What’s the problem?
The average internal diameter of an adult trachea is 1,5 – 2 cm and this doesn’t leave much room for expansion. Over-inflated cuffs could be killing off tracheal mucosa by restricting blood flow, causing problems such as tracheal stenosis: a long term condition which will need a multi-disciplinary team and some expensive surgery to fix, if it is fixable. This is money we shouldn’t be wasting, and avoidable morbidity we could be sparing our patients.
There are 3 commonly used clinical methods for inflating cuffs:
1. Palpation: Inflate cuff with air. Feel cuff between fingers. Decide the cuff feels right.
2. Pre-determined volume: Inflate cuff with pre-determined amount of air (10ml,15ml,20ml?).
3. Minimal leak: Inflate cuff. Listen for air leak during ventilation. Decide the leak is ‘minimal’.
It was demonstrated in multiple studies that even anaesthetists in theatre (whether experienced or not) were not able to achieve acceptable pressure range using clinical methods alone. Working in the out-of-hospital sphere or the emergency centre, we do not have the luxury of a quiet working environment so these methods are likely even less reliable in our environment. On top of this, a cuff inflated to pressures within the ‘safe zone’ feels a lot softer than I expected, and used less air than I had been taught to use.
Gold Standard = Cuff Pressure Manometer
What are we aiming for?
Visual demonstration of air-filled cuff pressure in flight:
A 50ml syringe to simulate the internal diameter of an adult trachea (it has a 3cm internal diameter, which is larger than an adult trachea). The manual cuff pressure manometer was attached to air filled ETT cuff via the extension set.
1. Before take off:
Cuff inflated to within safe limits.
2. Half way through our climb to altitude (Cabin altitude 3770 ft)
Cuff pressure is already well outside of safe limits.
3. Cruising altitude (cabin altitude 6470 ft)
Cuff pressure is almost 3 times the safe upper limit.
4. Reset the cuff pressure to within safe limits at cruising altitude
(cabin altitude 6470 ft)
5. Half way on the descent (cabin altitude 3230 ft)
Cuff is well below the low pressure limit – potential for aspiration increased
Saline for aeromedical transfers?
So, you’ve been told replacing the air with saline is second best. There are a few reasons why this isn’t true.
1. This is not what an ETT cuff is designed for or the approved usage as tested by the manufacturer
2. It is impossible to remove all of the air and replace it with saline, so there will be expansion (and increased pressure on the mucosa) with even a small increase in altitude. I have tried this personally over and over in a simulated airway, and there is always a residual bubble.
3. Once the cuff is full of saline, you can no longer measure the pressure: if you cannot guarantee the pressure the cuff is exerting on your mucosa, as you cannot measure the pressure then why do it?
4. The exchange itself: despite your best effort with your faithful suction, there will be some aspiration of secretions that have likely sat around the tube for as long as your patient has been intubated. Are you willing to expose your patients to this unnecessary aspiration? There is also a possible risk for adverse events such as accidental extubation or right main bronchus intubation if the procedure is not well controlled.
5. That tube will be most likely be exchanged as the ICU won’t keep water in the cuff: this exposes the patient to risk of an adverse event such as aspiration.
So please, in ALL of your intubated patients – remember the cuff.
Want to read more?
Some South African literature on the subject: