Comparison of mainstream (Capnostat 5) and two low-flow sidestream capnometers (VM-2500-S and Capnostream) in spontaneously breathing rabbits anesthetized with a Bain coaxial breathing system

ObjectiveTo evaluate agreement with PaCO₂ of two low sampling rate sidestream capnometers and a mainstream capnometer in rabbits and the effect of using high fresh gas flow from a Bain coaxial breathing system.Study designProspective, crossover study.AnimalsA total of 10 New Zealand White rabbits weighing 3.4 ± 0.3 kg [mean ± standard deviation (SD)].MethodsTwo sidestream analyzers (Viamed VM-2500-S and Capnostream 35) with a sampling rate of 50 mL minute^–1 and a mainstream capnometer (Capnostat 5) were tested. All capnometers used infrared spectroscopy and advanced microprocessor technology. Rabbits were anesthetized and intubated with noncuffed endotracheal tubes of 3 mm internal diameter and adequate seal. A sidestream sampling adapter or the mainstream capnometer was attached to the endotracheal tube and connected to a Bain coaxial breathing system. Oxygen (1.5 L minute^–1) delivered sevoflurane to maintain anesthesia. An auricular artery catheter allowed blood sampling for PaCO₂ analysis corrected to rectal temperature. Inspired and end-tidal carbon dioxide (Pe′CO₂) measurements were recorded during blood sample withdrawal. From each rabbit, 10 paired PaCO₂/Pe′CO₂ measurements were obtained. Each rabbit was recovered from anesthesia and was anesthetized again with an alternate capnometer after 1 week. Data were analyzed using Bland–Altman and two-way anova for repeated measures.ResultsAnalysis included 100 paired samples. Negative bias reflects underestimation of PaCO₂. Bland–Altman mean (±1.95 SD) was –16.7 (–35.2 to 1.8) mmHg for Capnostat 5, –27.9 (–48.6 to –7.2) mmHg for Viamed, and –18.1 (–34.3 to –1.9) mmHg for Capnostream. Viamed PaCO₂–Pe′CO₂ gradient was greater than other two capnometers.ConclusionsAll three capnometers underestimated PaCO₂. Capnostat 5 and Capnostream performed similarly.Clinical relevanceThese capnometers underestimated PaCO₂ in spontaneously breathing rabbits anesthetized using a Bain coaxial breathing system with high fresh gas flows.     

Assessing the influence of mechanical ventilation on blood gases and blood pressure in rattlesnakes

ObjectiveTo characterize the impact of mechanical positive pressure ventilation on heart rate (HR), arterial blood pressure, blood gases, lactate, glucose, sodium, potassium and calcium concentrations in rattlesnakes during anesthesia and the subsequent recovery period.Study designProspective, randomized trial.AnimalsTwenty one fasted adult South American rattlesnakes (Crotalus durissus terrificus).MethodsSnakes were anesthetized with propofol (15 mg kg⁻¹) intravenously, endotracheally intubated and assigned to one of four ventilation regimens: Spontaneous ventilation, or mechanical ventilation at a tidal volume of 30 mL kg⁻¹ at 1 breath every 90 seconds, 5 breaths minute⁻¹, or 15 breaths minute⁻¹. Arterial blood was collected from indwelling catheters at 30, 40, and 60 minutes and 2, 6, and 24 hours following induction of anesthesia and analyzed for pH, PaO₂, PaCO₂, and selected variables. Mean arterial blood pressure (MAP) and HR were recorded at 30, 40, 60 minutes and 24 hours.ResultsSpontaneous ventilation and 1 breath every 90 seconds resulted in a mild hypercapnia (PaCO₂ 22.4 ± 4.3 mmHg [3.0 ± 0.6 kPa] and 24.5 ± 1.6 mmHg [3.3 ± 0.2 kPa], respectively), 5 breaths minute⁻¹ resulted in normocapnia (14.2 ± 2.7 mmHg [1.9 ± 0.4 kPa]), while 15 breaths minute⁻¹ caused marked hypocapnia (8.2 ± 2.5 mmHg [1.1 ± 0.3 kPa]). Following recovery, blood gases of the four groups were similar from 2 hours. Anesthesia, independent of ventilation was associated with significantly elevated glucose, lactate and potassium concentrations compared to values at 24 hours (p < 0.0001). MAP increased significantly with increasing ventilation frequency (p < 0.001). HR did not vary among regimens.Conclusions and clinical relevanceMechanical ventilation had a profound impact on blood gases and blood pressure. The results support the use of mechanical ventilation with a frequency of 1–2 breaths minute⁻¹ at a tidal volume of 30 mL kg⁻¹ during anesthesia in fasted snakes.     

Effect of pressure support ventilation during weaning on ventilation and oxygenation indices in healthy horses recovering from general anesthesia

ObjectiveTo determine if pressure support ventilation (PSV) weaning from general anesthesia affects ventilation or oxygenation in horses.Study designProspective randomized clinical study.AnimalsTwenty client‐owned healthy horses aged 5 ± 2 years, weighing 456 ± 90 kg.MethodsIn the control group (CG; n = 10) weaning was performed by a gradual decrease in respiratory rate (f_R) and in the PSV group (PSVG; n = 10) by a gradual decrease in f_R with PSV. The effect of weaning was considered suboptimal if PaCO₂ > 50 mmHg, arterial pH < 7.35 plus PaCO₂ > 50 mmHg or PaO₂ < 60 mmHg were observed at any time after disconnection from the ventilator until 30 minutes after the horse stood. Threshold values for each index were established and the predictive power of these values was tested.ResultsPressure support ventilation group (PSVG) had (mean ± SD) pH 7.36 ± 0.02 and PaCO₂ 41 ± 3 mmHg at weaning and the average lowest PaO₂ 69 ± 6 mmHg was observed 15 minutes post weaning. The CG had pH 7.32 ± 0.02 and PaCO₂ 57 ± 6 mmHg at weaning and the average lowest PaO₂ 48 ± 5 mmHg at 15 minutes post weaning. No accuracy in predicting weaning effect was observed for f_R (p = 0.3474), minute volume (p = 0.1153), SaO₂ (p = 0.1737) and PaO₂/PAO₂ (p = 0.1529). A high accuracy in predicting an optimal effect of weaning was observed for V_T > 10 L (p = 0.0001), f_R/V_T ratio ≤ 0.60 breaths minute^?1 L^?1 (p = 0.0001), V_T/bodyweight > 18.5 mL kg^?1 (p = 0.0001) and PaO₂/FiO₂ > 298 (p = 0.0002) at weaning. A high accuracy in predicting a suboptimal effect of weaning was observed for V_T < 10 L (p = 0.0001), f_R/V_T ratio ≥ 0.60 breaths minute^?1 L^?1 (p = 0.0001) and Pe′CO₂ ≥ 38 mmHg (p = 0.0001) at weaning.Conclusions and clinical relevancePressure support ventilation (PSV) weaning had a better respiratory outcome. A higher V_T, V_T/body weight, PaO₂/FiO₂ ratio and a lower f_R/V_T ratio and Pe′CO₂ were accurate in predicting the effect of weaning in healthy horses recovering from general anesthesia.     

Evaluation of medetomidine-ketamine and dexmedetomidine-ketamine in Chinese water deer (Hydropotes inermis)

ObjectiveTo investigate physiological and sedative/immobilization effects of medetomidine or dexmedetomidine combined with ketamine in free-ranging Chinese water deer (CWD).Study designProspective clinical trial.Animals10 free-ranging adult Chinese water deer (11.0 ± 2.6 kg).MethodsAnimals were darted intramuscularly with 0.08 ± 0.004 mg kg^?1 medetomidine and 3.2 ± 0.2 mg kg^?1 ketamine (MK) or 0.04 ± 0.01 mg kg^?1 dexmedetomidine and 2.9 ± 0.1 mg kg^?1 ketamine (DMK) If the animal was still laterally recumbent after 60 minutes of immobilization, atipamezole was administered intravenously (MK: 0.4 ± 0.02 mg kg^?1, DMK: 0.2 ± 0.03 mg kg^?1). Heart rate (HR) respiratory rate (f_R) and temperature were recorded at 5-minute intervals. Arterial blood was taken 15 and 45 minutes after initial injection. Statistical analysis was performed using Student’s t-test or anova. p < 0.05 was considered significant.ResultsAnimals became recumbent rapidly in both groups. Most had involuntary ear twitches, but there was no response to external stimuli. There were no statistical differences in mean HR (MK: 75 ± 14 beats minute^?1; DMK: 85 ± 21 beats minute^?1), f_R (MK: 51 ± 35 breaths minute^?1; DMK; 36 ± 9 breaths minute^?1), temperature (MK: 38.1 ± 0.7 °C; DMK: 38.4 ± 0.5 °C), blood gas values (MK: PaO₂ 63 ± 6 mmHg, PaCO₂ 49.6 ± 2.6 mmHg, HCO₃^? 30.8 ± 4.5 mmol L^?1; DMK: PaO₂ 77 ± 35 mmHg, PaCO₂ 45.9 ± 11.5 mmHg, HCO₃^? 31.0 ± 4.5 mmol L^?1) and biochemical values between groups but temperature decreased in both groups. All animals needed antagonism of immobilization after 60 minutes. Recovery was quick and uneventful. There were no adverse effects after recovery.Conclusion and clinical relevanceBoth anaesthetic protocols provided satisfactory immobilisation. There was no clear preference for either protocol and both appear suitable for CWD.     

Partial pressure of end-tidal CO2 sampled via an intranasal catheter as a substitute for partial pressure of arterial CO2 in dogs

Objective: To demonstrate correlation and clinical usefulness of the partial pressure of end‐tidal CO₂ (ETCO₂) measurement by nasal catheter placement in sedated dogs with and without concurrent nasal oxygen administration as a substitute for partial pressure of arterial CO₂ (PaCO₂). Design: Prospective, cross‐over trial. Setting: University of Saskatchewan veterinary research laboratory. Animals: Six cross‐breed dogs with a mean (±SD) weight of 29.1±4.03 kg. Interventions: All dogs were sedated with 5 μg/kg medetomidine intravenously (IV) and an arterial catheter was placed in a dorsal pedal artery for removal of blood for gas analysis. A nasal catheter was placed in the ventral meatus and connected to a capnometer for ETCO₂ measurements in all dogs. Dogs receiving supplemental nasal oxygen had a second nasal catheter placed in the contralateral naris. Measurements and main results: In the group without nasal oxygen supplementation, the ETCO₂ measurement underestimated (negative bias) the PaCO₂ by ?2.20 mmHg with limits of agreement (95% confidence interval) of ?5.79, 1.39 mmHg. In the group receiving oxygen supplementation, ETCO₂ measurement underestimated (negative bias) the PaCO₂ by ?2.46 mmHg with limits of agreement (95% confidence interval) of ?8.42, 3.50 mmHg. Conclusions: The results of this study demonstrate that ETCO₂ monitoring via a nasal catheter provides a clinically acceptable substitute to arterial blood gas analysis as a means of monitoring ventilation in healthy, sedated dogs. The limits of agreement were within acceptable limits with and without concurrent insufflation of oxygen.     

Cardiovascular effects of intravenous vatinoxan (MK-467) in medetomidine–tiletamine–zolazepam anaesthetised red deer (Cervus elaphus)

ObjectiveTo determine the effect of intravenous vatinoxan administration on bradycardia, hypertension and level of anaesthesia induced by medetomidine–tiletamine–zolazepam in red deer (Cervus elaphus).Study design and animalsA total of 10 healthy red deer were included in a randomised, controlled, experimental, crossover study.MethodsDeer were administered a combination of 0.1 mg kg^–1 medetomidine hydrochloride and 2.5 mg kg^–1 tiletamine–zolazepam intramuscularly, followed by 0.1 mg kg^–1 vatinoxan hydrochloride or equivalent volume of saline intravenously (IV) 35 minutes after anaesthetic induction. Heart rate (HR), mean arterial blood pressure (MAP), respiration rate (f_R), end-tidal CO₂ (Pe′CO₂), arterial oxygen saturation (SpO₂), rectal temperature (RT) and level of anaesthesia were assessed before saline/vatinoxan administration (baseline) and at intervals for 25 minutes thereafter. Differences within treatments (change from baseline) and between treatments were analysed with linear mixed effect models (p < 0.05).ResultsMaximal (81 ± 10 beats minute^–1) HR occurred 90 seconds after vatinoxan injection and remained significantly above baseline (42 ± 4 beats minute^–1) for 15 minutes. MAP significantly decreased from baseline (122 ± 10 mmHg) to a minimum MAP of 83 ± 6 mmHg 60 seconds after vatinoxan and remained below baseline until end of anaesthesia. HR remained unchanged from baseline (43 ± 5 beats minute^–1) with the saline treatment, whereas MAP decreased significantly (112 ± 16 mmHg) from baseline after 20 minutes. Pe′CO₂, f_R and SpO₂ showed no significant differences between treatments, whereas RT decreased significantly 25 minutes after vatinoxan. Level of anaesthesia was not significantly influenced by vatinoxan.Conclusions and clinical relevanceVatinoxan reversed hypertension and bradycardia induced by medetomidine without causing hypotension or affecting the level of anaesthesia in red deer. However, the effect on HR subsided 15 minutes after vatinoxan IV administration. Vatinoxan has the potential to reduce anaesthetic side effects in non-domestic ruminants immobilised with medetomidine–tiletamine–zolazepam.     

Transcutaneous monitor approximates PaCO(2) but not PaO(2) in anesthetized rabbits

ObjectiveTo compare the accuracy of transcutaneous (tc) to arterial partial pressure of carbon dioxide (PaCO₂) and partial pressure of oxygen (PaO₂) in anesthetized rabbits.Study designProspective, randomized, experimental study.AnimalsEight healthy adult female New Zealand white rabbits weighing 4.05 ± 0.30 kg.MethodsIsoflurane anesthetized rabbits received six treatments in random order; PaCO₂ < 35, 35-45, and >45 mmHg and PaO₂ < 80, 100-200, >200 mmHg. Arterial and transcutaneous measurements were taken after 15 minutes of stabilization at each condition. Linear regression, correlation and Bland-Altman analysis were performed to compare PtcCO₂ to PaCO₂ and PtcO₂ to PaO₂.ResultsOver a range of measured PaCO₂ values from 21 to 67 mmHg (n = 24) mean bias for PtcCO₂ was -1 mmHg and the 95% limits of agreement were -7 to 5 mmHg. The correlation between PtcCO₂ and PaCO₂ was strong with R² value of 0.9454. Over the entire range of measured PaO₂ values (46-508 mmHg) mean bias for PtcO₂ was -61 mmHg and the 95% limits of agreement were -226 to 104 mmHg. Correlation was poor with R² = 0.5969. Comparing PtcO₂ to PaO₂ over a narrower range [PaO₂ < 150 mmHg (n = 13)] improved the correlation, with an R² value of 0.8518, mean bias of -7 mmHg and 95% limits of agreement from -33 to 19 mmHg.Conclusions and clinical relevanceIn healthy anesthetized rabbits, PtcCO₂ closely approximated PaCO₂. In contrast PtcO₂ underestimated PaO₂, particularly at high values. The PtcCO₂ sensor may be a useful noninvasive way to assess adequacy of ventilation in anesthetized rabbits.     

Total intravenous anesthesia in domestic chicken (Gallus gallus domesticus) with propofol alone or in combination with methadone,nalbuphine or fentanyl for ulna osteotomy

ObjectiveTo compare the propofol infusion rate and cardiopulmonary effects during total intravenous anesthesia with propofol alone and propofol combined with methadone, fentanyl or nalbuphine in domestic chickens undergoing ulna osteotomy.Study designProspective, randomized, experiment trial.AnimalsA total of 59 healthy Hissex Brown chickens weighing 1.5 ± 0.2 kg.MethodsAnesthesia was induced with propofol (9 mg kg^–1) administered intravenously (IV) and maintained with propofol (1.2 mg kg^–1 minute^–1) for 30 minutes. Birds were intubated and supplemented with 100% oxygen through a nonrebreathing circuit under spontaneous ventilation. Thereafter, each animal was randomly assigned to one of four groups: group P, no treatment; group PM, methadone (6 mg kg^–1) intramuscularly (IM); group PN, nalbuphine IM (12.5 mg kg^–1); and group PF, fentanyl IV (30 μg kg^–1 loading dose, 30 μg kg^–1 hour^–1 constant rate infusion). During the osteotomy surgery, the propofol infusion rate was adjusted to avoid movement of birds and provide adequate anesthesia. Pulse rate, invasive blood pressure, respiratory frequency, end-tidal carbon dioxide partial pressure (Pe′CO₂) and hemoglobin oxygen saturation (SpO₂) were recorded.ResultsData were available from 58 chickens. The mean ± standard deviation propofol infusion rate (mg kg^–1 minute^–1) for the duration of anesthesia was: group P, 0.81 ± 0.15; group PM, 0.66 ± 0.11; group PN, 0.60 ± 0.14; and group PF, 0.80 ± 0.07. Significant differences were P versus PM (p = 0.042), P versus PN (p = 0.002) and PF versus PN (p = 0.004). Pulse rate, blood pressure and SpO₂ remained acceptable for anesthetized birds with minor differences among groups. Values of Pe′CO₂ >60 mmHg (8 kPa) were observed in all groups.Conclusions and clinical relevanceMethadone and nalbuphine, but not fentanyl, decreased the propofol infusion rate required for anesthesia maintenance, but resulted in no obvious benefit in physiological variables.     

Anesthetic effects of ketamine–medetomidine–hydromorphone in dogs during high-quality,high-volume surgical sterilization program under field conditions

ObjectiveTo describe the anesthetic and adverse effects of an injectable anesthetic protocol in dogs as part of a high-volume sterilization program under field conditions in Belize.Study designProspective, observational, field study.AnimalsA total of 23 female and eight male dogs (14.2 ± 7.7 kg; age ≥ 8 weeks).MethodsUsing a volume per kg-based dose chart, dogs were administered ketamine (4.5 mg kg⁻¹), medetomidine (0.04 mg kg⁻¹) and hydromorphone (0.09 mg kg⁻¹) intramuscularly. After induction of anesthesia, an endotracheal tube was inserted and dogs were allowed spontaneous breathing in room air. Monitoring included peripheral oxygen saturation (SpO₂), mean arterial pressure (MAP), heart rate (HR), respiratory rate, rectal temperature and end-tidal carbon dioxide (Pe′CO₂). Meloxicam (0.2 mg kg⁻¹) was administered subcutaneously after surgery. Data were analyzed with linear models and chi-square tests (p < 0.05).ResultsOnset of lateral recumbency (3.4 ± 2 minutes) was rapid. Desaturation (SpO₂ < 90%) was observed at least once in 64.5% of dogs and was more frequent in large dogs (p = 0.019). Hypercapnia (Pe′CO₂ ≥ 50 mmHg; 6.7 kPa) was observed in 48.4% of dogs. MAP was 111 ± 19 mmHg, mean ± standard deviation. Hypertension (MAP ≥ 120 mmHg), bradycardia (HR ≤ 60 beats minute⁻¹) and tachycardia (HR ≥ 140 beats minute⁻¹) were observed in 45.2%, 16.1% and 3.3% of dogs, respectively. Hypotension and hypothermia were not observed. Sex was not significantly associated with any complication. Return of swallowing reflex and time to standing were 71 ± 23 and 152 ± 50 minutes after injection, respectively. Return of swallowing was significantly longer in large dogs.Conclusions and clinical relevanceAt the doses used, ketamine–medetomidine–hydromorphone was effective in dogs for high-volume sterilization. In this field setting, adverse effects included hypoventilation, hypoxemia and prolonged recovery.     

Comparison of cardiopulmonary effects of etorphine and thiafentanil administered as sole agents for immobilization of impala (Aepyceros melampus)

ObjectiveTo compare the cardiopulmonary effects of the opioids etorphine and thiafentanil for immobilization of impala.Study designTwo-way crossover, randomized study.AnimalsA group of eight adult female impala.MethodsImpala were given two treatments: 0.09 mg kg^–1 etorphine or 0.09 mg kg^–1 thiafentanil via remote dart injection. Time to recumbency, quality of immobilization and recovery were assessed. Respiratory rate, heart rate (HR), mean arterial blood pressure (MAP) and arterial blood gases were measured. A linear mixed model was used to analyse the effects of treatments, treatments over time and interactions of treatment and time (p < 0.05).ResultsTime to recumbency was significantly faster with thiafentanil (2.0 ± 0.8 minutes) than with etorphine (3.9 ± 1.6 minutes; p = 0.007). Both treatments produced bradypnoea, which was more severe at 5 minutes with thiafentanil (7 ± 4 breaths minute^–1) than with etorphine (13 ± 12 breaths minute^–1; p = 0.004). HR increased with both treatments but significantly decreased over time when etorphine (132 ± 17 to 82 ± 11 beats minute^–1) was compared with thiafentanil (113 ± 22 to 107 ± 36 beats minute^–1; p < 0.001). Both treatments caused hypertension which was more profound with thiafentanil (mean overall MAP = 140 ± 14 mmHg; p < 0.001). Hypoxaemia occurred with both treatments but was greater with thiafentanil [PaO₂ 37 ± 13 mmHg (4.9 kPa)] than with etorphine [45 ± 16 mmHg (6.0 kPa)] 5 minutes after recumbency (p < 0.001). After 30 minutes, PaO₂ increased to 59 ± 10 mmHg (7.9 kPa) with both treatments (p < 0.001).Conclusions and clinical relevanceThe shorter time to recumbency with thiafentanil may allow easier and faster retrieval in the field. However, thiafentanil caused greater hypertension, and ventilatory effects during the first 10 minutes, after administration.     

Comparison of mean heart rate in anaesthetized dachshunds and other breeds of dog undergoing spinal magnetic resonance imaging

ObjectiveClinical experience suggests that dachshunds are prone to bradycardia during general anaesthesia (GA). The study investigated mean heart rates in anaesthetized dachshunds and other breeds of dog.Study DesignRetrospective clinical study.AnimalsSixty one dachshunds and 62 dogs of other breeds met inclusion criteria.MethodsClinical records of small breed dogs undergoing GA for spinal Magnetic Resonance Imaging between September 2008 and March 2010 were identified and examined. Data collected included drugs administered, baseline heart (HR) and respiratory (f_R) rates and rectal temperature. The following information was noted from anaesthetic records: HR, f_R, mean non-invasive arterial pressure and end-tidal carbon dioxide (Pe′CO₂₎ and anaesthetic agent (Fe′agent) during the first 60 minutes of anaesthesia; rectal temperature at a time closest to the cessation of anaesthesia, ventilatory mode (spontaneous/mechanical) and fluid infusion rate. Univariate analysis with Student t-test and Fisher's test identified parameters significant in predicting a lowered HR. A multivariate analysis investigated their effect on the mean HR during GA.ResultsNo differences were found between groups regarding: age, baseline HR, baseline temperature, incidence of hypotension, Fe′agent, mean Pe′CO₂ and fluid infusion rate. Body mass was smaller for dachshunds (6.7 ± 1.5 kg) compared to other breeds (7.8 ± 1.8 kg) (p = 0.0005). The lowest HR recorded was lower in dachshunds (64 ± 19 beats minute^?1) compared to other breeds (72 ± 21 beats minute^?1) (p = 0.03). Mean HR was lower in dachshunds (75 ± 21 beats minute^?1) compared to other breeds (84 ± 21 beats minute^?1) (p = 0.02). Post-procedural temperature (°C) was lower in dachshunds (35.5 ± 1.1) compared to other breeds (36.1 ± 1.2) (p = 0.007) and anticholinergics were also administered more frequently (p = 0.026). Multivariate analysis identified that breed and mean Pe′CO₂ affected mean HR during anaesthesia.ConclusionThis study supported our hypothesis that dachshunds have a lower mean HR under GA than other small breed dogs.     

Evaluation of chemical restraint,isoflurane anesthesia and methadone or tramadol as preventive analgesia in spotted pacas (Cuniculus paca) subjected to laparoscopy

ObjectiveTo evaluate the efficacy and cardiopulmonary effects of ketamine–midazolam for chemical restraint, isoflurane anesthesia and tramadol or methadone as preventive analgesia in spotted pacas subjected to laparoscopy.Study designProspective placebo-controlled blinded trial.AnimalsA total of eight captive female Cuniculus paca weighing 9.3 ± 0.9 kg.MethodsAnimals were anesthetized on three occasions with 15 day intervals. Manually restrained animals were administered midazolam (0.5 mg kg^–1) and ketamine (25 mg kg^–1) intramuscularly. Anesthesia was induced and maintained with isoflurane 30 minutes later. Tramadol (5 mg kg^–1), methadone (0.5 mg kg^–1) or saline (0.05 mL kg^–1) were administered intramuscularly 15 minutes prior to laparoscopy. Heart rate (HR), respiratory rate, mean arterial pressure (MAP), peripheral oxygen saturation (SpO₂), end-tidal CO₂ partial pressure (Pe′CO₂), end-tidal concentration of isoflurane (Fe′Iso), pH, PaO₂, PaCO₂, bicarbonate (HCO₃^?), anion gap (AG) and base excess (BE) were monitored after chemical restraint, anesthesia induction and at different laparoscopy stages. Postoperative pain was assessed by visual analog scale (VAS) for 24 hours. Variables were compared using anova or Friedman test (p < 0.05).ResultsChemical restraint was effective in 92% of animals. Isoflurane anesthesia was effective; however, HR, MAP, pH and AG decreased, whereas Pe′CO₂, PaO₂, PaCO₂, HCO₃^? and BE increased. MAP was stable with tramadol and methadone treatments; HR, Fe′Iso and postoperative VAS decreased. VAS was lower for a longer time with methadone treatment; SpO₂ and AG decreased, whereas Pe′CO₂, PaCO₂ and HCO₃^? increased.Conclusions and clinical relevanceKetamine–midazolam provided satisfactory restraint. Isoflurane anesthesia for laparoscopy was effective but resulted in hypotension and respiratory acidosis. Tramadol and methadone reduced isoflurane requirements, provided postoperative analgesia and caused hypercapnia, with methadone causing severe respiratory depression. Thus, the anesthetic protocol is adequate for laparoscopy in Cuniculus paca; however, methadone should be avoided.     

Comparison of the effects of propofol or alfaxalone for anaesthesia induction and maintenance on respiration in cats

ObjectiveTo compare the effects of propofol and alfaxalone on respiration in cats.Study designRandomized, ‘blinded’, prospective clinical trial.AnimalsTwenty cats undergoing ovariohysterectomy.MethodsAfter premedication with medetomidine 0.01 mg kg⁻¹ intramuscularly and meloxicam 0.3 mg kg⁻¹ subcutaneously, the cats were assigned randomly into two groups: group A (n = 10) were administered alfaxalone 5 mg kg⁻¹ minute⁻¹ followed by 10 mg kg⁻¹ hour⁻¹ intravenously (IV) and group P (n = 10) were administered propofol 6 mg kg⁻¹ minute⁻¹ followed by 12 mg kg⁻¹hour⁻¹ IV for induction and maintenance of anaesthesia, respectively. After endotracheal intubation, the tube was connected to a non-rebreathing system delivering 100% oxygen. The anaesthetic maintenance drug rate was adjusted (± 0.5 mg kg⁻¹ hour⁻¹) every 5 minutes according to a scoring sheet based on physiologic variables and clinical signs. If apnoea > 30 seconds, end-tidal carbon dioxide (Pe′CO₂) > 7.3 kPa (55 mmHg) or arterial haemoglobin oxygen saturation (SpO₂) < 90% occurred, manual ventilation was provided. Methadone was administered postoperatively. Data were analyzed using independent-samples t-tests, Fisher's exact test, linear mixed-effects models and binomial test.ResultsManual ventilation was required in two and eight of the cats in group A and P, respectively (p = 0.02). Two cats in both groups showed apnoea. Pe′CO₂ > 7.3 kPa was recorded in zero versus four and SpO₂ < 90% in zero versus six cats in groups A and P respectively. Induction and maintenance dose rates (mean ± SD) were 11.6 ± 0.3 mg kg⁻¹ and 10.7 ± 0.8 mg kg⁻¹ hour⁻¹ for alfaxalone and 11.7 ± 2.7 mg kg⁻¹ and 12.4 ± 0.5 mg kg⁻¹ hour⁻¹ for propofol.Conclusion and clinical relevanceAlfaxalone had less adverse influence on respiration than propofol in cats premedicated with medetomidine. Alfaxalone might be better than propofol for induction and maintenance of anaesthesia when artificial ventilation cannot be provided.     

Association of partial pressure of carbon dioxide in expired gas and arterial blood at three different ventilation states in apneic chickens (Gallus domesticus) during air sac insufflation anesthesia

ObjectiveTo test whether partial pressure of CO₂ in expired gas (PēCO₂) predicts the partial pressure of CO₂ in arterial blood (PaCO₂) in apneic chickens during air sac insufflation anesthesia at three different ventilation states. Secondary objective: To determine the PēCO₂ at which apnea occurs during air sac insufflation anesthesia.Study designRandomized cross-over study.AnimalsTwenty-three healthy male white leghorn chickens.MethodsChickens were anesthetized via mask with isoflurane in oxygen and an air sac cannula was placed in the right abdominal air sac. Delivery of isoflurane in O₂ was transferred from the mask to the air sac cannula. The birds were maintained at a surgical plane of anesthesia and apnea was induced by adjusting gas flow; the PēCO₂ at apnea was recorded. The birds were then paralyzed and gas flow was adjusted to achieve three different PēCO₂s in random order: 43 mmHg (5.6 kPa) [hypoventilation]; 33 mmHg (4.3 kPa) [normoventilation]; and 23 mmHg (3.0 kPa) [hyperventilation]. After maintaining the target expired isoflurane concentration (EIso; 1.85 or 1.90%) and PēCO₂ for 15 minutes, arterial blood gas analysis was performed to determine the PaCO₂. The chickens were euthanized at the end of the experiment.ResultsBased on Bland-Altman comparisons, PēCO₂ was not strongly associated with PaCO₂ during the three ventilation states. The PēCO₂ at which apnea occurred varied {median (minimum, maximum): 35 (30, 48) mmHg [4.6 (3.9, 6.2) kPa]}.ConclusionsMeasured PēCO₂ cannot be used in a simple linear fashion to predict PaCO₂ in birds during air sac insufflation anesthesia. The PēCO₂ at which apnea occurs during air sac insufflation anesthesia is not predictable.Clinical relevanceArterial blood gases should be used to monitor CO₂ during air sac insufflation anesthesia to verify appropriate patient ventilation.     

The effect of low dose rocuronium bromide on eyeball position, muscle relaxation, and ventilation in dogs

A central eyeball position is often required during sedation or anaesthesia to facilitate examination of the eye. However, use of neuromuscular blockade to produce a central eye position may result in depressed ventilation. This study evaluated the eyeball position, muscle relaxation and changes in ventilation during general anaesthesia after the IV administration of 0.1 mg kg^?1 rocuronium. With client consent, 12 dogs of different breeds, body mass 27.2 ± 11.8 kg, aged 5.6 ± 2.8 years (mean ± SD) were anaesthetized for ocular examination. Pre‐anaesthetic medication was 0.01 mg kg^?1 medetomidine and 0.2 mg kg^?1 butorphanol IV. Anaesthesia was induced with propofol to effect and maintained with 10 mg kg^?1 hour^?1 propofol by infusion. The dogs were placed in left lateral recumbency, their trachea intubated and connected to a circle breathing system (Fi O₂ = 1.0). All dogs breathed spontaneously. The superficial peroneal nerve of the right hind leg was stimulated every 15 seconds with a train‐of‐four (TOF) stimulation pattern and neuromuscular function was assessed with an acceleromyograph (TOF‐Guard). Adequacy of ventilation was measured with the Ventrak 1550. After 10 minutes of anaesthesia to allow stabilisation of baseline values, 0.1 mg kg^?1 rocuronium was administered IV. Minute volume (Vm ), tidal volume (Vt ), respiratory rate (RR), Pe ′CO₂ and maximal depression of T1 and TOF ratio were measured. Data were analysed using a paired t‐test. The changes in the eyeball position were recorded. A total of 100 ± 33 seconds after the injection of rocuronium, T1 was maximally depressed to 62 ± 21% and the TOF ratio to 42 ± 18% of baseline values. Both variables returned to baseline after 366 ± 132 seconds (T1) and 478 ± 111 seconds (TOF). There was no significant reduction in Vm (2.32 ± 1.1 L minute^?1), Vt (124.1 ± 69.3 mL) and RR (10 ± 3.8 breaths minute^?1) and no increase in Pe ′CO₂ (6.5 ± 2.1 kPa (48.8 ± 16.1 mm Hg)) throughout the procedure. The eyeball rotated to a central position 35 ± 7 seconds after rocuronium IV and remained there for a minimum of 20 ± 7 minutes in all dogs. We conclude that rocuronium at a dose of 0.1 mg kg^?1 can be administered to dogs IV with minimal changes in ventilatory variables. The eyeball is fixed in a central position for at least 20 minutes, which greatly facilitates clinical examination.     

Effect of end-inspiratory pause on airway and physiological dead space in anesthetized horses

ObjectiveTo evaluate the impact of a 30% end-inspiratory pause (EIP) on alveolar tidal volume (V_Talv), airway (V_Daw) and physiological (V_Dphys) dead spaces in mechanically ventilated horses using volumetric capnography, and to evaluate the effect of EIP on carbon dioxide (CO₂) elimination per breath (Vco₂br^–1), PaCO_2, and the ratio of PaO₂-to-fractional inspired oxygen (PaO₂:FiO₂).Study designProspective research study.AnimalsA group of eight healthy research horses undergoing laparotomy.MethodsAnesthetized horses were mechanically ventilated as follows: 6 breaths minute^–1, tidal volume (V_T) 13 mL kg^–1, inspiratory-to-expiratory time ratio 1:2, positive end-expiratory pressure 5 cmH₂O and EIP 0%. Vco₂br^–1 and expired tidal volume (V_TE) of 10 consecutive breaths were recorded 30 minutes after induction, after adding 30% EIP and upon EIP removal to construct volumetric capnograms. A stabilization period of 15 minutes was allowed between phases. Data were analyzed using a mixed-effect linear model. Significance was set at p < 0.05.ResultsThe EIP decreased V_Daw from 6.6 (6.1–6.7) to 5.5 (5.3–6.1) mL kg^–1 (p < 0.001) and increased V_Talv from 7.7 ± 0.7 to 8.6 ± 0.6 mL kg^–1 (p = 0.002) without changing the V_TE. The V_Dphys to V_TE ratio decreased from 51.0% to 45.5% (p < 0.001) with EIP. The EIP also increased PaO₂:FiO₂ from 393.3 ± 160.7 to 450.5 ± 182.5 mmHg (52.5 ± 21.4 to 60.0 ± 24.3 kPa; p < 0.001) and Vco₂br^–1 from 0.49 (0.45–0.50) to 0.59 (0.45–0.61) mL kg^–1 (p = 0.008) without reducing PaCO₂.Conclusions and clinical relevanceThe EIP improved oxygenation and reduced V_Daw and V_Dphys, without reductions in PaCO₂. Future studies should evaluate the impact of different EIP in healthy and pathological equine populations under anesthesia.     

Evaluation of butorphanol, medetomidine and midazolam as a reversible narcotic combination in free-ranging African lions (Panthera leo)

ObjectiveTo evaluate the effects of the combination butorphanol, medetomidine and midazolam (BMM) and its reversibility in lions.Study designProspective clinical trial.AnimalsThirty free-ranging lions, 10 male and 20 female, weighing 81-210 kg.MethodsLions were immobilised with butorphanol mean 0.31 ± SD 0.034 mg kg^?1, medetomidine 0.052 ± 0.006 mg kg^?1, midazolam 0.21 ± 0.024 mg kg^?1 and hyaluronidase 1250 IU administered intramuscularly with a dart gun. Upon recumbency, physiological parameters and anaesthetic depth were monitored 10-15 minutes after darting (T1) and repeated every 10 minutes for a further 30 minutes (T2, T3, T4). Arterial blood gas analyses were performed at T1 and T4. At the end of the procedure, 45-60 minutes after initial darting, immobilisation was reversed with naltrexone 0.68 ± 0.082 mg kg^?1, atipamezole 0.26 ± 0.031 mg kg^?1, and flumazenil 0.0032 ± 0.0007 mg kg^?1 administered intravenously and subcutaneously.ResultsThe BMM combination rapidly induced immobilisation and lateral recumbency was reached within 7.25 ± 2.3 minutes. Median induction score [scored 1 (excellent) to 4 (poor)] was 1.4 (range 1-2). Cardio-respiratory parameters were stable. Heart rate varied from 32 to 72 beats per minute, respiratory rate from 14 to 32 breaths minute^?1 and rectal temperature from 36.6 to 40.3 °C. No sudden arousals were observed. Arterial blood gas analyses revealed a mean pH of 7.33, PaCO₂ of 33 mmHg and PaO₂ of 87 mmHg. Mild to moderate hypoxemia was seen in four lions. Recovery was smooth and lions were walking within 4.4 ± 4.25 minutes. Median recovery score [scored 1 (excellent) to 4 (poor)] was 1.3 (range 1-2).Conclusion and clinical relevanceThe drug combination proved to be effective in immobilising free-ranging healthy lions of both sexes with minimal cardio-respiratory changes.     

Cardiovascular,respiratory, electrolyte and acid–base balance during continuous dexmedetomidine infusion in anesthetized dogs

ObjectiveTo evaluate the cardiovascular, respiratory, electrolyte and acid–base effects of a continuous infusion of dexmedetomidine during propofol–isoflurane anesthesia following premedication with dexmedetomidine.Study designProspective experimental study.AnimalsFive adult male Walker Hound dogs 1–2 years of age averaging 25.4 ± 3.6 kg.MethodsDogs were sedated with dexmedetomidine 10 μg kg^?1 IM, 78 ± 2.3 minutes (mean ± SD) before general anesthesia. Anesthesia was induced with propofol (2.5 ± 0.5 mg kg^?1) IV and maintained with 1.5% isoflurane. Thirty minutes later dexmedetomidine 0.5 μg kg^?1 IV was administered over 5 minutes followed by an infusion of 0.5 μg kg^?1 hour^?1. Cardiac output (CO), heart rate (HR), ECG, direct blood pressure, body temperature, respiratory parameters, acid–base and arterial blood gases and electrolytes were measured 30 and 60 minutes after the infusion started. Data were analyzed via multiple linear regression modeling of individual variables over time, compared to anesthetized baseline values. Data are presented as mean ± SD.ResultsNo statistical difference from baseline for any parameter was measured at any time point. Baseline CO, HR and mean arterial blood pressure (MAP) before infusion were 3.11 ± 0.9 L minute^?1, 78 ± 18 beats minute^?1 and 96 ± 10 mmHg, respectively. During infusion CO, HR and MAP were 3.20 ± 0.83 L minute^?1, 78 ± 14 beats minute^?1 and 89 ± 16 mmHg, respectively. No differences were found in respiratory rates, PaO₂, PaCO₂, pH, base excess, bicarbonate, sodium, potassium, chloride, calcium or lactate measurements before or during infusion.Conclusions and clinical relevanceDexmedetomidine infusion using a loading dose of 0.5 μg kg^?1 IV followed by a constant rate infusion of 0.5 μg kg^?1 hour^?1 does not cause any significant changes beyond those associated with an IM premedication dose of 10 μg kg^?1, in propofol–isoflurane anesthetized dogs. IM dexmedetomidine given 108 ± 2 minutes before onset of infusion showed typical significant effects on cardiovascular parameters.     

A clinical study on the effect in horses during medetomidine-isoflurane anaesthesia, of butorphanol constant rate infusion on isoflurane requirements, on cardiopulmonary function and on recovery characteristics

ObjectiveTo test if the addition of butorphanol by constant rate infusion (CRI) to medetomidine–isoflurane anaesthesia reduced isoflurane requirements, and influenced cardiopulmonary function and/or recovery characteristics.Study designProspective blinded randomised clinical trial.Animals61 horses undergoing elective surgery.MethodsHorses were sedated with intravenous (IV) medetomidine (7 μg kg^?1); anaesthesia was induced with IV ketamine (2.2 mg kg^?1) and diazepam (0.02 mg kg^?1) and maintained with isoflurane and a CRI of medetomidine (3.5 μg kg^?1 hour^?1). Group MB (n = 31) received butorphanol CRI (25 μg kg^?1 IV bolus then 25 μg kg^?1 hour^?1); Group M (n = 30) an equal volume of saline. Artificial ventilation maintained end-tidal CO₂ in the normal range. Horses received lactated Ringer’s solution 5 mL kg^?1 hour^?1, dobutamine <1.25 μg kg^?1 minute^?1 and colloids if required. Inspired and exhaled gases, heart rate and mean arterial blood pressure (MAP) were monitored continuously; pH and arterial blood gases were measured every 30 minutes. Recovery was timed and scored. Data were analyzed using two way repeated measures anova, independent t-tests or Mann–Whitney Rank Sum test (p < 0.05).ResultsThere was no difference between groups with respect to anaesthesia duration, end-tidal isoflurane (MB: mean 1.06 ± SD 0.11, M: 1.05 ± 0.1%), MAP (MB: 88 ± 9, M: 87 ± 7 mmHg), heart rate (MB: 33 ± 6, M: 35 ± 8 beats minute^?1), pH, PaO₂ (MB: 19.2 ± 6.6, M: 18.2 ± 6.6 kPa) or PaCO_2. Recovery times and quality did not differ between groups, but the time to extubation was significantly longer in group MB (26.9 ± 10.9 minutes) than in group M (20.4 ± 9.4 minutes).Conclusion and clinical relevanceButorphanol CRI at the dose used does not decrease isoflurane requirements in horses anaesthetised with medetomidine–isoflurane and has no influence on cardiopulmonary function or recovery.     

Comparison of some cardiopulmonary effects of etorphine and thiafentanil during the chemical immobilization of blesbok (Damaliscus pygargus phillipsi)

ObjectiveTo determine the cardiopulmonary effects of etorphine and thiafentanil for immobilization of blesbok.Study designBlinded, randomized, two-way crossover study.AnimalsA group of eight adult female blesbok.MethodsAnimals were immobilized twice, once with etorphine (0.09 mg kg^–1) and once with thiafentanil (0.09 mg kg^–1) administered intramuscularly by dart. Immobilization quality was assessed and analysed by Wilcoxon signed-rank test. Time to final recumbency was compared between treatments by one-way analysis of variance. Cardiopulmonary effects including respiratory rate (?_R), arterial blood pressures and arterial blood gases were measured. A linear mixed model was used to assess the effects of drug treatments over the 40 minute immobilization period. Significant differences between treatments, for treatment over time as well as effect of treatment by time on the variables, were analysed (p < 0.05).ResultsThere was no statistical difference (p = 0.186) between treatments for time to recumbency. The mean ?_R was lower with etorphine (14 breaths minute^–1) than with thiafentanil (19 breaths minute^–1, p = 0.034). The overall mean PaCO₂ was higher with etorphine [45 mmHg (6.0 kPa)] than with thiafentanil [41 mmHg (5.5 kPa), p = 0.025], whereas PaO₂ was lower with etorphine [53 mmHg (7.1 kPa)] than with thiafentanil [64 mmHg (8.5 kPa), p < 0.001]. The systolic arterial pressure measured throughout all time points was higher with thiafentanil than with etorphine (p = 0.04). The difference varied from 30 mmHg at 20 minutes after recumbency to 14 mmHg (standard error difference 2.7 mmHg) at 40 minutes after recumbency. Mean and diastolic arterial pressures were significantly higher with thiafentanil at 20 and 25 minute measurement points only (p < 0.001).ConclusionsBoth drugs caused clinically relevant hypoxaemia; however, it was less severe with thiafentanil. Ventilation was adequate. Hypertension was greater and immobilization scores were lower with thiafentanil.