BMT Unit Infrastructure – Review

Author: Sujeet Kumar @sujeethemat

In this Review I will be briefly writing about some essential things to know about BMT Unit infrastructure. This piece is no way a complete guide to designing and constructing a BMT unit but a bare minimum which people involved in BMT procedure should know.

We need to have a “clean room” environment which reduces the chance of airborne infections in a neutropenic and immunocompromised patient. Basically its a airtight room with defined air entry point, defined flow pattern and defined exit point where provisions are made to reduce particulate contamination and control other environmental parameters such as temperature, humidity and pressure. How do we achieve that ?

Heating, ventilation, and air conditioning (HVAC) along with High Efficiency Particulate Air (HEPA) filter is the technology which ensures the making of “clean room” and this setup can be called as Air Handling Unit (AHU). Ideally a BMT room be as close to a “ISO 7 Clean Room” as possible.

An Ideal BMT room based on ISO 7 clean room Specification
Stringent ISO 7 Room Specifications >> An ISO 7 clean room (also known as Class 10,000 cleanroom) is a hard-sided wall manufactured facility that utilizes AHU and HEPA filtration systems to maintain air cleanliness levels in the BMT room such that at a given point of time a maximum of 10,000 particles of size ≥0.5µm are suspended per cubic foot in the room. Note that particles of size <0.5µm can be present in such rooms without any limit. Class 10,000 cleanroom filtration systems must provide a minimum of 60 air changes per hour. (However most BMT units have a cutoff of >12 air changes/hour).

Air Handling Unit (AHU)

Each room should have its own dedicated Air Handling Unit (AHU) to provide a minimum of 60 air changes per hour (However most BMT units have a cutoff of >12 air changes/hour). This means the fresh air entering the patient’s room is first treated through special filters. Treated fresh air then passes through 0.3 Micron High Efficiency Particulate Air Filter (HEPA). This HEPA filtered air passes through a laminar flow to reach the patient’s room at the desired humidity and temperature, which is comfortable for the patient.

Positive pressure requirements

Automatic and selective control system provides positive air pressure in the BMT room compared to the anteroom and the BMT corridor. This has been done to ensure that, on opening the door of the BMT Room or the ante room, no outside air from BMT Corridor can enter the patient’s room. Air pressure in Anteroom is 10-15 Pascal higher than the BMT corridor and air pressure in BMT room is 10-15 Pascal higher than the ante room.

Ante room is a small room between the corridor and the BMT room for maintaining positive air pressure, special hand washing (scrubbing) and wearing a sterile gown before entering the BMT room.

Image description: A is air handling unit which pumps conditioned HEPA filtered air into the BMT room and a laminar air flow is maintained. Air Exit point is added opposite to A to take air out of the BMT room. Air is pushed in BMT room such that a positive pressure is maintained in relation to ante room so even while opening the door the air comes out of the BMT room but no air can enter from ante room to BMT room. Similarly BMT corridor is at lower pressure so air flow is always in BMT Room > Ante Room > BMT corridor direction and not vice versa.

Minimizing particle generation and ensuring proper indoor sanitization

Stainless steel doors and vinyl surfaces are most practical to clean with disinfectants to maintain and protect patients from infections.

Water entry 

UV treated water: entire water entering into BMT unit should be UV treated (tube changings as per manufacturer guideline). Water entry into BMT rooms should be regulated by a 0.2-micron filter membrane applied on taps which is changed after each discharge.

The above mentioned criteria’s are stringent and in real world BMT units some speciation’s are altered as per resources available but idea to to get as close to ISO 7 Clean room specifications.

As per ICMR National guidelines for HCT 2020 : Centers doing BMT should include SOPs for air-handling (e.g. positive pressure, filtered air, or laminar airflow rooms) as well as monitoring of its quality. A minimum of 12 air exchanges per hour for a new unit and at least 6 air exchanges per hour for an old unit, functional for 6 or more months, is recommended. Support of trained house-keeping staff for maintaining the facility is also critical. (p28, 15.2.4).

Basic requirements of a Operational BMT unit >> Practical specifications

It is necessary to meet the following requirements for efficient infection prevention and control in the cleanrooms for patients after HSCT:

  • ≥ 12 air exchanges per hour
  • Central or point-of-use HEPA filters with 99.97% efficiency for removing particles ≥ 0.3 µm in diameter (Timing of change of filter as specified by manufactures manual is to be ensured)
  • Correct filtration is particularly critical in HSCT centers with ongoing construction and renovation
  • Continuous pressure monitoring should be installed and functioning especially while rooms are occupied and BMT is going on.
  • Self-closing doors (stainless steel doors are non dust generating and it is easier to apply disinfectant on these surfaces as compared to wooden doors) and to maintain constant pressure differentials of anterooms should be used to ensure appropriate air balance and to prevent any air entry from BMT corridor to BMT room via ante rooms.
  • Floor surfaces should be smooth, nonporous, and scrub able to minimize dust levels (vinyl flooring are best option in this regard as dust adhesion and generation by these surfaces are minimal)
  • HSCT recipients should be placed in single-patient rooms.
  • Hand hygiene includes both use of alcohol-based hand rubs and hand washing with soap (plain or antimicrobial) and water. Ante room should be equipped with hand washing stations.
  • Equipment and devices within BMT area should be cleaned, disinfected or sterilized, and maintained as directed by established guidelines.
  • Each BMT room should be equipped with Clean Hatch >> to take clean and sterile items inside BMT room (UV Treatment facility). Many centers practice a single clean hatch system which acts as single point of entry of objects into BMT area which is also an acceptable practice.
  • UV treated water: entire water entering into BMT unit should be UV treated (tube changings as per manufacture guideline). Water entry into BMT rooms should be regulated by 0.2-micron filter membrane applied on taps which is changed after each discharge. 

NOTE >> While HEPA filters are not absolutely required as a minimal requirement in newly established centers with less complicated transplant activities, they are certainly preferred and highly recommended as newly established centers expand their activities to include more complicated (especially allogeneic). HEPA (high efficiency particulate air) filters have shown efficacy in providing protection against acquisition of fungal infections in immune-compromised hematology patients, including HSCT patients.

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