The Efficacy of Active Warming in Prehospital Trauma Care: A Systematic Review and Meta-Analysis
Nicholas Lee
Mark Miller
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis systematic review and meta-analysis seeks to determine patient outcomes after active prehospital warming in trauma patients. The key point of this paper is that active warming may be effective at managing core body temperature in prehospital trauma patients.
Strengths: Use of 4 RCT’s, with over 1000 patients across all the studies.
Weaknesses: Small number of studies included (6), 2 of which were observational and non-randomized, and only 5 were included in the meta-analysis. Secondary outcomes only used 3 of the 6 studies. The studies come from places with differing pre-hospital capabilities/distances of travel with USA vs Europe vs Iraq/Cambodia. High risk of bias, variable study characteristics, such as varying levels of trauma, including minor trauma patients, differing location to measure CBT, differing measurements of cold discomfort, active warming measures etc.
Overall: Interesting study which adds to the limited literature regarding active rewarming as part of management of prehospital trauma patients but is limited by the studies that are included. Unfortunately, no major changes can be recommended, but it would be interesting to see if there is any difference if all patients treated were minor or major trauma, or if active rewarming translated to changes in morbidity/mortality, blood product use, and length of stay.
Comments:
1. P2L48 – When naming the “triad of death” perhaps the authors can add “hypothermia, acidosis, coagulopathy”, for the readers.
2. P5L154-155 – Odd sentence structure, but acceptable.
3. P11L236-248 – Understandable no statistical change in HR, when all the patients had minor trauma.
4. Same with the SBP as above comment (3).
Author Response
Comment 1: This systematic review and meta-analysis seeks to determine patient outcomes after active prehospital warming in trauma patients. The key point of this paper is that active warming may be effective at managing core body temperature in prehospital trauma patients.
Strengths: Use of 4 RCT’s, with over 1000 patients across all the studies.
Weaknesses: Small number of studies included (6), 2 of which were observational and non-randomized, and only 5 were included in the meta-analysis. Secondary outcomes only used 3 of the 6 studies. The studies come from places with differing pre-hospital capabilities/distances of travel with USA vs Europe vs Iraq/Cambodia. High risk of bias, variable study characteristics, such as varying levels of trauma, including minor trauma patients, differing location to measure CBT, differing measurements of cold discomfort, active warming measures etc.
Response 1: Thank you for your time in reviewing our manuscript. Wea re very grateful. We also completely agree with your comment here.
Comment 2: Overall: Interesting study which adds to the limited literature regarding active rewarming as part of management of prehospital trauma patients but is limited by the studies that are included. Unfortunately, no major changes can be recommended, but it would be interesting to see if there is any difference if all patients treated were minor or major trauma, or if active rewarming translated to changes in morbidity/mortality, blood product use, and length of stay.
Response 2: Again, we agree that classifying patients into major or minor trauma would be interesting but the studies do not give this information and hence a future study should incorporate this. Also, none of the studies reported AW versus changes in morbidity/mortality or blood product use or length of stay. We have added a few sentences in the discussion to add these very interesting perspectives from yourselves:
“Finally, none of the studies classified their injuries into minor or major trauma and so the effect of AW in these incidences cannot be determined. Likewise, none of the studies stated if AW led to changes in morbidity/mortality, the blood products used or length of stay. These parameters would all be interesting to consider in the design of high-quality studies to unequivocally determine if AW is beneficial“. See Lines 416-420.
Comment 3: P2L48 – When naming the “triad of death” perhaps the authors can add “hypothermia, acidosis, coagulopathy”, for the readers.
Response 3: Added, please see line 49.
Comment 4: P5L154-155 – Odd sentence structure, but acceptable.
Response 4: Apologies, sentence has been amended to read better. See Lines 155-157.
Comment 5: P11L236-248 – Understandable no statistical change in HR, when all the patients had minor trauma.
Response 5: Agreed.
Comment 6: Same with the SBP as above comment (3).
Response 6: Agreed.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors present a systematic review and meta-analysis examining the active prehospital warming of trauma patients.
The systematic review was undertaken with appropriate methodology. Six manuscripts meeting search criteria were identified for the meta-analysis inclusive of 1,062 patients.
As the authors state, the most frequently used definition of hypothermia is <350C although several of these studies used <360C as their definition. Using the conventional definition, very few of the patients studied were actually hypothermic on measurement of starting core body temperature (CBT). Also, trauma severity, types of thermometer used and active warming methodologies were variable. Ambient temperatures impacted these studies, in particular Husum et al excluded 8 patients from their analysis due to hyperthermia. Lundgren et al achieved rewarming in their passive group but the other studies showed a mild temperature drop in the passively rewarmed patients.
Mclellan et al 1, seems to be a valuable publication overlooked (perhaps rejected by the search criteria) in the literature review. This is a small, multi-national prospective cohort of trauma patients of which 11% were hypothermic when first assessed. Development of hypothermia or failure to improve CBT en route were deemed an unfavourable outcome. Most received both active and passive rewarming by a variety of methods. Unfavourable outcomes were associated with patients who were wet on presentation and those transported by ground transport. Revised trauma scores and ambient temperatures were reported.
The authors have appropriately highlighted that we should interpret their meta-analysis of these small, methodologically heterogenous and potentially biased studies with caution.
The authors state in their discussion and conclusion that the mean end CBT was statistically higher (0.60C) in the active warming group. This may be true but the clinical significance of this degree of temperature variation in a normothermic patient is questionable.
Sub analysis of heart rate, blood pressure and patient comfort seems superfluous as these factors are unlikely to be impacted by a normothermic CBT. There are too many other un-controlled variables impacting vital signs and discomfort beyond CBT. This section of the analysis unnecessarily complicates the manuscript.
The practicalities of active warming during EMS transport should be outlined in the discussion. Electric heating devices are often cumbersome and unsafe in an aeromedical environment. Active heating is usually achieved through warming of IV fluids, elevating the ambient temperature to a level uncomfortable for crew and the use of chemical heating pads.
Prevention of hypothermia is a neglected aspect of trauma care from the prehospital environment to the Emergency Department. This manuscript serves to emphasise the important role of hypothermia prevention and the need for further well designed trials to determine the best methods to achieve this in the field.
1. Mclellan H et al. Prehospital Active and Passive Warming in Trauma Patients. Air Medical Journal. 2023; Vol 42, Issue 4, 252-258.
Author Response
Comments 1: The authors present a systematic review and meta-analysis examining the active prehospital warming of trauma patients.
The systematic review was undertaken with appropriate methodology. Six manuscripts meeting search criteria were identified for the meta-analysis inclusive of 1,062 patients.
As the authors state, the most frequently used definition of hypothermia is <350C although several of these studies used <360C as their definition. Using the conventional definition, very few of the patients studied were actually hypothermic on measurement of starting core body temperature (CBT). Also, trauma severity, types of thermometer used and active warming methodologies were variable. Ambient temperatures impacted these studies, in particular Husum et al excluded 8 patients from their analysis due to hyperthermia. Lundgren et al achieved rewarming in their passive group but the other studies showed a mild temperature drop in the passively rewarmed patients.
Response 1: Thank you for taking the time to review our manuscript. We agree with all of this.
Comment 2: McLellan et al 1, seems to be a valuable publication overlooked (perhaps rejected by the search criteria) in the literature review. This is a small, multi-national prospective cohort of trauma patients of which 11% were hypothermic when first assessed. Development of hypothermia or failure to improve CBT en route were deemed an unfavourable outcome. Most received both active and passive rewarming by a variety of methods. Unfavourable outcomes were associated with patients who were wet on presentation and those transported by ground transport. Revised trauma scores and ambient temperatures were reported.
Response 2: This study did not meet our inclusion/exclusion criteria. However, we feel that the study is very interesting and have added a summary of the results in the discussion as it supported some of the assertions we were making in our study. Please see Lines 371-376.
Comment 3: The authors have appropriately highlighted that we should interpret their meta-analysis of these small, methodologically heterogenous and potentially biased studies with caution.
Response 3: Thank you.
Comment 4: The authors state in their discussion and conclusion that the mean end CBT was statistically higher (0.60C) in the active warming group. This may be true but the clinical significance of this degree of temperature variation in a normothermic patient is questionable.
Response 4: We agree but the systematic review deals with AW for trauma patients and so the use of AW in normothermic patients are not relevant here.
Comment 5: Sub analysis of heart rate, blood pressure and patient comfort seems superfluous as these factors are unlikely to be impacted by a normothermic CBT. There are too many other un-controlled variables impacting vital signs and discomfort beyond CBT. This section of the analysis unnecessarily complicates the manuscript.
Response 5: We believe that the analysis of these parameters are important since there are studies that have reported these as outcomes to active and passive warming. Hence, as the first systematic review in this area, we wanted to cover all of these parameters and work out if they were useful in understanding the benefits of AW versus passive warming.
Comment 6: The practicalities of active warming during EMS transport should be outlined in the discussion. Electric heating devices are often cumbersome and unsafe in an aeromedical environment. Active heating is usually achieved through warming of IV fluids, elevating the ambient temperature to a level uncomfortable for crew and the use of chemical heating pads.
Response 6: We have added a few sentences to cover this aspect. Thank you for the inclusion. Please see Lines 377-382.
Comment 7: Prevention of hypothermia is a neglected aspect of trauma care from the prehospital environment to the Emergency Department. This manuscript serves to emphasise the important role of hypothermia prevention and the need for further well designed trials to determine the best methods to achieve this in the field.
Response 7: We agree, thank you.
Round 2
Reviewer 1 Report
Comments and Suggestions for Authorsall comments addressed
Reviewer 2 Report
Comments and Suggestions for AuthorsRevised discussion section highlights the impracticalities of prehospital active warming makes the manuscript more readable.
