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Monday, February 29, 2016

Dr. Creed: Rules for PEEP

Warning: What follows is top secret information surreptitiously leaked to me via one of the nations elite pulmonologists from an elite teaching hospital. Read at your own risk. This is not edited.

Appendix 7
Rules for PEEP/ CPAP/ EPAPt:

So, when do you increase PEEP. To answer this we have to understand what PEEP is. 

PEEP is an abbreviation for Positive End Expiratory Pressure. When used on a ventilator it is called PEEP. When referring to noninvasive ventilation it is called EPAP, which is an abbreviation for End Positive Airway Pressure.  When used alone, it is referred to as CPAP (Continuous Positive Airway Pressure). 

Essentially, PEEP, EPAP, and CPAP are the same thing, only the terms vary depending on what type of machine is applying the pressure (ventilator, BiPAP, or CPAP machine). The unique terms help caregivers tell know what device is being referred to: Ventilator, CPAP, or BiPAP. 

Whether called PEEP, EPAP or CPAP, it is a constant flow during expiration to keep the pressure inside the airways above atmospheric pressure. It increases FRC, or Forced Residual Capacity. This is the amount of air left in the lungs at end expiration. By keeping some air inside the airways, it prevents them from collapsing. Essentially, it:
  • Prevents muscles of the upper airway from collapsing. Some individuals develop flaccid muscles around the upper airway that may collapse during end expiration, resulting in upper airway obstruction. This causes obstructive sleep apnea. It may result in apnea and hypoxemia. CPAP alone may keep upper airways from collapsing to keep these airways open. Studies have confirmed this, so RTs will usually agree with this theory
  • Alveoli may collapse at end expiration, resulting in V/Q mismatching and hypoxemia. CPAP, EPAP, and PEEP prevent these alveoli from collapsing, thus improving oxygenation. Studies have confirmed this, so RTs will usually support this theory too. 
  • By keeping atmospheric pressure in the lungs above room air atmospheric pressure, this helps to push fluid out of the lungs. It also prevents the buldup of fluid in the lungs. So, if you have a patient who you suspect might eventually get fluid in the lungs, PEEP will prevent it. So, even if the ABGs are normal, PEEP, CPAP and BIPAP might be indicated. No study has ever confirmed this, so RTs will usually argue with you, and contest that all PEEP does is reduce cardiac output (blood pressure) which reduces blood flow to the lungs. We doctors go by what sounds good, not by what's proven. It sounds good, so it must be true. 
Conventional uses for positive expiratory pressure.
  1. To keep airways open
  2. To improve oxygenation
Unconventional uses of positive expiratory pressure include. 

1.  You have a patient in renal failure. His ABGs come back pH 7.37, CO2 48, PO2 90.  The patient has a history of pulmonary edema due to renal failure. In order to prevent pulmonary edema, order BiPAP.

2.  You have a patient on a ventilator with the following settings. PEEP 5, Vt 500, rr 12, hr 89, SpO2 94, PO2 87, pH 7.39, CO2 39.  The patient has had trouble with pulonary edema. So, what do you do? You increase PEEP to 10. RTs will cringe, but you know it works because it feels good. 

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