Energy efficient airflow distribution methods for surgical microenvironment control in operating rooms

Abstract

With approximately 300 million surgeries performed worldwide each year, the operating room (OR) environment plays an important role in creating a satisfactory setting for all occupancies. However, there are currently several challenges within ORs, significantly affecting the well-being of the surgical team, patient safety, comfort, health, as well as the overall energy efficiency of the surgical environment.

Surgical site infections (SSI) pose a significant concern within healthcare settings, ranking as the third most common type of hospital-acquired infections (HAIs). The associated risk of infection varies from 2% to 13%, leading to substantial financial costs ranging from $400 to $3,000 per infection. The primary cause of SSI is the compromised immune response of the patient, making them vulnerable to invading microorganisms. The primary source of these microorganisms is believed to be bacteria-carrying particles (BCP) released by the surgical team and patient themselves. Ventilation systems play a crucial role in mitigating the presence of BCP, yet the absence of universally accepted standards for operating room (OR) ventilation parameters impedes effective measures to reduce patient exposure to BCP threats.

Airborne microbes released from infected patients represent a substantial hazard to the surgical team, particularly in cases involving infection diseases such as tuberculosis and severe acute respiratory syndrome (SARS-CoV-2). The risk of cross-infections has prompted the adoption of negative pressure operating rooms (ORs), a measure that has gained prominence, especially during the COVID-19 pandemic. Nevertheless, there exists a notable research gap in the assessment of the surgical team's exposure levels within these negative-pressure OR environments.

Inadvertent perioperative hypothermia (IPH), characterized by a core body temperature below 36 °C during surgery, is a prevalent issue with incidence rates ranging from 4% to as high as 90% in surgical cases. This condition of IPH can have severe consequences for patient health and recovery, including disruptions of using drug in metabolism, increased blood loss, coagulation problems, thermal discomfort, prolonged recovery times, and extended hospital stays. Furthermore, hypothermia elevates the risk of surgical site infections by approximately 50%. Consequently, the challenge of reducing the incidence of IPH has emerged as a prominent topic in ongoing research within this field.

Comparing with traditional turbulent mixing ventilation (TMV), though laminar airflow (LAF) operating rooms have shown promising results in maintaining cleaner surgical microenvironments, the issue of high energy consumption in LAF OR remains apparent, with an average consumption 34% higher than traditional turbulent mixing ventilation operating rooms. To promote the sustainable aspect of hospital ventilation, there is an urgent need to develop new types of ventilation solutions that secure a cleaner OR environment with higher energy efficiency.

This thesis extensively investigates the most influencing factors for safe and sufficient environment within operating rooms, where either negative pressure or positive pressure may be applied according to the property of diseases. The research scope of this thesis is mainly in the field of ventilation engineering and indoor environment. This encompasses an examination of exposure levels exposed by the surgical team to airborne microbes in negative pressure operating rooms (NPOR). This thesis also evaluates the impact of ambient air temperatures on the colony forming unit (CFU) level of surgical microenvironment in one OR with turbulent mixing ventilation. Furthermore, a human body heat transfer model has been developed to predict patients' core body temperatures to reduce the incidence of perioperative hypothermia. On the basis of traditional laminar airflow, a novel laminar airflow distribution solution is developed to minimize energy consumption while maintaining an ultra-clean surgical microenvironment.

The results of this thesis demonstrate that higher pressure difference in negative pressure TMV OR reduces the impact of the thermal plume above the patient's incision, thereby minimizing healthcare professionals' exposure to airborne viruses like COVID-19. In TMV OR, room air temperature significantly influences the development of thermal plume in surgical microenvironment. Lower air temperatures may lead to stronger thermal plume flow which may prevent deposition of particulate matter. However, higher temperatures may result in reduced shedding of skin scales (diameter larger than 5 µm) from the surgical team. This may contribute to fewer detected CFUs, which are the primary cause of surgical site infection. In addition, this thesis also demonstrates that the developed model for patient core temperature prediction may calculate core temperature. This model may be used as a valuable tool for preventing hypothermia in patients during surgeries.

Moreover, the novel airflow distribution method for ORs demonstrates substantial energy savings of up to 10% while maintaining high local air quality in the surgical microenvironment. This method provides an example for further development of operating room ventilation strategies, which may contribute to energy efficient ORs in the future.

In conclusion, this thesis offers key insights into influencing parameters and energy-efficient ventilation strategies for maintaining safe operating room environments. The findings underscore the impact of ventilation parameters on indoor air quality of ORs, which is crucial for future OR ventilation design. Additionally, the patient core temperature prediction model is proposed to enhance patient safety by predicting the adverse effect of the OR environment on hypothermia. The results of this thesis may contribute to future developments in new ventilation solutions for ORs.