Effects of a highly concentrated hypertonic saline-dextran volume expander on cardiopulmonary function in anesthetized normovolemic horses

Paula F. Moon From the Veterinary Medical Teaching Hospital (Moon), Department of Surgery (Snyder, Haskins), School of Veterinary Medicine, and Department of Human Physiology (Kramer, Perron), School of Medicine, University of California, Davis, CA 95616.

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Jack R. Snyder From the Veterinary Medical Teaching Hospital (Moon), Department of Surgery (Snyder, Haskins), School of Veterinary Medicine, and Department of Human Physiology (Kramer, Perron), School of Medicine, University of California, Davis, CA 95616.

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Steve C. Haskins From the Veterinary Medical Teaching Hospital (Moon), Department of Surgery (Snyder, Haskins), School of Veterinary Medicine, and Department of Human Physiology (Kramer, Perron), School of Medicine, University of California, Davis, CA 95616.

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Paul R. Perron From the Veterinary Medical Teaching Hospital (Moon), Department of Surgery (Snyder, Haskins), School of Veterinary Medicine, and Department of Human Physiology (Kramer, Perron), School of Medicine, University of California, Davis, CA 95616.

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George C. Kramer From the Veterinary Medical Teaching Hospital (Moon), Department of Surgery (Snyder, Haskins), School of Veterinary Medicine, and Department of Human Physiology (Kramer, Perron), School of Medicine, University of California, Davis, CA 95616.

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SUMMARY

Conventional fluid resuscitation is unsatisfactory in a small percentage of equine emergency surgical cases because the large volumes of fluids required cannot be given rapidly enough to adequately stabilize the horse. In anesthetized horses, the volume expansion and cardiopulmonary effects of a small volume of highly concentrated hypertonic saline-dextran solution were evaluated as an alternative initial fluid choice. Seven halothane-anesthetized, laterally recumbent, spontaneously ventilating, normovolemic horses were treated with a 25% NaCl-24% dextran 70 solution (hsd) at a dosage of 1.0 ml/kg of body weight, iv, infused over 10 minutes, and the effects were measured for 120 minutes after infusion. Plasma volume expansion was rapid and significant (from 36.6 ± 4.6 ml/kg to 44.9 ± 4.8 ml/kg), and remained significantly expanded for the duration of the experiment. Packed cell volume, total blood hemoglobin, and plasma protein concentrations significantly decreased, confirming rapid and sustained volume expansion with hemodilution. Cardiac index and stroke index immediately increased and remained high for the entire study (from 69.6 ± 15.3 ml/min/kg to 106.6 ± 28.4 ml/min/kg, and from 1.88 ± 0.49 ml/beat/kg to 2.50 ± 0.72 ml/beat/kg, respectively). Systemic vascular resistance significantly decreased immediately after hsd infusion and remained decreased for the duration of the study (from 1.41 ± 0.45 mm of Hg/ml/min/kg to 0.88 ± 0.22 mm of Hg/ml/min/kg). Arterial and venous blood oxygen content decreased significantly because of hemodilution, but actual oxygen transport transiently increased at the 10-minute measurement before returning toward baseline. Plasma osmolality and sodium significantly increased and remained high for the entire 120 minutes (from 293 ± 2 osm/L to 326 ± 9 mosm/L, and from 142.8 ± 3.3 mM/L to 159.0 ± 6.2 mM/L, respectively). Urine output increased in 5 of 7 horses within minutes of hsd infusion, but the mean increase was not statistically significant.

Three horses developed transiently severe, clinically apparent intravascular hemolysis and hemoglobinuria. One horse developed multiple single premature ventricular contractions during the infusion with no persistent ecg changes after infusion. The potential benefit of using hsd as a rapid volume expander in anesthetized horses was documented because infusion of 1 ml of hsd/kg rapidly increased plasma volume by approximately 8 ml/kg. Substantial side effects developed in these normovolemic horses, however, and this solution requires further investigation before it can be recommended in hemodynamically unstable horses.

SUMMARY

Conventional fluid resuscitation is unsatisfactory in a small percentage of equine emergency surgical cases because the large volumes of fluids required cannot be given rapidly enough to adequately stabilize the horse. In anesthetized horses, the volume expansion and cardiopulmonary effects of a small volume of highly concentrated hypertonic saline-dextran solution were evaluated as an alternative initial fluid choice. Seven halothane-anesthetized, laterally recumbent, spontaneously ventilating, normovolemic horses were treated with a 25% NaCl-24% dextran 70 solution (hsd) at a dosage of 1.0 ml/kg of body weight, iv, infused over 10 minutes, and the effects were measured for 120 minutes after infusion. Plasma volume expansion was rapid and significant (from 36.6 ± 4.6 ml/kg to 44.9 ± 4.8 ml/kg), and remained significantly expanded for the duration of the experiment. Packed cell volume, total blood hemoglobin, and plasma protein concentrations significantly decreased, confirming rapid and sustained volume expansion with hemodilution. Cardiac index and stroke index immediately increased and remained high for the entire study (from 69.6 ± 15.3 ml/min/kg to 106.6 ± 28.4 ml/min/kg, and from 1.88 ± 0.49 ml/beat/kg to 2.50 ± 0.72 ml/beat/kg, respectively). Systemic vascular resistance significantly decreased immediately after hsd infusion and remained decreased for the duration of the study (from 1.41 ± 0.45 mm of Hg/ml/min/kg to 0.88 ± 0.22 mm of Hg/ml/min/kg). Arterial and venous blood oxygen content decreased significantly because of hemodilution, but actual oxygen transport transiently increased at the 10-minute measurement before returning toward baseline. Plasma osmolality and sodium significantly increased and remained high for the entire 120 minutes (from 293 ± 2 osm/L to 326 ± 9 mosm/L, and from 142.8 ± 3.3 mM/L to 159.0 ± 6.2 mM/L, respectively). Urine output increased in 5 of 7 horses within minutes of hsd infusion, but the mean increase was not statistically significant.

Three horses developed transiently severe, clinically apparent intravascular hemolysis and hemoglobinuria. One horse developed multiple single premature ventricular contractions during the infusion with no persistent ecg changes after infusion. The potential benefit of using hsd as a rapid volume expander in anesthetized horses was documented because infusion of 1 ml of hsd/kg rapidly increased plasma volume by approximately 8 ml/kg. Substantial side effects developed in these normovolemic horses, however, and this solution requires further investigation before it can be recommended in hemodynamically unstable horses.

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