Permissive hypotension

OVERVIEW

Permissive hypotension is also known as hypotensive resuscitation and low volume resuscitation

• The concept remains controversial and is primarily applicable to the penetrating trauma patient
• It is considered part of damage control resuscitation, along with haemostatic resuscitation and damage control surgery

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. JAMA 1918;70(9): 620

APPROACH

• Allow SBP to fall low enough to avoid exsanguination but keep high enough to maintain perfusion
• Goal is to avoid disruption of an unstable clot by higher pressures and worsening of bleeding (“don’t pop the clot”)
• Avoids cyclic over-resuscitation that can lead to rebleeding and paradoxically exacerbate hypotension despite increased fluid resuscitation and subsequent complications
• Low BP is not the target, it is a compromise pending emergency surgical intervention
• Haemorrhage control is the goal, once this achieved (e.g. haemostasis and surgery) normalisation of haemodynamics is appropriate

PROBLEMS

• not widely accepted in Australia
• largely based on animal studies; no high level evidence other than a non-blinded semi-randomised study by Bickell et al, 1994
• varying interpretations of the meaning and goals of the permissive hypotension approach
• must not miss non-hemorrhagic causes of hypotension (e.g. tension pneumothorax, pericardial tamponade)
• a major caveat in the Australian setting is that there are often prolonged retrieval times for trauma patients in getting to a trauma center (e.g. >6h on average in Darwin)
• concerns in the setting of potential traumatic brain injury (TBI), as BTF guidelines support at target CPP of >60 mmHg and retrospective data suggests SBP <90 doubles mortality (see Wiles, 2013)
• appropriate BP varies with the individual (e.g. patients with chronic hypertension likely need higher blood pressures)

A MINIMAL VOLUME NORMOTENSIVE APPROACH

An alternative or variant approach is the normotensive resuscitation approach described by Scott Weingart:

• Target = MAP of 65 mmHg (assuming patient is adequately perfused at this blood pressure and there is not a coexistant head injury demanding a higher BP target)
  — targets above this risk “popping the clot”, fluid overload and dilutional coagulopathy
• If MAP < 65 – give fluids/ blood products
• If MAP > 65 – check perfusion (strong pulse, warm peripheries)
  -> MAP > 65 with good perfusion -> perform masterful inactivity
  -> MAP > 65 with poor perfusion -> give fentanyl 20-25 mcg (decreases catacholamine release resulting in vasodilation, if MAP drops <65 mmHg then give fluids/ blood products as above)

There is no high level evidence to support this approach

EVIDENCE

Bickell WH, Wall MJ Jr, Pepe PE, Martin RR, Ginger VF, Allen MK, Mattox KL. Immediate versus delayed fluid resuscitation for hypotensive patients with penetrating torso injuries. N Engl J Med. 1994 Oct 27;331(17):1105-9. PubMed PMID: 7935634. [Free Full Text]

• non- blinded semi-randomised prospective study
• n = 598 adults with penetrating torso injury and SBP <90mmHg
• an immediate resuscitation group (even days) and a delayed resuscitation group (odd days) (resuscitation started in OR, not ED)
• Outcome: mortality benefit favouring delayed resuscitation: 70% vs 62% (p= 0.04) even after correcting for the prehospital and emergency room time intervals
• Commentary and criticisms:
  • patients were generally generally young fit patients with penetrating trauma
  • took place in a high-volume trauma centre in Houston with very short door-to-theatre times
  • good baseline balance: demographics, mortality before reaching OR, time to OR
  • good separation: 1608 and 283 mL fluid given in ER in the two groups
  • high potential for bias: not blinded, not randomised
  • BP was actually the same in both groups regardless of whether resuscitation was immediate or delayed
  • crystalloid was used, not a modern haemostatic resuscitation
  • lacks external validity to settings where delayed presentations or blunt trauma predominates, or to traumatic brain injury

Dutton RP, Mackenzie CF, Scalea TM. Hypotensive resuscitation during active hemorrhage: impact on in-hospital mortality. J Trauma. 2002 Jun;52(6):1141-6. PubMed PMID: 12045644.

• RCT with n=110
• titrating the initial fluid therapy to SBP 70 mmHg versus 100 mmHg during active hemorrhage
• no difference in mortality
• commentary and criticisms:
  • small study with heterogeneous patients
  • BP was again similar in both groups regardless of the BP target (e.g. 100 ± 17 mmHg in the 70-mmHg group) suggesting physiological adaptation

Mapstone J, Roberts I, Evans P. Fluid resuscitation strategies: a systematic review of animal trials. J Trauma. 2003 Sep;55(3):571-89. Review. PubMed PMID: 14501908.

• meta-analysis of animal trials
• numerous small unblinded studies using animal models suggest permissive hypotension is beneficial in penetrating trauma (e.g. pig aortomy models)

VIDEO

In the video lecture below, Karim Brohi argues that the permissive hypotension approach also applies to the blunt trauma setting and is appropriate even in the context of coexistent traumatic brain injury. He argues that an approach that targets higher blood pressure in a haemorrhaging patient does not achieve these goals, it only leads to more fluid being given.

References and Links

LITFL

• CCC — Haemostatic resuscitation
• CCC — Major haemorrhage in trauma
• CCC — Damage control surgery and damage control resuscitation

Journal articles

• Bickell WH, Wall MJ Jr, Pepe PE, Martin RR, Ginger VF, Allen MK, Mattox KL. Immediate versus delayed fluid resuscitation for hypotensive patients with penetrating torso injuries. N Engl J Med. 1994 Oct 27;331(17):1105-9. PMID: 7935634. [Free Full Text]
• Cannon WB, Fraser J, Cowell E. The preventive treatment of wound shock. The Journal of the American Medical Association. 1918;70(9): 618-621
• Dutton RP, Mackenzie CF, Scalea TM. Hypotensive resuscitation during active hemorrhage: impact on in-hospital mortality. J Trauma. 2002 Jun;52(6):1141-6. PMID: 12045644.
• Mapstone J, Roberts I, Evans P. Fluid resuscitation strategies: a systematic review of animal trials. J Trauma. 2003 Sep;55(3):571-89. PMID: 14501908.
• Sapsford W. Should the ‘C’ in ‘ABCDE’ be altered to reflect the trend towards hypotensive resuscitation? Scand J Surg. 2008;97(1):4-11; discussion 12-3. PMID: 18450202.
• Wiles MD. Blood pressure management in trauma: from feast to famine? Anaesthesia. 2013 May;68(5):445-9. doi: 10.1111/anae.12249. Epub 2013 Apr 1. PubMed PMID: 23550831. [Free Full Text]

FOAM and web resources

• EMCrit — Severe Trauma with Karim Brohi (2012)
• EMCrit — Resuscitation of the Hemorrhagic Shock Patient in Trauma
• EMCrit — Trauma resuscitation of the critically ill hemorrhagic shock
• Trauma.org — Permissive Hypotension (Ken Mattox, 2003)