Fresh gas decoupling is a feature of the modern anesthesia workstation, where the fresh gas flow (FGF) is diverted into the reservoir bag and is not added to the delivered tidal volume, which thus remains constant. The present study aimed to investigate the entraining of the atmospheric air into the anesthesia breathing circuit in case the reservoir bag was disconnected.

METHODS

We conducted a simulator-based study, where the METI HPS simulator was connected to the anesthesia workstation. The effect of the disconnected reservoir bag was evaluated using oxygen (O2) and air or oxygen and nitrous oxide (N2O) as a carrier gas at different FGF rates. We disconnected the reservoir bag for 10 min during the maintenance phase. We recorded values for inspiratory O2, N2O, and sevoflurane. The time constant of the exponential process was estimated during reservoir bag disconnection.

RESULTS

The difference of O2, N2O and sevoflurane concentrations, before, during, and after reservoir bag disconnection was statistically significant at 0.5, 1, and 2 L/min of FGF (p < 0.001). The largest decrease of the inspired O2 concentrations (FIO2) was detected in the case of oxygen and air as the carrier gas and an FGF of 1 L/min, when oxygen decreased from median [25th-75th percentile] 55.00% [54.00-56.00] to median 39.50% [38.00-42.50] (p < 0.001). The time constant for FIO2 during reservoir bag disconnection in oxygen and air as the carrier gas, were median 2.5, 2.5, and 1.5 min in FGF of 0.5, 1.0, and 2 L/min respectively.

CONCLUSIONS

During the disconnection of the anesthesia reservoir bag, the process of pharmacokinetics takes place faster compared to the wash-in and wash-out pharmacokinetic properties in the circle breathing system. The time constant was affected by the FGF rate, as well as the gradient of anesthetic gases between the anesthesia circle system and atmospheric air.

End-tidal to Arterial Gradients and Alveolar Deadspace for Anesthetic Agents

BACKGROUND

According to the "three-compartment" model of ventilation-perfusion ((Equation is included in full-text article.)) inequality, increased (Equation is included in full-text article.)scatter in the lung under general anesthesia is reflected in increased alveolar deadspace fraction (VDA/VA) customarily measured using end-tidal to arterial (A-a) partial pressure gradients for carbon dioxide. A-a gradients for anesthetic agents such as isoflurane are also significant but have been shown to be inconsistent with those for carbon dioxide under the three-compartment theory. The authors hypothesized that three-compartment VDA/VA calculated using partial pressures of four inhalational agents (VDA/VAG) is different from that calculated using carbon dioxide (VDA/VACO2) measurements, but similar to predictions from multicompartment models of physiologically realistic "log-normal" (Equation is included in full-text article.)distributions.

METHODS

In an observational study, inspired, end-tidal, arterial, and mixed venous partial pressures of halothane, isoflurane, sevoflurane, or desflurane were measured simultaneously with carbon dioxide in 52 cardiac surgery patients at two centers. VDA/VA was calculated from three-compartment model theory and compared for all gases. Ideal alveolar (PAG) and end-capillary partial pressure (Pc'G) of each agent, theoretically identical, were also calculated from end-tidal and arterial partial pressures adjusted for deadspace and venous admixture.

RESULTS

Calculated VDA/VAG was larger (mean ± SD) for halothane (0.47 ± 0.08), isoflurane (0.55 ± 0.09), sevoflurane (0.61 ± 0.10), and desflurane (0.65 ± 0.07) than VDA/VACO2 (0.23 ± 0.07 overall), increasing with lower blood solubility (slope [Cis], -0.096 [-0.133 to -0.059], P < 0.001). There was a significant difference between calculated ideal PAG and Pc'G median [interquartile range], PAG 5.1 [3.7, 8.9] versus Pc'G 4.0[2.5, 6.2], P = 0.011, for all agents combined. The slope of the relationship to solubility was predicted by the log-normal lung model, but with a lower magnitude relative to calculated VDA/VAG.

CONCLUSIONS

Alveolar deadspace for anesthetic agents is much larger than for carbon dioxide and related to blood solubility. Unlike the three-compartment model, multicompartment (Equation is included in full-text article.)scatter models explain this from physiologically realistic gas uptake distributions, but suggest a residual factor other than solubility, potentially diffusion limitation, contributes to deadspace.

Minimal alveolar concentration for deep sedation (MAC-DS) in intensive care unit patients sedated with sevoflurane: A physiological study

BACKGROUND

Volatile anaesthetic agents, especially sevoflurane, could be an alternative for sedating ICU patients. In the operating theatre, volatile anaesthetic agents are monitored using minimal alveolar concentration (MAC). In ICU, MAC may be used to assess sedation level and may replace clinical scale especially when they are unusable. Therefore, we sought to investigate the minimal sevoflurane end-tidal concentration to achieved deep sedation in critical ill patients: MAC-deep sedation (MAC-DS).

METHODS

In a prospective interventional study, we included patients with a Richmond Assessment Sedation Score (RASS) of 0 without any sedation. We stepwise increased sevoflurane concentration level before assessing for deep sedation (RASS≤-3). MAC-DS was defined as the minimal sevoflurane MAC fraction or sevoflurane expiratory fraction (FeSevo) to get 90% and 95% of patients in deep sedation (MAC-DS 90 and MAC-DS 95, respectively).

RESULTS

Between June and November 2014, 30 patients were included (median age=60 years [interquartile range: 47-69]). Increasing sevoflurane MAC was correlated with a decrease in RASS values (r=-0.83, P<0.001). MAC-DS 90 and MAC-DS 95 were achieved at 0.42 MAC (CI 95 [0.38-0.46]) and 0.46 MAC (CI 95 [0.42-0.51]), respectively. FeSevo to achieve MAC-DS 90 and MAC-DS 95 was 0.72 (CI 95 [0.65-0.79]) and 0.80 (CI 95 [0.72-0.89]), respectively.

CONCLUSION

In this physiological study involving 30 ICU patients, MAC-DS, end-tidal sevoflurane concentration to get 95% of patients in deep sedation determined over more than 500 observations, is achieved at 0.8% of expired fraction of sevoflurane or at 0.5 age-adjusted MAC.

Development of a simple method for differential delivery of volatile anesthetics to the spinal cord of the rabbit

Emulsified volatile anesthetic can be directly injected into the circulation and eliminated from blood through lungs. Taking advantage of the unique pharmacokinetics of the emulsified volatile anesthetics, we aimed to develop a less traumatic method to differentially deliver them to the spinal cord of rabbit. Sixteen New Zealand White rabbits were randomly assigned to the isoflurane or sevoflurane group. A catheter was placed into the descending aorta, and emulsified isoflurane (8mg/kg/h) or sevoflurane (12mg/kg/h) was given respectively. The concentration and partial pressure of the anesthetics in the jugular and femoral vein were measured. Our results showed that the partial pressure for isoflurane was 3.91±1.11 mmHg and 12.61±1.60 mmHg (1.0MAC), and for sevoflurane was 3.89±1.00 mmHg and 19.92±1.84mmHg (1.0MAC), in the jugular vein and femoral vein, respectively. There was significant difference between jugular and femoral vein partial pressure for both isoflurane and sevoflurane groups (both P < 0.001). In conclusion, a simple and minimally invasive method has been successfully developed to selectively deliver isoflurane and sevoflurane to the spinal cord in the rabbit. Before the anesthetics taking action on the brain, 69% of isoflurane and 81% of sevoflurane were removed through lungs. This method can be used to investigate sites and mechanisms of volatile anesthetic action.

Effect of oral administration of gabapentin on the minimum alveolar concentration of isoflurane in dogs

OBJECTIVE

To determine the effect of oral administration of gabapentin (20 mg/kg) on the minimum alveolar concentration (MAC) of isoflurane in dogs.

ANIMALS

6 healthy adult dogs (3 males and 3 females with a mean ± SD body weight of 24.8 ± 1.3 kg).

PROCEDURES

Each dog was anesthetized twice. Dogs were initially assigned to 1 of 2 treatments (gabapentin [20 mg/kg, PO] followed 2 hours later by anesthesia maintained with isoflurane or anesthesia maintained with isoflurane alone). A minimum of 7 days later, dogs received the other treatment. The MAC of isoflurane was determined by use of an iterative bracketing technique with stimulating electrodes placed in the maxillary buccal mucosa. Hemodynamic variables and vital parameters were recorded at the lowest end-tidal isoflurane concentration at which dogs did not respond to the stimulus. Effect of treatment on outcome variables was analyzed by use of a paired t test.

RESULTS

Mean ± SD MAC of isoflurane was significantly lower when dogs received gabapentin and isoflurane (0.71 ± 0.12%) than when dogs received isoflurane alone (0.91 ± 0.26%). Mean reduction in MAC of isoflurane was 20 ± 14%. Hemodynamic variables did not differ significantly between treatments. Mean time to extubation was significantly less when dogs received gabapentin and isoflurane (6 ± 4 minutes) than when dogs received isoflurane alone (23 ± 15 minutes).

CONCLUSIONS AND CLINICAL RELEVANCE

Oral administration of gabapentin 2 hours before anesthesia maintained with isoflurane had a MAC-sparing effect with no effect on hemodynamic variables or vital parameters of dogs.

Most Hemodynamically Stable Method for Change From High to Low Anesthesia Flow: A Randomized Controlled Trial Comparing State Entropy, High Fresh Gas Flow for 10 Minutes, and 0.8 Ratio of End-Expired Agent Concentration to Inspired Agent Concentration

This study was undertaken to determine the most hemodynamically stable method to low-flow anesthesia (LFA) between 10-minute administration of high fresh gas flow, 0.8 equilibration ratio (Fe/Fi), and state entropy (SE) between 40 and 60, a marker for adequate depth of anesthesia. Change from high fresh gas flow to LFA was done in 3 groups of 30 patients each: group T (time): 10 minutes; group R (ratio): Fe/Fi = 0.8, and group SE: SE = 40 to 50. A decrease in mean blood pressure or heart rate was treated with ephedrine or atropine, with study termination at more than 2 boluses of either. In group SE, no patient required ephedrine or atropine. The requirement for ephedrine was statistically higher in groups R and T than group SE. Atropine requirement was statistically higher in group R vs groups T and SE. In group R, the mean (SD) time to LFA was 43.9 (20.37) minutes, and in group SE was 151.9 (74.4) seconds. Hypotension or bradycardia did not occur when LFA was started at SE of 40 to 50 after anesthesia induction compared with LFA at 10 minutes, which caused hypotension, and Fe/Fi of 0.8, which caused hypotension and bradycardia.

Effects of dexmedetomidine, with or without vatinoxan (MK-467), on minimum alveolar concentration of isoflurane in cats

OBJECTIVE

To characterize the effects of dexmedetomidine, with or without vatinoxan, on the minimum alveolar concentration of isoflurane (MACISO) in cats.

STUDY DESIGN

Randomized crossover experimental study.

ANIMALS

A group of six adult healthy male neutered cats.

METHODS

Cats were anesthetized with isoflurane in oxygen and instrumented. Dexmedetomidine was administered using a target-controlled infusion system to achieve 10 target plasma concentrations ranging from 0 to 40 ng mL-1. Additionally, vatinoxan or an equivalent volume of saline was administered using a target-controlled infusion system to achieve a target plasma concentration of 4 μg mL-1. Pulse rate (PR), respiratory rate, systolic arterial pressure (SAP), hemoglobin oxygen saturation, body temperature, end-tidal partial pressure of carbon dioxide and drug concentrations were measured. MACISO was determined at each target plasma dexmedetomidine concentration using the bracketing method and the tail clamp technique. Pharmacodynamic models were fitted to the plasma dexmedetomidine concentration-MACISO. Pharmacodynamic parameters were tested for equivalence, and if rejected, for difference.

RESULTS

Dexmedetomidine alone decreased MACISO in a plasma concentration-dependent manner. Maximum reduction was 77 ± 4%; the dexmedetomidine concentration producing 50% of the maximum decrease (IC50) was 0.77 ng mL-1. Vatinoxan increased MACISO in the absence of dexmedetomidine, decreased the potency of dexmedetomidine for its MACISO-reducing effect (IC50 = 12 ng mL-1) and lessened the maximum MACISO reduction (60 ± 14%). PR decreased less and SAP increased less when dexmedetomidine was administered with vatinoxan compared with saline.

CONCLUSION AND CLINICAL RELEVANCE

Vatinoxan altered the effect of dexmedetomidine on MACISO. A high plasma dexmedetomidine concentration in the presence of vatinoxan resulted in a large decrease in MACISO, with attenuation of dexmedetomidine-induced cardiovascular effects. The vatinoxan-dexmedetomidine combination may provide clinical benefits in isoflurane-anesthetized cats.

Effect of α2-adrenoceptor antagonism on the minimum alveolar concentration of isoflurane in cats

OBJECTIVE

To characterize the effect of α₂-adrenoceptor antagonism on the minimum alveolar concentration of isoflurane (MAC_ISO) in cats.

STUDY DESIGN

Prospective experimental study.

ANIMALS

A group of five healthy adult male neutered cats.

METHODS

Cats were anesthetized with isoflurane in oxygen and instrumented. MAC_ISO was determined in duplicate in five cats, before and during administration of atipamezole (250 μg kg^-1 followed by 250 μg kg^-1 hour^-1) using the bracketing technique and tail clamping. Estimates of MAC_ISO obtained before and during administration of atipamezole were compared using a two-tailed paired t test.

RESULTS

MAC_ISO during atipamezole administration (mean ± standard deviation 2.73% ± 0.07%) was significantly larger than before atipamezole administration (1.95% ± 0.13%; p < 0.0001).

CONCLUSION AND CLINICAL RELEVANCE

The role of α₂-adrenoceptors in inhaled anesthetic-induced immobility may be larger than previously thought. Antagonism of an α₂-adrenoceptor agonist during inhalation anesthesia may result in an increase in MAC disproportionate to the MAC reduction induced by the agonist.

Genetic variability affects absolute and relative potencies and kinetics of the anesthetics isoflurane and sevoflurane in Drosophila melanogaster

Genetic variability affects the response to numerous xenobiotics but its role in the clinically-observed irregular responses to general anesthetics remains uncertain. To investigate the pharmacogenetics of volatile general anesthetics (VGAs), we developed a Serial Anesthesia Array apparatus to expose multiple Drosophila melanogaster samples to VGAs and behavioral assays to determine pharmacokinetic and pharmacodynamic properties of VGAs. We studied the VGAs isoflurane and sevoflurane in four wild type strains from the Drosophila Genetic Reference Panel, two commonly used laboratory strains (Canton S and w 1118 ), and a mutant in Complex I of the mitochondrial electron transport chain (ND23 60114 ). In all seven strains, isoflurane was more potent than sevoflurane, as predicted by their relative lipid solubilities, and emergence from isoflurane was slower than from sevoflurane, reproducing cardinal pharmacokinetic and pharmacodynamic properties in mammals. In addition, ND23 60114 flies were more sensitive to both agents, as observed in worms, mice, and humans carrying Complex I mutations. Moreover, we found substantial variability among the fly strains both in absolute and in relative pharmacokinetic and pharmacodynamic profiles of isoflurane and sevoflurane. These data indicate that naturally occurring genetic variations measurably influence cardinal pharmacologic properties of VGAs and that flies can be used to identify relevant genetic variations.

Effect of fentanyl and lidocaine on the end-tidal sevoflurane concentration preventing motor movement in dogs

OBJECTIVE To determine effects of fentanyl, lidocaine, and a fentanyl-lidocaine combination on the minimum alveolar concentration of sevoflurane preventing motor movement (MAC_NM) in dogs. ANIMALS 6 adult Beagles. PROCEDURES Dogs were anesthetized with sevoflurane in oxygen 3 times (1-week intervals). Baseline MAC_NM (MAC_NM-B) was determined starting 45 minutes after induction of anesthesia. Dogs then received 1 of 3 treatments IV: fentanyl (loading dose, 15 μg/kg; constant rate infusion [CRI], 6 μg/kg/h), lidocaine (loading dose, 2 mg/kg; CRI, 6 mg/kg/h), and the fentanyl-lidocaine combination at the same doses. Determination of treatment MAC_NM (MAC_NM-T) was initiated 90 minutes after start of the CRI. Venous blood samples were collected at the time of each treatment MAC_NM measurement for determination of plasma concentrations of fentanyl and lidocaine. RESULTS Mean ± SEM overall MAC_NM-B for the 3 treatments was 2.70 ± 0.27 vol%. The MAC_NM decreased from MAC_NM-B to MAC_NM-T by 39%, 21%, and 55% for fentanyl, lidocaine, and the fentanyl-lidocaine combination, respectively. This decrease differed significantly among treatments. Plasma fentanyl concentration was 3.25 and 2.94 ng/mL for fentanyl and the fentanyl-lidocaine combination, respectively. Plasma lidocaine concentration was 2,570 and 2,417 ng/mL for lidocaine and the fentanyl-lidocaine combination, respectively. Plasma fentanyl and lidocaine concentrations did not differ significantly between fentanyl and the fentanyl-lidocaine combination or between lidocaine and the fentanyl-lidocaine combination. CONCLUSIONS AND CLINICAL RELEVANCE CRIs of fentanyl, lidocaine, and the fentanyl-lidocaine combination at the doses used were associated with clinically important and significant decreases in the MAC_NM of sevoflurane in dogs.

Venous blood gas analytes during isoflurane anesthesia in black-tailed prairie dogs (Cynomys ludovicianus)

OBJECTIVE

To describe changes in venous blood gas analytes during isoflurane anesthesia in black-tailed prairie dogs (Cynomys ludovicianus).

DESIGN

Prospective study.

ANIMALS

16 black-tailed prairie dogs.

PROCEDURES

Black-tailed prairie dogs were placed in an anesthesia chamber for induction of general anesthesia, which was maintained with isoflurane in oxygen delivered via mask. Immediately following anesthetic induction, a venous blood sample was obtained from the medial saphenous vein; a second venous blood sample was obtained just prior to anesthetic gas shutoff. An evaluation of venous blood gas analytes was performed on each sample. General linear mixed models with repeated measures were used for data analyses.

RESULTS

Median anesthetic time was 90 minutes (range, 60 to 111 minutes). A significant increase from immediately after induction to completion of anesthesia was observed in Pco2 and mean blood chloride ion, BUN, and creatinine concentrations. A decrease in Po2, mean blood pH, and anion gap was observed from induction of anesthesia to completion. No significant differences during anesthesia were observed in mean base excess or blood bicarbonate, sodium, potassium, calcium, magnesium, blood glucose, lactate, and total CO2 concentrations. No complications occurred during or after anesthesia for any animal.

CONCLUSIONS AND CLINICAL RELEVANCE

Examination of prairie dogs often requires general anesthesia, with isoflurane currently the inhalation agent of choice. Results suggested respiratory acidosis and relative azotemia may occur during isoflurane anesthesia of prairie dogs. Given the increased risk associated with anesthesia in small mammals and the propensity for respiratory disease in prairie dogs, insight into physiologic changes associated with isoflurane anesthesia in healthy prairie dogs can aid in perioperative evaluation and anesthetic monitoring in this rodent species.

Effects of oxymorphone hydrochloride or hydromorphone hydrochloride on minimal alveolar concentration of desflurane in sheep

OBJECTIVE

To establish the minimum alveolar concentration (MAC) of desflurane and evaluate the effects of 2 opioids on MAC in sheep.

ANIMALS

8 adult nulliparous mixed-breed sheep.

PROCEDURES

A randomized crossover design was used. Each sheep was evaluated individually on 2 occasions (to allow assessment of the effects of each of 2 opioids), separated by a minimum of 10 days. On each occasion, sheep were anesthetized with desflurane in 100% oxygen, MAC of desflurane was determined, oxymorphone (0.05 mg/kg) or hydromorphone (0.10 mg/kg) was administered IV, and MAC was redetermined. Physiologic variables and arterial blood gas and electrolyte concentrations were measured at baseline (before MAC determination, with end-tidal desflurane concentration maintained at 10%) and each time MAC was determined. Timing of various stages of anesthesia was recorded for both occasions.

RESULTS

Mean ± SEM MAC of desflurane was 8.6 ± 0.2%. Oxymorphone or hydromorphone administration resulted in significantly lower MAC (7.6 ± 0.4% and 7.9 ± 0.2%, respectively). Cardiac output at MAC determination for desflurane alone and for desflurane with opioid administration was higher than that at baseline. No difference was identified among hematologic values at any point. Effects of oxymorphone and hydromorphone on durations of various stages of anesthesia did not differ significantly.

CONCLUSIONS AND CLINICAL RELEVANCE

MAC of desflurane in nulliparous adult sheep was established. Intravenous administration of oxymorphone or hydromorphone led to a decrease in MAC; however, the clinical importance of that decrease was minor relative to the effect in other species.

Propofol Pharmacokinetics and Estimation of Fetal Propofol Exposure during Mid-Gestational Fetal Surgery: A Maternal-Fetal Sheep Model

BACKGROUND

Measuring fetal drug concentrations is extremely difficult in humans. We conducted a study in pregnant sheep to simultaneously describe maternal and fetal concentrations of propofol, a common intravenous anesthetic agent used in humans. Compared to inhalational anesthesia, propofol supplemented anesthesia lowered the dose of desflurane required to provide adequate uterine relaxation during open fetal surgery. This resulted in better intraoperative fetal cardiac outcome. This study describes maternal and fetal propofol pharmacokinetics (PK) using a chronically instrumented maternal-fetal sheep model.

METHODS

Fetal and maternal blood samples were simultaneously collected from eight mid-gestational pregnant ewes during general anesthesia with propofol, remifentanil and desflurane. Nonlinear mixed-effects modeling was performed by using NONMEM software. Total body weight, gestational age and hemodynamic parameters were tested in the covariate analysis. The final model was validated by bootstrapping and visual predictive check.

RESULTS

A total of 160 propofol samples were collected. A 2-compartment maternal PK model with a third fetal compartment appropriately described the data. Mean population parameter estimates for maternal propofol clearance and central volume of distribution were 4.17 L/min and 37.7 L, respectively, in a typical ewe with a median heart rate of 135 beats/min. Increase in maternal heart rate significantly correlated with increase in propofol clearance. The estimated population maternal-fetal inter-compartment clearance was 0.0138 L/min and the volume of distribution of propofol in the fetus was 0.144 L. Fetal propofol clearance was found to be almost negligible compared to maternal clearance and could not be robustly estimated.

CONCLUSIONS

For the first time, a maternal-fetal PK model of propofol in pregnant ewes was successfully developed. This study narrows the gap in our knowledge in maternal-fetal PK model in human. Our study confirms that maternal heart rate has an important influence on the pharmacokinetics of propofol during pregnancy. Much lower propofol concentration in the fetus compared to maternal concentrations explain limited placental transfer in in-vivo paired model, and less direct fetal cardiac depression we observed earlier with propofol supplemented inhalational anesthesia compared to higher dose inhalational anesthesia in humans and sheep.

In Vivo Measurement in Pigs of Wash-In Kinetics of Xenon at its Site of Action

BACKGROUND

Xenon (Xe) in many respects is an ideal anaesthetic agent. Its blood/gas partition coefficient is lower than that of any other anaesthetic, enabling rapid induction of and emergence from anaesthesia. While the whole body kinetics during wash-in of inhalational anaesthesia is well known, data describing the pharmacokinetics of xenon in the cerebral compartment at the site of action are still largely missing.

METHODS

In order to illuminate xenon's cerebral pharmacokinetics, we anaesthetised five pigs and measured arterial, mixed- and sagittal sinus-venous blood, as well as end-expiratory gas concentrations of xenon by gas chromatography-mass spectrometry (GCMS) up to 30 minutes after starting the anaesthetic gas mixture.

RESULTS

Despite xenon's fast onset of effect the half-time for equilibration between xenon concentration in arterial blood and at the site of action is measured to be 1.49 ± 0.04 minutes versus 3.91 ± 0.1 minutes. Successful loading of xenon in the brain during inhalational anesthesia was accomplished after approximately 15 minutes although the end-expiratory xenon concentration reached a plateau after 7 minutes. Thus cerebral xenon uptake rate is only moderate, xenon fast onset of action being largely due to its extremely fast alveolar uptake.

CONCLUSIONS

To ensure safety and precise control during anaesthesia we need a profound knowledge about to what extent the measured end-tidal concentrations reflect the drug concentrations in the target tissue. The results of this study expand our knowledge about the temporal characteristics of xenon´s pharmacokinetics at its site of action and provide the basis for appropriate clinical protocols and experimental designs of future studies.

Navigator® and SmartPilot® View are helpful in guiding anesthesia and reducing anesthetic drug dosing

BACKGROUND

The recently introduced Navigator® (GE Healthcare, Helsinki, Finland) and SmartPilot® View (Dräger Medical, Lübeck, Germany) show the concentrations and predicted effects of combined anesthetic drugs, and should facilitate more precisely their titration. Our aim was to evaluate if Navigator® or SmartPilot® View guided anesthesia was associated with a good quality of analgesia, depth of hypnosis and may reduce anesthetic requirements.

METHODS

We performed a prospective non-randomized study. Sixty ASA I-II patients undergoing balanced general anesthesia for abdominal and plastic surgery were enrolled. Patients were divided in 4 groups. Group 1 (N. 15) and group 3 (N. 15) were cases in whom anesthesia was performed with standard monitoring plus the aid of Navigator® (Nav) or SmartPilot® View (SPV) display. Group 2 (N. 15) and group 4 (N. 15) were controls in whom anesthesia was performed with standard monitoring (heart rate, NIBP, SpO2, end-tidal CO2, end-expired sevoflurane concentration, train of four, Bispectral Index [Aspect Medical Systems, Natick, MA, USA] or Entropy [GE Healthcare]). Patients' vital parameters and end-expired sevoflurane concentration were recorded during anesthesia.

RESULTS

All patients recovered uneventfully and showed hemodynamic stability. End-tidal sevoflurane concentrations values [median (min-max)], during maintenance of anesthesia, were significantly (P<0.05) lower in SPV [1.1% (0.8-1.5)] and Nav [1%(0.8-1.8)] groups compared to SPV-control group [1.5%(1-2.5)] and Nav-control group [1.5%(0.8-2)]. BIS and entropy values were respectively higher in the SPV group [53 (46-57)] compared to the control group [43 (37-51)] (P<0.05) and Nav group [53 (43-60)] compared to the control group [41 (35-51)] (P<0.05). No significant differences in Remifentanil dosing were observed in the four groups.

CONCLUSION

Navigator® and SmartPilot® View may be of clinical use in monitoring adequacy of anesthesia. Both displays can optimize the administration and monitoring of anesthetic drugs during general anesthesia and may reduce the consumption of volatile anesthetic agents.

[The Hemodynamics and Bispectral Index Score during Lower Abdominal Surgery under Balanced Anesthesia with the Two Different Combination Doses of Desflurane and Remifentanil]

BACKGROUND

The purpose of this study was to examine the hemodynamics and bispectral index score during lower abdominal surgery under balanced anesthesia with the two different combination doses of desflurane and remifentanil.

METHODS

Twenty patients undergoing total hysterectomy were allocated into two groups; 1) 10 patients received 4.5% end-tidal concentration of desflurane combined with remifentanil 0.125 μg x kg(-1) x min(-1) (H group) and 2) 10 patients received 3.0% end-tidal concentration of desflurane combined with remifentanil 0.2 μg x kg(-1) X min(-1) (L group). Mean arterial pressure (MAP), heart rate (HR) and BIS were recorded 5 times (on admission to operating room, immediately before surgery, 5 minutes after the skin incision, at the moment of uterine extraction and during retroperitoneal closure).

RESULTS

MAP and HR during surgery did not increase compared with those on admission to operating room, and BIS was unchanged throughout the study in both two groups.

CONCLUSIONS

The patients could be anesthetized adequately during lower abdominal surgery under balanced anesthesia with the two different combination doses of desflurane and remifentanil.

Intraoperative awareness risk, anesthetic sensitivity, and anesthetic management for patients with natural red hair: a matched cohort study

PURPOSE

The red-hair phenotype, which is often produced by mutations in the melanocortin-1 receptor gene, has been associated with an increase in sedative, anesthetic, and analgesic requirements in both animal and human studies. Nevertheless, the clinical implications of this phenomenon in red-haired patients undergoing surgery are currently unknown.

METHODS

In a secondary analysis of a prospective trial of intraoperative awareness, red-haired patients were identified and matched with five control patients, and the relative risk for intraoperative awareness was determined. Overall anesthetic management between groups was compared using Hotelling's T(2) statistic. Inhaled anesthetic requirements were compared between cohorts by evaluating the relationship between end-tidal anesthetic concentration and the bispectral index with a linear mixed-effects model. Time to recovery was compared using Kaplan-Meier analysis, and differences in postoperative pain and nausea/vomiting were evaluated with Chi square tests.

RESULTS

A cohort of 319 red-haired patients was matched with 1,595 control patients for a sample size of 1,914. There were no significant differences in the relative risk of intraoperative awareness (relative risk = 1.67; 95% confidence interval 0.34 to 8.22), anesthetic management, recovery times, or postoperative pain between red-haired patients and control patients. The relationship between pharmacokinetically stable volatile anesthetic concentrations and bispectral index values differed significantly between red-haired patients and controls (P < 0.001), but without clinical implications.

CONCLUSION

There were no demonstrable differences between red-haired patients and controls in response to anesthetic and analgesic agents or in recovery parameters. These findings suggest that perioperative anesthetic and analgesic management should not be altered based on self-reported red-hair phenotype.

[Our experience of the clinical use of desflurane]

Despite the widespread use of inhalational anaesthetics in modern medical practice it is still unable to create an "ideal" anesthetic, which meets the following requirements--maximum performance, security, and manageability. Desflurane is an inhalational anaesthetic, which first appeared on Russian market in 2013, according to the specifications meet the above-mentioned requirements. The results of the use of Desflurane during anaesthesia in 157 patients of the Cancer Department and Department of Oral and Maxillofacial Surgery at the Burdenko Main Military Clinical Hospital are given. The main advantages are the rapid achievement of Desflurane required depth of anaesthesia, minimal effects on the cardiovascular system, good handling, fast and safe awakening of the patient after surgery, which can make it "anaesthetic of choice" for long surgical procedures and outpatient surgery.

Influence of prior determination of baseline minimum alveolar concentration (MAC) of isoflurane on the effect of ketamine on MAC in dogs

The objective of this study was to determine if prior measurement of the minimum alveolar concentration (MAC) of isoflurane influences the effect of ketamine on the MAC of isoflurane in dogs. Eight mixed-breed dogs were studied on 2 occasions. Anesthesia was induced and maintained using isoflurane. In group 1 the effect of ketamine on isoflurane MAC was determined after initially finding the baseline isoflurane MAC. In group 2, the effect of ketamine on isoflurane MAC was determined without previous measure of the baseline isoflurane MAC. In both groups, MAC was determined again 30 min after stopping the CRI of ketamine. Plasma ketamine concentrations were measured during MAC determinations. In group 1, baseline MAC (mean ± SD: 1.18 ± 0.14%) was decreased by ketamine (0.88 ± 0.14%; P < 0.05). The MAC after stopping ketamine was similar (1.09 ± 0.16%) to baseline MAC and higher than with ketamine (P < 0.05). In group 2, the MAC with ketamine (0.79 ± 0.11%) was also increased after stopping ketamine (1.10 ± 0.17%; P < 0.05). The MAC values with ketamine were different between groups (P < 0.05). Ketamine plasma concentrations were similar between groups during the events of MAC determination. The MAC of isoflurane during the CRI of ketamine yielded different results when methods of same day (group-1) versus separate days (group-2) are used, despite similar plasma ketamine concentrations with both methods. However, because the magnitude of this difference was less than 10%, either method of determining MAC is deemed acceptable for research purposes.

The interaction of nitrous oxide and fentanyl on the minimum alveolar concentration of sevoflurane blocking motor movement (MACNM) in dogs

The study objective was to determine the effects of 70% nitrous oxide (N2O) and fentanyl on the end-tidal concentration of sevoflurane necessary to prevent movement (MACNM) in response to noxious stimulation in dogs. Six healthy, adult, intact male, mixed-breed dogs were used on 3 occasions in a randomized crossover design. After induction of anesthesia with sevoflurane, each of the following treatments was randomly administered: fentanyl loading dose (Ld) of 15 μg/kg and infusion of 6 μg/kg per hour [treatment 1 (T1)], 70% N2O (T2), or fentanyl (Ld of 15 μg/kg and infusion of 6 μg/kg per hour) combined with 70% N2O (T3). Each dog received each of the 3 treatments once during the 3-week period. Determination of MACNM was initiated 90 min after the start of each treatment. The values were compared using the baseline MACNM, which had been determined in a previous study on the same group of dogs. Data were analyzed using a mixed-model analysis of variance (ANOVA) and Tukey-Kramer tests, and expressed as least squares mean ± SEM. The baseline MACNM decreased by 36.6 ± 4.0%, 15.0 ± 4.0%, and 46.0 ± 4.0% for T1, T2, and T3, respectively (P < 0.05), and differed (P < 0.05) among treatments. Mean fentanyl plasma concentrations did not differ (P ≥ 0.05) between T1 (3.70 ± 0.56 ng/mL) and T3 (3.50 ± 0.56 ng/mL). The combination of fentanyl and N2O resulted in a greater sevoflurane MACNM sparing effect than either treatment alone.

A pharmacokinetic study of 48-hour sevoflurane inhalation using a disposable delivery system (AnaConDa®) in ICU patients

BACKGROUND

Little is known regarding sevoflurane kinetics and toxicity during long-term sedation of intensive care unit (ICU) patients using the AnaConDa® system. The objective of the present study was to establish a pharmacokinetic description of 48-h sevoflurane administration, and to estimate plasma concentrations of metabolites.

METHODS

Forty-eight hour sedation with sevoflurane vaporized via an AnaConDa® device, with an end-tidal concentration objective of 1.5% (v/v), was initiated in 12 non-obese patients who did not have hepatic or renal failure but who required sedation for more than 48 h in our ICU. Plasma sevoflurane, hexafluoroisopropanol, and fluoride concentrations were determined over this time period and pharmacokinetic analysis was performed.

RESULTS

The mean plasma concentration of sevoflurane was 76 mg/L at 24 h and 70 mg/L at 48 h. Wash-out of plasma sevoflurane correlated with a rapid decrease in the mean end-tidal sevoflurane level. The mean free plasma fraction of hexafluoroisopropanol never exceeded 8 mg/mL. The mean fluoride concentration was 0.8 µmol/L on day 0, 51.7 µmol/L on day 1, and 68.1 µmol/L on day 2 (P<0.0001). The distribution volume was 53 L, the elimination constant 2.9 h-1, the transfer constant from compartment 1 to compartment 2 (K1-2) 1.2 h-1, the K2-1 0.26 h-1, the half-life of elimination 3.78 h, and the total clearance 156 L/h.

CONCLUSION

Following 48 hours of sedation using sevoflurane inhalation administered using an AnaConDa® delivery device, sevoflurane washout was rapid. Plasma fluoride levels accumulated over the study period without apparent nephrotoxicity.

Ventilation with increased apparatus dead space vs positive end-expiratory pressure: effects on gas exchange and circulation during anesthesia in a randomized clinical study

Atelectasis formation can be reduced by positive end-expiratory pressure (PEEP), but resulting increases in intrathoracic pressure could affect circulation. We have earlier demonstrated that increased tidal volumes with larger apparatus dead space improves oxygenation and sevoflurane uptake. In the present study, we hypothesize that isocapnic ventilation with increased tidal volumes increases oxygen and sevoflurane uptake similar to ventilation with PEEP, but with less impact on cardiac output. Thirty patients, with ASA physical status 1 or 2, scheduled for elective open colon surgery were randomly assigned to be ventilated with either PEEP at 10 cm H20 (PEEP, 15 patients) or increased tidal volumes achieved with larger apparatus dead space but with zero end-expiratory pressure (DS group, 15 patients). Oxygen tension and arterial sevoflurane concentration were significantly higher in the DS group (P < .05). Cardiac output decreased significantly less in the DS group compared with the PEEP group (5% and 33%, respectively; P < .05). Consequently, isocapnic ventilation with increased tidal volumes using apparatus dead space increased oxygen and sevoflurane tensions in arterial blood and preserved cardiac output better than did PEEP.

[Application of desflurane in anaesthesiology]

Desflurane (Des)--is a modern inhalation anaesthetic available in Russia since August, 2013. Des is a halogenated ether; its chemical structure is 2-difluoromethoxy-1-1-1-2-tetrafluoroethane (C3H2F6O). Special thermocompensated evaporators are used for Des dosing. Low solubility in blood and tissues of an organism causes fast absorption and elimination of Des. Blood/gas distribution ratio of Des is 0.42. Des distinctive properties are high saturated vapor pressure, super short duration of action and average power. Furthermore it is characterized by the minimal metabolism and lack of interaction with soda lime. Des is used for general anesthesia in a cardiac surgery neurosurgery, out-patient surgery, pediatric practice and other areas of surgery. Des has more positive qualities and fewer limitations, than other inhalation anaesthetics (halothane, isoflurane, sevoflurane). High cost of the anaesthetic is compensated by quality and controllability of anaesthesia and reduction of stay time in recovery unit. Fast elimination of the anaesthetic from a body allows reducing a frequency of complications connected with violation of upper airway and hypoxemia, promotes early discontinuation of artificial ventilation, reducing somnolence, earlier restoring a muscular tone in the postoperative period.

Desflurane concentrations and consumptions during low flow anesthesia

BACKGROUND

Desflurane is the least soluble and most expensive inhalation agent. Hence, low flow technique is suitable for anesthesia with desflurane. However, one of the disadvantages of low flow technique is the discrepancy among the end-tidal concentration, inspired concentration, and vaporizer setting.

OBJECTIVE

To measure the concentrations of desflurane at different sites of the anesthesia circuit by varying fresh gas flow (FGF) rates but fixing expired concentration.

MATERIAL AND METHOD

Thirty ASA PS I-II adult patients were enrolled in this crossover study. After induction of anesthesia and ten minutes of wash-in period, the flow meters of oxygen and air were then adjusted to maintain FiO2 at 0.3 with the random sequences of FGF rates at 0.5, 1 and 2 L x min(-1). Desflurane vaporizer was adjusted to obtain 5% end-tidal desflurane concentration (FeDES) throughout the study period. After FeDES reached the target and was stable for 20 minutes, inspired concentration ofdesflurane (FiDES) and delivered desflurane concentration at fresh gas outlet (FdDES) were measured. Lastly, the consumption of desflurane was calculated.

RESULTS

FdDES was higher than FiDES in every FGF rates. FdDES at FGF 0.5 L x min(-1) (6.13 +/- 0.12) was significantly higher than FdDES at 1 and 2 L x min(-1) (5.68 +/- 0.08, 5.54 +/- 0.07, respectively), but not significantly different between FGF 1 and 2 L x min(-1). FeDES/FdDES at FGF 0.5, 1 and 2 L.min(-1) were 0.82 +/- 0.014, 0.88 +/- 0.012 and 0.87 +/- 0.011, respectively. There was no significant difference of FeDES/FdDES between FGF 1 and 2 L x min(-1), but there was significant difference between FGF 1 and 0.5 L x min(-1) with the p-value < 0.001. The calculated liquid desflurane consumption per hour at FGF rate of 0.5, 1 and 2 L x min(-1) were 8.77 +/- 0.17, 16.28 +/- 0.24 and 31.73 +/- 0.41 mL x hr(-1).

CONCLUSION

Using FGF 2 L x min(-1) has no advantage over FGF 1 L x min(-2), because they both have the similar FdDES. Regarding at FGF 0.5 and 1 L x min(-1), the delivered concentration has to be increased to obtain the desired expired concentration with more intense at FGF 0.5 L x min(-1) because there are more discrepancies between FdDES and FeDES.

[Inhalation anaesthesia and total intravenous anaesthesia for hepatic resections]

Recently number of surgeries in patients with pathology of the liver increases. Therefore optimal and safe anaesthetic management for these surgeries is very topical. The article deals with analysis of 51 anaesthesia cases: 26 cases (51%) of multimodal balanced anaesthesia with sevoflurane inhalation and 25 cases (49%) of multimodal balanced anaesthesia with continuous propofol infusion. Both techniques provide optimal anaesthetic protection, however sevoflurane use influences on the liver metabolism more significantly.

Influence of carbon dioxide insufflation of the neck on intraocular pressure during robot-assisted endoscopic thyroidectomy: a comparison with open thyroidectomy

BACKGROUND

Increased intraocular pressure (IOP) during surgery can result in serious ophthalmic complications. We hypothesized that carbon dioxide (CO₂) insufflation of the neck during endoscopic thyroidectomy would constrict the jugular veins mechanically, causing elevated venous pressure and thus elevated IOP. We compared IOP changes at each step of open thyroidectomy (OT) versus robot-assisted endoscopic thyroidectomy (RET) METHODS: Perioperatively, IOP was measured at six time points in patients undergoing OT (n = 18) or RET with CO₂ insufflation (n = 19). Anesthesia, ventilatory strategy, intravenous infusions, and surgical positioning were standardized

RESULTS

In both groups, induction of anesthesia reduced IOP, but surgical positioning with the neck in extension had no effect on IOP. In the OT group, IOP remained unchanged during anesthesia. In the RET group, CO₂ insufflation significantly increased IOP to an average of 3.6 ± 3.0 mmHg higher than the previous measurement (P < 0.001), and this IOP increase persisted immediately before gas deflation. These elevated IOP values during CO₂ insufflation in the RET group were significantly higher than those at corresponding time points in the OT group. However, these elevated IOP values were similar to the pre-anesthetic baseline IOP CONCLUSION: CO₂ insufflation of the neck at pressure of 6 mmHg increased the IOP significantly compared with open thyroidectomy. However, this increase in IOP could be balanced by an anesthetic-induced IOP-lowering effect, thereby having no clinical significance in patients with normal IOP undergoing robot-assisted endoscopic thyroidectomy.

Prior determination of baseline minimum alveolar concentration (MAC) of isoflurane does not influence the effect of ketamine on MAC in rabbits

The objective of this study was to compare the effect on the minimum alveolar concentration (MAC) of isoflurane when ketamine was administered either after or without prior determination of the baseline MAC of isoflurane in rabbits. Using a prospective randomized crossover study, 8 adult, female New Zealand rabbits were allocated to 2 treatment groups. Anesthesia was induced and maintained with isoflurane. Group 1 (same-day determination) had the MAC-sparing effect of ketamine [1 mg/kg bodyweight (BW) bolus followed by a constant rate infusion (CRI) of 40 μg/kg BW per min, given by intravenous (IV)], which was determined after the baseline MAC of isoflurane was determined beforehand. A third MAC determination was started 30 min after stopping the CRI. Group 2 (separate-day determination) had the MAC-sparing effect of ketamine determined without previous determination of the baseline MAC of isoflurane. A second MAC determination was started 30 min after stopping the CRI. In group 1, the MAC of isoflurane (2.15 ± 0.09%) was significantly decreased by ketamine (1.63 ± 0.07%). After stopping the CRI, the MAC was significantly less (2.04 ± 0.11%) than the baseline MAC of isoflurane and significantly greater than the MAC during the CRI. In group 2, ketamine decreased isoflurane MAC (1.53 ± 0.22%) and the MAC increased significantly (1.94 ± 0.25%) after stopping the CRI. Minimum alveolar concentration (MAC) values did not differ significantly between the groups either during ketamine administration or after stopping ketamine. Under the study conditions, prior determination of the baseline isoflurane MAC did not alter the effect of ketamine on MAC. Both methods of determining MAC seemed to be valid for research purposes.

[Impact of beach chair position on the value of bispectral index during general anesthesia]

BACKGROUND

Although the bispectral index (BIS) has been established as a common index of anesthetic depth, there is a possibility that head-up position may influence BIS values under general anesthesia. This study examined whether beach chair position with 57 degrees head-up would cause the variation of BIS values during shoulder surgery.

METHODS

Two groups of patients were scheduled for surgery, one was supine position group, and the other was beach chair position group. Anesthesia was induced with propofol and rocuronium, and maintained with sevoflurane (end-tidal concentration 1.0-1.2%). The BIS values were recorded manually until 120 minutes after the onset of positioning and evaluated at each 30 min interval.

RESULTS

There was no time-dependent difference in BIS values during supine position. In contrast, BIS values in beach chair position group showed a marked downward-trend through the measurement period. End-tidal anesthetic gas concentration and mean blood pressure did not significantly differ between the groups consistently.

CONCLUSIONS

To our knowledge, this is the first report of the effect of beach chair position on BIS values intraoperatively. This result indicates that the beach chair position causes a time-dependent decrease in BIS under general anesthesia.

Brief review: theory and practice of minimal fresh gas flow anesthesia

PURPOSE

The aim of this brief review is to provide an update on the theory regarding minimal fresh gas flow techniques for inhaled general anesthesia. The article also includes an update and discussion of the practical aspects associated with minimal-flow anesthesia, including the advantages, potential limitations, and safety considerations of this important anesthetic technique.

PRINCIPAL FINDINGS

Reducing the fresh gas flow to < 1 L·min(-1) during maintenance of anesthesia is associated with several benefits. Enhanced preservation of temperature and humidity, cost savings through more efficient utilization of inhaled anesthetics, and environmental considerations are three key reasons to implement minimal-flow and closed-circuit anesthesia, although potential risks are hypoxic gas mixtures and inadequate depth of anesthesia. The basic elements of the related pharmacology need to be considered, especially pharmacokinetics of the inhaled anesthetics. The third-generation inhaled anesthetics, sevoflurane and desflurane, have low blood and low tissue solubility, which facilitates rapid equilibration between the alveolar and effect site (brain) concentrations and makes them ideally suited for low-flow techniques. The use of modern anesthetic machines designed for minimal-flow techniques, leak-free circle systems, highly efficient CO(2) absorbers, and the common practice of utilizing on-line real-time multi-gas monitor, including essential alarm systems, allow for safe and cost-effective minimal-flow techniques during maintenance of anesthesia. The introduction of new anesthetic machines with built-in closed-loop algorithms for the automatic control of inspired oxygen and end-tidal anesthetic concentration will further enhance the feasibility of minimal-flow techniques.

CONCLUSIONS

With our modern anesthesia machines, reducing the fresh gas flow of oxygen to 0.3-0.5 L·min(-1) and using third-generation inhaled anesthetics provide a reassuringly safe anesthetic technique. This environmentally friendly practice can easily be implemented for elective anesthesia; furthermore, it will facilitate cost savings and improve temperature homeostasis.

Minimal alveolar concentration of sevoflurane inhibiting the reflex pupillary dilatation after noxious stimulation in children and young adults

BACKGROUND

In children, sevoflurane is the most commonly used anaesthetic. Its excellent haemodynamic tolerance gives it a wide therapeutic index. This halogenated agent can abolish movement [minimal alveolar concentration (MAC)] or haemodynamic responses (MACBAR) to noxious stimulus in children as in adults. Reflex pupillary dilatation (RPD) has been demonstrated as a very sensitive measure of noxious stimulation. In order to investigate the effect of sevoflurane on the RPD, a subcortical reflex, we determined the MAC of sevoflurane inhibiting the RPD in 50% of the subjects in response to skin incision (MACpup) in pre- and post-pubertal subjects.

METHODS

We included 30 pre-pubertal children and 19 post-pubertal subjects. Patients received sevoflurane at preselected concentrations according to an 'up and down' design, and after a steady-state period, skin incision was performed. The RPD was considered as significant when the pupillary diameter increased by more than 100%. Heart rate (HR) and bispectral index (BIS) changes were analysed according to the pupillary response.

RESULTS

The MACpup of sevoflurane was 4.8% (95% confidence interval, 4.6-5.1%) in pre-pubertal children vs 3.4% (3.5-3.3%) in post-pubertal subjects (P<0.001). Inhibition of RPD was always associated with lack of significant HR response. In pre-pubertal children receiving high concentrations of sevoflurane, RPD in response to noxious stimulation was frequently associated with lack of HR response and low BIS values.

CONCLUSIONS

MACpup was higher than MAC and close to the MACBAR. Inhibition of RPD in pre-pubertal children required higher sevoflurane concentrations compared with post-pubertal subjects, suggesting that the relationship between the brain structure sensitivities may differ with brain maturation.

Heart rate limitation and cardiac unloading in sevoflurane post-conditioning

BACKGROUND

Sevoflurane post-conditioning (SePost) has been found to alleviate ischemic myocardial reperfusion injury through the activation of prosurvival kinases. Lowered myocardial oxygen demand from reduced cardiac work may also contribute to cardioprotection, and is much less well-studied. Our aim was to examine the simultaneous effects of SePost on cardiac work (here, rate-pressure product, RPP) and myocardial infarct size in a porcine model.

METHODS

Anesthetized 25 kg pigs were randomly allocated to two groups and underwent 45 min regional coronary artery balloon occlusion and subsequent 2 h reperfusion. SePost (n = 10) was given as sevoflurane 1.5-3% end-tidal concentration during reperfusion while controls (n = 12) were untreated. Aortic blood pressure was measured directly, while mixed-venous oxygen saturation and cardiac output were measured in the pulmonary artery. Cardiac work was determined as RPP. Post-mortem, histologic myocardial infarct size (IS), and area at risk were determined in transverse heart slices after tetrazolium stain.

RESULTS

Myocardial infarct size was reduced from (control) 55.0 (mean) ± 13.6% (standard deviation) to 32.5 ± 13.4% in group SePost (P = 0.0009). During reperfusion, SePost resulted in lower heart rate (P = 0.0003), cardiac output (P = 0.0123), mixed-venous oxygen saturation (P = 0.0103), blood pressure, and RPP (P < 0.0001). RPP was highly correlated to IS (P = 0.0055).

CONCLUSION

SePost (1.5-3%) reduced infarct size after regional myocardial ischemia in vivo and reduced cardiac work was significantly correlated to myocardial salvage.

Intravenous landiolol, a novel β(1)-adrenergic blocker, reduces the minimum alveolar concentration of sevoflurane in women

STUDY OBJECTIVE

To investigate the effect of intravenous (IV) landiolol, a novel β(1)-adrenergic blocker, on the minimum alveolar concentration (MAC) of sevoflurane in adult women.

DESIGN

Prospective, randomized study.

SETTING

University hospital.

PATIENTS

42 ASA physical status 1 and 2 women, aged 24-57 years, who were scheduled to undergo elective abdominal surgery.

INTERVENTIONS

Anesthesia was induced in all patients by vital capacity rapid inhalation induction of sevoflurane. In the landiolol group, administration of landiolol began when patients took a vital-capacity breath: 0.125 mg/kg/min for one minute and then 0.04 mg/kg/min. Normal saline was administered in the control group.

MEASUREMENTS

MAC was determined by a technique adapted from the conventional up-down method.

MAIN RESULTS

The MAC of sevoflurane was 2.2% ± 0.2% in the control group and 1.7% ± 0.2% in the landiolol group, a statistically significant difference (P = 0.0005).

CONCLUSIONS

IV landiolol reduces the MAC of sevoflurane in women by approximately 20%.

[Pharmacokinetic and pharmacodynamic characteristics of the domestic sevoflurane for transabdominal hysterectomy]

OBJECTIVE

To evaluate the clinical efficacy of domestic sevoflurane by comparing the pharmacokinetic and pharmacodynamic characteristics of domestic sevoflurane and an imported product.

METHODS

Eighty patients undergoing general anesthesia for transabdominal hysterectomy were equally randomized into domestic sevoflurane group and imported sevoflurane group. The following data were recorded and compared: vital signs; change of sevoflurane concentrations in the induction period and recovery period; the time when inhaled sevoflurane concentration reached half of the pre-set concentration of the vaporizer; the time when the end-tidal sevoflurane concentration reached half of the pre-set concentration of the vaporizer; the time when the end-tidal sevoflurane concentration reached half of inhaled sevoflurane concentration; the time of the end-tidal sevoflurane concentration reached 0. 8 MAC in the induction period; the recovery time; the extubation time; and time to recovery of consciousness.

RESULTS

The general conditions of the two groups were not significantly different. The pharmacokinetic and pharmacodynamic parameters at the intra-operative time points as well as the minimal alveolar concentration, the inspired and end-tidal sevoflurane concentrations, and the time to recovery of consciousness also showed no significant differences between the two groups.

CONCLUSION

The domestic sevoflurane has similar pharmacokinetic and pharmacodynamic characteristics as the imported products. It can serve as a cost-effective product for transabdominal hysterectomy.

Increased lung clearance of isoflurane shortens emergence in obesity: a prospective randomized-controlled trial

BACKGROUND

There is a concern that obesity may play a role in prolonging emergence from fat-soluble inhalational anaesthetics. We hypothesized that increased pulmonary clearance of isoflurane will shorten immediate recovery from anaesthesia and post-anaesthesia care unit (PACU) stay in obese patients.

METHODS

After Ethics Review Board approval, 44 ASA I-III patients with BMI>30 kg/m(2) undergoing elective gynaecological or urological surgery were randomized after completion of surgery to either an isocapnic hyperpnoea (IH) or a conventional recovery (C) group. The anaesthesia protocol included propofol, fentanyl, morphine, rocuronium and isoflurane in air/O(2) . Groups were compared using unpaired t-test and ANOVA.

RESULTS

Minute ventilation in the IH group before extubation was 22.6 ± 2.7 vs. 6.3 ± 1.8 l/min in the C group. Compared with C, the IH group had a shorter time to extubation (5.4 ± 2.7 vs. 15.8 ± 2.7 min, P<0.01), initiation of spontaneous ventilation (2.7 ± 2.3 vs. 6.5 ± 4.5 min, P<0.01), BIS recovery >75 (3.2 ± 2.3 vs. 8.9 ± 5.8 min, P<0.01), eye opening (4.6 ± 2.9 vs. 13.6 ± 7.1 min, P<0.01) and eligibility for leaving the operating room (7.1 ± 2.9 vs. 19.9 ± 11.9 min, P<0.01). There was no difference in time for eligibility for PACU discharge.

CONCLUSION

Increasing alveolar ventilation enhances anaesthetic elimination and accelerates short-term recovery in obese patients.

[Mass-spectrometric investigation of degradation of the inhalation anesthetic sevoflurane in flow anesthesia]

The highest concentration of the Sevoflurane degradation product in the gas mixture was 65 ppm. Biochemical analysis did not reveal any nephro- and hepatotoxic effect.

[Concept of mechanisms of anesthetic and therapeutic properties of xenon]

The molecular theory of L. Poling is a genius example of scientific prediction, made in the middle of 20th century, when the studies about clathrates and methods of roentgen structured analysis were doing their first steps. The views expressed in this message are some additions on the structure of xenon clathrates, function-free xenon water associates and the use of cameras in the liberated associates of the water molecules, for the process of supramolecular detoxification and attempts to develop this theory more widely, to better understand the mechanisms of xenon anesthesia and treatment for further justification of its therapeutic features as well as for the use of other inert gases (Ar, Kr) in modern medicine.

[Comparison of atracurium, cisatracurium and vecuronium during anaesthesia for laparoscopic surgery]

BACKGROUND

The aim of the study was to compare the intubating conditions, onset time, and duration of action of atracurium, cisatracurium, and vecuronium, when used for muscle relaxation in laparoscopic surgery with carbon dioxide inflation. In trying to find an "ideal" relaxant we compared the relative potency of these drugs, and also measured pH, PaCO2 and skin temperature.

METHODS

Ninety-five ASA I and II patients were randomly allocated to three groups, to receive atracurium (I), cisatracurium (II), or vecuronium (III), during propofol/fentanyl anaesthesia. Neuromuscular transmission was monitored using accelerography (TOF GUARD). Patients were intubated after the injection of 0.5 mg kg-1 atracurium (I), 0.1 mg kg(-1) cisatracurium (II), or 0.1 mg kg(-1) vecuronium (III). Muscle relaxation was maintained with incremental doses of 0.1 0.2 mg kg(-1) and 0.03 mg kg(-1) of the relaxants respectively, given after a second response to TOF stimulation was noted. Recovery time was defined as the time from a maximal block (TOF=0) to spontaneous recovery of TOF 75%.

RESULTS

Conditions for performing tracheal intubation were noted to be excellent in groups I and III, and good in group II. The mean recovery time was significantly shorter in groups II and III, than in group I. No significant correlations were found between the duration of neuromuscular blockade and pH, PaCO2 or palm skin temperature.

CONCLUSIONS

Vecuronium, besides providing excellent conditions for tracheal intubation, had the fastest onset time and optimal duration of action. We found the drug to be the most suitable for laparoscopic surgery.

Xenon as an anesthetic agent

Discovered in 1898 by British chemists, xenon is a rare gas belonging to the noble gases of the periodic table. Xenon is used in many different ways, from high-intensity lamps to jet propellant, and in 1939, its anesthetic properties were discovered. Xenon exerts its anesthetic properties, in part, through the noncompetitive inhibition of N-methyl-D-aspartate receptors. Currently, xenon is being used primarily throughout Europe; however, the high price of manufacturing and scavenging the noble gas has discouraged more widespread use. As technology in anesthetic delivery improves, xenon is being investigated further as a possible replacement for nitrous oxide as an inhalational agent. This article reviews the anesthetic properties of xenon and current and potential research about the gas.

Inhalation anesthetics: a review

Inhalation agents represent a basic drug used in modern balanced anesthesia. In the present review, the pharmacokinetics, effectiveness and clinical effects of inhalation agents on different systems are discussed. Data concerning the metabolism and related toxicity of halogenated agents is reviewed, with particular regard to the problem of chronic exposure to traces of anesthetic gases in the operating room. The cardioprotective effect of halogenated agents and the actual role of nitrous oxide and xenon are discussed. The different mechanisms of action of the inhalation agents and the evolution from a unitary theory of inhaled anesthetics to a multiple mechanism concept are presented.

Low-flow anaesthesia at a fixed flow rate

AIMS AND OBJECTIVES

This study attempts to assess the safety of low-flow anaesthesia (LFA) at fixed flow rates with particular reference to the incidence of a decline in FiO(2) below safe levels of 0.3 and to determine whether LFA can be used safely in the absence of an FiO(2) monitor.

METHODS

A total of 100 patients undergoing procedures under general anaesthesia at fresh gas flows of 300 ml/min of O(2) and 300 ml/min of N(2)O were monitored while maintaining the dial setting of isoflurane at 1.5% for 2 h. The changes in gas composition were analysed and even a single recording of FiO(2) of <0.3 was considered sufficient to render the technique unsafe in the absence of gas monitors.

RESULTS

The lowest recorded value of FiO(2) was 31% (v/v%). There was no incidence of adverse events necessitating the conversion from low flows to conventional flows.

CONCLUSIONS

We conclude that low flows of 300 ml/min of N(2)O and 300 ml/min of oxygen can be used safely for a period of 2 h without the use of monitors for gas analysis of oxygen and agent in adult patients weighing between 40 and 75 kgs.

Balanced anesthesia with remifentanil and desflurane: clinical considerations for dose adjustment in adults

BACKGROUND

The intraoperative combination of volatile anesthetics with opioids is a well-accepted technique because of its hemodynamic stability and side effects. This study in adults was designed to determine the pharmacodynamic interactions between different dosages of remifentanil and desflurane in response to skin incision.

METHODS

A total of 60 patients were enrolled in this study. Patients were prospectively randomized to receive 0, 0.1, 0.15, or 0.25 microg/kg/min remifentanil. Anesthesia was induced with remifentanil, propofol, and succinylcholine. Thereafter, a group-specific desflurane concentration was administered using Dixon's up-and-down technique. After a "wash out" and equilibration period, patients were observed for defense movements up to 1 minute after skin incision. Mean arterial pressure and heart rate were recorded before induction of anesthesia (baseline), at surgical incision, as well as 2 and 4 minutes thereafter. Time until extubation was assessed after stopping desflurane and remifentanil at the end of the surgery.

RESULTS

Remifentanil at 0.1, 0.15, or 0.25 microg/kg/min reduced desflurane requirements by 74, 83, and 90 percent, respectively. The time course of mean arterial pressure did not differ between the study groups. However, compared with the group without remifentanil, heart rate was significantly lower in patients receiving 0.15 or 0.25 microg/kg/min remifentanil. No difference between the groups was observed with regard to extubation time.

CONCLUSION

Remifentanil reduces in a dose-dependent manner the desflurane requirements for skin incision without increasing recovery time. An infusion rate higher than 0.1 microg/kg/min results in a significantly decreased heart rate.