ANESTHESIA IN A CAPTIVE JUVENILE BLACK RHINOCEROS (DICEROS BICORNIS) FOR MAGNETIC RESONANCE IMAGING AND COMPUTED TOMOGRAPHY

Abstract

Veterinary Technician | FEBRUARY 2010 E1 M any veterinarians and veterinary technicians are intimidated by anesthesia of foals. General anesthetic principles for adult horses apply to foals; however, because of their age and size, foals are at risk for certain complications during anesthesia, and there are a few special considerations for determining adjustments in their anesthetic protocol. Neonatal foals (i.e., younger than 1 month) have rapidly changing cardiovascular and pulmonary physiologies as they develop adult systems, and, therefore, they have an increased risk of anesthetic-related death and/or complications. During the first week of life, a foal's risk of anesthesia-related death is seven times higher than that of an adult horse.1 At 1 to 4 months of age, foals still have a higher risk for anesthetic complications and/or death, but their risk level is closer to that of adult horses. The Transition to Adult PhysiologyIn utero, foals have cardiac shunts (foramen ovale, ductus arteriosus [FIGURE 1]) that permit low-pressure circulation of blood. The foramen ovale permits most blood to be shunted from the right atrium into the left atrium, thereby bypassing the lungs. In addition, the relatively low-oxygen environment in utero leads to constriction of pulmonary vessels and dilation of the ductus arteriosus. Because the foal's pulmonary arterial resistance is higher than its systemic arterial resistance, most pulmonary arterial blood is shunted through the ductus arteriosus into the aorta, with the remaining blood perfusing the lungs. During birth, neonatal foals begin the transition to a right-sided, adult cardiovascular and pulmonary physiology. The initial breaths and lung expansion after parturition (delivery) decrease pulmonary vascular resistance, increasing pulmonary blood flow. The foramen ovale and the ductus arteriosus close because of an increase in Pao 2 (partial pressure of oxygen, arterial) and a decrease in prostaglandins. A thin layer of tissue initially closes these shunts, which permanently close over a few weeks if the foal is normal. However, if a pathologic state, such as prematurity or infection, leads to hypoxemia, acidemia (e.g., pH <7.4), or hypercarbia (Paco 2 [partial pressure of CO 2 , arterial]: >45 mm Hg), these shunts may reopen, and pulmonary hypertension may occur.Neonatal foals younger than 1 week have a high resting heart rate (e.g., 60 to 120 beats/min [bpm]), high respira- Glossary Acidemia-the state of low blood pH (e.g., arterial blood gas pH <7.4)Cardiac output-the amount of blood pumped per minute by the heart Chest (thoracic) wall-the boundary of the thoracic cavityChronotropic agent-an agent that alters the heart rate (e.g., a positive chronotropic agent increases the heart rate) Hypercarbia (hypercapnia)-excess carbon dioxide in the blood, resulting in respiratory acidosisHypoxemia-decreased partial pressure of oxygen in the blood (<60 mm Hg)Inotrope-an agent that alters the force of muscular contraction (e.g., a positive inotrope causes a stronger cardiac cont...

Etorphine-Ketamine Constant Rate Infusion for Maintenance of Anaesthesia in a Compromised White Rhinoceros (Ceratotherium simum)

“…We maintained anaesthesia using an etorphine-ketamine CRI. In clinical settings, inhalation drugs such as halothane [16], isoflurane [10, 15, 19, 27], and sevoflurane [14] have been used to maintain anaesthesia in rhinoceroses. However, inhalant anaesthesia requires bulky equipment, especially for large animals, and may be impractical and expensive to use outside of a clinical setting [28].…”

Pharmacokinetics of intravenous propofol in southern white rhinoceros (Ceratotherium simum simum) after intramuscular etorphine-butorphanol-medetomidine-azaperone

“…After propofol was administered, the animals were moved into lateral recumbency onto cushioned pads for the duration of the procedure (Figure 2). The timing and dose of propofol were extrapolated from equid species, prior case reports, [5][6][7] and the experiences of the authors.…”

“…Muscle rigidity, often associated with the use of potent opioids, further complicates intubation. 2,6 While hydraulic wedge jacks have been used to help open the jaws to permit manual orotracheal intubation, 5,7 there are challenges with using this equipment, and delaying intubation can cause a significant compromise in an animal that may also be suffering from drug-induced respiratory depression during recumbency.…”