4.3 Infection Control, Equipment Decontamination, Disposable Filters, and Spaulding Classification

4.3 Infection Control & Equipment Decontamination

Pulmonary function testing involves forced expiratory maneuvers, hyperventilation, and aerosol generation, creating a potential vector for cross-contamination between patients and healthcare personnel. Maintaining rigorous infection control practices, adhering to medical device processing guidelines, utilizing high-efficiency inline filters, and managing laboratory air ventilation are essential components of technical quality assurance.

---

Pathogen Transmission Modes in the PFT Laboratory

Diagnostic respiratory procedures generate high-velocity airflow and droplets, exposing equipment and personnel to multiple transmission pathways:

1. Direct Contact Transmission: Person-to-person physical transfer of micro-organisms (e.g., via unwashed hands between patient encounters).
2. Indirect Contact Transmission: Contact with contaminated intermediate objects (fomites), such as reusable noseclips, outer equipment surfaces, or calibration syringes.
3. Droplet Transmission: Large infectious droplets (>5 µm) generated during coughing or forced exhalations traveling short distances (<3 feet) onto mucosal surfaces.
4. Airborne Transmission: Small infectious droplet nuclei (≤5 µm) containing pathogens such as Mycobacterium tuberculosis, varicella-zoster, measles, or SARS-CoV-2 remaining suspended in air currents for extended periods.

---

The Spaulding Classification Scheme for PFT Equipment

The Spaulding Classification System categorizes medical instruments based on the degree of infection risk involved in their clinical use, dictating the required level of decontamination:

                                Spaulding Medical Device Classification
                                                  │
         ┌────────────────────────────────────────┼────────────────────────────────────────┐
         ▼                                        ▼                                        ▼
     CRITICAL                               SEMI-CRITICAL                            NON-CRITICAL
Enters sterile tissue/bloodstream      Contacts intact mucous membranes            Contacts intact skin only
         │                                        │                                        │
         ▼                                        ▼                                        ▼
   Sterilization                       High-Level Disinfection (HLD)              Low/Intermediate Disinfection
(Autoclave, EtO, Gas Plasma)               (OPA, Glutaraldehyde)                    (Quat Wipes, Alcohol)

Detailed PFT Categorization & Decontamination Standards

---

High-Efficiency Disposable Inline Filters

Modern PFT laboratories universally utilize single-patient disposable barrier filters placed between the patient's mouth and the flow transducer to prevent internal circuit contamination.

Filtration Performance Specifications

According to ATS/ERS standards, inline bacterial/viral filters must meet strict physical and mechanical performance metrics:

• Filtration Efficiency: Must achieve >99.9% Bacterial Filtration Efficiency (BFE) and >99.9% Viral Filtration Efficiency (VFE) for micro-organisms down to 0.1–0.3 microns.
• Airflow Resistance: Filter resistance must be <1.5 cmH2O/L/sec at a flow rate of 14.0 L/sec. Excessive filter resistance restricts maximal expiratory flow, causing artificial reductions in $PEFR$, $FEV_1$, and $FEF_{25-75%}$.
• Instrument Dead Space: Filter anatomical dead space should be minimal (typically <50 to 70 mL) to prevent false elevations in calculated lung volume ($FRC, TLC$) or baseline rebreathing.

   [Patient] ──> [Disposable Filter (>99.9% Efficiency, <1.5 cmH2O Resistance)] ──> [Pneumotachometer / Flow Sensor]

---

Laboratory Ventilation & Airborne Isolation Standards

Testing patients with suspected airborne communicable diseases (e.g., open Mycobacterium tuberculosis) demands strict environmental engineering controls.

Negative Pressure & Air Exchange Rates (ACH)

• Air Changes per Hour (ACH): The number of times the total room air volume is completely exhausted and replaced per hour.
• Regulatory Standards (CDC / HRSA): PFT testing rooms and airborne isolation suites must maintain 6 to 12 Air Changes per Hour (ACH) (minimum 6 ACH for existing facilities; minimum 12 ACH for newly constructed or renovated facilities).
• Negative Pressure Gradient: The room pressure must remain negative relative to surrounding hallways (at least -2.5 Pascals or -0.01 inches of water gauge), causing air to flow inward into the testing room rather than out into public corridors.
• Air Filtration & Exhaust: Exhaust air must be vented directly outdoors away from fresh air intakes or passed through HEPA (High-Efficiency Particulate Air) filters (99.97% efficient at 0.3 microns) prior to recirculation.

Room Clearance Time Calculations

Following an aerosol-generating maneuver by a patient with suspected airborne infection, the room must remain vacant for a specified clearance duration based on the room's ACH before another patient or unprotected staff member enters:

$\text{Clearance Time (99.9\% removal)} = \frac{\ln(1000)}{\text{ACH}} \cdot 60\text{ minutes}$

• At 6 ACH, 99.9% removal requires 69 minutes.
• At 12 ACH, 99.9% removal requires 35 minutes.

---

Standard Precautions & Quality Control Integration

1. Hand Hygiene: Performed immediately before applying PPE, before patient contact, after removing gloves, and after handling contaminated equipment.
2. Personal Protective Equipment (PPE): Staff must wear N95 or PAPR respirators, eye protection, gowns, and gloves during aerosol-inducing bronchial challenge testing or when treating patients on airborne precautions.
3. Biological Control (BioQC) Verification: When transitioning equipment or changing filter types, technologists must run daily BioQC checks to confirm that filter dead space and resistance have not altered baseline equipment calibration.