Causes, Effects and Methods of Monitoring Gas Exchange Disturbances during Equine General Anaesthesia.

Horses, due to their unique anatomy and physiology, are particularly prone to intraoperative cardiopulmonary disorders. In dorsally recumbent horses, chest wall movement is restricted and the lungs are compressed by the abdominal organs, leading to the collapse of the alveoli. This results in hypoventilation, leading to hypercapnia and respiratory acidosis as well as impaired tissue oxygen supply (hypoxia). The most common mechanisms disturbing gas exchange are hypoventilation, atelectasis, ventilation-perfusion (V/Q) mismatch and shunt. Gas exchange disturbances are considered to be an important factor contributing to the high anaesthetic mortality rate and numerous post-anaesthetic side effects. Current monitoring methods, such as a pulse oximetry, capnography, arterial blood gas measurements and spirometry, may not be sufficient by themselves, and only in combination with each other can they provide extensive information about the condition of the patient. A new, promising, complementary method is near-infrared spectroscopy (NIRS). The purpose of this article is to review the negative effect of general anaesthesia on the gas exchange in horses and describe the post-operative complications resulting from it. Understanding the changes that occur during general anaesthesia and the factors that affect them, as well as improving gas monitoring techniques, can improve the post-aesthetic survival rate and minimize post-operative complications.

Ossifying Fibroma in the Nasal Cavity of a 2-Year-Old Horse.

A 2-year-old mare of an unknown breed was referred to the clinic due to undetermined breathing difficulties. Physical examination revealed painless swelling rostral to the nasoincisive notch and a large, firm mass protruding from the left nostril. Radiographic examination of the head revealed a mass occupying the left nasal cavity and a displaced and hypoplastic last premolar of the left maxilla. The CT scan showed a well-demarcated heterogeneous mass measuring 22 × 9 × 5 cm (length × height × width) in the left nasal cavity attached to the roots of the displaced tooth and conchae. The surgery was performed on the standing horse. Firstly, due to the oblique position of the displaced tooth, the extraction was performed extra-orally through the trephination and repulsion of the maxillary bone. In the next step, a direct surgical approach was chosen for the caudal part of the mass via the osteotomy of the left nasal bone. The mass was bluntly separated from the conchae and removed through the nostril using Fergusson forceps. The histopathological characteristics of the mass led to the diagnosis of ossifying fibroma. The horse recovered completely in seven months, without recurrence after two years.