Microbiological evaluation

The challenge of microbiological evaluation is to distinguish between bacterial invasion and colonization.

Blood cultures or cultures of deep-tissue biopsy specimens generally are more clinically significant than are cultures of superficial swab spec­imens or aspiration of the pressure ulcer (Rudensky B, 1992).

However, aspirated samples of clinically non-infected ulcers have also been shown to contain bacteria in 30% of cases (Nicolle LE, 1994).

Guidelines for microbiological evakluation are :

On the basis of the aforementioned information, it can be concluded that

(1) superficial swab cultures generally reflect colonization rather than infection and are not useful clinically,

(2) needle aspirations are difficult to interpret and either should not be used or should be interpreted with caution, and

(3) culture results by themselves, even results of bone culture or culture of other deep-tissue biopsy specimens, should not be used as the sole criterion for infection without clinical or histo-pathological evidence of infection.

 

 

Imaging Studies

Imaging studies are useful in the evaluation of pressure ulcers for determination of the presence of osteomyelitis and for de­lineation of the extent of deep-tissue involvement.

 

Plain radiography.

Plain radiographs have a limited role in the evaluation of pressure ulcers.

Bony changes, such as periosteal reactive changes and heterotopic new bone formation usually associated with osteomyelitis, can also be present in non-infected pressure ulcers.

Furthermore, lytic bony lesions rarely are seen in cases of osteomyelitis associated with pressure ulcers (Darouiche RO, 1994).

Sinograms can be useful to define the extent of the ulcer, but their value probably has diminished with the avail­ability of CT and MRI.

 

CT and MRI.

CT may be more useful for definition of the extent of deep soft-tissue damage associated with pressure ulcers.

Although highly specific, CT has a relatively low sen­sitivity for the diagnosis of associated osteomyelitis (11%) (Lewis VL, 1988).

MRI is more useful for the detection of osteomyelitis associated with pressure ulcers.

 

Radionuclide scintigraphy.

Although 3-phase technetium-99m diphosphate bone scans and gallium scintigraphy are very useful in the diagnosis of hematogenous osteomyelitis, they have been shown to lack specificity for the detection of osteomyelitis caused by pressure ulcers (Bergstrom N, 1994).

 

 

Therapy

The goals of treatment of infected pressure ulcers are to re­solve the infection and to aid in wound healing. Implemen­tation of the appropriate therapy requires an understanding of the risk factors and pathophysiology that lead to pressure ulcer formation.

 

Treatment to aid in wound healing.

Attention should be given to promoting healing of the pressure ulcer itself, in ad­dition to treating infection.

This requires ameliorating both intrinsic and extrinsic risk factors and providing meticulous local wound care.

Although many intrinsic risk factors for the development of pressure ulcers are not amenable to intervention, some comorbid conditions associated with delayed wound healing, such as poor nutritional status, congestive heart failure, and diabetes mellitus, can be optimally controlled (Herman LE, 1989).

 

Dressings that maintain a moist wound environment facilitate healing and can be used for autolytic debride-ment (Kerstein MD, 2001).

Synthetic dressings reduce caregiver time, cause less discomfort, and potentially provide more consistent moisture (Hess CT, 2002).

These dressings include transpar­ent films, hydrogels, alginates, foams, and hydrocolloids.

Transparent films effectively retain moisture, and may be used alone for partial-thickness ulcers or combined with hydrogels or hydrocolloids for full-thickness wounds. hydrogels can be used for deep wounds with light exudate. Alginates and foams are highly absorbent and are useful for wounds with moderate to heavy exudate. hydrocol-loids retain moisture and are useful for promoting auto-lytic debridement.

Dressing selection is dictated by clinical judgment and wound characteristics; no moist dressing (including saline-moistened gauze) is superior (Bouza C, 2005).

 

There is evidence that patients who have a high protein intake may experience improved wound healing, compared with patients who have an inadequate caloric intake of protein.

Supplemen­tation with enteral feeding, however, has not been demonstrated to improve wound healing or prevent pressure ulcers (Thomas DR, 1997).

 

Reduction of extrinsic factors (in particular, pressure relief) is a cornerstone of therapy.

There is no evidence to determine an optimal patient repositioning schedule, and schedules may need to be determined empirically (Whitney J, 2006).

According to rec­ommendations from the Agency for Health Care Policy and Research, patients who are bedridden should be repo­sitioned every two hours (AHCPR, 2007).

To minimize shear, the head of the bed should not be elevated more than 30 degrees and should be maintained at the lowest degree of elevation needed to prevent other medical complications, such as aspiration and worsening congestive heart failure symptoms.

Mechanical devices to lower pressure can be classified as either static or dynamic. Static devices, such as foam- or fluid-filled mattresses or supports, maintain constant pressure when the patient is not moving, but they disperse pressure over a greater area than do standard bed mattresses.

These devices are appropriate for patients who can assume different positions without bearing weight on the ulcer and without compressing the support material (Bergstrom N, 1994).

For patients who cannot avoid bearing weight on the ulcer or who are not healing as expected, a dynamic pressure-relieving de­vice, such as an air-fluid bed, may be a better choice.

These devices change their support by alternating currents of air to redistribute pressure against the body, and they can achieve a greater degree of pressure reduction than can static devices.

Thus, most authorities recommend the use of dynamic beds for the management of persons with stage III to stage IV pressure ulcers and for those that do not respond to standard therapy (Bergstrom N, 1994).

 

Local wound care is another fundamental component of pressure ulcer therapy. Debridement of necrotic tissue, appro­priate dressing selection, and surgical repair are all important aspects of wound care, and these have been extensively reviewed elsewhere (Goode PS, 1997).

Sharp debridement is needed if infection occurs or to remove thick and exten­sive eschar. Healing after sharp debridement requires adequate vascularization; thus, vascular assessment for lower extremity ulcers is recommended (RNAO, 2007).

Enzymatic debridement is useful in the long-term care of patients who cannot toler­ate sharp debridement; however, it takes longer to be effec­tive and should not be used when infection is present (Püllen R, 2002).

 

Treatment of infection.

A combination of surgical and medical interventions may be required.

Surgical debridement is necessary to remove necrotic tissue and drain abscesses. Sys­temic antimicrobial therapy should be used for patients with serious pressure ulcer infections, including those with spreading cellulitis, osteomyelitis, or bacteremia.

 

Because of the high as­sociated mortality, empiric antibiotics are appropriate if bacteremia or sepsis is suspected. Administration of topical anti­biotics is not indicated.

The choice of antibiotics is based on the current understand­ing of the microbiology of infected pressure ulcers. Because such infections usually are polymicrobial, therapeutic regimens should be directed against both gram-positive and gram-negative facultative organisms as well as anaerobic organisms