The concept of permissive hypotension was first described nearly a century ago by Cannon: Medical Assignment, TCD, Ireland

Permissive Hypotension; Hemorrhage; Resuscitation; Blood Pressure.

The concept of permissive hypotension was first described nearly a century ago by Cannon et al. Who describe a resuscitation strategy that allows restriction of crystalloid fluid administration while accepting blood pressures below the normal threshold until definitive hemostasis is achieved.

Mechanistically, aggressive fluid resuscitation may increase hydrostatic
pressure, Dislodge hemostatic clots and result in dilutional coagulopathy as well as hypothermia. These physiologic interactions would therefore contribute to the propagation of the lethal triad of hypothermia, acidosis, and coagulopathy, thereby leading to increased hemorrhage and mortality. Animal studies suggest that aggressive fluid administration may be harmful in subjects with uncontrolled hemorrhage.

In porcine models with penetrating aortic injuries, Sondeen, and colleagues Demonstrated that rebleeding occurs when blood pressure increases over a mean arterial pressure (MAP) of 64 ± 2 mm Hg and systolic blood pressure (SBP) of 94 ± 3 mm Hg. Animal studies comparing permissive hypotension strategies to conventional resuscitation targets in rat models with active hemorrhage demonstrated reduced blood loss volumes while maintaining similar cardiac output and end-organ perfusion.

In human subjects, large-volume crystalloid resuscitation has been associated with significant morbidity including acute lung injury, abdominal compartment syndrome, prolonged duration of mechanical ventilation, intensive care length of stay, and overall length of stay

Study Eligibility Criteria Population

We included studies evaluating adult patients with penetrating or blunt traumatic injury and suspicion of hemorrhage. Civilian or military patient populations were both eligible. We excluded studies of patients with isolated head injuries.

Intervention

The intervention of interest was any resuscitation strategy wherein a comparatively lower blood pressure, determined by either MAP or SBP, is tolerated in relation to the control resuscitation strategy. There were no limitations regarding specific blood pressure targets, types, or volumes of fluid administration.

Control

The control was any resuscitations strategy wherein a comparatively higher blood pressure, determined by MAP or SBP, is tolerated in relation to the intervention resuscitation strategy. There were no limitations regarding specific blood pressure targets, types, or volumes of fluid administration.

Outcome

The primary outcome of interest was in-hospital or 30-day mortality. Secondary outcomes of interest included blood loss volumes, blood product utilization, and complications of fluid restriction or administration

Study Design

We included randomized controlled trials and quasirandomized trials. Given the expected paucity of literature, pilot studies were deemed appropriate for inclusion.

Search Strategy and Data Sources

We searched the MEDLINE and EMBASE databases from January 1946 to June 2017 using a predefined search strategy developed under the guidance of a health information specialist with expertise in systematic reviews and clinical experts in the field of trauma (J.L. and M.M.).

The search strategy was comprised of MESH terms and keywords such as “permissive hypotension,” “controlled resuscitation,” “hypotensive resuscitation,” and “delayed resuscitation”. We used Cochrane filters for
randomized controlled trials and human studies.