This study was supported in part by a grant (CRI09050-1) from Chonnam National University Hospital Research Institute of Clinical Medicine.
Augmentation of the Cooling Capacity of Refrigerated Fluid by Minimizing Heat Gain of the Fluid Using a Simple Method of Cold Insulation
Version of Record online: 2 JUN 2010
© 2010 by the Society for Academic Emergency Medicine
Academic Emergency Medicine
Volume 17, Issue 6, pages 673–675, June 2010
How to Cite
Lee, B. K., Jeung, K. W., Lee, S. C., Min, Y. I., Ryu, H. H., Kim, M. J., Lee, H. Y. and Heo, T. (2010), Augmentation of the Cooling Capacity of Refrigerated Fluid by Minimizing Heat Gain of the Fluid Using a Simple Method of Cold Insulation. Academic Emergency Medicine, 17: 673–675. doi: 10.1111/j.1553-2712.2010.00748.x
- Issue online: 2 JUN 2010
- Version of Record online: 2 JUN 2010
- Received September 6, 2009; revision received November 17, 2009; accepted November 24, 2009.
- fluid therapy;
Objectives: This study was undertaken to determine how rapidly refrigerated fluids gain heat during bolus infusion and to determine whether the refrigerated fluids could be kept cold by a simple cold-insulation method.
Methods: One liter of refrigerated fluid was run through either a 16-gauge catheter (16G(–) and 16G(+) groups) or an 18-gauge catheter (18G(–) and 18G(+) groups) while monitoring the temperature in the fluid bag and the outflow site. In the 16G(+) and the 18G(+) groups, the fluid bag was placed with an ice pack inside an insulating sleeve during the fluid run.
Results: In the 16G(–) and the 18G(–) groups, the outflow temperature increased to 10–12°C during the fluid run. Meanwhile, outflow temperatures in the 16G(+) and the 18G(+) groups remained below 4.6 and 6.8°C, respectively. The temperatures differed significantly between the 16G(–) and the 16G(+) groups (p < 0.001) and between the 18G(–) and the 18G(+) groups (p < 0.001), respectively.
Conclusions: Substantial heat gain occurred in the refrigerated fluid even during the relatively short duration of bolus infusion. The heat gain could, however, be easily minimized by cold insulation of the fluid bag.
ACADEMIC EMERGENCY MEDICINE 2010; 17:673–675 © 2010 by the Society for Academic Emergency Medicine
Intravenous (IV) infusion of refrigerated fluid has been extensively used for the induction of hypothermia after cardiac arrest.1–3 Although it is a simple technique, the infusion of refrigerated fluid has been regarded as only moderately effective for reducing core temperature. In several studies, cooling rates only ranged from 0.7 to 0.8°C/L of refrigerated fluid infused.1–3
Ideally, the refrigerated fluid should be kept cold during infusion. However, theoretically, the refrigerated fluid can warm up considerably before reaching the patient because heat can flow down a temperature gradient from the ambient air to the refrigerated fluid during the infusion. The relative ineffectiveness of refrigerated fluids for IV cooling may have resulted partially from heat gain in the refrigerated fluid that negated the benefits of chilling the fluid, since an average of 20 to 30 minutes were required for infusion in the above studies.
This study was designed to determine the heat gains in the fluid bag and IV tubing during bolus infusion of 1 L of refrigerated fluid and to determine whether the refrigerated fluid could be kept cold during infusion by cold insulation of the fluid bag, using a commercially available insulating sleeve and an ice pack.
This was a laboratory investigation that was designed to simulate refrigerated fluid infusion for the induction of therapeutic hypothermia. Four groups, which differed according to catheter size and whether cold insulation of the fluid bag was used, were tested for comparison of warming trends during fluid runs.
The study was performed in a resuscitation room of an emergency department (ED). Every window and door of the resuscitation room was closed and every radiant energy source, such as a heat lamp, was turned off during the experiments. Each fluid bag was kept dry and was stored in the refrigerator (2°C) for at least 24 hours before use. After being taken from the refrigerator, the fluid was connected to an 180-cm-long, 2.8-mm internal diameter, ambient-temperature IV tubing (15 drops/mL, Cosmo Medical Inc., Metro Manila, Philippines) and hung on an IV pole. The height of the fluid level of the drip chamber above the end of the IV tubing was 88 cm for all trials. Two thermocouple probes (MT-23/8, Physitemp Instruments Inc., Clifton, NJ) were inserted via a rubber port into the fluid bag, and via a rubber injection port into the IV tubing, with the thermocouple threaded distally to the end of the IV tubing. The thermocouple probes were connected to BAT-12 digital thermometers (Physitemp Instruments Inc., Clifton, NJ).
The fluid run was started 2 minutes after taking the fluid bag from the refrigerator. A 1-L bag of lactated Ringer’s solution (Choongwae Pharma Co., Seoul, Korea) was used for each fluid run. Fluid was run through either a 16-gauge catheter (BD IV Catheter, Becton Dickinson Korea Ltd., Gumi, Korea) for the 16G(–) and the 16G(+) groups, or an 18-gauge catheter for the 18G(–) and the 18G(+) groups, at a wide-open rate to simulate a bolus infusion. In the 16G(–) and the 18G(–) groups, the fluid bag was exposed to room air during the fluid run. In the 16G(+) and the 18G(+) groups, the fluid bag was placed inside a commercially available, 2-L insulating sleeve (Liquitainer Wrap, Source Vagabond Systems, Tirat Carmel, Israel) with a reusable ice pack (Ice power 20 [18.0 × 9.7 × 4.3 cm], Windax, Seoul, Korea) after being taken from the refrigerator, so that the refrigerated fluid was in contact with the ice pack within the insulating sleeve during the fluid run.
During fluid runs, temperature data were collected at 1-minute intervals. Each experiment was repeated 10 times for each group. During each trial, concurrent ambient temperature and ambient humidity measurements were obtained from a thermometer/hygrometer (TH-611, Bokjung Scale, Seoul, Korea).
Continuous variables were investigated for normality by use of the Shapiro-Wilk test. Results are presented as mean (± standard deviation [SD]) for normally distributed variables and as median and interquartile range (IQR) for nonnormally distributed variables. The differences between the four groups were analyzed using either one-way analysis of variance (ANOVA) or the Kruskal-Wallis test. A repeated measures ANOVA with Bonferroni adjustments was used to assess the effects of group on temperatures. Values of p < 0.05 were considered to indicate statistical significance.
Ambient temperature was maintained at 26.1°C (±1.0°C) and ambient humidity at 36.5% (IQR = 29.0%–43.0%) during the study period. They were not different between the groups. The refrigerated fluids were run over 18.6 minutes (IQR = 17.8–19.6 minutes) in the 18G(–) group and over 18.4 minutes (IQR = 18.0–18.7 minutes) in the 18G(+) group (p = 0.705). Meanwhile, the refrigerated fluids were run over 12.3 minutes (IQR= 11.7–12.7 minutes) in the 16G(–) group and over 12.6 minutes (IQR 12.3–13.3 minutes) in the 16G(+) group (p = 0.199).
All four groups had essentially the same bag temperature just before taking the fluid bag from the refrigerator (p = 0.345). The changes in fluid bag and outflow temperatures during each run are shown in Figure 1. Both bag and outflow temperatures differed significantly between the 16G(–) and the 16G(+) groups (p < 0.001), and between the 18G(–) and the 18G(+) groups (p < 0.001). Fluid bag temperatures did not differ significantly between the 16G(–) and the 18G(–) groups or between the 16G(+) and the 18G(+) groups. Outflow temperatures did not differ significantly between the 16G(–) and the 18G(–) groups (p = 0.366), but they differed significantly between the 16G(+) and the 18G(+) groups (p = 0.001).
At 1 minute after the start of the fluid run, the temperature gradient between the outflow site and the fluid bag (Toutflow-fluid bag) was 2.1°C (±0.3°C) in the 16G(–) group and 2.8°C (±0.4°C) in the 18G(–) group. Thereafter, Toutflow-fluid bag continued to decrease in both groups until measurement ended (Figure 1). Toutflow-fluid bag differed significantly between the two groups (p = 0.001).
In this study, when 1 L of 2–3°C refrigerated fluid was administered via standard IV tubing without insulation, the outflow temperature increased rapidly to 10–12°C during bolus infusion, which indicates that substantial heat gain occurs in the refrigerated fluid during IV cooling. The heat gain was, however, easily minimized by cold insulation of the fluid bag using an insulating sleeve and an ice pack.
Heat gain in refrigerated fluid during infusion can occur both in the fluid bag and in the IV tubing. In this study, the Toutflow-fluid bag, which indicates heat gain along the length of the IV tubing, differed significantly between the 16G(–) and the 18G(–) groups. The fluids were run under the same preparation conditions, except that the catheters connected to the IV tubing differed between the 16G(–) and the 18G(–) groups. Thus, the difference in infusion rate produced the above differences in the Toutflow-fluid bag. This finding indicates that increasing the rate of infusion significantly reduces heat gain in the refrigerated fluid in the IV tubing. Meanwhile, despite the Toutflow-fluid bag decreasing over time, the outflow temperatures increased over time both in the 16G(–) and the 18G(–) groups. These findings suggest that the increase in the outflow temperature over time is likely more attributable to heat gain of the fluid in the fluid bag than along the IV tubing.
On the basis of the findings in this study, cold insulation of the fluid bag, using an insulating sleeve and an ice pack, should help to increase the rate of cooling. This is important because the speed of cooling is a key factor in realizing the protective effects of hypothermia.4–8 We believe that cold insulation of the fluid bag, using an insulating sleeve and an ice pack, is one of the most practical and cost-effective options for speeding up the process of IV cooling, because all that is required, after purchase of a $14.40 insulating sleeve and a $1–$2 ice pack, is a minor alteration in refrigerated fluid infusion—that is, placing the fluid bag with an ice pack inside the insulating sleeve.
The study was performed in an ED to simulate an in-hospital setting. In prehospital settings, much variation exists in the ambient conditions encountered, which may limit the field application of these results. Also, we did not assess the efficacy of refrigerated fluid infusion on lowering core temperature. Further prospective clinical studies are needed to ascertain the clinical efficacy of cold insulation methods.
Substantial heat gain occurs in refrigerated fluid during the relatively short duration of bolus infusion. The heat gain could, however, easily be minimized by cold insulation of the fluid bag using a commercially available insulating sleeve and an ice pack. Therefore, we recommend the use of cold insulation of the fluid bag as an accessory tool when the clinical decision is made to induce hypothermia using infusion of refrigerated fluid.