Acute Respiratory Failure

Question 1

Acute Respiratory Failure

Answer 1

Mechanical
Hypercapnic

Question 2

Oxygen saturation

Answer 2

PaO2 - FiO2, alveolar pressure, PaCO2
Diffusing capacity
Ventilation
Perfusion
Ventilation pefusion matching

Question 3

Alveolar pressure

Answer 3

Alveolar pressure = sum of all composition (O2, CO2, H2O, N2)

Answer 4

Alveolar ventilation = RR x (Vt - Vd)

Anatomical dead space constant
Physiological dead space depends on vent perfusion gradient

Question 5

Pathophysiology

Answer 5

Low inspired PO2 - high altitude
Hypoventilation
Ventilation-perfusion mismatch
- shunting
- dead space ventilation
Diffusion abnormality

Question 6

Sites Causing Hypoventilation

Answer 6

Neuro- brainstem, spinal cord, nerves, NMJ
Respi - airway down to alveolus

Question 7

Shunt

Answer 7

Blood perfusion in area where there is no ventilation
Mixing with fully ventilated
Over time blood will be shunted from areas with no ventilation to areas with good ventilation

Question 8

Dead space ventilation

Answer 8

Areas with good ventilation but no blood perfusion

Question 9

Diffusion abnormality

Answer 9

Disrupted interface between alveoli and blood vessel

Question 10

Clinical

Answer 10

Respiratory compensation
- Tachypnoea
Sympathetic stimulation
- Tachycardia
- Hypertension (early)
- Sweating
Tissue hypoxia
- AMS
- HR down, hypotension
Haemoglobin desaturation
- Cyanosis (cut off 90% on ODC)

Question 11

Oxygen Delivery

Answer 11

O2 delivery = CO x O2 content x 10

O2 content = O2 sat x Hb x 1.37 + 0.003 x PaO2

Question 12

Pitfalls

Answer 12

Poor peripheral perfusion - false SpO2
Poor adherent / positioned probe
Lipaemia
Nails

Question 13

Treatment

Answer 13

Trear the cause
Oxygen therapy
CPAP - reduces shunt
by recruiting partially collapsed alveoli
Mechanical ventilation

Question 14

When to ventilate

Answer 14