PEEP - More than a Marshmallow Confection
Source: The Chicken Hub
Positive End-Expiratory Pressure (PEEP) is intrinsically present in all of us. Variations in this physiological pressure value may exist based on lung pathologies, and other disease states, but in most healthy individuals 3-5 cm H2O is normal. PEEP, as advertised is simply the pressure that resides in the lungs at the end of the expiratory phase.
Try this ventilation exercise from the comfort of your home or fire/EMS station.
Inhale normally over the course of 1 second; exhale normally over the course of 2 seconds...STOP!! The small pressure that remains in your lungs prior to that next breath is physiologic or baseline PEEP.
The main reason this residual pressure exist is to prevent atelectasis or collapse and improve oxygen delivery. Many lung pathologies can disrupt this normal gas exchange (O2 <-> CO2) traffic pattern. Stiff and/or wet lungs is something we want to avoid. Chronic problems like emphysema, bronchitis, and pulmonary edema can cause our lung configurations to change drastically. Alterations in shape, reduced alveolar surface area, and washing out of surfactant are just a few things to consider. With some disease processes this internal/residual PEEP may not be enough. These patients frequently summon 911 and we may have to offer additional forms of extrinsic or intrinsic PEEP. This can be done invasively (mechanical ventilation) or non-invasively (CPAP/BiPAP, BVM + PEEP valve). These additional tools can help the patient oxygenate and ventilate [these terms are related, but actually different processes] so that crucial oxygen delivery to tissues and end organs can be enhanced. Physics tells us that increasing these pressures with something like PEEP can assist oxygen's ability to cross the alveolocapillary membrane and therefore, increase its content in the blood.
Like most interventions though, our efforts may come at a cost or have consequences that we should be cognizant of -- these include the following hemodynamic, pulmonary, and even brain related changes:
Increased intrathoracic pressures which can affect preload [hypotension]
The above bullet affects euvolemic and hypovolemic patients more....
May occasionally reduce cerebral perfusion pressure [Debatable] (CPP=MAP-ICP)
Increased systemic vascular resistance [be cautious in distributive shock states]
Can cause lung injury if used incorrectly
Watch for hyperinflation or overdistention (w/ or w/o airflow obstruction) - reduce tidal volume and/or respiratory rate -- it's all about balance!
With the risks behind us, I'd like to end with some more of the positives behind PEEP and its many applications.
Great airway &