The influence manufacturers have on negative-pressure wound therapy research.

BACKGROUND: Studies investigating the effects of negative-pressure wound therapy using the Chariker-Jeter system (gauze-based interface) and the vacuum-assisted closure system often have outcomes that favor one particular system. This study attempts to examine whether manufacturer involvement could be related to the outcomes of these scientific studies. METHODS: A literature review was undertaken to identify a cohort of studies that compared these two forms of negative-pressure wound therapy. Clinical outcomes studies, basic research studies, and published conference abstracts were included. Allthe articles' abstracts and conclusions were given to five surgeons, who were blinded to the titles and authors. They were individually asked to record what they would consider to be the take-home message of each article (in terms of which system is superior). After categorizing each study according to the system that it appears to favor, the level of manufacturer involvement in each study was evaluated. The relationship between the outcome of a study and the level of manufacturer involvement in that study was then investigated. RESULTS: Of the total of 24 studies found to match the inclusion criteria, 22 were considered to favor a particular system (the other two were categorized as impartial). Of the 24 studies, 19 had some form of manufacturer involvement. Of the 19 that had some form of manufacturer involvement, 18 had outcomes that were deemed beneficial to the involved manufacturer, whereas one was deemed to have an impartial outcome. CONCLUSIONS: This study suggests that manufacturer involvement in these studies (regardless of level) correlates with the outcomes being beneficial to the involved manufacturer in almost all cases. Potential reasons for this and the implications thereof are discussed.

Does a zone of increased perfusion exist around negative-pressure dressings?

BACKGROUND: Although recent work has demonstrated that perfusion adjacent to a negative-pressure wound therapy dressing is decreased, laser Doppler studies have indicated that there is a zone of increased perfusion a couple of centimeters away. The existence of such a zone of increased perfusion is counterintuitive to the fact that negative-pressure wound therapy has been shown to increase tissue pressure. This study, using an alternative to laser Doppler, evaluated whether such a zone exists. METHODS: Six volunteers were randomized into three groups to test different suction pressures (-75, -125, and -400 mmHg). Each volunteer would have two dressings applied on either side of the lower back. A thermal imaging camera was used to assess perfusion around the dressing during different phases (e.g., "Suction on" and "Suction off"). The mean area under the curve for each phase was compared with those of other phases by means of one-way analysis of variance. Each condition (phase) was compared in a systematic manner with every other by means of Fisher's least significant difference for post hoc comparisons. A Pearson's correlation was determined to test the effects of the different suction pressure groups. RESULTS: No significant difference could be demonstrated for the area under the curve for the different phases. There was no significant correlation between the three suction pressures tested and the difference between the mean area under the curve for "Dressing on, no suction" and the two "Suction on" periods (Pearson correlation = 0.24; p > 0.4). CONCLUSIONS: Thermographic evaluation of tissue around a negative-pressure dressing did not demonstrate a zone of increased perfusion, contrary to other studies, which used laser Doppler. This is in keeping with recent work demonstrating that negative-pressure wound therapy increases tissue pressure while the dressing is applying suction. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, V.

Avoiding futile damage control laparotomy.

BACKGROUND: The age of a patient, lowest pre-operative pH and lowest core temperature are significant predictors of mortality in patients undergoing damage control surgery (DCS). An equation had previously been devised based on these three variables, which could predict which patients would die despite undergoing DCS (100% positive predictive value, 25% sensitivity). The aim of this study was to validate this equation by testing it on a different cohort of patients undergoing DCS. PATIENTS AND METHODS: A retrospective validation study of patients who underwent DCS over a four-year period (1998-2001) was undertaken. The lowest pre-operative pH, lowest pre-operative core temperature and age were recorded and the equation was used to predict which patients were "unsalvageable". This was then compared to the true outcomes of these patients. RESULTS: A total of 73 case notes were analysed for the period 1998-2001. The equation predicted that eight patients were unsalvageable. All eight patients died (100% positive predictive value), despite DCS being utilised. A further 25 of the rest of the "potentially salvageable" patients also died (24% sensitivity). When data of the original study (2002-2004) was combined with the current study data, the cohort totalled 145 patients, of whom 53 died (37%). Thirteen of these would have been predicted as unsalvageable with a 100% positive predictive value, had the equation been used during this time. CONCLUSION: Both the positive predictive value and sensitivity of the equation remain consistent. When resources are overwhelmed by multiple casualties, this equation could prove useful in identifying patients in whom surgery may be futile, allowing surgical triage to be directed in a more efficient manner.

The paradox of negative pressure wound therapy--in vitro studies.

Negative-pressure wound therapy (NPWT) has revolutionised wound care. Yet, it is still not understood how hypobaric tissue pressure accelerates wound healing. There is very little reported on the relevant physics of any substance subjected to suction in this manner. The common assumption is that applying suction to a substance is likely to result in a reduction of pressure in that substance. Although more than 250 research articles have been published on NPWT, there are little data verifying whether suction increases or decreases the pressure of the substance it is applied to. Clarifying this basic question of physics is the first step in understanding the mechanism of action of these dressings. In this study, pressure changes were recorded in soft plasticene and processed meat, using an intracranial tissue pressure microsensor. Circumferential, non-circumferential and cavity NPWT dressings were applied, and pressure changes within the underlying substance were recorded at different suction pressures. Pressures were also measured at 1cm, 2 cm and 3 cm from the NPWT placed in a cavity. In all three types of NPWT dressings, the underlying substance pressure was increased (hyperbaric) as suction pressure increased. Although there was a substantial pressure increase at 1cm, the rise in pressure at the 2-cm and 3-cm intervals was minimal. Substance pressure beneath all types of NPWT dressing is hyperbaric in inanimate substances. Higher suction pressures generate greater substance pressures; however, the increased pressure rapidly dissipates as the distance from the dressing is increased. The findings of this study on inanimate objects suggest that we may need to review our current perception of the physics underlying NPWT dressings. Further research of this type on living tissues is warranted.

Pneumocephalus following gunshot injury to the thoracic vertebral column: a case report.

Subarachnoid pleural fistula (SPF) following injury to the vertebral column is an extremely rare complication and is usually described after blunt trauma. We report the first case of SPF with pneumocephalus due to a gunshot wound to the spine.

Negative-pressure wound therapy I: the paradox of negative-pressure wound therapy.

BACKGROUND: Does negative-pressure wound therapy reduce or increase the pressure of wound tissues? This seemingly obvious question has never been addressed by a study on living tissues. The aim of this study was to evaluate the nature of tissue pressure changes in relation to negative-pressure wound therapy. METHODS: Three negative-pressure wound therapy dressing configurations were evaluated-circumferential, noncircumferential, and those within a cavity-on 15 human wounds, with five wounds in each category. Tissue pressure changes were recorded (using a strain gauge sensor) for each 75-mmHg increment in suction, up to -450 mmHg. In the circumferential and noncircumferential groups, tissue pressure was also measured over a 48-hour period at a set suction pressure of -125 mmHg (n = 10). RESULTS: In all three groups, mean tissue pressure increased proportionately to the amount of suction applied (p < 0.0005). Mean tissue pressure increments resulting from the circumferential dressings were significantly higher than those resulting from the noncircumferential (p < 0.0005) or cavity group (p < 0.0005); however, there was no significant difference between the latter two groups (p = 0.269). Over the 48-hour period, there was a significant mean reduction in the (increased) tissue pressure (p < 0.04 for circumferential and p < 0.0005 for noncircumferential), but in only three of 10 cases did this reduce to pressures less than those before dressing application. CONCLUSIONS: Negative-pressure wound therapy increases tissue pressure proportionately to the amount of suction, although this becomes less pronounced over 48 hours. This suggests that negative-pressure wound therapy dressings should be used with caution on tissues with compromised perfusion, particularly when they are circumferential.

Negative-pressure wound therapy II: negative-pressure wound therapy and increased perfusion. Just an illusion?

BACKGROUND: A recent study demonstrated that negative-pressure wound therapy increases underlying tissue pressure. This finding is incongruous with studies using laser Doppler that show that perfusion is immediately increased on initiation of suction. This study investigated perfusion in negative-pressure wound therapy using two alternative modalities. METHODS: Radioisotope perfusion imaging was used to determine perfusion beneath circumferential negative-pressure wound therapy dressings on 20 healthy hands (n = 20). Ten hands received suction pressures of -400 mmHg and 10 received -125 mmHg, with the contralateral hand used as a control without any suction. Transcutaneous partial pressure of oxygen was used to determine perfusion beneath noncircumferential negative-pressure wound therapy dressings on 12 healthy legs (n = 12), with each volunteer being sequentially randomized to receive suction pressures of -400 and -125 mmHg, respectively. RESULTS: Tissues undergoing circumferential negative-pressure wound therapy demonstrated a mean reduction in perfusion of 40 +/- 11.5 percent (p < 0.0005) and 17 +/- 8.9 percent (p < 0.0005) at suction pressures of -400 mmHg and -125 mmHg, respectively. Perfusion reduction at -400 mmHg was significantly greater than at -125 mmHg (p < 0.015). In the noncircumferential negative-pressure wound therapy group, there was a mean reduction in transcutaneous partial pressure of oxygen of 7.35 +/- 7.4 mmHg (p < 0.0005) and 5.10 +/- 7.4 mmHg (p < 0.0005) at suction pressures of -400 mmHg and -125 mmHg, respectively. There was a tendency for greater reductions in the -400 mmHg group, but this was not significantly different from the -125 mmHg group (p = 0.07). CONCLUSIONS: These findings demonstrate that perfusion beneath negative-pressure wound therapy decreases for increasing suction pressure. Thus, it is suggested that negative-pressure wound therapy should be used with caution on tissues with compromised vascularity, particularly when used circumferentially.