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The viability of soft tissues in elderly subjects undergoing hip surgery

Age and Ageing, March, 1998 by Dan L. Bader, Steven H. White

Introduction

Pressure sores are a major cause of morbidity and prolonged hospital stay. Although the overall prevalence in hospitals in the UK is about 9% [1], this figure rises with age and ill-health [2]. Versluysen [3] reported an incidence of 32% overall in elderly patients who were admitted for elective hip surgery or management of proximal femoral fractures. Of these, 17% were present on admission, and of the remainder, 34% developed sores within the first week and a further 24% in the second week. In this comprehensive study, 16% developed a sore on the day of operation, suggesting that the day of surgery appears to be a critical period for sores to develop [4].

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If body tissues are subjected to pressures which are applied in a non-uniform manner, then localized tissue damage can result. This occurs in many situations in which the body is placed on a support surface. Thc resulting stress and strain fields within the soft tissues may be sufficient to impair both the local blood supply, causing hypoxia, and the lymphatic circulation, resulting in an accumulation of toxic intracellular metabolites. If unfavourable interface conditions are prolonged, cell necrosis will follow, leading to local tissue breakdown and the development of pressure sores. Prolonged ischaemia reperfusion may also promote tissue damage [5], possibly due to the production of oxygen-derived free radicals [6].

The sacrum and greater trochanters have minimal soft tissue covering and have an inherent high compressive stiffness; these are two of the most common sites for pressure necrosis. The biomechanical changes associated with ageing may also predispose the soft tissues to breakdown in elderly people. Intermittent reductions in interface pressure allow higher pressures to be tolerated over prolonged time periods [7]. This forms the basis of pressure relief regimes, which are performed by regular turning of susceptible patients and lifting off of the support surface. The nature of tissue recovery following ischaemia is determined by the resilience of the specific tissues, including the blood and lymph vessels, systolic blood pressure and the reactive hyperaemic response. All these factors are likely to be affected by age [8].

The protective process of discrete movement associated with ischaemic discomfort is present in the normal sleep pattern but is obliterated during deep levels of surgical anaesthesia. Sudden reperfusion, as with rapid intravascular fluid administration, or sudden release of the source of external pressure, can be harmful as they can cause local capillary collapse, exacerbating the ischaemia and resulting in necrosis [9]. Elderly patients undergoing surgical treatment tot proximal femoral fracture are at still greater risk of pressure sore development for they have severely limited mobility, often sit or lie on hard surfaces and are unable to turn due to the painful hip fracture [10]. They may also be malnourished [11]. Cardiac failure and atherosclerosis further impair the skin's circulation, and sensation may also be affected as a result of a stroke, analgesia or pre-medication.

The Oxford Pressure Monitor provides an accurate measure of the pressure distribution at the patient-support interface [12]. However, the measurement of interface pressure alone is not sufficient to alert the clinician to potential areas of tissue breakdown. Some measure of tissue viability is required which is dependent upon an adequate supply of nutrients as supplied by the blood. Transcutaneous oxygen tension measurements ([T.sub.c][PO.sub.2]) have been used to objectively assess tissue viability in various clinical conditions, such as ischaemic limbs [13]. There is wide variation in the integrated pressure and time which the soft tissues will tolerate [14]. The applied pressures to produce, for example, a 50% reduction in the unloaded resting value of [T.sub.c][PO.sub.2] range from 3.0 kPa (22 mmHg) to 12.2 kPa (92 mmHg). This highlights the individual nature of the tissue response, which should be determined before clinical guidelines of safe pressure levels can be established.

The present study investigates the effects of support pressures on objective measures of soft tissue viability in a group of elderly patients undergoing surgery for fracture of the proximal femur.

Materials and methods

Ethical approval of this study was obtained from the central Oxford research ethics committee. The study comprised 10 patients--seven women and three men--who underwent dynamic hip screw fixation of their proximal femoral fractures. The mean age was 84 years (range 67-95 years).

On admission to the ward, skin traction was applied to the patient's leg to stabilize the fracture. Intramuscular analgesia was usually administered. The median waiting time between admission and surgery was 12 h (range 2-72 h). Intravenous fluid rehydration was provided in the interim. Fracture fixation was performed with the patient supported on a standard orthopaedic table which is both hard and narrow to give good stability and ease of access for the surgeon (Figure 1). The sacrum and coccyx transmitted the whole weight of the lower trunk through a small surface area. The patient's feet were supported in shoes attached to the table by adjustable arms to allow positioning and traction of the lower limbs. The reactive force against traction was a small area, a circular cylindrical support against the perineum. The following measurements were made at the sacrum anti the contralateral hip:

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The viability of soft tissues in elderly subjects undergoing hip surgery

Age and Ageing, March, 1998 by Dan L. Bader, Steven H. White

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