Median effective dose of isoflurane, sevoflurane, and desflurane in green iguanas

OBJECTIVE: To determine the median effective dose (ED(50); equivalent to the minimum alveolar concentration [MAC]) of isoflurane, sevoflurane, and desflurane for anesthesia in iguanas. ANIMALS: 6 healthy adult green iguanas. PROCEDURE: In unmedicated iguanas, anesthesia was induced and maintained with each of the 3 volatile drugs administered on separate days according to a Latin square design. Iguanas were endotracheally intubated, mechanically ventilated, and instrumented for cardiovascular and respiratory measurements. During each period of anesthesia, MAC was determined in triplicate. The mean value of 2 consecutive expired anesthetic concentrations, 1 that just permitted and 1 that just prevented gross purposeful movement in response to supramaximal electrical stimulus, and that were not different by more than 15%, was deemed the MAC. RESULTS: Mean +/- SD values for the third MAC determination for isoflurane, sevoflurane, and desflurane were 1.8 +/- 0.3%, 3.1 +/- 1.0%, and 8.9 +/- 2.1% of atmospheric pressure, respectively. The MAC for all inhaled agents was, on average, 22% greater for the first measurement than for the third measurement. CONCLUSIONS AND CLINICAL RELEVANCE: Over time, MACs decreased for all 3 agents. Final MAC measurements were similar to values reported for other species. The decrease in MACs over time may be at least partly explained by limitations of anesthetic uptake and distribution imposed by the reptilian cardiorespiratory system. Hence, for a constant end-tidal anesthetic concentration in an iguana, the plane of anesthesia may deepen over time, which could contribute to increased morbidity during prolonged procedures.     

Determination of the minimum alveolar concentration of isoflurane in llamas

OBJECTIVE: To determine the minimum alveolar concentration (MAC) of isoflurane (ISO) in llamas. STUDY DESIGN: Prospective study. ANIMALS: Eight adult neutered male llamas (9 +/- 1 years [x +/- SD], 177 +/- 29 kg). METHODS: Anesthesia was induced and maintained in otherwise unmedicated llamas with a mixture of ISO in oxygen administered through a standard small-animal, semi-closed circle system using an out-of-circle, agent-specific vaporizer. The time from mask placement to intubation was recorded. Inspired and end-tidal (ET) ISO was sampled continuously. At each anesthetic concentration, a constant ET ISO was maintained for at least 20 minutes before application of a noxious electrical stimulus (50 volts, 5 Hz, 10 ms for up to 1 minute). A positive or negative response to the stimulus was recorded, and ET ISO then increased (if positive response) or decreased (if negative response) by 10% to 20%. Individual MAC was the average of multiple determinations. Body temperature was maintained at 37 +/- 1 degrees C. Selected cardiopulmonary variables (heart rate [HR], respiratory rate [RR], arterial blood pressure [ABP]) and ET ISO were recorded at hourly intervals from first ISO. Arterial blood was collected for pH, PCO2, PO2 analysis and measurement of packed cell volume (PCV) and total protein (TP) at 2 hour intervals. Following MAC determination, the anesthetic was discontinued and llamas were allowed to recover. Duration and quality of recovery were noted. RESULTS: The time from start of induction by mask to completion of intubation took 19.1 +/- 4.8 minutes. The MAC of ISO corrected to one atmosphere at sea level (barometric pressure 760 mm Hg) in these llamas was 1.05 +/- 0.17%. Mean ABP increased from 70 +/- 26 mm Hg at the end of the first hour of anesthesia to 102 +/- 7 mm Hg measured at the end of the sixth hour of anesthesia. ET ISO decreased from 2.06 +/- 0.10% to 1.27 +/- 0.07% over the same time period, but MAC did not change with time. The duration from first ISO to discontinuation of ISO averaged 6.19 +/- 0.9 hours. Animals were able to support their heads in a sternal posture at 23 +/- 10 minutes, and stood 62 +/- 26 minutes following discontinuation of the anesthetic. CONCLUSION: The MAC for ISO is similar to, but slightly lower than, values reported for other species. CLINICAL RELEVANCE: Knowledge of MAC may facilitate appropriate clinical use and provide the basis for future investigation of ISO in llamas.     

The Minimum Alveolar Concentration of Desflurane in Cats

Eight adult cats, 4 male and 4 female, (3.5 ± 0.9 [SD] kg) were used to determine the minimum alveolar concentration (MAC) of desflurane. Desflurane (DES) anesthesia was induced in a 20 L chamber with an oxygen inflow of 10 L/min and the DES vaporizer set at 18%. After 3.5 ± 0.5 min, the cats were removed from the chamber and anesthesia was maintained via mask (14% DES, 3L/min O₂) until successful intubation. Anesthesia was maintained with DES in oxygen at a flow of at least 200 mL/kg/min through a nonrebreathing circuit. The time from the start of induction to completion of intubation was 6.2 ± 1.1 min. Esophageal temperature was maintained between 37.8°C and 38.6°C. Hand-collected end-tidal gas samples were obtained from a catheter positioned inside the lumen of the endotracheal tube. Inspired and end-tidal DES concentrations were measured with a Biochem 8100 anesthetic agent monitor that was calibrated with known gas standards and modified to accept hand-collected samples. A constant alveolar concentration of DES was maintained for at least 15 minutes, then a clamp was applied to the tail and the cat observed for gross purposeful movement. The end-tidal DES was then increased (if a positive response) or decreased (if a negative response) by 20% and the test repeated after 15 minutes of constant conditions. The final iteration was 10%. The MAC of DES in these cats was 9.79 ± 0.70 vol %. The F_A/F_I ratio for desflurane was always greater than 0.97.     

Evaluation of induction characteristics and hypnotic potency of isoflurane and sevoflurane in healthy dogs

OBJECTIVE: To determine induction characteristics and the minimum alveolar concentration (MAC) at which consciousness returned (MACawake) in dogs anesthetized with isoflurane or sevoflurane. ANIMALS: 20 sexually intact male Beagles. PROCEDURES: In experiment 1, 20 dogs were randomly assigned to have anesthesia induced and maintained with isoflurane or sevoflurane. The MAC at which each dog awoke in response to auditory stimulation (MACawake-noise) was determined by decreasing the end-tidal concentration by 0.1 volume (vol %) every 15 minutes and delivering a standard audible stimulus at each concentration until the dog awoke. In experiment 2, 12 dogs received the same anesthetic agent they were administered in experiment 1. After duplicate MAC determination, the end-tidal concentration was continually decreased by 10% every 15 minutes until the dog awoke from anesthesia (MACawake). RESULTS: Mean induction time was significantly greater for isoflurane-anesthetized dogs (212 seconds), compared with the sevoflurane-anesthetized dogs (154 seconds). Mean+/-SD MACawake-noise was 1.1+/-0.1 vol % for isoflurane and 2.0+/-0.2 vol % for sevoflurane. Mean MAC was 1.3+/-0.2 vol % for isoflurane and 2.1+/-0.6 vol % for sevoflurane, and mean MACawake was 1.0+/-0.1 vol % for isoflurane and 1.3+/-0.3 vol % for sevoflurane. CONCLUSIONS AND CLINICAL RELEVANCE: Sevoflurane resulted in a more rapid induction than did isoflurane. The MACawake for dogs was higher than values reported for both agents in humans. Care should be taken to ensure that dogs are at an appropriate anesthetic depth to prevent consciousness, particularly when single-agent inhalant anesthesia is used.     

The effect of the duration of propofol administration on recovery from anesthesia in cats

OBJECTIVE: To determine the effect of induction, a 30-minute, and a 150-minute infusion of propofol on the rate of recovery in cats. STUDY DESIGN: Randomized, cross-over, prospective experimental study. ANIMALS: Six healthy adult spayed female cats (mean 4.3, range 2-7 years old) weighing 3.9 +/- 0.5 kg. METHODS: Cats received each of three treatments: anesthetic induction with propofol (T1), induction followed by a 30-minute infusion (T30) and induction followed by a 150-minute infusion (T150). Propofol infusions were increased or decreased to maintain a sluggish pedal withdrawal reflex. Animals were monitored throughout the anesthetic period and during the recovery. Venous blood samples were collected from a central venous catheter before anesthesia and at 30 minutes for the 30-minute infusion and at 30, 60, 90, 120 and 150 minutes for the 150-minute infusion. The ability of the cat to lift its head, crawl, stand and walk without ataxia was recorded at 5, 10, 20, 40, 60, 80, 120, 160, 180, 210 and 240 minutes after the completion of propofol administration. Data from physiological values were analyzed using either a Student's t-test (30-minute infusion) or an anova (150-minute infusion). A nonparametric Friedman test (and post-hoc Tukey's Studentized range test) was used to determine whether there were differences in the time taken to recover. Results were considered significant if p < 0.05. RESULTS: Time taken to walk without ataxia was significantly greater in T150 (148 +/- 40 minutes) compared with T1 (80 +/- 15 minutes) and T30 (74 +/- 26 minutes). (No other recovery times were significantly different). Anesthesia with propofol was accompanied by a moderate but significant respiratory depression and a decrease in PCV and total protein. CONCLUSIONS AND CLINICAL RELEVANCE: Prolonged anesthesia with propofol in healthy cats may be associated with a delayed recovery.     

Anesthetic Potency of Desflurane in the Horse: Determination of the Minimum Alveolar Concentration

Objective — To determine the minimum alveolar concentration (MAC) of desflurane (DES) in the horse.
Study Design — Prospective study.
Animals — Six healthy adult horses (three males and three females) weighing 370 ±16 kg and aged 9 ±2 years old.
Methods — Anesthesia was induced with DES vaporized in oxygen via a face mask connected to a large-animal, semiclosed anesthetic circle system. The horses were endotracheally intubated and positioned in right lateral recumbency. Inspired and end-tidal DES were monitored using a calibrated Ohmeda RGM 5250 multigas analyzer (Ohmeda-BOC, Spain). The MAC of desflurane that prevented gross purposeful movement in response to 60 seconds of noxious electrical stimulation of oral mucous membranes was determined.
Results — The time from the start of DES administration to lateral recumbency was 6.1 ±0.9 min. The MAC of DES in these horses was 7.6 ±0.4%. Time required for the animal to regain sternal recumbency after 98 ±4 minutes of anesthesia was 6.6 ±0.5 minutes and the time to standing was 14.3 ±2.7 minutes.
Conclusions — The MAC of desflurane in these horses was 7.6 ±0.4%. DES provided a rapid induction to, and recovery from, anesthesia.
Clinical Relevance — Desflurane offers the potential for more precise control during anesthesia, and may allow a faster and uneventful recovery. It is important to know the MAC of an inhalant to use it clinically.     

Assessment of the relationship of bispectral index values, hemodynamic changes, and recovery times associated with sevoflurane or propofol anesthesia in pigs

OBJECTIVE: To evaluate bispectral index (BIS) values in pigs during anesthesia maintained with sevoflurane-fentanyl or propofol-fentanyl as a predictor of changes in hemodynamic parameters and duration of recovery from anesthesia. ANIMALS: 12 pigs. PROCEDURE: Pigs were randomly allocated to undergo 1 of 2 anesthetic regimens. Anesthesia was induced with propofol (2 mg/kg, i.v.); 6 pigs were administered sevoflurane via inhalation (1 minimum alveolar concentration [MAC] at a fresh gas flow rate of 3 L/min; group I), and 6 were administered propofol (11 mg/kg/h, i.v.; group II). All pigs received fentanyl (2.5 mg/kg, i.v., q 30 min). After abdominal surgery, pigs were allowed to recover from anesthesia. Cardiovascular variables and BIS values were recorded at intervals throughout the procedure; duration of recovery from anesthesia was noted. RESULTS: No correlation was established between arterial blood pressure and BIS and between heart rate and BIS. Mean BIS at discontinuation of administration of the anesthetic agent was greater in group-II pigs (65.2 +/- 10.6 minutes) than in group-I pigs (55.8 +/- 2.9 minutes). However, recovery from anesthesia was significantly longer in group II (59.80 +/- 2.52 minutes) than in group I (9.80 +/- 2.35 minutes). CONCLUSIONS AND CLINICAL RELEVANCE: In swine anesthetized with sevoflurane or propofol and undergoing abdominal surgery, the BIS value derived from an electroencephalogram at the end of anesthesia was not useful for predicting the speed of recovery from anesthesia. Moreover, BIS was not useful as a predictor of clinically important changes in arterial blood pressure and heart rate in those anesthetized pigs.     

Prolonged anesthesia with desflurane and fentanyl in dogs during conventional and laparoscopic surgery

OBJECTIVE: To determine the effects of prolonged anesthesia with desflurane in dogs undergoing laparotomy or abdominal laparoscopy. DESIGN: Randomized prospective study. ANIMALS: 20 adult mixed-breed dogs. PROCEDURE: Dogs were randomly assigned to 1 of 2 groups with 10 dogs/group. Anesthesia was induced with propofol and maintained with desflurane and fentanyl, and pyloroplasty was performed. In 10 dogs, a ventral midline laparotomy was performed; in the other 10, abdominal laparoscopy was performed. Dogs were monitored for cardiovascular and respiratory responses (ECG, oxygen saturation [SpO2], arterial blood pressure, rectal temperature, end-tidal partial pressure of carbon dioxide [PETCO2], and expired desflurane concentration). Recovery times were recorded. RESULTS: Mean +/- SD duration of anesthesia was 201 +/- 25 minutes for dogs undergoing laparotomy and 287 +/- 15 minutes for dogs undergoing laparoscopy. Anesthesia was accompanied by hypotension that was less severe in dogs undergoing laparoscopy. Heart rate did not vary significantly during anesthesia. The SpO2 was > 97% in all dogs at all times, and PETCO2 remained within reference limits. Recovery times for dogs that underwent laparotomy were not significantly different from those for dogs that underwent laparoscopy. Mean +/- SD time to standing was 13.6 +/- 2.4 minutes for dogs that underwent laparotomy and 12.5 +/- 2.9 minutes for dogs that underwent laparoscopy. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that induction of anesthesia with propofol and maintenance with desflurane and fentanyl is safe in dogs undergoing abdominal surgery.     

The influence of butorphanol dose on characteristics of xylazine-butorphanol-propofol anesthesia in horses at altitude

OBJECTIVE: To characterize behavioral and physiological responses to short-term, unsupplemented intravenous (IV) anesthesia in healthy horses at high altitude (2240 m), and to test the hypothesis that the dose of butorphanol modifies the response of the horse to propofol anesthesia following xylazine pre-medication. STUDY DESIGN: Randomized prospective butorphanol dose cross-over experimental design. Animals Eight healthy horses, 13 +/- 6 (mean +/- SD) years of age, and weighing 523 +/- 26 kg. METHODS: Each horse was anesthetized three times with at least 3 weeks between each anesthesia. After collecting pre-drug data, xylazine (0.5 mg kg(-1)) was given IV. Five minutes later butorphanol was given IV according to a randomized order of three doses: 0.025, 0.05 and 0.075 mg kg(-1). Five minutes later, anesthesia was induced with propofol, 2 mg kg(-1) IV. Data on heart rate (HR) and respiratory rate (f(r)), mean arterial blood pressure, P(a)O(2), P(a)CO(2) and pH(a) were collected before, during and for 60 minutes following anesthesia, and quality of induction and recovery was scored. RESULTS: The pre-drug values for the three butorphanol groups did not differ. The combined pre-drug values from the 24 studies were HR, 33 +/- 7 beats minute(-1); f(r), 11 +/- 3 breaths minute(-1); P(a)O(2), 67 +/- 7 mmHg; P(a)CO(2), 36 +/- 4 mmHg; and pH(a), 7.42 +/- 0.04. Five minutes after anesthetic induction P(a)O(2) decreased and P(a)CO(2) increased 14.5 +/- 7.7 and 5.1 +/- 4.9 mmHg, respectively, but returned to pre-drug levels within 15 minutes of anesthetic recovery. There were no significant butorphanol dose-related differences in physiological results, anesthetic induction and recovery quality scores or recovery time. CONCLUSIONS AND CLINICAL RELEVANCE: Dose of butorphanol did not markedly influence study results. Notably, low P(a)O(2) values related to geographic location of study and general anesthesia indicates a narrow margin of error for hypoxemia-related complications in anesthetized horses breathing unsupplemented air at high altitude.     

The effect of hypovolemia due to hemorrhage on the minimum alveolar concentration of isoflurane in the dog

OBJECTIVE: To determine the effect of hypovolemia on the minimum alveolar concentration (MAC) of isoflurane in the dog. STUDY DESIGN: Randomized, cross-over trial. ANIMAL POPULATION: Six healthy intact mixed breed female dogs weighing 18.2-29.0 kg. METHODS: Dogs were randomly assigned to determine the MAC of isoflurane in a normovolemic or hypovolemic state with a minimum of 18 days between trials. On both occasions, anesthesia was initially induced and maintained for 40 minutes with isoflurane delivered in oxygen while vascular catheters were placed in the cephalic vein and dorsal metatarsal artery. In dogs assigned to the hypovolemic group, 30 mL kg(-1) of blood was removed at 1 mL kg(-1) minute(-1) from the arterial catheter. All dogs were allowed to recover from anesthesia. Thirty minutes after the discontinuation of isoflurane, anesthesia was re-induced with isoflurane in oxygen delivered by face mask. The tracheas were intubated, and connected to an anesthetic machine with a Bain anesthetic circuit. Mechanical ventilation was instituted at a rate of 10 breaths minute(-1) with the tidal volume set to deliver 10-15 mL kg(-1). Airway gases were monitored continuously and tidal volume was adjusted to maintain an end-tidal carbon dioxide level of 35-40 mmHg (4.67-5.33 kPa). Body temperature was maintained at 37-38 degrees C (98.6-100.4 degrees F). The MAC determination was performed using an electrical stimulus applied to the toe web and MAC was defined as the mean value of end-tidal isoflurane between the concentrations at which a purposeful movement did and did not occur in response to the electrical stimulus. The MAC values were compared between groups using a Student's t-test. RESULTS: The MAC of isoflurane was significantly less in hypovolemic dogs (0.97 +/- 0.03%) compared with normovolemic dogs (1.15 +/- 0.02%) (p < 0.0079). CONCLUSIONS AND CLINICAL RELEVANCE: The MAC of isoflurane is reduced in dogs with hypovolemia resulting from hemorrhage. Veterinarians should be prepared to deliver a lower percentage of isoflurane to maintain anesthesia in hypovolemic dogs during diagnostic and therapeutic procedures.     

The cardiac anesthetic index of isoflurane in green iguanas

OBJECTIVE: To determine the cardiac anesthetic index (CAI) of isoflurane in green iguanas and whether butorphanol affected the CAI. DESIGN: Prospective randomized controlled trial. ANIMALS: 7 healthy mature iguanas. PROCEDURE: In 5 iguanas, CAI was determined after induction of anesthesia with isoflurane alone, and in 5 iguanas, CAI was determined after induction of anesthesia with isoflurane and IM administration of butorphanol (1 mg/kg [0.45 mg/lb]). Three iguanas underwent both treatments. Animals were equilibrated for 20 minutes at 1.5 times the minimum alveolar concentration (MAC) of isoflurane and observed for evidence of cardiovascular arrest. If there was no evidence of cardiovascular arrest, end-tidal isoflurane concentration was increased by 20%, and animals were allowed to equilibrate for another 20 minutes. This process was repeated until cardiovascular arrest occurred or vaporizer output could no longer be consistently increased. The CAI was calculated by dividing the highest end-tidal isoflurane concentration by the MAC. RESULTS: None of the iguanas developed cardiovascular arrest and all survived. Mean +/- SD highest end-tidal isoflurane concentration during anesthesia with isoflurane alone (9.2 +/- 0.60%) was not significantly different from mean concentration during anesthesia with isoflurane and butorphanol (9.0 +/- 0.43%). The CAI was > 4.32. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that the CAI of isoflurane in green iguanas is > 4.32 and not affected by administration of butorphanol. Isoflurane appears to be a safe anesthetic in green iguanas.     

A technique to depress desflurane vapor pressure

OBJECTIVE: To determine whether the vapor pressure of desflurane could be decreased by using a solvent to reduce the anesthetic molar fraction in a solution (Raoult's Law). We hypothesized that such an anesthetic mixture could produce anesthesia using a nonprecision vaporizer instead of an agent-specific, electronically controlled, temperature and pressure compensated vaporizer currently required for desflurane administration. ANIMAL: One healthy adult female dog. PROCEDURE AND RESULTS: Propylene glycol was used as a solvent for desflurane, and the physical characteristics of this mixture were evaluated at various molar concentrations and temperatures. Using a circle system with a breathing bag attached at the patient end and a mechanical ventilator to simulate respiration, an in-circuit, nonprecision vaporizer containing 40% desflurane and 60% propylene glycol achieved an 11.5% +/- 1.0% circuit desflurane concentration with a 5.2 +/- 0.4 (0 = off, 10 = maximum) vaporizer setting. This experiment was repeated with a dog attached to the breathing circuit under spontaneous ventilation with a fresh gas flow of 0.5 L minute(-1). Anesthesia was maintained for over 2 hours at a mean vaporizer setting of 6.2 +/- 0.4, yielding mean inspired and end-tidal desflurane concentrations of 8.7% +/- 0.5% and 7.9% +/- 0.7%, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Rather than alter physical properties of vaporizers to suit a particular anesthetic agent, this study demonstrates that it is also possible to alter physical properties of anesthetic agents to suit a particular vaporizer. However, propylene glycol may not prove an ideal solvent for desflurane because of its instability in solution and substantial-positive deviation from Raoult's Law.     

The effect of general anesthesia and abdominal surgery upon plasma thromboxane B concentrations in horses

OBJECTIVE: To compare the effect of anesthesia alone with anesthesia and abdominal surgery on plasma thromboxane B(2) concentrations in horses. STUDY DESIGN: Non-randomized experimental study. ANIMALS: Six male mixed-bred horses (5-12 years, 350 +/- 18 kg). METHODS: All horses were anesthetized for 2.5 hours using halothane, and a month later abdominal surgery was performed using the same anesthetic technique with a similar duration. The schedule of anesthesia included pre-medication with diazepam (0.1 mg kg(-1) IM), followed by xylazine (2.2 mg kg(-1) IV), and 10 minutes later anesthesia was induced with ketamine hydrochloride (2.2 mg kg(-1) IV). After orotracheal intubation, anesthesia was maintained with halothane. Blood samples for the determination of thromboxane B(2) (TXB(2)) were obtained before, at induction, at 60 minutes after halothane was first inspired, and at recovery from anesthesia as well as at the corresponding stages of the experimental abdominal surgery (before induction, prior to laparotomy, enterectomy, enteroanastomosis, abdominal wall closure). RESULTS: Baseline value for the anesthesia group was 76 +/- 12 pg mL(-1) and increased (p < 0.001) after 1 hour of anesthesia to 265 +/- 40 pg mL(-1). With surgery, the corresponding value was 285 +/- 21 pg mL(-1) (hour 1, p < 0.001) and 210 +/- 28 pg mL(-1) (hour 2, p < 0.001), respectively. These were not different from anesthesia alone. CONCLUSION: The increased concentrations of thromboxane B(2) between 1 and 2.5 hours of halothane anesthesia and during the corresponding stages of the surgical intervention suggested that the anesthetic technique caused a significant increase in thromboxane B(2) and that surgery did not appear to contribute to this response.     

Relationship of bispectral index to minimum alveolar concentration multiples of sevoflurane in cats

OBJECTIVE: To determine the relationship between bispectral index (BIS) and minimum alveolar concentration (MAC) multiples of sevoflurane in cats. ANIMALS: 8 domestic cats. PROCEDURE: Each cat was anesthetized twice with sevoflurane. First, the MAC of sevoflurane for each cat was determined by use of the tail clamp method. Second, cats were anesthetized with sevoflurane at each of 5 MAC multiples administered in random order. Ventilation was controlled, and after a 15-minute equilibration period at each MAC multiple of sevoflurane, BIS data were collected for 5 minutes and the median value of BIS calculated. RESULTS: The mean (+/- SD) MAC of sevoflurane was 3.3 +/- 0.2%. The BIS values at 0.5 MAC could not be recorded as a result of spontaneous movement in all 8 cats. The BIS values at 2.0 MAC were confounded by burst suppression in all 8 cats. Over the range of 0.8 to 1.5 MAC, BIS values decreased significantly with increasing end-tidal sevoflurane concentrations. Mean (+/- SD) BIS measurements were 30 +/- 3, 21 +/- 3, and 5 +/- 2 at 0.8, 1.0, and 1.5 MAC, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Values of BIS are inversely and linearly related to end-tidal sevoflurane concentrations in anesthetized cats, and BIS may be a useful predictor of CNS depression in this species. The consistently low BIS values recorded in this study suggest that clinical BIS end points used to titrate anesthetic agents in humans may not be applicable to cats.     

Cardiopulmonary effects of administration of a combination solution of xylazine, guaifenesin, and ketamine or inhaled isoflurane in mechanically ventilated calves

OBJECTIVE: To compare the cardiopulmonary effects of administration of a solution of xylazine, guaifenesin, and ketamine (XGK) or inhaled isoflurane in mechanically ventilated calves undergoing surgery. ANIMALS: 13 male calves 2 to 26 days of age. Procedures-In calves in the XGK group, anesthesia was induced (0.5 mL/kg) and maintained (2.5 mL/kg/h) with a combination solution of xylazine (0.1 mg/mL), guaifenesin (50 mg/mL), and ketamine (1.0 mg/mL). For calves in the isoflurane group, anesthesia was induced and maintained with isoflurane in oxygen. The rates of XGK infusion and isoflurane administration were adjusted to achieve suitable anesthetic depth. All calves received 100% oxygen and were mechanically ventilated to maintain end-tidal carbon dioxide concentrations from 35 to 40 mm Hg and underwent laparoscopic bladder surgery through an abdominal approach. Cardiopulmonary variables were measured before induction and at intervals up to 90 minutes after anesthetic induction. RESULTS: The quality of induction was excellent in all calves. The XGK requirements were 0.57 +/- 0.18 mL/kg and 2.70 +/- 0.40 mL/kg/h to induce and maintain anesthesia, respectively. Heart rate was significantly lower than baseline throughout the anesthetic period in the XGK group. Systolic arterial blood pressure was significantly higher in the XGK group, compared with the isoflurane group, from 5 to 90 minutes. Cardiac index was lower than baseline in both groups. Differences between groups in cardiac index and arterial blood gas values were not significant. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of XGK resulted in excellent anesthetic induction and maintenance with cardiopulmonary alterations similar to those associated with isoflurane in mechanically ventilated calves.     

Inhalant anesthetic requirement in cats is animal-dependent

Minimum alveolar concentration (MAC) of an inhalant is an indicator of its anesthetic potency. Individuals vary in their sensitivity to anesthetic agents as demonstrated by different individual MAC values. We hypothesized that individual animal sensitivity would be maintained with different inhalant anesthetics. As part of separate studies, six female DSH cats, aged 24 ± 2.5 (mean ± SD) months and weighing 3.5 ± 0.3 kg, were studied similarly on three separate occasions over a 12‐month period to determine the MAC of isoflurane (ISO), sevoflurane (SEVO), and desflurane (DES), respectively. In each study, chamber induction was followed by orotracheal intubation, and anesthesia was maintained via a nonrebreathing circuit. ECG, pulse oximetry, Doppler systolic blood pressure, end‐tidal gases, and esophageal temperature were monitored. End‐tidal gases were hand‐sampled from a catheter whose tip lay level with the distal end of the ET tube. Gases were analyzed by Raman spectrometry and, for each agent, the analyzer was calibrated with at least three gas standards. MAC was determined in triplicate using standard tail‐clamp technique. Data were analyzed by two‐way anova followed by Tukey's test and significant differences were found. Average MACs (%) for ISO, SEVO, and DES were 1.90 ± 0.18, 3.41 ± 0.65, and 10.27 ± 1.06, respectively. Body temperatures, Doppler systolic blood pressure, and SpO₂ were recorded at the time of MAC determinations for ISO, SEVO, and DES were 38.3 ± 0.3, 38.6 ± 0.1, 38.3 ± 0.35 °C; 71 ± 8, 75 ± 16, 88 ± 12 mm Hg; 99 ± 1, 99 ± 1, 99 ± 1%, respectively. Both the anesthetic agent and the individual cat had significant effects on MAC (p = 0.0001 and 0.0185, respectively). MAC varied between individuals and cats were consistent in their order of sensitivity to inhalant anesthetics across the three agents. Within this group of cats, the relationship of individual MAC to the group MAC for each of the three inhalant agents was maintained. This suggests that any individual may be consistently more or less sensitive to a variety of inhalant agents.     

The efficacy of alfaxalone for immersion anesthesia in koi carp (Cyprinus carpio)

ObjectiveTo characterize the physiologic and behavioral effects of a single induction dose and two maintenance doses of alfaxalone delivered by water immersion in the anesthesia of koi (Cyprinus carpio).Study designProspective, within-subject complete crossover design.AnimalsSix adult koi (Cyprinus carpio) with a median body weight of 344.5 g (range 292.0–405.0 g).MethodsKoi were immersed in water containing 10 mg L^?1 alfaxalone until immobile and then maintained with alfaxalone at either 1 or 2.5 mg L^?1 via a recirculating water system. Times for anesthetic induction and recovery periods were recorded. Physiologic and blood gas parameters were evaluated before, during and after the anesthetic trial. Response to noxious stimuli was also assessed.ResultsMedian anesthesia induction time for all fish was 5.4 minutes. Median recovery time was 11.8 and 26.4 minutes in the 1.0 and 2.5 mg L^?1 doses, respectively, which were significantly different (p = 0.04). Cessation of opercular movement occurred in 0/6 and 4/6 fish exposed to 1.0 and 2.5 mg L^?1 dose respectively. No difference was observed in median heart rate over the duration of the anesthetic events. Response to noxious stimulation was 4/6 and 0/6 in the 1.0 and 2.5 mg L^?1 doses respectively. Oxygenation and ventilation did not change during the experiment, but there was a significant decrease in blood pH along with an increase in blood lactate concentration.Conclusion and clinical relevanceAdministration of alfaxalone, via water immersion, as an induction and maintenance anesthesia agent provided rapid and reliable anesthesia of koi with no mortality. The maintenance dose of 2.5 mg L^?1 was sufficient to prevent response to noxious stimuli but was associated with a clinically relevant depression in opercular rate.     

Use of sevoflurane for anesthetic management of horses during thoracotomy

OBJECTIVE: To evaluate sevoflurane as an inhalation anesthetic for thoracotomy in horses. ANIMALS: 18 horses between 2 and 15 years old. PROCEDURE: 4 horses were used to develop surgical techniques and were euthanatized at the end of the procedure. The remaining 14 horses were selected, because they had an episode of bleeding from their lungs during strenuous exercise. General anesthesia was induced with xylazine (1.0 mg/kg of body weight, IV) followed by ketamine (2.0 mg/kg, IV). Anesthesia was maintained with sevoflurane in oxygen delivered via a circle anesthetic breathing circuit. Ventilation was controlled to maintain PaCO2 at approximately 45 mm Hg. Neuromuscular blocking drugs (succinylcholine or atracurium) were administered to eliminate spontaneous breathing efforts and to facilitate surgery. Cardiovascular performance was monitored and supported as indicated. RESULTS: 2 of the 14 horses not euthanatized died as a result of ventricular fibrillation. Mean (+/- SD) duration of anesthesia was 304.9 +/- 64.1 minutes for horses that survived and 216.7 +/- 85.5 minutes for horses that were euthanatized or died. Our subjective opinion was that sevoflurane afforded good control of anesthetic depth during induction, maintenance, and recovery. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of sevoflurane together with neuromuscular blocking drugs provides stable and easily controllable anesthetic management of horses for elective thoracotomy and cardiac manipulation.     

Cardiopulmonary and acid-base effects of desflurane and sevoflurane in spontaneously breathing cats

The cardiopulmonary effects of desflurane and sevoflurane anesthesia were compared in cats breathing spontaneously. Heart (HR) and respiratory (RR) rates; systolic (SAP), diastolic (DAP) and mean arterial (MAP) pressures; partial pressure of end tidal carbon dioxide (PETCO2), arterial blood pH (pH), arterial partial pressure of oxygen (PaO2) and carbon dioxide (PaCO2); base deficit (BD), arterial oxygen saturation (SaO2) and bicarbonate ion concentration (HCO3) were measured. Anesthesia was induced with propofol (8+/-2.3mg/kg IV) and maintained with desflurane (GD) or sevoflurane (GS), both at 1.3 MAC. Data were analyzed by analysis of variance (ANOVA), followed by the Tukey test (P<0.05). Both anesthetics showed similar effects. HR and RR decreased when compared to the basal values, but remained constant during inhalant anesthesia and PETCO2 increased with time. Both anesthetics caused acidemia and hypercapnia, but BD stayed within normal limits. Therefore, despite reducing HR and SAP (GD) when compared to the basal values, desflurane and sevoflurane provide good stability of the cardiovascular parameters during a short period of inhalant anesthesia (T20-T60). However, both volatile anesthetics cause acute respiratory acidosis in cats breathing spontaneously.     

Minimum alveolar concentration of isoflurane in green iguanas and the effect of butorphanol on minimum alveolar concentration

OBJECTIVE: To determine minimum alveolar concentration (MAC) of isoflurane in green iguanas and effects of butorphanol on MAC. DESIGN: Prospective randomized trial. ANIMALS: 10 healthy mature iguanas. PROCEDURE: in each iguana, MAC was measured 3 times: twice after induction of anesthesia with isoflurane and once after induction of anesthesia with isoflurane and IM administration of butorphanol (1 mg/kg [0.45 mg/lb]). A blood sample was collected from the tail vein for blood-gas analysis at the beginning and end of the anesthetic period. The MAC was determined with a standard bracketing technique; an electrical current was used as the supramaximal stimulus. Animals were artificially ventilated with a ventilator set to deliver a tidal volume of 30 mL/kg (14 mL/lb) at a rate of 4 breaths/min. RESULTS: Mean +/- SD MAC values during the 3 trials (2 without and 1 with butorphanol) were 2.0 +/- 0.6, 2.1 +/- 0.6, and 1.7 +/- 0.7%, respectively, which were not significantly different from each other. Heart rate and end-tidal partial pressure of CO2 were also not significantly different among the 3 trials. Mean +/- SD heart rate was 48 +/- 10 beats/min; mean end-tidal partial pressure of CO2 was 22 +/- 10 mm Hg.There were no significant differences in blood-gas values for samples obtained at the beginning versus the end of the anesthetic period. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that the MAC of isoflurane in green iguanas is 2.1% and that butorphanol does not have any significant isoflurane-sparing effects.