Clinical Importance of Mechanical Ventilation in the Anesthesia Patient

How can we provide SAFE mechanical ventilation for our anesthetized patients?

The veterinary professional should have a full working knowledge of how the anesthesia machine works and understand what the “normal” vital signs are in the patient (heart rate, blood pressure, oxygen saturation, respiratory rate and character of a normal breath, end tidal caron dioxide levels), as these are often altered by general anesthesia and mechanical ventilation. Include a pressure alarm to monitor safe pressures. There are a few guidelines to consider. Consider the below for an optimal ventilation strategy.

Since patient carbon dioxide and oxygen gas exchange is controlled by the user during manual or mechanical ventilation, observing and maintaining normal values via capnography, pulse oximetry and hands on monitoring is essential. Removal of carbon dioxide is primarily achieved through minute volume. The PIP should fall in the 15-20 cm H2O pressure range. Whether choosing a high ventilation rate with low tidal volume or a low rate with high volume, the effects will be similar. 

For time or volume cycled ventilators, calculate the tidal volume first. Observe the patient’s thoracic cavity to assure bilateral chest expansion and maintain a PIP of 15-20 cm H2O pressure. In a pressure cycled ventilator, the inspiratory pressure is set, and chest expansion is observed and adjusted as needed. Observe blood pressure as increasing thoracic cavity expansion may decrease venous return, which may or may not impact mean arterial pressures. The inspiratory time should always be less than the expiratory time as this will allow full expansion of the thoracic cavity, move gas in and out of the alveoli and lastly, allow enough time for recoiling of the lungs. Some mechanical ventilators have internal respirometry that measures each patient’s ventilation needs. This type of ventilator has a wider safety range. When weaning a patient from the mechanical ventilator, allow the patient to build of carbon dioxide to trigger normal ventilation as this is determined by the respiratory center in the brain. You can decrease the rate and volume or continue to manually support ventilation needs until the patient has returned to normal breathing volume and . Always observe carbon dioxide parameters until patient is regaining consciousness as well as blood oxygen via a pulse oximeter and pink color of mucosa.