Influence of advanced wound matrices on observed vacuum pressure during simulated negative pressure wound therapy.

Biomaterials and negative pressure wound therapy (NPWT) are treatment modalities regularly used together to accelerate soft-tissue regeneration. This study evaluated the impact of the design and composition of commercially available collagen-based matrices on the observed vacuum pressure delivered under NPWT using a custom test apparatus. Specifically, testing compared the effect of the commercial products; ovine forestomach matrix (OFM), collagen/oxidized regenerated cellulose (collagen/ORC) and a collagen-based dressing (CWD) on the observed vacuum pressure. OFM resulted in an ∼50% reduction in the observed target vacuum pressure at 75 mmHg and 125 mmHg, however, this effect was mitigated to a ∼0% reduction when fenestrations were introduced into the matrix. Both collagen/ORC and CWD reduced the observed vacuum pressure at 125 mmHg (∼15% and ∼50%, respectively), and this was more dramatic when a lower vacuum pressure of 75 mmHg was delivered (∼20% and ∼75%, respectively). The reduced performance of the reconstituted collagen products is thought to result from the gelling properties of these products that may cause occlusion of the delivered vacuum to the wound bed. These findings highlight the importance of in vitro testing to establish the impact of adjunctive therapies on NPWT, where effective delivery of vacuum pressure is paramount to the efficacy of this therapy.

Evaluation of Tissue Apposition and Seroma Prevention in an Ovine Model of Surgical Dead Space Using a Novel Air-Purged Vacuum Closure System.

Background: Postoperative complications associated with seroma formation resulting from surgical dead space continue to present a challenge in modern surgery. There is an unmet need for new technologies that address surgical dead space as well as prevent seroma formation and associated downstream postoperative complications. Methods: The novel implantable tissue apposition and drainage system ENIVO was developed and tested in a bilateral ovine external abdominal oblique (EAO) resection model of surgical dead space. The ENIVO system is a portable powered pump and wound interface featuring air-purged vacuum closure (APVC) that delivers a sustained level of vacuum pressure (80 and 100 mmHg) to the treatment site with an intermittent burst of sterile filtered air through the implanted wound interface. Seroma area, seroma volume, and drain migration were assessed at postoperative days 7 and 14, and all animals were euthanized at day 28 with gross assessment of treatment efficacy including the presence of residual seroma and tissue apposition. Results: The bilateral model created relatively uniform defects of ~120 cm2 following excision of ~30 to 50 g of EAO muscle. Median seroma area of ENIVO-treated defects was statistically smaller than standard of care (SoC)-treated defects at days 7 and 14. Median seroma volume at 14 days was significantly reduced in ENIVO-treated defects relative to SoC-treated defects [1.3 (IQR 0.0-79.5) mL and 188.5 (IQR 27.6-342.9) mL, respectively]. At postoperative day 28, 40% (n = 4/10) of SoC defects showed a residual seroma, whereas in contrast, none of the ENIVO-treated defects showed signs of a residual seroma. Median tissue apposition scoring was higher in the ENIVO treatment group [3 (IQR 3-3)] compared with the SoC group [3 (IQR 0-3)]. Conclusions: The ENIVO system represents a new approach to dead space management and seroma prevention and was shown to outperform a SoC surgical drain in a challenging large defect model of surgical dead space management and seroma prevention.

Nasogastric aspiration as an indicator for feed absorption in model-based glycemic control in neonatal intensive care.

BACKGROUND: STAR (stochastic targeted) is a glycemic control model-based framework for critically ill neonates that has shown benefits in reducing hypoglycemia and hyperglycemia. STAR uses a stochastic matrix method to forecast future changes in a patient's insulin sensitivity and then applies this result to a physiological model to select an optimal insulin treatment. Nasogastric aspiration may be used as an indicator to suggest periods of care when enteral feed absorption is compromised, improving the performance of glycemic control. An analysis has been carried out to investigate the effect of poorly absorbed feeds on glycemic control. METHOD: Clinical data were collected from eight patients on insulin therapy and enteral feed, which included large or significantly milky aspirates. Patients had a median gestational age of 25 weeks and postnatal age of 5.5 days. Virtual patients were created using the NICING model, and insulin sensitivity (SI) profiles were fit. Alternative feed profiles were generated whereby enteral feed absorption was redistributed with time to account for poor feed absorption. The effect of poor feed absorption, as indicated by aspirates, is investigated. RESULTS: The average percentage change of SI 4 h before a significant aspirate was 1.16%, and 1.49% in the 4 h following the aspirate. No distinct relationship was found between the fractional change in SI and the volume of the aspirate. Accounting for aspirates had a clinically negligible impact on glycemic control in virtual trials. CONCLUSION: Accounting for aspirates by manipulating enteral feed profiles had a minimal influence on both modeling and controlling glycemia in neonates. The impact of this method is clinically insignificant, suggesting that a population constant for the rate of glucose absorption in the gut adequately models feed absorption within the STAR framework.