Use of a laryngeal mask airway in rabbits during isoflurane anesthesia

The purpose of this study was to find out if an LMA (#1 LMA‐Classic) would provide a better airway than a face mask in spontaneously breathing anesthetized rabbits, and to test if it could be used for mechanically controlled ventilation. Sixteen rabbits (4.1 ± 0.8 kg, mean ± SD) were assigned randomly to three treatment groups; face mask with spontaneous ventilation (FM‐SV; n = 5), LMA with spontaneous ventilation (LMA‐SV; n = 5), and LMA with controlled ventilation (LMA‐CV; n = 6). Rabbits were anesthetized in dorsal recumbency using a circle circuit at constant ET isoflurane (2.3%, Datex airway gas monitor) and constant rectal temperature (38.85 °C) for 2 hours. PaCO₂, PaO₂, minute volume, tidal volume (Wright's respirometer), and Pe CO₂ were measured at 15 minute intervals. Two individuals in the FM‐SV group had PaCO₂ >100 mm Hg (>13.3 kPa). One rabbit in the FM‐SV had PaO₂ <80 mm Hg (<10.7 kPa). All FM‐SV rabbits showed signs of airway obstruction and two were withdrawn from the study at 45 and 90 minutes, respectively, because of cyanosis. Tidal volume could not be measured in the FM‐SV group. No signs of airway obstructions were observed in either of the LMA groups. Four rabbits in the LMA‐CV group developed gastric tympany, and one of these refluxed after 110 minutes. The significance of differences between the two spontaneously breathing groups and between the two LMA groups were measured using Wilcoxon's rank sum test (with significance assumed at p < 0.05). There were no statistical differences between FM‐SV and LMA‐SV in any variable tested. PaCO₂ and Pe ′CO₂ were less in the LMA‐CV group than in the LMA‐SV group, while PaO₂, tidal volume, and minute volume were all more. We conclude that biologically, the LMA provides a better airway than the face mask during spontaneous breathing and that it can be used for IPPV, but that gastric tympany is likely to occur during IPPV.     

Evaluation of laryngeal mask as an alternative to endotracheal intubation in cats anesthetized under spontaneous or controlled ventilation

OBJECTIVE: To compare the cardiorespiratory effects and incidence of gastroesophageal reflux with the use of a laryngeal mask airway (LMA) or endotracheal tube (ET) in anesthetized cats during spontaneous (SV) or controlled ventilation (CV). STUDY DESIGN: Prospective randomized experimental trial. ANIMALS: Thirty-two adult crossbred cats, weighing 2.7 +/- 0.4 kg. METHODS: The cats were sedated with intramuscular (IM) methotrimeprazine (0.5 mg kg(-1)) and buprenorphine (0.005 mg kg(-1)), followed 30 minutes later by induction of anesthesia with intravenous (IV) thiopental (12.5-20 mg kg(-1)). An ET was used in 16 cats and an LMA in the remaining 16 animals. Anesthesia was maintained with 0.5 minimum alveolar concentration (0.6%) of halothane in oxygen using a Mapleson D breathing system. Cats in both groups were further divided into two equal groups (n = 8), undergoing either SV or CV. Neuromuscular blockade with pancuronium (0.06 mg kg(-1)) was used to facilitate CV. Heart and respiratory rates, direct arterial blood pressure, capnometry (PE'CO2) and arterial blood gases were measured. Gastric reflux and possible aspiration was investigated by intragastric administration of 5 mL of radiographic contrast immediately after induction of anesthesia. Cervical and thoracic radiographs were taken at the end of anesthesia. Data were analyzed using anova followed by Student-Newman-Keuls, Kruskal-Wallis or Friedman test where appropriate. RESULTS: Values for PaCO2 and PE'CO2 were higher in spontaneously breathing cats with the LMA when compared with other groups. Values of PaO2 and hemoglobin oxygen saturation did not differ between groups. Gastroesophageal reflux occurred in four of eight and two of eight cats undergoing CV with ET or LMA, respectively. There was no tracheal or pulmonary aspiration in any cases. CONCLUSIONS AND CLINICAL RELEVANCE: The use of an LMA may be used as an alternative to endotracheal intubation in anesthetized cats. Although aspiration was not observed, gastric reflux may occur in mechanically ventilated animals.     

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.     

Cardiopulmonary responses to experimentally induced gastric dilatation in isoflurane-anesthetized dogs.

Gastric dilatation was experimentally induced in 6 anesthetized dogs maintained with constant-dose isoflurane in oxygen. An intragastric balloon was used to distend the stomach with a constant 30 mm of Hg pressure for 3.5 hours. The PaCO2 was maintained between 35 and 45 mm of Hg, using intermittent positive-pressure ventilation. Cardiopulmonary measurements prior to stomach distension (baseline) were compared with measurements taken during 0.1, 0.5, 1.0, 1.5, 2.5, and 3.5 hours of stomach distension by analyzing the change from baseline in a randomized-block analysis with each dog as a block. After distending the stomach, cardiac index increased (P less than 0.01) from 1.5 to 3.5 hours. Stroke volume did not change, thus the increase in the cardiac index was attributable to an increase in heart rate. During inflation, increases were observed in systemic arterial, pulmonary arterial, and right atrial pressure. Respiratory frequency was unchanged; however, to maintain PaCO2 constant, it was necessary to progressively increase peak airway pressure. Although PaO2 tended to decrease during gastric dilation, the dogs were never hypoxemic. These results indicate that when our methods are used to maintain a constant anesthetic dose of isoflurane in oxygen, an observed increase in cardiovascular performance is expected. This differs from other studies in anesthetized dogs that have shown reduction in cardiovascular performance following gastric dilatation.     

Use of laryngeal mask airway compared to endotracheal tube with positive-pressure ventilation in anesthetized swine

OBJECTIVE: To compare the ease of placement and ventilatory parameters of a laryngeal mask airway (LMA) with an endotracheal tube (ETT) in anesthetized swine during positive-pressure ventilation (PPV). STUDY DESIGN: Prospective, randomized, experimental trial. ANIMALS: Nine young domestic swine, weighing between 40 and 49 kg (mean 45.1 kg), being used for a separate terminal surgical study. METHODS: The pigs were immobilized with tiletamine/zolazepam, 2.7-3.6 mg kg(-1), intramuscularly, followed by isoflurane in oxygen delivered by facemask. The lungs were mechanically ventilated through an ETT or an LMA, in random order, during the anesthetic period. Positive-pressure ventilation was adjusted to maintain end-tidal CO2 (Pe'CO2) between 35 and 45 mmHg, with peak inspiratory pressure (P(insp)) of 15-23 cmH2O. Buprenorphine, 0.3 mg intramuscularly, was given to each pig after instrumentation. Isoflurane vaporizer settings were adjusted to maintain a surgical plane of anesthesia. Respiratory rate (RR), tidal volume (V(T)), minute volume (V(E)), and Pe'CO2 were measured and recorded at 5-minute intervals. After the collection of 1 hour of data, the alternate airway was placed. Swine were given at least 30 minutes to stabilize and another hour of data were recorded. At the time of airway placement, the ease of placement was assessed based on time and the number of personnel required. Data were analyzed using paired Student's t-test or Wilcoxon signed rank test where appropriate. RESULTS: Laryngeal mask airways were significantly easier to place than ETT. Values for V(T) and V(E) were not significantly different between treatments. Peak inspiratory pressures were higher in ETT-ventilated swine. CONCLUSIONS AND CLINICAL RELEVANCE: An LMA may be used as an alternative to an ETT in mechanically-ventilated anesthetized swine. Use of an LMA may reduce time and personnel required for placement of an airway.     

Cardiopulmonary effects of controlled versus spontaneous ventilation in pigeons anesthetized for coelioscopy

OBJECTIVE: To evaluate the cardiorespiratory effects of controlled versus spontaneous ventilation in pigeons anesthetized for coelioscopy. DESIGN: Prospective study. ANIMALS: 30 healthy adult pigeons (Columbia livia). PROCEDURE: During isoflurane anesthesia, 15 pigeons were allowed to breathe spontaneously (SP group) and 15 were mechanically ventilated (MV group) by use of a pressure-limited ventilator. In each group, cardiopulmonary variables (including end-tidal CO2 concentration [ETCO2]) were measured before (baseline), during, and after coelioscopy. An arterial blood sample was collected for blood gas analyses from each pigeon before coelioscopy and after the procedure, when the caudal thoracic air sac was still open. RESULTS: At baseline, hypoventilation was greater in the SP group than the MV group. Compared with the SP group values, ETCO2 overestimated PaCO2 to a greater degree in the MV group. Cardiovascular variables were not different between groups. After coelioscopy (when the air sac was open), PaCO2 had decreased significantly from baseline in the MV group. In the SP group, hypoventilation worsened despite an increase in respiratory rate. After coelioscopy, PaO2 in the SP group had decreased from baseline and was lower than PaO2 in the MV group; arterial blood pressure and heart rate in the MV group had decreased from baseline and were lower than values in the SP group. CONCLUSIONS AND CLINICAL RELEVANCE: In adult pigeons, controlled ventilation delivered by a pressure-limited device was not associated with clinically important adverse cardiopulmonary changes but may be associated with respiratory alkalosis and cardiovascular depression when air sac integrity has been disrupted.     

Hemodynamic response of calves to tiletamine-zolazepam-xylazine anesthesia.

Six healthy Holstein calves were anesthesized with isoflurane in O2 and instrumented for hemodynamic studies. A saphenous artery was catheterized for measurement of blood pressure and withdrawal of blood for determination of the partial pressure of carbon dioxide (PaCO2), oxygen (PaO2), and arterial pH (pHa). Respiration was controlled throughout the study. The ECG and EEG were monitored continuously. A thermodilution catheter was passed via the right jugular vein into the pulmonary artery for determination of cardiac output and measurement of central venous pressure, pulmonary arterial pressure, and pulmonary capillary wedge pressure. Baseline values (time 0) were recorded following recovery from isoflurane. Tiletamine-zolazepam (4 mg/kg)-xylazine (0.1 mg/kg) were administered IV immediately after recording baseline values. Values were again recorded at 5, 10, 20, 30, 40, 50, and 60 minutes after injection. Changes in left ventricular stroke work index, PaCO2, and pHa were insignificant. Arterial blood pressure and systemic vascular resistance increased above baseline at 5 minutes and then gradually decreased below baseline at 40 minutes, demonstrating a biphasic response. Values for pulmonary capillary wedge pressure, pulmonary arterial pressure, central venous pressure, and PaO2 were increased above baseline from 5 to 60 minutes. Stroke volume, stroke index, and right ventricular stroke work index were increased from 20 or 30 minutes to 60 minutes. Pulmonary vascular resistance increased at 10 minutes, returned to baseline at 20 minutes, and was increased again at 60 minutes. Heart rate, cardiac output, cardiac index, and rate pressure product were decreased at 5 minutes, and with the exception of cardiac output, remained so for 60 minutes. Cardiac output returned to the baseline value at 30 minutes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cardiovascular and respiratory measurements in awake and isoflurane-anesthetized horses

Circulatory and respiratory function was monitored in nonmedicated, spontaneously breathing horses (n = 7) immediately before, during, and 1 hour after 85 +/- 4.1 (X +/- SEM) minutes of constant 1.57% isoflurane in O2 anesthesia. Comparison of values during anesthesia with those obtained while horses were awake revealed a significant (P less than 0.05) decrease in arterial blood pressure that was related to a slight, but insignificant, decrease in cardiac output and peripheral vascular resistance. Although isoflurane anesthesia and recumbency resulted in a significant (P less than 0.05) decrease in stroke volume, cardiac output did not decrease significantly because heart rate tended to increase. Isoflurane and recumbency also significantly (P less than 0.05) increased PaCO2, peak expiratory gas flow, total expiratory time, and PCV and significantly decreased PaO2, minute expired ventilation, and the ratio of peak inspired to expired gas flow. Differences imposed by isoflurane anesthesia were reversed by 1.5 hour after anesthesia.     

Arterial to end-tidal CO2 tension and alveolar dead space in halothane- or isoflurane-anesthetized ponies

The correlation between end-tidal partial pressure of CO2 (PETCO2) and arterial (PaCO2) was determined for spontaneously breathing ponies under halothane or isoflurane anesthesia. The PETCO2 was useful as a trend indicator of PaCO2 during the first 60 minutes of halothane or isoflurane anesthesia when PaCO2 values were less than 60 to 70 mm of Hg. Halothane anesthesia lasting greater than 90 minutes was associated with PaCO2 values in excess of 60 to 70 mm of Hg, a large arterial- to end-tidal PCO2 difference (PaCO2-PETCO2) and a significant increase in alveolar dead space. These effects were not seen during the same period of isoflurane anesthesia. Arterial blood gas analysis is therefore recommended during halothane anesthesia when the PETCO2 is greater than 60 to 70 mm of Hg. A decrease in alveolar capillary perfusion relative to alveolar ventilation is the most likely cause for the increase in alveolar dead space during halothane anesthesia. Based on these findings, isoflurane may be superior to halothane for prolonged anesthesia of spontaneously breathing horses.     

Capnographic Monitoring during Anesthesia with Controlled Ventilation in the Horse

Forty-five horses were maintained on halothane or isoflurane anesthesia for at least 90 minutes and received positive pressure ventilation after the first 30 minutes of anesthesia. Parameters monitored included end-tidal partial pressure of carbon dioxide (ETPCO2), arterial blood pressure, and arterial blood gases and pH. There was a statistically significant correlation between end-tidal carbon dioxide and arterial partial pressure of carbon dioxide (PaCO2) for both halothane and isoflurane anesthesia. There was no significant correlation between end-tidal carbon dioxide and either body weight or systolic blood pressure. No statistically significant difference was found in arterial to end-tidal carbon dioxide difference nor in alveolar dead space because of time or positioning over anesthetic periods of up to 3 hours. It is concluded that end-tidal carbon dioxide monitoring is a satisfactory measure of changes in respiratory acid-base balance with inhalation anesthesia in horses when ventilation is controlled.     

Effects of duration of isoflurane anesthesia and mode of ventilation on intracranial and cerebral perfusion pressures in horses

OBJECTIVE: To test the hypothesis that isoflurane-anesthetized horses during controlled ventilation and spontaneous ventilation exhibit temporal changes in cerebral hemodynamics, as measured by intracranial pressure and cerebral perfusion pressure, that reflect temporal changes in systemic arterial pressure. ANIMALS: 6 healthy adult horses. PROCEDURE: Horses were anesthetized in left lateral recumbency with 1.57% isoflurane in O2 for 5 hours in 2 experiments by use of either controlled ventilation (with normocapnia) or spontaneous ventilation (with hypercapnia) in a randomized crossover design. Intracranial pressure was measured with a subarachnoid strain-gauge transducer. Carotid artery pressure, central venous pressure, airway pressures, blood gases, and minute ventilation also were measured. RESULTS: Intracranial pressure during controlled ventilation significantly increased during constant dose isoflurane anesthesia and thus contributed to decreasing cerebral perfusion pressure. Intracranial pressure was initially higher during spontaneous ventilation than during controlled ventilation, but this difference disappeared over time; no significant differences in cerebral perfusion pressures were observed between horses that had spontaneous or controlled ventilation. CONCLUSIONS AND CLINICAL RELEVANCE: Cerebral hemodynamics and their association with ventilation mode are altered over time in isoflurane-anesthetized horses and could contribute to decreased cerebral perfusion during prolonged anesthesia.     

Induction and recovery characteristics and cardiopulmonary effects of sevoflurane and isoflurane in bald eagles

OBJECTIVE: To compare induction and recovery characteristics and cardiopulmonary effects of isoflurane and sevoflurane in bald eagles. Animals-17 healthy adult bald eagles. PROCEDURES: Anesthesia was induced with isoflurane or sevoflurane delivered in oxygen via a facemask in a crossover design with 4 weeks between treatments. Eagles were intubated, allowed to breathe spontaneously, and instrumented for cardiopulmonary measurements. Time to induction, extubation, and recovery, as well as smoothness of recovery, were recorded. RESULTS: Administration of sevoflurane resulted in a significantly quicker recovery, compared with isoflurane. Temperature, heart rate, and respiratory rate significantly decreased over time, whereas systolic (SAP), diastolic (DAP), and mean arterial blood pressure (MAP) significantly increased over time with each treatment. Temperature, heart rate, SAP, DAP, and MAP were significantly higher with isoflurane. Blood pH significantly decreased, whereas PaCO(2) significantly increased over time with each treatment. Bicarbonate and total carbon dioxide concentrations significantly increased over time with each treatment; however, there was a significant time-treatment interaction. The PaO(2) and arterial oxygen saturation increased over time with isoflurane and decreased over time with sevoflurane with a significant time-treatment interaction. Six eagles developed cardiac arrhythmias with isoflurane, as did 4 with sevoflurane anesthesia. CONCLUSIONS AND CLINICAL RELEVANCE: Isoflurane and sevoflurane administration resulted in smooth, rapid induction of and recovery from anesthesia similar to other species. Isoflurane administration resulted in tachycardia, hypertension, and more arrhythmias, compared with sevoflurane. Sevoflurane was associated with fewer adverse effects and may be particularly beneficial in compromised bald eagles.     

Comparison of the effects of caffeine and doxapram on respiratory and cardiovascular function in foals with induced respiratory acidosis

OBJECTIVE: To determine and compare the effects of caffeine and doxapram on cardiorespiratory variables in foals during isoflurane-induced respiratory acidosis. ANIMALS: 6 clinically normal foals (1 to 3 days old). PROCEDURES: At intervals of > or = 24 hours, foals received each of 3 IV treatments while in a steady state of hypercapnia induced by isoflurane anesthesia (mean +/- SD, 1.4 +/- 0.3% endtidal isoflurane concentration). After assessment of baseline cardiorespiratory variables, a low dose of the treatment was administered and variables were reassessed; a high dose was then administered, and variables were again assessed. Sequential low- and high-dose treatments included doxapram (loading dose of 0.5 mg/kg, followed by a 20-minute infusion at 0.03 mg/kg/min and then 0.08 mg/kg/min), caffeine (5 mg/kg and 10 mg/kg), and saline (0.9% NaCl) solution (equivalent volumes). RESULTS: Administration of doxapram at both infusion rates resulted in a significant increase in respiratory rate, minute ventilation, arterial blood pH, PaO(2), and arterial blood pressure. These variables were also significantly higher during doxapram administration than during caffeine or saline solution administration. There was a significant dose-dependent decrease in PaCO(2) and arterial bicarbonate concentration during doxapram treatment. In contrast, PaCO(2) increased from baseline values after administration of saline solution or caffeine. The PaCO(2) value was significantly lower during doxapram treatment than it was during caffeine or saline solution treatment. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that doxapram restored ventilation in a dose-dependent manner in neonatal foals with isoflurane-induced hypercapnia. The effects of caffeine on respiratory function were indistinguishable from those of saline solution.     

The effects of spontaneous and mechanical ventilation on central cardiovascular function and peripheral perfusion during isoflurane anaesthesia in horses

OBJECTIVE: To compare the effects of spontaneous breathing and mechanical ventilation on haemodynamic variables, including muscle and skin perfusion measured with laser Doppler flowmetery, in horses anaesthetized with isoflurane. STUDY DESIGN: Prospective controlled study. ANIMALS: Ten warm-blood trotter horses (five males, five females). Mean mass was 492 kg (range 420-584 kg) and mean age was 5 years (range 4-8 years). MATERIALS AND METHODS: After pre-anaesthetic medication with detomidine (10 microg kg(-1)) anaesthesia was induced with intravenous (IV) guaifenesin and thiopental (4-5 mg kg(-1) IV) and maintained using isoflurane in oxygen. The horses were positioned in dorsal recumbency. In five animals breathing was initially spontaneous (SB) while the lungs of the other five were ventilated mechanically using intermittent positive pressure ventilation (IPPV). Total anaesthesia time was 4 hours with the ventilatory mode changed after 2 hours. During anaesthesia, heart rate (HR) cardiac output (Qt) stroke volume (SV) systemic arterial blood pressures (sAP), and pulmonary arterial pressure (pAP) were recorded. Peripheral perfusion was measured in the semimembranosus and gluteal muscles and on the tail skin using laser Doppler flowmetry. Arterial (a) and mixed venous (v) blood gases, pH, haemoglobin concentration [Hb], haematocrit (Hct), plasma lactate concentration and muscle temperature were measured. Oxygen content, venous admixture (s/Qt) oxygen delivery (DO(2)) and oxygen consumption (VO(2)) were calculated. RESULTS: During mechanical ventilation, HR, sAP, pAP, Qt, SV, Qs/Qt and PaCO(2) were lower and PaO(2) was higher compared with spontaneous breathing. There were no differences between the modes of ventilation in the level of perfusion, DO(2), VO(2), [Hb], (Hct), or plasma lactate concentration. After the change from IPPV to SB, left semimembranosus muscle and skin perfusion improved, while muscle perfusion tended to decrease when SB was changed to IPPV. Low-frequency flow motion was seen twice as frequently during IPPV compared with SB. CONCLUSIONS: Mechanical ventilation impaired cardiovascular function compared with SB in horses during isoflurane anaesthesia. Muscle and skin perfusion changes occurred with ventilation, although further studies are needed to elucidate the underlying mechanisms.     

Investigation into the use of the laryngeal mask airway in pentobarbital anesthetized dogs

OBJECTIVE: To investigate the use of the laryngeal mask airway (LMA) in dogs. STUDY DESIGN: Prospective experimental study. ANIMALS: Eight healthy adult mixed breed dogs weighing from 15 to 20 kg. METHODS: The dogs were anesthetized with intravenous pentobarbital. An LMA was introduced after the induction of anesthesia and 1 L/min O2 plus 1 L/min air was delivered using a circle anesthetic system. Respiratory rate, tidal volume, arterial O2 saturation (pulse oximetry), end tidal CO2, inspired fraction of O2, pulse rate, and mean arterial blood pressure were measured after the insertion of the LMA and 30, 60, 90, and 120 minutes afterwards. RESULTS: There were no changes in respiratory rate, tidal volume, arterial O2 saturation, and pulse rate during anesthesia. End tidal CO2 decreased significantly by the end of anesthesia and ventilation appeared satisfactory. CONCLUSIONS: An LMA appeared to be an alternative option to maintain the patency of the airway in dogs. CLINICAL RELEVANCE: This device may allow safe maintenance of an airway in dogs when intubation is difficult or when it interferes with the procedure (eg, cervical myelography).     

A case of spontaneous venous embolism with carbon dioxide during laparoscopic surgery in a pig

BACKGROUND: Carbon dioxide (CO2) embolism is a possible complication of capnoperitoneum during laparoscopic surgery. Experimentally induced venous CO2 embolism has been studied in pigs. In this paper we report a case of spontaneous CO2 embolism. OBSERVATIONS: A 4-month-old Large White pig weighing 20 kg underwent experimental laparoscopic surgery under general anaesthesia. Monitoring consisted of pulse oximetry, capnography, airway pressure, electrocardiography, invasive arterial and central venous blood pressures, and arterial blood-gas analysis. Shortly after the start of laparoscopy and onset of CO2 insufflation, sudden decreases in end-tidal CO2 (Pe'CO2), haemoglobin saturation of oxygen (SpO2), systolic arterial blood pressure and heart rate were observed. Airway pressure increased and pulmonary compliance decreased simultaneously. Insufflation was immediately discontinued and epinephrine (2 mg IV), atropine (0.5 mg IV) and a 50 mL bolus of a polygeline solution were administered without effect. At this time arterial blood-gas analysis revealed a pH of 7.29 and a PaCO2 of 6.8 kPa (51.2 mmHg); PaO2 was 26.6 kPa (199.5 mmHg). After 4 minutes asystole occurred. CONCLUSIONS: The sudden decrease of Pe'CO2 and lung compliance combined with the sudden decrease in systolic blood pressure, heart rate and a poor response to resuscitation suggest a case of fatal gaseous venous embolism.     

Comparison of cardiopulmonary effects of isoflurane and halothane after atropine-guaifenesin-thiamylal anesthesia for rumenotomy in steers

Cardiopulmonary effects were assessed in 12 yearling steers anesthetized with guaifenesin and thiamylal sodium, intubated, and allowed to breathe isoflurane or halothane in oxygen spontaneously. Light surgical anesthesia, determined using eye position as a clinical indication of anesthetic depth, was maintained during surgical placement of a rumen cannula. Heart rate and respiratory rate were measured while the steers were standing quietly (baseline). Atropine (0.06 mg/kg of body weight, IM) was given after baseline measurements were taken. Heart rate, respiratory rate, arterial blood pressures, pHa, PaCO2, PaO2, arterial [HCO3-], esophageal temperature, and end-tidal anesthetic concentration were measured every 15 minutes for 90 minutes after induction of anesthesia. Mean heart rate increased significantly (P less than 0.05) above baseline in the isoflurane group at 15 and 30 minutes. Mean respiratory rate increased significantly (P less than 0.05) above baseline in the halothane group at 45 minutes. At 45 minutes, mean respiratory rate was lower (P less than 0.05) in the isoflurane group, compared with that in the halothane group. Mean values for arterial blood pressures and arterial gases were similar for both agents at comparable times. Mean end-tidal isoflurane concentrations were less than mean end-tidal halothane concentrations at each comparable time during maintenance of similar anesthetic depth. Maintenance of anesthesia with isoflurane resulted in higher heart rates and lower respiratory rates, compared with maintenance of anesthesia with halothane in these steers.     

Effects of body position and ventilation/compression ratios during cardiopulmonary resuscitation in cats

Eighteen cats were anesthetized and were randomly assigned to 2 groups (9 cats/group). Cardiopulmonary resuscitation (CPR) was performed on each cat, with the cat in dorsal (group 1) or lateral (group 2) recumbency, by administering 5 external cardiac compressions/1 interposed (diastolic) ventilation (American Heart Association [AHA] technique; n = 3 cats/technique), simultaneous compression and ventilation (SCV; n = 3 cats/technique), or SCV with 1 interposed (diastolic) ventilation every tenth compression (SCV/DV; n = 3 cats/technique). Fourteen of the 18 cats were resuscitated. Central aortic and venous pressures were determined concurrently with lead II electrocardiography. Arterial blood samples were collected during the base-line period (after pressure fluctuations had stabilized, with the cats spontaneously breathing room air), 2.5 minutes after the onset of arrest (defined as the cessation of aortic pressure fluctuations), and after 10 minutes of CPR. Arterial blood gas values during the base-line period or during the period of arrest were not significantly different between group-1 and group-2 cats. After CPR, arterial pH and bicarbonate values were not significantly different between groups or between technique categories. The PaCO2 values were significantly lower in cats resuscitated by SCV or by SCV/DV than in cats resuscitated by AHA (P less than 0.05). The PaO2 values were significantly (P less than 0.001) higher in group-2 cats than in group-1 cats and were significantly (P less than 0.001) different between each technique category, with cats resuscitated by AHA having the lowest PaO2 and cats resuscitated by SCV/DV having the highest PaO2. Body position, CPR technique, sex, weight, or arterial blood gas values after CPR were not predictors of successful resuscitation.     

The effects of ketamine on the minimum alveolar concentration of isoflurane in cats

OBJECTIVES: To determine the minimum alveolar concentration (MAC) of isoflurane during the infusion of ketamine. STUDY DESIGN: Prospective, experimental trial. ANIMALS: Twelve adult spayed female cats weighing 5.1 +/- 0.9 kg. METHODS: Six cats were anesthetized with isoflurane in oxygen, intubated and attached to a circle-breathing system with mechanical ventilation. Catheters were placed in a peripheral vein for the infusion of fluids and ketamine, and the jugular vein for blood sampling for the measurement of ketamine concentrations. An arterial catheter was placed to allow blood pressure measurement and sampling for the measurement of PaCO2, PaO2 and pH. PaCO2 was maintained between 29 and 41 mmHg (3.9-5.5 kPa) and body temperature was kept between 37.8 and 39.3 degrees C. Following instrumentation, the MAC of isoflurane was determined in triplicate using a tail clamp method. A loading dose (2 mg kg(-1) over 5 minutes) and an infusion (23 microg kg(-1) minute(-1)) of ketamine was started and MAC was redetermined starting 30 minutes later. Two further loading doses and infusions were used, 2 mg kg(-1) and 6 mg kg(-1) with 46 and 115 microg kg(-1) minute(-1), respectively and MAC was redetermined. Cardiopulmonary measurements were taken before application of the noxious stimulus. The second group of six cats was used for the measurement of steady state plasma ketamine concentrations at each of the three infusion rates used in the initial study and the appropriate MAC value determined from the first study. RESULTS: The MAC decreased by 45 +/- 17%, 63 +/- 18%, and 75 +/- 17% at the infusion rates of 23, 46, and 115 microg kg(-1) minute(-1). These infusion rates corresponded to ketamine plasma concentrations of 1.75 +/- 0.21, 2.69 +/- 0.40, and 5.36 +/- 1.19 microg mL(-1). Arterial blood pressure and heart rate increased significantly with ketamine. Recovery was protracted. CONCLUSIONS AND CLINICAL RELEVANCE: The MAC of isoflurane was significantly decreased by an infusion of ketamine and this was accompanied by an increase in heart rate and blood pressure. Because of the prolonged recovery in our cats, further work needs to be performed before using this in patients.     

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.