Just a Note of Explanation: Some of these procedures are not commonly employed today. However, they are included here since they were part of the services provided by the Pulmonary Diagnostic Laboratory at UWHC when this communication was distributed, and as such were central to the Laboratory QA/CQI initiatives.
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The purpose of this packet is to briefly explain the content(s) of the various Special Studies as performed by this laboratory. They are as follows:
A. Pulmonary Exercise Tests
Purpose: For evaluation of dyspnea on exertion, unexplained dyspnea, ventilatory response to increasing workloads, disability evaluation, efficacy and need for supplemental oxygen, and for quantification of pulmonary and cardiovascular dysfunction, along with early detection of pulmonary dysfunction.
Includes: Oxygen Uptake (VO2), Carbon Dioxide Output (VCO2), Respiratory Exchange Ratio (RER; aka RQ), Minute Ventilation (MV), Respiratory Rate (RR), Tidal Volume (VT), Heart Rate (HR), Blood Pressure (BP), Pulse Oximetry (SpO2).
1. Non-Invasive
After obtaining resting (baseline) measurements, the subject undergoes a progressive multi-stage test either on a treadmill or electronically braked bicycle ergometer. Testing may be terminated by: abnormal physiologic response (i.e., systolic BP > 220 mm Hg, diastolic BP decrease by 20 mm Hg, SpO2 decreases to 88%, cardiac arrhythmias, HR exceeds > 85% predicted maximum), or subject discontinues testing. Baseline arterial blood gas is analyzed along with direct measurement of oxy- and carboxyhemoglobin to confirm/validate pulse oximeter reading.
2. Invasive
Arterial cannulation is performed and blood sampled at rest, during exercise at various steady-state levels (e.g., 25, 50, 75% actual maximum work rate). Testing is performed on either a electronically braked bicycle ergometer or treadmill and terminated as with “Non-Invasive” Exercise Testing.
3. For Desaturation Only
Expired gas analysis is NOT performed. Along with BP and HR response, designed to assess subject’s oxyhemoglobin desaturation during progressively increasing, or steady, workload on the treadmill.
Includes: Baseline ABG with direct measurements of SaO2% and HbCO% to validate SpO2% readings. Because of the limitations associated with pulse oximeters, arterial cannulation is recommended for multiple blood gas analyses.
B. Bronchoprovocation
Purpose: To assess airway hyperreactivity to external stimuli.
Includes: FVC, FEV1, PEF, FEF 25-75%, Raw, sGaw, VTG
Methods:
1. Methacholine Chloride
Abbreviated Protocol: Baseline studies are performed and the subject’s response to inhalation of aerosolized placebo (0.9% of NaCl) followed by one to four inhalations of aerosolized Methacholine Chloride (concentrations of 5 mg/ml and 25 mg/ml), via dosimeter is made. If extreme hyperreactivity is suspected by medical history, then the Standard Protocol will be employed which, after placebo administration, employs a dose-doubling protocol beginning with 0.625 mg/ml Methacholine Chloride.
**NOTE: According to Laboratory Policy, Technologists will not administer any of the above mentioned aerosol products if the subject’s FEV1/FVC is < 70% predicted unless a physician is present.
2. Exercise Induced
Baseline studies are performed and subject is placed on a treadmill and exercised until symptomatic or unable to tolerate the procedure any longer; 85% predicted maximum HR is sustained for 4 – 8 minutes during exercise. SpO2 and BP are also monitored during exercise period. Upon completion of exercise, Pulmonary Diagnostic procedures are repeated at regular intervals up to one hour post-exercise.
**Note: Laboratory offers frigid air challenge in conjunction with exercise as cold/dry air may precipitate bronchoconstriction in some susceptible individuals.
3. Other
Baseline studies are performed and subject’s response to antigen or chemical inhalation is made. Dose, length of exposure and regularity of testing is determined after Pulmonary Consultation with Medical Director, Pulmonary Diagnostic Services.
C. Nutrition Analysis (Indirect Calorimetry)
Purpose: To assess subject’s resting metabolic rate, substrates utilized and quantification of parenteral/supplemental feedings. Recent studies suggest the Harris-Benedict Equation may significantly underestimate caloric requirements (especially in metabolically stressed patients), and that Indirect Calorimetry is the preferred method since it measures the patient’s actual metabolic rate.
Measurements: VO2, VCO2, VE, RR, MV, VT (Tidal Volume)
Calculations: R (VCO2/VO2), Ventilatory Equivalents (VE/VO2, VE/VCO2), Metabolic Rate (MetRate), Resting Energy Expenditure (REE), % Carbohydrate (%CHO), % Fat and % Protein.
**Note: A 12 hour (minimum) urinary nitrogen is necessary for % Carbohydrate (%CHO), % Fat and % Protein calculations.
D. Ventilatory Drive
1. Carbon Dioxide
Purpose: Provides an index of the sensitivity of the central chemoreceptors to carbon dioxide through the analysis of the ventilatory response to a constantly increasing CO2 stimulus.
Measurements: VE, PETCO2, PETO2, FICO2, FIO2, SpO2
2. Hypoxic:
Purpose: To assess the functioning of the peripheral arterial chemoreceptors to hypoxic stimulus with the central chemoreceptor stimulus being controlled by maintaining a constant end-tidal CO2.
Measurements: VE, PETCO2, PETO2, FICO2, FIO2, SpO2
E. Arterial Venous Shunt
Purpose: To determine that portion of the cardiac output that does not exchange with alveolar gas. Shunt studies are useful in subject’s who are “refractory” to supplemental oxygen.
Measurements: Standard ABG parameters after the subject has breathed 100% oxygen for 25-30 minutes
Calculations: % Shunt (QSP/QT)
F. Pulmonary Mechanics
Purpose: Compliance measurements provide information about the elastic properties of the lung, whereas Dynamic Compliance detects the presence of covert airways disease in its earliest stages. Work of Breathing measures the contributions of resistive and elastic components (work) during tidal breathing.
Includes: Static Compliance, Specific Compliance (Cl/FRC), Maximum Lung Elastic Recoil (Pel), Co-Efficient of Retraction (Pel/TLC), Dynamic Compliance (Cdyn), Pulmonary Resistance and Work of Breathing.
G. Transdiaphragmatic Pressures
Purpose: When combined with other non-specific, aggregate measurements of total respiratory muscle strength (“Respiratory Muscle Forces”), quantifies the contribution of the diaphragm to those generated by the muscle of ventilation.
Includes: Transdiaphragmatic Pressures (Pdi), and Tension-time Indices (TTI)
H. Occlusion Pressures
Purpose: To determine/gauge central ventilatory (respiratory) drive through random measurement of airway occlusion 0.1 seconds (or 100 milliseconds) after the onset of inspiration. May be performed with or without breathing a hypercarbic mixture of gas and is applicable to spontaneous breathing, as well as mechanically ventilated patients.
**Note: This procedure has been demonstrated to be a useful predictor for evaluating the success, or failure, to wean from mechanical ventilation.
I. Home Oxygen Dose Determination
1. Rest Only
Purpose: To determine optimal, resting level, supplemental oxygen liter flow for hypoxemic patients. Can be performed with inpatients or outpatients and is especially important for hypercarbic subjects.
**NOTE: Required by Medicare and some insurance companies.
Includes: Standard room air ABG followed by another sampling 20 minutes after low flow oxygen administration (if baseline SaO2 < 85%). Subject may have “Desaturation Exercise” Study performed to assess SpO2 response to increasing workloads.
2. Oxygen Dose Determination / Titration During Exercise
Along with BP and HR response, designed to assess subject desaturation during progressively increasing, or steady, workload on the treadmill. If desaturation (by SpO2) occurs, supplemental oxygen is applied and titrated to maintain SpO2% at a physician prescribed level. The subject is retested at the same workload following appropriate rest period.
Includes: Baseline ABG with direct measurements of SaO2% and HbCO% to validate SpO2% readings. Because of the limitations associated with pulse oximeters, arterial cannulation is recommended for multiple blood gas analyses
J. Air Flight Simulation (HAST)
Purpose: Patients with moderate pulmonary or cardiac dysfunction, who may not qualify for home oxygen prescriptions, may indeed, be at significant risk for hypoxemic events during air travel, since during high altitude air flight, cabin pressure is not equal to ground level barometric pressure.
Note: In one study, inspired partial pressure of oxygen declined from 159 mm Hg at sea level to 127 mm Hg at 6,200 feet and then further declined to 113 mm Hg at 9,000 feet.
Includes: Room air arterial blood gas with pulse oximeter monitoring (SpO2). Subject then breathes an air source, for 15 minutes, that simulates “cruising altitudes” while he/she is continuously monitored by SpO2. An arterial blood gas is drawn after 15 minutes, or if SpO2 falls to 88%, whichever occurs first. If the subject is hypoxemic at this point, then an air travel prescription is indicated.
K. Breath Hydrogen Testing
Purpose: To assess lactose intolerance, which causes production of hydrogen gas.
Includes: Baseline concentration of exhaled hydrogen from a NPO subject. If the baseline hydrogen concentration is acceptable, the subject ingests a lactose (or other carbohydrate) mixture. Expired gas analysis is performed on a regular basis for up to 4 hours.
L. Infant / Toddler Pulmonary Diagnostic Tests
Purpose: To aid in diagnosis, follow the natural history of lung growth or diseases starting in infancy, evaluate therapeutic responses and allow for prediction of risk of subsequent pulmonary dysfunction based upon initial testing.
Includes: VT / Flow-Volume Loops, FRC, Crs, Rrs and Hug (VmaxFRC): Pre- and Post-Drug if baseline studies abnormal as well as Pre- and Post-Head Positioning for Upper Airway Assessment.
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