If the bag is deflated: there is not enough reserve in the breathing system for the patient to take a complete inspiration. Negative pressure will develop in the breathing system and the patient’s airway. This could cause pulmonary oedema, decreasing gas exchange efficiency. If the bag is deflated, fresh gas flow should be increased. If the bag is over-inflated: this could mean that either the scavenging system does not work or the fresh gas flow is too high. The first hypothesis can be deadly for the patient if the pressure in the system increases. The first thing to do is, therefore, to check the pressure in the breathing system and verify what is wrong with the scavenging system (pop-off valve closed, active aspiration turned off, etc.) If the pressure is normal, it might just mean that the fresh gas flow is too high and it could be reduced. As long as the pressure in the breathing system is close to atmospheric pressure, there is no risk of having an over-inflated breathing bag. It can only be detrimental for the monitoring of the respiratory rate if the breathing bag is used to count the rate. On a Bain circuit, decreasing the fresh gas flow can cause rebreathing of CO2. It is therefore recommended to monitor inspired CO2 if fresh gas flow is decreased below 150-300 ml/kg/min on a Bain circuit.

The size of the breathing bag should be enough for the patients to take a deep inspiration without emptying the bag. Usually, 5 to 10 times the tidal volume (which is 10-15 ml/kg in dogs and cats) is considered enough. Practically, a bag of 1 L per 10 kg BW (rounded up) can be used. For instance, for a 20 kg dog, a 2-liter bag should be enough.

The choice should be made based on the pros and cons of each circuit (see next question) but it can also be easily made based on the weight of the patient. Below 5 kg, a Bain circuit is often recommended because the patient might not be strong enough to breathe against the resistance of the rebreathing circuit. Above 10 kg, the rebreathing circuit should be used, as patients are generally strong enough to overcome the resistance of the valves and soda lime. Additionally, above 10-15 kg, the use of a Bain circuit is not economical. Between 5 and 10 kg is a gray zone. The patient might not be strong enough to overcome resistance. However, using a rebreathing system decreases oxygen, inhalant waste and temperature loss.

To decrease exposure to waste anaesthetic gases, it is recommended to: Leak test all equipment Avoid mask induction and induction boxes Intubate and inflate cuff for all patients Connect breathing system and leak test ET-tube before turning on the vaporizer Use low-flow anesthesia Cap breathing system when not in use Ventilate the recovery area (15-20 air changes per hour and no recirculation of air in the hospital) Fill vaporizer at the end of day Carry out regular maintenance It is also recommended to monitor waste anesthetic gases every six months on the premises.

Generally speaking, dead space can be defined either as a volume of gas that is rebreathed without a change of composition, or the volume of respiratory tract that does not participate in gas exchange. Different kinds of dead space have been defined: Anatomical dead space: it is the volume that is breathed and does not reach the alveoli (i.e., tracheobronchial tree and upper respiratory airway). Physiological dead space: it is the volume that is breathed that does not participate in CO2 elimination. Mechanical dead space: it is the volume in the equipment (endotracheal tube, capnograph, breathing circuit) that is re-breathed without a change of composition. Anatomical and physiological dead spaces are nearly similar in normal healthy patients. They will differ in some pathological conditions, such as shunts (ventilation of alveoli without perfusion)

Ideally, soda lime should be changed before its exhaustion. Different methods exist to know when soda lime is exhausted and are detailed in the documents available online (link). If the anesthesia workload is fairly constant, it is possible to change soda lime on a regular basis (for example, every Monday). If not, it should be replaced if rebreathing occurs, if color changes or after a given time. Monitoring that soda lime is efficient should be done even if the soda lime is changed regularly, or if the color is normal, or even if it has just been changed. The only reliable monitoring to make sure the soda lime is effective is the capnometer. The other methods are not, and could appear normal in the face of exhausted soda lime. If the patient rebreathes CO2, soda lime should be changed even if it is white or if it has just been changed.

Yes, complete monitoring that is adapted to the patient should be used. What “complete” is differs from one patient to another. Additionally, monitoring is not only about having the monitoring installed. It also means actively monitoring the patient and making sure every measured parameter stays in a normal range. A retrospective study showed that the use of the pulse oximeter and the monitoring of pulse during anesthesia decrease the risk of mortality in cats (80,000 anaesthetic and sedation procedures) (Brodbelt, Pfeiffer and al. 2007). Other monitoring methods were not included in this study as they were rarely used at this time. In human medicine, the use of the pulse oximeter and a capnometer can prevent 93% of complications during anesthesia (Tinker, Dull and al. 1989). Clinically, noninvasive monitoring, especially if they can be installed rapidly, should be used for every patient. These include pulse oximeter, capnometer, ECG, and noninvasive blood pressure monitoring. The other devices (invasive or longer to set up, such as invasive blood pressure monitoring) should be used when needed.

Below 36°C, hypothermia can have harmful consequences for the patient, such as: Decreasing anesthesia needs, potentially causing an overdose Arrhythmia, bradycardia, decreased response to anticholinergic drugs Shivering increases oxygen consumption in the face of cardiovascular instability and inability to provide enough oxygen Reduced coagulation Decreased immune response Clinically, the most common complication is a prolonged recovery caused by a relative overdose. In addition to being harmful to the patient, this also interferes with the efficacy of the anesthesia and surgery team by adding workload that could have been prevented. Therefore, a core temperature above 36°C is recommended. However, be careful not to induce hyperthermia when keeping a patient warm. Continuous monitoring of core temperature is therefore advised.

A video and a text illustrating every step can be found on the website. To summarize, the following elements should be checked: Integrity of the system (visual inspection) Oxygen source Flowmeter Vaporizer Leak in the anesthesia machine Connection to the appropriate breathing circuit Valves and soda lime, if applicable Size of the respiratory bag High-pressure leak test Internal tubing (coaxial) tubing test, if applicable Pop-off valve Scavenging system.

Anesthesia ventilator typically delivers intermittent positive pressure ventilation (IPPV). It can be beneficial to any patient with respiratory issues, such as hypoxemia and hypoventilation. Under anesthesia, the main concern is hypoventilation. It is easily diagnosed by a capnometer. This is fairly common during anesthesia but often undiagnosed in the absence of a capnograph. An end-tidal CO2 above 50 mmHg can be used as a threshold to ventilate a healthy patient. However, this should be adapted to the patient as some diseases may limit the use of ventilators (e.g., some cardiovascular diseases). Additionally, when using a ventilator, the anesthesia team can dedicate their time to monitoring the patient instead of concentrating on bagging it, improving efficacy and safety.

Every machine should be checked before anesthesia. Minimally, this should include a leak test, a visual integrity check, a verification that nothing is missing, that the appropriate breathing circuit, with the proper breathing bag, is attached to the machine and finally, that there are no cracks or holes in any tubing (including internal tubes if coaxial). This should take less than a minute.

As long as 1/2 to 2/3 of the canister contains active granules, you need not make changes. When you do replace the contents of the canister, you need only discard those granules that have become discolored. If you are unsure of the state of the granules, simply crumble a few in your fingers. Active granules will feel soft and crumble easily. Depleted granules will feel firm and brittle. Use gloves when you handle the granules to avoid skin irritation. Be careful not to return the crushed granules to the canister, as they are a source of dust. Both moisture and heat are natural by-products of the reaction between sodalime (or baralime) and carbon dioxide. Because moisture condenses and accumulates within the canister and is a source of contamination, it is important to clean and dry this part of your anesthetic machine, as well as the unidirectional dome valves, weekly.

Vaporizers should be serviced yearly to avoid corrosion of the internal components and to ensure reliable performance. Proper servicing should be performed in a service laboratory. A sure sign of the need for servicing is a sticky control dial. Although isoflurane vaporizers do not accumulate thymol preservative as do the halothane vaporizers, it is still wise to have the wicks and 0-ring seals changed and the calibration checked yearly.