Balloon Dilation of Congenital Subaortic Stenosis in the Dog

Balloon dilation during cardiac catheterization was evaluated for the treatment of congenital subaortic stenosis (SAS) in nine dogs. Under general anesthesia, bilateral cardiac catheterization was performed through the right jugular vein and carotid artery. Thermodilution cardiac output, and left ventricular and aortic root pressures and angiograms were obtained before and after balloon dilation. Balloons measuring 18–20 mm in diameter and 30–40 mm in length were positioned across the stenosis and three inflations 4–5 minutes apart were performed. There was no significant change in cardiac output, aortic pressure, or degree of aortic regurgitation after balloon dilation. For the entire group balloon dilation resulted in significant decreases in left ventricular systolic pressure (-61.2 ± 37.2 mm Hg [mean change ± SD], range -14 to -123), mean systolic pressure gradient (-39.6 ± 24.4 mm Hg, range –8.4 to -72.2), and peak systolic pressure gradient (-64.3 ± 46.5 mm Hg, range –17 to –143). Calculated left ventricular outflow cross-sectional area increased significantly (+.4 ± .5 cm², range –.06 to + 1.30). Clinical signs improved in the five symptomatic dogs. Individual hemodynamic responses varied widely, but the magnitude of improvement correlated with the severity of obstruction. Three dogs showed a decrease of 60% or greater (≥100 mm Hg), and six dogs showed a decrease of 25–50% (17–71 mm Hg) in peak systolic gradient after balloon dilation. Complications were frequent but most were transient and manageable. These preliminary results suggest that balloon dilation can acutely decrease outflow resistance in dogs with SAS and may be effective therapy for some affected dogs.     

Arteriovenous Fistulas as an Aid in Blood Collection from Canine Blood Donors

To facilitate blood collection from blood donor dogs, arteriovenous fistulas were established between the common carotid arteries and external jugular veins in five adult dogs. Twelve to 16 mm, side-to-side anastomoses were created using simple interrupted 6–0 polypropylene sutures. Starting 1 month after the surgical procedure, 500 ml of blood was collected from each dog as required. Electrocardiography, thoracic radiography, and cardiac output and rate were used to monitor cardiac changes. Blood flow characteristics, and proliferative and dystrophic cellular changes occurring in the vessels were documented in one dog.
The mean blood collection times were 2 minutes and 45 seconds from the fistula site and 9.0 minutes from the opposite jugular vein. Ventricular hypertrophy and myocardial changes were observed on electrocardiogram in two dogs, and radiographic evidence of pulmonary hypertension was noted in three dogs. Reversed blood flow was documented in the common carotid artery and external jugular vein distal to the arteriovenous fistula. Four dogs were still in use as blood donors 1 to 1 1/2 years after establishment of the fistulas. Clinical signs of congestive heart failure were not observed.     

A technique for central venous pressure measurement in normal horses

Objective – To investigate a technique of central venous pressure (CVP) measurement using a newly developed catheter in healthy adult horses. Design – Prospective experimental study. Setting – University research facility. Animals – Twenty healthy adult horses. Interventions – An equine central venous catheter was inserted into the jugular vein to a length of approximately 80 cm from the mid‐cervical region in an attempt to catheterize the pulmonary artery. Pulmonary arterial catheterization was confirmed by echocardiography. Insertion distance and pressure were measured at this location with a disposable manometer. The catheter was then withdrawn until presence in the right atrium was confirmed by echocardiography. Insertion distance and pressure were also measured at this location. The catheter was then withdrawn in 5 cm increments until exiting the jugular insertion site with pressure measured at each location. All pressure measurements were taken with the manometer zero position at the point of the shoulder. Measurements and Main Results – Pulmonary artery catheterization was successful in 16 of 20 horses. Mean pulmonary arterial pressure was 23.8 cm H₂O (17.5 mm Hg) (95% confidence interval [CI] 20.9–26.7 cm H₂O [15.4–19.6 mm Hg]). Mean right atrial pressure was 8.3 cm H₂O (6.1 mm Hg) (95% CI 7.1–9.4 cm H₂O [5.2–6.9 mm Hg]). Right atrial pressure was compared with pressures recorded at sequential insertion distances and resulted in a recommendation for catheter insertion of at least 40 cm for CVP measurement in adult horses. Jugular venous pressure measurement was statistically different from CVP measurement. Conclusions – This catheter measurement technique is well tolerated in normal horses. Routine clinical use of this equine central venous catheter may improve our ability to monitor patients and improve patient care and outcomes of ill horses in hospital.     

Intraocular pressures in the Beagle dog

Using a Schiotz tonometer, measurements of intraocular pressure were made on 128 conscious Beagles of 5–36 months and on twelve anaesthetized Beagles aged 3–5 years. The normal range of pressures was between 10 and 31 mm Hg; up to 3 years no significant age or sex differences were found.
Résumé. L'auteur a mesuré à l'aide d'un tonomètre Schiotz la pression oculaire de 128 chiens beagles éveillés, âgés de 5 à 36 mois, et de douze chiens beagles anesthésiés, âgés de 3 à 5 ans. La tension normale oscille entre 10 et 31 mm Hg; jusqu'à l'âge de 3 ans, on n'observe aucune différence significative suivant l'âge ou le sexe.
Zusammenfassung. Unter Verwendung des Schiötzschen Tonometers wurden Messungen des Augeninnendrucks an 128 nicht narkotisierten Beagle-Hunden im Alter von 5 bis 36 Monaten und an zwölf narkotisierten Beagle-Hunden im Alter von 3–5 Jahren durchgeführt. Der normale Druckbereich lag zwischen 10 und 31 mm Hg; bis zum Alter von 3 Jahren wurden keine signifikanten Alters— oder Geschlechtsunterschiede dabei festgestellt.     

High-Frequency Jet Ventilation in Anesthetized, Paralyzed Dogs and Cats Via Transtracheal and and Endotracheal Tube Routes

The ability of the SAV 6 high-frequency jet ventilator to effectively ventilate three anesthetized, paralyzed cats (3.2–4.2 kg), two small dogs (7.2 and 10.0 kg), six medium-sized dogs (20.5–25.0 kg), and three large dogs (36.0–43.0 kg) via a 14-gauge (dogs) or a 16-gauge (cats) catheter placed percutaneously into the trachea via the cricothyroid membrane or into a preplaced endotracheal tube was evaluated. The lowest driving pressure within the range of 0.25 to 2.0 kg/cm² (1 kg/cm²= 14.2 psi) and the highest cycle rate within the range of 60 to 240 per minute that would generate a PaCO₂ of 30 ± 3 mm Hg were determined.
All animals could be ventilated to a PaC0₂ of 30 ± 3 mm Hg by the endotracheal tube and transtracheal route, except the largest dogs, which couid be ventilated to an average PaC0₂ of 36 mm Hg by the transtracheal route. The transtracheal route consistently required higher driving pressures and lower cycle rates than did the endotracheal tube route. Cats could be ventilated with a driving pressure of 0.25 kg/cm²; small dogs could be ventilated with 0.5 to 1.0 kg/cm₂; medium-sized dogs with 1.0 to 1.5 kg/cm²; and large dogs with 1.5 to 2.0 kg/cm².
The SAV 6 high-frequency jet ventilator can effectively ventilate cats and dogs (7.2–43.0 kg) via a transtracheal catheter and an endotracheal tube.     

Heterotopic implantation of a porcine bioprosthetic heart valve in a dog with aortic valve endocarditis

CASE DESCRIPTION: A 5-year-old male German Shepherd Dog was evaluated because of a 5-month history of progressive lethargy, weight loss, and heart failure. CLINICAL FINDINGS: On physical examination, bounding femoral pulses and systolic and diastolic murmurs were detected. Echocardiography revealed severe aortic valve insufficiency (AVI) and a large vegetative lesion on the aortic valve consistent with aortic valve endocarditis. The AVI velocity profile half-time was 130 milliseconds; the calculated peak systolic pressure gradient across the aortic valve was 64 mm Hg. Left ventricular diameter during diastole was 63.6 mm (predicted range, 40.2 to 42 mm) and during systole was 42.9 mm (predicted range, 25.4 to 27 mm). Systolic, diastolic, and mean arterial blood pressures were 120, 43, and 65 mm Hg, respectively. TREATMENT AND OUTCOME: To palliate severe AVI, the descending aorta was occluded (duration, 16.75 minutes) and heterotopic implantation of a porcine bioprosthetic heart valve in that vessel was performed. After surgery, systolic, diastolic, and mean arterial blood pressures were 115, 30, and 61 mm Hg, respectively, in the forelimb and 110, 62, and 77 mm Hg, respectively, in the hind limb. Within 6 months, the AVI velocity profile half-time had increased to 210 milliseconds, indicating diminished severity of AVI. After 24 months, the dog was able to engage in vigorous exercise; no pulmonary edema had developed since surgery. CLINICAL RELEVANCE: Heterotopic bioprosthetic heart valve implantation into the descending aorta during brief aortic occlusion appears feasible in dogs and may provide substantial palliation for dogs with severe AVI.     

Submaximal Exercise Testing Using Lactate Threshold and Venous Oxygen Tension as Endpoints in Normal Dogs and in Dogs With Heart Failure

Twelve normal dogs and 7 dogs with experimentally induced heart failure were chronically instrumented to measure hemodynamic variables and blood gas tensions at rest and during graded treadmill exercise. Three groups of 4 normal dogs each (group 1, 15 to 20 kg; group 2, 21 to 30 kg; group 3, 31 to 40 kg) were exercised on a treadmill at a 16% grade at 1, 2, and 3 miles per hour, and at a 22% and a 26% grade at 3 miles per hour (5 total exercise levels) until blood lactate concentration increased to a value greater than 1 mmol/L. Blood lactate concentration and blood gas tensions were measured 5 and 15 minutes after starting exercise, and cardiac output was measured between 8 and 10 minutes of exercise. Results indicated that the same exercise protocol could be used for dogs ranging in size from 15 to 40 kg. Blood lactate concentration increased in normal dogs at varying workloads, but always at or above a workload of 3 miles per hour at a 16% grade. Dogs with class IV heart failure always experienced an increase in blood lactate concentration when walked at 1 mile per hour at a 16% grade for 5 minutes. A femoral vein Po₂ between 21 and 24 mm Hg in normal dogs, and between 16 and 22 mm Hg in dogs with heart failure was always associated with an increase in blood lactate concentration. The primary problem with this exercise protocol was the unwillingness of some dogs to walk on the treadmill during the preselection phase. We conclude that we have devised a submaximal exercise test that can be used to evaluate exercise capability in dogs ranging in size from 15 to 40 kg, that the described exercise protocol can be used to identify decreased flow reserve in dogs with class IV heart failure induced by rapid ventricular pacing, and that either femoral vein oxygen tension or blood lactate concentration can be used as the endpoint for submaximal exercise testing in dogs. J Vet Intern Med 1996;10:21–27. Copyright©1996 by the American College of Veterinary Internal Medicine.     

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.     

Cardiopulmonary effects of intrathoracic insufflation in dogs

This study was designed to quantify the effects of incremental positive insufflation of the intrathoracic space on cardiac output (CO), heart rate (HR), arterial pressure (AP), central venous pressure (CVP), and percent saturation of hemoglobin with oxygen (SPO2) in anesthetized dogs. Seven healthy, adult dogs from terminal teaching laboratories were maintained under anesthesia with isoflurane delivered with a mechanical ventilator. The experimental variables were recorded before introduction of an intrathoracic catheter, at intrathoracic pressures (IP) of 0 mm Hg, 3 mm Hg insufflation, and additional increments of 1 mm Hg insufflation thereafter until the SPO2 remained <85% despite increases in minute volume. Finally the variables were measured again at 0 mm Hg IP. The cardiac output and systolic and diastolic AP significantly (P < 0.05) decreased at 3 mm Hg IP. Significant decreases in SPO2 were seen at 10 mm Hg IP. Significant increase in CVP was noted at 6 mm Hg IP. Heart rate decreased significantly at 5 to 6 mm Hg IP but was not decreased above 6 mm Hg IP. Given the degree of CO decrease at low intrathoracic pressures, insufflation-aided thoracoscopy should be used with caution and at the lowest possible insufflation pressure. Standard anesthetic monitoring variables such as HR and AP measurements may not accurately reflect the animal's cardiovascular status.     

Evaluation of a portocaval venograft and ameroid ring for the occlusion of intrahepatic portocaval shunts in dogs

OBJECTIVE:To evaluate the use of a portocaval venograft and ameroid constrictor in the surgical management of intrahepatic portosystemic shunts (PSS). STUDY DESIGN: Prospective, clinical study. Animal Population: Ten client-owned dogs with intrahepatic PSS. METHODS: Portal pressure was measured after temporary suture occlusion of the intrahepatic PSS. In dogs with an increase in portal pressure greater than 8 mm Hg, a single extrahepatic portocaval shunt was created using a jugular vein. An ameroid ring was placed around the venograft and the intrahepatic PSS was attenuated. Transcolonic pertechnetate scintigraphy was performed before surgery, 5 days after surgery, and 8 to 10 weeks after surgery. Dogs with continued portosystemic shunting were evaluated further by laparotomy or portography. Clinical outcome and complications were recorded. RESULTS: Mean (+/- SD) portal pressure increased from 6 +/- 3 to 19 +/- 6 mm Hg with PSS occlusion; in all 10 dogs, the increase in portal pressure was greater than 8 mm Hg. There were no intraoperative complications, and, after creation of the portocaval shunt, the intrahepatic PSS could be completely ligated in 8 of 10 dogs. The final portal pressure was 9 +/- 4 mm Hg. Postoperative complications included coagulopathy and death (1 dog), ascites (3 dogs), and incisional discharge (3 dogs). Five of 8 dogs had continued portosystemic shunting at 8 to 10 weeks after surgery. Multiple extrahepatic PSS were demonstrated in 4 of these dogs. Clinical outcome was excellent in all 9 surviving dogs. CONCLUSIONS AND CLINICAL SIGNIFICANCE: The surgical technique resulted in a high incidence of multiple extrahepatic PSS. Short-term clinical results were promising, but long-term outcome must be evaluated further.     

Techniques for isolation and performance of the perfused guinea pig working heart

This study demonstrated new approaches which enabled evaluating the work performance in both ventricles of an isolated guinea pig heart. By changing the right atrial filling pressure (RAFP, preload) from 6 to 20 mm of Hg at a constant aortic pressure (Pa, 20 mm of Hg), cardiac output, stroke volume, aortic flow, coronary flow, cardiac work, O2 consumption, CO2 output, as well as end-diastolic ventricular, and pulmonary arterial pressures increased. Cardiac contractility and both ventricular systolic pressures reached peak values between 12 and 14 mm of Hg of RAFP and then gradually decreased. With graded increases of Pa (afterload) from 10 to 45 mm of Hg at a fixed RAFP (8 mm of Hg), coronary flow, cardiac contractility, cardiac work, cardiac O2 consumption, glucose utilization rate, and pulmonary arterial and both ventricular systolic pressures increased. Although aortic flow decreased with an increase in Pa, cardiac output, stroke volume, and coronary resistance did not show significant changes. Furthermore, cardiac mechanical efficiency decreased with an increase of pre- or afterload of the perfused isolated heart. These findings indicate that the total working heart model is suitable for studying cardiac functions.     

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.     

Baroreceptor control of heart rate in chickens (Gallus domesticus)

The baroreceptor control of heart rate was examined in nonanesthetized, nonrestrained, White Leghorn chickens (n = 10) by measuring the heart period response to modest increases in systolic blood pressure induced by IV boluses of phenylephrine (0.04 micrograms/g). In each animal, a sciatic artery and a femoral vein were chronically instrumented for the measurement of blood pressure and heart rate, together with venous access. Sustained and consistent cardiac slowing was seen in all chickens in response to small increases in systolic pressure. The mean slope of the regression equation between heart period and systolic pressure was 13.9 +/- 0.8 s X 10(-4)/mm of Hg. This sensitivity was reduced to 2.1 +/- 1.5 s X 10(-4)/mm of Hg by anesthetizing the chickens with isoflurane (inspired concentrations of 1%).     

Sevoflurane anesthesia in desert tortoises (Gopherus agassizii).

The effects of sevoflurane on anesthesia induction, recovery, ventricular pressures, heart rate, ventricular pH, blood gas values, and electrolytes were evaluated in desert tortoises (Gopherus agassizii). Tortoises were orotracheally intubated while awake and ventilated manually with 3-7% sevoflurane in oxygen (1 L/min) to achieve desired expired sevoflurane concentrations. Data, consisting of induction time, recovery time, systolic, diastolic, and mean ventricular pressures, heart rate, ventricular pH, blood gas values, and electrolytes, were collected prior to anesthesia and sequentially at 2.50% and 3.75% expired sevoflurane as measured at the junction of the endotracheal tube and the breathing circuit. Blood pressure was measured and blood samples were collected through a 25-ga needle passed through a cardiac access port that was placed while the tortoises were in dorsal recumbency. Mean (+/-SE) induction time was 2.55+/-0.55 min, recovery time was 27.58+/-7.55 min, and duration of anesthesia was 105+/-12 min. Mean (+/-SD) values for systolic, diastolic, and mean ventricular pressures in awake tortoises were 28+/-3 mm Hg, 22+/-2 mm Hg, and 24+/-2 mm Hg, respectively. Sevoflurane (2.5% expired) significantly decreased systolic (14+/-3 mm Hg), diastolic (12+/-1 mm Hg), and mean (13+/-1 mm Hg) ventricular pressures compared with those of awake tortoises. Ventricular pressures did not decrease further with increasing depth of anesthesia. Heart rate (32+/-4 beats/min) did not change significantly under sevoflurane anesthesia. Sevoflurane administration increased ventricular PO2 but did not change Na+, K+, or iCa++ concentrations. Sevoflurane appears to provide safe and effective anesthesia with rapid induction and recovery.     

Evaluation of peripheral and central venous pressure in awake dogs and cats

OBJECTIVE: To determine whether peripheral venous pressure (PVP) was correlated with central venous pressure (CVP) when measured by use of different catheter sizes, catheterization sites, and body positions in awake dogs and cats. ANIMALS: 36 dogs and 10 cats. PROCEDURES: Dogs and cats with functional jugular and peripheral venous catheters were enrolled in the study. Peripheral venous catheters (18 to 24 gauge) were placed in a cephalic, lateral saphenous, or medial saphenous vein. Central venous catheters (5.5 to 8.5 F) were placed in the jugular vein and advanced into the cranial vena cava. Catheters were connected to pressure transducers and a blood pressure monitor capable of displaying 2 simultaneous pressure tracings. For each animal, the mean of 5 paired measurements of PVP and CVP was calculated. The relationship between PVP and CVP when measured by use of different catheter sizes, catheterization sites, and body positions was determined. RESULTS: Mean +/- SD PVP was 5.7 +/- 5.8 mm Hg higher than CVP in dogs and 6.0 +/- 6.9 mm Hg higher than CVP in cats. However, results of multiple regression analysis did not indicate a significant correlation between PVP and CVP, regardless of catheter size, catheter position, or body position. The relationship was weak in both dogs and cats. CONCLUSIONS AND CLINICAL RELEVANCE: The PVP was poorly correlated with CVP when different catheter sizes, catheterization sites, and patient positions were evaluated. Peripheral venous pressure should not be used to approximate CVP in awake dogs and cats.     

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.     

The Natural Clinical History of Canine Congenital Subaortic Stenosis

The demographics and natural clinical history of canine congenital subaortic stenosis (SAS) were evaluated by retrospective analysis of 195 confirmed cases (1967 to 1991), 96 of which were untreated and available for follow-up evaluation. Of these, 58 dogs had left ventricular outflow systolic pressure gradients available for assessment of severity. All 195 dogs were used for demographic analysis. Breeds found to be at increased relative risk included the Newfoundland (odds ratio, 88.1; P < .001), Rottweiler (odds ratio, 19.3; P < .001), Boxer (odds ratio, 8.6; P < .001), and Golden Retriever (odds ratio, 5.5; P < .001). Dogs with mild gradients (16 to 35 mm Hg) and those that developed infective endocarditis or left heart failure were diagnosed at older ages than those with moderate (36 to 80 mm Hg) and severe (>80 mm Hg) gradients. Of 96 untreated dogs, 32 (33.3%) had signs of illness varying from fatigue to syncope; 11 dogs (11.3%) developed infective endocarditis or left heart failure. Exercise intolerance or fatigue was reported in 22 dogs, syncope in 11 dogs, and respiratory signs (cough, dyspnea, tachypnea) in 9 dogs. In addition, 21 dogs (21.9%) died suddenly. Sudden death occurred mainly in the first 3 years of life, primarily but not exclusively, in dogs with severe obstructions (gradient, > 80 mm Hg; odds ratio, 16.0; P < .001). Infective endocarditis (6.3%) and left heart failure (7.3%) tended to occur later in life and in dogs with mild to moderate obstructions. Left heart failure was uncommon in the absence of additional congenital defects or infective endocarditis. Dogs with mild obstructions lived longer than other groups and tended to remain asymptomatic. The majority of dogs with severe obstructions died before 3 years of age and had a high prevalence (8 of 15) of sudden death. The prognosis for long-term survival in dogs with untreated mild or moderate SAS is favorable (median survival, 30.5 and 51.1 months, respectively), while the prognosis for dogs with severe SAS is very poor (median survival, 18.9 months).     

Re-evaluation of a portocaval venograft without an ameroid constrictor as a method for controlling portal hypertension after occlusion of intrahepatic portocaval shunts in dogs

OBJECTIVE: To evaluate the use of a portocaval venograft without an ameroid constrictor in the surgical management of intrahepatic portosystemic shunts (PSS). STUDY DESIGN: Prospective clinical study. ANIMALS: Seven dogs with intrahepatic PSS. METHODS: Portal pressure was measured after temporary suture occlusion of the intrahepatic PSS. In dogs with an increase in portal pressure > or =8 mm Hg or signs of portal hypertension, a single extrahepatic portocaval shunt was created using a jugular vein. Clinical outcome and complications were recorded. RESULTS: The mean (+/-SD) portal pressure increased from 5.9+/-1.6 to 17.9+/-4.1 mm Hg with PSS occlusion. There were no intraoperative complications and, after creation of the portocaval shunt, the intrahepatic PSS could be completely ligated in all dogs. The final portal pressure was 9.6+/-1.9 mm Hg. Complications developed during postoperative hospitalization in 5 dogs and included incisional discharge (4 dogs), ascites (3), ventricular premature contractions (2), and melena, bloody diarrhea, neurologic signs, coagulopathy, and aspiration pneumonia (each in 1 dog). Six dogs died or were euthanatized with clinical signs related to depression, inappetance, abdominal pain, vomiting, melena, and abdominal distention, with a median survival of 82 days (range, 20-990 days). One dog was clinically normal at 33 months after surgery. CONCLUSIONS: Clinical signs observed in 6 dogs after surgery were consistent with portal hypertension. Use of a portocaval venograft without an ameroid constrictor may reduce the likelihood of hepatic vascular development, thereby increasing the risk of life-threatening portal hypertension should the venograft suddenly occlude. CLINICAL RELEVANCE: Use of a portocaval venograft without an ameroid constrictor to control portal hypertension after ligation of an intrahepatic PSS cannot be recommended.     

Pulmonic stenosis in dogs: balloon dilation improves clinical outcome

Medical records of 81 dogs with severe pulmonic stenosis from 2 referral centers were examined retrospectively. Forty dogs underwent balloon valvuloplasty (BV), which was performed by 1 operator, whereas 41 did not. The mean age at latest follow-up was 41.5 months. A statistical comparison of the clinical outcome and survival was performed. Dogs revealing clinical signs at presentation showed a 16-fold increase in risk of death compared with asymptomatic dogs (P < .001). Statistical analyses demonstrated that an increase of 1 mm Hg in transstenotic pressure gradient (PG) at presentation was associated with a 3% increase in hazard rate (P < .001). Thirty-seven dogs survived BV with a median reduction in PG of 46%. The median preoperative PG was 120 mm Hg, and median PG 24 hours postoperatively was 55 mm Hg with a median of 55 mm Hg 6 months post-BV. Twenty (49%) of the non-BV (NBV) dogs remained asymptomatic at last follow-up. Fourteen (34%) of the NBV dogs died or were euthanized because of heart disease related to pulmonic stenosis. Twelve of these dogs died suddenly, whereas only 1 of the BV dogs died suddenly. After adjusting for PG, clinical signs at presentation, and age, BV or dilation was associated with a 53% reduction in hazard rate (P = .005). This study indicates that BV, when performed by an experienced operator, appears to be successful both in alleviating clinical signs and in prolonging survival in dogs with severe pulmonic stenosis.     

Hemodynamics in the guinea pig after anesthetization with ketamine/xylazine

The resting hemodynamics were determined in 8 guinea pigs after they were anesthetized with ketamine/xylazine. Measurements were made of blood pressure, heart rate, cardiac output, arterial blood gases, and pH. These measurements were obtained initially at 4 to 5 hours after an injection (IM) of ketamine HCl (25 mg) and xylazine (0.15 mg) was given to anesthetize the animals for catheterization (period 1), again 5 days after the operation (period 2), and finally 4 to 5 hours after a 2nd injection of ketamine/xylazine (period 3). There were no differences in heart rates, respiratory rates, or cardiac outputs among the 3 study periods. However, arterial blood pressure was slightly, but significantly, lowered after, and presumably due to, instrumentation (62 +/- 4 mm of Hg, P less than 0.05) when compared with the 5-day postoperative period (67 +/- 7 mm of Hg) or after the readministration of anesthetics (66 +/- 7 mm of Hg). The partial pressure of carbon dioxide in the arterial blood was slightly lower (4 mm of Hg, P less than 0.05) in both acutely postanesthetic periods (period 1 and period 3) than in the same animals at postoperative day 5 (period 2). This study has demonstrated that resting hemodynamics measured shortly after this anesthesia with ketamine/xylazine are not largely different from those in chronically instrumented animals.