Indications and Use of Peri-Operative Mechanical Ventilation for Animals Undergoing Respiratory Surgery

Introduction:
Typically, the use of mechanical ventilation is reserved for patients with severe hypoxemia or severe hypoventilation that have failed to respond to supportive therapy. The most common reasons for instituting mechanical ventilation include severe aspiration pneumonia, severe trauma, upper airway obstruction and cervical intervertebral disc disease. What is becoming more common is the use of mechanical ventilation during the perioperative period in patients requiring either upper airway or thoracic wall surgery.

Recognising the need to ventilate:
Hypoxemia is defined as an arterial partial pressure of oxygen (PaO2) < 80 mm Hg, corresponding to a hemoglobin saturation (SpO2) < 95% usually merits some form of oxygen supplementation. Severe hypoxemia as defined by a PaO2 < 60 mm Hg (corresponding to a SpO2 < 90%) is the level that usually require mechanical ventilation.

The other major consideration for mechanical ventilation is hypoventilation which is defined as an increase in the arterial partial pressure of carbon dioxide (PaCO2). Hypoventilation ensues due to a decrease in alveolar ventilation. Severe hypoventilation is defined as a PaCO2 > 60 mm Hg and can be an indication for mechanical ventilation should the patient fail to improve with standard therapy for the underlying disease. Possible causes of hypoventilation (or ventilatory failure) requiring mechanical ventilation include brain disease, high cervical spinal cord disease, peripheral neuropathies, neuromuscular junction diseases, or primary myopathies.  [...]