Surgical Humidification (HumiGard™) Reduces Bacterial Load in an Open Spine Animal Infection Model

Objectives Evaporative cooling of surgical wounds during surgery was overlooked as a modifiable factor in reducing surgical site infections (SSIs). HumiGard ^TM is a system which delivers warm and humidified air to the wound bed intraoperatively to prevent tissue cooling and drying. This study investigated the potential for HumiGard™ to reduce bacterial load in a porcine model of spine surgery. Methods Open spine surgery was simulated in a porcine model. The wound surface was inoculated with ~10 ⁶ CFU/mL of Staphylococcus aureus and remained exposed for 180 minutes to the ambient theatre conditions (control) or warm humidified air (HumiGard) (n=6 per group). Wounds were re-opened three days post-surgery and biopsies were collected for bacterial enumeration and histological analyses. Results The growth of Staphylococcus aureus was 84% less in the HumiGard muscles than control at Day 3 post-surgery (p=0.031). Large bacterial colonies infiltrated the deeper muscle tissues in control, while the HumiGard muscles had smaller bacterial colonies confined to the superficial zone. Neutrophil proportion in the HumiGard group (34% ± 5.1%) was lower than control (65% ± 6.1%) (p=0.005). In contrast, the proportion of mononuclear cells was higher in HumiGard tissues (66% ± 5.1%) than control (35% ± 6.1%) (p=0.005), implying a transition from the pro-inflammatory to the reparative stage of wound healing. Conclusions In this animal study, maintaining physiological temperature and humidity of open wounds during surgery reduced bacterial growth and advanced the wound healing process. HumiGard may offer a protective benefit by reducing the risk of SSIs following orthopaedic surgery.