Temperature Modulation of Pressure Ulcer Formation: Using a Swine Model

Paul A. Iaizzo, PhD

Disclosures

Wounds. 2004;16(11) 

In This Article

Abstract and Introduction

Developing reliable animal models as a means to study the etiology, prevention, and/or treatment of pressure ulcers is not a simple task. Numerous considerations need to be evaluated for appropriateness, such as similarity of the cutaneous layers to those of humans, reproducibility of injuries, the effects of administered anesthetic or analgesic agents, the locations of the created lesions, the typical rates of healing (controls), and/or the overall health status of the animals. The author's laboratory previously developed one such model: a porcine model to aid in investigations of pressure ulcer formation, healing, and prevention. The author and colleagues specifically studied the relationships between temperature, pressure, and time in the formation of cutaneous and/or deep tissue injuries. To do so, an apparatus and procedure were created to apply 12 metal discs (each with a diameter of 51mm) to the dorsal aspect of the swine. At equal pressures ranging between 10-150mmHg, four discs were applied for 1 to 10 hour periods, while their temperatures were servo-controlled between 25-45°C. The severity of resultant tissue injuries correlated with increases in applied parameters. Briefly, no damage was observed in the superficial or deep tissues underlying the sites of the 25°C pressure discs even with 10 hours of applied pressure. Only deep tissue damage resulted from the application of the 35°C discs for five hours, and the application of higher temperatures for shorter durations caused both cutaneous and subdermal damage. In addition, degrees of healing could be easily monitored in such animals for months and was typically uniform relative to the degree of induced damage. This animal model of temperature-modulated pressure ulcers has the potential for significant use in all major areas of this field, i.e., wound formation, healing, and prevention. The use of this approach on transgenic individuals or those with induced disease would also be of great interest.

There remains a need to optimize various animal models to investigate cutaneous and/or pressure-related ulcers. Singer and McClain recently noted that significant medical advances are dependent on the performance of fundamental basic and clinical research, and a key component of a comprehensive strategy is the development and validation of standardized experimental animal models.[1] To this end, the author's laboratory sought to develop a comprehensive swine model to evaluate and reproducibly create cutaneous and/or deep tissue injuries that were the result of imposed pressures to the skin at various temperatures for given durations.[2,3,4,5,6,7] As with many wound models involving cutaneous tissues, domestic swine were employed in the author and colleagues' approach due to the fact that pigs' skin resembles that of humans both structurally and functionally.[1,2,8,9,10]

Although extensive literature exists concerning pressure ulcers, no clear consensus is apparent for the etiology of such wounds, and this is likely dependent on multiple factors.[11,12,13,14,15,16,17] To illustrate the prevailing uncertainties, previously reported animal studies show the progression of a pressure ulcer may occur in either direction, i.e., from muscle upward[12,13,14] or from the upper dermis downward.[15] The application of elevated pressure (approximately > 90mmHg) over time (several hours) on a bony prominence is believed to be the primary factor in the causation of these ulcers.[6,10] Other ancillary factors include the magnitude of shear, friction, and/or moisture.[14] However, it has been shown that pressure thresholds for wound causation (defined by other models) are routinely surpassed clinically without apparent damage to tissue, e.g., in paraplegic patients without other complications as reported by Patterson and Fisher.[16] On the other hand, other patients may experience tissue damage before such determined thresholds are reached; hence, supplementary physiological factors, which include age, nutrition, psychologic factors, sensory loss, mobility, and/or temperature, warrant consideration.[18,19] It is noteworthy that the role of temperature in the causation of pressure ulcers has not been well explored. With such variations, it is a challenge to develop a reliable model for such responses. Yet, the author's laboratory was able to do so using creative engineering approaches. The following is a brief summary of protocols, instrumentation, and methodologies employed for producing reproducible wounds and a description of several potential means for their assessment that were part of the author's series of investigations. The reproducibility and consistency of the created wounds were established by histological evaluation of the application sites.

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