EXAM #2: RESPIRATORY FAILURE: ACUTE AND CHRONIC Flashcards
What is respiratory failure?
Failure of the lung to perform one or both of its gas exchange functions:
1) Oxygenation
2) Carbon dioxide elimination
What is acute respiratory failure? What is important general principle to keep in mind about acute respiratory failure?
Abrupt onset i.e. minutes to hours
- Reversible
E.g. drug overdose preventing ventilation or pneumonia preventing oxygenation
What is chronic respiratory failure? What is important general principle to keep in mind about acute respiratory failure?
Insidious
- Irreversible
E.g. neuromuscular disease preventing ventilation or pulmonary fibrosis preventing oxygenation
What is the definition of acute on chronic respiratory failure?
- 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.
What are the reference numbers for PaO2 and PCO2 for respiratory “failure?”
- PaO2 less than 60 mmHg (Hypoxemic)
- PCO2 greater than 50 mmHg (Hypercapneic)
What determines the normal PaO2?
Age, normal PaO2 decrease with increasing age
*FYI, PaO2= 100.1 - 0.32(age)
What is the normal PaCO2?
40 mmHg
What is Type I respiratory failure?
Hypoxemic respiratory failure
What is Type II acute respiratory failure?
Hypercapnic respiratory failure
What is Type III respiratory failure?
Perioperative i.e. within any of the phases of surgery (pre-op, intraoperative, and post-op)
What is Type IV respiratory failure?
Respiratory failure that occurs in the setting of shock
What causes hypoxemia? What is the most common cause of hypoxemia?
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
What is the A-a gradient? Why is this important?
- 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.
What are the four causes an increased A-a gradient?
Increased A-a gradient may occur in:
1) Shunting
2) V/Q mismatch
3) Aging
4) Diffusion impairments
If hypoxemia or the A-a gradient improves with supplemental oxygen, what do you know?
There is V/Q mismatch
If hypoxemia or the A-a gradient does NOT improve with oxygen, what do you know?
Shunt i.e. V/Q is 0 b/c there is perfusion without ventilation
What are the basic tests that should be ordered in the setting of respiratory failure?
1) ABG
2) CXR
3) EKG
4) Labs e.g.
- CBC w/ diff
- CMP
- BNP
- D-dimer
- Lactic acid
What is the P/F ratio? What is the utility of the P/F ratio?
PaO2/FiO2 ratio that indicates severity of hypoxemia
- Mild= 300-200
- Moderate= 200-100
- Severe= Less than 100
How are patients with respiratory failure initially managed?
1) Supplemental oxygen
2) IV access
3) Vital sign monitoring
What are the advanced measures to support patients with respiratory failure?
1) Optimize Hb concentration, CO, lactic acid
2) Treat underlying cause
3) Support ventilation/ respiration with:
- Mechanical ventilation
- High flow Nasal Cannula
- ECMO
What is the basic premise of pure hypercapnic respiratory failure? What lab test is virtually diagnostic for acute hypercapnic respiratory failure?
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
What are the basic causes of hypercapnia?
1) Hypoventilation
- Neuromuscular disorder
- CNS depression
2) Increased production e.g. sepsis, trauma, burns…etc.
3) Airway obstruction
4) Impairment of respiratory muscles
What is the effect of an acute increase/decrease in CO2 of 10 on pH?
Increase= decrease pH by 0.08 Decrease= increased pH by 0.08
What is the effect of a chronic increase/decrease in CO2 of 10 on pH?
Increase= decrease pH by 0.03 Decrease= increased pH by 0.03
In acute respiratory acidosis, for every 10 increased CO2, how much does the kidney increase HCO3-? Chronic?
Acute= every 10 CO2 increases HCO3- by 1 Chronic= every 10 CO2 increases HCO3- by 3
In acute respiratory alkalosis, for a decrease in 10 CO2, what happens to HCO3-? Chronic?
Acute= every 10 CO2 decreases HCO3- by 2 Chronic= every 10 CO2 decreases HCO3- by 5
What patient population has benefited from noninvasive mechanical ventilation?
- AECOPD (acute exacerbation of COPD)
- CHF
What are the three mechanisms of acute exacerbations of respiratory failure in pateints with underlying hypercapnia?
1) Worsened V/Q mismatch
2) Attenuated hypoxic ventilatory drive
3) Haldane effect: oxygen binding releases bound CO2, increasing PaCO2
What are the clinical indications of chronic respiratory failure?
1) Polycythemia
2) Elevated CO2
3) Normal pH with elevated PaCO2
4) Elevated bicarbonate
5) Clubbing
What are the guidelines for assisting patients to stop smoking?
1) Set quit date
2) Referral to cessation clinic
3) Pharmacologic therapy/ nicotine replacement esp. if:
- 1 ppd+
- Cig within min. of waking up
What vaccines do patients with chronic respiratory failure need?
1) Pertussis booster
2) Influenza
3) Pneumococcal
- Prevnar 13
What has research demonstrated in regards to oxygen therapy and survival in respiratory failure-?
Improvement in survival in patients that MEET CRITERIA
What qualifys a patient for supplemental oxygen?
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%
What are the absolute contraindications to a lung transplant?
1) Major organ dysfunction
2) HIV, HCV, HBV
3) Active malignancy within 2 years
4) Severe non-osteoporotic MSK disease
5) Substance abuse
