In special critical situations, there are not enough ventilators in the hospital, but there are some empty anaesthetic machines, can an anaesthetic machine be used instead of a ventilator? What is the difference between the two?

Before confirming whether an anaesthetic machine can be used as a ventilator, let’s understand some of the uses of anaesthetic machines and ventilators, and the differences between the two.

1. Mode of breathing.

This should be the first difference that comes to mind. Generally speaking, breathing is divided into spontaneous, assisted and controlled breathing. Due to the use of muscle relaxants, the anaesthetic machine is almost always a controlled breathing mode (VCV, PCV, PCV-VG, etc.). , whereas the main modes of ventilator are assisted and spontaneous breathing (SIMV, CPAP, etc.). Fortunately, most mid- to high-end anaesthesia machines are equipped with SIMV mode. The respiratory mode of the anaesthesia machine has been used in clinical anaesthesia for many years. Of course, it is difficult for the anaesthesia machine to fully implement all the functions of a ventilator due to the differences in the internal airways of the two machines.

2. Humidifiers.

The humidifier is the obvious sign of a ventilator and the tubing supplies are different. Due to the short duration of the procedure, most medical anaesthesia machines are not equipped with a humidifier and instead use an artificial nose for hydration. The humidifier is usually placed between the inspiratory valve and the patient. The exhaled gas condenses and accumulates in a stagnant cup on the exhalation tube. The carbon dioxide absorber is located upstream of the humidifier and only passes through the sodium calcium when inhaled, so the humidifier does not cause significant loss of absorber.

3. Fresh air flow regulation.

The ventilator is open circuit and all exhaled gas is expelled from the body. A medical anaesthesia machine is a semi-closed circuit where some of the gas is reabsorbed and the reading of the pressure drop in the membrane cartridge is the amount of reabsorbed gas (actually fresh gas is mixed with the exhaled breath). As the carbon dioxide in the reabsorbed gas is absorbed by the sodium and calcium, it is recommended that the flow of fresh gas be increased to reduce the amount of reabsorbed gas in actual use and thus reduce the rate of sodium and calcium consumption; therefore, more oxygen may be saved with an anaesthetic machine than with a ventilator.

Can an anaesthetic machine replace a ventilator?

Strictly speaking, the role of an anaesthesia machine and a ventilator are different, comparing the role of a ventilator for ventilatory counselling and respiratory support with the role of an anaesthesia machine for administering inhalation anaesthesia to patients.
This means that among the uses of the anaesthetic machine is the role of helping the patient to receive respiratory support itself.

Therefore, in exceptional and critical cases, if the hospital does not have enough ventilators, an anaesthetic machine may be a more reliable alternative, and most hospitals, especially doctors who know how to use ventilators, basically have a good grasp of how to use an anaesthetic machine and can get up to speed quickly.

Of course, even if an anaesthetic machine can be called a replacement for a ventilator, it must be noted that it is only a [temporary] replacement – after all, there are differences between the anaesthetic machine and the ventilator in terms of their own use, and the methods and modes of use will be different.