Reworked the problem of hospital environment, especially transmission of infections, and the emergence of critical areas, address the quality of your indoor air (IAQ: Indoor Air Quality) as recommended by expert bodies. IAQ compared the two hospitals, one ancient and one built to replace, in operating rooms, rooms transplant (ABMT and liver) and UCI. Thermohygrometric parameters were measured simultaneously and ventilation, carbon oxides, and particulates and VOC fungi (Aspergillus), in a similar operation in both hospitals. The detection fungi was also evaluated throughout the time. We calculated the areas required for critical patients according to their prevalence. Was found in new construction better ventilation effectiveness, absence of biological contamination, but the presence of VOCs. Given the limited space for more critical patients, we propose a model with predictable sustainable maintenance benefits, individual rooms and block all specific conditioning.