College Answer

 “Damage  control  resuscitation”  as applied to the management  of the major trauma patient integrates permissive  hypotension,  haemostatic  resuscitation and damage control surgery.

Outline  the  key  principles  of  each  of  these  three  strategies,  including  the rationale.

a.   Permissive hypotension

1. Keep SBP low enough to avoid exsanguination but high enough to maintain perfusion.

2. Relates to disruption of an unstable clot by higher pressures and worsening of bleeding.

b.  Haemostatic resuscitation

i.       Correct hypothermia

1.    Decreases platelet responsiveness.
2.    Increases platelet sequestration in liver and spleen
3.    Reduces Factor function eg Factors XI and XII
4.    Alters fibrinolysis

ii.       Correct acidosis

1.    pH strongly effects activity of Factors V, VIIa and X.
2.    Acidosis inhibits thrombin generation
3.    Cardiovascular  effects of acidosis (pH <7.2) – decreased  contractility  and CO,  vasodilatation  and  hypotension,  bradycardia  and  increased dysrhythmias.

iii.       Treat coagulopathy early and aggressively

1.    Many coagulopathic  changes  occur early after trauma,  therefore  need to correct early.
2.   Use much higher FFP to PRBC ratios (1:1/2:3) than previously used. Is associated with improved survival.
3.    Higher platelet to PRBC transfusion ratios also becoming more popular but evidence is less clear.
4.    Cryoprecipitate  provides an additional option for Factor replacement  for a lower volume of fluid.
5.    rFVIIa has been used in trauma, but off label and anecdotally.

iv.       The use of blood  products  instead  of isotonic  crystalloid  fluid aiming  for limited volume replacement

1.    Large   volume   crystalloids   can   lead   to   dilutional   coagulopathy   and exacerbate bleeding.
2.    Crystalloids  have  no  O2  carrying  capacity  and  do  little  to  correct  the anaerobic metabolism and O2 debt associated with shock.
3.    Need less volume of blood product  therefore  likely to be less tissue and organ (eg lung, small intestine mucosa) oedema and failure (eg pulmonary oedema, abdominal compartment syndrome)
4.   Hypertonic saline is another option (proven restored microvascular flow, decreased tissue oedema, attenuated inflammatory response).

c.   Damage control surgery

1.    Management     of    the     metabolic    derangement     of    ongoing    bleeding supersedes the need for definitive surgery
2.    Abbreviated operations that control haemorrhage and contain spillage from the alimentary and urogenital tracts.
3.    Rapid   transfer   to  ICU   for   correction   of   acidosis,   coagulopathy   and hypothermia
4.    Definitive operation is deferred.
5.    These operations tend to have a high complication rate
6.    Survival is given preference over morbidity.

Discussion

Permissive hypotension

Definition:

• Allowing a subnormal MAP in a trauma patient;
• " The strategic decision to delay the initiation of fluid resuscitation and limit the volume of resuscitation fluids/blood products administered to the bleeding trauma patient by targeting a lower than normal blood pressure, usually a systolic blood pressure of 80–90 mmHg or a mean arterial pressure (MAP) of 50 mmHg" - Kaafarani et al, 2014

Rationale:

• In penetrating trauma, a lower MAP may improve hemostasis.
• Improved hemostasis may result in smaller transfusions, decreased coagulopathy, and less transfusion-associated adverse events

Key principles:

• Goal is hemostasis, rather than the actual low blood pressure
• MAP of 50 appears to be associated with decreased transfusion requirements but not increased adverse events

Haemostatic resuscitation

Definition:

• Rapid correction of hemostasis-impairing factors, such as hypothermia hypocalcemia and acidosis
• Resuscitation with a balanced combination of blood products, which in combination resemble the composition of whole blood, aiming to avoid dilutional coagulopathy.

Rationale:

• Unbalanced transfusion strategies lead to depletion of coagulation factors and exacerbation of dilutional coagulopathy.

Key principles:

• Early and aggressive transfusion of blood products aiming for a ratio of PRBCs, FFP, and platelets that approximates 1:1:1
• Use of hemostatic agents such as tranexamic acid (strongly supported by evidence)

Damage control surgery

An excellent article on this is available from 2004 (Critical Care Clinics)

Definition:

• Rapid termination of an operation after control of life-threatening bleeding and contamination followed by correction of physiologic abnormalities and definitive management.

Rationale:

• Hypothermia, acidosis, and coagulopathy render attempts at definitive surgical repair less likely to succeed.
• The surgical control of immediately lifethreatening injuries and the establishment of haemostasis must be achieved early, but definitive management can be delayed in most cases.
• Definitive management can take place safely once the physiological abnormalities are corrected.

Key principles:

• Control of haemorrhage
• Control of contamination
• Use of temporary shunts to bypass ligated vascular injuries
• Delay of abdominal closure, or temporary wound closure