Starting off in student anaesthetics - A Brief Guide to the Ventilator

When you begin your anaesthetics placement - it's likely you won't have a notion what is going on.

Don't worry - everyone felt like this the first time they walked toward a ventilator. 

Take your time and orientate yourself to the anaesthetics machine - it's essentially a big machine/bellow that moves vapour-laden gas into the patient's lungs in a closed-circuit. There's a tube from the machine going IN to the patient and one for the gasses when they are exhaled from the patient. The vaporisers (sevoflurane is yellow coded) are situated on the machine and they change the liquid you put into them into a vapour which are then added to the inhaled gases. The machine interprets all the volumes (ml),  flows (L/min) and pressures (cmH2O) and fires out lots of numbers that tell you various things. The machine will tell you about the volume of breathes the patient is either taking (or being put into the patient by the machine), it will also calculate CO2 output of the patient and track it as a waveform called capnography. The machine furthermore calculates the pressure of the closed system and calls them airway pressures - you essentially don't want these do be above 30cmH2O - or damage can occur to the lungs. PEEP is the peak end expiratory pressure generated by the machine - it stops the alveoli collapsing and is often set around 4-5cmH2O - but this goes up and down as appropriate.  Just ask your supervisor if you can sit and play around with the machine settings.

You should also know what MAC is - MAC is a measure of potency and is defined as the minimum alveolar concentration at steady-state that prevents reaction to a standard surgical stimulus (skin incision) in 50% of patients at 1 atmosphere (i.e. sea level). This measurement is done at steady state (assuming a constant alveolar concentration for 15 minutes), under the assumption that this allows for an equilibration between the gasses in the alveoli, the blood and the brain. End-tidal agent monitoring is used by modern anaesthetic monitors to calculate MAC.

If you're feeling like you could watch a short course in introducing the anaesthetic machine - HERE is a good idea to start - watching all the videos.

Otherwise, below is a good video showing an anaesthetic machine check.