Airflow distribution for minimizing human exposure to airborne contaminants in healthcare facilities
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Hospital-acquired infections (HAIs) have been a persistent problem in hospitals for over a century and are associated with significant mortality, morbidities and increasing healthcare cost. There is strong evidence that airborne transmission of infectious contaminants in health care facilities plays a significant role in development of hospital-acquired infections (HAIs). In this context, ventilation solutions, such as diluting and removing airborne contaminants in hospitals, play a crucial role in reducing the risk of airborne transmission of HAIs. Efficient airflow distribution solutions have emerged during the past decades, such as laminar airflow systems (LAFs) in operating rooms (ORs) that have become part of the guidelines for the prevention of hospital acquired infections. However, their use has recently been widely debated with a growing number of clinical studies that showed no evidence of LAF systems superiority compared to traditional ventilation systems in reducing the risk of surgical site infections (SSIs). There are many factors that may disrupt the downward LAF distribution in the operating microenvironment, including medical equipment and the thermal plume generated by the patient. On the other hand, guidelines for airflow distribution systems in patient rooms have not attracted much attention compared with operating rooms, and rely mostly on traditional airflow distribution systems such as mixing ventilation. New, advanced ventilation systems call for a paradigm shift in ventilation guidelines for patient rooms. This thesis diagnoses and investigate factors affecting the airflow distribution efficiency in delivering clean air to the human microenvironment air to reduce exposure in the OR and patient room. The objectives of the present work are (i) to examine the effects of medical equipment and a patient’s thermal plume on the airflow distribution and human exposure in the operating microenvironment of an OR equipped with LAF systems and (ii) to examine under what supply airflow conditions can protected occupied zone ventilation (POV) decrease the risk of human exposure in a single-bed hospital ward compared to traditional ventilation strategies without deteriorating the occupant’s draft risk. The results of this thesis found that medical equipment positioned above the patient and the patient’s thermal plume disrupt the uniform downward LAF in ORs. The velocity distribution created by the collision of surgical lights and LAF results in a turbulent airflow zone formed behind the lights that at up to 40 cm below the lights was characterized by downward velocities lower than 0.05 m/s. The velocity distribution created by collision between the patient’s thermal plume and the opposing laminar airflow resulted in decelerated downward LAF velocity at some points close to the patient to one-third of the LAF supply velocity. Even so, the LAF dominated the thermal plume and the velocity measurements in the proximity of the patient did not fall below 0.1 m/s. Also, both the shape and position of surgical lights are shown to have an impact on the size and velocity distribution of the turbulent airflow formed behind lights. The results of this thesis also showed that the presence of medical equipment above the operating microenvironment significantly increased airborne contamination and human exposure to airborne pathogens. Therefore, an ideal surgical environment should not have lights positioned directly above the operating microenvironment but still close enough to illuminate the wound area. This may also imply that the future design of surgical lighting systems in operating rooms should reconsider the conventional use of surgical lamps. Further, the findings of this thesis showed that POV strategy is effective compared to traditional airflow distribution systems in a patient room with a lying patient and a healthcare worker. Additionally, compared to alternative ventilation systems for patient wards, such as displacement and low-turbulence downward ventilation systems, the exposure risk to airborne pathogens was independent of the posterior position of a lying patient. The healthcare worker’s contaminant exposure was highly dependent on the supply air velocity from the slot diffuser. This research shows that POV system may protect the patient and medical staff in patient wards and isolation rooms where there is a very high risk of airborne infection and where movement between the infected and protected zone is restricted or prohibited. The results of this thesis can be used as evidence that designers and manufactures should provide solutions for medical equipment with a minimal detrimental effect on the laminar airflow distribution. Also, the findings of this thesis can be used as evidence that patient room guidelines should reconsider the use of advanced air distribution methods as POV strategies instead of traditional ventilation systems such as mixing ventilation.