HVAC in Operation Theatres In Hospitals

No area of the hospital requires more careful control of the aseptic condition of the environment than does the surgical suite. The systems serving the operating rooms, including cystoscopic and fracture rooms, require careful design to reduce to a minimum the concentration of airborne organisms.

The greatest amount of the bacteria found in the operating room comes from the surgical team and is a result of their activities 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 contamination in this highly sensitive area.

Operating Rooms.

Studies of operating-room air distribution devices and observation of installations in industrial clean rooms indicate that delivery of the air from the ceiling, with a downward movement to several exhaust inlets located on opposite walls, is probably the most effective air movement pattern for maintaining the concentration of contamination at an acceptable level.

Completely perforated ceilings, partially perforated ceilings, and ceiling- mounted diffusers have been applied successfully ( Operating room suites are typically in use no more than 8 to 12 h per day (excepting trauma centers and emergency departments). For energy conservation, the air-conditioning system should allow a reduction in the air supplied to some or all of the operating rooms when possible. Positive space pressure must be maintained at reduced air volumes to ensure sterile conditions.

The time required for an inactive room to become usable again must be considered. Consultation with the hospital surgical staff will determine the feasibility of this feature. A separate air exhaust system or special vacuum system should be provided for the removal of anesthetic trace gases . Medical vacuum systems have been used for removal of nonflammable anesthetic gases (NFPA Standard 99).

One or more outlets may be located in each operating room to permit connection of the anesthetic machine scavenger hose. Although good results have been reported from air disinfection of operating rooms by irradiation, this method is seldom used. The reluctance to use irradiation may be attributed to the need for special designs for installation, protective measures for patients and personnel, constant monitoring of lamp efficiency, and maintenance.

The following conditions are recommended for operating, catheterization, cystoscopic, and fracture rooms:

1. The temperature set point should be adjustable by surgical staff over a range of 17 to 27°C.
2. Relative humidity should be kept between 45 and 55%.
3. Air pressure should be maintained positive with respect to any adjoining rooms by supplying 15% excess air.
4. Differential pressure indicating device should be installed to permit air pressure readings in the rooms. Thorough sealing of essential to maintaining readable pressure.
5. Humidity indicator and thermometers should be located for easy observation.
6. Filter efficiencies should be in accordance with Table 1.
7. Entire installation should conform to the requirements of NFPA Standard 99, Health Care Facilities.
8. All air should be supplied at the ceiling and exhausted or returned from at least two locations near the floor for minimum ventilating rates). Bottom of exhaust outlets should be at least 75 mm above the floor. Supply diffusers should be of the unidirectional type. High-induction ceiling or sidewall diffusers should be avoided.
9. Acoustical materials should not be used as duct linings unless 90% efficient minimum terminal filters are installed downstream of the linings. Internal insulation of terminal units may be encapsulated with approved materials. Duct-mounted sound traps should be of the packless type or have polyester film linings over acoustical fill.
10. Any spray-applied insulation and fireproofing should be treated with fungi growth inhibitor.
11. Sufficient lengths of watertight, drained stainless steel duct should be installed downstream of humidification equipment to assure complete evaporation of water vapor before air is discharged into the room. Control centers that monitor and permit adjustment of temperature,humidity, and air pressure may be located at the surgical supervisor’s desk.

Obstetrical Areas.

The pressure in the obstetrical department should be positive or equal to that in other areas.

Delivery Rooms. The design for the delivery room should conform to the requirements of operating rooms.

Recovery Rooms

Postoperative recovery rooms used in conjunction with the operating rooms should be maintained at a temperature of 24°C and a relative humidity between 45 and 55%. Because the smell of residual anesthesia sometimes creates odor problems in recovery rooms, ventilation is important, and a balanced air pressure relative to the air pressure of adjoining areas should be provided.

Nursery Suites

Air conditioning in nurseries provides the constant temperature and humidity conditions essential to care of the newborn in a hospital environment. Air movement patterns in nurseries should be carefully designed to reduce the possibility of drafts. All air supplied to nurseries should enter at or near the ceiling and be removed near the floor with the bottom of exhaust openings located at least 75 mm above the floor. Air system filter efficiencies should conform to Table 1. Finned tube radiation and other forms of convection heating should not be used in nurseries.

Full-Term Nurseries

A temperature of 24°C and a relative humidity from 30 to 60% are recommended for full-term nurseries, examination rooms, and work spaces. The maternity nursing section should be controlled similarly to protect the infant during visits with the mother. The nursery should have a positive air pressure relative to the work space and examination room, and any rooms located between the nurseries and the corridor should be similarly pressurized relative to the corridor. This prevents the infiltration of contaminated air from outside areas.

Special Care Nurseries

These nurseries require a variable range temperature capability of 24 to 27°C and a relative humidity from 30 to 60%. This type of nursery is usually equipped with individual incubators to regulate temperature and humidity. It is desirable to maintain these same conditions within the nursery proper to accommodate both infants removed from the incubators and those not placed in incubators. The pressurization of special care nurseries should correspond to that of full-term nurseries.

Observation Nurseries

Temperature and humidity requirements for observation nurseries are similar to those for full-term nurseries. Because infants in these nurseries have unusual clinical symptoms, the air from this area should not enter other nurseries. A negative air pressure relative to the air pressure of the workroom should be maintained in the nursery. The workroom, usually located between the nursery and the corridor, should be pressurized relative to the corridor. Emergency Rooms. Emergency rooms are typically the most highly contaminated areas in the hospital as a result of the soiled condition of many arriving patients and the relatively large number of persons accompanying them. Temperatures and humidities of offices and waiting spaces should be within the normal comfort range. Trauma Rooms. Trauma rooms should be ventilated in accordance with requirements in Table 3. Emergency operating rooms located near the emergency department should have the same temperature, humidity, and ventilation requirements as those of operating rooms. Anesthesia Storage Rooms. Anesthesia storage rooms must be ventilated in conformance with NFPA Standard 99. However, mechanical ventilation only is recommend