Karim Brohi describes the concept of permissive hypotension, also termed hypotensive resuscitation, as a necessary evil rather than a treatment or goal in the resuscitation of the patient in hemorrhagic shock. [3][21] Permissive hypotension is an adjunct to a newer approach to trauma resuscitation called damage control resuscitation. It is a temporizing measure that allows a patient to be left in a hypotensive state in an attempt to minimize the amount of blood lost and risk of increasing the MAP to the point that the clots are "blown" off of the injured vessels. Blood pressures as low as 80-90 systolic are allowed without the need for fluid resuscitation. A mean arterial pressure (MAP) of at least 65 is the desired end point for permissive hypotension. The calculation for MAP: ((2 x diastolic) + systolic) / 3 [6]
Using fluid boluses or massive transfusions of blood products to raise the blood pressure in patients who are actively bleeding causes several issues for the patient. One problem is that increasing the mean arterial pressure (MAP) contributes to a great risk of dislodging or "blowing" a clot off of the vessel from which it is trying to stop the bleeding. [24] There is also a great risk of inducing a dilution coagulopathy and hyperchloremic acidosis with infusion of large amounts of crystalloids, further complicating the clinical picture. Small fluid boluses of 200–250 mLs are appropriate to maintain a MAP of at least 65. This is what is needed in order to perfuse the brain and other vital organs.
Brohi also describes a phenomenon in trauma resuscitation in which the patient is subject to what is called cyclic hyper-resuscitation. When the target for resuscitation is normalization of the patient's blood pressure, the patient receives a cycle of large fluid boluses to raise the blood pressure until it reaches a normal end-point. But once the patient's blood pressure drops again, the patient receives another large bolus. The blood pressure normalizes again until the hemorrhage causes another drop in the blood pressure. This cyclic hyper-resuscitation contributes to the dilatational and consumptive coagulopathy that the patient is likely to suffer from and makes it difficult for the body to form clots. [21]
Resuscitation of the patient in hemorrhagic shock requires a concerted and systemized cycle of assessment, intervention, and reassessment for the patient to have the best chance at a favorable outcome. Prehospital EMS providers must be aware that trauma and more importantly hemorrhagic shock are time-sensitive processes that require a surgeon for definitive treatment. Emphasis should be on hemorrhage control, preservation of body heat, and rapid transport to the nearest appropriate trauma center.
