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Wednesday, August 21, 2013

What Tracheal Cuff Pressure Measurement is Ideal?

The latest evidence suggests the cuff pressure
should be set at greater than 30 cm H20
in order to prevent aspiration.
So what is the ideal cuff pressure for endotracheal cuffs?  You may hear opposing answers on this, as some people may recommend high pressures, while others may recommend lower pressures.  The reasons behind either response are logical.  I will go over them both here briefly.

It's kind of a catch 22 actually, whereby too much pressure can result in complications, and too little can result in complications.

First, however, a little history.  The following quote comes from my post "Respiratory Therapy History: 1700-1950:  Evolution of Intubation and Mechanical Ventilation
1893: Cuffed Endotracheal Tube:  It must have also been discovered early on that air was leaking around the tubes, instead of inflating the lungs.  Likewise, some patients must have vomited when the tube was inserted past the gag reflex, and this would have caused aspiration pneumonia, which would spell doom for most patients back then.  Physicians must have sought some means of securing the airway around the tube. According to the 55th anniversary publication of the German Society of Anaesthesiology and Intensive care,
Victor Eisenmenger became the first to use an endotracheal tube that had a cuff on the distal end of the tube that was connected by a pilot line to a pilot balloon.  Air was inserted with a syringe into the pilot line, and both cuffs would become inflated.  The physician would know the distal cuff was inflated when the pilot cuff was inflated. Such a system was soon adapted by other physicians.  
A monometer should be used to check
cuff pressureafter performing MOV or MLV.
This "ideal" pressure should then be recorded.
However, as time went by, there must have developed concerns about necrosis caused by high cuff pressures blocking blood flow.  Subsequent studied made physicians aware of the following facts:
  • Cuff pressures greater than 5 mm Hg contribute to lymphatic flow obstruction (edema)
  • Cuff pressure greater than 18 mm Hg can cause venous flow obstruction (congestion)
  •  Cuff pressure greater than 30 mm Hg can completely stop arterial-capillary blood flow (ischemia
Also, according to Stewart and company: 
  • Cuff pressure greater than 27 cm H20 is associated with a 75% reduction in blood flow to the trachea at the cuff
  • Cuff pressure greater than 48 cm H20 can completely stop capillary blood flow (2)
  • Cuff pressure greater than 50  cm H20 can cause total obstruction of tracheal blood flow (2)
According to Stewart and company, over-inflated cuff pressures increased the risk for the following: (2)
  • Ischemia
  • Inflammation
  • Ischemia
  • Granulation
  • Ulceration
  • Necrosis (death)
So this began the recommendation for low cuff pressures.  When I attended RT School from 1995-6 the recommendation was to never exceed 24 mm Hg in the cuff.  Some current respiratory and nursing texts continue to chime for this, as noted by the nursing book "Best Practices: Evidence-Based Nursing Procedures:"
The ideal pressure (known as minimal occlusion volume) is the lowest amount needed to seal the airway.  Many authorities recommend maintaining a cuff pressure lower than venous perfusion pressure -- usually about 16-24 cm H20.  (More than 24 cm H20 may exceed venous perfusion pressure.)  Actual cuff pressure will vary with each patient, however.  To keep pressure within safe limits, measure minimal occlusive volume at least once per shift or as directed by your facilities policy.  Cuff pressure can be measured by a respiratory therapist or by the nurse.  (1, page 350)
Personally, I have never seen a nurse do it, although that's just how it is where I work.  I know for a fact by speaking with respiratory therapists, nurses, speech therapists and physicians, that who performs this procedure varies from one institution to the next.

So this was the recommendation that caught fire and is still commonly taught, as you can see from the above quote from a nursing text.

However, concerns about the rise of ventilator associated pneumonia (VAP) lead to a rethinking of the old recommendation.  Studies performed showed that upper airway secretions could still leak past a cuff, and this was linked as a likely or possible cause of VAP.  So studies were performed to determine the ideal pressure for preventing VAP.

Now, there is a catch 22 to the risk of complications due to high cuff pressures, and this is the increased risk of complications due to too low of cuff pressures.  A study (I wrote about here) by A. Chendrasekhar and G.A. Timberlake concluded the following:
The average ETT cuff pressure required to maintain secretions above the cuff was 29.5 ± 3.2 cm H2
Steward and company notes the following:
Patients can also be at risk if the cuff pressure is too low.  The minimal occlusion cuff pressure required for positive pressure ventilation, to prevent aspiration, is approximately 27 cm H20.  Aspiration is shown to occur with intracuff pressures of approximately 20 cm H20. Thus, there is a narrow range of cuff pressures required to maintain a functionally safe seal while not exceeding capillary blood pressure. (2)
 The 2003 study by S.L. Stewart and company concluded the following pressures were ideal to prevent VAP: (2)
  • 25-40 cm H20
  • 18-30 mm Hg  (2)
The following were determined by S.L. Stewart and company as less than ideal: (2)
  • Greater than 40 cm H20
  • Greater than 30 mm Hg (2)
  • Less than 25 cm H20
  • Less than 18 mm Hg
So by going by the old recommendations that no patient should have an ETT cuff pressure higher than 24, we were automatically exposing some of these patients to a higher risk for getting VAP.  The newer recommendations (if we go by the numbers of Stewart and company) allow clinicians to shoot for an ideal, as opposed to a number.

What is idea for each patient will be different.  You don't want to use 40 cm H20 when 20 cm H20 is ideal.  On the other hand, you don't want to use 20 cm H2O when 40 cm H20 is ideal.  To obtain the ideal number use minimal occluding volume (MOV) or minimal leak technique (MLV), and check the pressure with a manometer.  That's it.  If you get 40, you get 40.  Chart the pressure, and go about your business.  

The idea here is that every patient is different.  Some may have lots of loose tissue and require higher pressures, while another patient may require less pressure.  Or, as noted by Stewart and company: 
The goal in using cuffed endotracheal tubes is to achieve a seal between the cuff and the trachea with a pressure great enough to prevent aspiration but not so high that tracheal blood flow will be impeded.  
This new evidence meant rethinking what had already been inculcated in the minds of nurses and respiratory therapists for years: that tracheal cuff pressure should never exceed 24.  Teachers chimed that cuff pressure should be determined by MLT or MOV, and if the cuff pressure was to high, the air was let out until the pressure was less than 24.

I always hated this method, because many times I'd get a pressure of 40 and panic.  I'd be afraid to chart this number because the guidelines recommended no greater than 24.  So you'd deflate the cuff and then risk aspiration.  It just didn't seem right.  My coworkers noted the same.  

The problem with this method is you were putting pressure into the cuff based on a made up number, 24, whereas some patients require a pressure greater than this (sometimes even 40), especially if the ETT is too small for the airway, or if the tissue in the patient's airway is excessively soft (which may happen in larger patients, or patients who present with sleep apnea).  

In the early 2000s our institution investigated a new ventilator bundle set and protocol that would be in compliance with the most recent studies, or in compliance with best practice evidence.  Among the new data was the new recommendation that cuff pressures be higher as compared to lower.

There was, however, according to Stewart and company, no set standard in how air is inserted into the cuff. The study showed that MLT and MOV techniques are only estimates, and are unreliable.  The experts therefore concluded that the best method is to inflate the cuff (perhaps by using MLT or MOV) and then measuring the cuff pressure to make sure it's not too high or too low, or that it's between 25-40 cm H20.  

Best Practice Guidelines (as incorporated by the Keystone Committee) recommend performing MOV or MLT, and then checking the cuff pressure with a manometer. Once this is done, you record the pressure in the patient's chart.  The idea here is that lawyers want to see that you documented there was enough air in the cuff.  This evidence may prevent your hospital from being sued for not doing your part in preventing the preventable. 

So this began the recommendation for higher pressures. Or, rather, for ideal pressures as opposed to low pressures.  Since every patient is unique, every patient will have a unique ideal pressure.  

I spoke with a speech therapist who works exclusively with tracheotomy patients at one of Americas larger metropolitan hospitals, and he said that if concerns persist about blocking blood flow around the cuff: 
To avoid side effects due to high cuff pressures, adjust the location of the cuff by moving the tube up or down 1-2 cm every day, or once per shift.  Some physicians where I work actually write this as an order. 
So, to answer our question:  what is the ideal cuff pressure for endotracheal cuffs?  If we go by the best studies, it should be between 25-40 cm H20 or 18-30 mm HG.  However, you may also consider keeping it higher than 30, as opposed to less than 24.  

Our hospital policy, in accordance to best practice evidence as put together by the Keystone Committee, is to keep the pressure greater than 20.  However, as the latest evidence is reviewed during upcoming meetings, I surmise the recommendation will be updated. 

  1. Munden, Julie, editor, Best practices: Evidence-based Nursing Procedures," 2007, 2nd edition, WY,  Lippincott Williams and Wilkins, page 350
  2. Stewart, S.L., Secrest, J.A., et al, "A comparison of endotracheal tube cuff pressure using estimation techniques and direct intracuff measurement," American Association of Nurse Anesthetists Journal, 2003, 71 (6), pages 443-447
  3. Chendrasekhar, A., G.A. Timberlake, "Endotracheal cuff pressure threshold for prevention for nosocomial pneumonia," Journal of Applied Research,,, accessed 8/21/2013

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