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

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.

Exceptionally stable fluorous emulsions for the intravenous delivery of volatile general anesthetics

BACKGROUND

IV delivery of volatile fluorinated anesthetics has a number of potential advantages when compared with the current inhalation method of administration. We reported previously that the IV delivery of sevoflurane can be achieved through an emulsion composed of a linear fluorinated diblock copolymer, a stabilizer, and the anesthetic. However, this original emulsion was subject to particle size growth that would limit its potential clinical utility. We hypothesized that the use of bulkier fluorous groups and smaller polyethylene glycol moieties in the polymer design would result in improved emulsion stability while maintaining anesthetic functionality.

METHODS

The authors prepared emulsions incorporating sevoflurane, perfluorooctyl bromide as a stabilizing agent, and combinations of linear fluorinated diblock copolymer and a novel dibranched fluorinated diblock copolymer. Emulsion stability was assessed using dynamic light scattering. The ability of the emulsions to induce anesthesia was tested in vivo by administering them intravenously to 15 male Sprague-Dawley rats and measuring loss of the forepaw righting reflex.

RESULTS

20% (volume/volume) sevoflurane emulsions incorporating mixtures of dibranched and linear diblock copolymers had improved stability, with those containing an excess of the dibranched polymers displaying stability of particle size for more than 1 yr. The ED50s for loss of forepaw-righting reflex were all similar, and ranged between 0.55- 0.60 ml/kg body weight.

CONCLUSIONS

Hemifluorinated dibranched polymers can be used to generate exceptionally stable sevoflurane nanoemulsions, as required of formulations intended for clinical use. IV delivery of the emulsion in rats resulted in induction of anesthesia with rapid onset and smooth and rapid recovery.

[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.

Fluoropolymer-based emulsions for the intravenous delivery of sevoflurane

BACKGROUND

The intravenous delivery of halogenated volatile anesthetics has been previously achieved using phospholipid-stabilized emulsions, e.g., Intralipid. However, fluorinated volatile anesthetics, such as sevoflurane, are partially fluorophilic and do not mix well with classic nonfluorinated lipids. This effect limits the maximum amount of sevoflurane that can be stably emulsified in Intralipid to 3.5% vol/vol. This is a significant limitation to the potential clinical use of Intralipid-based emulsions.

METHODS

The authors prepared a 20% vol/vol sevoflurane emulsion using a novel fluorinated surfactant and tested its effectiveness and therapeutic index by administering it to male Sprague-Dawley rats via intravenous injection into the jugular vein. The median effective dose to induce anesthesia (ED50), the median lethal dose (LD50), and the therapeutic index (LD50/ED50) were determined. Anesthesia was measured by loss of the forepaw righting reflex.

RESULTS

The ED50 and LD50 values were found to be 0.41 and 1.05 ml emulsion/kg body weight, respectively. These lead to a therapeutic index of 2.6, which compares favorably with previously determined values of emulsified isoflurane, as well as values for propofol and thiopental.

CONCLUSIONS

A novel semifluorinated surfactant was able to considerably increase the maximum amount of stably emulsified sevoflurane compared with Intralipid. These formulations can be used to rapidly induce anesthesia with bolus dosing from which recovery is smooth and rapid.

A minimally invasive metabolic test with intramuscular injection of halothane 5 and 6 vol% to detect probands at risk for malignant hyperthermia

We hypothesised that intramuscular halothane injection increases local Pco(2) concentrations in malignant hyperthermia susceptible (MHS) but not in non-susceptible (MHN) individuals. Pco(2) probes with attached microtubing catheters for halothane injection were placed into the lateral vastus muscle of eight MHS and eight MHN probands. Following equilibration, a single bolus of 200 microl halothane 5 and 6 vol% was injected. Pco(2) was measured spectrophotometrically. Baseline Pco(2) concentrations were similar between groups. Maximum Pco(2) and maximum rate of Pco(2) increase was significantly enhanced by halothane 5 and 6 vol% in MHS compared to MHN probands. Systemic haemodynamic and metabolic parameters did not differ between both groups. Local halothane application induces a hypermetabolic reaction with a significant Pco(2) increase in MHS compared to MHN probands, indicating a susceptibility to malignant hyperthermia. Intramuscular halothane injection with Pco(2) measurement seems to be a suitable method for the development of a minimally invasive metabolic test to diagnose malignant hyperthermia susceptibility.