This paper reviews the previous attempts to evaluate the Indoor Air Quality (IAQ), investigatespreviously proposed IAQ factors and analyses the evaluation methods of these factors. The presentwork introduces, also, a new hypothesis of the optimum HVAC airside system design of the surgicaloperating theatres to achieve the comfort and hygiene levels. The present work is devoted to proposeand formulate a new scale capable of adequately evaluating the airflow pattern in the surgicaloperating theatres. The proposed new scale is proposed to cover the local and overall air qualityevaluations. A new Neuro fuzzy technique was applied to derive measures for indoor air qualityindices. Indoor Air Quality (IAQ) is more critical in healthcare facilities due to the dangerous microbialand chemical agents present and the increased susceptibility of the patients. Hospitals and otherhealthcare facilities are complex environments that require ventilation for comfort and to controlhazardous emissions. Surgical operating theatre is the most important and complex zone in thehospital, and requires more careful control of the aseptic conditions of the environment. Most of theprevious researches aiming at evaluating the IAQ were based on the evaluation of the air distributiondepending on the residence and leaving age of the air supplied to the enclosure. Other attempts werealso reported to indicate the effectiveness of contaminant removal by the entire airflow pattern as anindication to the IAQ.This paper recommends some designs of the supply air outlets to provide the vertically downwardairflow as a practical solution. The near ceiling and near floor extract ports are to be used instead ofthe hypothetical complete floor extract as a practical solution.