7. Pulmonary Function Tests

Pulmonary Function Tests (PFT’s) Scott Stevens D.O. Gannon University College of Health Sciences Graduate Program • Department of Nursing Pulmonary Function Tests (PFT’s) • A nonspecific term used most often to describe only spirometry • Pulmonary tests include: chest x-ray (CXR), arterial blood gas (ABG), Spirometry with FEV1sec, FVC, FEV1/FVC, FEF 25-75, Flowvolume loops, Ventilation-perfusion (V/Q) scan, Pulse oximetry (SpO2), SaO2 from ABG, Mixed venous oxygen (PvO2) and saturation from pulmonary artery catheter PFT Indications • Possible pneumonectomy or lobectomy • Surgery of upper abdomen • History of pulmonary disease: COPD, bronchitis, emphysema, pulmonary fibrosis, significant smoking history • Severe obesity, obstructive sleep apnea (OSA), pickwickian syndrome (obesity, decreased pulmonary function, polycythemia) • Evidence of pulmonary dysfunction during history and physical exam – Dyspnea = shortness of breath, SOB – DOE = dyspnea on exertion Patients at risk for post-op pulmonary complications • • • • • Significant history of pulmonary disease Thoracic or abdominal (esp. upper) surgery Obesity Long-term smokers Elderly patients (>70 yrs) High risk PFT results • FEV1 < 2L • FEV1/FVC < 0.5 • VC < 15cc/Kg in adult & < 10cc/Kg in child • VC < 40 to 50% than predicted Why get PFT’s preoperatively? • By estimating pulmonary reserve one can better plan and predict pre-, intra- and postoperative pulmonary care requirements Preoperatively • Goal is to treat any reversible conditions, optimize pt • Bronchodilators: testing will show any improvement with treatment, adjust doses • Most important in patients with a >15% improvement in FEV1 after treatment • Bronchitis: optimize patient – respiratory therapy, bronchodilators for bronchospasm – antibiotics to treat infection, sputum for culture and sensitivity (C&S) • Optimize CHF Intraoperatively • Ventilator adjustments – Severe emphysema requires longer expiratory times (normal I:E is 1:2, so in COPD  1:3) – Closely monitor peak inspiratory pressures (PIP) to avoid rupturing an emphysematous bleb – CO2 retainers: EtCO2 should be keep near the pt’s baseline, a rapid correction will lead to metabolic alkalosis • Bronchospasm: avoid *histamine releasing drugs – Pentothal (STP), Morphine (MSO4), Atracurium, Mivacurium, Neostigmine – Tx with nebulized albuterol Postoperatively • Extubation: – If FEV1 is >50% predicted than extubation probably will not be effected – If FEV1 is between 25 – 50%, with some hypoxemia and hypercarbia – prolonged intubation probable – If FEV1 is <25% predicted – only life saving procedures should be done, regional anesthesia if possible, long term ventilatory support, possible inability to wean from ventilator, tracheostomy probable • *Extubation criteria: – – – – VSS, awake & alert, resp. rate < 30 ABG on FiO2 of 40%  PaO2 >70 and PaCO2 <55 MIF is more negative than -20cm H2O Vital capacity (VC) > 15cc/Kg Acute respiratory failure • *Intubation criteria: – Mechanics: RR>35, VC <15cc/Kg in adult or <10cc/Kg in child, MIF more neg. than -20cmH2O – Oxygenation: PaO2 < 70mmHg on FiO2 of 40%, A-a gradient > 350mmHg on 100% O2 – Ventilation: PaCO2 > 55 (except in chronic hypercarbia), Vd/Vt > 0.6 (remember normal dead space is 30%) – Clinical: airway burn, chemical burn, epiglottis, mental status change, rapidly deteriorating pulmonary status, fatigue Normal CXR Expiratory CXR Inspiratory CXR (same pt) Expiratory CXR for pneumothorax (PTX) Tension Pneumothorax CHF or excessive IV fluids RUL consolidation  aspiration ABG • Results: pH / PCO2 / PO2 / bicarbonate / base excess • Usually obtained from radial, brachial, femoral, axillary, or dorsalis pedis artery • Drawn in heparinized syringe • Must be measured within 15 minutes or glycolysis will occur with lactic acid production, decreased pH, and increased PCO2 • Sample can be stored on ice for 1 to 2 hours • Heparin may significantly lower PCO2 by dilution, esp. in children when small samples taken ABG normal values • • • • • pH: 7.35 – 7.45 PCO2: 35 – 45 mmHg PO2: 75 – 105 mmHg Bicarbonate: 20 – 26 mmoles/L Base excess: -3 to +3 mmoles/L pH • Acidemia = blood pH < 7.35 • Alkalemia = blood pH > 7.45 • Acidosis = a process which causes acid to accumulate • Alkalosis = a process which causes alkali accumulation • Altered pH  next determine if respiratory (CO2) or metabolic (HCO3-) • Buffers: substance that can absorb or donate H+ – Bicarb(HCO3-), Hb, serum proteins, phosphate(HPO4-) PaCO2 • Hypercapnia – increased CO2 • Hypocapnia – decreased CO2 • *Rule: an increase of PCO2 by 10 mmHg causes a decrease in pH by 0.08, likewise, a decrease of PCO2 by 10 mmHg will increase pH by 0.08 – So an acute increase in CO2 to 60 should cause a drop in pH to 7.24 • • • • • • • • • PaO2 Hypoxemia = decreased PO2 in blood, < 75 Hypoxia = a low O2 state A-a gradient – a measure of efficiency of lung PAO2 = (PB-PH2O)*(FiO2) – (PaCO2/0.8) PAO2 = (760-47)*(0.21) – (40/0.8) = 100 PAO2 = (760-47)*(0.5) – (40/0.8) = 306 PAO2 = (760-47)*(1) – (40/0.8) = 663 Normal A-a = approximately (Age / 3) A-a gradient is widened during anesthesia and with intrinsic lung Dz: PTX, PE, shunt, V/Q mismatch, diffusion problems • A-a gradient is normal with hypoventilation or low FiO2 • Tx is supplemental O2, adjust ventilation, tx atelectasis, add PEEP, tx underlying cause Bicarbonate • A calculated value from: • Values alter due to acidosis/alkalosis • Base excess is calculated directly using PaCO2, pH, and bicarbonate values • Rule: a decrease in bicarb. by 10 mmoles decreases the pH by 0.15, likewise, an increase in bicarb. By 10 mmoles increases pH by 0.15 • A bicarb. of 13 would result in a pH of 7.25 • Total body bicarb. deficit = (base deficit * wt in Kg * 0.4), in mEq/L, usually replace ½ of deficit [H+] = 24 * (PaCO2/[HCO3-]) Respiratory Acidosis • Low pH & High PaCO2 • Acute and chronic causes: – – – – – Hypoventilation with hypercarbia CNS depression – trauma, drugs Decreased FRC – obesity Upper or lower airway obstruction COPD, asthma, pulmonary fibrosis • After 1-2 days renal compensation occurs – H+ excreted by kidney and HCO3- reabsorbed into blood to partially correct pH Respiratory Alkalosis • High pH & Low PaCO2 • Hyperventilation with hypocarbia • Causes: hypoxic respiration, CNS Dz, encephalitis, anxiety, narcotic withdrawl, pregnancy, early septic shock, hypermetabolic states, artificial ventilation • Renal compensation will occur causing increased excretion of HCO3- and decreased secretion of H+ which partially corrects pH Metabolic Acidosis • Low pH & Low HCO3• Causes: lactic acidosis from hypoperfusion, DKA, renal Dz with bicarb loss (anion gap and K+), HCO3loss in diarrhea, ASA ingestion, high protein intake • Respiratory compensation (central chemoreceptors) with hypocarbia, more rapid than renal compensation, partial correction • Kidneys may increase H+ excretion Metabolic Alkalosis • High pH & High HCO3• Causes: bicarb. infusion, metabolism of lactate or citrate, loss of H+ from vomiting or excessive NGT suctioning • Respiratory compensation by limited hypoventilation due to eventual hypoxic drive, partial correction • Kidneys may increase bicarb. excretion in urine Spirometry FEV-1 second • After maximal inspiration, the volume of air that can be forcefully expelled in one second • Effort dependent • Normally between 3 – 5 L • Also reported as percent predicted • Also reported as a percent of FVC – FEV1 / FVC  normally > 75% • Most important clinical tool in assessing the severity of airway obstructive disease FEV1 Degree of risk in obstructive lung disease • RISK Normal Mild Moderate Severe Extreme FEV1 / FVC > 75 60-75 45-60 35-45 < 35 Flow-Volume loop Flow-volume loops • Helps distinguish between upper airway obstruction (extrathoracic) and generalized pulmonary disease (intrathoracic) • An extrathoracic obstruction decreases inspiratory flow • An intrathoracic obstruction decreases expiratory flow FEF 25-75 • Forced expiratory flow at 25 to 75% of FVC • Effort independent • Reflects collapse of small airways, peripheral airways • Sensitive indicator of early airway obstruction MVV or MBC • • • • Maximal voluntary ventilation Maximal breathing capacity “will to live” test The maximal amount of air a pt can exhale in one minute at maximal effort (hyperventilation) • Extremely effort dependent, nonspecific • Tests motivation, mechanics, strength, and endurance • A decrease has been shown to predict increased morbidity and mortality in pts undergoing thoracic surgery That’s All For Today