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
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