What type of respiratory defect causes patients to become hypercapnic?
Ventilatory Failure (you aren’t blowing off enough O2)
PaCO2 ~ 1/ventilation
What is the #1 most common cause of hypoxia?
V/Q (ventilation/perfusion) mismatch
- V/Q mismatch is a problem because you’re wasting cardiac output on areas that aren’t being ventilated so the blood perfusing these areas doesn’t exchange any gas
- Meanwhile there is less blood perfusing the areas that actually need gas assume that cardiac output from the right side is constant.
***What are the 5 causes of Hypoxemia?
Normal A-a gradient:
- Anemia
- Hypoventilation
Elevated A-a gradient:
- R to L shunt
- V/Q inequality
- Diffusion Limitation
What are some causes of Hypercapnic Respiratory Failure?
ANYTHING that suppresses breathing. • Central Hypoventilation (opiates) • Muscle (pump) failure (Muscular Dystrophy, Myopathies, Myasthenia gravis, ALS) • Botulism • Guillian Barre Syndrome • Airway Obstruction
What are some causes of left shift in Hbg?
• Is left shift an increased or decreased affinity for binding?
- Hypothermia
- Alkalosis
- Fetal Hbg
- Carbon Monoxide
=> Left Shift = increased affinity for binding
Evaluation of someone with Respiratory Failure: • Hx and Physical • Vital Signs and Pulse Oximetry • CXR • EKG • ABG (arterial blood gas) • CBC •Electrolytes • Sputum and blood cultures, UA • Helical CT (often 1st to check for PE)
Evaluation of someone with Respiratory Failure: • Hx and Physical • Vital Signs and Pulse Oximetry • CXR • EKG • ABG (arterial blood gas) • CBC • Electrolytes • Sputum and blood cultures, UA • Helical CT (often 1st to check for PE)
Would you use a pulmonary function test in someone with acute respiratory failue?
NO - this is a method to evaluate people with chronic respiratory failure
What is the 1st thing you do to treat the patient when they come in with respiratory failure?
• how does this treatment also aid in Dx?
- PUT THEM ON SUPPLEMENTAL O2
* if it doesn’t correct then you know you’re dealing with a SHUNTING issue
Differentiate the use of Albuterol, Ipratropium, and Formoterol in the treatment of COPDs?
Albuterol: treats asthma
Ipratropium: treats COPD
Formoterol: Rapid onset and LONG ACTING
Why can’t corticosteroids eliminate all bronchospasm?
PENETRATION - if they can’t access the tissue then they can’t activate ß2 receptors
What are some ques to determine if someone is tired as a result of respiratory failure?
- Increase Somnolence
- Decreasing RR
- Decreased Respiratory Excursions
- Borderline O2 sat. (may not see this if you’re giving the patient supplemental O2).
What is the ABG likely to reveal in someone with respiratory failure?
Hypercapnia
What do you do when the CO2 starts going up in a patient with respiratory failure?
put them on ASSISTED VENTILATION
T or F: exhalation will be prolonged in patients with COPD.
True, this is why their FEV1/FVC is reduced
T or F: PaO2 makes a large contribution to blood O2.
False, PaO2 is only a small fraction of blood O2
What are 4 causes of increased CO2 retention after supplmental O2?
- Blunting of Hypoxic Drive
- Worsening of V/Q mismatch
- Haldane Effect
- Neuromuscular Fatigue
Why does the V/Q mismatch become more significant on supplemental O2?
Worsening of V/Q mismatch:
• supplemental O2 abolishes hypoxic induced vasoconstriction of pulmonary vasculature
- Poorly ventilated areas of the lung start getting perfused
- These areas are not functional so you start perfusing areas that can’t exchange O2 and the V/Q mismatch gets worse
What is the Haldane Effect?
- In hypoxic individuals CO2 binds to Hbg
- Supplemental O2 raises both PaO2 and SaO2
- CO2 gets kicked off of Hbg and replaced with O2
- CO2 has to go somewhere so it dissolves in the blood to raise the PCO2
How should you manage a patient experiencing bronchospasm that is precipitating respiratory failure?
- Bronchodilators
- Hydration
- SYSTEMIC Corticosteroids
- Treat the precipitating cause
What will be ABG look like for a patient who is getting tired as a result of respiratory failure?
They will become increasingly hypercapnic.
You should consider assisted breathing, mechanical ventilation, or intubation in these patients.
