Blood Gases and function tests and ventilation

Question 0

What is the pCO2 equation?

Answer 0

PCO2 = 0.863 x (CO2 production/alveolar ventilation)

Question 1

What is important to remember about assessing alveolar ventilation?

Answer 1

Cannot assess it just by looking at a patient

Question 2

What are the physiologic processes that can cause hypoventilation?

Answer 2

Reduced total ventilation

Normal total but increased dead space ventilation

Question 3

What can cause alveolar hyperventilation?

Answer 3

Increased central respiratory drive - from pain or anxiety, compensation for metabolic acidosis

Question 4

What is a compensated respiratory acidosis?

Answer 4

Near normal ph with high bicarbonate and pCO2

Question 5

What determines if the lungs are doing a good job getting oxygen from atmosphere to blood?

Answer 5

The A-a gradient

Difference between oxygen in alveoli and oxygen in arterial blood

Question 6

What is an elevated A-a gradient?

Answer 6

Anything over 15 mm Hg

Increases with age

Question 7

How can high A-a gradient due to diffusion block be recognized?

Answer 7

Only reduces arterial blood ox during things like exercise, not at rest
Happens in fibrotic lung diseases

Question 8

How can high A-a gradient due to v:q mismatch be recognized?

Answer 8

Reduced ventilation but normal perfusion

Most common cause

Question 9

How can high A-a gradient due to a shunt be recognized?

Answer 9

pO2 not increased even if patient breaths 100% oxygen

R to L shunt suspected if paO2 <95% while patient breathing 100% oxygen

Question 10

What is suspected if paO2 is not affected but SaO2 is decreased?

Answer 10

Carbon monoxide poisoning

Question 11

When can SpO2 differ from SaO2?

Answer 11

When SaO2 <85% - ignore SpO2
Can be normal in CO poisoning
No info about alveolar ventilation or acid base balance
Inaccurate in patient with poor perfusion of extremities (shock)

Question 12

How can cyanide poisoning be recognized?

Answer 12

Adequately oxygenated blood is reaching the tissue but tissue cannot utilize it
Consequences of tissue hypoxia but all stats are normal

Question 13

What are the five causes of tissue hypoxia?

Answer 13

Reduced pAO2
Reduced paO2 with normal pAO2
Reduced CaO2 with normal paO2 (anemia, CO poisoning)
Reduced tissue perfusion (hypotension, arterial occlusion)
Reduced tissue oxygen utilization (cyanide poisoning)

Question 14

How is the A-a gradient calculated?

Answer 14

A-a = (150 - 1.25(paCO2)) - pAO2

Question 15

How can bicarbonate be determined to assess renal compensation ?

Answer 15

Henderson hasselbach equation

PH = 6.1 + log(HCO3-/0.03paCO2)

Question 16

What are the five common indications for PFTs?

Answer 16

Assessment of patient with pulm complaints
Determine pattern of respiratory impairment
Serial evaluations
Pre-OP assessment
Occupational or environmental reasons

Question 17

What are four categories of information obtained from PFTs?

Answer 17

Lung volumes and capacities
Flow rates
Diffusing capacity
Maximal inspiratory pressure and maximum expiratory pressure

Question 18

What is total lung capacity?

Answer 18

Total volume of gas within lungs after maximal inspiration

Question 19

What is residual volume?

Answer 19

Volume of gas remaining in lungs after maximal expiration

Question 20

What is vital capacity?

Answer 20

Volume of gas expired when inspiring all the way to TLC and exhaling down to RV
Largest volume of air that can be moved into or out of the lungs
Made up of IRV, TV, ERV

Question 21

What is functional residual capacity?

Answer 21

Volume of gas in lungs at resting state (during tidal breathing)

Question 22

How does spirometry work?

Answer 22

Deep inspiratory breath to TLC then forced exhalation to RV

Measure how fast and how long

Question 23

What values can you obtain from spirometry and which can’t you?

Answer 23

Can get FEV1 and FVC
Cannot get RV, TLC, or FRC
Does provide inspiratory capacity

Question 24

What is normal FEV1/FVC?

Answer 24

70-80%

Question 25

What are possible methods of measuring lung volumes?

Answer 25

``` Body plethysmography (patient sits in box and performs maneuvers, uses boyles law) Dilutional lung volumes using helium dilution or nitrogen washout - severe COPD may cause falsely low value, use other method These measure FRC ```

Question 26

How can different lung volumes be calculated if FRC is obtained?

Answer 26

FRC - ERV = RV IC + FRC = TLC VC + RV = TLC TLC is important for diagnosing restrictive lung diseases

Question 27

What are the gold guidelines for defining airflow OBSTRUCTION?

Answer 27

FEV1/FVC less than 70%

Question 28

Other than a fixed ratio, what value can be used to determine if obstruction is present?

Answer 28

Lower limits of normal | Obstructive if ratio below the 5th percentile of predicted

Question 29

What is FEF 25-75%?

Answer 29

Expired airflow rate between the 25 and 75% points on a forced expiratory Spirogram Average flow rate over middle half of expiration Indicates status of medium to small airways Can detect early stages of obstruction when ratio still normal

Question 30

What is a flow volume loop?

Answer 30

``` Forced expiration and inspiration curves create closed loop Y axis is flow X axis is volume Above x axis is expiratory flow Below x axis is inspiratory flow ```

Question 31

What is the pattern of restrictive lung diseases on PFTs?

Answer 31

``` FEV1 and FVC both decreased Ratio is normal or increased TLC is decreased Convex pattern on flow volume loop Low DLCO suggests fibrosis ```

Question 32

What is the differential diagnosis of restrictive lung disease?

Answer 32

``` PAINT pleural diseases Alveolar diseases Interstitial lung diseases Neuromuscular diseases Thoracolumbar ```

Question 33

What is the DLCO?

Answer 33

Diffusing capacity of lung for carbon monoxide | Rate at which CO is absorbed from alveolar gas by pulmonary capillaries

Question 34

What are the disease processes that lead to a reduced diffusing capacity?

Answer 34

Respiratory: Emphysema, Interstitial lung disease, Pulmonary vascular disease (isolated reduced, other stats normal) Anemia (reduces) and polycythemia (increases) affect hemoglobin availability

Question 35

What do MIP and MEP help measure?

Answer 35

Strength of respiratory muscles

Question 36

What is the obstructive pattern on PFTs?

Answer 36

Reduced ratio and reduced FEF 25-75 Scooped out appearance of expiratory limb on flow volume loop Presence of bronchodilator response in asthma Elevated TLC and RV Reduced DLCO FEV1 <50% indicates severe

Question 37

When is mechanical ventilation indicated?

Answer 37

Acute setting for critically ill patients Respiratory failure - oxygenation or ventilation Controlled setting for support while patient under anesthesia for operation Supportive not curative - must fix underlying disease process

Question 38

What is the mode of ventilators?

Answer 38

Pattern of cycling used to drive gas flow from ventilator to patient - volume or pressure regulated Most deliver fixed volume

Question 39

When is controlled mechanical ventilation (CMV) used?

Answer 39

Ventilator provides full support and doesn't allow patient to support own ventilation - cannot take spontaneous breaths Effective under general anesthesia, comatose, unable to make any inspiratory effort Not used in patients capable of spontaneous breathing

Question 40

When is assist control ventilation (AC) used?

Answer 40

Ventilator assists patients breath to provide full tidal volume breath Back up rate and full tidal volume breath if patient does not initiate a spontaneous breath Awake, moderately sedated (post OP), or fully paralyzed patients

Question 41

When is synchronized intermittent mandatory ventilation (SIMV) used?

Answer 41

Ventilator delivers preset number of breaths per minute at specific tidal volume Patient can spontaneously breath - not assisted

Question 42

When is pressure support ventilation (PS) used?

Answer 42

Patient determines inflation volume and respiratory cycle - requires spontaneously breathing patient Pre selected pressure assists during inspiration

Question 43

When is pressure control ventilation (PC) used?

Answer 43

Very little participation by patient | Pressures and breathing times set by clinician

Question 44

What is a normal tidal volume setting?

Answer 44

8-10 | Lower in ARDS to protect lung from high pressures during inspiration (leads to volutrauma, barotrauma, atelectotrauma)

Question 45

What is the positive end expiratory pressure (PEEP) when using ventilators?

Answer 45

Collapse of airspaces at end of expiration common in ventilators - causes atelectasis PEEP reduces alveoli closing/opening and can improve oxygenation

Question 46

What is CPAP?

Answer 46

Continuous positive airway pressure Patient breathing spontaneously No support provided - splints open airways Set pressure delivered during inspiration and expiration Used mostly in obstructive sleep apnea and cardiogenic pulm edema

Question 47

What is BiPAP?

Answer 47

Patient breathing spontaneously Provides two pressures - inspiratory positive airway and expiratory positive airway Primarily in COPD when carbon dioxide elimination is needed

Question 48

What is extracorporeal membranous oxygenation (ECMO)?

Answer 48

Supports gas exchange | Removes blood from patient and circulates it through artificial lung

Question 49

When is ECMO used?

Answer 49

In ARDS Mostly in neonatal population Limited use in adult respiratory failure