Respiratory Failure

Question 1

3 Types of Resp Fail and Pathophysiology of Ea

Answer 1

• Oxygenation Failure
  
  • Disease of lung itself –> dec PaO2
  • Inc A-a gradient
  • PaCO2 is maintained or dec if minute ventilation inc
• Ventilation Failure
  
  • Pure hypercapnia
  • Neuromuscular or chest wall disease –> dec in minute ventilation –> inc PaCO2
  • A-a gradient stays the same
  • PaO2 either stays the same or dec overtime
• Oxygenation-Ventilation Failure (combo)
  
  • Usually oxygenation failure first –> eventually cannot maintain minute ventilation / cannot inc minute ventilation enough –> hypercapnia

Question 2

Causes of Ea Type of Resp Fail

Answer 2

Oxygenation - V/Q mismatch, shunt, diffusion impairment (fibrosis, interstitial inflammation, pulmonary HTN)

Ventilation - hypoventilation (narcotics, stroke, encephalitis, meningitis, ALS, MG, Guillain-Barre, phrenic injury, morbid obesity or severe kyphosis) OR high altitude

Combo - ARDS, cardiogenic pulmonary edema, severe acute asthma, COPD

Question 3

2 Groups of Supp Oxygen Delivery Methods

Answer 3

• Group 1 - FO2 of 1.0 (nasal cannula, simple mask, non-rebreather mask)
• Group 2 - variable FO2 (pressurize masks - venturi and aerosol)
• *The lower the selected FO2, the more room air is entrained

Question 4

What 3 things determine FIO2?

Answer 4

1- FO2 being delivered

2- Flow rate of delivered gas

3- Patient’s inspiratory flow rate

**If inspiratory flow rate is much greater than delivery flow rate then more room air enters lungs to make up the diff–> lower FIO2 (delivery rates are slowest for nasal cannula then simple mask then non-rebreather masks)

Question 5

How does V/Q mismatch respond to supplemental oxygen v. shunt?

Answer 5

• V/Q Mismatch - even w/ severe V/Q mismatch, PaO2 improves w/ inc FIO2
  
  • Even poorly ventilated alveoli fill w/ oxygen
• Shunt - less of an improvement w/ supplemental oxygen; may be refractory if more severe shunting
  
  • Many alveoli are totally unventilated so does not help if inc FIO2

Question 6

3 Indications for Mechanical Vent

Answer 6

1- Sig resp acidosis

2- Impending vent failure (marked inc or dec in RR)

3- Arterial hypoxemia that is refractory to supplemental oxygen

Question 7

PEEP

Answer 7

• when mech vent is set to add pos pressure during expiration too (rather than pressure falling to 0 w/ vent)
• Causes pos alveolar pressure at end of expiration; alveoli have inc vol at end of expiration AND inc pleural pressure at end of expiration

Question 8

Pros and Cons of PEEP

Answer 8

• Pros - prevents collapse of alveoli
• Cons - over-distention –> alveolar rupture OR PEEP inc pleural p which inc p in R atrium –> less gradient for venous return –> dec CO which will dec tissue oxygen delivery