Quality Control of Pulmonary Diagnostic Systems

Transcription

1 Quality Control of Pulmonary Diagnostic Systems James P. Sullivan, BA, RPFT Pulmonary Diagnostic Laboratories Memorial Sloan Kettering Cancer Center New York, New York QA, QC and QI: what s the difference? Quality Control: systematic use of methods to ensure the device conforms to standards. Quality Assurance: does the device meet requirements? Quality Improvement: programs to improve or enhance the performance of a device or procedure. Continuous Quality Improvement: ongoing QI programs. Why are QA and QI Important? If it moves air, we can get a number 1

2 Mechanical Devices: Calibration Syringes: Can be used for both calibration and control for flow volume, gas dilution and DLco. Mechanical Simulator Devices: For flow, VTG and DLco. Calibration vs. Control: Calibration: create device correction factors Control: verify accuracy of correction factors Human Controls: Human Biologic Standard (HBS): Also referred to as bio QC Should be healthy non smokers asthmatics need not apply Both mechanical and human controls should be run when troubleshooting equipment problems, and again to confirm proper (accurate) operation after repair. Human Controls: pros Requires no additional equipment or set up time. Works on all measurements. Checks the entire system. The absolute best way to really learn how to instruct your patients and operate your system. Almost all labs have a suitable HBS QC subject. 2

3 Human Controls: cons Not as reproducible and consistent; up to 5% variance is acceptable, which is not good enough Not all technologists are suitable subjects for HBS QA Diurnal variations may limit reliability Technologist resistance Mechanical Devices: pros All labs have a calibration syringe. Highly reproducible and consistent. Mechanical Devices: cons May be costly and complicated. May not check the entire system. What if the device itself is faulty? How is the accuracy of the device checked? 3

4 The ideal ongoing QA program will be a combination of both human and mechanical controls. Calibration Syringes: 3 L is the common standard. All labs should have at least two 3 L syringes, one to calibrate and one to verify. 5 L is very desirable, because this volume more closely approximates more patients. 7 L is best. Syringes should be serviced (cleaned, lubricated and calibrated) as per manufacturer s recommendations. Syringe connectors should be replaced regularly. Calibration Syringes: FVC: perform FVL at clinically relevant flows; should return syringe volume +/ 3%, i.e., L using 3 L syringe. FRC He or N 2 : perform FRC measurement with different volumes; should return syringe volume plus deadspace. D L co: D L co should be essentially zero; this procedure essentially checks for leaks in the system. VA should be syringe volume plus deadspace. 4

5 Morgan Scientific VTG Simulator: SensorMedics Plethysmograph Simulator Isothermal Lung Analog Ruppel s Manual of Pulmonary Function Testing, 9 th Edition 5

6 Hans Rudolph: Flow Volume Simulator and Resistance Standards: Hans Rudolph D L co Simulator: Reference Literature All pulmonary laboratories should have various reference literature available, including, but not limited to: Department policy and procedure manuals Vendors operating manuals All installation records, including initial control studies Corrective action logs ATS/ERS Statements and Lab Manual AARC CPGs Recent pulmonary diagnostics text (Ruppel/Mottram, Wanger, Wasserman, etc.) 6

7 Human Biologic Standard Controls Collect at least 20 sets of ATS compliant data for each control parameter. To be done on properly maintained and functioning analyzer after a successful calibration. Usual control parameters are FVC, FEV 1, FRC, TLC, DLco and VA. Attempt to perform the baseline studies at different times of the day to better duplicate real world conditions. Human Biologic Standard Controls Calculate mean and SD for each parameter. Enter data onto spreadsheet for calculation and graphing. In a normal data distribution: 65% of data will be within ±1 SD of the mean, 95% of data will be within ±2 SD of the mean, 99% of data will be within ±3 SD of the mean. 7

8 Human Biologic Standard Controls General QA Rules: ±2 SD are considered warning limits. Values between 2 and 3 SD indicate an error and the procedure should be repeated. Values beyond ±3 SD are unacceptable and troubleshooting procedures should commence. FVC Lung Volumes 8

9 DLco Westgard Rules 9

10 FVC This method uses both the tracer gas and carbon monoxide in the DLco mixture to calculate the VA. This is done by calculating the ratios of the expired to inspired gases (both the tracer and CO). A calibration syringe s volume at full extension is always the same. Calibration syringes dilute; they do not diffuse. The expected result for DLco at all stroke volumes is zero. 10

11 The expected result for VA (hereafter called target volume) is: the overall syringe volume, plus the adapter deadspace, plus the instrument deadspace (including the filter, if used). This is true no matter what the starting syringe volume is. If the stroke starts with the syringe completely closed, the test gas will be diluted only by the deadspace of the syringe, connector and instrument. If the syringe plunger is pulled out halfway before it is attached to the device, the dilution will be 50% plus the deadspace of the syringe, connector and instrument. VA should be the same whether the expired to inspired CO or tracer ratio is used. IVC ( ATPS) expired gas inspired gas This is the formula for the target volume (ATPS): We can calculate the target volume by measuring: the inspired volume, and, the difference between the expired and expired gases. If the IVC is too low or high, i.e., a flow measurement issue, the VA will be off in the same direction. If the IVC is within range and the VA is high a leak or a malfunctioning valve permitting excess dilution. If the VA calculated by tracer dilution gives an accurate VA result and the VA measured by CO dilu on does not problem with the CO analyzer. If the VA measured by CO is accurate and the tracer measurement is not problem with the tracer analyzer. 11

12 Initial work on this method began in At least two systems from CareFusion, MGC Diagnostics, Morgan Scientific and nspire were used. The 5 L syringe on the Hans Rudolph DLco Simulator was used. Advantages over Hans Rudolph DLco Simulator: More sensitive in detecting analyzer alinearity. Much less expensive and complex. Can better detect flow and individual analyzer problems. Known Limitations: The syringe must be removed from the system between trials and completely flushed (same with the HR device). Deadspace of syringe must be known. Second collar that is adjustable is needed on syringe shaft. Syringe must be precisely set for each volume. The greater the gas dilution, the less sensitive this method is. 12

13 Work to be done: Development of an adapter that increases mixing of test and deadspace gases in the syringe. Spreadsheet with correction factors for current pulmonary systems completed. Questions or Comments? James P. Sullivan, BA, RPFT Supervisor, Pulmonary Diagnostic Laboratories Memorial Sloan Kettering Cancer Center New York, New York (212)