When are the seeds of postoperative pressure sores sown?

Pressure sores are often thought to be slothful chronic wounds forming slowly because of poor nursing.¹ In fact, they are acute injuries which develop rapidly when compression of tissues causes ischaemia and necrosis during serious illness and trauma, including surgery.² Many of the situations predisposing to pressure sores are well known (though often less well acted on), but those that arise before, during, and after surgery deserve more attention than they have received. In the United States it has been suggested that up to a quarter of pressure sores that develop in hospital originate in the operating theatre.³

Protracted squeezing of tissues between weight bearing surfaces and bony prominences cannot account for the whole pathogenesis of bedsores. An endogenous factor must be invoked that is common to the diverse conditions predisposing to pressure injury—namely, old age, malnutrition, alcohol abuse, diabetes, advanced cancer, terminal illness, sepsis, and vascular and neurological disease. These are all conditions in which multiple organs tend to fail because of failure of the microcirculation. Accordingly, pressure sores should be viewed as the result of yet another organ failure—that of the peripheral circulation. The microcirculation has long been overlooked as an organ whose function can fail. When it does, normally harmless pressures damage tissues.⁴

The pathophysiology of peripheral circulatory failure includes impairment of capillary vasomotion and of reactive hyperaemia—the vasodilation in response to hypoxia and catabolites. Blood flow is diverted through arteriovenous shunts away from capillaries. Capillary thrombosis, tissue hypoxia, and necrosis result, even though total tissue blood flow need not be reduced.⁵ Pressure sores are thus the pathological result of peripheral circulatory failure. But when do peripheral circulatory failure and pressure sores threaten surgical patients? In vulnerable patients the seeds of postoperative pressure sores, like those of postoperative deep vein thrombosis, are often sown in the operating theatre, and, as with venous thrombosis, prophylaxis must begin before surgery.

Indeed, particularly in emergency surgery, predisposing conditions arise before the patient even reaches the operating theatre. Lying on standard accident and emergency department trolleys generates high pressures on the sacrum and heels, and long waiting times are common.⁶ Dehydration due to withholding of oral fluids increases tissue deformability.² Effective analgesia is unlikely to be given at this stage (or later for that matter), and pain prevents patients from moving and increases oxygen demand⁷—both factors that endanger tissues.

Anaesthetists’ drugs may precipitate peripheral tissue damage. Sedatives, hypnotics, and anaesthetics reduce awareness of pressure discomfort and induce immobility. They may cause hypotension and peripheral hypoperfusion.⁸ Vasoactive amines reverse hypotension at the expense of tissue perfusion. Excess oxygen may cause overproduction of toxic free radicals in elderly patients (S Muravchick, Age Anaesthesia Association and British Geriatrics Society, London, 1998). It is surprising that no study has yet addressed the likely link between anaesthesia—spinal or general—with its hypotensive episodes and the development of pressure sores; this may be because anaesthetists are usually unaware of damages suffered by tissues in theatre (S Muravchick, Age Anaesthesia Association and British Geriatrics Society, London, 1998).

Conditions on the operating table itself may also predispose to pressure sores. The use of warming blankets under patients increases the risk of pressure damage.⁹ Extracorporeal circulation for cardiovascular procedures has been shown to be associated with pressure sores, most of which developed intraoperatively.¹⁰ Elderly patients with femoral neck fractures—another high risk group—develop them early, “chiefly in the first week,” remarked Sir James Paget in 1862.¹¹ They often appear on the day of operation.⁶ It is not just the patient, but every part of his or her body, that must survive the operation. A full thickness peripheral tissue injury is a disaster and a justifiable cause of litigation. Clinicians should take care to ensure adequate peripheral perfusion in pressure areas during operations on susceptible individuals. The development of effective pressure relieving supports for use in theatre is long overdue. Large celled alternating pressure mattress overlays, as used in wards, may be too unstable, but smaller celled models may be adequate and are worth testing in well designed studies.

Guidelines for postoperative management rarely recommend pressure relieving supports in high risk situations, although sores may be prevented if they are used.⁹ Instead, emphasis is placed on “early ambulation.” However, when impossible, because of illness or debilitation, ambulation consists of sitting—“early angulation” (VV Kakkar, personal communication). Weak patients are slumped in chairs, where it is more difficult for them to move and pressure relief is less effective than on pressure relieving mattresses.² Nursing postoperative patients in chairs causes exhaustion, reduces peripheral blood flow, and prevents sleep (which is essential for healing). Failing postural reflexes aggravate hypotension, dependent oedema forms, and renal function is depressed. Placing the feet on a footstool does not help and increases pressure on the buttocks and heels. Compression stockings do not control oedema and can themselves cause pressure sores.⁴ In a crossover study, pressure sores were found to be less frequent in patients with fractures allowed to sit for two hours or less per session than in those in whom chair nursing was unlimited.¹² Postoperative epidural analgesia, which can decrease sensation and mobility, has been associated with the development of severe sacral sores in elderly patients (IA Donovan, personal communication).

Until the prevention and management of peripheral circulatory failure, both inside and outside the operating theatre, becomes part of every doctor’s training, pressure injuries will continue to torture patients and keep their carers busy when it is too late.