The Anesthetic and Physiologic Effects of an Intravenous Administration of a Halothane Lipid Emulsion (5% vol/vol)

Anesthetic Potency of Intravenous Infusion of 20% Emulsified Sevoflurane and Effect on the Blood-Gas Partition Coefficient in Dogs

BACKGROUND

Intravenous (IV) infusions of volatile anesthetics in lipid emulsion may increase blood lipid concentration, potentially altering the anesthetic agent's blood solubility and blood-gas partition coefficient (BGPC). We examined the influence of a low-lipid concentration 20% sevoflurane emulsion on BGPC, and the anesthetic potency of this emulsion using dogs.

METHODS

We compared BGPC and anesthetic characteristics in 6 dogs between the IV anesthesia of emulsion and the sevoflurane inhalation anesthesia in a randomized crossover substudy. Minimum alveolar concentrations (MACs) were determined by tail-clamp stimulation by using the up-and-down method. Blood sevoflurane concentration and partial pressure were measured by gas chromatography; end-tidal sevoflurane concentration was measured using a gas monitor. The primary outcome was BGPC at the end of IV anesthesia and inhalation anesthesia. Secondary outcomes were time to loss/recovery of palpebral reflex, finish intubation and awakening, MAC, blood concentration/partial pressure at MAC and awakening, correlation between blood partial pressure and gas monitor, and the safety of emulsions.

RESULTS

BGPC showed no difference between IV and inhaled anesthesia (0.859 [0.850-0.887] vs 0.813 [0.791-0.901]; P = .313). Induction and emergence from anesthesia were more rapid in IV anesthesia of emulsion than inhalation anesthesia. MAC of emulsion (1.33% [1.11-1.45]) was lower than that of inhalation (2.40% [2.33-2.48]; P = .031), although there was no significant difference in blood concentration. End-tidal sevoflurane concentration could be estimated using gas monitor during IV anesthesia of emulsion. No major complications were observed.

CONCLUSIONS

IV anesthesia with emulsion did not increase the BGCP significantly compared to inhalation anesthesia. It was suggested that the anesthetic potency of this emulsion may be equal to or more than that of inhalation.

General anesthesia with an injectable 8% v/v sevoflurane lipid emulsion administered intravenously to dogs

OBJECTIVE

To evaluate the potential of an intravenous (IV) sevoflurane formulation for maintenance of general anesthesia in dogs.

STUDY DESIGN

Prospective crossover design.

ANIMALS

Six healthy, mature, mixed-breed dogs, four males and two females, weighing 11.7 ± 3.4 kg.

METHODS

Anesthesia was induced and maintained with propofol IV for instrumentation. Baseline measurements were recorded before administration of either sevoflurane in oxygen (Sevo-Inh) or lipid-emulsified sevoflurane 8% v/v in 30% Intralipid IV (Sevo-E), 0.5 mL kg(-1) over 5 minutes followed by an infusion at 0.1-0.3 mL kg(-1)  minute(-1) . Dogs were breathing spontaneously. The 'up-and-down' technique was used to determine the minimum alveolar concentration (MAC) of sevoflurane. Over 120 minutes, a tail clamp was applied every 15 minutes and sevoflurane administration was adjusted depending on the response. End-tidal sevoflurane concentration and variables were recorded at 30, 60, 90, and 120 minutes: heart rate (HR), systemic arterial pressure (sAP), respiratory rate (fR ), end-tidal carbon dioxide tension, hemoglobin oxygen saturation (SaO2 ), arterial pH and blood gases, blood urea nitrogen, alanine aminotransferase, creatine kinase, gamma-glutamyl transferase, and aspartate aminotransferase.

RESULTS

There were no significant differences between treatments for HR, sAP, fR , SaO2 , and biochemical variables (p > 0.05). pH and HCO3-were significantly decreased, and PaCO2 increased from baseline in Sevo-E (p < 0.05). MAC was significantly lower for Sevo-E than for Sevo-Inh, although the required dose of sevoflurane (g hour(-1) ) to maintain general anesthesia was not significantly different between treatments.

CONCLUSIONS AND CLINICAL RELEVANCE

Administration of 8% v/v sevoflurane lipid emulsion IV was effective in maintaining general anesthesia in dogs, but resulted in moderate cardiopulmonary depression, metabolic and respiratory acidosis. The amount of sevoflurane (g hour(-1) ) required to maintain general anesthesia was significantly lower for inhaled than for IV sevoflurane.

Comparison of the effects of propofol and emulsified isoflurane alone or combined with dexmedetomidine on induction of anesthesia in dogs

OBJECTIVE

To compare the respective effects of propofol and emulsified isoflurane administered alone and in combination with dexmedetomidine on the quality of induction of anesthesia, physiological variables and recovery in dogs.

STUDY DESIGN

Prospective, randomized, experimental trial.

ANIMALS

Thirty-six adult mixed-breed dogs.

METHODS

Animals were randomly assigned to one of four induction protocols: propofol alone (group P); emulsified isoflurane alone (group EI); both propofol and dexmedetomidine (group PD), or both emulsified isoflurane and dexmedetomidine (group EID). Pulse rate (PR), respiratory rate (fR ), non-invasive arterial blood pressure and arterial blood gases were measured at baseline, before induction, immediately after intubation (time 0), and at 5 minute intervals until the dog began to swallow and the trachea was extubated. The quality of induction and recovery, and degree of ataxia were scored by a single investigator unaware of group assignment. The durations of anesthesia and recovery, and the incidence of adverse events were recorded.

RESULTS

There were no clinically significant differences among the groups in induction quality. Systolic arterial pressure was lower in EID compared with P at 5 minutes. PR and fR were lower in PD and EID compared with P after induction. The PaCO2 at 5 minutes was higher than at baseline in group P. Ataxia score was lower in EID than in P. Time from induction to extubation and time from extubation to sternal recumbency were lower in EID compared with PD.

CONCLUSIONS AND CLINICAL RELEVANCE

There were no clinically significant differences among the groups in induction quality. In PD and EID, but not in P, PR and fR were decreased after induction. The EID combination resulted in smooth and rapid induction and recovery and thus may be useful clinically for induction of anesthesia.

Synthesis, emulsification and self-assembly properties of sugar-containing semifluorinated amphiphiles

Surfactants with two and three monosaccharide-based heads and a perfluoroalkyl tail have been synthesized. Perfluoroalkyl C3-symmetric triol and C2-symmetric diol were conveniently prepared via Cu-catalyzed azide-alkyne cycloaddition between a fluorous alkyne and tertiary and secondary azides, respectively. Glycosylation of the perfluoroalkyl diol and triol led to orthoester-type structures, which were evaluated for their capacity to stabilize aqueous emulsions of highly fluorinated anesthetics. The self-assembly properties of the tri-sugar amphiphile were examined by transmission electron microscopy.

Comparison of anaesthetic and analgesic effects of emulsified isoflurane used alone or combined with lidocaine and fentanyl in dogs

AIM

The objective of this study was to investigate the effects of a combination of emulsified isoflurane, lidocaine, and fentanyl (EI-L-F) compared with the efficacy of emulsified isoflurane alone (EI), a combination of emulsified isoflurane and lidocaine (EI-L) or emulsified isoflurane and fentanyl (EI-F) for anaesthetising dogs.

METHODS

Eight mongrel dogs were anesthetised with EI (8 mL/kg/hour), EI-L (3 mg/kg/hour lidocaine and 6 mL/kg/hour of emulsified isoflurane), EI-F (1.5 μg/kg/hour fentanyl and 6 mL/kg/hour of emulsified isoflurane), and EI-L-F (5 mL/kg/hour of emulsified isoflurane, 1 μg/kg/hour of fentanyl and 2.4 mg/kg/hour of lidocaine). Each dog received all four treatments and there was a 15-day washout period between the treatments. The dogs' anaesthesia and analgesia scores and physiological parameters were determined before and 5, 10, 20, 30, 40, 50, 60, 70 and 80 minutes after the administration of anaesthetic agents.

RESULTS

The dogs in each of the four groups became laterally recumbent within 1 minute. Respiration rate and heart rate increased (p<0.05) during the first 5 minutes of anaesthesia in all groups. Respiration rate in the EI-F-L group was higher (p=0.037) than other groups from 30 to 50 minutes. Heart rate was higher in the EI than EI-F-L group (p=0.018) from 10 to 20 minutes, then returned to near baseline. Arterial oxygen saturation decreased during the period of anaesthesia but was higher (p=0.032) from 10 to 50 minutes in EI-F-L group than in other groups. The total anaesthesia scores in the EI-L-F group were higher than the EI and EI-L groups (p<0.05). The mean time to body movement was 5 (SD 2), 5 (SD 2), 7 (SD 2) and 8 (SD 2) minutes for the EI, EI-L, EI-F and EI-F-L groups, respectively. The mean time to standing was 8 (SD 2), 9 (SD 2), 10 (SD 2) and 13 (SD 3) minutes for the EI, EI-L, EI-F and EI-F-L groups, respectively. No excitement was observed during recovery after anaesthesia.

CONCLUSIONS

The EI-F-L combination that was used in this study provided an adequate anaesthesia effect in dogs, which was characterised by adequate analgesia and muscle relaxation without any complications.

[In-vivo diagnosis of malignant hyperthermia susceptibility: a microdialysis study]

BACKGROUND

In malignant hyperthermia (MH), volatile anesthetics induce hypermetabolism, lactic acidosis and rhabdomyolysis in predisposed patients. The authors hypothesized that intramuscular caffeine and halothane application would increase local lactate concentration in MH susceptible (MHS) individuals more than in non-susceptible (MHN) subjects without initiating the full MH syndrome.

METHODS

In 14 MHS, 12 MHN and 7 control individuals, microdialysis probes were placed in the rectus femoris muscle and perfused with Ringer's solution at 1 microl/min. After equilibration, 250 microl caffeine (80 mM) was injected through the first microdialysis probe, halothane 10 vol% dissolved in soybean oil was perfused through a second microdialysis probe and a third probe was used for control measurements. Dialysate samples were analyzed for lactate spectrophotometrically. Systemic hemodynamic and metabolic parameters were measured. Data are presented as median and quartiles.

RESULTS

Intramuscular caffeine and halothane significantly increased local peak concentrations of lactate in MHS probands [5.0 mM (3.4-8.1 mM) and 3.7 mM (2.6-5.0 mM), respectively] compared to MHN [1.6 mM (1.3-2.0 mM) and 1.9 mM (1.6-2.0 mM)] or control individuals [2.1 mM (1.9-2.3 mM) and 2.0 mM (1.6-2.1 mM)]. This was accompanied by a higher serum creatine kinase level in the MHS group. Hemodynamic and metabolic parameters were normal in the investigated groups.

CONCLUSION

Intramuscular caffeine and halothane application induces a temporary and abnormal increase of local lactate in MHS individuals. No serious systemic side effects occurred. This study presents evidence that metabolic monitoring with local stimulation by caffeine and halothane may allow a minimally invasive diagnosis of MH susceptibility.

Pharmacokinetics of 1,8-cineole, a dietary toxin, in the brushtail possum (Trichosurus vulpecula): Significance for feeding

1,8-Cineole (cineole) is a Eucalyptus leaf toxin that defends against predation by herbivores such as the brushtail possum (Trichosurus vulpecula). The aim of the current study was to characterize the pharmacokinetics of cineole in the possum to improve understanding about how possums can avoid cineole toxicity when eating a Eucalyptus diet. Nine male possums were trapped in the wild and acclimated to captivity; a subcutaneous port was then implanted for venous blood sampling. Cineole was administered intravenously (10 and 15 mg kg(-1)) via a lateral tail vein and orally (30, 100 and 300 mg kg(-1)) by gavage, and blood concentrations of cineole and its metabolites were determined by gas chromatography. Cineole had a large terminal volume of distribution (V(z) = 27 l kg(-1)) and a high clearance (43 ml min(-1) kg(-1)), equal to hepatic blood flow. The terminal half-life was approximately 7 h. Oral bioavailability was low (F = 0.05) after low doses, but increased tenfold with dose, probably due to saturable first-pass metabolism. These findings indicate that when possums feed on a cineole diet, they eat until the cineole consumed is sufficient to saturate pre-systemic metabolism, leading to a rapid rise in bioavailability and cineole blood levels, and a cessation of the feeding bout. This is the first report on the pharmacokinetics of a dietary toxin in a wild herbivore, and provides insights into the interactions between the blood concentration of a plant secondary metabolite and the browsing behaviour of a herbivore.

An in-vivo metabolic test for detecting malignant hyperthermia susceptibility in humans: a pilot study

INTRODUCTION

In vitro contracture testing to diagnose malignant hyperthermia (MH) susceptibility requires a muscle biopsy, which may be associated with severe side effects for the patient. After investigation of several different protocols, we present a less invasive metabolic test that involves IM injection of caffeine and halothane, and subsequent measurement of interstitial lactate to differentiate between MH susceptible (MHS) and MH non-susceptible (MHN) individuals.

METHODS

Two microdialysis probes with attached microtubing for trigger injection were inserted into the lateral vastus muscle of eight previously diagnosed MHS patients (representing three genetic variants Gly2434Arg, Thr2206Met, and Arg614Cys), seven MHN patients, and seven control individuals. After equilibration and lactate baseline recording, a single bolus of 200 muL caffeine 80 mM and a suspension of 200 muL halothane 4%V/V in soy bean oil (triggers) were injected locally. Lactate was measured spectrophotometrically. Data are presented as medians and interquartile ranges.

RESULTS

Although baseline lactate values were similar in the investigated groups before trigger injection, caffeine increased local lactate in MHS patients significantly more (2.0 [1.8-2.6] mM) than in MHN (0.8 [0.6-1.1] mM) or in control individuals (0.8 [0.6-0.8 mM]). Similarly, halothane lead to a significant lactate increase in MHS compared to MHN and control individuals (8.6 [3.7-8.9] mM vs 0.9 [0.5-1.1] mM and 1.7 [0.9-2.3] mM, respectively). However, a relevant increase of lactate was observed in one MHN and in two control individuals. Systemic hemodynamic and metabolic variables did not differ between the investigated groups.

DISCUSSION

Metabolic monitoring of IM lactate after local caffeine and halothane injection may allow less invasive testing to detect MH susceptibility, without systemic side effects.

Emulsified isoflurane produces cardiac protection after ischemia-reperfusion injury in rabbits

BACKGROUND

In this study, we examined the cardioprotective effects of parental emulsified isoflurane compared with inhaled isoflurane.

METHODS

Thirty-two rabbits were subjected to 30 min of myocardial ischemia induced by temporary ligation of the left anterior descending coronary artery followed by 3 h of reperfusion. Before left anterior descending coronary artery occlusion, the rabbits were randomly allocated into one of four groups (eight for each group): group C, no ischemia preconditioning treatment; group IS, inhaled isoflurane 1.1% end-tidal; group EI, a continuous infusion of 8% emulsified isoflurane to an end-tidal concentration of 0.64%; and group IN, a continuous infusion of 30% Intralipid started 30 min. Treatments were started 30 min before ischemia followed by a 15 min washout period for isoflurane groups. Myocardial infarct volume, lactate dehydrogenase, and creatine kinase levels were measured and changes in mitochondrial ultrastructure assessed after 3 h myocardial reperfusion.

RESULTS

Myocardial infarct size 3 h after reperfusion was lower in groups IS and EI compared with groups C and IN (20% +/- 8%, 18% +/- 8%, 39% +/- 6%, and 34% +/- 9%, respectively, P < 0.01). There were no differences in myocardial infarct size between groups IS and EI or between groups C and IN. Plasma lactate dehydrogenase and creatine kinase levels were lower in group IS (456 +/- 58 U/L and 1725 +/- 230 U/L) and group EI (451 +/- 54 U/L and 1686 +/- 444 U/L) 3 h after myocardial reperfusion compared with groups C (676 +/- 82 U/L and 2373 +/- 529 U/L; P < 0.01). Mitochondrial ultrastructure changes were less pronounced in groups IS and EI compared with group C.

CONCLUSIONS

Our results indicate that, in rabbits, i.v. emulsified isoflurane provides similar myocardial protection against ischemia-reperfusion injury as inhaled isoflurane.

Xenon blocks the induction of synaptic long-term potentiation in pain pathways in the rat spinal cord in vivo

BACKGROUND

Xenon's (Xe) mechanisms for producing anesthesia and analgesia are not fully understood. We tested the effect of Xe equilibrated in a lipid formulation or normal saline on spinal C-fiber-evoked potentials and on the induction of synaptic long-term potentiation (LTP).

METHODS

C-fiber-evoked field potentials were recorded in the superficial lumbar spinal cord in response to supramaximal electrical stimulation of the sciatic nerve. Anesthesia was maintained with isoflurane in one-third O2 and two-thirds N2O. Xe equilibrated at a concentration of 600 microL/mL of Lipofundin MCT(R) 20%, (n = 5) or solvent alone (n = 3), and Xe equilibrated at a concentration of 100 microL/mL of normal saline (n = 7) or saline alone (n = 7) was given IV under apnea. High-frequency stimulation of the sciatic nerve was applied 60 min after the injection of Xe-containing formulations or solvents [to induce LTP].

RESULTS

High-frequency stimulation potentiated C-fiber-evoked potentials to 156% +/- 14% (mean +/- sem) of control. Low-dose Xe in saline 0.9% blocked the induction of LTP. High-dose Xe equilibrated in MC(R) 20% showed no additional effect when compared with the solvent, which blocked the induction of LTP.

CONCLUSION

Low-dose Xe in saline 0.9% revealed no antinociceptive, but preventive, action in spinal pain pathways.

Pharmacologic modulation of skeletal muscle metabolism: a microdialysis study

Microdialysis is a valuable tool to measure tissue responses. We hypothesized that skeletal muscle metabolism can be modulated by microdialysis applied drugs which alter cytosolic calcium concentration. With approval of the local animal care committee, the hind limbs of sacrificed male Sprague Dawley rats were perfused either with Ringer's solution or with dantrolene 1 microM at 30 ml hr(-1) and 21 degrees. Microdialysis probes in both hind limbs were perfused at 1 microl min(-1) either with sorbitol 80 mM, calcium 20 mM, 40 mM, 80 mM, caffeine 40 mM, 80 mM, and halothane 10 vol% respectively, and at the contralateral adductor muscle with Ringer as control. Lactate was measured spectrophotometrically in the dialysate at 15 min. intervals. Lactate levels as measured by intramuscular microdialysis were not influenced by intramuscular application of sorbitol 80 mM compared to control measurements with Ringer's solution. Local application of calcium 20 mM, 40 mM, 80 mM, caffeine 40 mM, 80 mM, and halothane 10 vol% via microdialysis increased lactate concentrations, while organ perfusion by dantrolene 1 microM reduced the caffeine-induced lactate increase. Modulation of intramuscular lactate metabolism by exogenous compounds via microdialysis probes generates new insights in skeletal muscle metabolism.

The Dose-Response Relationship and Regional Distribution of Lactate After Intramuscular Injection of Halothane and Caffeine in Malignant Hyperthermia-Susceptible Pigs

We hypothesized that IM halothane and caffeine injection increases local lactate concentration dose-dependently in malignant hyperthermia-susceptible (MHS) and nonsusceptible (MHN) pigs and that the hypermetabolic reaction measured by regional distribution of lactate and carbon dioxide is limited to a small muscle volume. Microdialysis probes were placed in the hindlimbs of 7 MHS and 7 MHN pigs and perfused with Ringer's solution. After equilibration, boluses of increasing halothane and caffeine concentrations were injected. For the second hypothesis regarding regional distribution, microdialysis probes were positioned in 7 MHS and 6 MHN pigs at the injection site for halothane and caffeine and at a distance of 10 mm and 25 mm. Lactate was measured in the dialysate by spectrophotometry. In addition, PCO2 was measured in the halothane experiments. Halothane and caffeine increased IM lactate dose-dependently in MHS pigs significantly more than in MHN pigs. Lactate and PCO2 were increased only at the injection site but not at 10 mm and 25 mm distance. MH susceptibility leads to a leftward shift of the dose-response curve for IM lactate after local injection of halothane and caffeine. The increase of lactate and carbon dioxide levels after local MH trigger injection is limited to a small area around the probe.

The efficacy and safety of intravenous emulsified isoflurane in rats

Although direct IV injection of liquid volatile anesthetics is usually lethal, anesthesia using emulsified halothane and isoflurane without adverse effects has been safely induced in animals. We identified the safe concentration of emulsified volatile anesthetic preparations and determined the dose-response relationship of IV emulsified isoflurane and propofol in rats. Liquid/gas partition coefficients of desflurane, sevoflurane, isoflurane, enflurane, and halothane in 20% and 30% Intralipid were measured and used to calculate their saturated concentrations. Unsaturated emulsified isoflurane was prepared by adding liquid isoflurane to 30% Intralipid. The loss of forepaw righting reflex was taken as induction of anesthesia, and disappearance of electrocardiogram was taken as death. The median effective induction dose (ED50) and median lethal dose (LD50) of emulsified isoflurane were 0.072 and 0.216 mL/kg liquid isoflurane, respectively. The ED50 and LD50 of propofol were 5.89 mg/kg and 18.19 mg/kg, respectively. Time to return of forepaw righting reflex after injection of emulsified isoflurane (38 +/- 18 s) was significantly shorter than with propofol (101 +/- 62 s; P < 0.05). Anesthesia was successfully induced in rats by IV emulsified isoflurane with a comparable safety index and certain safety factor as propofol. Recovery of anesthesia after IV emulsified isoflurane was faster than with propofol.

Lipid emulsions reduce NMDA-evoked currents

Membrane currents conducted by the NMDA receptor channels were investigated in cultured cortical neurons and TsA cells transfected with NR1-1a/NR2A subunits of the NMDA receptor. The whole-cell recording technique was used. Current transients evoked by bath application of NMDA for 5 s were characterized by a fast peak and a slow decay to 46.1 +/-15.5% of the peak level at the end. When NMDA was applied in combination with various lipid emulsions (Intralipid, ClinOleic, Lipofundin or Abbolipid, the NMDA-induced currents were reduced, although this reduction did not affect the fast peak, it did affect the decay phase. The amount of reduction depended on the concentration of the lipids (in the case of Abbolipid diluted at 1:40, the current at the end of the 5-s drug application was approximately 2/3 of control). When Abbolipid was applied 40 s before NMDA, peak and late current were reduced to approximately 2/3. The effect of current reduction was the same at either of the two chosen membrane potentials (-80 and +40 mV) which indicates that the effect was not mediated by contamination of the emulsions with Mg(2+). The current reduction produced by Abbolipid was about the same in native neuronal cells and in TsA cells expressing the NR1-1a/NR2A subunits. The current-reducing effect of the lipid emulsions may add to the anesthetic, analgesic and neuroprotective effects seen with hypnotics administered by way of lipid carriers.

Xenon incorporated in a lipid emulsion inhibits NMDA receptor channels

BACKGROUND

Over the past decade hyperpolarized (129)xenon incorporated in lipid emulsions has been studied for the purpose of imaging enhancement in radiology. Xenon (Xe), a NMDA (N-methyl-D-aspartate)-receptor antagonist, has neuroprotective properties even at subanesthetic concentrations. Thus, its intravenous administration for this purpose deserves further evaluation. In this study, we investigated in an in vitro model the effect of Xe, incorporated in a lipid emulsion (Lipofundin MCT(R) 20%), on the NMDA receptor channel of cortical neurons of the mouse.

METHODS

Pulses of 50 micro M of NMDA solution were extracellularly applied to the cells for 10 s, and the elicited membrane currents (I) were recorded while the membrane potential (V) was clamped at -80 mV. Either Lipofundin MCT(R) 20% or aqueous solution was loaded with Xe and applied simultaneously with the NMDA pulses by means of a multibarreled pipette attached to a battery of infusion-pumps.

RESULTS

Xenon equilibrated in Lipofundin(R) caused a concentration-dependent and reversible inhibition of NMDA-induced currents (maximal Xe content [Xemax]: 190 micro l ml-1). The inhibitory effect was equivalent compared with the effect of Xe dissolved in aqueous solution (Xemax: 89 micro l ml-1) even though the Xe content of the lipid solution was almost doubled. Further enhancement of the Xe content by saturating both the lipid emulsion and the aqueous solutions with Xe (Xemax: 256 micro l ml-1) did not increase the inhibitory action on NMDA-receptors.

CONCLUSION

The data demonstrate that Xe dissolved in Lipofundin MCT(R) 20% inhibits NMDA-receptors. Lipid emulsions enriched with Xe may serve as a carrier and a reservoir for Xe.