Nitrate poisoning in cattle

Summary In a series of experiments the effect of administering KNO(2) was studied, during parturition, on the capability of oxygen transport of maternal blood and on oxygen transfer to foetal blood. The following blood parameters were analysed, MHb percentage, pO(2), O(2)-saturation, pH, pCO(2), and (NO(2)) in maternal arterial blood (carotid art.) and venous blood (jugular vein) and in foetal arterial blood (umbilical art.) and venous blood (umbilical vein). The relative O(2)-saturation was calculated from the estimated O(2)-saturation by multiplying with the factor Hb (mmol/1) minus MHb (mmol/1), divided by Hb (mmol/1). In addition, blood pressure in the carotid artery, heart rate, and respiration rate in the dam were continuously recorded for some hours. A dosage of 9 to 12 mg of NO(2)/kg body weight intravenously or of 30 mg of NO(2)/kg body weight orally to the dam caused much higher MHb percentages and NO(2) contents in the maternal blood than in the foetal blood. In maternal blood the ratio of NO(2) content td MHb percentage was proportional to that in foetal blood. In the arterial blood, MHb percentages were almost as high as in the venous blood. After administering of nitrite, relative O(2)-saturation dropped simultaneously with the increase in methaemoglobin. Nitrite treatment caused a drop in the maternal blood pressure; heart rate and respiration rate increased. O(2)-saturation in the blood in the umbilical vein was much lower in the animals with nitrite treatment than in those without. These experimental results show clearly that the oxygen capacity of the blood decreases after nitrite treatment. In pregnant cows the oxygen supply to the foetus will be adversely affected after nitrate intake, especially by the lower oxygen transfer via the placenta, though hardly at all by methaemoglobin formation in the foetal blood. When the oxygen transfer to the foetal blood decreases too sharply, intra-uterine death and ultimately abortion may result.     

Co-oximetry in clinically healthy dogs and effects of time of post sampling on measurements

Objectives : Co‐oximetry is a complex and valuable laboratory method that measures haemoglobin species and oxygenation status by multi‐wavelength spectrophotometry. The purpose of this study was to establish reference intervals for clinically healthy dogs and to determine the effect of time of analyses and sex of animals on the accuracy of results. Methods : Blood was collected from 27 healthy adult dogs of various breeds and sex. Co‐oximetry was performed on a CCX co‐oximeter that measures eight haemoglobin and oxygen transport related parameters: carboxyhaemoglobin (COHb), deoxyhaemoglobin (HHb), oxyhaemoglobin (O₂Hb), methaemoglobin (MetHb), total haemoglobin (tHb), oxygen saturation (SO₂%), oxygen content (O₂Ct) and oxygen capacity (O₂Cap). Results : Results obtained after 2 and 4 hours were not significantly different from those obtained immediately after sampling. But after 48 hours, the results for total haemoglobin, oxygen saturation, oxyhaemoglobin, oxygen content and oxygen capacity were significantly lower, and carboxyhaemoglobin and deoxyhaemoglobin values were significantly higher than determination immediately after sampling. Gender had no significant impact on co‐oximetry values. Clinical Significance : Co‐oximetry offers several advantages compared with other methods, including ease of use, increased accuracy and greater differentiation among haemoglobin species.     

Low central venous oxygen saturation is associated with increased mortality in critically ill dogs

Objectives : To investigate relationships between central venous oxygen saturation (ScvO₂) and survival to hospital discharge in dogs. Central venous oxygen saturation is an accessible measure of the balance between systemic oxygen delivery and consumption. Methods : Prospective observational cohort study, enrolling 126 client‐owned dogs with central venous catheters. Central venous oxygen saturation was measured over the 24 hours following intensive care unit admission. Poor outcome was defined as death or euthanasia performed for moribund status. Regression analysis identified independent predictors of non‐survival and physiologic parameters associated with central venous oxygen saturation. Area under the receiver operator curve analysis identified a cut‐off point of central venous oxygen saturation, below which central venous oxygen saturation decrease was associated with increased mortality risk. Results : Mortality risk was 30·9%. Low central venous oxygen saturation was associated with poor outcome (P<0·05). Area under the receiver operator curve analysis selected a central venous oxygen saturation of 68% as the point below which a fall in central venous oxygen saturation was associated with increased mortality risk. For each 10% drop in central venous oxygen saturation below 68%, odds of non‐survival increased by 2·66 times (P=0·0002, 95% confidence interval of odds ratio=1·45 to 4·85). Central venous oxygen saturation was equivalent to lactate in predicting non‐survival. Predictors of central venous oxygen saturation (packed cell volume, mean arterial blood pressure, fever, % arterial haemoglobin saturation as measured by pulse oximeter) were consistent with hypothesised physiologic mechanisms. Clinical Significance : Central venous oxygen saturation was a strong mortality predictor. Further work is needed to determine if therapy targeting central venous oxygen saturation can reduce mortality in canine intensive care unit patients.     

Central venous blood gas and acid-base status in conscious dogs and cats

To determine the reference level of central venous oxygen saturation (ScvO₂) and clinical efficacy of central venous blood gas analysis, partial pressures of oxygen and carbon dioxide, pH, oxygen saturation, base excess (B.E.) and HCO₃ concentration were compared between simultaneously obtained central venous and arterial blood samples from conscious healthy 6 dogs and 5 cats. Comparisons between arteriovenous samples were performed by a paired t-test and Bland-Altman analysis. Between arteriovenous samples, B.E. showed good agreement, but there were significant differences in other parameters in the dogs, and no good agreement was detected in cats. The ScvO₂ in dogs and cats were 82.3 ± 3.5 and 62.4 ± 13.5%, respectively. Central venous blood gas analysis is indispensable, especially in cats.     

Optimal endpoints of resuscitation and early goal-directed therapy

Objective: To review the available endpoints of shock resuscitation, including traditional perfusion parameters, oxygen‐transport variables, lactate, base deficit (BD), venous oxygen saturation, and gastric mucosal pH, and to discuss the currently accepted methods of assessing successful reversal of oxygen (O₂) debt in shock patients. Human‐based studies: Early goal‐directed therapy has unequivocally been shown to positively affect outcome in human patients experiencing cardiovascular shock. However, specific endpoints of resuscitation to target in critically ill patients remain controversial. Reliance on traditional endpoints of resuscitation (heart rate [HR], blood pressure [BP]) appears insufficient in detection of ongoing tissue hypoxia in shock states. A multitude of publications exist suggesting that indirect indices of global (lactate, base deficit, mixed/central venous oxygen saturation), regional (gastric intramucosal pH [pH_i]) and cellular (transcutaneous oxygen) oxygenation are more successful in outcome prediction and in assessing adequacy of resuscitative efforts in this patient population. Veterinary‐based studies: While there are several large studies evaluating endpoints of resuscitation in experimental canine shock models, this author was unable to find similar research pertaining to small animal veterinary patients. The few articles in which blood lactate is evaluated for prognostic purposes in canine patients are included in this review. Data sources: Veterinary and human literature review. Conclusions: Optimization of early resuscitative efforts has proven to have a survival benefit in human shock patients, and major strides have been made in determining which endpoints of resuscitation to target in this patient population. Similar clinical trials designed to evaluate indices of ongoing global and regional tissue hypoxia in small animal veterinary shock patients are warranted.     

Responses of Blue Catfish and Channel Catfish to Environmental Nitrite

Abstract

In nitrite-exposure experiments, percent methemoglobin, plasma nitrite concentration, and plasma chloride ion concentration were compared between channel catfish Ictalurus punctatus and blue catfish I. furcatus exposed to sublethal levels of nitrite for 48 h at 25°C. In nitrite-recovery experiments, fish exposed to elevated environmental nitrite for 12 h were transferred to freshwater, and blood characteristics were monitored during the 24-h recovery period. Blue catfish appeared to be more resistant to environmental nitrite than channel catfish. Methemoglobin levels (percent of hemoglobin in methemoglobin form) were significantly lower in blue catfish than in channel catfish. Maximum plasma nitrite concentrations were 137 mg NO₂-/L plasma in blue catfish and 164 mg NO₂-/L plasma in channel catfish. Percent methemoglobin and plasma nitrite concentration were closely correlated. Plasma chloride decreased initially with exposure to nitrite but quickly returned to control levels. Blue catfish exposed to nitrite at 10°C required 1 week to recover when placed in nitrite-free water. The methemoglobin reductase enzyme apparently functioned at a slow rate in fish acclimated to cold temperatures.     

Intravenous catheterisation of foetus and mare in late pregnancy: management and respiratory, circulatory and metabolic effects.

The uterine and umbilical vessels of 12 pregnant ponies were catheterised to study foetal metabolism. The effects of this procedure on maternal and foetal cardiovascular, respiratory, metabolic and adrenocortical activity were monitored during and after surgery. Premedication with acepromazine-butorphanol-detomidine was followed by induction of anaesthesia with detomidine and ketamine and maintenance, using mechanical ventilation, with halothane in oxygen and nitrous oxide. Mean maternal arterial blood pressure was greater than 70 mmHg during anaesthesia and arterial oxygen tension remained over 100 mmHg. The foetuses were adequately oxygenated but were hypercapnic and lactic acidaemic. Most maternal and foetal blood gases and metabolites had returned to normal by 24 h, although foetal plasma lactate fell more slowly. The maternal adrenocortical discharge was less severe than reported previously and plasma cortisol had fallen to basal levels by 48 h after surgery. Foetal plasma cortisol remained low and did not change during or after surgery. Arterio-venous metabolite and gas tension differences across the uterine and umbilical circulations were slightly greater at operation than in the recovery period, suggesting that uteroplacental perfusion may have been impaired during surgery. Post-operative recovery of the mare and foetus was satisfactory and subsequent problems associated with the foetal catheters were not related to the anaesthesia or surgery.     

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.     

Hemodynamic effects of sevoflurane in spontaneously breathing cats

Sevoflurane has recently been introduced in feline anesthesia. However, its cardiovascular effects have not, to our knowledge, been reported in this species. Six healthy cats, aged 1.81 ± 0.31 years (mean ± SEM) and weighing 3.47 ± 0.11 kg, were studied. Anesthesia was induced and maintained with sevoflurane in oxygen. Body temperature was maintained between 38.5 and 39.55 °C. After instrumentation, end‐tidal sevoflurane concentration was randomly set at 1.25, 1.5, and 1.75 times the individual minimum alveolar concentration (MAC), determined in a previous study, according to a Latin Square Design. Thirty minutes of stabilization was allowed after each change of concentration. ECG and heart rate, systemic and pulmonary arterial pressures, central venous pressure (CVP), and core body temperature were continuously monitored and recorded. Inspired and end‐tidal oxygen, carbon dioxide, and sevoflurane concentrations were measured using a Raman spectrometer, calibrated every 80 minutes with three calibration gases of known sevoflurane concentration (1, 2, and 5%). Moreover, at selected times, pulmonary artery occlusion pressure and cardiac output (thermodilution) were measured, and arterial and mixed venous blood samples were collected for pH and blood gas analysis, hemoglobin concentration, hemoglobin oxygen saturation, packed cell volume (PCV) and total protein determination, and lactate concentration measurement. Cardiac index (CI), stroke index (SI), systemic and pulmonary vascular resistance indices, rate‐pressure product, left and right ventricular stroke work indices (LVSWI and RVSWI, respectively), arterial and mixed venous oxygen contents, oxygen delivery, oxygen consumption, and oxygen utilization ratio were calculated. Data were analyzed by a Repeated Measure Latin Square Design followed by a Tukey's test for 2 × 2 comparisons. Arterial pH significantly decreased from 7.40 ± 0.05 to 7.29 ± 0.07 with the administration of increasing concentrations of sevoflurane. Similarly, LVSWI decreased from 3.72 ± 0.60 to 2.60 ± 0.46 g m^?2. Mean arterial pressure, PaO₂, mixed venous pH, CI, SI, and oxygen delivery tended to decrease dose‐dependently, whereas CVP, PaCO₂, Pv CO₂, PCV, and arterial and mixed venous hemoglobin concentrations tended to increase dose‐dependently with the administration of sevoflurane. However, these trends did not reach statistical significance, possibly because of the limited number of animals studied. Sevoflurane seemed to induce dose‐dependent cardiovascular depression in cats.     

Cardiopulmonary effects of thoracoscopy in anesthetized normal dogs

Objective To evaluate the effect of an open‐chest condition on oxygen delivery in anesthetized dogs. Study design Prospective, controlled experimental study. Animals Eight clinically normal adult Walker Hound dogs weighing 25.6–29.2 kg. Methods Eight anesthetized dogs underwent an open‐chest operation after the insertion of thoracoscopy cannulae in the lateral chest walls . A Swan Ganz catheter was used to both measure hemodynamic parameters and obtain mixed venous blood samples for blood gas analysis. A dorsal pedal catheter was placed to both measure arterial blood pressure and obtain blood samples for blood gas analysis. Oxygen delivery index and oxygen extraction ratio were calculated. A randomized block anova for repeated measures was used to evaluate the effect of the treatment on hemodynamic and pulmonary parameters. Results Creation of an open chest did not significantly affect oxygen delivery index (DO₂I; p = 0.545). It induced a significant decrease in arterial oxygen partial pressure (PaO₂; p = 0.018) and arterial oxygen content (CaO₂; p = 0.025). It induced a significant increase in shunt fraction (p = 0.023), physiologic dead space (p = 0.015), and alveolar‐arterial oxygen difference (p = 0.019). Arterial partial pressure of carbon dioxide (PaCO₂; p = 0.766) and arterial hemoglobin oxygen saturation (SaO₂; p = 0.178) were not significantly affected. Diastolic (DPAP; p = 0.050) and mean (MPAP; p = 0.033) pulmonary arterial pressures were significantly increased by opening the chest. Other hemodynamic parameters were not significantly affected. Conclusions Opening the thoracic cavity is not detrimental to hemodynamic function and oxygen delivery in normal dogs, although impaired gas exchange does occur. Clinical relevance Close monitoring of patients is recommended during open‐chest thoracoscopy as adverse effects on gas exchange can contribute to hypoxemia.     

The relationship of muscle perfusion and metabolism with cardiovascular variables before and after detomidine injection during propofol–ketamine anaesthesia in horses

Objectives To study in horses (1) the relationship between cardiovascular variables and muscle perfusion during propofol–ketamine anaesthesia, (2) the physiological effects of a single intravenous (IV) detomidine injection, (3) the metabolic response of muscle to anaesthesia, and (4) the effects of propofol–ketamine infusion on respiratory function. Study design Prospective experimental study. Animals Seven standardbred trotters, 5–12 years old, 416–581 kg. Methods Anaesthesia was induced with intravenous (IV) guaifenesin and propofol (2 mg kg^?1) and maintained with a continuous IV infusion of propofol (0.15 mg kg^?1 minute^?1) and ketamine (0.05 mg kg^?1 minute^?1) with horses positioned in left lateral recumbency. After 1 hour, detomidine (0.01 mg kg^?1) was administered IV and 40–50 minutes later anaesthesia was discontinued. Cardiovascular and respiratory variables (heart rate, cardiac output, systemic and pulmonary artery blood pressures, respiratory rate, tidal volume, and inspiratory and expiratory O₂ and CO₂) and muscle temperature were measured at pre‐determined times. Peripheral perfusion was measured continuously in the gluteal muscles and skin using laser Doppler flowmetry (LDF). Muscle biopsy samples from the left and right gluteal muscles were analysed for glycogen, creatine phosphate, creatine, adenine nucleotides, inosine monophosphate and lactate. Arterial blood was analysed for PO₂, PCO₂, pH, oxygen saturation and HCO₃. Mixed venous blood was analysed for PO₂, PCO₂, pH, oxygen saturation, HCO₃, cortisol, lactate, uric acid, hypoxanthine, xanthine, creatine kinase, creatinine, aspartate aminotransferase, electrolytes, total protein, haemoglobin, haematocrit and white blood cell count. Results Circulatory function was preserved during propofol–ketamine anaesthesia. Detomidine caused profound hypertension and bradycardia and decreased cardiac output and muscle perfusion. Ten minutes after detomidine injection muscle perfusion had recovered to pre‐injection levels, although heart rate and cardiac output had not. No difference in indices of muscle metabolism was found between dependent and independent muscles. Anaerobic muscle metabolism, indicated by decreased muscle and creatine phosphate levels was evident after anaesthesia. Conclusion Muscle perfusion was closely related to cardiac output but not arterial blood pressure. Total intravenous anaesthesia with propofol–ketamine deserves further study despite its respiratory depression effects, as the combination preserves cardiovascular function. Decreases in high‐energy phosphate stores during recovery show that muscle is vulnerable after anaesthesia. Continued research is required to clarify the course of muscle metabolic events during recovery.     

Review papers

Summary

After reviewing of the sources of lead poisoning in birds, the diagnostic value of several clinicopathologic parameters for the diagnosis of plumbism in birds is discussed. These parameters include venous lead concentration, plasma δ‐aminolaevulinic acid dehydratase concentration (ALA‐D), aminolaevulinic‐acid (ALA) excretion in urine, free erythrocytic protoporphyrin (FEPP) and zinc protoporphyrin (ZPP) concentrations in venous blood, and the percentage of fluorocytes, reticulocytes, and erthyrocytes with basophilic stippling in peripheral blood.

The CaNa₂ EDTA lead mobilization test is also mentioned.     

The effects of 2 levels of the inspired oxygen fraction on blood gas variables in propofol-anesthetized dogs with high intracranial pressure

The influence of 2 different levels of the inspired oxygen fraction (FiO₂) on blood gas variables was evaluated in dogs with high intracranial pressure (ICP) during propofol anesthesia (induction followed by a continuous rate infusion [CRI] of 0.6 mg/kg/min) and intermittent positive pressure ventilation (IPPV). Eight adult mongrel dogs were anesthetized on 2 occasions, 21 d apart, and received oxygen at an FiO₂ of 1.0 (G100) or 0.6 (G60) in a randomized crossover fashion. A fiberoptic catheter was implanted on the surface of the right cerebral cortex for assessment of the ICP. An increase in the ICP was induced by temporary ligation of the jugular vein 50 min after induction of anesthesia and immediately after baseline measurement of the ICP. Blood gas measurements were taken 20 min later and then at 15-min intervals for 1 h. Numerical data were submitted to Morrison’s multivariate statistical methods. The ICP, the cerebral perfusion pressure and the mean arterial pressure did not differ significantly between FiO₂ levels or measurement times after jugular ligation. The only blood gas values that differed significantly (P < 0.05) were the arterial oxygen partial pressure, which was greater with G100 than with G60 throughout the procedure, and the venous haemoglobin saturation, that was greater with G100 than with G60 at M0. There were no significant differences between FiO₂ levels or measurement times in the following blood gas variables: arterial carbon dioxide partial pressure, arterial hemoglobin saturation, base deficit, bicarbonate concentration, pH, venous oxygen partial pressure, venous carbon dioxide partial pressure and the arterial-to-end-tidal carbon dioxide difference.     

Cardiopulmonary effects of combined xylazine-guaiphenesin-ketamine infusion and extradural (inter-coccygeal lidocaine) anaesthesia in calves

Objective To investigate the cardiopulmonary effects of a xylazine–guaiphenesin–ketamine infusion combined with inter‐coccygeal extradural (lidocaine) anaesthesia in calves. Study design Prospective study. Animals Five Holstein Friesian calves (one steer, four heifers) aged 6 weeks weighing 65.2 ± 2.7 kg. Materials and methods Calves were anaesthetized with isoflurane in oxygen for instrumentation. At least 12 hours later, xylazine (0.2 mg kg^?1 IM) was given. After 15 minutes, an infusion of xylazine hydrochloride (0.1 mg mL^?1), guaiphenesin (50 mg mL^?1) and ketamine (1 mg mL^?1) (X–G–K) was infused at a rate of 1.1 mL kg^?1 hour^?1 IV. Oxygen (4 L minute^?1) was delivered by nasotracheal tube 30 minutes later. Inter‐coccygeal (Co₁–Co₂) extradural anaesthesia (lidocaine 2%, 0.18 mL kg^?1) was administered 30 minutes later. Cardiopulmonary variables were obtained in the unsedated standing calves 10 minutes after xylazine, 15 and 30 minutes after X–G–K without O₂, 15 and 30 minutes after X–G–K with O₂ and 5, 15, 30, 45 and 60 minutes after extradural anaesthesia. Data were analysed using a repeated measurement analysis of variance including an autoregressive covariance structure of order 1 (correlations at different time intervals). Results Xylazine caused significant (p < 0.05) decreases in heart rate (HR), cardiac output (Qt) and index (CI), stroke volume and stroke index, mean, systolic and diastolic arterial blood pressure (MAP, SAP, DAP), left (LVWSI) and right ventricular stroke work index (RVWSI), mean, systolic and diastolic pulmonary arterial pressure (MPAP, SPAP, DPAP), arterial pH, arterial oxygen tension (P_aO₂), arterial base excess, arterial HCO₃^? concentration, arterial saturation, packed cell volume, arterial and venous oxygen content (C_aO₂, C_vO₂), O₂ consumption and O₂ delivery (V?O₂, ?O₂). Increases in systemic vascular resistance (SVR) and pulmonary vascular resistance (PVR) were observed. During X–G–K infusion without O₂, HR, Qt and CI increased gradually while SVR, PVR and MAP decreased. Left ventricular stroke work index and P_aO₂ remained constant, while O₂ supplementation improved P_aO₂. Coccygeal extradural anaesthesia had little effect on cardiopulmonary variables. Respiratory rate (f) and P_aCO₂ significantly increased over the experiment. Conclusions and clinical relevance Xylazine caused adverse cardiopulmonary effects in calves. Improvement occurred during xylazine–guiaphenesin–ketamine infusion. Cardiac index and arterial blood pressure remained below baseline values while sustained increases in respiration rate and P_aCO₂ were observed. Inter‐coccygeal extradural anaesthesia had only minor effects. Oxygen supplementation proved advantageous during guiaphenesin, ketamine and xylazine infusion in healthy calves in combination with coccygeal extradural anaesthesia induced persistent cardiopulmonary depression.     

The effects of ice-water storage on blood gas and acid–base measurements

Objective: To determine the effects of storage of arterial and venous blood samples in ice water on blood gas and acid–base measurements. Design: Prospective, in vitro, laboratory study. Setting: School of veterinary medicine. Subjects: Six healthy dogs. Measurements and main results: Baseline measurements of partial pressure of oxygen (PO₂), partial pressure of carbon dioxide (PCO₂), pH, hemoglobin concentration (tHb), oxyhemoglobin saturation, and oxygen content (ContO₂) were made. Bicarbonate (HCO₃) and standard base excess (SBE) were calculated. Arterial and venous blood samples were separated into 1 and 3 mL samples, anaerobically transferred into 3 mL plastic syringes, and stored in ice water for 6 hours. Measurements were repeated at 15, 30 minutes, and 1, 2, 4, and 6 hours after baseline measurements. Arterial (a) PO₂ increased significantly from baseline after 30 minutes of storage in the 1 mL samples and after 2 hours in the 3 mL samples. Venous (v) PO₂ was significantly increased from baseline after 4 hours in the 1 mL samples and after 6 hours in the 3 mL samples. The pHa significantly decreased after 2 hours of storage in the 1 mL samples and after 4 hours in the 3 mL samples. In both the 1 and 3 mL samples, pHv decreased significantly only after 6 hours. Neither the arterial nor the venous PCO₂ values changed significantly in the 1 mL samples and increased only after 6 hours in the 3 mL samples. No significant changes in tHb, ContO₂, SBE, or HCO₃ were detected. Conclusions: The PO₂ of arterial and venous blood increased significantly when samples were stored in plastic syringes in ice water. These increases are attributable to the diffusion of oxygen from and through the plastic of the syringe into the blood, which occurred at a rate that exceeded metabolic consumption of oxygen by the nucleated cells.     

Accuracy of pulse oximetry and capnography in healthy and compromised horses during spontaneous and controlled ventilation

The objective of this prospective clinical study was to evaluate the accuracy of pulse oximetry and capnography in healthy and compromised horses during general anesthesia with spontaneous and controlled ventilation. Horses anesthetized in a dorsal recumbency position for arthroscopy (n = 20) or colic surgery (n = 16) were instrumented with an earlobe probe from the pulse oximeter positioned on the tip of the tongue and a sample line inserted at the Y-piece for capnography. The horses were allowed to breathe spontaneously (SV) for the first 20 min after induction, and thereafter ventilation was controlled (IPPV). Arterial blood, for blood gas analysis, was drawn 20 min after induction and 20 min after IPPV was started. Relationships between oxygen saturation as determined by pulse oximetry (S_pO₂), arterial oxygen saturation (S_aO₂)_, arterial carbon dioxide partial pressure (P_aCO₂), and end tidal carbon dioxide (P_(et)CO₂), several physiological variables, and the accuracy of pulse oximetry and capnography, were evaluated by Bland–Altman or regression analysis. In the present study, both S_pO₂ and P_(et)CO₂ provided a relatively poor indication of S_aO₂ and P_aCO₂, respectively, in both healthy and compromised horses, especially during SV. A difference in heart rate obtained by pulse oximetry, ECG, or palpation is significantly correlated with any pulse oximeter inaccuracy. If blood gas analysis is not available, ventilation to P_(et)CO₂ of 35 to 45 mmHg should maintain the P_aCO₂ within a normal range. However, especially in compromised horses, it should never substitute blood gas analysis.     

Pulmonary gas exchange and plasma lactate in horses with gastrointestinal disease undergoing emergency exploratory laparotomy: a comparison with an elective surgery horse population

Objective: To characterize pulmonary gas exchange and arterial lactate in horses with gastrointestinal disease undergoing anesthesia, compared with elective surgical horses, and to correlate these variables with postoperative complications and mortality. Study Design: Prospective clinical study. Animals: Horses undergoing emergency laparotomy for acute intestinal disease (n=50) and healthy horses undergoing elective surgery in dorsal recumbency (n=20). Methods: Arterial blood gas analysis was performed at predetermined intervals on horses undergoing a standardized anesthetic protocol. Alveolar–arterial oxygen gradient was calculated. Predictive factors for postoperative complications and death in colic horses were determined. Results: Arterial oxygen tension (P_aO₂) varied widely among horses in both groups. P_aO₂ significantly increased in the colic group after exteriorization of the ascending colon. P_aO₂ and alveolar–arterial oxygen gradient were not significantly different between groups, and neither were correlated with horse outcome. Arterial lactate in recovery ≥5 mmol/L was associated with a 2.25 times greater relative risk of complications and lactate ≥7 mmol/L was associated with a 10.5 times higher relative risk of death. Conclusion: Colic horses in this population were not more likely to be hypoxemic than elective horses, nor was gas exchange impaired to a greater degree in colic horses relative to controls. Arterial lactate sampled immediately after anesthetic recovery was predictive for postoperative complications and death.     

Hemodynamic effects of intravenous lidocaine in isoflurane anesthetized cats

Lidocaine dose‐dependently decreases the minimum alveolar concentration (MAC) of isoflurane in cats. The purpose of this study was to determine the hemodynamic effects of six lidocaine plasma concentrations in isoflurane anesthetized cats. Six cats were studied. After instrumentation, end‐tidal isoflurane concentration was set at 1.25 times the individual minimum alveolar concentration (MAC), which was determined in a previous study. Lidocaine was administered intravenously to target pseudo‐steady state plasma concentrations of 0, 3, 5, 7, 9, and 11 μg ml^–1, and isoflurane concentration was reduced to an equipotent concentration, determined in a previous study. Cardiovascular variables; blood gases; PCV; total protein and lactate concentrations; and lidocaine and monoethylglycinexylidide concentrations were measured at each lidocaine target concentration, before and during noxious stimulation. Derived variables were calculated. Data were analyzed using a repeated measures anova , followed by a Tukey test for pairwise comparisons where appropriate. One cat was excluded from analysis because the study was aborted at 7 μg ml^–1 due to severe cardiorespiratory depression. Heart rate, cardiac index, stroke index, right ventricular stroke work index, total protein concentration, mixed‐venous PO₂ and hemoglobin oxygen saturation, arterial and mixed‐venous bicarbonate concentrations, and oxygen delivery were significantly lower during lidocaine administration than when no lidocaine was administered. Mean arterial pressure, central venous pressure, pulmonary artery pressure, systemic and pulmonary vascular resistance indices, PCV, arterial and mixed‐venous hemoglobin concentrations, lactate concentration, arterial oxygen concentration, and oxygen extraction ratio were significantly higher during administration of lidocaine than when no lidocaine was administered. Most changes were significant at lidocaine target plasma concentrations of 7 μg ml^–1 and above. Noxious stimulation did not significantly affect most variables. Despite significantly decreasing in inhalant requirements, when combined with isoflurane, lidocaine produces greater cardiovascular depression than an equipotent dose of isoflurane alone. The use of lidocaine to reduce isoflurane requirements is not recommended in cats.     

The anti-nociceptive and cardiopulmonary effects of extradural fentanyl–xylazine in sheep

Objective To compare the anti‐nociceptive effects of extradural xylazine, fentanyl and a xylazine–fentanyl combination in sheep, and to measure the cardiopulmonary effects of the xylazine–fentanyl combination. Study design Prospective, randomized study. Animals Twenty‐five half‐merino ewes 2–4 years of age and body mass 54.2 ± 1.1 kg. Methods Six sheep in group 1 received 0.2 mg kg^?1 xylazine by extradural injection, six in group 2 received fentanyl 1.5 µg kg^?1 and 13 in group 3 received the combination of both treatments. In all groups, drugs were mixed with saline (0.15 mL kg^?1 before injection). Pulmonary and carotid arterial catheters were placed in seven sheep of group 3 which were used to evaluate cardiopulmonary effects. Anti‐nociception was determined by the response to electrical stimulation (40 V for 1.5 milliseconds) of the left flank and by superficial and deep muscular ‘pinpricking’ stimulation of the pelvic and thoracic limbs and thoracolumbar region. Results Lack of response to electrical stimulation at the left flank was present in 10 ± 1.1 minutes (mean ± SEM) (group 1) and in 4.5 ± 0.5 minutes in group 3. The duration of lack of response to electrical stimulation at the left flank was 96 ± 6 minutes in group 1 and 315 ± 6 minutes in group 3. Responses persisted in group 3. Significant decreases (p < 0.05) in cardiac output 30, 45, 60 and 90 minutes after injection, and in cardiac work at 30 and 45 minutes were observed in the seven animals of group 3. Arterial blood pH was lowest at 90 minutes, arterial bicarbonate was lowest at 60 minutes and values for both arterial and mixed venous base excess increased significantly at 60 and 90 minutes. There was no significant change from baseline values in heart rate, mean arterial blood pressure, respiratory rate, body temperature, systemic vascular resistance, arterial and mixed venous PO₂, PCO₂, oxygen saturation, blood oxygen content, haemoglobin concentration, mixed venous blood bicarbonate and pH. Conclusions Fentanyl decreases the onset time and prolongs the duration of anti‐nociception produced by xylazine. The combination decreases cardiac output but is without significant respiratory effects. Clinical relevance Further studies are required to show that surgery is possible in sheep after extradural xylazine–fentanyl injection.     

Blood gas analysis and cooximetry in retired racing Greyhounds

Objective – The purposes of this study were to evaluate the oxygen affinity of hemoglobin (Hb) in healthy retired racing Greyhounds via cooximetry, and to establish reference intervals for blood gases and cooximetry in this breed. Design – Prospective clinical study. Setting – University Teaching Hospital. Animals – Fifty‐seven Greyhounds and 30 non‐Greyhound dogs. Interventions – Venous blood samples were collected from the jugular vein and placed into heparinized tubes. The samples were analyzed within 30 minutes of collection using a blood gas analyzer equipped with a cooximeter. Measurements and Main Results – Greyhounds had significantly higher pH, PO₂, oxygen saturation, oxyhemoglobin, total Hb, oxygen content, and oxygen capacity and significantly lower deoxyhemoglobin and P₅₀ when compared with non‐Greyhound dogs. Conclusion – These findings support the fact that this breed is able to carry a higher concentration of total oxygen in the blood. As reported previously, this breed also has lower P₅₀ and, therefore, high oxygen affinity. In light of recent findings suggesting that in certain tissues a high affinity for oxygen is beneficial, this adaptation may be of benefit during strenuous exercise.