"Injection of a fluid that will increase blood pressure has dangers in itself... If the pressure is raised before the surgeon is ready to check any bleeding that might take place, blood that is sorely needed may be lost."- Walter Cannon, 1918
Permissive Hypotensionis also known as hypotensive resuscitation or low volume resuscitation
What is it?
A resuscitation strategy in the critically ill trauma patient (primarily applicable to penetrating trauma but also adapted to blunt trauma) where we allow the systolic BP to remain as low as necessary to avoid exsanguination while still maintaining critical end organ perfusion. (typically defined as appropriate mental status & or the presence of a radial pulse)
The Thought Process:"Don't pop the clot"...
By allowing lower blood pressures we avoid the potential disruption of an unstable fresh clot and thus worsening bleeding caused by higher BP's.
In other words...
"Elevation of blood pressure to pre injury levels and prior to operative control of the bleeding site results in progressive and repeated re-bleeding, now with decreased platelets and clotting factors in each aliquot of blood loss." - Dr. Kenneth Mattox
At what pressure does the "clot pop?"
We don't know exactly... but in large animal "uncontrolled hemorrhage" models, the clot is popped at approximately 80mmHg.
The Ultimate Goal in Trauma: Stop the Bleeding
Achieving a specific low BP is not necessarily the goal but rather this resuscitation strategy serves as a temporizing measure pending definitive surgical intervention
Avoid a cycle of over-resuscitation that can lead to rebleeding and thus exacerbate hypotension
Once hemorrhage control is obtained, normalization of hemodynamics is typically indicated
In the trauma patient, hypotension IS NOT ALWAYSfrom hemorrhage (In fact approximately 1/3 of hypotensive trauma patients are hypotensive from causes other than blood loss)... our patients can not afford for us to miss the tension penumothorax, pericardial tamponade, or medical cause for their hypotension
A strategy of permissive hypotension should be reserved for patients without suspected concomitant traumatic brain injury (TBI) and is NOT appropriate for isolated TBI. The Brain Trauma Foundation guidelines clearly emphasize the importance of avoiding hypotension in TBI as data suggests that a single SBP < 90mmHg is associated with a doubling of mortality and increased morbidity in this unique patient population
The appropriate BP we should be targeting with hypotensive resuscitation varies with each individual patient (based on age, medical history etc. i.e. a patient with uncontrolled hypertension will need a higher BP to maintain critical organ perfusion)
For more information:
Going to the source - the original NEJM article:
Bickell, W, Wall, M, Pepe, P, Martin, R, Ginger, V, Allen, M, & Mattox, K. (1994) Immediate versus Delayed Fluid Resuscitation for Hypotensive Patients with Penetrating Torso Injuries. New England Journal of Medicine. 331 (17). 1105-1109.