CJSM Blog Journal Club — Can Cold IV Saline Mitigate the Effects of Exertional Heat Illness?

It’s November, and our sixth and final edition of 2018 has just published.  One of the original research articles in this edition is: Effects of Intravenous Cold Saline on Hyperthermic Athletes Representative of Large Football Players and Small Endurance Runners. 

Our Jr. Assoc. Editor Jason L Zaremski, MD  is today reprising his role as guest author for the CJSM blog journal club  and will take us through his read of the study.  Join in the conversation over this important new, original research by reading the article and the blog post below.  As ever, we love your comments:  you may give them here on the blog or Tweet them to us at @cjsmonline.

We’re nearing the end of 2018.  As the Journal publishing crew gets ready to celebrate Thanksgiving, we want to thank you for visiting us on this blog and reading and contributing to CJSM.

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Introduction:  The winter Journal Club commentary for the Clinical Journal of Sports Medicine (CJSM) will be a review of an original research manuscript highlighting an alternative method for treating exertional heat illness (EHI). As many of us in the sports medicine community are fully aware, EHI is a potentially devastating pathophysiological process that is treatable if timely and efficient action is taken.  Speed is of the essence. Heat stroke, a type of EHI where core body temperature is greater than 40°C/104°F, can result in significant central nervous system morbidity, and even death, if not treated immediately.

Morrison and colleagues performed a novel study assessing the effects of intravenous cold saline (IVCS) on hyperthermic collegiate football players and cross country runners. As the authors note, the use of cold saline infusion has not been studied for its effects on hyperthermic athletes, though it has been studied for rapid cooling for patients who have had cardiovascular and/or neurological insults in order to induce “therapeutic hypothermia.”

Purpose/Specific Aim(s):  To evaluate the cooling effects of IVCS (4°C/39°F) on hyperthermic athletes and compare to the effects of room temperature normal saline (RTNS) (22°C). A secondary aim was to assess if body composition had an effect on IVCS cooling rates.

Methods/Design: This was a prospective, laboratory study with a crossover design. All participants completed a hyperthermia protocol with an exercise-induced heating followed by a 30-minute treatment consisting of IV infusion of either IVCS or RTNS. Treatment was randomized. Each participant subsequently returned to the laboratory no sooner than 72 hours after their first trial (of either IVCS or RTNS) to perform the same hyperthermia protocol and receive their other treatment condition (IVCS or RTNS). This study was IRB approved.

Participants: 12 healthy male participants between 20-25 years old in total: [2 current NCAA Division II football (FB) players, 2 previous NCAA Division II FB players, and 2 prior High School FB players as well as 3 current NCAA Division II Cross Country (CC) runners and 3 former High School CC Runners]. Physical characteristic were obtained for all participants (height, weight, mass, body fat (BF), lean body mass (LBM), body surface area (BSA), and BSA/mass). There were large differences in mass (kg), BF (%), LBM (kg), BSA (m²), and BSA/mass (cm²/kg) between FB and CC athletes.  Active athletes were in their respective off-seasons. All participants were medically screened for any cardiovascular, musculoskeletal, or respiratory conditions before participating in the study; they were excluded if they had a history of heat related illness, were ill at the time of the experimental trials, or were taking medications or supplements that affected thermoregulation or fluid balance.

Variables:

Dependent variables: Total ΔT_re (ending T_re – starting T_re) and cooling rate [total ΔT_re/time (minutes)].

Independent variable: Saline condition (Cold v Room).

Body Composition Variables: BSA, BSA-to-mass ratio (BSA/ mass), LBM, and %BF.

T_re = Rectal Temperature

Data Acquisition:

Baseline Data:  The day of the trial, athletes were dressed in standard workout clothes. Each study participant provided a urine sample and was fitted with a heart rate (HR) monitor to gather HR data throughout the exercise and treatment procedures. Body composition including total body mass (kg), LBM (kg), and % BF were measured using a BodPod body composition tracking system.

 

Core Temperature Monitoring: T_re was continuously monitored throughout the exercise and cooling protocols using a rectal probe. T_re was then recorded for each session.

 

Exercise Protocol: Participants entered a climate controlled chamber where they were seated in an upright position for 10 minutes before exercise to acclimate to the environment (ambient temperature about 39°C/102.2°C and Relative humidity about 40%). Participants then performed a submaximal to maximal dynamic protocol, (10 minutes of riding a stationary bike alternating with jogging on a 2% incline treadmill until a T_re of 39.5°C (103°F) or exhaustion). Participants consumed fluids as desired during the exercise protocol. When a T_re of 39.5°C or exhaustion was reached, participants were immediately removed from the chamber and moved into the treatment area for administration of the treatment protocol.

 

Measurements during Exercise Protocol:

Every 5 minutes: T_re and HR

Every 15 minutes: Wet bulb globe temperature (WBGT), ambient temperature (T_a), Relative Humidity (RH), Global temperature (T_g) within the chamber.

 

Definition of Exhaustion: The inability to continue exercising or with the onset of heat related illness symptoms.

 

Intravenous Infusion Protocol:

The saline infusion protocol used was similar to previously published methods. After exercise, subjects were administered either randomly assigned IVCS or RTNS. Participants were infused with two 1-L bags. The relative volume of saline infused was 22.8 ± 6.1 mL/kg body mass. T_re was monitored and recorded every minute until the completion of the infusion to assess the rate of cooling/minute. The average infusion rate was 66 mL/min. The total infusion time was 30.6 ± 1.7 minutes. The WBGT, T_a, RH, and T_g, were monitored and recorded every 15 minutes to ensure consistency between trials. Blood pressure and HR were measured and recorded every 5 minutes to ensure safety.

 

Statistical Measures:  As the authors note, statistical analysis was performed using the Statistical Package of Social Sciences (v.22; SPSS, Chicago, IL). Paired t tests were used to determine differences in the cooling rate and the total ΔT_re between trials. Independent t tests were used to evaluate group differences in all physical characteristics and pre-exercise, as well as the environmental conditions during the infusion protocols. Pearson correlations were used to examine the relationship between cooling rate and total body, %BF, LBM, BSA, and BSA/mass for the IVCS trials. Significance was set at P= 0.05 for all comparisons.

 

Results/Outcomes:

There were no differences in environmental conditions during treatment between the RTNS and IVCS trials. There were no significant differences in pretrial Urine Specific Gravity (USG) between the IVCS and RTNS trials. There were significant differences in the total ΔT_re between IVCS and RTNS and in the cooling rate between IVCS and RTNS. There were also significant and strong correlations between the IVCS cooling rate and TBM, total BSA, BSA/mass, and % BF. There was a non-significant correlation with LBM.

 

Strengths:

This was a well-designed prospective laboratory study. Protocols used by the authors have been previously published. The authors were very thorough in assessing different body types (American FB players versus CC runners) and association in cooling rates between IVCS and RTNS. Attempts were made to reproduce in vitro conditions comparable to conditions an athlete might encounter in vivo during warm periods of training or competition.

 

Weaknesses:

While this was a well done study, the number of subjects was low.  Strength of study results would be enhanced if there were greater numbers in each sport studied. The design of the study also resulted in a lack of blinding. This study compared IVCS to RTNS, not IVCS to CWI (which is the standard of care of EHI). It would be interesting to appreciate the cooling rate comparison of IVCS vs CWI in this study and if cooling rates with CWI were comparable to the study cited in the manuscript by Fowles-Godek et al. from JAT in 2014 that the authors cited. Furthermore, the authors concluded that IVCS had a cooling rate of 0.066 C°/min, which is considered unacceptable (e.g. less than <0.078 C°/min). Moreover, IV infusion of hyperthermia treatment requires knowledge of electrolyte concentrations to confirm there is no concern of hyponatremia. Finally, the total infusion time was 30.6 ± 1.7 minutes. This is a significant amount of time to infuse IVCS at a rate that is approximately 2.3-5.3 times slower than CWI (0.066 C°/min vs 0.15-0.35 C°/min). Lastly, IVCS requires obtaining appropriate supplies that are readily available (IV kit, Cold Water Normal Saline) and medical team members that can perform an IV infusion.

 

Conclusion:

1. The authors concluded that rapid cooling of hyperthermic individuals with IV saline infusion is more effective when the saline bag is chilled (4°C) before treatment and produced greater cooling rates than RTNS.

 

2. Body composition has a significant impact on the cooling rates.

 

3. IVCS infusion should be considered as an effective first aid treatment of hyperthermic individuals (that are not hyponatremic) when CWI is not available and EHI is suspected.

 

Clinical Relevance:

As the authors astutely proposed, if CWI is not available for immediate EHI, if readily available IVCS could be considered as an alternative method for hyperthermia and for transportation to the hospital and emergency department.