Does Equi-Minimum Alveolar Concentration Value Ensure Equivalent Analgesic or Hypnotic Potency?: A Comparison between Desflurane and Sevoflurane.

BACKGROUND: Minimum alveolar concentration (MAC) has traditionally been used to compare the potency of volatile anesthetics. However, as it reflects the spinal mechanism of immobility rather than the cerebral mechanism of analgesia and hypnosis, it is doubtful that equi-MAC connotes equivalent analgesic or hypnotic potency. The level of analgesia and hypnosis can be assessed using surgical pleth index and bispectral index (BIS) values, respectively. This study was designed to compare the surgical pleth index and BIS values produced by equi-MAC of desflurane and sevoflurane in patients undergoing single-agent volatile anesthesia. METHODS: Eighty-nine patients were randomly allocated to two groups receiving either desflurane (n = 44) or sevoflurane (n = 45). Anesthesia was only maintained with assigned volatile anesthetic of age-corrected 1.0 MAC. Surgical pleth index values as an analgesic estimate and BIS values as a hypnotic estimate were obtained under standard tetanic stimulation. RESULTS: Post-stimulation surgical pleth index values (mean ± SD), the primary outcome, were significantly lower for the desflurane group than those for the sevoflurane group (49 ± 10 vs. 64 ± 14, difference, 15 [95% CI, 10 to 20], P < 0.001). The desflurane group showed significantly lower poststimulation BIS values (median [interquartile range]) than the sevoflurane group (36 [31 to 41] vs. 41 [38 to 47], difference, 6 [95% CI, 2 to 9], P = 0.001). CONCLUSIONS: During a steady-state of 1.0 MAC, desflurane and sevoflurane did not cause similar surgical pleth index and BIS values under the standardized nociceptive stimulus. These findings suggest that equi-MAC of desflurane and sevoflurane may not ensure equivalent analgesic or hypnotic potency. VISUAL ABSTRACT: An online visual overview is available for this article at http://links.lww.com/ALN/B726.

Halothane: how should it be used in a developing country?

The anaesthetic agent halothane is still widely used in developing countries including the Islamic Republic of Iran because of its low price. Because of halothane-induced hepatitis, a rare complication, it has been replaced by other inhalation anaesthetics in Western countries; it has been suggested by some Iranian professionals that the Islamic Republic of Iran should do the same. We evaluated various dimensions of this replacement through a literature review to assess the incidence of halothane-induced hepatitis and costs of anaesthetics in the country. We also conducted a questionnaire survey of 30 anaesthesiology/gastroenterology experts about their views on the subject. The results indicate that the incidence of halothane hepatitis in the Islamic Republic of Iran is very low and could mostly be avoided by strict adherence to guidelines. Complete withdrawal of halothane in the Islamic Republic of Iran might not be appropriate at present. Comprehensive cost-effectiveness studies are needed before a decision is made on complete replacement of halothane with other anaesthetics.

Safety and risks of nitrous oxide labor analgesia: a review.

INTRODUCTION: This review of the safety and risks of nitrous oxide (N(2) O) labor analgesia presents results of a search for evidence of its effects on labor, the mother, the fetus, the neonate, breastfeeding, and maternal-infant bonding. Concerns about apoptotic damage to the brains of immature mammals exposed to high doses of N(2) O during late gestation, possible cardiovascular risks from hyperhomocysteinemia caused by N(2) O, a hypothesis that children exposed to N(2) O during birth are more likely to become addicted to amphetamine drugs as adults, and possible occupational risks for those who provide care to women using N(2) O/O(2) labor analgesia are discussed in detail. METHODS: Research relevant to the 4 special concerns and to the effects of N(2) O analgesia on labor and the mother-child dyad were examined in depth. Three recent reviews of the biologic, toxicologic, anesthetic, analgesic, and anxiolytic effects of N(2) O; 3 reviews of the safety of 50% N(2) O/oxygen (O(2) ) in providing analgesia in a variety of health care settings; and a 2002 systematic review of N(2) O/O(2) labor analgesia were used. RESULTS: Nitrous oxide analgesia is safe for mothers, neonates, and those who care for women during childbirth if the N(2) O is delivered as a 50% blend with O(2) , is self-administered, and good occupational hygiene is practiced. Because of the strong correlation between dose and harm from exposure to N(2) O, concerns based on effects of long exposure to high anesthetic-level doses of N(2) O have only tenuous, hypothetical pertinence to the safety of N(2) O/O(2) labor analgesia. DISCUSSION: Nitrous oxide labor analgesia is safe for the mother, fetus, and neonate and can be made safe for caregivers. It is simple to administer, does not interfere with the release and function of endogenous oxytocin, and has no adverse effects on the normal physiology and progress of labor.

Manejo anestésico en paciente pediátrico con síndrome de Hurler / Anesthetic management of pediatric patient with Hurler syndrome

La mucopolisacaridosis (MPS) es un trastorno hereditario degenerativo progresivo, causado por la acumulación excesiva intralisosomal de glicoaminoglicanos en diversos tejidos. Estos cúmulos producen hipertrofia celular, produciendo alteración de las funciones y de la estructura de los tejidos involucrados. El síndrome de Hurler es un tipo de MPS caracterizado por una vía aérea difícil, considerándose la vía aérea más dificil de la anestesia pediátrica. Además pueden presentar retraso mental progresivo y miocardiopatías. Presentamos un caso de un niño de 4 años de edad diagnosticado de síndrome de Hurler sometido a anestesia general para la colocación de un reservorio en yugular interna derecha. Discutimos manejo anestésico de estos pacientes.

Mucopolysaccharidosis (MPS) is a hereditary progressively degenerative disease caused by excessive intralysosomal accumulation of glycosaminoglycans in various tissues. This accumulation causes cellular hypertrophy, altering functions and the structure of the tissues involved. Hurler syndrome is a type of MPS, characterized by a difficult respiratory tract, considered the most problematic one for pediatric anesthesia; it may also present progressive mental retard and myocardiopathies. We describe a case of a 4-year-old child diagnosed with Hurler syndrome who underwent general anesthesia for placement of a reservoir in his right internal jugular vein. We analyzed the anesthetic handling of these patients.

A mucopolissacaridose (MPS) é uma doença hereditária degenerativa progressiva causada pelo acúmulo intralisossomal excessivo de glicoaminoglicanos em diversos tecidos. Esse acúmulo produz hipertrofia celular, que por sua vez altera as funções e estrutura dos tecidos envolvidos. O síndrome de Hurler é um tipo de MPS caracterizado por uma via aérea difícil, considerada a mais problemática para a anestesia pediátrica, que também pode apresentar retardo mental progressivo e miocardiopatias. Descrevemos o caso de um criança de 4 anos de idade, diagnosticada de síndrome de Hurler e submetida a anestesia geral para a colocação de um dispositivo reservatório na jugular interna direita. Analisamos o manejo anestésico destes pacientes.

[Low flow anaesthesia with isoflurane and sevoflurane in the dog]. / Low-flow-Anästhesie mit Isofluran und Sevofluran beim Hund.

The aim of the present study was to compare the safety and efficacy of sevoflurane and isoflurane during low flow anaesthesia (fresh gas flow (FGF) 14 ml/kg/min) as well as to compare the consumption of both anaesthetics. Data were gathered from 60 dogs assigned for surgery under general anaesthesia with an expected duration of 75 minutes or longer. All dogs were induced with 0.6 mg/kg (maximum 25 mg) l-methadone and 1 mg/kg (maximum 25 mg) diazepam i.v.. Anaesthesia was maintained with isoflurane (group 1) or sevoflurane (group 2) in a mixture with 50% O2 and 50% N2O as carrier gases, under controlled ventilation. Monitoring included electrocardiogram, body temperature, the temperature of in- and exspired gases, arterial oxygen saturation, arterial blood pressure as well as a continuous monitoring of inhaled and exhaled gas concentrations (O2, N2O, CO2, isoflurane, sevoflurane). The consumption of isoflurane and sevoflurane as well as the dogs' recovery times were evaluated for both groups. In all groups the inspired oxygen concentrations ranged above the minimum value of 30 Vol% during low flow anaesthesia, with an arterial oxygen saturation above 97%. End tidal concentration of CO2, heart rate and arterial blood pressure were within the physiological ranges and showed no differences between the two groups. Recovery time was significantly shorter after sevoflurane compared to isoflurane anaesthesia, whilst the consumption of sevoflurane was higher than that of isoflurane. Sevoflurane appears to be as clinically safe as isoflurane in low flow anaesthesia. Even considering that sevoflurane is more expensive than isoflurane, the use of the low flow technique decreases the cost of anaesthesia due to the reduced volatile anaesthetic consumption.

Isoflurane is an effective alternative to ketamine/xylazine/acepromazine as an anesthetic agent for the mouse electroretinogram.

The electroretinogram (ERG) is an essential measure of retinal function for studying mouse models of retinal disease. Ketamine, in combination with xylazine and/or acepromazine, is the most commonly used anesthetic agent. Although it works well in most situations, some fragile mouse strains have high mortality rates with this ketamine cocktail. We compared isoflurane with the ketamine cocktail in a longitudinal study of light-adapted and dark-adapted ERGs in C57BL/6J mice. Waveforms were averaged, oscillatory potentials (OPs) were extracted by digital filtration, and key ERG parameters were analyzed. The ERG waveforms were qualitatively similar with both anesthetics, and the male and female ERG parameters did not show significant differences. For light-adapted ERGs, b-wave amplitude and implicit time, and wavelet index were decreased under isoflurane anesthesia, whereas for dark-adapted ERGs, a- and b-wave implicit times were decreased and wavelet index was increased. The dark-adapted b-wave amplitude showed a significant inverse correlation with animal weight and age. Rod phototransduction gain and the Naka-Rushton n and R (max) parameters were the same for both anesthetics, and only the Naka-Rushton log k parameter was significantly elevated for isoflurane anesthesia. We propose that isoflurane is a satisfactory alternative to the ketamine cocktail for anesthesia in the mouse ERG. Precise quantitative comparisons, however, should only employ study designs using isoflurane versus isoflurane, or ketamine versus ketamine. Moreover, in light of the effects of both isoflurane and the ketamine cocktail on blood glucose levels, it would be prudent to control the fasting state of the animals in quantitative ERG studies.

Sevoflurane: are there differences in products?

Sevoflurane is currently available in the United States from two manufacturers: Ultane (Abbott Laboratories, Inc.) and a generic product, Sevoflurane Inhalation Anesthetic (Baxter Healthcare Corp.). These products are rated therapeutically equivalent by the Food and Drug Administration, but there are some differences. Ultane is made in a single-step synthetic process and generic sevoflurane is manufactured using a three-step process. Ultane contains >300 ppm water and generic sevoflurane contains < or =130 ppm water. Ultane is supplied in a plastic polyethylene naphthalate polymer bottle, while generic sevoflurane is supplied in lacquer-lined aluminum bottles. The manufacturing processes and impurities, sevoflurane degradation resulting from Lewis acid reactions, and suitability of nonglass containers for sevoflurane are discussed.

Minimum alveolar concentration of isoflurane in mechanically ventilated Dumeril monitors.

OBJECTIVE: To determine minimum alveolar concentration (MAC) of isoflurane in mechanically ventilated Dumeril monitors (Varanus dumerili). DESIGN: Prospective study. ANIMALS: 10 healthy adult Dumeril monitors. PROCEDURE: Anesthesia was induced with isoflurane in oxygen delivered through a face mask. Monitors were endotracheally intubated, and end-tidal and inspired isoflurane concentrations were continuously measured. After equilibration at an end-tidal-to-inspired isoflurane concentration ratio of >0.9 for 20 minutes, an electrical stimulus (50 Hz, 50 V) was delivered to the ventral aspect of the tail for up to 1 minute and the monitor was observed for purposeful movement. End-tidal isoflurane concentration was then decreased by 10%, and equilibration and stimulation were repeated. The MAC was calculated as the mean of the lowest end-tidal isoflurane concentration that prevented positive response and the highest concentration that allowed response. A blood sample for blood gas analysis was collected from the tail vein at the beginning and end of the anesthetic period. RESULTS: Mean +/- SD MAC of isoflurane was 1.54 +/- 0.17%. Mean heart rates at the upper and lower MAC values were 32.4 +/- 3 beats/min and 34 +/- 4.5 beats/min, respectively. During the experiment, PaCo2 decreased significantly from 43.1 mm Hg to 279 mm Hg and blood pH and HCO3 concentration increased significantly from 7.33 to 7.64 and from 25.3 to 32.9 mmol/L, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: The MAC of isoflurane in Dumeril monitors was similar to that reported in mammals but lower than values reported in other reptiles. This difference may be reflective of the more advanced cardiovascular physiologic features of monitor lizards.

Professor Joseph Warren Horton (1889-1967): biological engineer.

Joseph Warren Horton graduated with a degree in electrical engineering from the Massachusetts Institute of Technology (MIT) in 1914. He became involved in the early development of electrical measurement devices, televised image transmission, and the detection of underwater sound transmission. In the mid-1930s he was appointed the first leader of the newly created Department of Biological Engineering at MIT and in this position he made major contributions to the application of physics to human physiology, in particular by increasing the safety of explosive inhalational anaesthetic agents.

Minimum alveolar concentration of sevoflurane in spontaneously breathing llamas and alpacas.

OBJECTIVE: To determine the minimum alveolar concentration (MAC) of sevoflurane in spontaneously breathing llamas and alpacas. DESIGN: Prospective study. ANIMALS: 6 healthy adult llamas and 6 healthy adult alpacas. PROCEDURE: Anesthesia was induced with sevoflurane delivered with oxygen through a mask. An endotracheal tube was inserted, and a port for continuous measurement of end-tidal and inspired sevoflurane concentrations was placed between the endotracheal tube and the breathing circuit. After equilibration at an end-tidal-to-inspired sevoflurane concentration ratio > 0.90 for 15 minutes, a 50-Hz, 80-mA electrical stimulus was applied to the antebrachium until a response was obtained (ie, gross purposeful movement) or for up to 1 minute. The vaporizer setting was increased or decreased to effect a 10 to 20% change in end-tidal sevoflurane concentration, and equilibration and stimulus were repeated. The MAC was defined as the mean of the lowest end-tidal sevoflurane concentration that prevented a positive response and the highest concentration that allowed a positive response. RESULTS: Mean +/- SD MAC of sevoflurane was 2.29 +/- 0.14% in llamas and 2.33 +/- 0.09% in alpacas. CONCLUSIONS AND CLINICAL RELEVANCE: The MAC of sevoflurane in llamas and alpacas was similar to that reported for other species.

Use of propofol-isoflurane as an anesthetic regimen for cesarean section in dogs.

OBJECTIVE: To evaluate use of propofol-isoflurane as an anesthetic regimen for cesarean section in dogs and to compare this protocol with epidural analgesia and anesthesia induced with thiopental sodium. DESIGN: Prospective study. ANIMALS: 141 bitches admitted for cesarean section. PROCEDURE: General anesthesia was induced with propofol in 141 dogs undergoing cesarean section. After intubation, anesthesia was maintained by means of inhalation of isoflurane (0.5 to 2.0%), administered in a 65:35 mixture of oxygen:nitrous oxide. After induction, 20 minutes were allowed to elapse before delivery of puppies was begun. Viability of neonates was ascertained immediately after surgery. Owners were interviewed by telephone to determine survival of puppies during the postoperative period. Survival rates from this study were compared with those from cesarean section performed on dogs under epidural analgesia or under general anesthesia induced with thiopental sodium. RESULTS: Induction, maintenance, and recovery were problem free in all bitches. Of 412 puppies delivered by cesarean section, 293 (71%) survived, 13 (3%) were born alive but died within 20 minutes of delivery, and 106 (26%) were stillborn. Survival rate for puppies from dams induced with propofol-isoflurane was similar to that for puppies from dams receiving epidural analgesia. Survival rate for puppies delivered by cesarean section performed on dams under general anesthesia was higher for dams induced with propofol than for dams induced with thiopental sodium. CLINICAL IMPLICATIONS: General anesthesia induced with propofol and maintained with isoflurane is acceptable for performing cesarean section in dogs.

Comparison of two techniques of narcotic-induced anesthesia for use during recording of magnetic motor evoked potentials in dogs.

OBJECTIVE: To compare 2 types of narcotic-induced anesthesia for recording of transcranial magnetic motor evoked potentials (TMMEP) in dogs. DESIGN: The effect of different doses of sufentanil and midazolam and of sufentanil and nitrous oxide on onset latencies and peak-to-peak, amplitudes of TMMEP was evaluated and compared. ANIMALS: 18 neurologically normal dogs. PROCEDURE: Premedication with droperidol and fentanyl. Induction and maintenance of anesthesia either with sufentanil and midazolam or with sufentanil and nitrous oxide. Recording of TMMEP from the extensor carpi radialis muscle of the forelimb and from the cranial tibial muscle of the hind limb. RESULTS: Both types of narcotic anesthesia induced dose-dependent suppression of TMMEP; compared with baseline recordings, latencies increased, amplitudes decreased, and reproducibility became poorer with increasing dose of the anesthetics. Using surgical-depth doses of the anesthetics, TMMEP could still be recorded in all dogs with sufentanil and nitrous oxide, but not with sufentanil and midazolam anesthesia. CONCLUSIONS: Sufentanil and nitrous oxide anesthesia was superior to sufentanil and midazolam anesthesia for TMMEP recording. CLINICAL RELEVANCE: In small animal medicine, and in dogs in particular, spinal cord diseases are among the most frequently encountered neurologic disorders. The development of techniques for recording TMMEP in anesthetized dogs allows noninvasive evaluation of transmission along descending motor pathways of the spinal cord.