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in Journal of the American Veterinary Medical Association
in Journal of the American Veterinary Medical Association

Summary

The hemodynamic effects of 2 dosages of ephedrine were studied in 6 dogs anesthetized with isoflurane only (end-tidal concentration equivalent to 1.5 times minimum alveolar concentration). Following instrumentation, baseline (time 0) measurements included heart rate (hr), respiratory rate, mean arterial blood pressure (map), cardiac output, and blood gas tensions. Cardiac index (ci), stroke volume (sv), systemic vascular resistance (svr), arterial oxygen content (Cao2 ), and oxygen delivery and consumption (Do2 and Vo2 , respectively) were calculated. Three dogs were given ephedrine iv at a dosage of 0.1 mg/kg of body weight, and 3 dogs were given ephedrine iv at a dosage of 0.25 mg/kg. Measurements were recorded at 5, 10, 15, 30, and 60 minutes. Each dog then received the alternate dosage of ephedrine, and measurements were again recorded at the same intervals. Effects of ephedrine varied with dosage. Neither dosage was associated with significant changes in pH, Pao2 , Paco2 , Vo2 , or respiratory rate. Ephedrine at a dosage of 0.1 mg/kg caused transient significant increases in map, ci, sv, Cao2 , and Do2 , significant decreases in hr and svr, and a late, slight decrease in Cao2 . Ephedrine at a dosage of 0.25 mg/kg caused a greater and more prolonged increase in map, as well as increases in ci, sv, and svr, and a decrease in hr. The higher dosage of ephedrine also caused a pronounced increase in hemoglobin concentration and CaO2 , resulting in a 20 to 35% increase in Do2 throughout the 60-minute experiment.

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in American Journal of Veterinary Research

Abstract

Objective—To determine effects of sedation achieved by xylazine (XYL) or acepromazine (ACE) on cardiopulmonary function and uterine blood flow in cows in late gestation.

Animals—8 cows between 219 and 241 days of gestation.

Procedure—Doses of ACE (0.02 mg/kg) or XYL (0.04 mg/kg) were administered IV. Measurements were obtained to determine cardiopulmonary effects and oxygen delivery to the uterus.

Results—Heart rate was not significantly affected by administration of ACE, but it decreased markedly after administration of XYL. Uterine artery flow was decreased at all times by XYL and was always less than for ACE. Xylazine increased uterine vascular resistance through 30 minutes and caused reduced PaO2 and increased PaCO2 at all time periods. Acepromazine caused a 5% decrease in PaO2 only at 5 minutes. Xylazine reduced oxygen delivery by 59% at 5 minutes and 32% at 45 minutes. In contrast, ACE caused a nonsignificant reduction of oxygen delivery by 16% at 15 minutes and a return to baseline values by 45 minutes

Conclusions and Clinical Relevance—Xylazine markedly reduces flow and availability of oxygenated blood to the uterus, which may critically impair delivery of oxygen to the fetus at a stressful and important time of development or delivery. Acepromazine was associated with slight reductions of much shorter duration. When XYL is used to sedate pregnant cows, it could impose physiologic distress on the fetus and potentially increase fetal morbidity and mortality. When sedation of the dam is desirable, ACE could be an alternative to XYL. (Am J Vet Res 2002;63:1695–1699)

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in American Journal of Veterinary Research

Objective

To measure cardiopulmonary variables, including cardiac index, in dogs with naturally acquired gastric dilatation-volvulus (GDV).

Design

Prospective clinical study.

Animals

6 dogs with GDV.

Procedure

In addition to typical medical and surgical management of GDV, the dorsal metatarsal and pulmonary arteries and right atrium of the dogs were catheterized to obtain cardiopulmonary measurements before and during anesthesia and surgery.

Results

All dogs underwent gastropexy but none required gastrectomy. Mean cardiac index and mean arterial blood pressure for this small population of dogs with GDV were not significantly different from those reported for clinically normal awake or anesthetized dogs.

Conclusions and Clinical Relevance

Dogs with naturally acquired GDV without gastric necrosis may not have the classic characteristics, including decreased cardiac index and hypotension, of hypovolemic circulatory shock. (J Am Vet Med Assoc 1999;215:484—488).

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in Journal of the American Veterinary Medical Association

SUMMARY

Objective

To determine the cardiopulmonary effects of anesthesia induced and maintained with isoflurane (ISO) in cats.

Animals

8 healthy cats between 1 and 5 years old.

Procedure

Anesthesia was induced with ISO in oxygen. Two anesthetic depths were maintained in each cat; mean alveolar concentrations (MAC) were 1.3 and 2.0 times MAC. Ventilation was either spontaneous or controlled. Each cat received each treatment combination according to a Latin square design. Cardiopulmonary measurements were made after 20 minutes of constant conditions with each combination of anesthetic depth and ventilatory mode.

Results

Cardiac index was not different between ISO doses, but 2.0 MAC ISO reduced arterial blood pressure and total peripheral resistance. Cardiac index and systolic arterial blood pressure were reduced by controlled ventilation. The PaCO2 and pulmonary artery pressure were highest in association with 2.0 MAC ISO during spontaneous ventilation. Changes in pHa were attributable to changes in PaCO2 .

Conclusions

2.0 MAC ISO causes hypotension and hypercapnia; however, cardiac index is maintained. Hypercapnia may be abolished with controlled ventilation, but at the expense of reduced cardiac index. 1.3 MAC ISO results in minimal cardiopulmonary depression, especially when healthy cats are allowed to breathe spontaneously.

Clinical Relevance

Hypoventilation associated with untoward physiologic responses to 2.0 MAC may be overcome with controlled ventilation, but results in marked reduction in cardiovascular performance; thus, use of 2.0 MAC ISO should be avoided in cats. (Am J Vet Res 1998;59:182–185)

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in American Journal of Veterinary Research

Design—

To determine whether hemodynamic responses of halothane-anesthetized horses undergoing surgical procedures depended on anesthetic induction protocols used, and to determine whether hemodynamic responses to surgical manipulation could be detected.

Design—

Prospective experimental study without controls.

Animals—

36 clinically normal horses.

Procedure—

Horses were allotted to 5 groups according to anesthetic induction protocol: acepromazine/guaifene-sin/thiamylal, acepromazine/guaifenesin/ketamine, xyla-zine/guaifenesin/thiamylal, xylazine/guaifenesin/ketamine, and xylazine/diazepam/ketamine. Anesthesia was maintained with halothane. Hemodynamic measurements and blood gas values were obtained prior to the start of surgery, during surgery, and after surgery.

Results—

Few differences in hemodynamic measurements existed between horses in which anesthesia was induced by 5 anesthetic induction protocols, whether prior to the start of surgery or for pooled values for all 3 measurement periods. Hemodynamic responses to surgical manipulation were marked and included increased mean arterial pressure and systemic vascular resistance, and decreased cardiac index and oxygen delivery.

Clinical Implications—

Choice of anesthetic induction protocol has little impact on hemodynamic function during surgery in halothane-anesthetized horses. Surgical stimulation may increase blood pressure, but does not improve cardiac index or oxygen delivery. (J Am Vet Med Assoc 1996;208:252-257)

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in Journal of the American Veterinary Medical Association

Objective

To determine whether end-tidal partial pressure of carbon dioxide (Petco 2) was a reliable estimate of Paco2 in dogs undergoing thoracotomy.

Design

Case series.

Animals

18 dogs that underwent thoracotomy.

Procedure

Paco2 and Petco 2 were measured shortly after induction of anesthesia, while dogs were breathing spontaneously; 5 minutes prior to initial skin incision, while dogs were receiving intermittent positive-pressure ventilation (IPPV); 5, 30, and 60 minutes after the thoracic cavity was opened, while dogs were receiving IPPV; and after the thoracic cavity was closed and evacuated, when dogs were again breathing spontaneously. For each period, arterial-end-tidal difference in partial pressure of carbon dioxide (Paco2-Petco 2) was compared with Paco2-Petco 2 for the preceding period.

Results

Significant changes in Paco2-Petco 2 from one period to the next were not detected except when values obtained 5 minutes after the thoracic cavity was opened were compared with values obtained 5 minutes before incision. The Paco2-Petco 2 was not constant for individual dogs.

Clinical Implications

Petco 2 was not a reliable indicator of adequacy of ventilation during thoracotomy in these dogs, because it differed greatly from Paco2, and Pac02-PETC02 was not consistent. (J Am Vet Med Assoc 1998; 212:377-379)

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in Journal of the American Veterinary Medical Association

Summary

The uterine hemodynamic response to maternal positioning in dorsal recumbency was evaluated in 7 conscious pregnant cows during the third trimester. Anesthetic or sedative drugs were not administered. Uterine artery flow was measured, using a previously implanted ultrasonic flow probe. Catheters implanted in the uterine artery and vein were used for measurement of blood pressure and for blood sample collections. Heart rate, systemic arterial pressure, uterine arterial blood flow, arterial and venous oxygen and carbon dioxide tensions, and pH were measured in cows in standing position. Cows were cast with ropes and positioned in dorsal recumbency, then measurements were repeated at 15 and 30 minutes. Compared with standing measurements, dorsal recumbency caused 50% increase in heart rate and 44% increase in arterial blood pressure. Uterine artery flow did not change significantly. Despite increased ventilation, arterial oxygenation was reduced during dorsal recumbency. There were minimal differences between measurements at 15 and 30 minutes of dorsal recumbency.

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in American Journal of Veterinary Research

Summary

Cardiopulmonary and behavioral responses to detomidine, a potent α2-adrenergic agonist, were determined at 4 plasma concentrations in standing horses. After instrumentation and baseline measurements in 7 horses (X̄ ± sd for age and body weight, 6 ± 2 years, and 531 ± 48.5 kg, respectively), detomidine was infused to maintain 4 plasma concentrations: 2.1 ± 0.5 (infusion 1), 7.2 ± 3.5 (infusion 2), 19.1 ± 5.1. (infusion 3), and 42.9 ± 10 (infusion 4) ng/ml, by use of a computer-controlled infusion system.

Detomidine caused concentration-dependent sedation and somnolence. These effects were profound during infusions 3 and 4, in which marked head ptosis developed and all horses leaned heavily on the bars of the restraining stocks. Heart rate and cardiac index decreased from baseline measurements (42 ± 7 beats/min, 65 ± 11 ml·kg of body weight−1·min−1) in linear relationship with the logarithm of plasma detomidine concentration (ie, heart rate = −4.7 [loge detomidine concentration] + 44.3, P < 0.01; cardiac index = −10.5 [loge detomidine concentration] + 73.6, P < 0.01). Second-degree atrioventricular block developed in 5 of 7 horses during infusion 3, and in 6 of 7 horses during infusion 4. Mean arterial blood pressure increased significantly from 118 ± 11 mm of Hg at baseline to 146 ± 27 mm of Hg at infusion 4. Similar responses were observed for mean pulmonary artery and right atrial pressures. Systemic vascular resistance (baseline, 182 ± 28 mm of Hg·ml−1·min−1·kg−1) increased significantly during infusions 3 and 4 (to 294 ± 79 and 380 + 58, respectively). Plasma atrial natriuretic peptide concentration was significantly increased with increasing detomidine concentration (20.4 ± 3.8 pg/ml at baseline to 33.5 ± 9.1 at infusion 4). There were few significant changes in respiration rate and arterial blood gas and pH values. We conclude that maintenance of steady-state detomidine plasma concentrations resulted in cardiopulmonary changes that were quantitatively similar to those induced by detomidine bolus administration in horses.

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in American Journal of Veterinary Research