Respiratory Failure

Question 1

inhalation occurs against what forces?

Answer 1

elastic and resistive

Question 2

function of theupper airway

Answer 2

humidification
defence
stay open to allow inhalation

Question 3

what does surfactant do?

Answer 3

improves compliance by reducing surface tension of fluid lining alveoli.
prevents alveoli collapse

Question 4

why does gas exchange occur?

Answer 4

difference between partial pressures of O2 and CO2 between alveoli and pulmonary capillary across the A-C membrane. normally very efficitent

Question 5

normal arterial blood gas values

Answer 5

O2=100
CO2=45
HCO3=22-30
O2 sat = >95%
pH=7.4

Question 6

what is the A-a gradient adn what would cause an elevation in it?

Answer 6

it is the difference in partial pressures of oxygen between the arteriole (A) and the alveoli (a)
elevation of the gradient indicates impaired gas exchange

Question 7

calculation for A-a gradient?

Answer 7

=(150-1.25xPaCo2) - PaO2

Question 8

what is respiratory failure?

Answer 8

impairment of gas exchange between air and circulating blood leading to the inability to maintain arterial blood gas concentrations either by impairing exchange in the alveoli or inability to bring air in or out of the lungs

Question 9

what is type 1 respiratory failure?

Answer 9

impaired gas exchange leading to hypoxaemia paO2<60mmHg

Question 10

what is type 2 respiratory failure?

Answer 10

impaired ventilation leading to hypercapnia PaCO2>50mmHg

Question 11

causes of hypoxaemia

Answer 11

1. reduced inspired O2
2. VQ mismatch (pneumonia, PE)
3. impaired diffusion (COPD, fibrosis)
4. shunt (total VQ mismatch, incluides where blood bypasses lungs altogether)
5. reduced ventilation

Question 12

what could cause hypercapnoea

Answer 12

1. respiratory depression
2. blocked airways
3. respiratory pump failure
4. muscle fatigue

Question 13

signs of respiratory failure

Answer 13

accessory muscle use
altered state of consicousness/drowsiness
confusion
increased resp rate (or decreased in severe)
low O2 saturation
cyanosis

Question 14

investigations for suspected respiratory failure

Answer 14

arterial blood gases

investigations into cause eg CXR, bloods, CTPA, VQ scan, lung function/spirometry

Question 15

management principles of respiratory failure

Answer 15

1. maintain O2 delivery (not too high in blue bloaters)
2. reduce work of breathing
3. maintain pH, electrolytes
4. target the cause
5. analgesia (dont cause depression tho)
6. calories

Question 16

what is acute respiratory distress syndrome?

Answer 16

mass release of inflammatory mediators increases pulmonary capillary permeability leading to edema and diffusion impairment leading to impaired gas exchange and increased work of breathing

Question 17

how can you go from type 1 to type 2 respiratory failure?

Answer 17

increased drive and work of breathing to compensate for hypoxemia leads to respiratory muscle fatigue, reducing ventilation and raising co2 levels