How Much Pressure Does a Pressure Dressing Press? A Pilot Study Quantifying the Effects of a Pressure Dressing on the Post-Cesarean Section Incision

Theoretically, different types of surgical wound dressings serve many functions: protecting the wound from trauma and contamination, reducing the risk of postoperative hematoma and seroma formation, providing compression of dead space, preventing heat and fluid loss, absorbing exudate, limiting wound disruption, and providing an aesthetically pleasing appearance.¹ Since no single dressing exemplifies all of these attributes, the characteristics of a particular surgical incision must be assessed to determine which goals are most important.
A “pressure dressing” consists of a nonadherent bandage applied over the incision that is covered by a bulky, absorbent layer and a stretchable adhesive. Application of a pressure dressing over a wound is intended to compress dead space and prevent hematoma and seroma formation. Decreased seroma formation is associated with decreased wound disruption, a complication that causes significant morbidity and cost.² Theoretically, the pressure dressing improves hemostasis by preventing venous capillary blood loss and exudate. Conversely, application of the pressure dressing limits the ability to visually assess ongoing bleeding in the subcutaneous tissues in the immediate postoperative period. Additionally, the pressure dressing may cause increased discomfort to the patient when it is in place and when it is removed. Finally, the added adhesive may irritate and/or disrupt the surrounding skin. Given the paucity of data supporting the theoretical benefits of pressure dressings for abdominal incisions and the potentially deleterious effects of their use, the authors designed a pilot study to determine the increase in pressure exerted by a pressure dressing after a primary cesarean section.

Materials and Methods

The Brigham and Women’s Hospital Institutional Review Board approved the study protocol prior to the initiation of the study. The study population consisted of women undergoing scheduled cesarean sections. Five subjects meeting these criteria were tested over a 3-month period. Each subject’s height and weight were recorded and body mass index calculated.
A Stryker 295 Intra-Compartmental Pressure Monitor System (Stryker Surgical, Kalamazoo, Mich) was used to obtain the pressure readings. This instrument is designed for monitoring tissue pressures for the diagnosis of compartment syndrome. Measurements are taken by inserting the pressure probe into the subcutaneous space.
In this study, a pressure dressing consisted of a gauze dressing (TELFA® Dressing, Kendall Company, Mansfield, Mass) covered by 2 bulky abdominal gauze pads, covered by tape (Elastoplast®, BSN-Jobst, Inc., Rutherford College, NC) applied downward anteriorly over the incision and secured to the skin out to the mid-axillary lines bilaterally. This is the standard pressure dressing used in the authors’ institution.
The cesarean section technique was performed based on the preferences of the attending surgeon. Prior to closing the skin, a tissue pressure monitor catheter was inserted into the subcutaneous tissues. The skin was then closed by either staples or a subcutaneous suture. A baseline tissue pressure reading was taken and recorded. A second reading was taken after the application of a gauze dressing alone. The pressure dressing was then applied and a final measurement was taken. The surgeon was blinded to all pressure reading measurements until after the dressing was placed. The pressure catheter was then removed.
Statistical analysis was performed using a Microsoft Excel spreadsheet. Means were compared using a t test.

Results

Five patients were tested. The characteristics and pressures are presented in Table 1.
The mean pressure with the gauze dressing alone was 1.8 mmHg, which was not significantly different from the baseline mean tissue pressure of 1.4 mmHg (P = 0.08). The mean pressure after the application of the pressure dressing was 6.6 mmHg. This was significantly different from the pressure applied by the gauze dressing (P < 0.005).

Discussion

This study demonstrates an increase in the pressure in the subcutaneous tissue after a pressure dressing was applied. However, it is not clear that this increase is likely to translate into a meaningful clinical outcome. To improve hemostasis, the pressure of a “pressure dressing” must collapse the vessels to allow platelet aggregation, plug formation, and formation of a fibrin clot.³ As blood flows down the pressure gradient, the lowest pressure point in the cardiovascular system is the right atrium; pressure there is estimated at 0–8 mmHg in a healthy heart. Therefore, in order to collapse the venous capillary vessels in the subcutaneous tissues, a dressing should need to exert at least 8 mmHg of pressure. Similarly, exudate in subcutaneous tissue is determined by a combination of oncotic and hydrostatic pressure; decreasing seroma formation from exudate should also require significantly higher tissue pressures than this study demonstrated.
There are several limitations to broadly applying clinical significance to the data in this small pilot study. First, the sample size was small—the study only assessed 5 subjects. Second, if application of pressure to the incision is judged to be a desirable outcome, other materials and taping procedures may be more effective than gauze and tape.⁴ Third, the authors did not measure the pressure exerted by a dressing over time; measurements were taken immediately after the adhesive tape was applied to the pressure dressing (though it is likely the peak pressure was applied at that point and decreased over time). Finally, even in the case that a more effective, long lasting method of applying a pressure dressing is defined, the question remains as to whether there is a clinically meaningful change in outcome. Previous studies examining pressure dressings applied to other types of incisions have failed to show a decrease in complications, such as hematoma formation.⁵ One study in cardiac catheterization patients demonstrated that application of a thin transparent dressing was equally effective in preventing hematoma formation in the groin and was more comfortable.⁶

Conclusion

Pressure dressings seem to increase the pressure in the subcutaneous tissues of patients who have undergone cesarean section through a Pfannenstiel incision. However, in theory, the increases in pressure demonstrated by this study may not be sufficient to overcome capillary venous pressure in these tissues, and therefore, the pressure dressing may not be able to decrease hematoma formation. Pressure dressings may cause increased patient discomfort and can be associated with skin trauma. Given the data presented herein that theoretically questions the efficacy of pressure dressings for preventing wound hematomas, a trial assessing their clinical value would be appropriate.