The aim of this study is to compartmentalize various components of NPWT and indigenously devise methods or equipment to make it affordable, efficient and safe to the patient.
The pump is a suction machine with an adjustable pressure guage capable of delivering 100-125 mm Hg negative pressure. A machine that works with a diaphragm is silent and doesn’t disturb the patient.
The timer switch is a standalone device, which looks like an extension box [Figures [Figures77 and and8].8]. The working voltage of the circuit is 12 volts, which does not pose an electric hazard to the patient. Only one component in this circuit generated heat (regulated IC7812) and this is taken care by using a heat sink.
The circuit diagram and components required are provided [Figure 6 and Table 3]. Separation of timer from the suction pump has the advantage of allowing the components to function independently of each other in case of break down. This circuit is sturdy and can function without breakdown for long periods. It has continuously worked up to 7-8 days without interruption, except to change dressing.
Dressing materials were procured from readily available source to bring further down cost of consumables. The PVA sponge was rendered medical grade by repeated washes with water until 50cc of the wash water upon vigorous shaking did not produce a foam that maintained itself longer than 10 seconds. This indicates that any inclusions in the sponge, which could leach out and have adverse effects, have been effectively removed. Sponge is then autoclaved before use.
The trackpad is a patented design of KCI (Kinetic Concepts Inc, San Antonio, Tx) and it provides uniform suction over the wound. An identical effect is attained by the perforated tube, which has a large area over which negative pressure is developed. It also traverses a longer distance within the sponge than the track pad.
The same study was done in 2008 by Shalom et al. who devised a homemade vacuum assisted closure system. However draw backs of this system are continuous pressure from wall suction device and lack of intermittent sub atmospheric pressure. Hence the dressing might be applied only in areas where wall suction is available. This method severely limits the mobility of the patient and blocks precious hospital beds since wall suction is out there only in intensive care units and step down settings. Another major drawback of this method is an absence of the timer switch.
In our study clear steridrapes were used to seal the wound, whereas other authors made use of povidine iodine impregnated drapes. They claim that these drapes could achieve prolonged control of bacterial growth compared to conventional drapes.
There are specific limitations to this kind of studies, since an exact control group does not exist. There is an element of subjectivity in deciding which wound required NPWT and those who might be treated with saline dressing. In open fractures variables resembling fracture morphology, contamination and duration from time of injury to NPWT application haven’t been taken into account. Hence, most of our data has been compared with historically matched controls.