Permissive hypotension

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Permissive hypotension or hypotensive resuscitation

coagulation factors that help form and stabilize a clot, hence making it harder for the body to use its natural mechanisms to stop the bleeding. These factors are aggravated by hypothermia (if fluids are administered without being warmed first it will cause body temperature to drop).[3][4][5][6][7][8]

It is becoming common in

prehospital and trauma center fluid resuscitation versus delayed onset of fluid resuscitation (fluid not administered until patients reached the operating room). A more recent study (2011) performed by the Baylor Group on patients who required emergency surgery secondary to hemorrhagic shock was randomized to a mean arterial pressure (MAP) of 50mmHg versus 65mm Hg. The lower MAP group was found to need less total IV fluids, used fewer blood products, had lower early mortality (within the first 24 hours - which accounts for a large portion of mortality in trauma patients) and trended towards lower 30-day mortality and less postoperative coagulation, concluding that permissive hypotension is safe.[11] Two large human trials of this technique have been conducted, which demonstrated the safety of this approach relative to the conventional target (greater than 100 mmHg), and suggested various benefits, including shorter duration of hemorrhage and reduced mortality.[12][13] Johns Hopkins group performed a retrospective cohort review from National Trauma Data Bank that found a statistically significant difference in mortality for patients treated with pre-hospital intravenous fluids.[14]
Clinical data from well-controlled, prospective trials applying the concept of permissive hypotension in trauma patients are still missing.

Pathophysiology

Following injury, the otherwise healthy individual has a natural ability to clot off bleeding. The higher the pressure in your vessels, the harder it is for the bleeding to stop, since the fluid essentially "pushes" the clot out and consequently the bleeding resumes. In more technical terms: hypotension facilitates in vivo coagulation. This is especially true in patients who still have active bleeding. Attempts to normalize blood pressure in case of uncontrolled bleeding as in patients with penetrating trauma, may result in increased blood loss and worse outcomes. In this context, restriction of fluid resuscitation may actually improve outcomes. This concept has been supported by animal studies that have demonstrated aggressive fluid resuscitation increases the volume of hemorrhaging fluid to a significant level as well as increased mortality.[15][16]

Another issue with aggressive fluid resuscitation is the potential for

Triad of Death
" that is feared by all trauma specialists.

The

myocardial
(heart muscle) function.

It is important to remember that permissive hypotension is a temporary measure to improve outcomes until the source of bleeding is controlled. There are issues associated with prolonged permissive hypotension (> 90 min considered prolonged where detrimental effects outweigh benefits according to most recent animal studies - no human data available to date)

mitochondrial dysfunction, and lactic acidosis among others. It is also possible that other substances, such as estrogen (17 beta-estradiol) could allow for longer models of permissive hypotension. In a rat model of hemorrhagic shock, estrogen was able to reduce some of the negative effects of prolonged permissive hypotension as well as prolong long-term survival.[18]

Contraindications

Patients with preexisting

autoregulatory
curve to the right for hypertensive patients.

Permissive hypotension relies on the heart's ability to pump fluid through the body efficiently. Less

angina pectoris) may not. Applying permissive hypotension to the latter patient category may result in decreased coronary perfusion and result in ischemic damage to the heart and potentially myocardial infarction (heart attack).[2]

Permissive hypotension may also be contraindicated in patients with

renal (kidney) function, where hypotension may induce sludge (thickening of the blood) and lead to occlusion of the vessel lumen. It is also recommended that fluid loading should be used, instead of permissive hypotension, for those with crush syndrome.[19]

A high percentage of

morbidity when compared with patients who were normotensive. The concomitant presence of hypoxia and hypotension upon admission resulted in a 75% mortality.[20] Evidence strongly suggests that the avoidance or minimization of hypotension during the acute and postinjury period following traumatic brain injury had the highest likelihood of improving outcomes of any one single therapeutic maneuver.[21]
Therefore, managing a patient with traumatic brain injury and continuing bleeding elsewhere becomes a balance between meeting the demands of the brain versus the demands of the body, which should be addressed by the experienced anesthesiologist, surgeon and emergency physician.

Current Recommendations

  • Britain: Resuscitation to maintain a palpable radial pulse (indicative of systolic blood pressure 80-90mm Hg) in ongoing hemorrhage in soldiers and to maintain only a palpable central pulse (ex. carotid), indicative of systolic blood pressure of 60mm Hg with penetrating torso trauma.[22]
  • United States: US Military follows permissive hypotension. Any patient that experiences altered mental status or becomes unconscious (systolic blood pressure less than or equal to 50mmHg) is resuscitated to restore mentation or systolic blood pressure of 70mmHg.[23][24][25][26][27]
  • Israel: Israeli Military also follows permissive hypotension and follows similar guidelines as the United States.[28]

References

  1. .
  2. ^ a b Schweiz Med Wochenschr 2000;130:1516–24
  3. ^ Kowalenko T, et al. J Trauma. 1992, 33:349-53
  4. ^ Stahel PF, et al. Injury. 2009, 40 (4, suppl):S27-35.
  5. ^ Brickell WH, et al. Circ Shock. 1989, 28:321-32
  6. ^ Stern SA, et al. Ann Emerg Med. 1993, 22:155-63
  7. ^ Geeraedts, Jr LMG, et al. Injury. 2009, 40:11-20.
  8. ^ Shen L, et al. J Clin Invest. 1983, 71:1336-1341
  9. PMID 8608703
    .
  10. penetrating
    torso injuries. N Engl J Med 1994;331:1105–9.
  11. ^ Morrison CA, et al. J Trauma. 2011, 70:652-63.
  12. PMID 7935634
    .
  13. .
  14. ^ Haut ET, et al. Ann. Surg. 2011, 253:371-7
  15. ^ Kowalenko T, Stern S, Dronen S, Wang X. Improved outcome with hypotensive resuscitation of uncontrolled hemorrhagic shock in a swine model. J Trauma 1992;33: 349–53.
  16. ^ Stern SA, Dronen SC, Birrer P, Wang X. Effect of blood pressure on hemorrhage volume and survival in a near-fatal hemorrhage model incorporating a vascular injury [see comments]. Ann Emerg Med 1993;22:155–63.
  17. ^ Li, T, et al. Anesthesiology. 2011, 114:111-9
  18. ^ Kozlov AV, et al. Mol Med. 2010, 16:254-61
  19. ^ Garcia, Tony (1 May 2010). "Recognizing and Treating Crush Syndrome". FireEngineering.com. Retrieved 10 October 2013.
  20. ^ Chesnut RM, Marshall LF, Klauber MR, Blunt BA, Baldwin N, Eisenberg HM, et al. The role of secondary brain injury in determining outcome from a severe head injury. J Trauma 1993;34:216–22.
  21. ^ Chesnut RM. Avoidance of hypotension: condition sine qua non of successful severe head-injury management. J Trauma 1997;42:S4–S9.
  22. ^ Revel M, et al. J Trauma 2003, 54(5,suppl):S63-S67.
  23. ^ Butler FK, et al. Mil Med. 2000. 165(4, suppl):1-48.
  24. ^ Peace FJ, et al. Mil Med. 1999, 164:653-5
  25. ^ Champion HR. J Trauma 2003, 54(5,suppl):S7-12.
  26. ^ Champion HR. J Truma. 2003, 54(5,suppl):S7-12)
  27. ^ MacKinnon MA. Air Medical Journal. 2005, 24: 70-72.
  28. ^ Krauz MM. "Fluid Resuscitation for the trauma patient." Trauma, Critical Care and Surgical Emergencies: A Case and Evidence-Based Textbook. Eds. Rabinovici R, Frankel HL, Kirton OC. Pages 1-7, 2010.