Intravenous Injection of Liquid Halothane

The Effects of Volatile Anesthetics on Lung Ischemia-Reperfusion Injury: Basic to Clinical Studies

Case reports from as early as the 1970s have shown that intravenous injection of even a small dose of volatile anesthetics result in fatal lung injury. Direct contact between volatile anesthetics and pulmonary vasculature triggers chemical damage in the vessel walls. A wide variety of factors are involved in lung ischemia-reperfusion injury (LIRI), such as pulmonary endothelial cells, alveolar epithelial cells, alveolar macrophages, neutrophils, mast cells, platelets, proinflammatory cytokines, and surfactant. With a constellation of factors involved, the assessment of the protective effect of volatile anesthetics in LIRI is difficult. Multiple animal studies have reported that with regards to LIRI, sevoflurane demonstrates an anti-inflammatory effect in immunocompetent cells and an anti-apoptotic effect on lung tissue. Scattered studies have dismissed a protective effect of desflurane against LIRI. While a single-center randomized controlled trial (RCT) found that volatile anesthetics including desflurane demonstrated a lung-protective effect in thoracic surgery, a multicenter RCT did not demonstrate a lung-protective effect of desflurane. LIRI is common in lung transplantation. One study, although limited due to its small sample size, found that the use of volatile anesthetics in organ procurement surgery involving "death by neurologic criteria" donors did not improve lung graft survival. Future studies on the protective effect of volatile anesthetics against LIRI must examine not only the mechanism of the protective effect but also differences in the effects of different types of volatile anesthetics, their optimal dosage, and the appropriateness of their use in the event of marked alveolar capillary barrier damage.

The Effectiveness and Stability of a 20% Emulsified Sevoflurane Formulation for Intravenous Use in Rats

BACKGROUND

Halogenated volatile anesthetics can be safely and rapidly administered to animals and humans using emulsion formulations. However, they must be administered simultaneously with a high dose of lipids. Increasing the concentration of volatile anesthetics may solve this clinical issue. Moreover, careful observation is needed when the emulsion is injected because anaphylactic reactions have been reported.

METHODS

We prepared a 20% sevoflurane lipid emulsion and administered it to 69 male Sprague-Dawley rats via the tail vein. The median effective dose (ED50) for the loss of righting reflex and the median lethal dose (LD50) were determined. ED50 and LD50 values were calculated using nonlinear regression, and data were fitted with a cumulative Gaussian model using GraphPad Prism. Measurements of vital signs and evaluation of the presence of adverse effects associated with continuous infusion of emulsions were verified. Stability of the emulsion was assessed by measuring particle size at 365 days and sevoflurane concentrations after opening the vial at 180 minutes.

RESULTS

The ED50 and LD50 were 0.47 mL/kg (95% confidence interval [CI], 0.46-0.48) and 1.13 mL/kg (95% CI, 1.07-1.18), respectively. The therapeutic index (LD50/ED50) was 2.41 (95 CI%, 2.23-2.59), which compares favorably with therapeutic index of a fluoropolymer-based emulsion of sevoflurane, propofol, and thiopental. There were no adverse effects associated with the continuous infusion of emulsions. Particle size of the emulsion at 365 days after preparation was 78.9 ± 3.8 nm (±SD), and sevoflurane concentration at 180 minutes after opening the vial was 19.0% ± 0.6% (±SD).

CONCLUSIONS

We prepared a 20% sevoflurane lipid emulsion using caprylic triglyceride (i.e., medium-chain triglyceride). In rats, this emulsion was an effective anesthetic and was not associated with adverse events. The emulsion was stable after consecutive evaluation for 365 days and for 180 minutes after the vial was opened.

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.

The anesthetic and physiologic effects of an intravenous administration of a halothane lipid emulsion (5% vol/vol)

The i.v. administration of < or = 9 mL of nonvaporized liquid halothane causes significant pulmonary damage, cardiovascular decompensation, and death. To determine whether liquid halothane mixed in a lipid emulsion would alter these toxic effects, six swine were evaluated in a randomized cross-over study. The pulmonary, analgesic, hemodynamic, and histopathologic effects of liquid halothane (25 mL) mixed with a liquid carrier (475 mL, Liposyn III 20%) and administered by constant infusion were compared with halothane administered by a calibrated vaporizer. Three swine received the halothane lipid emulsion (HLE), followed by inhaled halothane. Three additional swine received inhaled halothane, followed by the HLE. There were no changes in pulmonary compliance or arterial blood gases during or after the administration of equivalent volumes of halothane (13.75 mL) either by infusion of HLE or by inhalation of halothane. The end-tidal halothane concentration for the minimum alveolar anesthetic concentration was 0.79% +/- 0.08% during HLE administration and 1.13% +/- 0.12% for inhaled halothane (P < 0.001). Hemodynamic variables and blood halothane levels by gas chromatography were measured at end-tidal concentrations of 0.6%, 1.2%, and 1.8%. Blood halothane levels (mg/mL) were significantly higher (P < 0.05) after the administration of HLE at end-tidal halothane concentrations of 1.2% (0.49 +/- 0.19 vs 0.82 +/- 0.18) and 1.8% (0.79 +/- 0.17 vs 1.29 +/- 0.34). When compared at equivalent blood levels, HLE caused fewer changes in the left ventricular end-diastolic pressure, mean arterial pressure, and dP/dt than inhaled halothane. There was no evidence of pulmonary histopathologic damage 4-8 h after the infusion of 500-700 mL of HLE. This novel method of delivery of a volatile anesthetic seems to lack the toxicity of direct i.v. administration of liquid halothane. It may be a useful alternative to traditional administration via a vaporizer.

IMPLICATIONS

Halothane causes pulmonary dysfunction and death when given i.v. in liquid form. Six swine received a halothane lipid emulsion i.v. to evaluate the anesthetic and physiologic effects. No pulmonary toxicity or deaths were associated with the halothane lipid emulsion. The anesthetic profile was similar to delivery of halothane via a vaporizer.

Anaesthesia by intravenous emulsified isoflurane in mice

An emulsion of isoflurane in Intralipid for intravenous (iv) injection was formulated and its anaesthetic properties determined in mice. The major advantage of iv delivery of volatile agents is to accelerate the induction of anaesthesia by circumventing the anesthetic circuitry and the lung's functional residual capacity. Isoflurane was added to Intralipid in varying concentrations. The ED50 (n = 34) and LD50 (n = 20) were determined by a single iv bolus injection. Anaesthesia was also induced and maintained for 30 min (n = 5) by continuous infusion and the time to emergence was measured. The ED50 and LD50 were 0.7 +/- 0.2 microliter and 2.4 +/- 0.2 microliter of isoflurane equivalent respectively. An average infusion rate of 1.6 +/- 0.4 microliters.min-1 of isoflurane equivalent was required for maintenance following which the average emergence time was 193 +/- 35 secs. The only negative effect was local skin ulceration with an inadvertent interstitial injection. We conclude that iv induction and maintenance with emulsified isoflurane in Intralipid can be carried out with safety and reproducibility in the mouse. Further larger animal studies are warranted assessing the haemodynamic, toxicological, physiochemical and pharmacokinetic characteristics of these and other similar preparations.

Systemic and local toxicity in the rat of methyl tert-butyl ether: a gallstone dissolution agent

Methyl tert-butyl ether (MTBE) is an organic solvent that has been used to dissolve gallstones via a percutaneous transhepatic catheter into the gallbladder. To test whether MTBE might cause serious tissue injury if accidentally infused outside the gallbladder, the effect of MTBE (0.2 ml/kg) injected into the hepatic parenchyma, or administered intravenously or intraperitoneally, was examined in the rat. The toxicity of isopropyl acetate (IPA), an organic solvent with a similar chemical structure, was examined similarly. Intracaval injection of MTBE caused the highest mortality (100%). Mortality was less (59%) after intrahepatic injection and still less (17%) after peripheral vein injection. Most animals died instantaneously from cardiorespiratory arrest. Almost all animals that were injected with MTBE intrahepatically or intravenously showed localized areas of congestion, hemorrhage, and interstitial edema in the lungs. These changes were more severe in rats which survived for 24 hr than in those which died sooner. In those rats receiving intrahepatic injections, most rats which survived for 24 hr had liver necrosis at the site of injection. Intraperitoneal injection of MTBE produced 100% survival with only 1/5 rats showing a mild pulmonary injury at autopsy. IPA had toxic effects similar to those evoked by MTBE. To test whether tumor necrosis factor was involved in organ injury, serum levels were measured; they remained unchanged. These experiments indicate that two organic solvents, MTBE and IPA, are cytotoxic to local tissues and cause severe, and often fatal, lung damage when infused into a central vein. Less toxicity occurred if solvents were given into a peripheral or portal vein or intraperitoneally.(ABSTRACT TRUNCATED AT 250 WORDS)