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Minnesota Vikings, Eden Prairie, MN (Otte); Athletic Training Division, Ohio State University, Columbus, OH (Merrick); and Athletic Training Department, Indiana State University, Terre Haute, IN (Ingersoll, Cordova)
Minnesota Vikings, Eden Prairie, MN (Otte); Athletic Training Division, Ohio State University, Columbus, OH (Merrick); and Athletic Training Department, Indiana State University, Terre Haute, IN (Ingersoll, Cordova)
Minnesota Vikings, Eden Prairie, MN (Otte); Athletic Training Division, Ohio State University, Columbus, OH (Merrick); and Athletic Training Department, Indiana State University, Terre Haute, IN (Ingersoll, Cordova)
Minnesota Vikings, Eden Prairie, MN (Otte); Athletic Training Division, Ohio State University, Columbus, OH (Merrick); and Athletic Training Department, Indiana State University, Terre Haute, IN (Ingersoll, Cordova)
CYOTHERAPY IS COMMONLY used for the treatment of acute musculoskeletal trauma. The acute use of cryotherapy is based on the belief that it can reduce secondary hypoxic and enzymatic injury.
have reported IM temperature at specific depths relative to the subcutaneous adipose layer. With a 30-minute ice-bag application to the thigh, 1cm subadipose IM temperature has been reported to decline by 9.7°C,
By measuring the decrease in IM temperature with cryotherapy, we believe that we are indirectly measuring the effectiveness of the treatment. Although a decrease in tissue temperature is believed to limit secondary injury
researchers have not yet attempted to describe the optimal temperature for limiting secondary injury with acute trauma.
One factor suspected to influence the ability of cryotherapy to cool tissues is subcutaneous adipose tissue thickness. Subcutaneous adipose tissue insulates the body against heat loss.
Individual differences in adipose tissue thickness result in different degrees of insulation. Considering the variation in the thickness of adipose tissue that exists between patients of various body types and the insulating effects of this adipose tissue, it is difficult to justify a standard duration clinical protocol for cryotherapy. Although this difficulty in justifying a standard duration seems intuitive, the specific effect of adipose thickness on cryotherapy treatment duration has not yet been described. Given this, clinical cryotherapy treatments are typically applied for 20 to 30 minutes regardless of adipose tissue thickness.
from our laboratory, the thickness of the subcutaneous adipose tissue layer appears to explain some degree of the variation in reported IM temperatures. We have speculated that adipose thickness might also have an influence on the necessary duration of cryotherapy treatments such that patients with different adipose tissue thickness may need different cryotherapy treatment durations to reach similar tissue temperatures. However, we have not previously examined the relationship between adipose thickness and necessary cooling time, nor have we been able to find such an examination in the literature. Therefore, the purpose of this study was to examine the effects of subcutaneous adipose tissue thickness on the cryotherapy duration necessary to produce a standardized IM cooling effect. Because no optimal IM temperature has yet been reported, we have elected to use a fairly typical effect, a reduction of 7°C from baseline, as our defined standard effect in this study.
Methods
A between-groups design was used. The independent variable was adipose tissue thickness as represented by anterior thigh skinfold thickness. The 4 levels of the independent variable were skinfold of 0 to 10mm (n=10), 11 to 20mm (n=20), 21 to 30mm (n=11), and 31 to 40mm (n=6). The dependent variable was continuous cryotherapy duration necessary to produce an IM temperature reduction of 7°C from baseline at a depth of 1cm subadipose in the anterior thigh.
Participants
Forty-seven (29 women, 18 men) healthy volunteers gave informed consent and volunteered to participate in this study (mean age ± standard deviation [SD], 23±3y; height, 168.0±17.1cm; mass, 71.1±21.1kg). All subjects were healthy and reported being free of vascular disease and neurologic disorders as determined through a health status questionnaire. Subjects with skinfold measurements greater than 40mm were excluded from this study because technical limitations prevented proper placement of the IM temperature sensor in such individuals. The School of Health and Human Performance Human Subjects Committee at Indiana State University approved the procedures used in this study.
Instruments
A portable temperature data logger (Model U-22100-00)a and thermocouples were used for all temperature measurements. Fine-wire implantable type-T thermocouples (diameter,.23mm, Model U-08506-70),a inserted using a sterile hypodermic needle (21G×3.8cm), were used for IM temperature measurements. Implantable thermocouples were disinfected by immersion in CidexPlus 3.4% glutaraldehyde solutionb for a minimum of 20 minutes. Ambient temperature measurements were made using an exposed-junction type-T thermocouple (Model U-08505-85).a Skinfold calipers (Slim Guide)c were used to measure anterior thigh skinfold thickness. This type of caliper was used because it allows for measurement of larger skinfolds than is possible with the more common Lange-type calipers.
Experimental procedures
Subjects were positioned supine on a treatment table while wearing shorts and t-shirts. The vertical, midanterior thigh skinfold was measured using the standard technique.
Dividing this measurement in half yielded a reasonable estimate of the thickness of the adipose tissue. Adding 1cm to this thickness provided the depth at which the IM thermocouple was to be implanted, resulting in a placement at 1cm deep to the adipose layer, as has been previously described.
Using hair clippers,d the skin over the thermocouple insertion site was prepared by removing the hair from a 4×4cm area on the anterior thigh halfway between the anterior superior iliac spine and the superior pole of the patella. This area was cleaned by first wiping it with an alcohol swab and then swabbing it with a povidone-iodine surgical scrub solution for 30 seconds in a circular pattern moving out from the center.
a single, implantable thermocouple was inserted in the center of the swabbed area using a sterile hypodermic needle oriented perpendicular to the skin. Depth of insertion was controlled by means of a mark made on the lead of the thermocouple, 6cm from its tip. Subtracting the measured distance between the skin surface and this mark allowed for calculation of the actual insertion depth of the thermocouple. As mentioned previously, the thermocouples were inserted to a depth equal to half the skinfold measurement plus 1cm. Immediately after thermocouple insertion, the hypodermic needle was carefully withdrawn along the thermocouples lead wire, leaving the thermocouple in the tissue. After needle removal, actual insertion depth was remeasured to ensure that the thermocouple had not been accidentally withdrawn. The thermocouple lead was then secured to the skin using 2 pieces of 2×2cm Dermaclear tape.b One piece of tape was placed directly over the point where the thermocouple lead entered the thigh and a second piece to secure the lead to the thigh approximately 5cm from the insertion site. A nonimplantable thermocouple was kept free of contact to measure ambient temperature.
Treatment sessions consisted of applying ice to the prepared area on the anterior thigh. The treatment began with a 2-minute pretreatment baseline period during which temperature was measured every 30 seconds. The temperatures were quite stable during this period, and the temperature at the end of the 2-minute period was used as the baseline. The target temperature at which the treatment would be concluded was a decrease of 7°C from this baseline. Following pretreatment baseline measurement, a 750g bag of crushed icee with the air evacuated was placed over the thermocouple insertion site on the anterior thigh. Temperature data were continually recorded at 30-second intervals until the IM temperature decreased by 7°C and the temperature was at or below this level for 60 seconds. The initial time at which the 7°C drop was reached was recorded as the dependent variable.
After the application period, the Teflon®-coated thermocouples were carefully withdrawn, wiped clean, and disinfected by immersion in CidexPlus. Hypodermic needles were disposed of in a sharps container. The small needle stick wound was dressed with antibiotic ointment and adhesive bandages. Each subject was given a wound care sheet outlining the signs of infection and providing instructions on the care of the wound.
Statistical procedures
A 1-way analysis of variance was used to determine if the 4 skinfold groups differed on time to cool 7°C from baseline. To identify specific group differences, post hoc tests were performed by using the Tamhane T2 multiple-comparison procedure because it does not assume homogeneity of variance
and our data violated homogeneity (Levene statistic3,43=.007). Experimentwise type I error rate (α) was set a priori at P equal to.05.
Results
Mean time for 1cm subadipose IM temperature to decrease 7°C differed across groups (F3,43=62.46, P=.000, η2=.81, 1−β=1.0). Differences were observed between all groups (all pairwise instances of the Tamhane T2; P≤.03), with thicker adipose requiring longer cooling time. The relationships of group to cooling time were as follows (mean ± SD): 31 to 40mm (58.6±11.7min), 21 to 30mm (37.8±9.6min), 11 to 20mm (23.3±6.7min), and 0 to 10mm (8.0±3.4min) (fig 1).
Fig. 1Cryotherapy duration to decrease thigh 1cm subadipose IM temperature 7°C (mean ± SD).
Cryotherapy is thought to slow the metabolic processes of cells within and adjacent to the site of injury, perhaps allowing them to better survive the sequelae of primary injury.
It is believed that a reduction in the metabolic demand of a tissue through local hypothermia allows for sustained life under the conditions that follow acute trauma.
quantified adenosine triphosphate (ATP) and phosphocreatine levels using 31P nuclear magnetic resonance in amputated cat hindlimbs. They reported that, with the exception of 1°C, lower storage temperatures resulted in better ATP sparing. At 1°C, on the other hand, tissues used more ATP than in limbs at higher temperatures. Therefore, it would appear that when tissues are cooled to 1°C, stimulation of some ATP degrading process occurs.
were below 20°C, the study has somewhat limited clinical applicability in treating acute musculoskeletal injury.
Because the optimal IM temperature at which cryotherapy is effective is not yet known, we chose to use a fairly typical temperature change of 7°C as our dependent variable. A review of literature relating to the anterior thigh and various forms of cryotherapy revealed a change of at least 7°C has occurred with nearly all similar treatment durations and forms of cryotherapy.
We do not intend to imply that a change of 7°C is in any way optimal or that it has a sound theoretical basis as a target temperature for cryotherapy treatments. We merely used this temperature because it was fairly representative of a “typical” treatment, and we therefore were working on the assumption that the positive effects associated with cryotherapy would occur with such a treatment. Our purpose was not to examine the efficacy of cryotherapy but to examine a specific aspect of its application.
Cooling time
Clinically, cryotherapy is typically applied using a predetermined treatment mode and duration. For acute care, the most common protocol is probably applying ice bags or immersing the body part in ice water for 10 to 30 minutes or ice massage for 7 to 10 minutes.
During these applications, the temperature of skin decreases, followed by the temperature of subcutaneous and then muscular tissues, respectively, as heat is absorbed initially from the superficial tissues and subsequently from the underlying muscle by the ice treatment. We observed that the thickness of the subcutaneous tissues, particularly adipose tissue, appears to affect the rate of thermal conduction. As the thickness of adipose tissue increases, the time needed for heat to be transferred through it must also increase.
The ability of adipose thickness to influence cooling time is related to its thermodynamic properties. The thermal conductivity of adipose tissue is low (.19W·[m·°C])−1) when compared with other biologic tissues (skin,.96W·[m·°C]−1; muscle,.64W·[m·°C]−1).
The relatively low value of these thermodynamic properties suggests that heat does not transfer well through adipose tissue. In other words, the insulating effect of adipose is somewhat greater than other tissues. Similarly, the greater the thickness of the adipose, the greater the distance that heat must be conducted, also prolonging the time necessary for IM cooling.
Investigations attempting to correlate adipose tissue thickness to IM temperature present conflicting results.
Intuitively, we would expect to see an indirect relationship between adipose thickness and IM cooling during cryotherapy where, as adipose gets thicker, we would expect to see less cooling. Such a relationship has been observed in previous studies.
). These low correlations suggest that adipose tissue thickness may have little effect on the ability to predict IM temperature. At the same time, these low correlations must be examined in proper context. In the study by Jutte et al,
adipose thickness was examined with several other variables in a multiple correlation study, and it is possible that some of the variance that might otherwise be accounted for by adipose was redundant with other variables, leading to a small partial correlation. In the other study showing a small correlation, Zemke et al
reported that the relationship was direct as mentioned earlier. This counterintuitive suggestion that thicker adipose tissue leads to improved cooling causes us to have reservations about drawing inferences based on the data they reported. Although these 2 studies show small relationships, there are also data to suggest that body composition and IM temperature possess a strong relationship (r=.81)
Our data suggest that adipose thickness does indeed have a strong influence on cooling. Across all groups, cooling time increased rather dramatically as skinfold thickness increased (fig 1). Although a 20-minute treatment will produce a typical effect in patients with skinfolds of less than 20mm, patients with skinfolds between 20 and 30mm require nearly twice as long (38min) and patients with skinfolds in the 30 and 40mm range require 3 times as long, an almost unheard of 59-minute treatment, to produce the very same temperature effect. Based on our findings, we offer table 1 as a clinical recommendation for cryotherapy duration required to produce a typical cooling effect. Note that we are not implying that this effect is optimal. Optimal cooling has yet to be adequately identified.
Table 1Recommendations for cryotherapy treatment duration to produce a typical effect in most patients
Skinfold Thickness
Required Treatment Duration
0–10mm
12min
11–20mm
30min
21–30mm
40min
31–40mm
60min
NOTE. Recommendations should produce a standardized effect but not necessarily an optimal effect. Optimal temperature and treatment duration to reach it are presently unknown.
We have observed that the current common practice of using standardized treatment durations for patients regardless of their adipose thickness yields nonuniform temperature changes. For example, at 20 minutes into the treatment, substantially different changes in tissue temperature were observed between subjects with differing adipose thickness (fig 3).
Fig. 3IM temperature change across groups at 20 minutes of cryotherapy.
We speculate that these differing temperature effects might produce differing clinical outcomes. A standard treatment of 20 minutes, or of any other common length for that matter, is inadequate when the goal is to produce standardized IM temperature changes in patients with differing body compositions. Instead, we recommend using a varying range of cryotherapy durations that are based on the relative thickness of the adipose at the treatment site (table 1). Again, note that the treatment durations that we recommend are intended to produce a relatively uniform cooling effect in subjects with widely differing adipose thickness. They are intended to produce a typical treatment and not necessarily an optimal treatment. Although it is reasonable to speculate that our different groups would require different cooling durations to reach an optimal IM temperature, the exact duration needed to reach such an optimal temperature is not known because the optimal temperature has not yet been identified.
Conclusions
We observed that as the thickness of adipose tissue increases, the cryotherapy treatment duration required to decrease IM temperature by a standard amount (7°C) increases rather dramatically. We suggest that the current common clinical practice of applying cold for 10 to 30 minutes is only adequate for relatively lean patients and is not at all adequate for patients with skinfolds exceeding 20mm. We suggest that skinfold thickness be used as a guide when determining cryotherapy duration. This implies that, whenever possible, skinfold thickness should be measured or, at the very least, estimated before the use of cryotherapy.
☆1Supported by a Graduate Student Research Grant, School of Graduate Studies, Indiana State University.
☆2No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated.
☆3Correspondence to Mark A. Merrick, PhD, ATC, Athletic Training Division, Ohio State University, 1583 Perry St, Columbus, OH 43210-1234, e-mail: [email protected] . Reprints are not available.
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