Consider pulse pressure variation (PPV) as a method to monitor volume responsiveness in your mechanically ventilated ED patients.
The theory behind PPV:
When a positive pressure breath is delivered via the ventilator, pleural pressure rises and causes a decrease in venous return, right heart filling, and right heart output.
Simultaneously, the positive pressure breath causes an increase in left heart filling and a decrease in left heart afterload. This is reflected clinically as an increase in blood pressure.
Within a few beats, the decreased right heart output is transmitted to the left heart resulting in a decrease in blood pressure during expiration.
Patients who are volume depleted can have significant differences in blood pressure between inspiration and expiration - i.e. a large variation in pulse pressure.
PPV values > 12% have been shown to identify patients who are volume responsive.
Importantly, PPV works best in vented patients who have no spontaneous respiratory effort, are in sinus rhythm, and receiving 8 ml/kg tidal volumes.
References
Magder S. Hemodynamic monitoring in the mechanically ventilated patient. CurrOpinCrit Care 2011;17:36-42.
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