In operating rooms across the world, there are patients who are hypoventilating and relying on a dedicated veterinary team member to breathe for them. What if instead of having to breathe for the patient, record vitals, empty the suction canister, open suture, get the owner on the phone, give a fluid bolus, and train a new technician all at once there was a way to simplify things?
But wait there is……….
You could use a mechanical ventilator to breathe for your patient. Using a mechanical ventilator to administer intermittent positive pressure ventilation for your patient can provide several positive outcomes.
The first and most obvious is that you can free up a staff member from having to give the patient breaths. This allows this team member to more closely watch the physiologic parameters and be overall more attentive to the patient’s care.
Secondly, the breath size (tidal volume) and rate given via mechanical ventilation are consistent. Consistent ventilation leads to consistent uptake of inhalational anesthetic agents and a more even plane of anesthesia - this means there is a decreased likelihood of your patient waking up. Everyone benefits when we don’t have those roller coaster anesthetic events! More reliable uptake of inhalant anesthesia can mean that you may need to adjust your initial vaporier settings downwards to as not to get your patient deeper under general anesthesia than you meant.
There are some negative effects associated with positive pressure ventilation. The administration of higher airway pressures can cause a decrease in venous return and therefore cardiac output. This is much more pronounced in the patient who is hypovolemic.
In addition, using a ventilator adds complexity to the anesthetic event. It is one more piece of equipment that can malfunction. Before using a ventilator, it is important to familiarize yourself with the normal function, adjustable parameters, and troubleshooting steps of your particular machine.
The goal when using an anesthesia ventilator is to maintain physiologic homeostasis. The pulse oximetery reading should be 99-100% and ETCO2 should be 35-45 mmHg. I always set the ventilator before induction at the low end of the patient’s tidal volume (calculated at 10-15ml/kg for canine patients and 8-10ml/kg for feline) and start with a respiratory rate of 10 for dogs and 12 for cats. After I get the initial ETCO2 reading, I make my adjustments to get my ETCO2 within normal limits while keeping my airway pressure between about 12 - 17 cmH20. Finally, whenever possible, physically look at your patient during positive pressure ventilation and assess chest wall excursion.
Positive pressure ventilation should also be used carefully or avoided on patients suspected of having pneumothorax, pulmonary bullae, or large tumors.
In short, the use of a ventilator is an excellent tool to help consistently ventilate for your patients and help keep them on a more even plane of anesthesia. Any anesthesia machine with a bag port can have a ventilator attached to it and most veterinary specific ventilators are relatively easy to use!
If you are interested in learning about how to use a ventilator or in purchasing one consider attending a CE course on the topic or reaching out to an AVTAA or ACVAA member on the topic. They can help your practice get started in the right direction!