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Block 5 - Pulm and Skeletal > Blood Gases and function tests and ventilation > Flashcards

Blood Gases and function tests and ventilation Flashcards

0
Q

What is the pCO2 equation?

A

PCO2 = 0.863 x (CO2 production/alveolar ventilation)

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1
Q

What is important to remember about assessing alveolar ventilation?

A

Cannot assess it just by looking at a patient

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2
Q

What are the physiologic processes that can cause hypoventilation?

A

Reduced total ventilation

Normal total but increased dead space ventilation

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3
Q

What can cause alveolar hyperventilation?

A

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

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4
Q

What is a compensated respiratory acidosis?

A

Near normal ph with high bicarbonate and pCO2

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5
Q

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

A

The A-a gradient

Difference between oxygen in alveoli and oxygen in arterial blood

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6
Q

What is an elevated A-a gradient?

A

Anything over 15 mm Hg

Increases with age

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7
Q

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

A

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

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8
Q

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

A

Reduced ventilation but normal perfusion

Most common cause

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9
Q

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

A

pO2 not increased even if patient breaths 100% oxygen

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

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10
Q

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

A

Carbon monoxide poisoning

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11
Q

When can SpO2 differ from SaO2?

A

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)

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12
Q

How can cyanide poisoning be recognized?

A

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

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13
Q

What are the five causes of tissue hypoxia?

A

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)

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14
Q

How is the A-a gradient calculated?

A

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

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15
Q

How can bicarbonate be determined to assess renal compensation ?

A

Henderson hasselbach equation

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

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16
Q

What are the five common indications for PFTs?

A

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

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17
Q

What are four categories of information obtained from PFTs?

A

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

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18
Q

What is total lung capacity?

A

Total volume of gas within lungs after maximal inspiration

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19
Q

What is residual volume?

A

Volume of gas remaining in lungs after maximal expiration

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20
Q

What is vital capacity?

A

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

21
Q

What is functional residual capacity?

A

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

22
Q

How does spirometry work?

A

Deep inspiratory breath to TLC then forced exhalation to RV

Measure how fast and how long

23
Q

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

A

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

24
Q

What is normal FEV1/FVC?

A

70-80%

25
Q

What are possible methods of measuring lung volumes?

A 
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
26
Q

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

A

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

27
Q

What are the gold guidelines for defining airflow OBSTRUCTION?

A

FEV1/FVC less than 70%

28
Q

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

A

Lower limits of normal

Obstructive if ratio below the 5th percentile of predicted

29
Q

What is FEF 25-75%?

A

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

30
Q

What is a flow volume loop?

A 
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
31
Q

What is the pattern of restrictive lung diseases on PFTs?

A 
FEV1 and FVC both decreased
Ratio is normal or increased
TLC is decreased
Convex pattern on flow volume loop
Low DLCO suggests fibrosis
32
Q

What is the differential diagnosis of restrictive lung disease?

A 
PAINT
pleural diseases
Alveolar diseases
Interstitial lung diseases
Neuromuscular diseases
Thoracolumbar
33
Q

What is the DLCO?

A

Diffusing capacity of lung for carbon monoxide

Rate at which CO is absorbed from alveolar gas by pulmonary capillaries

34
Q

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

A

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

35
Q

What do MIP and MEP help measure?

A

Strength of respiratory muscles

36
Q

What is the obstructive pattern on PFTs?

A

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

37
Q

When is mechanical ventilation indicated?

A

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

38
Q

What is the mode of ventilators?

A

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

39
Q

When is controlled mechanical ventilation (CMV) used?

A

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

40
Q

When is assist control ventilation (AC) used?

A

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

41
Q

When is synchronized intermittent mandatory ventilation (SIMV) used?

A

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

42
Q

When is pressure support ventilation (PS) used?

A

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

43
Q

When is pressure control ventilation (PC) used?

A

Very little participation by patient

Pressures and breathing times set by clinician

44
Q

What is a normal tidal volume setting?

A

8-10

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

45
Q

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

A

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

46
Q

What is CPAP?

A

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

47
Q

What is BiPAP?

A

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

48
Q

What is extracorporeal membranous oxygenation (ECMO)?

A

Supports gas exchange

Removes blood from patient and circulates it through artificial lung

49
Q

When is ECMO used?

A

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

Block 5 - Pulm and Skeletal (19 decks)

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