Air conditioning requirements in hospitals

Lt Col (Dr) SKM Rao

Microbiological transmission in healthcare setting is inevitably a very potential risk. The main routes are droplets, contact, common vehicle and air borne transmissions. Infection control for patients, healthcare providers and visitors is of paramount importance in the healthcare process in medical facilities. Proper air conditioning of medical care facilities is helpful in prevention and treatment of diseases.

Continual advances in medicine and technology have led to the development in medical care processes as many new complex diagnostic and therapeutic procedures have been added to the armamentarium of medical care. There is a need for constant evaluation of air conditioning needs of the hospitals and medical facilities for better patient care.

Need for air conditioning of hospital facilities

Proper air conditioning is helpful in the prevention and treatment of diseases. The factors determining the need for air conditioning in hospital facilities are:

(a) The need to restrict air movement within and between various departments.

(b) The specific requirements for ventilation and filtration to dilute and remove contaminants in the form of airborne microorganisms, viruses, odour, hazardous chemicals and radioactive substances.

(c) Different types of temperature and humidity requirements for various areas.

(d) Permit accurate control of environmental conditions.

(e) Control of air quality and air movement

Infection Sources and Control Measures

Bacterial Infection. Infectious bacteria are transported by air. Droplet or infectious agents of 5 mm or less in size can remain airborne indefinitely. It has been shown that 90 to 95 per cent effective filters remove 99.9 per cent of all bacteria present in hospitals.

Viral Infection

Epidemiological evidence and other studies indicate that many of the air borne viruses that transmit infections are sub- micron in size, thus there is no known method to effectively eliminate 100 per cent of the viable particles. HEPA filters and/or Ultra-Low Penetration (ULPA) filters provide the greatest efficiency currently available. Therefore, the isolation rooms with appropriate ventilation pressure relationships are the primary means used to prevent the spread of airborne viruses in the hospital environment.

Outdoor air in comparison to room air is virtually free of bacteria and viruses. Infection control problems frequently involve a bacterial or viral source within the hospital. Ventilation air dilutes the viral and bacterial contamination within the hospital. Properly designed, constructed and maintained ventilation systems preserve the correct pressure relationship between functional areas; they remove airborne infectious agents from hospital environment.

Indoor Air Quality in Hospitals

Indoor air quality in hospital is a complex multi-faceted issue. Contaminants come with dust, air and visitors as well as originate inside the hospital complex and threaten the quality of environment. Most common contaminants are microbes and organic compounds. Ventilation and filtration provides a means of combating contaminants by diluting their concentration.

Acceptable indoor air quality can be achieved by following the fundamental principles:

(a) Contaminant source control.

(b) Proper ventilation.

(c) Humidity management.

(d) Adequate filtration.

The temperature and humidity conditions in hospital environment can inhibit or promote the growth of bacteria and activate or deactivate viruses. Ventilation systems are used to provide air virtually free of dust, dirt, odour, chemicals and radioactive pollutants.

Contamination can be dispersed into the air of the hospital environment by one of the many routine activities of normal patient care. Because of the dispersal of bacteria resulting from such necessary activities, air-handling system should provide air movement patterns to minimise the spread of contamination.

The sense of thermal comfort results from an interaction between temperature, relative humidity, air movement, clothing, activity levels and individual physiology. The temperature and relative humidity measurements are indicators of thermal comfort. The medical care needs of patients require thermal comfort provided by air conditioning system.

Operating Room Air Conditioning Requirements

The primary task of the ventilation system in an operating room is to provide an acceptable indoor climate for personnel and patients, to remove odour, released anaesthetic gases and to reduce the risk of infection in the operating area. The greatest amount of bacteria found in operating rooms comes from the surgical team and is a result of their activity during surgery.

During an operation most members of the surgical team are in the vicinity of the operating table, creating the undesirable situation of concentrating contaminants in this highly sensitive area. Studies of operating room air distribution systems and various air delivery systems indicate that these are the most effective methods for air movement pattern in operation theatres for limiting the concentration of contaminants to an acceptable level.

Thermal Comfort for Surgical Team

During an operation, heat is released according to the activity of the human body. The heat gain from the members of the operating team owing to the nervous energy released is shown in table 1.

The total heat production per hour caused by the staff, operation room lighting and equipment may be about 2 KW or 1750 Kcal/h.

Operating Room Ventilation

To maintain oxygenation for 10 persons in the operating room, a volume of about 28 m 3 of air will be required per hour. How much outside air is required for the dilution of odour will depend on the nature and intensity of odour producing sources. It is indicated by some studies that air supplied at 0.24 m 3 per minute per person is the critical level of odour suppression.

A ventilation rate of 10 air changes per hour reduces the level of any contamination present in the air by about 99 per cent. 15 to 20 air changes per hour should be sufficient for comfort, to ensure pressurisation in the operation room and to maintain considerable control of airborne micro organisms in an operation room of the size of about 40 sq metre, if an average surgical team is involved. Another study shows that bacteriological contamination of the air is markedly reduced by the use of ultra clean air filters.

Airborne contamination in operating room is mainly derived from the personnel in the operation theatre and their activities. The number of individuals present, ventilation and airflow implements the bacterial count in operation theatre. Proper design and ventilation of operation theatre is the most important means of controlling airborne infection in operation theatre.

Empty Operation Theatre

The empty operation theatre should have:

a) Less than 35 colony-forming units (CFU) of bacteria/m 3 of air.

b) Less than one CFU of Clostridium perfingens or Staphylococcus aureus in 30 m 3.

c) During operation less than 180 CFU/ m3 of air using ultra clean laminar flow in the theatre.

d) Less than 20 CFU/ m 3 at the periphery of the enclosure and less than 10 CFU/ m3 at the centre.

Direction of Air Flow

Direction of airflow should be from clean to less clean areas. Airflow rate of 0.28 -0.47 m /sec is desirable across an open door to prevent back flow into cleaner area. In Ultra clean air enclosure, the airflow should not be less than 0.2 m/sec at one metre above the door is desired.

Isolation Rooms

Patients harbour transmittable microorganisms. Various modes of transmission contaminate the environment creating the necessity to control infections. Available systems are:

a) Standard Pressure Room- for patients who require contact or droplet isolation. (Class- S)

b) Negative Pressure Room - for patients who require airborne droplet nuclei isolation to reduce transmission of disease via the air-borne route. (Class-N)

c) Requirement of separate exhaust system dedicated to each room, removing a quantity of air greater than that of the supply system.

d) Maintain an air change rate greater than or equal to 12 air changes per hour or 145 litres per second per patient.

e) Directs the exhaust directly to outside.

f) Positive Pressure Room- rooms with a positive pressure relative to the ambient pressure to isolate immunocompromised patients such as certain transplant and oncology patients. The aim is to reduce the risk of airborne transmission of infection to susceptible patients (Class-P)

Isolation Room Pressures

Air Lock Function

a) Provides a barrier against loss of pressurisation and against entry/ exit of contaminated air in/out of the isolation room when the door to the airlock is opened.

(b) Provides a controlled environment in which protective garments can be donned without contamination before entry into the isolation room.

(d) Provides a controlled environment in which equipment and supplies can be transferred from isolation room without contaminating the surrounding areas.

Humidity Control

One of the aspects of humidity is that bacteriological microorganisms ride on dust particles whose attract ability to one another is favoured by low relative humidity resulting in increased static energy. Low relative humidity is reported to be suitable for Klebsiella pneumoniae activity. There is a three-fold decrease in the biological decay of a hospital strain of Staphylococcus at 75 per cent relative humidity as compared to 39 per cent relative humidity. High humidity in the hospital enhances the danger of growth of Pseudomonas aeruginosa.

Humidity in operation room is believed to contribute to the prevention of dehydration of exposed tissue. At relative humidity of about 50 per cent, a very thin invisible film of moisture forms on the operation equipment and other surfaces. This film of moisture conducts static electricity to earth before a spark producing potential is built up. To minimise the explosion risk , the relative humidity required is 40-65 per cent.

Conclusion

The benefit to the clientele, prompt recovery, restoration of quality of life, disability limitation, prevention of hospital acquired infection, enhancing the productivity of the equipment and staff cannot be quantified in to the exact financial terms. A single case of hospital acquired infection requires at least double the duration of stay in hospital, which leads the antibiotic cost to manifold, leads to increase in the cost due to management of antecedent complications and loss of productive man-hours, justifies the case for air conditioning. The hospitals/medical institution deals with life of the clientele, the lives saved by providing appropriate therapeutic, diagnostic and treatment facilities justify that the investment for air conditioning is a small cost for better quality care to the patients.

The writer is officer in charge with the Hospital Projects, Army Hospital, New Delhi