Arterial blood gas anomaly in canine hepatobiliary disease

Arterial blood gas analysis is an important diagnostic and monitoring tool for respiratory abnormalities. In human medicine, lung complications often occur as a result of liver disease. Although pulmonary complications of liver disease have not been reported in dogs, we have frequently encountered hypoxemia in dogs with liver disorders, especially extrahepatic biliary obstruction. In addition, respiratory disorders account for 20% of perioperative fatalities in dogs. Therefore, in this study, we evaluated the respiratory status in dogs with hepatobiliary disease by arterial blood gas analysis. PaO₂ and PaCO₂ were measured. Alveolar-arterial oxygen difference (AaDO₂), the indicator of gas exchange efficiency, was calculated. Compared to healthy dogs (control group), hepatobiliary disease dogs had significantly lower PaO₂ and higher AaDO₂. Hypoxemia (PaO₂ of ≤80 mmHg) was observed in 28/71 dogs with hepatobiliary disease. AaDO₂ was higher (≥30 mmHg) than the control group range (11.6 to 26.4 mmHg) in 32/71 hepatobiliary disease dogs. By classifying type of hepatobiliary disease, dogs with extrahepatic biliary obstruction and chronic hepatitis showed significantly lower PaO₂ and higher AaDO₂ than in a control group. Dogs with chronic hepatitis also had significantly lower PaCO₂. The present study shows that dogs with hepatobiliary disease have respiratory abnormalities more than healthy dogs. Preanesthetic or routine arterial blood gas analysis is likely beneficial to detect the respiratory abnormalities in dogs with hepatobiliary disease, especially extrahepatic biliary obstruction and chronic hepatitis.     

A comparison of the effects of carbon dioxide and medical air for abdominal insufflation on respiratory parameters in xylazine-sedated sheep undergoing laparoscopic artificial insemination

AIMS: To determine if abdominal insufflation with medical air will improve oxygenation and ventilation parameters when compared to insufflation with CO₂ in xylazine-sedated sheep undergoing laparoscopic artificial insemination (AI).

METHODS: Forty-seven sheep underwent oestrus synchronisation and were fasted for 24 hours prior to laparoscopic AI. Each animal was randomised to receive either CO₂ or medical air for abdominal insufflation. An auricular arterial catheter was placed and utilised for serial blood sampling. Respiratory rates (RR) and arterial blood samples were collected at baseline, after xylazine (0.1?mg/kg I/V) sedation, 2 minutes after Trendelenburg positioning, 5 minutes after abdominal insufflation, and 10 minutes after being returned to a standing position. Blood samples were collected in heparinised syringes, stored on ice, and analysed for arterial pH, partial pressure of arterial O₂ (PaO₂), and CO₂ (PaCO₂). The number of ewes conceiving to AI was also determined.

RESULTS: Repeated measures ANOVA demonstrated temporal effects on RR, PaO₂, PaCO₂ and arterial pH during the laparoscopic AI procedure (p<0.001), but no difference between insufflation groups (p>0.01). No sheep experienced hypercapnia (PaCO₂>50?mmHg) or acidaemia (pH<7.35). Hypoxaemia (PaO₂<70?mmHg) was diagnosed during the procedure in 14/22 (64%) ewes in the CO₂ group compared with 8/23 (35%) ewes in the medical air group (p=0.053). Overall, 15/20 (75%) ewes in the CO₂ group conceived to AI compared with 16/22 (72.7%) in the medical air group (p=0.867).

CONCLUSIONS AND CLINICAL RELEVANCE: There were no statistical or clinical differences in RR, PaO₂, PaCO₂, pH, or conception to AI when comparing the effects of CO₂ and medical air as abdominal insufflation gases. None of the sheep experienced hypercapnia or acidaemic, yet 42% (19/45) of sheep developed clinical hypoxaemia, with a higher percentage of ewes in the CO₂ group developing hypoxaemia than in the medical air group. Based on the overall analysis, medical air could be utilised as a comparable alternative for abdominal insufflation during laparoscopic AI procedures.     

Postoperative oxygenation in healthy dogs following mechanical ventilation with fractions of inspired oxygen of 0.4 or >0.9

ObjectiveTo evaluate arterial oxygenation during the first 4 postoperative hours in dogs administered different fractions of inspired oxygen (FiO₂) during general anesthesia with mechanical ventilation.Study designProspective, randomized clinical trial.AnimalsA total of 20 healthy female dogs, weighing >15 kg and body condition scores 3–7/9, admitted for ovariohysterectomy.MethodsDogs were randomized to breathe an FiO₂ >0.9 or 0.4 during isoflurane anesthesia with intermittent positive pressure ventilation. The intraoperative PaO₂:FiO₂ ratio was recorded during closure of the linea alba. Arterial blood was obtained 5, 60 and 240 minutes after extubation for measurement of PaO₂ and PaCO₂ (FiO₂ = 0.21). Demographic characteristics, duration of anesthesia, PaO₂:FiO₂ ratio and anesthetic agents were compared between groups with Wilcoxon tests. The postoperative PaO₂, PaCO₂, rectal temperature, a visual sedation score and events of hypoxemia (PaO₂ < 80 mmHg) were compared between groups with mixed-effects models or generalized linear mixed models.ResultsGroups were indistinguishable by demographic characteristics, duration of anesthesia, anesthetic agents administered and intraoperative PaO₂:FiO₂ ratio (all p > 0.08). Postoperative PaO₂, PaCO₂, rectal temperature or sedation score were not different between groups (all p > 0.07). During the first 4 postoperative hours, hypoxemia occurred in three and seven dogs that breathed FiO₂ >0.9 or 0.4 during anesthesia, respectively (p = 0.04).Conclusions and clinical relevanceThe results identified no advantage to decreasing FiO₂ to 0.4 during anesthesia with mechanical ventilation with respect to postoperative oxygenation. Moreover, the incidence of hypoxemia in the first 4 hours after anesthesia was higher in these dogs than in dogs breathing FiO₂ >0.9.     

Individualized positive end-expiratory pressure following alveolar recruitment manoeuvres in lung-healthy anaesthetized dogs: a randomized clinical trial on early postoperative arterial oxygenation

ObjectiveTo assess and compare the effect of intraoperative stepwise alveolar recruitment manoeuvres (ARMs), followed by individualized positive end-expiratory pressure (PEEP), defined as PEEP at maximal respiratory system compliance + 2 cmH₂O (PEEP_maxCrs+2), with that of spontaneous ventilation (SV) and controlled mechanical ventilation (CMV) without ARM or PEEP on early postoperative arterial oxygenation in anaesthetized healthy dogs.Study designProspective, randomized, nonblinded clinical study.AnimalsA total of 32 healthy client-owned dogs undergoing surgery in dorsal recumbency.MethodsDogs were ventilated intraoperatively (inspired oxygen fraction: 0.5) with one of the following strategies: SV, CMV alone, and CMV with PEEP_maxCrs+2 following a single ARM (ARM1) or two ARMs (ARM2, the second ARM at the end of surgery). Arterial blood gas analyses were performed before starting the ventilatory strategy, at the end of surgery, and at 5, 10, 15, 30 and 60 minutes after extubation while breathing room air. Data were analysed using Kruskal-Wallis and Friedman tests (p < 0.050).ResultsAt any time point after extubation, PaO₂ was not significantly different between groups. At 5 minutes after extubation, PaO₂ was 95.1 (78.1–104.0), 93.8 (88.3–104.0), 96.9 (86.6–115.0) and 89.1 (87.6–102.0) mmHg in the SV, CMV, ARM1 and ARM2 groups, respectively. PaO₂ decreased at 30 minutes after extubation in the CMV, ARM1 and ARM2 groups (p < 0.050), but it did not decrease after 30 minutes in the SV group. Moderate hypoxaemia (PaO₂, 60–80 mmHg) was observed in one dog in the ARM1 group and two dogs each in the SV and ARM2 groups.Conclusions and clinical relevanceIntraoperative ARMs, followed by PEEP_maxCrs+2, did not improve early postoperative arterial oxygenation compared with SV or CMV alone in healthy anaesthetized dogs. Therefore, this ventilatory strategy might not be clinically advantageous for improving postoperative arterial oxygenation in healthy dogs undergoing surgery when positioned in dorsal recumbency.     

Continuous positive airway pressure administered via face mask in tranquilized dogs

Objective – To evaluate the tolerance of a continuous positive airway pressure (CPAP) mask in tranquilized dogs and compare PaO₂ in arterial blood in dogs receiving oxygen with a regular face mask or CPAP mask set to maintain a pressure of 2.5 or 5 cm H₂O. Design – Prospective, randomized clinical study. Setting – University teaching hospital. Animals – Sixteen client‐owned dogs without evidence of cardiopulmonary disease were studied. Interventions – Eight animals were randomly assigned to each of 2 treatment groups: group A received 2.5 cm H₂O CPAP and group B received 5 cm H₂O CPAP after first receiving oxygen (5 L/min) by a regular face mask. Animals were tranquilized with acepromazine 0.05 mg/kg, IV and morphine 0.2 mg/kg, IM. An arterial catheter was then placed to facilitate blood sampling for pHa, PaO₂, and PaCO₂ determinations before and after treatments. Direct mean arterial pressure, heart rate, respiratory rate, and temperature were also recorded after each treatment. Measurements and Main Results – CPAP administration was well tolerated by all animals. The mean arterial pressure, heart rate, respiratory rate, temperature, PaCO₂, and pHa, did not differ at any time point between groups. Differences were seen in oxygenation; in group A, PaO₂ significantly increased from a mean of 288.3±47.5 mm Hg with a standard mask to a mean of 390.3±65.5 mm Hg with the CPAP mask and in group B, PaO₂ increased similarly from 325.0±70.5 to 425.2±63.4 mm Hg (P<0.05); no differences were detected between the 2 CPAP treatments. Conclusions – In healthy tranquilized dogs noninvasive CPAP is well tolerated and increases PaO₂ above values obtained when using a regular face mask.     

Preliminary Results of Behavioral and Cardiopulmonary Effects of a Constant Rate Infusion of Remifentanil–Xylazine for Sedation in Horses

Standing surgical procedures are performed commonly in horses under sedation. The use of a xylazine and remifentanil combination has not been investigated in horses. We proposed to evaluate behavioral and cardiopulmonary effects of an intravenous (IV) infusion of xylazine with remifentanil for sedation in horses. Xylazine (0.8 mg/kg IV) followed in 3 minutes by remifentanil (0.0005 mg/kg IV), and a constant rate infusion of xylazine and remifentanil (0.65 mg/kg/h; 0.0225 mg/kg/h, respectively) was administered in three horses. Heart rate, respiratory rate (RR), arterial blood pressures, quality of sedation, pH, partial pressure of arterial CO₂ (PaCO₂), partial pressure of arterial O₂ (PaO₂), ataxia, sedation, and sedation overall outcome were assessed. Heart rate and RR remained within normal values during sedation without significant changes from baseline. Systolic, mean, and diastolic arterial blood pressures were increased during sedation. There were no significant changes in pH, PaCO₂, and PaO₂. Sedation developed immediately after injection of xylazine in the three horses but did not increase after remifentanil bolus or IV infusion of both drugs. None of the mares had ataxia. Adverse effects during and after sedation were present: excitement, increase in locomotor activity, and decrease in the gastrointestinal motility. The combination of xylazine and remifentanil sedation protocol produces adverse effects. This protocol cannot be recommended for clinical conditions, at the described doses.     

Hypoxaemia during anaesthesia in seven horses with colic

Anaesthetic records of horses with colic anaesthetised between June 1987 and May 1989 were reviewed. pH and blood gas analyses were performed during 157 operations from which the horses were allowed to recover. A PaO₂ of 8.0 kPa or less was measured during anaesthesia in seven of these horses. The horses were of different breeds, ages and sexes. Anaesthesia was induced with xylazine, guaifenesin and ketamine in four horses and with xylazine, guaifenesin and thiobarbiturate in three horses. Anaesthesia was maintained with inhalation anaesthetic agent and oxygen: isoflurane in five horses, halothane in one horse, and initially halothane but later isoflurane in one horse. Systolic arterial pressures during anaesthesia ranged from 80 to 150 mmHg, diastolic arterial pressures were between 60 and 128 mmHg, and heart rates were between 28 and 44 beats /min. Controlled ventilation was initiated at the start of anaesthesia. PaCO₂ exceeded 6.7 kPa in three horses but was subsequently decreased by adjustment of the ventilator. PaO₂ of 8.0 kPa or less was measured during early anaesthesia, with one exception, and persisted for the duration of anaesthesia. The horses' inspired air was supplemented with oxygen during recovery from anaesthesia, at which time measurement of blood gases in three horses revealed no increase in PaO₂. Recovery from anaesthesia was uneventful. The surgical problems involved primarily the large intestine in five horses and the small intestine in two horses. Six horses were discharged from the hospital alive; one horse was reanaesthetised later the same day and destroyed without regaining consciousness. We concluded that none of the objective values recorded during the pre-anaesthetic evaluation could have been used to predict the complication of intraoperative hypoxaemia. We observed that once hypoxaemia developed it persisted for the duration of anaesthesia and even into the recovery period when the horses were in lateral recumbency and regaining consciousness. We assume that the altered metabolism from anaesthetic agents and hypothermia combined with adequate peripheral perfusion contributed to the lack of adverse consequences in six of the horses. The contribution of hypoxaemia to the deteriorating condition of the seventh horse is speculative.     

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.     

Pulsed delivery of inhaled nitric oxide counteracts hypoxaemia during 2.5 hours of inhalation anaesthesia in dorsally recumbent horses

Objective The study aimed to investigate the effect of varying pulse lengths of inhaled nitric oxide (iNO), and 2.5 hours of continuous pulse‐delivered iNO on pulmonary gas exchange in anaesthetized horses. Study Design Experimental study. Animals Six Standardbred horses. Methods Horses received acepromazine, detomidine, guaifenesin, thiopentone and isoflurane in oxygen, were positioned in dorsal recumbency and were breathing spontaneously. iNO was on average pulsed during the first 20, 30, 43 or 73% of the inspiration in 15 minute steps. The pulse length that corresponded to the highest (peak) partial pressure of arterial oxygen (PaO₂) in the individual horses was determined and delivered for a further 1.5 hours. Data measured or calculated included arterial and mixed venous partial pressures of O₂ and CO₂, heart rate, respiratory rate, expired minute ventilation, pulmonary and systemic arterial mean pressures, cardiac output and venous admixture. Data (mean ± SD) was analysed using anova with p < 0.05 considered significant. Results Although the pulse length of iNO that corresponded to peak PaO₂ varied between horses, administration of all pulse lengths of iNO increased PaO₂ compared to baseline. The shortest pulse lengths that resulted in the peak PaO₂ were 30 and 43% of the inspiration. Administration of iNO increased PaO₂ (12.6 ± 4.1 kPa [95 ± 31 mmHg] at baseline to a range of 23.0 ± 8.4 to 25.3 ± 9.0 kPa [173 to 190 mmHg]) and PaCO₂ (8.5 ± 1.2 kPa [64 ± 9 mmHg] to 9.8 ± 1.5 kPa [73 ± 11 mmHg]) and decreased venous admixture from 32 ± 6% to 25 ± 6%. The increase in PaO₂ and decrease in venous admixture was sustained for the entire 2.5 hours of iNO delivery. Conclusions The improvement in arterial oxygenation during pulsed delivery of iNO was significant and sustained throughout 2.5 hours of anaesthesia. Clinical relevance Pulsed iNO potentially could be used clinically to counteract hypoxemia in anaesthetized horses.     

Neurological Manifestations of Hypothyroidism: A Retrospective Study of 29 Dogs

Neuromuscular signs in association with hypothyroidism are described in 29 dogs. Eleven dogs had lower motor neuron signs, 9 had peripheral vestibular deficits, 4 had megaesophagus, and 5 had laryngeal paralysis. Primarily older (mean = 9.5 years), large-breed dogs were affected, and there was no sex or breed predisposition. Duration of clinical signs before presentation ranged from 2 to 8 weeks (mean = 5 weeks). The diagnosis was based on (1) results of neurological examination (29 dogs); (2) electromyographic abnormalities (18 dogs), including fibrillation potentials (n = 18), positive sharp waves (n = 15), and complex repetitive discharges (n = 4); (3) high serum cholesterol concentration (10 dogs; mean = 335 mg/dL); (4) low response to thyroid-stimulating hormone (29 dogs; mean T₄ prestimulation concentration = 0.8 μg/dL; mean T₄ poststimulation = 1.2 μg/dL); and (5) good response to thyroxine supplementation (26 dogs). Dogs with vestibular deficits had abnormal brainstem auditory-evoked responses (BAER), including increased latencies of P₁-P₆ and decreased amplitude of P_4,5-N₅. Seven other dogs had similar BAER abnormalities without manifesting clinical signs of vestibular involvement. Three dogs with vestibular signs had fibrillation potentials and positive sharp waves without exhibiting lower motor neuron signs. All dogs were supplemented with levothyroxine (0.02 mg/kg P0 bid). The follow-up period ranged between 6 and 30 months (mean, 14 months). Serum T₄ concentrations were measured at least 3 times for each dog every 2 months (mean T₄ concentration = 2.6 μg/dL). All but 1 dog with lower motor neuron signs and 1 dog with vestibular signs recovered after 2 months (mean, 57 days). Signs of megaesophagus became progressively less severe over 4 months. Dogs with laryngeal paralysis improved partially after 5 months. We suggest that either vestibular or lower motor neuron signs, megaesophagus, or laryngeal paralysis may be the only clinical signs of an underlying, more generalized polyneuropathy associated with hypothyroidism. Electro-diagnostic abnormalities may be detected before clinical disease develops.     

Effects of Carbon Dioxide Insufflation and Body Position on Blood Gas Values in Horses Anesthetized for Laparoscopy

The objective of the study was to describe the effects of carbon dioxide pneumoperitoneum and Trendelenburg position on arterial blood gas values in horses anesthetized for laparoscopy. The study design was a prospective case series using 14 healthy adult horses anesthetized for elective laparoscopic surgery. All horses in the study were maintained under anesthesia with halothane in oxygen with intermittent positive-pressure ventilation. A pneumoperitoneum of 15 mmHg or less was achieved with carbon dioxide, and horses were tilted to a 35-degree Trendelenburg position to allow the completion of laparoscopic cryptorchidectomy (n = 13) or ovariectomy (n = 1). Heart rate, mean arterial pressure, and arterial blood gases were recorded at six time intervals throughout the procedure. Results of the study indicated a pH that decreased and partial pressure of carbon dioxide (PaCO₂) and mean arterial pressure that increased over time and differed significantly from baseline during Trendelenburg position. Partial pressure of oxygen (PaO₂) was significantly lower than baseline after assumption of Trendelenburg position and did not improve on return to normal recumbency and abdominal pressure. As body weight increased, pH and PaO₂ decreased and PaCO₂ increased. We concluded that horses placed in Trendelenburg position have changes that are transient, with the exception of PaO₂. Heavier horses have a greater change in pH, PaCO₂, and PaO₂ than lighter horses during abdominal insufflation and Trendelenburg position. The changes incurred during CO₂ abdominal insufflation and Trendelenburg position are transient, with the exception of a decreased PaO₂. Heavy horses undergoing abdominal insufflation and Trendelenburg position should be closely monitored for critical cardiopulmonary values.     

The effect of moderate hypovolemia on cardiopulmonary function in dogs

Objective: To collate canine cardiopulmonary measurements from previously published and unpublished studies in instrumented, unsedated, normovolemic and moderately hypovolemic dogs. Design: Collation of data obtained from original investigations in our research laboratory. Setting: Research laboratory, School of Veterinary Medicine. Subjects: Sixty‐eight dogs. Interventions: Subjects were percutaneously instrumented with an arterial catheter and a thermodilution cardiac output catheter. A femoral artery catheter was percutaneously placed for blood removal. Measurements and main results: Body weight, arterial and mixed‐venous pH and blood gases, arterial, pulmonary arterial, pulmonary artery occlusion, and central venous blood pressure, cardiac output, and core body temperature were measured. Body surface area, bicarbonate concentration, standard base excess, cardiac index (CI), stroke volume, systemic and pulmonary vascular resistance, left and right ventricular work and stroke work indices, left and right rate‐pressure product, alveolar PO₂, alveolar–arterial PO₂ gradient, arterial and mixed‐venous and pulmonary capillary oxygen content, oxygen delivery, oxygen consumption, oxygen extraction, venous admixture, arterial and venous blood carbon dioxide content, arterial–venous carbon dioxide gradient, carbon dioxide production were calculated. In 68 dogs, hypovolemia sufficient to decrease mean arterial blood pressure (ABPm) to an average of 62 mmHg, was associated with the following changes: arterial partial pressure of carbon dioxide (PaCO₂) decreased from 40.0 to 32.9 mmHg; arterial base deficit (BDa) increased from ?2.2 to ?6.3 mEq/L; lactate increased from 0.85 to 10.7 mm /L, and arterial pH (pHa) did not change. Arterial partial pressure of oxygen (PaO₂) increased from 100.5 to 108.3 mmHg while mixed‐venous PO₂ (PmvO₂) decreased from 49.1 to 34.1 mmHg. Arterial and mixed‐venous oxygen content (CaO₂ and CmvO₂) decreased from 17.5 to 16.5 and 13.8 to 9.6 mL/dL, respectively. The alveolar–arterial PO₂ gradient (A‐a PO₂) increased from 5.5 to 8.9 mmHg while venous admixture decreased from 2.9% to 1.4%. The ABPm decreased from 100 to 62 mmHg; pulmonary arterial pressure (PAPm) decreased from 13.6 to 6.4 mmHg; and pulmonary arterial occlusion pressure (PAOP) decreased from 4.9 to 0.1 mmHg. CI decreased from 4.31 to 2.02 L/min/m². Systemic and pulmonary vascular resistance (SVRI and PVRI) increased from 1962 to 2753 and 189 to 269 dyn s/cm⁵, respectively. Oxygen delivery (DO₂) decreased from 787 to 340 mL/min/m² while oxygen consumption (VO₂) decreased from 172 to 141 mL/min/m². Oxygen extraction increased from 20.9% to 42.3%. Conclusions: Moderate hypovolemia caused CI and oxygen delivery to decrease to 47% and 42% of baseline. Oxygen extraction, however, doubled and, therefore, oxygen consumption decreased only to 82% of baseline.     

Pulmonary Hypertension Induced in Dogs by Hypoxia at Different High-Altitude Levels

Chronic natural hypoxia at 2300 m altitude induces mild pulmonary hypertension (PH) in healthy dogs. The influence of more severe hypoxia on the same group of dogs was evaluated by re-examining such dogs at 3500 m, after they had regularly exercised at this altitude level for half a year. Despite severe hypoxaemia at 3500 m (P _aO₂ 52±5 mmHg), none of the dogs developed erythrocytosis, and their PCV at 3500 m (48%±4%) did not differ from that at 2300 m (49%±4%). There was a tendency towards an elevated systemic BP, with a significant increase in diastolic BP (105±13 mmHg at 3500 m versus 98±17 at 2300 m). Tricuspid regurgitation (TR) was detected in 7 dogs at 3500 m compared to 8 dogs at 2300 m. The mean TR V _max was significantly higher at 3500 m, and all 7 dogs had systolic PH at 3500 m (33.6–54.8 mmHg), when PH was defined as TR V _max 2.8 m/s, i.e. a peak pressure gradient >30 mmHg. Hence, in dogs, increasing altitude and the concomitant hypoxia result in a progressively more pronounced PH and an elevated systemic BP. Intermittent severe hypoxaemia of around 50 mmHg may not cause erythrocytosis in healthy dogs, even over a prolonged period.     

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.     

Oxygen reserve index as a noninvasive indicator of arterial partial pressure of oxygen in anaesthetized donkeys: a preliminary study

ObjectiveTo evaluate the oxygen reserve index (ORI) as a noninvasive estimate of the PaO₂ during moderate hyperoxaemia [100–200 mmHg (13.3–26.6 kPa)], and to determine ORI values identifying PaO₂ > 100, > 150 (20.0 kPa) and > 200 mmHg in anaesthetized donkeys with an inspired fraction of oxygen (FiO₂) > 0.95.Study designProspective observational study.AnimalsA group of 28 adult standard donkeys aged (mean ± standard deviation) 4 ± 2 years and weighing 135 ± 15 kg.MethodsDonkeys were sedated intramuscularly with xylazine and butorphanol; anaesthesia was induced with ketamine and diazepam and maintained with isoflurane in oxygen. An adhesive sensor probe was applied to the donkey’s tongue and connected to a Masimo pulse co-oximeter to determine ORI values. An arterial catheter was inserted into an auricular artery. After ORI signal stabilization, the value was noted and PaO₂ determined by blood gas analysis. The Pearson correlation coefficient was used to assess the relationship between ORI and PaO₂ for oxygen tension < 200 mmHg (< 26.6 kPa). The Youden index was used to identify the value of ORI that detected PaO₂ > 150 and 200 mmHg (20.0 and 26.6 kPa) with the highest sensitivity and specificity.ResultsA total of 106 paired measurements were collected. A mild positive correlation was observed between ORI and PaO₂ for values < 200 mmHg (26.6 kPa; r = 0.52). An ORI > 0.0, > 0.1 and > 0.3 indicated a PaO₂ > 100, > 150 and > 200 mmHg (13.3, 20.0 and 26.6 kPa) with negative predictive values > 94%.Conclusions and clinical relevanceORI may provide a noninvasive indication of PaO₂ > 100, > 150 and > 200 mmHg (13.3, 20.0 and 26.6 kPa) in anaesthetized donkeys with an FiO₂ > 0.95, although it does not replace blood gas analysis for assessment of oxygenation.     

Evaluation of lung ventilation distribution using electrical impedance tomography in standing sedated horses with capnoperitoneum

ObjectiveTo determine changes in distribution of lung ventilation with increasing intra-abdominal pressure (IAP) from carbon dioxide (CO₂) insufflation in standing sedated horses.Study designProspective experimental study.AnimalsA group of six healthy adult horses.MethodsEach horse was sedated with acepromazine, detomidine and butorphanol and sedation maintained with a detomidine infusion. The horse was restrained in a stocks system and a 32 electrode electrical impedance tomography (EIT) belt was wrapped around the thorax at the fifth–sixth intercostal space. EIT images and arterial blood samples for PaO₂ and PaCO₂, pH and lactate concentration were obtained during capnoperitoneum at 0 (baseline A), 5, 8 and 12 mmHg as IAP increased and at 8, 5, 0 (baseline B) mmHg as IAP decreased. At each IAP, after a 2 minute stabilization period, EIT images were recorded for ≥ 2 minutes to obtain five consecutive breaths. Statistical analysis was performed using anova for repeated measures with Geisser-Greenhouse correction and a Tukey’s multiple comparison test for parametric data. The relationship between PaO₂ and the center of ventilation in the ventral-dorsal (CoV-VD) and right-left (CoV-RL) directions or total impedance change as a surrogate for tidal volume (ΔZV_T) were tested using linear regression analysis. Significance was assumed when p ≤ 0.05.ResultsThere were no significant changes in CoV-VD, CoV-RL, PaO₂, PaCO₂, lactate concentration, pH, heart rate and respiratory rate with targeted IAP. There was a significant decrease in ΔZV_T compared with baseline A at 5 mmHg IAP as IAP was increased.Conclusions and clinical relevanceCapnoperitoneum causes a significant decrease in ΔZV_T in standing sedated horses with increasing IAP.     

Hemodynamic,respiratory and sedative effects of progressively increasing doses of acepromazine in conscious dogs

ObjectiveTo evaluate the effects of progressively increasing doses of acepromazine on cardiopulmonary variables and sedation in conscious dogs.Study designProspective, experimental study.AnimalsA group of six healthy, adult, mixed-breed dogs weighing 16.5 ± 5.0 kg (mean ± standard deviation).MethodsDogs were instrumented with thermodilution and arterial catheters for evaluation of hemodynamics and arterial blood gases. On a single occasion, acepromazine was administered intravenously to each dog at 10, 15, 25 and 50 μg kg^–1 at 20 minute intervals, resulting in cumulative acepromazine doses of 10 μg kg^–1 (ACP₁₀), 25 μg kg^–1 (ACP₂₅), 50 μg kg^–1 (ACP₅₀) and 100 μg kg^–1 (ACP₁₀₀). Hemodynamic data and sedation scores were recorded before (baseline) and 20 minutes after each acepromazine dose.ResultsCompared with baseline, all acepromazine doses significantly decreased stroke index (SI), mean arterial pressure (MAP) and arterial oxygen content (CaO₂) with maximum decreases of 16%, 17% and 21%, respectively. Cardiac index (CI) decreased by up to 19% but not significantly. Decreases of 26–38% were recorded for oxygen delivery index (DO₂I), with significant differences for ACP₅₀ and ACP₁₀₀. Systemic vascular resistance index (SVRI) and heart rate did not change significantly. No significant difference was found among acepromazine doses for hemodynamic data. After ACP₁₀, mild sedation was observed in five/six dogs and moderate sedation in one/six dogs, whereas after ACP₂₅, ACP₅₀ and ACP₁₀₀, moderate sedation was observed in five/six or six/six dogs.Conclusions and clinical relevanceIn conscious dogs, acepromazine decreased MAP, SI, CaO₂ and DO₂I, but no significant dose effect was detected. SVRI was not significantly changed, suggesting that the reduction in MAP resulted from decreased CI. The ACP₂₅, ACP₅₀ and ACP₁₀₀ doses resulted in moderate sedation in most dogs; ACP₁₀ resulted in only mild sedation.     

Effects of Intermittent Positive Pressure Ventilation on Cardiopulmonary Function in Horses Anesthetized with Total Intravenous Anesthesia Using Combination of Medetomidine,Lidocaine, Butorphanol and Propofol (MLBP-TIVA)

Effects of intermittent positive pressure ventilation (IPPV) on cardiopulmonary function were evaluated in horses anesthetized with total intravenous anesthesia using constant rate infusions of medetomidine (3.5 µg/kg/hr), lidocaine (3 mg/kg/hr), butorphanol (24 µg/kg/hr) and propofol (0.1 mg/kg/min) (MLBP-TIVA). Five horses were anesthetized twice using MLBP-TIVA with or without IPPV at 4-week interval (crossover study). In each occasion, the horses breathed 100% oxygen with spontaneous ventilation (SB-group, n=5) or with IPPV (CV-group, n=5), and changes in cardiopulmonary parameters were observed for 120 min. In the SB-group, cardiovascular parameters were maintained within acceptable ranges (heart rate: 33–35 beats/min, cardiac output: 27–30 l/min, mean arterial blood pressure [MABP]: 114–123 mmHg, mean pulmonary arterial pressure [MPAP]: 28–29 mmHg and mean right atrial pressure [MRAP]: 19–21 mmHg), but severe hypercapnea and insufficient oxygenation were observed (arterial CO₂ pressure [PaCO₂]: 84–103 mmHg and arterial O₂ pressure [PaO₂]: 155–172 mmHg). In the CV-group, normocapnea (PaCO₂: 42–50 mmHg) and good oxygenation (PaO₂: 395–419 mmHg) were achieved by the IPPV without apparent cardiovascular depression (heart rate: 29–31 beats/min, cardiac output: 17–21 l /min, MABP: 111–123 mmHg, MPAP: 27–30 mmHg and MRAP: 15–16 mmHg). MLBP-TIVA preserved cardiovascular function even in horses artificially ventilated.     

Transnasal laryngoscopy for the diagnosis of laryngeal paralysis in dogs

Four dogs with clinical signs of laryngeal paralysis and three normal dogs were evaluated with transnasal laryngoscopy. Six of these dogs subsequently underwent standard laryngoscopy. For transnasal laryngoscopy, a video endoscope was passed through the left nasal passage after intramuscular sedation and topical anesthesia. The laryngeal opening was observed during spontaneous ventilation. Laryngeal paralysis was diagnosed in four dogs and was confirmed with traditional laryngoscopy in three dogs. Normal motion of the arytenoid cartilages was present in the other three dogs; however, two required mechanical stimulation of the laryngeal mucosa for full evaluation. Transnasal laryngoscopy provided a means for diagnosing laryngeal paralysis in dogs without general anesthesia.     

Comparative effects of three different ventilatory treatments on arterial blood gas values and oxygen extraction in healthy anaesthetized dogs

ObjectiveTo compare the effect of invasive continuous positive airway pressure (CPAP), pressure-controlled ventilation (PCV) with positive end-expiratory pressure (PEEP) and spontaneous breathing (SB) on PaO₂, PaCO₂ and arterial to central venous oxygen content difference (CaO₂-CcvO₂) in healthy anaesthetized dogs.Study designProspective randomized crossover study.AnimalsA group of 15 adult male dogs undergoing elective orchidectomy.MethodsDogs were anaesthetized [buprenorphine, medetomidine, propofol and isoflurane in an air oxygen (FiO₂= 0.5)]. All ventilatory treatments (CPAP: 4 cmH₂O; PCV: 10 cmH₂O driving pressure; PEEP, 4 cmH₂O; respiratory rate of 10 breaths minute^–1 and inspiratory-to-expiratory ratio of 1:2; SB: no pressure applied) were applied in a randomized order during the same anaesthetic. Arterial and central venous blood samples were collected immediately before the start and at 20 minutes after each treatment. Data were compared using a general linear mixed model (p < 0.05).ResultsMedian PaO₂ was significantly higher after PCV [222 mmHg (29.6 kPa)] than after CPAP [202 mmHg (26.9 kPa)] and SB [208 mmHg (27.7 kPa)] (p < 0.001). Median PaCO₂ was lower after PCV [48 mmHg (6.4 kPa)] than after CPAP [58 mmHg (7.7 kPa)] and SB [56 mmHg (7.5 kPa)] (p < 0.001). Median CaO₂-CcvO₂ was greater after PCV (4.36 mL dL^–1) than after CPAP (3.41 mL dL^–1) and SB (3.23 mL dL^–1) (p < 0.001). PaO₂, PaCO₂ and CaO₂-CcvO₂ were no different between CPAP and SB (p > 0.99, p = 0.697 and p = 0.922, respectively).Conclusions and clinical relevanceCPAP resulted in similar arterial oxygenation, CO₂ elimination and tissue oxygen extraction to SB. PCV resulted in improved arterial oxygenation and CO₂ elimination. Greater oxygen extraction occurred with PCV than with CPAP and SB, offsetting its advantage of improved arterial oxygenation. The benefit of invasive CPAP over SB in the healthy anaesthetized dog remains uncertain.