Relevance of induced and accidental hypothermia after trauma-haemorrhage – what do we know from experimental models in pigs? Hildebrand et al. Intensive Care Medicine Experimental 2014, 2:16

Presented by : Dr A. Byford-Brooks

Background

  • ‘Lethal triad of trauma’ current model
  • Induced, rather than accidental hypothermia, in animal models has shown potential benefit including:
    • Anti-inflammatory
    • Haemodynamic
    • Reduction of metabolic stress
  • Coagulopathy still a concern
  • Method and technique of cooling could be key

Objectives

  • Benefits/Risks of induced hypothermia
  • Methods of inducing hypothermia
  • Magnitude/Timing/Speed/Duration

Design and Setting

  • Literature review up to July 2013
  • Porcine models of trauma, haemorrhage or combined trauma-haemorrhage
  • Accidental or induced hypothermia
  • Keywords: ‘accidental hypothermia’, ‘spontaneous hypothermia’,‘induced hypothermia’, ‘therapeutic hypothermia’, ‘pigs’, ‘swine’, ‘trauma’, ‘injury’, ‘hemorrhage’, ‘fracture’ and ‘bleeding’
  • 36 papers in total

Subjects

  • Porcine models
  • Haemorrhage

1. Controlled à CVC and/or arterial line as %BW

2. +/- Uncontrolled à Surgical insult e.g. Combos of visceral +/- vascular +/- bony trauma

  • Hypothermia

Range:10-35 degrees Celcius (33 deg commonest)

Time: 20mins – 11.5h (2hrs commonest)

Interventions

  • Delay until resuscitation
    • Approximately 0-30s for uncontrolled
    • Approximately 30-40min for controlled
  • Type of resuscitation fluid
    • Crystalloid/colloid (n=19)
    • Blood products (n=3)
    • Combination (n=10)
    • None (n=4)
  • Method of cooling
    • Intraperitoneal packs
    • Cold IVI
    • Cooling blankets
    • Icepacks
    • Roller pump (heparin-free) or CPB (heparin)
  • Method of warming
    • Intraperitoneal lavage
    • Warm IVI
    • Bair hugger
    • Roller pump or CPB
    • No warming

Outcomes

  • Endpoints
    • Mortality
    • Haemostasis
    • Correction of coagulopathy
    • Organ damage e.g. Lactate
    • Use and/or dose of agents being studied e.g. Factor concentrates or haemostatic agents

Conclusions

  • If normothermic – induce hypothermia after primary haemostasis in solid organ damage
  • If accidental hypothermia – correct until haemostats achieved then induce hypothermia (ICU)
  • Rapid cooling better than slow e.g. 2 degrees/min (roller pumps!)
  • Intracorporeal cooling better than extracorporeal (unless also rapid)
  • 34 degrees a good endpoint
  • For aortic trauma – DHCA not more than 60 mins and 10 degrees better than 5 degrees
  • Adequate anaesthesia and relaxation key
  • Rewarming around 0.5 degrees/h
  • No derangements in TEG, coag or Plt between 33-35 degrees
  • Hypothermia reduces plasma levels of inflammatory markers
  • Acidosis in some models due to increased fatty acid vs CHO metabolism and/or slow vs rapid cooling

Strengths

  • Early look at a controversial topic with live subjects
  • Considered multiple models of trauma
  • Compared cooling/rewarming goals and techniques
  • Duration and magnitude of hypothermia

Weaknesses

  • Studies
    • Huge variety in study protocols
    • Circumstances of trauma still artificial and unrealistic
    • Small sample sizes (often <50 total)
    • Type of anaesthesia variable
    • Resuscitation methods (i.e. Crystalloids)
    • Hypothermia often secondary to the study aim
  • Species-specific differences
    • Pigs are hypercoagulopathic compared to humans
    • Acute coagulopathy of trauma (ACOT) has yet to be demonstrated in pigs
    • Despite polytrauma and crystalloid+++, many studies could not induce a coagulopathy
    • Different haemodynamic physiology
  • Long-term effects not investigated
    • Rebleeding
    • Infection
    • Delayed rebound inflammatory response
    • Organ dysfunction on rewarming
    • Posttraumatic apoptosis
  • Subjects with ‘disease states’ not investigated
    • Human population older with comorbidites

Implications

  • Analysis of long-term outcomes not considered
    • Expensive
    • Essentially requires a staffed ICU for the pigs!
  • May lead initially to pragmatic, single-intervention studies on ICU in humans
    • For example in a similar manner to  post-operative cooling in a similar way to out of hospital cardiac arrest or traumatic brain injury
  • Investigation of role of roller pumps in tight thermoregulation and resuscitation

Potential for impact

  • Unlikely to alter current clinical practice with regards to the Lethal Triad
  • However studies suggest mild hypothermia to 34 degrees may not be as deleterious as we think