The cardiopulmonary effects of severe blood loss in anesthetized horses.

The research involves the study of the immediate cardiopulmonary effects of severe hemorrhage in horses under anesthesia. The effects were studied by taking vital measurements as blood was drawn out, and the conclusion shows that there were significant drops in several critical parameters but the heart rate and hematocrit remained stable.

Subjects and methods

• The study was a prospective experimental study, involving nine horses: three geldings and six mares.
• The horses on average were around 14.4 years old and weighed 486 kg.
• The horses were sedated using xylazine, guaifenesin, ketamine and either halothane or isoflurane.
• Key cardiovascular variables were monitored along with other parameters such as hematocrit, total solids, capillary refill time (CRT), and color of the mucus membrane.
• Throughout the trial, blood was drawn from the carotid artery into sterilized bags for measures and these samples were also used for arterial blood gas analysis.

Resulting Measures

• An average of 53 ml per kg of horse bodyweight of blood was collected over a duration of about 39 minutes.
• These tests revealed that the hematocrit decreased moderately upon the induction of anesthesia, but it did not fluctuate significantly during blood loss.
• Total solids also saw a decrease during both induction of anesthesia and the period of blood loss.
• Blood pressure including systolic, diastolic, and pulse pressure wore away as blood was lost from the horse.
• The heart rate was not significantly affected under these conditions.
• Capillary refill time increased from an average of 1.6 seconds to 4.8 seconds along with blood loss.
• There was a progressive deteriotation in the color of the mucous membrane.
• The arterial PO2 also significantly reduced over the period of blood loss.

Conclusions

• The research concluded that during acute severe blood loss in an anesthetized horse, hematocrit and heart rate remained largely unchanged.
• However, arterial blood pressure, pulse pressure, and arterial PO2 decreased as the volume of blood loss increased.
• Additionally there were changes in the color of the mucous membranes and CRT as blood loss escalated.
• These results suggest that hematocrit and heart rate don’t change significantly in response to acute severe blood loss, whereas other parameters such as blood pressure and arterial PO2 are highly sensitive to blood loss.