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.     

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.     

Effects of changing body position on oxygenation and arterial blood pressures in foals anesthetized with guaifenesin, ketamine, and xylazine

ObjectiveTo investigate the impact of a change in body position on blood gases and arterial blood pressures in foals anesthetized with guaifenesin, ketamine, and xylazine.Study designProspective, randomized experimental study.AnimalsTwelve Quarter Horse foals, age of 5.4 ±0.9 months and weighing 222 ± 48 kg.MethodsFoals were anesthetized with guaifenesin, ketamine, and xylazine for 40 minutes in lateral recumbency and then assigned to a change in lateral recumbency after hoisting (Group 1, n = 6), or no change (Group 2, n = 6). Oxygen 15 L minute^?1 was insufflated into the endotracheal tube throughout anesthesia. Arterial blood pressure, heart rate, respiratory rate (f_R), inspired fraction of oxygen (FiO₂), and end-tidal carbon dioxide (Pe’CO₂) were measured every 5 minutes. Arterial pH and blood gases [arterial partial pressure of oxygen (PaO₂), arterial partial pressure of carbon dioxide (PaCO₂)] were measured at 10, 30, and 40 minutes after induction, and 5 minutes after hoisting. Alveolar dead space ventilation and PaO₂/FiO₂ were calculated. Two repeated measures models were used. All hypothesis tests were two-sided and significance level was α = 0.05. All values are presented as least square means ± SE.ResultsValues at time-matched points from the two groups were not significantly different so they were combined. Arterial partial pressure of oxygen decreased significantly from 149 ± 14.4 mmHg before hoisting to 92 ± 11.6 mmHg after hoisting (p=0.0013). The PaO₂/FiO₂ ratio decreased from 275 ± 30 to 175 ± 24 (p=0.0055). End-tidal carbon dioxide decreased significantly from 48.7 ± 1.6 to 44.5 ± 1.2 mmHg (p=0.021). Arterial partial pressure of carbon dioxide, blood pressures and heart rates measured 5 minutes after hoisting were not different from measurements obtained before hoisting.Conclusion and clinical relevanceHoisting decreased PaO₂ in anesthetized healthy foals. Administration of supplemental oxygen is recommended to counter the decrease in oxygenation and PaO₂ measurement is necessary to detect early changes.     

Arterial blood gas tensions during recovery in horses anesthetized with apneustic anesthesia ventilation compared with conventional mechanical ventilation

ObjectiveTo compare PaO₂ and PaCO₂ in horses recovering from general anesthesia maintained with either apneustic anesthesia ventilation (AAV) or conventional mechanical ventilation (CMV).Study designRandomized, crossover design.AnimalsA total of 10 healthy adult horses from a university-owned herd.MethodsDorsally recumbent horses were anesthetized with isoflurane in oxygen [inspired oxygen fraction = 0.3 initially, with subsequent titration to maintain PaO₂ ≥ 85 mmHg (11.3 kPa)] and ventilated with AAV or CMV according to predefined criteria [10 mL kg^–1 tidal volume, PaCO₂ 40–45 mmHg (5.3–6.0 kPa) during CMV and < 60 mmHg (8.0 kPa) during AAV]. Horses were weaned from ventilation using a predefined protocol and transferred to a stall for unassisted recovery. Arterial blood samples were collected and analyzed at predefined time points. Tracheal oxygen insufflation at 15 L minute^–1 was provided if PaO₂ < 60 mmHg (8.0 kPa) on any analysis. Time to oxygen insufflation, first movement, sternal recumbency and standing were recorded. Data were analyzed using repeated measures anova, paired t tests and Fisher’s exact test with significance defined as p < 0.05.ResultsData from 10 horses were analyzed. Between modes, PaO₂ was significantly higher immediately after weaning from ventilation and lower at sternal recumbency for AAV than for CMV. No PaCO₂ differences were noted between ventilation modes. All horses ventilated with CMV required supplemental oxygen, whereas three horses ventilated with AAV did not. Time to first movement was shorter with AAV. Time to oxygen insufflation was not different between ventilation modes.ConclusionsAlthough horses ventilated with AAV entered the recovery period with higher PaO₂, this advantage was not sustained during recovery. Whereas fewer horses required supplemental oxygen after AAV, the use of AAV does not preclude the need for routine supplemental oxygen administration in horses recovering from general anesthesia.     

Use of gastric balloon manometry for estimation of intra-abdominal pressure in horses

Reasons for performing study: Standing laparoscopic procedures, facilitated by abdominal insufflation with carbon dioxide, are being employed to an increasingly greater extent in horses. However, a sustained increase in abdominal pressure may be life‐threatening. A practical method for intra‐abdominal pressure (IAP) assessment is imperative. Although indirect methods for estimating IAP have been extensively studied in man, little work has been performed in veterinary medicine. Objectives: To investigate the utility of gastric manometry for purposes of evaluating IAP in horses. Methods: Gastric pressure (P_ga) was estimated by balloon manometry in 8 healthy, mature horses, before and during a 30 min passive pneumoperitoneum induced by right paralumbar puncture. The balloon manometer was positioned within the gastric lumen and inflated using 2 separate volumes of air: 10 and 50 ml. P_ga Gastric pressure was determined at baseline (0) and 5, 15 and 30 min after induction of passive pneumoperitoneum. Intra‐abdominal pressure was measured directly by right paralumbar puncture using an 8 gauge needle at baseline and immediately following establishment of passive pneumoperitoneum. Results: Baseline IAP values were negative and increased (P≤0.05) during development of passive pneumoperitoneum. However, recorded P_ga measurements for both inflation volumes were positive before (baseline) and during the course of the passive pneumoperitoneum. Measured P_ga values did not correlate with IAP at any time. Conclusions and potential relevance: Our results suggest that the indirect method used in human patients for estimating IAP by P_ga is not applicable for horses.     

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.     

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.     

Effects of Carbon Dioxide Insufflation Combined With Changes in Body Position on Blood Gas and Acid-Base Status in Anesthetized Llamas (Llama glama)

Objective— To study the combined effects of intra-abdominal CO₂ insufflation with changes in body position during laparoscopy in xylazine-ketamine-halothane anesthetized llamas. Study Design— Prospective, controlled study. Animals— Nine castrated, male llamas weighing 114 ± 23 kg, 3 to 13 years old. Methods— Three llamas (preliminary study [PS] group) were used to study the effect of right lateral, dorsal, and left lateral recumbency on gas exchange and acid-base status. The other six (experimental study [ES] group) were used to study the combined effects of changes in body position and CO₂ insufflation to an intraabdominal pressure of 10 to 12 mm Hg. Heart rate, respiratory rate, and indirect arterial blood pressures (systolic [SAP], mean [MAP], and diastolic [DAP]) were recorded every 5 minutes during anesthesia. Arterial blood gases (PaO₂ and PaCO₂) and acid-base status (pHa and HCO₃) were measured immediately after induction of anesthesia and before each change of position. Results— In the PS group, significant decreases in SAP, MAP and PaCO₂ and increases in PaO₂ and pHa were observed when the llamas were turned from right lateral to dorsal recumbency. Values for HCO_-3 were lower than the postinduction values, but they remained unaffected by the changes in position. In the ES group, values for MAP were significantly lower when the llamas were placed in dorsal and left lateral recumbency than those observed during right lateral recumbency. Arterial O₂ tension during right lateral recumbency was lower but returned to preinsufflation values when the llamas were placed in the dorsal position. All llamas recovered uneventfully within 30 minutes after termination of anesthesia. Conclusions— Insufflation of CO₂ and changing body position induce minor and transient changes in cardiovascular and respiratory function. Clinical Relevance— Laparoscopy with mild intra-abdominal CO₂ insufflation (10 to 12 mm Hg) can be used safely in spontaneously breathing llamas anesthetized with xylazine, ketamine, and halothane.     

Aerosolized salbutamol (albuterol) improves PaO2 in hypoxaemic anaesthetized horses – a prospective clinical trial in 81 horses

Objective To compare the arterial pH and blood gas values, heart rate and mean arterial blood pressure, in hypoxaemic anaesthetized horses, before and after treatment, with a salbutamol (albuterol) aerosol. Animal population Eighty‐one client‐owned horses weighing between 114 and 925 kg. Fifty‐seven underwent emergency abdominal surgery and 24 were anaesthetized for elective procedures. Materials and methods Pre‐anaesthetic medication included xylazine, detomidine, butorphanol and morphine, alone or in various combinations. Induction of anaesthesia was achieved with guaifenesin and ketamine, diazepam and ketamine, or guaifenesin and thiopental. The trachea of all animals was intubated and anaesthesia maintained with either halothane (33 horses) or isoflurane (48 horses) in oxygen. Heart rate and rhythm were monitored continuously. Arterial blood pressure was monitored directly, and arterial blood collected for pH and blood gas analyses. When arterial PaO₂ fell below 9.3 kPa (70 mm Hg) and failed to respond to corrective measures including positive pressure ventilation and treatment of hypotension (mean arterial blood pressures <70 mm Hg), a salbutamol aerosol (2 µg kg^?1) was delivered via the endotracheal tube. Twenty minutes later, a second arterial blood sample was analysed. Results There were no significant differences in mean arterial blood pressure, heart rate, arterial pH, base excess and bicarbonate before and after treatment. Arterial O₂ tension increased significantly from a mean ± SD of 8.3 ± 1.7 kPa (62.4 ± 13.1 mm Hg) before administration to 15.9 ± 9.8 kPa (119.4 ± 57.7 mm Hg) after treatment. There was a small but significant decrease in PaCO₂ from 7.4 ± 1.5 kPa (55.2 ± 11.2 mm Hg) to 7.0 ± 1.3 kPa (52.9 ± 9.8 mm Hg) between sample times. No changes in heart rhythm were observed. A high percentage (approximately 70%) of animals sweated following treatment. Conclusions Salbutamol administered at a dose of 2 µg kg^?1 via the endotracheal tube of anaesthetized horses with PaO₂ values less than 9.3 kPa (70 mm Hg) resulted in an almost two‐fold increase in PaO₂ values within 20 minutes of treatment. No changes in heart rate or mean arterial blood pressure were associated with the use of salbutamol in this study. The improvement in PaO₂ may be a result of bronchodilatation and improved ventilation, increased perfusion secondary to an increase in cardiac output, or a combination of these two factors. Cardiac output and ventilation–perfusion distribution were not measured in this study; therefore, the reason for the increase in PaO₂ values cannot be conclusively determined. Clinical relevance Administration of a salbutamol aerosol is a simple but effective technique that can be used to improve PaO₂ values in hypoxaemic horses during inhalant anaesthesia with no apparent detrimental side effects.     

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.     

Influence of pneumoperitoneum and postural change on the cardiovascular and respiratory systems in dogs

We investigated the influence of pneumoperitoneum#(PP) and postural change under inhalation anesthesia with isoflurane, which is routinely used in dogs, on the cardiovascular and respiratory systems. As test animals, 6 adult beagles were used. To induce anesthesia, atropine, butorphanol and propofol were intravenously injected. Anesthesia was maintained with 1.3 MAC (1.7%) isoflurane. The following were the experiment conditions: I:E ratio, 1:1.9; tidal air exchange, 20 ml/kg; and ventilation frequency, 14 times/min. Respiration was regulated so that the PaCO₂ was approximately 35 to 40 mmHg before the start of the experiment. PP with CO₂ (intraperitoneal pressure 15 mmHg) and a postural change (15°C) was performed during the experiment. As parameters of circulatory kinetics, heart rate (HR), mean aortic pressure (MAP), mean pulmonary arterial pressure (MPAP), central venous pressure (CVP), femoral venous pressure (FVP) and cardiac output (CO) were measured. As parameters of respiratory kinetics, airway pressure (PAW) and blood gas (BG) were measured. There were significant increases in HR, MAP, MPAP, CVP, FVP, CO, PAW and PaCO₂ after PP in the horizontal position. There were significant increases in CVP, FVP, PAW and PaCO₂ after PP in the Trendelenburg position. There were significant increases in the MPAP, CVP, FVP, PAW and PaCO₂ after PP in the inverse Trendelenburg position. There was a significant difference in FVP after PP between the Trendelenburg position and inverse Trendelenburg position. The results of this experiment suggest that appropriate anesthesia control, such as changing the ventilation conditions after PP, is required for laparoscopic surgery under inhalation anesthesia with isoflurane.     

Cardiopulmonary effects associated with head-down position in halothane-anesthetized ponies with or without capnoperitoneum

Objective To compare the cardiopulmonary effects of the head‐down position, with or without capnoperitoneum, in halothane‐anesthetized horses. Study design Prospective randomized study. Animals Five ponies (four mares, one stallion; bodyweight 302 ± 38.4 kg [mean ± SD]) were used. Methods The ponies were anesthetized with xylazine, guiafenesin, ketamine, and maintained with halothane/oxygen and lungs were ventilated to 40 ± 2 mm Hg (5.3 ± 0.3 kPa) end‐tidal CO₂ tension. After baseline cardiopulmonary measurements, ponies were kept in horizontal position for 30 minutes, then tilted head‐down 30° to the horizontal position for 60 minutes, and then returned to a horizontal position for final measurements. Capnoperitoneum (intra‐abdominal pressure: 12 mm Hg [1.6 kPa]) was introduced after baseline cardiopulmonary measurements, until 5 minutes before the final measurements (treatment INS). Ponies in the control treatment (CON) did not receive capnoperitoneum. Cardiopulmonary data were collected every 10 minutes following the baseline measurements until recovery. Results In the head‐down position, in both treatments, significant decreases were observed in PaO₂, and significant increases were observed in PaCO₂, right atrial blood pressure, arterial to end‐tidal CO₂ gradient, calculated V_d/V_t and ratios. During the head‐down position, in CON there was decreased cardiac index, and in INS, there were decreases in arterial plasma pH and increases in mean systemic arterial and airway pressures. Treatment INS developed ventilation–perfusion mismatch earlier in the study, and had longer recovery times compared to CON. Conclusion Cardiac index and systemic blood pressure appeared to be preserved in INS during the head‐down position, but ventilation–perfusion mismatch appeared earlier with head‐down position and capnoperitoneum. Clinical relevance Healthy ponies tolerate capnoperitoneum at 12 mm Hg (1.6 kPa) intra‐abdominal pressure when tilted head down 30° to the horizontal position.     

Cardiovascular effects of insufflation of the abdomen with carbon dioxide in standing horses sedated with detomidine

OBJECTIVE: To determine the cardiovascular effects of 60 minutes of abdominal insufflation with CO2 to an intra-abdominal pressure of 15 mm Hg in standing horses receiving a constant rate infusion of detomidine. ANIMALS: 5 horses. PROCEDURE: Horses were randomly allocated into treatment or control groups. A washout period of a minimum of 7 days separated the 2 experimental periods of the crossover study. Catheters were placed into the right atrium, pulmonary artery, jugular vein, and right transverse facial artery after lidocaine infiltration. All horses were sedated with detomidine (8.54 microg/kg/h, i.v.). Horses in the treatment group received abdominal insufflation with CO2 via a laparoscopic cannula to a final and constant intra-abdominal pressure of 15 mm Hg for 60 minutes. Systemic arterial pressure, right atrial pressure, heart rate, cardiac output, core body temperature, and the pH and gas tensions of arterial and mixed venous blood were obtained. Cardiac index and systemic vascular resistance were calculated. Data were collected in 3 stages: preinsufflation (-10 and -5 minutes), insufflation (0, 15, 30, 45, and 60 minutes), and postinsufflation (70 and 80 minutes). The quality of sedation and level of analgesia were determined. RESULTS: The PaO2 of horses in the treatment group was significantly higher after 60 minutes of pneumoperitoneum than in the control group. Core body temperature decreased significantly from baseline in both groups. CONCLUSIONS AND CLINICAL RELEVANCE: A 60-minute period of abdominal insufflation to an intra-abdominal pressure of 15 mm Hg did not induce significant cardiovascular abnormalities in healthy horses.     

Post‐anesthetic pulmonary edema in two horses

Case 1 A two‐year old, 462 kg Standard bred horse was anesthetized for arthroscopy and castration. During anesthesia, hyperemia of the mucosal membranes and urticaria were noticed. During 5 hours of anesthesia subcutaneous edema of the eyelids and neck region developed. In the recovery box, the orotracheal (OT) tube was left in situ and secured in place with tape. Following initial attempts to stand, the horse became highly agitated and signs consistent with pulmonary edema developed subsequently. Arterial hypoxemia (PaO₂: 3.7 kPa [28 mmHg]) and hypocapnia (PaCO₂: 3.1 kPa [23 mmHg]) were confirmed. Oxygen and furosemide were administered. The horse was assisted to standing with a sling. Therapy continued with bilateral intra‐nasal oxygen insufflation. Ancillary medical therapy included flunixin meglumine, penicillin, gentamycin and dimethylsulfoxide. Following 7 hours of treatment the arterial oxygen tensions began to increase towards normal values. Case 2 An 11‐year old, 528 kg Paint horse was anesthetized for surgery of a submandibular mass. The 4‐hour anesthetic period was unremarkable. The OT tube was left in situ for the recovery. During recovery, the horse was slightly agitated and stood after three attempts. Clinical signs consistent with pulmonary edema and arterial hypoxemia (PaO₂: 5 kPa [37.5 mmHg]) subsequently developed following extubation. Respiratory signs resolved with medical therapy, including unilateral nasal oxygen insufflation, furosemide, flunixin meglumine and dimethylsulfoxide. The diagnosis of pulmonary edema in these horses was made by clinical signs and arterial blood‐gas analysis. While pulmonary radiographs were not taken to confirm the diagnosis, the clinical signs following anesthesia support the diagnosis in both cases. The etiology of pulmonary edema was most likely multifactorial.     

Blood Gas Values During Intermittent Positive Pressure Ventilation and Spontaneous Ventilation in 160 Anesthetized Horses Positioned in Lateral or Dorsal Recumbency

One hundred sixty horses were anesthetized with xylazine, guaifenesin, thiamylal, and halothane for elective soft tissue and orthopedic procedures. Horses were randomly assigned to one of four groups. Group 1 (n = 40): Horses positioned in lateral (LR_G1,; n = 20) or dorsal (DR_G1,; n = 20) recumbency breathed spontaneously throughout anesthesia. Group 2 (n = 40): Intermittent positive pressure ventilation (IPPV) was instituted throughout anesthesia in horses positioned in lateral (LR_G2; n = 20) or dorsal (DR_G2; n = 20) recumbency. Group 3 (n = 40): Horses positioned in lateral (LR_G3; n = 20) or dorsal (DR_G3; n = 20) recumbency breathed spontaneously for the first half of anesthesia and intermittent positive pressure ventilation was instituted for the second half of anesthesia. Group 4 (n = 40): Intermittent positive pressure ventilation was instituted for the first half of anesthesia in horses positioned in lateral (LR_G4; n = 20) or dorsal (DR_G4; n = 20) recumbency. Spontaneous ventilation (SV) occured for the second half of anesthesia. The mean time of anesthesia was not significantly different within or between groups. The mean time of SV and IPPV was not significantly different in groups 3 and 4. Variables analyzed included pH, PaCO₂, PaO₂, and P(A-a)O₂ (calculated). Spontaneous ventilation resulted in significantly higher PaCO₂ and P(A-a)O₂ values and significantly lower PaO₂ values in LR_G1, and DR_G1, horses compared with LR_G2 and DR_G2 horses. Intermittent positive pressure ventilation resulted in normocarbia and significantly lower P(A-a)O₂ values in LR_G2 and DR_G2 horses. In LR_G2 the Pao₂ values significantly increased from 20 minutes after induction to the end of anesthesia. The PaO₂ and P(A-a)O₂ values were not significantly different from the beginning of anesthesia after IPPV in DR_G2 or DR_G3. The PaO₂ values significantly decreased and the P(A-a)O₂ values significantly increased after return to SV in horses in LR_G4, and DR_G4. The PaO₂ values were lowest and the P(A-a)O₂ values were highest in all horses positioned in dorsal recumbency compared with lateral recumbency and in SV horses compared with IPPV horses. The pH changes paralleled the changes in PaCO₂. Blood gas values during right versus left lateral recumbency in all groups were also evaluated. The PaO₂ values were significantly lower and the P(A-a)O₂ values were significantly higher during SV in horses positioned in left lateral (LR_LG1) compared with right lateral (LR_RG1) recumbency. No other significant changes were found comparing left and right lateral recumbency. Arterial hypoxemia (PaO₂ < 60 mm Hg) developed in 35% of DR_G1 horses and 20% of DR_G2 horses at the end of anesthesia. Arterial hypercarbia (PaCO₂= 50–60 mm Hg) developed in DRoi horses. Arterial hypoxemia that developed in 20% of DR_G3 horses was not improved with IPPV. Arterial hypoxemia developed in 55% of DR_G4 horses after return to SV. Some DR_G4 horses with hypoxemia also developed hypercarbia, whereas some had PaCO₂ values within normal limits. Arterial hypoxemia developed in one LR_G1, and two LR_G4, horses. Hypercarbia developed in onlv one LR_G4 horse.     

Effect of body position on the arterial partial pressures of oxygen and carbon dioxide in spontaneously breathing,conscious dogs in an intensive care unit

Objective – To evaluate the effect of body position on the arterial partial pressures of oxygen and carbon dioxide (PaO₂, PaCO₂), and the efficiency of pulmonary oxygen uptake as estimated by alveolar‐arterial oxygen difference (A‐a difference). Design – Prospective, randomized, crossover study. Setting – University teaching hospital, intensive care unit. Animals – Twenty‐one spontaneously breathing, conscious, canine patients with arterial catheters placed as part of their management strategy. Interventions – Patients were placed randomly into lateral or sternal recumbency. PaO₂ and PaCO₂ were measured after 15 minutes in this position. Patients were then repositioned into the opposite position and after 15 minutes the parameters were remeasured. Measurements and Main Results – Results presented as median (interquartile range). PaO₂ was significantly higher (P=0.001) when patients were positioned in sternal, 91.2 mm Hg (86.0–96.1 mm Hg), compared with lateral recumbency, 86.4 mm Hg (73.9–90.9 mm Hg). The median change was 5.4 mm Hg (1.1–17.9 mm Hg). All 7 dogs with a PaO₂<80 mm Hg in lateral recumbency had improved arterial oxygenation in sternal recumbency, median increase 17.4 mm Hg with a range of 3.8–29.7 mm Hg. PaCO₂ levels when patients were in sternal recumbency, 30.5 mm Hg (27.3–32.7 mm Hg) were not significantly different from those in lateral recumbency, 32.2 mm Hg (28.3–36.0 mm Hg) (P=0.07). The median change was ?1.9 mm Hg (?3.6–0.77 mm Hg). A‐a differences were significantly lower (P=0.005) when patients were positioned in sternal recumbency, 21.7 mm Hg (17.3–27.7 mm Hg), compared with lateral recumbency, 24.6 mm Hg (20.4–36.3 mm Hg). The median change was ?3.1 mm Hg (?14.6–0.9 mm Hg). Conclusions – PaO₂ was significantly higher when animals were positioned in sternal recumbency compared with lateral recumbency, predominantly due to improved pulmonary oxygen uptake (decreased A‐a difference) rather than increased alveolar ventilation (decreased PaCO₂). Patients with hypoxemia (defined as PaO₂<80 mm Hg) in lateral recumbency may benefit from being placed in sternal recumbency. Sternal recumbency is recommended to improve oxygenation in hypoxemic patients.     

Apneic oxygenation in anesthetized ponies and horses

Apneic oxygenation was studied in six ponies for 30 minutes, and six horses for 10 minutes. Arterial blood was sampled at regular intervals for measurement of oxygen and carbon dioxide tensions (PaO₂ and PaCO₂) and calculation of alveolar-arterial oxygen tension difference (PAO₂-PaO₂). In both groups of animals, PaO₂ decreased rapidly during the first 3 minutes of apnea, then more slowly. Although the mean value was above 100 mmHg at 10 minutes, there was considerable inter-animal variability. Before apnea, PAO₂-PaO₂ was slightly, but not significantly, larger in horses than in ponies and increased in both groups during the first 3 minutes of apnea, after which the increase was slower. There was no significant difference between ponies and horses up to 10 minutes, suggesting that PAO₂-PaO₂ is independent of body size. In ponies, the PAO₂-PaO₂ did not change significantly between 10 and 30 minutes. Final PaO₂ could not be correlated with initial PaO₂ or initial PAO₂-PaO₂. The rate of rise of PAO₂-PaO₂ could not be predicted from baseline values. The rate of rise of PaCO₂ was similar and fairly constant in ponies and horses, and did not contribute to the rapid initial decrease in PaO₂. It appears that apneic oxygenation should not be used in the equine species, since it is impossible to predict in which animals the technique is safe for more than a few minutes.     

Hyoscine‐N‐butylbromide premedication on cardiovascular variables of horses sedated with medetomidine

ObjectiveTo evaluate the effects of intravenous (IV) or intramuscular (IM) hyoscine premedication on physiologic variables following IV administration of medetomidine in horses.Study designRandomized, crossover experimental study.AnimalsEight healthy crossbred horses weighing 330 ± 39 kg and aged 7 ± 4 years.MethodsBaseline measurements of heart rate (HR), cardiac index (CI), respiratory rate, systemic vascular resistance (SVR), percentage of patients with second degree atrioventricular (2^oAV) block, mean arterial pressure (MAP), pH, and arterial partial pressures of carbon dioxide (PaCO₂) and oxygen (PaO₂) were obtained 5 minutes before administration of IV hyoscine (0.14 mg kg^?1; group HIV), IM hyoscine (0.3 mg kg^?1; group HIM), or an equal volume of physiologic saline IV (group C). Five minutes later, medetomidine (7.5 μg kg^?1) was administered IV and measurements were recorded at various time points for 130 minutes.ResultsMedetomidine induced bradycardia, 2^oAV blocks and increased SVR immediately after administration, without significant changes in CI or MAP in C. Hyoscine administration induced tachycardia and hypertension, and decreased the percentage of 2^oAV blocks induced by medetomidine. Peak HR and MAP were higher in HIV than HIM at 88 ± 18 beats minute^?1 and 241 ± 37 mmHg versus 65 ± 16 beats minute^?1 and 192 ± 38 mmHg, respectively. CI was increased significantly in HIV (p ≤ 0.05). Respiratory rate decreased significantly in all groups during the recording period. pH, PaCO₂ and PaO₂ were not significantly changed by administration of medetomidine with or without hyoscine.Conclusion and clinical relevanceHyoscine administered IV or IM before medetomidine in horses resulted in tachycardia and hypertension under the conditions of this study. The significance of these changes, and responses to other dose rates, requires further investigation.     

Transcutaneous Oxygen and Carbon Dioxide Monitoring in Normal Cats

Feasibility of noninvasive oxygenation and ventilation monitoring using continuous transcutaneous oxygen (PO₂-_TC) and carbon dioxide (PCO₂-_TC) measurements was investigated in six healthy adult male cats anesthetized with isoflurane. Concurrent arterial blood gases, inspired oxygen concentration (FIO₂), end-tidal carbon dioxide (ETCO₂), PO₂-_TC were recorded during hyperoxia/normocapnia, normoxia/normocapnia, hypoxia/normocapnia, hypocapnia/hyperoxia, and hypercapnia/hyperoxia. Dorsolateral thorax and dorsal pelvis probe sites were evaluated. Probe site did not significantly affect the parameters. During normoxia and hypoxia, mean PO₂-_TC was insignificantly greater than mean PaO₂ (p > 0.154), but during hyperoxia PO₂-_TC was less than Pao₂ (p < 0.002). At each assessment (except hypercapnia for the dorsal pelvis probe site) PCO₂- _TC was greater than PaCO₂. Correlations between PO₂-_TC and FIO₂ (p < 0.05), and PaO₂ (p <0.001), and between PCO₂-_TCand ETCO₂ (p < 0.001), and PaCO₂ (p < 0.05) were good; however, the measured values of PO₂-_TC and PCO₂-_TC were not directly comparable to the measured values of PaO₂ and PaCO₂, respectively. Clinical utility of transcutaneous monitoring in cats will require development of the appropriate conversion equation for carbon dioxide and modifications for practical application.     

Guaifenesin-Ketamine-Xylazine Infusions to Provide Anesthesia in Donkeys

The purpose of this study was to determine a satisfactory combination of guaifenesin, ketamine, and xylazine (GKX) that would produce safe and satisfactory total intravenous anesthesia in donkeys for use under field conditions. Donkeys require higher amounts of ketamine in GKX to achieve satisfactory anesthetic levels without producing excessive depression with guaifenesin. Five adult standard donkeys (average weight, 264 kg) were anesthetized with 1.5 mg/mL ketamine, 0.5 mg/mL xylazine, 50 mg/mL guaifenesin (GKX-1); 2.0 mg/mL ketamine, 0.5 mg/mL xylazine, 50 mg/mL guaifenesin (GKX-2); or 2.0 mg/mL ketamine, 0.75 mg/mL xylazine, 50 mg/mL guaifenesin (GKX-3). For the first trial, two donkeys received GKX-1, two received GKX-2, and one received GKX-3. One donkey received GKX-1, one received GKX-2, and three received GKX-3 for the second trial. In the final trial, two received GKX-1, two received GKX-2, and one received GKX-3. Donkeys were sedated with xylazine (1.1 mg/kg body weight) intravenously, and anesthesia was induced using intravenous GKX-1, GKX-2, or GKX-3. Anesthesia was maintained for 45 minutes; temperature, respiration rate, heart rate, hemoglobin saturation, partial pressure of arterial oxygen (PaO₂), partial pressure of carbon dioxide in arterial gas (PaCO₂), and pH were measured. There was no significant difference between combinations for temperature, respiration rate, heart rate, hemoglobin saturation, PaCO₂, or pH. At 30 and 45 minutes, GKX-3 produced significantly (P < .05) lower PaO₂ values than GKX-1 and GKX-2. GKX-3 is not recommended for field use in donkeys because of respiratory depression (PaO₂= 48.7 [±5.84] and 46.0 ± 3.11 mmHg at 30 and 45 minutes, respectively), whereas more voluntary movement was apparent with GKX-1. GKX-2 produced satisfactory anesthesia without significant respiratory depression in donkeys and should produce safe and effective anesthesia in donkeys under field conditions.