The cardiopulmonary effects of severe blood loss in anesthetized horses.
OBJECTIVE
To characterize the acute cardiopulmonary effects of severe hemorrhage in anesthetized horses.


METHODS
Prospective experimental study.


METHODS
Three geldings and six mares, aged 14.4 +/- 2.7 years, weighing 486 +/- 41 kg (range: 425-550 kg).


METHODS
Horses were anesthetized using xylazine, guaifenesin, ketamine and halothane or isoflurane. Cardiovascular variables, hematocrit, total solids, capillary refill time (CRT) and color of mucous membranes were measured as blood was collected from the carotid artery into sterile plastic bags. Arterial blood gas analysis was also performed.


RESULTS
The average amount of blood collected from these horses was (mean +/- SD) 53 +/- 4.8 mL kg(-1) bodyweight (range: 23-32 kg) over 39 +/- 4 minutes. Hematocrit decreased from 38 +/- 3 to 32 +/- 2% after induction of anesthesia and did not change significantly over the period of blood loss. Total solids decreased significantly after induction of anesthesia, and over the period of blood loss. Systolic, mean, diastolic and pulse pressures decreased as blood was lost. Heart rate did not change significantly. Capillary refill time increased from 1.6 +/- 0.4 seconds to 4.8 +/- 1.3 seconds as blood loss increased. Mucous membrane color deteriorated progressively. Arterial PO2 decreased significantly over the period of blood loss.


CONCLUSIONS
Hematocrit and heart rate do not change significantly during acute severe hemorrhage in the anesthetized horse. Arterial blood pressure, pulse pressure and PaO2 decrease as blood loss increases. Changes in mucous membrane color and CRT also occur as blood loss increases.


CONCLUSIONS
During severe hemorrhage in the inhalant-anesthetized horse, both heart rate and hematocrit remain unchanged. Blood pressure decreases and changes in arterial PO2 correlate most strongly with volume of blood lost.
D000771:Anesthesia, Intravenous / Q000662:veterinary*; D019162:Anesthetics, Combined; D018685:Anesthetics, Inhalation / Q000008:administration & dosage*; D000818:Animals; D001784:Blood Gas Analysis / Q000662:veterinary; D016063:Blood Loss, Surgical / Q000662:veterinary; D001794:Blood Pressure; D005260:Female; D006140:Guaifenesin / Q000008:administration & dosage; D006221:Halothane / Q000008:administration & dosage; D006439:Hemodynamics; D006470:Hemorrhage / Q000473:pathology / Q000503:physiopathology / Q000662:veterinary*; D006734:Horse Diseases / Q000503:physiopathology*; D006736:Horses / Q000502:physiology*; D007530:Isoflurane / Q000008:administration & dosage; D007649:Ketamine / Q000008:administration & dosage; D008297:Male; D011446:Prospective Studies; D012720:Severity of Illness Index; D014991:Xylazine / Q000008:administration & dosage
D019162:Anesthetics, Combined; D018685:Anesthetics, Inhalation; D014991:Xylazine; D006140:Guaifenesin; D007649:Ketamine; D007530:Isoflurane; D006221:Halothane