EXAM #2: RESPIRATORY FAILURE: ACUTE AND CHRONIC

Question 1

What is respiratory failure?

Answer 1

Failure of the lung to perform one or both of its gas exchange functions:

1) Oxygenation
2) Carbon dioxide elimination

Question 2

What is acute respiratory failure? What is important general principle to keep in mind about acute respiratory failure?

Answer 2

Abrupt onset i.e. minutes to hours
- Reversible

E.g. drug overdose preventing ventilation or pneumonia preventing oxygenation

Question 3

What is chronic respiratory failure? What is important general principle to keep in mind about acute respiratory failure?

Answer 3

Insidious
- Irreversible

E.g. neuromuscular disease preventing ventilation or pulmonary fibrosis preventing oxygenation

Question 4

What is the definition of acute on chronic respiratory failure?

Answer 4

• This a patient with chronic respiratory failure/ increased baseline oxygen requirements
• CO2 retention enough to drop pH below 7.3 is diagnostic for acute respiratory failure

*Thus, in the patient with chronic respiratory failure, an acute drop in pH below 7.3 is acute on chronic failure.

Question 5

What are the reference numbers for PaO2 and PCO2 for respiratory “failure?”

Answer 5

• PaO2 less than 60 mmHg (Hypoxemic)

- PCO2 greater than 50 mmHg (Hypercapneic)

Question 6

What determines the normal PaO2?

Answer 6

Age, normal PaO2 decrease with increasing age

*FYI, PaO2= 100.1 - 0.32(age)

Question 7

What is the normal PaCO2?

Answer 7

40 mmHg

Question 8

What is Type I respiratory failure?

Answer 8

Hypoxemic respiratory failure

Question 9

What is Type II acute respiratory failure?

Answer 9

Hypercapnic respiratory failure

Question 10

What is Type III respiratory failure?

Answer 10

Perioperative i.e. within any of the phases of surgery (pre-op, intraoperative, and post-op)

Question 11

What is Type IV respiratory failure?

Answer 11

Respiratory failure that occurs in the setting of shock

Question 12

What causes hypoxemia? What is the most common cause of hypoxemia?

Answer 12

1) V/Q mismatch*
- Under ventilation i.e. airway or interstitial lung disease
- Overperfusion e.g. PE
2) Shunt
3) Hypoventilation
4) Diffusion impairment
5) Low FiO2

V/Q mismatch is the most common cause of hypoxemia

Question 13

What is the A-a gradient? Why is this important?

Answer 13

• The A-a gradient refers to the difference between PAO2 (alveolar oxygen pressure) and – PaO2 (arterial oxygen pressure)
• A normal resting A-a gradient in healthy middle aged adults ~ 5-10 mmHg

*Calculation of the A-a gradient is useful in determining the etiology of hypoxemia. In conditions of high altitude or hypoventilation ,the lung parenchyma is normal; thus, the A-a gradient should be within normal limits. PaO2 is low but only because PAO2 is low, but transfer of gas from “A” to “a” is normal. In contrast, diffusion defects, ventilation-perfusion mismatch, or right-to-left shunting, in which oxygen is not effectively transferred from the alveoli to the blood results in an elevated A-a gradient.

Question 14

What are the four causes an increased A-a gradient?

Answer 14

Increased A-a gradient may occur in:

1) Shunting
2) V/Q mismatch
3) Aging
4) Diffusion impairments

Question 15

If hypoxemia or the A-a gradient improves with supplemental oxygen, what do you know?

Answer 15

There is V/Q mismatch

Question 16

If hypoxemia or the A-a gradient does NOT improve with oxygen, what do you know?

Answer 16

Shunt i.e. V/Q is 0 b/c there is perfusion without ventilation

Question 17

What are the basic tests that should be ordered in the setting of respiratory failure?

Answer 17

1) ABG
2) CXR
3) EKG
4) Labs e.g.
- CBC w/ diff
- CMP
- BNP
- D-dimer
- Lactic acid

Question 18

What is the P/F ratio? What is the utility of the P/F ratio?

Answer 18

PaO2/FiO2 ratio that indicates severity of hypoxemia

• Mild= 300-200
• Moderate= 200-100
• Severe= Less than 100

Question 19

How are patients with respiratory failure initially managed?

Answer 19

1) Supplemental oxygen
2) IV access
3) Vital sign monitoring

Question 20

What are the advanced measures to support patients with respiratory failure?

Answer 20

1) Optimize Hb concentration, CO, lactic acid
2) Treat underlying cause
3) Support ventilation/ respiration with:
- Mechanical ventilation
- High flow Nasal Cannula
- ECMO

Question 21

What is the basic premise of pure hypercapnic respiratory failure? What lab test is virtually diagnostic for acute hypercapnic respiratory failure?

Answer 21

Alveolar ventilation is unable to remove CO2 fast enough

*Hypercapnea that develops rapidly enough to drop pH below 7.3 is virtually diagnostic for acute hypercapnic respiratory failure

Question 22

What are the basic causes of hypercapnia?

Answer 22

1) Hypoventilation
- Neuromuscular disorder
- CNS depression
2) Increased production e.g. sepsis, trauma, burns…etc.
3) Airway obstruction
4) Impairment of respiratory muscles

Question 23

What is the effect of an acute increase/decrease in CO2 of 10 on pH?

Answer 23

Increase= decrease pH by 0.08 
Decrease= increased pH by 0.08

Question 24

What is the effect of a chronic increase/decrease in CO2 of 10 on pH?

Answer 24

Increase= decrease pH by 0.03 
Decrease= increased pH by 0.03

Question 25

In acute respiratory acidosis, for every 10 increased CO2, how much does the kidney increase HCO3-? Chronic?

Answer 25

Acute= every 10 CO2 increases HCO3- by 1 
Chronic= every 10 CO2 increases HCO3- by 3

Question 26

In acute respiratory alkalosis, for a decrease in 10 CO2, what happens to HCO3-? Chronic?

Answer 26

Acute= every 10 CO2 decreases HCO3- by 2
Chronic= every 10 CO2 decreases HCO3- by 5

Question 27

What patient population has benefited from noninvasive mechanical ventilation?

Answer 27

• AECOPD (acute exacerbation of COPD)

- CHF

Question 28

What are the three mechanisms of acute exacerbations of respiratory failure in pateints with underlying hypercapnia?

Answer 28

1) Worsened V/Q mismatch
2) Attenuated hypoxic ventilatory drive
3) Haldane effect: oxygen binding releases bound CO2, increasing PaCO2

Question 29

What are the clinical indications of chronic respiratory failure?

Answer 29

1) Polycythemia
2) Elevated CO2
3) Normal pH with elevated PaCO2
4) Elevated bicarbonate
5) Clubbing

Question 30

What are the guidelines for assisting patients to stop smoking?

Answer 30

1) Set quit date
2) Referral to cessation clinic
3) Pharmacologic therapy/ nicotine replacement esp. if:
- 1 ppd+
- Cig within min. of waking up

Question 31

What vaccines do patients with chronic respiratory failure need?

Answer 31

1) Pertussis booster
2) Influenza
3) Pneumococcal
- Prevnar 13

Question 32

What has research demonstrated in regards to oxygen therapy and survival in respiratory failure-?

Answer 32

Improvement in survival in patients that MEET CRITERIA

Question 33

What qualifys a patient for supplemental oxygen?

Answer 33

1) PaO2 less than 55 mmHg or SaO2 less than 88%
2) PaO2 from 56-59 if
- ECG shows cor pulmonale
- Pedal edema
- Hct greater than 55%

Question 34

What are the absolute contraindications to a lung transplant?

Answer 34

1) Major organ dysfunction
2) HIV, HCV, HBV
3) Active malignancy within 2 years
4) Severe non-osteoporotic MSK disease
5) Substance abuse