American Journal of Emergency Medicine (2012) 30, 1385-1388

Original Contribution

A simple method of maintaining chilled saline in the prehospital setting^?,??

Derek L. Isenberg MD^a,?, Michael J. Pasirstein MD^b

^aDepartment of Emergency Medicine, Mercy Catholic Medical Center, Philadelphia PA 19143

^bDrexel University College of Medicine, Philadelphia, PA

Received 29 June 2011; revised 1 October 2011; accepted 10 October 2011

Abstract

Objective: Mild therapeutic hypothermia has been shown to improve neurologic outcomes after sudden cardiac arrest. Therapeutic hypothermia should be started as soon as return of spontaneous circulation occurs. However, saline is difficult to keep chilled in the prehospital environment. We sought to determine whether a cooler and ice packs could keep saline cold under prehospital conditions.

Methods: In Phase 1 of the experiment, two 1000-mL bags of prechilled 0.9% normal saline were placed in a cooler with 3 ice packs. An additional bag of 1000-mL 0.9% normal saline remained outside the cooler as a control. Over 9 consecutive days, we measured the ambient air temperature and the temperature of each bag of saline every 4 hours. In Phase 2 of the experiment, the cooler was kept sealed, and the temperature of the saline was measured after 24 hours.

Results: The mean temperatures over 24 hours ranged as follows: ambient temperature, 24?C to 27.2?C; bottom bag, 0.6?C to 3.5?C; top bag, 1.4?C to 5.7?C; and control bag, 9.8?C to 26.8?C. A t test was used to compare the chilled saline against the control bag. Statistical significance (P b .05) was achieved at all times. In phase 2 of the experiment, after 24 hours, 100% of the bottom bags and 93% of the top bags were less than 6?C.

Conclusions: Our data demonstrate that saline can be kept chilled in ambulances for 24 hours using ice packs and coolers. The estimated cost is less than $50.00 per ambulance. Using coolers and ice packs is an inexpensive way for emergency medical service agencies to initiate prehospital hypothermia.

(C) 2012

Introduction

Mild therapeutic hypothermia has been shown to improve neurologic outcomes after cardiac arrest [1-6]. In the most current American Heart Association (AHA) and International

^? The authors report no outside funding or conflicts of interest.

^?? Previously presented at the National Association of Emergency Medical Services Physicians, January 2010, Bonita Spring, FL.

* Corresponding author. Tel.: +1 904 373 8034; fax: +1 215 748 9027.

E-mail address: [email protected] (D.L. Isenberg).

Liaison Committee on Resuscitation guidelines for cardiac arrest, therapeutic hypothermia received a class I recommen- dation for comatose survivors of cardiac arrest secondary to ventricular fibrillation and a class IIa recommendation for survivors of cardiac arrest secondary to asystole or pulseless electrical activity [7].

In sudden cardiac arrest, return of spontaneous circulation often occurs in the prehospital environment. Previous studies have shown that hypothermia can be safely accomplished in the prehospital environment [8-14].

Several methods have been proposed to allow emer- gency medical services EMS to cool patients in the

0735-6757/$ – see front matter (C) 2012 doi:10.1016/j.ajem.2011.10.007

prehospital environment. These interventions include Surface cooling measures (ice packs and cooling blankets), intranasal cooling systems [15], and cold normal saline [8-10,13,16].

Because of the variety of environments in which EMS operates, maintaining chilled saline represents a significant challenge. Often, EMS agencies cannot place refrigerators in their ambulances because of monetary restraints. In addition, refrigerators require a constant supply of electricity, a feature not found on many ambulances.

A previous study has shown that a cooler and ice packs can maintain saline chilled in a laboratory setting at temperatures of up to 50?C [17]. We hypothesized that a similar setup of ice packs and coolers could keep saline cool under actual prehospital conditions.

Methods

Mercy EMS serves 8 municipalities on the southwest border of Philadelphia. Mercy EMS operates 3 Advanced life support ambulances, 4 basic life support ambulances, and 1 ALS quick response vehicle. The 7 ambulances operate out of firehouses. These units are parked inside of the firehouses when not in use. None of the ambulance bays are air-conditioned, and none of the ambulances are plugged into a ground outlet for temper- ature control. The ALS quick response vehicle is parked outside when not in use.

For each of the 3 ALS ambulances and the ALS quick response vehicle, we purchased a 16-quart cooler Igloo Corporation, Katy, TX and 3 foam cold packs (Polar Foam Packs; Tegrant Corporation, Montgomeryville, PA). Both the cooler and the cold packs are readily available at retail merchants. From our hospital pharmacy, we obtained 1000- mL bags of 0.9% saline (Abbot Laboratories Abbott Park, IL). The saline bags were cooled to approximately 4?C in a standard refrigerator in preparation for use.

Each cooler was set up in the following manner: 1 cold pack was placed in the bottom of cooler, then a 1000-mL bag of 0.9% saline, a cold pack, a 1000-mL bag of 0.9% saline,

Fig. 1 Mean temperatures of saline bags and ambient temperature (asterisk indicates P b .05 for all comparisons).

Fig. 2 Fractile percentage of bags 4?C or less at 24 hours.

and a cold pack on top. A temperature probe was inserted into each bag of saline through the port for the intravenous set. Each temperature probe was connected to a K-type thermometer (Lutron, Taipei Taiwan). In this phase of the experiment, the cooler was not a closed system. The lid of the cooler had to be kept ajar to allow for measurements of the fluid bags every 4 hours.

The cooler was then placed in the patient care compartment of the ambulance. An additional bag of 1000- mL 0.9% saline remained outside the cooler as a control. A thermometer was attached to the cooler to record the ambient temperature.

The experiment was conducted during August 2010. Ambulance crews were instructed to take the following measurements every 4 hours: temperature of the bottom bag, temperature of the top bag, temperature of the control bag, and ambient temperature in the ambulance.

In phase 2 of our experiment, we measured the temperature of top and bottom bags at the end of 24 hours during 7 consecutive days later in August 2010. This was done with the lid of the cooler closed for all 24 hours. The probe was not inserted into the IV bag until after 24 hours had elapsed. Phase 2 was also conducted during the summer months.

All measurements were recorded by the EMS providers and transferred into a Microsoft Excel spreadsheet (Micro- soft Corporation, Redmond, WA). Data were analyzed using a 2-tailed paired t test to compare the temperatures of the bottom bag and top bag of chilled saline against the control bag.

We also reported the fractile percentages of bags with temperatures less than 4?C and 6?C at the end of each 4-hour

Fig. 3 Fractile percentage of bags 6?C or less at 24 hours.

Table 1 Fractile percentage of bags at 24 hours (phase2)
	<=4?C	<=6?C
Top bag	93%	100%
Bottom bag	79%	93%

period. We also report the percentages of chilled saline bags less than 6?C during the follow-up experiment.

Results

The mean ambient temperatures over 24 hours ranged from 24?C to 27.2?C (Fig. 1). The mean temperature of the bottom bag of saline ranged from 0.6?C at 4 hours to 3.5?C at 24 hours. The mean temperature of top bag was 1.4?C at 4 hours and 5.7?C at 24 hours. The mean temperature of the control bag was 9.8?C at 4 hours and 26.8?C at 24 hours.

The mean temperatures of the top and bottom bags of saline were compared with the temperature of the control bag at all 4-hour intervals. Statistical significance (P b .05) was achieved at all time points.

At 12 hours, 100% of the bottom bags and 84.9% of the top bags were less than 4?C (Fig. 2). One hundred percent of the bottom bags and 93.9% of the top bags were less than 6?C (Fig. 3). At 24 hours, 93.6% of the bottom bags and 75% of the top bags were less than 6?C; 93.6% of the bottom bags and 56.3% of the top bags were less than 4?C.

During the follow-up experiment, 100% of the bottom bags and 94% of the top bags were less than 6?C (Table 1).

Discussion

With the 2010 AHA guidelines giving therapeutic hypothermia a level I recommendation, this modality is becoming a standard of care for patients with return of spontaneous circulation after nonTraumatic cardiac arrest.

In some EMS systems, such as New York City, victims of cardiac arrest are only transported to hospitals that provide postcardiac arrest hypothermia.

Early intra-arrest cooling may lead to better outcomes than starting cooling after return of spontaneous circulation [15,18,19]. In the future, prehospital hypothermia may be used for neuroprotection in other conditions such as stroke, lung injury, and spinal cord injury [20-23].

Our data demonstrate that saline can be kept chilled in ambulances for 24 hours using cold packs and coolers. The experiments were done under “real-life” conditions during the warmest part of the summer. Although a substantial amount of the top bags warmed to over 6?C during the initial phase of the experiment, phase 2 of our experiment showed that the cooler and cold packs reliably kept both bags of fluid under 6?C. We find little evidence of the superiority of saline

chilled to 4?C over 6?C. Although the infusion of normal saline at 4?C is safe, we know of no advantage over infusion saline at 6?C [16].

The estimated cost of our setup is less than $50.00 per ambulance including the coolers and the cold packs.

Our experimental design required the coolers be slightly ajar to allow for the temperature probes to be connected to the external thermometers. In the initial experimental design, 25% of the top bags were warmer than 6?C. However, measuring the saline bags in the second experiment showed that the coolers did in fact keep the saline chilled below 6?C. Although a previous study of out-of-hospital therapeutic hypothermia used chilled at saline 4?C, there are no published guidelines that recommend a specific tempera- ture for the infusion of chilled saline. The AHA, in its 2010 guidelines for postarrest care, does not make any recommendations as to the temperature of chilled saline or even the timing of when the saline should be given [7]. There are animal models that suggest that hypothermia provides better neurologic outcomes the earlier it is started, but there are no human research studies to validate this [18,24]. We feel that 6?C is an adequate temperature for saline to begin cooling Postcardiac arrest patients in the prehospital environment. Achieving a goal temperature range of 32?C to 34?C in the prehospital environment is not the purpose of this study. By initiating therapeutic hypothermia with chilled saline, the cooling process can be continued upon arrival at the emergency department where

additional methods can be used.

Conclusion

Using coolers and cold packs, changed every 24 hours, is an inexpensive way for EMS agencies to initiate prehospital hypothermia.

References

1. Holzer M, Behringer W, Schorkhuber W, Zeiner A, Sterz F, Laggner AN, et al. Mild hypothermia and outcome after CPR. Hypothermia for Cardiac Arrest (HACA) Study Group. Acta Anaesthesiol Scand Suppl 1997;111:55-8.
2. Bernard SA, Gray TW, Buist MD, Jones BM, Silvester W, Gutteridge G, et al. Treatment of comatose survivors of out-of- hospital cardiac arrest with induced hypothermia. N Engl J Med 2002;346(8):557-63.
3. Belliard G, Catez E, Charron C, Caille V, Aegerter P, Dubourg O, et al. Efficacy of therapeutic hypothermia after out-of-hospital cardiac arrest due to ventricular fibrillation. Resuscitation 2007;75(2):252-9.
4. Castrejon S, Cortes M, Salto ML, Benittez LC, Rubio R, Juarez M, et al. Improved prognosis after using mild hypothermia to treat cardiorespiratory arrest due to a cardiac cause: comparison with a control group. Rev Esp Cardiol 2009;62(7):733-41.
5. Holzer M, Bernard SA, Hachimi-Idrissi S, Roine RO, Sterz F, Mullner

M. Hypothermia for neuroprotection after cardiac arrest: systematic review and Individual patient data meta-analysis. Crit Care Med 2005;33(2):414-8.

1. Hinchey PR, Myers JB, Lewis R, De Maio VJ, Reyer E, Licatese D, et al. Improved out-of-hospital Cardiac arrest survival after the sequential implementation of 2005 AHA guidelines for compressions, ventilations, and induced hypother- mia: the Wake County experience. Ann Emerg Med 2010;56(4): 348-57.
2. Peberdy MA, Callaway CW, Neumar RW, Geocadin RG, Zimmerman JL, Donnino M, et al. Part 9: post-cardiac arrest care: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation 2010;122(18 Suppl 3): S768-86.
3. Kim F, Olsufka M, Carlbom D, Deem S, Longstreth Jr WT, Hanrahan M, et al. Pilot study of rapid infusion of 2 L of 4 degrees C normal saline for induction of mild hypothermia in hospitalized, comatose survivors of out-of-hospital cardiac arrest. Circulation 2005;112(5): 715-9.
4. Kim F, Olsufka M, Longstreth Jr WT, Maynard C, Carlbom D, Deem S, et al. Pilot randomized clinical trial of prehospital induction of mild hypothermia in out-of-hospital cardiac arrest patients with a rapid infusion of 4 degrees C normal saline. Circulation 2007;115(24): 3064-70.
5. Kamarainen A, Virkkunen I, Tenhunen J, Yli-Hankala A, Silfvast T. Induction of therapeutic hypothermia during pre- hospital CPR using ice-cold intravenous fluid. Resuscitation 2008;79(2):205-11.
6. Kamarainen A, Virkkunen I, Tenhunen J, Yli-Hankala A, Silfvast T. Prehospital therapeutic hypothermia for comatose survivors of cardiac arrest: a randomized controlled trial. Acta Anaesthesiol Scand 2009;53(7):900-7 [Randomized Controlled Trial].
7. Kamarainen A, Virkkunen I, Tenhunen J, Yli-Hankala A, Silfvast T. Prehospital induction of therapeutic hypothermia during CPR: a pilot study. Resuscitation 2008;76(3):360-3.
8. Hammer L, Vitrat F, Savary D, Debaty G, Santre C, Durand M, et al. Immediate prehospital hypothermia protocol in comatose survivors of out-of-hospital cardiac arrest. Am J Emerg Med 2009;27(5):570-3.
9. Skulec R, Truhlar A, Seblova J, Dostal P, Cerny V. Pre-hospital cooling of patients following cardiac arrest is effective using even low volumes of cold saline. Crit Care 2010;14(6):R231.
10. Castren M, Nordberg P, Svensson L, Taccone F, Vincent JL, Desruelles D, et al. Intra-arrest transnasal evaporative cooling: a randomized, prehospital, multicenter study (PRINCE: Pre-ROSC IntraNasal Cooling Effectiveness). Circulation 2010;122(7):729-36.
11. Bernard S, Buist M, Monteiro O, Smith K. Induced hypothermia using large volume, ice-cold intravenous fluid in comatose survivors of out- of-hospital cardiac arrest: a preliminary report. Resuscitation 2003;56(1):9-13.
12. Kampmeyer M, Callaway C. Method of cold saline storage for prehospital induced hypothermia. Prehosp Emerg Care 2009;13(1): 81-4.
13. Abella BS, Zhao D, Alvarado J, Hamann K, Vanden Hoek TL, Becker LB. Intra-arrest cooling improves outcomes in a murine cardiac arrest model. Circulation 2004;109(22):2786-91.
14. Bruel C, Parienti JJ, Marie W, Arrot X, Daubin C, Du Cheyron D, et al. Mild hypothermia during advanced life support: a preliminary study in out-of-hospital cardiac arrest. Crit Care 2008;12(1):R31.
15. Kim JH, Lee JY, Suk K. Therapeutic hypothermia in brain injuries and relatED diseases. Recent Pat Inflamm Allergy Drug Discov 2011;5(2): 155-64.
16. Hong SB, Koh Y, Lee IC, Kim MJ, Kim WS, Kim DS, et al. Induced hypothermia as a new approach to lung rest for the acutely injured lung. Crit Care Med 2005;33(9):2049-55.
17. Hammer MD, Krieger DW. Hypothermia for acute ischemic stroke: not just another neuroprotectant. Neurologist 2003;9(6):280-9.
18. Polderman KH. Induced hypothermia and Fever control for prevention and treatment of neurological injuries. Lancet 2008;371(9628): 1955-69 [Review].
19. Kuboyama K, Safar P, Radovsky A, Tisherman SA, Stezoski SW, Alexander H. Delay in cooling negates the beneficial effect of mild resuscitative cerebral hypothermia after cardiac arrest in dogs: a prospective, randomized study. Crit Care Med 1993;21(9):1348-58 [Research Support, Non-U.S. Gov’t].