Sevoflurane anaesthesia in chickens during spontaneous and controlled ventilation

A crossover study design was used to investigate the dose-related effects of sevoflurane at end-tidal concentrations of 2.2 to 4.4 per cent on the respiratory rate, blood gases, heart rate, arterial blood pressure and ocular signs of chickens during spontaneous and controlled ventilation. The mean (sd) carbon dioxide partial pressure (PaCO2) increased as the concentration of sevoflurane increased, and was 86 (29) mmHg at an end-tidal concentration of 4.4 per cent during spontaneous ventilation, but was maintained between 29 and 42 mmHg during controlled ventilation. The heart rate increased as the concentration of sevoflurane increased during spontaneous ventilation, but did not change during controlled ventilation. Sevoflurane decreased arterial blood pressure during both spontaneous and controlled ventilation, but a dose-dependent decrease in arterial blood pressure was observed only during controlled ventilation. The mean arterial blood pressure at an end-tidal concentration of 4.4 per cent was significantly higher during spontaneous ventilation than during controlled ventilation. Controlled ventilation prevented the increases in PaCO2 and heart rate that were observed during spontaneous ventilation. The decrease in arterial blood pressure during spontaneous ventilation was less than that during controlled ventilation, possibly owing to the effects of hypercapnia.     

Cardiovascular effects of halothane anesthesia after diazepam and ketamine administration in beavers (Castor canadensis) during spontaneous or controlled ventilation

Fourteen adult beavers (Castor canadensis) weighing 16.5 +/- 4.14 kg (mean +/- SD) were anesthetized for surgical implantation of radio telemetry devices. Beavers were anesthetized with diazepam (0.1 mg/kg) and ketamine (25 mg/kg) administered IM, which provided smooth anesthetic induction and facilitated tracheal intubation. Anesthesia was maintained with halothane in oxygen via a semiclosed circle anesthetic circuit. Values for heart rate, respiratory rate, esophageal temperature, direct arterial blood pressure, end-tidal halothane concentration, and end-tidal CO2 tension were recorded every 15 minutes during the surgical procedure. Arterial blood samples were collected every 30 minutes to determine pH, PaO2, and PaCO2. Values for plasma bicarbonate, total CO2, and base excess were calculated. Ventilation was spontaneous in 7 beavers and controlled to maintain normocapnia (PaCO2 approx 40 mm of Hg) in 7 others. Vaporizer settings were adjusted to maintain a light surgical plane of anesthesia. Throughout the surgical procedure, all beavers had mean arterial pressure less than 60 mm of Hg and esophageal temperature less than 35 C. Mean values for arterial pH, end-tidal CO2, PaO2, and PaCO2 were significantly (P less than 0.05) different in spontaneously ventilating beavers, compared with those in which ventilation was controlled. Respiratory acidosis during halothane anesthesia was observed in spontaneously ventilating beavers, but not in beavers maintained with controlled ventilation. All beavers recovered unremarkably from anesthesia.     

Dose-related cardiovascular effects of isoflurane in chickens during controlled ventilation

We studied cardiovascular effects of isoflurane in chickens during controlled ventilation. Following the determination of the minimal anesthetic concentration from the response to clamping of a digit, dose-related effect of isoflurane on heart rate and arterial pressure were studied. The minimal anesthetic concentration of isoflurane was 1.25 +/- 0.13% (mean +/- SD, n=9). There was a dose-dependent decrease in arterial pressure. The heart rate did not change significantly over a range of 1 to 2 times the minimal anesthetic concentration.     

Anesthetic potency and cardiopulmonary effects of sevoflurane in goats: comparison with isoflurane and halothane.

The anesthetic potency and cardiopulmonary effects of sevoflurane were compared with those of isoflurane and halothane in goats. The (mean +/- SD) minimal alveolar concentration (MAC) was 0.96 +/- 0.12% for halothane, 1.29 +/- 0.11% for isoflurane, and 2.33 +/- 0.15% for sevoflurane. Cardiopulmonary effects of sevoflurane, halothane and isoflurane were examined at end-tidal concentrations equivalent to 1, 1.5 and 2 MAC during either spontaneous or controlled ventilation (SV or CV). During SV, there were no significant differences in respiration rate, tidal volume and minute ventilation between anesthetics. Dose-dependent decreases in both tidal volume and minute ventilation induced by halothane were greater than those by either sevoflurane or isoflurane. Hypercapnia and acidosis induced by sevoflurane were not significantly different from those by either isoflurane or halothane at 1 and 1.5 MAC, but were less than those by halothane at 2 MAC. There was no significant difference in heart rate between anesthetics during SV and CV. During SV, all anesthetics induced dose-dependent decreases in arterial pressure, rate pressure product, systemic vascular resistance, left ventricular minute work index and left ventricular stroke work index. Systemic vascular resistance with isoflurane at 2 MAC was lower than that with sevoflurane. During CV, sevoflurane induced dose-dependent circulatory depression (decreases in arterial pressure, cardiac index, rate pressure product, systemic vascular resistance, left ventricular minute work index and right ventricular minute work index), similar to isoflurane. Halothane did not significantly alter systemic vascular resistance from 1 to 2 MAC.     

Minimum anesthetic concentration and cardiovascular dose-response relationship of isoflurane in cinereous vultures (Aegypius monachus)

This study aimed to determine the minimum anesthetic concentration (MAC) and dose-related cardiovascular effects of isoflurane during controlled ventilation in cinereous vultures (Aegypius monachus). The MAC was determined for 10 cinereous vultures as the midpoint between the end-tidal isoflurane concentration that allows gross purposeful movement and that which prevents the movement in response to clamping a pedal digit. Immediately after the MAC was determined, the cardiovascular effects of isoflurane at 1.0, 1.5, and 2.0 times the MAC were investigated in seven of the 10 birds. The MAC of isoflurane for 10 cinereous vultures during controlled ventilation was 1.06 +/- 0.07% (mean +/- SD). When the isoflurane concentration was increased to 1.5 and 2.0 times the MAC, there was significant dose-dependent decrease in the arterial blood pressure. However, the heart rate did not change over a range of 1.0 to 2.0 times the MAC.     

Anesthetic management with sevoflurane and oxygen for orthopedic surgeries in racehorses

Eighty-five thoroughbred racehorses with various types of fracture were subjected to arthroscopic surgery (44 horses) or internal fixation (41 horses) under sevoflurane anesthesia. The mean end-tidal sevoflurane concentration during anesthesia ranged from 2.5 to 2.8%. PaCO2 was maintained between 50 and 65 mmHg by controlled ventilation. The mean arterial blood pressure was maintained above 65 mmHg by infusion of dobutamine and fluids, however, heart rate significantly increased with time. Recovery from anesthesia was calm and smooth in almost all cases. No apparent complication was observed during and after anesthesia in all cases. Therefore, sevoflurane anesthesia is considered to be safe and useful for orthopedic surgery in racehorses.     

Effect of inhalation of isoflurane at end-tidal concentrations greater than, equal to, and less than the minimum anesthetic concentration on bispectral index in chickens

OBJECTIVE: To determine the effect of inhalation of isoflurane at end-tidal concentrations greater than, equal to, and less than the minimum anesthetic concentration (MAC) on bispectral index (BIS) in chickens. Animals-10 chickens. PROCEDURES: For each chicken, the individual MAC of isoflurane was determined by use of the toe-pinch method. After a 1-week interval, chickens were anesthetized with isoflurane at concentrations 1.75, 1.50, 1.25, 1.00, and 0.75 times their individual MAC (administered from higher to lower concentrations). At each MAC multiple, a toe pinch was performed and BIS was assessed and correlated with heart rate, blood pressure, and an awareness score (derived by use of a visual analogue scale). RESULTS: Among the chickens, mean +/- SD MAC of isoflurane was 1.15 +/- 0.20%. Burst suppression was detected at every MAC multiple. The BIS and awareness score were correlated directly with each other and changed inversely with increasing isoflurane concentration. Median (range) BIS values during anesthesia at 1.75, 1.50, 1.25, 1.00, and 0.75 MAC of isoflurane were 25 (15 to 35), 35 (25 to 45), 35 (20 to 50), 40 (25 to 55), and 50 (35 to 65), respectively. Median BIS value at extubation was 70 +/- 9. Values of BIS correlated with blood pressure, but not with heart rate. Blood pressure changed with end-tidal isoflurane concentrations, whereas heart rate did not. CONCLUSIONS AND CLINICAL RELEVANCE: Assessment of BIS can be used to monitor the electrical activity of the brain and the degree of unconsciousness in chickens during isoflurane anesthesia.     

Cardiovascular and Pulmonary Effects of Sevoflurane Anesthesia in Horses

The effects of 1.0, 1.5, and 2.0 minimum alveolar concentration (MAC) of sevoflurane on hemodynamic, pulmonary and blood chemistry variables were measured during spontaneous and controlled ventilation in healthy horses. Sevoflurane was the only anesthetic drug administered to the horses. In a dose-dependent manner, sevoflurane significantly decreased ( P <.05) mean arterial blood pressure, cardiac output, and stroke volume. There was a progressive decrease in peripheral vascular resistance and an increase in heart rate as the concentration of sevoflurane was increased, but the differences were not significant. During spontaneous ventilation there was a dose-dependent decrease in respiratory rate that caused a decrease in the minute volume. As the dose of sevoflurane increased, the arterial carbon dioxide tension also increased ( P <.05). All blood chemistries remained within normal limits. Recovery from anesthesia was without incident. In conclusion, sevoflurane induces a dose-dependent decrease in hemodynamic variables and pulmonary function in horses that is not greatly different from that of other approved inhalant anesthetics.     

Anesthetic indices of sevoflurane and isoflurane in unpremedicated dogs

OBJECTIVE: To compare the anesthetic index of sevoflurane with that of isoflurane in unpremedicated dogs. DESIGN: Randomized complete-block crossover design. ANIMALS: 8 healthy adult dogs. PROCEDURE: Anesthesia was induced by administering sevoflurane or isoflurane through a face mask. Time to intubation was recorded. After induction of anesthesia, minimal alveolar concentration (MAC) was determined with a tail clamp method while dogs were mechanically ventilated. Apneic concentration was determined while dogs were breathing spontaneously by increasing the anesthetic concentration until dogs became apneic. Anesthetic index was calculated as apneic concentration divided by MAC. RESULTS: Anesthetic index of sevoflurane (mean +/- SEM, 3.45 +/- 0.22) was significantly higher than that of isoflurane (2.61 +/- 0.14). No clinically important differences in heart rate; systolic, mean, and diastolic blood pressures; oxygen saturation; and respiratory rate were detected when dogs were anesthetized with sevoflurane versus isoflurane. There was a significant linear trend toward lower values for end-tidal partial pressure of carbon dioxide during anesthesia with sevoflurane, compared with isoflurane, at increasing equipotent anesthetic doses. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that sevoflurane has a higher anesthetic index in dogs than isoflurane. Sevoflurane and isoflurane caused similar dose-related cardiovascular depression, but although both agents caused dose-related respiratory depression, sevoflurane caused less respiratory depression at higher equipotent anesthetic doses.     

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.     

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.     

Minimal Anesthetic Concentration and Cardiopulmonary Dose Response of Isoflurane in Ducks

The minimal anesthetic concentration (MAC) for isoflurane was determined during spontaneous ventilation in nine male Peking ducks (7 to 12 weeks of age; 3.0 +/- 0.4 kg). While each bird was awake, arterial blood was collected for analysis of pH, PaCO2, and PaO2. After anesthesia was induced with isoflurane in oxygen, MAC was determined for isoflurane in each bird during spontaneous ventilation in a manner similar to MAC determinations in mammals. Pulmonary dose-response data were collected at 1 MAC and 1.5 MAC. Anesthetic index (Al; an index of anesthetic-induced apnea) was calculated from ducks that became apneic. The MAC for isoflurane was 1.30 +/- 0.23% (mean +/- SD). There was a dose-dependent decrease in ventilation as evidenced by a statistically significant increase in PaCO2. Apnea or unacceptable hypercarbia (PaCO2 greater than 110 mm Hg), or both, were common occurrences at end-tidal isoflurane concentrations greater than 1.5 MAC. Anesthetic index calculated from four ducks was 1.65 +/- 0.13 (mean +/- SEM). There was no significant difference between the means of either heart rate or mean arterial blood pressure in birds at 1.0 and 1.5 MAC.     

Evaluation of intraocular pressure in association with cardiovascular parameters in normocapnic dogs anesthetized with sevoflurane and desflurane

The objective of this study was to determine intraocular pressure (IOP) and cardiac changes in normocapnic dogs maintained under controlled ventilation and anesthetized using sevoflurane or desflurane. Sixteen healthy adult mixed-breed dogs, seven males and nine females, weighing 10-15 kg were used. The dogs were randomly assigned to one of two groups composed of eight animals anesthetized with sevoflurane (SEVO) or desflurane (DESF). In both groups, anesthesia was induced with propofol (10 mg/kg), and neuromuscular blockade was achieved with rocuronium (0.6 mg/kg/h i.v.). No premedication was given. Ventilation was adjusted to maintain end-tidal carbon dioxide partial pressure at 35 mmHg. Anesthesia was maintained with 1.5 minimum alveolar concentration (MAC) of sevoflurane or desflurane. In both groups IOP was measured by applanation tonometry (Tono-Pen) before induction of anesthesia. IOP, mean arterial pressure (MAP), heart rate (HR), cardiac index (CI) and central venous pressure (CVP) were also measured 45 min after the beginning of inhalant anesthesia and then every 20 min for 60 min. A one-way repeated measures anova was used to compare data within the same group and Student's t-test was used to assess differences between groups. P < 0.05 was considered statistically significant. Measurements showed normal IOP values in both groups, even though IOP increased significantly from baseline during the use of desflurane. IOP did not differ between groups. CI in the desflurane group was significantly greater than in the sevoflurane group. Sevoflurane and desflurane have no clinically significant effects on IOP, MAP, HR, CI or VCP in the dog.     

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.     

A comparison of cardiorespiratory variables during isoflurane-fentanyl and propofol-fentanyl anaesthesia for surgery in injured cats

OBJECTIVE: To compare haemodynamic and respiratory variables during isoflurane-fentanyl (IF) and propofol-fentanyl (PF) anaesthesia for surgery in injured cats. STUDY DESIGN: Prospective, randomized, controlled clinical study. ANIMALS: Thirty-three client-owned injured cats undergoing orthopaedic surgery. MATERIALS AND METHODS: Pre-anaesthetic medication was intravenous midazolam 1 mg kg(-1), butorphanol 0.4 mg kg(-1) and ketamine 2 mg kg(-1). Anaesthesia was induced with propofol (P) and maintained with either: (a) a continuous rate infusion (CRI) of fentanyl (F) 0.02 mg kg(-1) hour(-1) and isoflurane (initial end-tidal concentration of 1%), (b) a fentanyl CRI (dose as before) and sevoflurane (initial end-tidal concentration of 2%) or (c) a CRI of propofol (12 mg kg(-1) hour(-1)). All three techniques were given to effect until surgical anaesthesia was achieved. Heart rate and rhythm (ECG), mean arterial blood pressure, respiratory rate, tidal volume and end-tidal CO(2) concentration were recorded. Venous blood gas analysis was performed before and after sedation, and at the end of anaesthesia. Blood chemistry and blood cell counts were assessed before, at the end of, and 24 hours after anaesthesia. The variables recorded from cats anaesthetized with IF and PF were compared. RESULTS: Mean end-expiratory isoflurane concentration was 1.19 +/- 0.19%. The propofol infusion rate was 11.4 +/- 0.8 mg kg(-1) hour(-1). No significant differences between the two groups in heart rate were identified; no cardiac dysrhythmias were recorded. Mean arterial blood pressure was significantly lower in IF cats during skin incision (p = 0.01), during surgery without intense surgical stimulation (p < 0.01) and during surgery with intense surgical stimulation (p = 0.01). Nine of 11 cats in the IF group were markedly hypotensive (34-49 mmHg) while seven of 11 cats in group PF were mildly hypotensive (49-59 mmHg). One of 11 cats in group IF and nine of 11 cats in group PF required intermittent positive pressure ventilation (IPPV) to maintain end-tidal CO(2) levels below 6.66 kPa (50 mmHg). CONCLUSION AND CLINICAL RELEVANCE: Despite the necessity to ventilate the lungs of cats in the PF group, arterial blood pressure was better maintained. Propofol-fentanyl anaesthesia is better for surgery in injured cats providing the means to impose IPPV are available.     

Minimal Anesthetic Concentration and Cardiopulmonary Dose-Response of Halothane in Ducks

The minimal anesthetic concentration (MAC) for halothane and cardiopulmonary dose-responses at several concentrations of halothane were determined during spontaneous ventilation in nine young adult Pekin ducks. The MAC for halothane was 1.04 +/- 0.11 (mean +/- SD). There were dose-dependent decreases in ventilation, significant reductions in inspiratory and expiratory times, and prolongation of expiratory pause times. The end-tidal halothane concentration at apnea in five ducks was less than 1.53% and anesthetic index was less than 1.51. Heart rate increased significantly as the concentration of halothane was increased, but arterial blood pressure did not change. Cardiac arrhythmias developed in five ducks at end-tidal halothane concentrations as low as 1.15%, and one duck died of cardiac arrest.     

Cardiopulmonary Effects of Using Carbon Dioxide for Laparoscopic Surgery in Dogs

Cardiopulmonary effects of laparoscopic surgery were investigated in five crossbred dogs (21 ± 1.9 kg). Premedicated dogs were anesthetized with thiopental and maintained with halothane at 1.5 times minimum alveolar concentration in oxygen. Controlled ventilation maintained partial pressure of end-tidal co₂ at 40 ± 2 mm Hg. Vecuronium was used for skeletal muscle relaxation. After instrumentation and stabilization, baseline measurements were made of cardiac output (thermodilution technique), mean systemic, mean pulmonary arterial and pulmonary wedge pressures, heart rate, saphenous vein and central venous pressures, and minute ventilation. Baseline arterial and mixed venous blood samples were drawn for analysis of pH, Pao₂, Paco₂, Pvo₂, Pvco₂, and bicarbonate concentrations. Systemic and pulmonary vascular resistances, oxygen delivery and consumption, shunt fraction, and dead space ventilation were calculated using standard formulas. Abdominal insufflation using co₂ to a pressure of 15 mm Hg for 180 minutes resulted in significant ( P <.05) increases in heart rate (15 to 180 minutes), minute ventilation (75 to 135 minutes), and saphenous vein pressure (15 to 180 minutes), and decreases in pH (60 to 180 minutes) and Pao₂ (60 to 180 minutes). For 30 minutes after desufflation, there was a significant decrease in Pao₂, and increases in cardiac output, o₂ delivery, and heart rate, compared with baseline. There was a significant increase in shunt fraction and decrease in pH at 15 minutes after desufflation only. The changes were within physiologically acceptable limits in these healthy, ventilated dogs.     

Comparison of the effect of propofol and sevoflurane on the urethral pressure profile in healthy female dogs

OBJECTIVE: To compare the effects of propofol and sevoflurane on the urethral pressure profile in female dogs. ANIMALS: 10 healthy female dogs. PROCEDURE: Urethral pressure profilometry was performed in awake dogs, during anesthesia with sevoflurane at 1.5, 2.0, and 3.0% end-tidal concentration, and during infusion of propofol at rates of 0.4, 0.8, and 1.2 mg/kg/min. A consistent plane of anesthesia was maintained for each anesthetic protocol. Maximum urethral pressure, maximum urethral closure pressure, functional profile length, and functional area were measured. RESULTS: Mean maximum urethral closure pressure of awake dogs was not significantly different than that of dogs anesthetized with propofol at all infusion rates or with sevoflurane at 1.5 and 2.0% end-tidal concentration. Functional area in awake dogs was significantly higher than in anesthetized dogs. Functional area of dogs during anesthesia with sevoflurane at 3.0% end-tidal concentration was significantly lower than functional area for other anesthetic protocols. Individual differences in the magnitude of effects of propofol and sevoflurane on urethral pressures were observed. CONCLUSIONS AND CLINICAL RELEVANCE: Sevoflurane is an alternative to propofol for anesthesia in female dogs undergoing urethral pressure profilometry. Use of these anesthetics at appropriate administration rates should reliably distinguish normal from abnormal maximum urethral closure pressures and functional areas. Titration of anesthetic depth is a critical component of urodynamic testing.     

Assessment of halothane and sevoflurane anesthesia in spontaneously breathing rats

OBJECTIVE: To characterize halothane and sevoflurane anesthesia in spontaneously breathing rats. ANIMALS: 16 healthy male Sprague-Dawley rats. PROCEDURE: 8 rats were anesthetized with halothane and 8 with sevoflurane. Minimum alveolar concentration (MAC) was determined. Variables were recorded at anesthetic concentrations of 0.8, 1.0, 1.25, and 1.5 times the MAC of halothane and 1.0, 1.25, 1.5, and 1.75 times the MAC of sevoflurane. RESULTS: Mean (+/- SEM) MAC for halothane was 1.02 +/- 0.02% and for sevoflurane was 2.99 +/- 0.19%. As sevoflurane dose increased from 1.0 to 1.75 MAC, mean arterial pressure (MAP) decreased from 103.1 +/- 5.3 to 67.9 +/- 4.6 mm Hg, and PaCO2 increased from 58.8 +/- 3.1 to 92.2 +/- 9.2 mm Hg. As halothane dose increased from 0.8 to 1.5 MAC, MAP decreased from 99 +/- 6.2 to 69.8 +/- 4.5 mm Hg, and PaCO2 increased from 59.1 +/- 2.1 to 75.9 +/- 5.2 mm Hg. Respiratory rate decreased in a dose-dependent fashion from 88.5 +/- 4.5 to 58.5 +/- 2.7 breaths/min during halothane anesthesia and from 42.3 +/- 1.8 to 30.5 +/- 4.5 breaths/min during sevoflurane anesthesia. Both groups of rats had an increase in eyelid and pupillary aperture with an increase in anesthetic dose. CONCLUSIONS AND CLINICAL RELEVANCE: An increase in PaCO2 and a decrease in MAP are clinical indicators of an increasing halothane and sevoflurane dose in unstimulated spontaneously breathing rats. Increases in eyelid aperture and pupil diameter are reliable signs of increasing depth of halothane and sevoflurane anesthesia. Decreasing respiratory rate is a clinical indicator of an increasing dose of halothane.     

Cardiovascular effects of sevoflurane in Holstein calves

Objective The purpose of this study was to determine the cardiovascular effects of sevoflurane in calves. Study design Prospective experimental study. Animals Six, healthy, 8–12‐week‐old Holstein calves weighing 80 ± 4.5 (mean ± SEM) kg were studied. Methods Anesthesia was induced by face‐mask administration of 7% sevoflurane in O₂. Calves tracheae were intubated, placed in right lateral recumbency, and maintained with 3.7% end‐tidal concentration sevoflurane for 30 minutes to allow catheterization of the auricular artery and placement of a Swan‐Ganz thermodilution catheter into the pulmonary artery. After instrumentation, administration of sevoflurane was temporarily discontinued until mean arterial pressure was > 100 mm Hg. Baseline values were recorded and the vaporizer output increased to administer 3.7% end‐tidal sevoflurane concentration. Ventilation was controlled to maintain normocapnia. The following were recorded at 5, 10, 15, 30 and 45 minutes after collection of baseline data and expressed as the mean value (± SEM): direct systolic, diastolic, and mean arterial blood pressures; cardiac output; mean pulmonary arterial pressure; pulmonary arterial occlusion pressure, heart rate; and pulmonary arterial temperature. Cardiac index and systemic and pulmonary vascular resistance values were calculated using standard formulae. Arterial blood gases were analyzed at baseline, and at 15 and 45 minutes. Differences from baseline values were determined using one‐way analysis of variance for repeated measures with post‐hoc differences between mean values identified using Dunnet's test (p < 0.05). Results Mean time from beginning sevoflurane administration to intubation of the trachea was 224 ± 9 seconds. The mean end‐tidal sevoflurane concentration at baseline was 0.7 (± 0.11)%. Sevoflurane anesthesia was associated with decreased arterial blood pressure at all sampling times. Mean arterial blood pressure decreased from a baseline value of 112 ± 7 mm Hg to a minimum value of 88 ± 4 mm Hg at 5 minutes. Compared with baseline, arterial pH was decreased at 15 minutes. Pulmonary arterial blood temperature was decreased at 15, 30 and 45 minutes. Arterial CO₂ tension increased from a baseline value of 43 ± 3 to 54 ± 4 mm Hg (5.7 ± 0.4 to 7.2 ± 0.3 kPa) at 15 minutes. Mean pulmonary arterial pressure was increased at 30 and 45 minutes. Pulmonary arterial occlusion pressure increased from a baseline value of 18 ± 2 to 23 ± 2 mm Hg at 45 minutes. There were no significant changes in other measured variables. All calves recovered from anesthesia uneventfully. Conclusion We conclude that sevoflurane for induction and maintenance of anesthesia was effective and reliable in these calves and that neither hypotension nor decreased cardiac output was a clinical concern. Clinical relevance Use of sevoflurane for mask induction and maintenance of anesthesia in young calves is a suitable alternative to injectable and other inhalant anesthetics.