Pulmonary Function Tests (PFT

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Pulmonary Function Tests (PFTs)

• Scott Stevens D.O.
• Gannon University
• College of Health Sciences
• Graduate Program Department of Nursing

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Pulmonary Function Tests (PFTs)

• 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, Flow-volume
  loops, Ventilation-perfusion (V/Q) scan, Pulse
  oximetry (SpO2), SaO2 from ABG, Mixed venous
  oxygen (PvO2) and saturation from pulmonary
  artery catheter

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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

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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 (gt70 yrs)

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High risk PFT results

• FEV1 lt 2L
• FEV1/FVC lt 0.5
• VC lt 15cc/Kg in adult lt 10cc/Kg in child
• VC lt 40 to 50 than predicted

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Why get PFTs preoperatively?

• By estimating pulmonary reserve one can better
  plan and predict pre-, intra- and post-operative
  pulmonary care requirements

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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 gt15
  improvement in FEV1 after treatment
• Bronchitis optimize patient
• respiratory therapy, bronchodilators for
  bronchospasm
• antibiotics to treat infection, sputum for
  culture and sensitivity (CS)
• Optimize CHF

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Intraoperatively

• Ventilator adjustments
• Severe emphysema requires longer expiratory times
  (normal IE is 12, so in COPD ? 13)
• Closely monitor peak inspiratory pressures (PIP)
  to avoid rupturing an emphysematous bleb
• CO2 retainers EtCO2 should be keep near the
  pts 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

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Postoperatively

• Extubation
• If FEV1 is gt50 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 lt25 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 lt 30
• ABG on FiO2 of 40 ? PaO2 gt70 and PaCO2 lt55
• MIF is more negative than -20cm H2O
• Vital capacity (VC) gt 15cc/Kg

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Acute respiratory failure

• Intubation criteria
• Mechanics RRgt35, VC lt15cc/Kg in adult or
  lt10cc/Kg in child, MIF more neg. than -20cmH2O
• Oxygenation PaO2 lt 70mmHg on FiO2 of 40, A-a
  gradient gt 350mmHg on 100 O2
• Ventilation PaCO2 gt 55 (except in chronic
  hypercarbia), Vd/Vt gt 0.6 (remember normal dead
  space is 30)
• Clinical airway burn, chemical burn,
  epiglottis, mental status change, rapidly
  deteriorating pulmonary status, fatigue

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Normal CXR
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Expiratory CXR
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Inspiratory CXR (same pt)
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Expiratory CXR for pneumothorax (PTX)
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Tension Pneumothorax
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CHF or excessive IV fluids
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RUL consolidation ? aspiration
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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

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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

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pH

• Acidemia blood pH lt 7.35
• Alkalemia blood pH gt 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-)

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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

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PaO2

• Hypoxemia decreased PO2 in blood, lt 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

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Bicarbonate

• A calculated value from
• H 24 (PaCO2/HCO3-)
• 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

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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

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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

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Metabolic Acidosis

• Low pH Low HCO3-
• Causes lactic acidosis from hypoperfusion, DKA,
  renal Dz with bicarb loss (anion gap and K),
  HCO3- loss 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

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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

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Spirometry
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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 gt 75
• Most important clinical tool in assessing the
  severity of airway obstructive disease

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FEV1
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Degree of risk in obstructive lung disease

• RISK FEV1 / FVC
• Normal gt 75
• Mild 60-75
• Moderate 45-60
• Severe 35-45
• Extreme lt 35

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Flow-Volume loop
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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

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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

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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

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