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Abstract

Objective

To study the effects of inhalation anesthetic agents on the response of horses to 3 hours of hypoxemia.

Design

Controlled crossover study.

Animals

Five healthy adult horses.

Procedure

Horses were anesthetized twice: once with halothane, and once with isoflurane in O2. Anesthetized horses were positioned in left lateral recumbency. Constant conditions for the study began at 2 hours of anesthesia. A constant agent dose of 1.2 minimum alveolar concentration, PaO2 of 50 ± 5 mm of Hg, and PaCO2 of 45 ± 5 mm of Hg were maintained for 3 hours. Circulatory measurements were made at 0.5, 1, 2, and 3 hours of hypoxemia (anesthesia hours 2.5, 3, 4, and 5). Blood was collected from horses for biochemical analyses before anesthesia, within a few minutes after standing, and at 1, 2, 4, and 7 days after anesthesia.

Results

Cardiac index was greater (P = 0.018) during isoflurane than halothane anesthesia. Cardiac index remained constant during the 3 hours of hypoxemia during halothane anesthesia, whereas it decreased from the baseline during isoflurane anesthesia. Marginally nonsignificant P values for an agent difference were detected for arterial O2 content (P = 0.051), and oxygen delivery (P = 0.057). Serum activities of aspartate transaminase (P = 0.050) and sorbitol dehydrogenase (P = 0.017) were higher in halothane-anesthetized horses than in isoflurane-anesthetized horses. Circulatory function was better in hypoxemic horses anesthetized with isoflurane than with halothane. Isoflurane resulted in less muscular injury in hypoxemia horses than did halothane anesthesia. Halothane anesthesia and hypoxemia were associated with hepatic insult.

Conclusion

Isoflurane is better than halothane for hypoxemic horses.(Am J Vet Res 1996;57:351-360)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To determine whether a detergent can prevent most of the early effects of IV infusion with Escherichia coli endotoxin (< 100 ng/kg of body weight) in horses: marked pulmonary hypertension, acute leukopenia, and fever.

Animals

8 healthy adult horses (4 male, 4 female), 415 to 615 kg.

Design and Procedure

Control and detergent experiments were performed in each horse while it was awake but sedated. In control experiments, 10 to 100 ng of E coli endotoxin/kg was given. In detergent experiments, 100 mg of detergent/kg was given 1 hour before injecting endotoxin, similar to the control experiments.

Results

In control experiments, pulmonary arterial pressure increased transiently over 40 minutes by 33 ± 8 mm of Hg (mean ± SD; P < 0.001), then returned to baseline. Circulating leukocytes decreased to 47 ± 19% (P < 0.02) of baseline by 1 hour after endotoxin, then increased above baseline by 6 hours. Rectal temperature increased by 0.7 ± 0.4 C (P < 0.01). In detergent experiments, the increase in pulmonary arterial pressure was much less than that in the control experiments (8 ± 7 mm of Hg; P < 0.001). Circulating leukocytes did not decrease, and the increase in rectal temperature after endotoxin was blocked.

Conclusions

This attenuation of the response to endotoxin may occur because the normal steps in the response of pulmonary intravascular macrophages (ie, endocytosis of endotoxin and subsequent release of inflammatory mediators) are altered by the detergent. This low-technology, inexpensive, and safe treatment could be an important new clinical tool for veterinarians in combating endotoxemia. (Am J Vet Res 1996;57:1063–1066)

Free access
in American Journal of Veterinary Research

Summary

The effect of 3 plasma concentrations of alfentanil on the minimum alveolar concentration (mac) of halothane in horses was evaluated. Five healthy geldings were anesthetized on 3 occasions, using halothane in oxygen administered through a mask. After induction of anesthesia, horses were instrumented for measurement of blood pressure, airway pressure, and end-tidal halothane concentrations. Blood samples, for measurement of pH and blood gas tensions, were taken from the facial artery. Positive pressure ventilation was begun, maintaining PaCO 2, at 49.1 ± 3.3 mm of Hg and airway pressure at 20 ± 2 cm of H2O. The mac was determined in triplicate, using a supramaximal electrical stimulus of the oral mucous membranes. Alfentanil infusion was then begun, using a computer-driven infusion pump to achieve and maintain 1 of 3 plasma concentrations of alfentanil. Starting at 30 minutes after the beginning of the infusion, mac was redetermined in duplicate. Mean ± sd measured plasma alfentanil concentration during the infusions were 94.8 ± 29.0, 170.7 ± 29.2 and 390.9 ± 107.4 ng/ml. Significant changes in mac were not observed for any concentration of alfentanil. Blood pressure was increased by infusion of alfentanil and was dose-related, but heart rate did not change. Pharmacokinetic variables of alfentanil were determined after its infusion and were not significantly different among the 3 doses.

Free access
in American Journal of Veterinary Research

Summary

Seven horses (4 anesthetized and 3 awake) and 2 ponies (anesthetized) were studied to evaluate the high sensitivity of the pulmonary circulation of the horse to various blood-borne particles, and to establish the presence of intravascular macrophages in the lung. Pulmonary and systemic pressures and cardiac output before and during particle injection were measured in some animals. An anesthetized foal had a large increase in pulmonary arterial pressure (32 and 34 mm of Hg) within 1 minute of IV administration of small test doses of radioactively labeled liposomes (2.5 μmol/kg of body weight) or a 1% suspension of blue pigment (0.3 ml/kg), respectively. Quantitative real-time gamma camera imaging of the foal revealed high retention of the labeled liposomes during the first pass through the lungs; retention persisted throughout the experiment. Postmortem analysis revealed 55 and 47% lung retention of liposomes and blue pigment, respectively. The 2 anesthetized ponies had increased pulmonary artery pressure of 34 ± 7 mm of Hg, decreased cardiac output, and 42% lung retention after administration of 1% blue pigment (0.2 ml/kg), whereas 3 awake horses had increased pressure of 28 ± 9 mm of Hg after 1.8 × 108 (1.8-μm-diameter) latex microspheres/kg. None of the injected particles caused vascular obstruction, and they do not cause pulmonary vascular reactivity in species that lack pulmonary intravascular macrophages. Finally, 3 horses (1 anesthetized and 2 awake) were infused Iv with small doses of the blue pigment, and their lungs were perfusion-fixed to identify specific labeling of the pulmonary intravascular macrophages. These cells were fully differentiated macrophages, contained blue pigment in phagocytes, and were tightly adherent to the pulmonary capillary endothelium. At this time, horses (order Perissodactyla) are the only species outside the mammalian order Artiodactyla (sheep, pig, cattle) documented to have reactive intravascular macrophages. Compared with other species, low doses of particles induced marked hemodynamic responses; horses appear to be more sensitive to IV administered particles than are other species studied.

Free access
in American Journal of Veterinary Research