Permissive Hypotension
Permissive hypotension strategies withhold or minimize fluids as long as cerebral perfusion is evident and systolic blood pressures remain above a threshold value of 70 to 80 mm Hg. This low-volume strategy should be maintained until bleeding is controlled. Proponents of permissive hypotension suggest that administration of crystalloid may aggravate the inflammatory response, increase blood loss before definitive hemostasis, and increase transfusion requirements, which could further exacerbate early inflammation and late immunosuppression. Studies have examined the safety of permissive hypotension or restrictive resuscitation strategies in the prehospital,emergency department, and intraoperative phases of care. The landmark study by Bickell and colleagues63 compared victims of penetrating torso trauma randomized
to traditional fluid resuscitation or delayed resuscitation in the field and emergencydepartment. The delayed group received no more than 100 mL of fluid before arrival in the operating room. Patients in the delayed group demonstrated a significant survival benefit (70% vs 62%), fewer complications, and a shorter hospital length of stay when compared with the traditional resuscitation group. Another prehospital study of patients with traumatic amputation found that restrictive prehospital fluid resuscitation strategies resulted in improved survival.64 A study by Morrison and colleagues65 compared low (50) versus traditional (65) mean arterial pressure goals to guide intraoperative resuscitation. The lower mean arterial pressure group experienced significantly less blood loss, had fewer transfusions, and had less crystalloid
administered compared with the traditional group. The lower group had significantly improved early survival (98% vs 83%) and maintained a trend toward improved mortality at 30 days. As with the study by Bickell and colleagues,63 the beneficial effects were most significant for victims of penetrating trauma. Unfortunately, few other studies have been able to replicate these positive effects, and active debate continues regarding the benefits of permissive hypotension. Its application, if used,should be limited to penetrating torso trauma victims.