06 Ventilation - Boards and Beyond

Fibrosis

  • deposition of fibrous tissues in lungs, destroys alveoli
  • barrier created by fibrous tissue

Shunt

V/Q < 1

  • so extreme V/Q = 0
  • shunting as if blood bypassed lung

  • anatomic: large congenital defect (VSD)

  • normal

  • left alveoli with V/Q of 0
  • result hypoxemia when blood mixed
  • hyperventilation cannot increase PaO2: blood only goes through healthy alveoli, still mixing at end. Only way to resolve is to resolve shunting (take out mucous plug)
  • no hypercapnea: more CO2 is pulled with hyperventilation

V/Q > 1

  • PE clotting blood
  • O2 in arterial will be normal, no hypoxemia if pure dead space
  • No blood to left, more blood to right: reduced V/Q, less than 99% O2 sat coming out (V/Q mistmach)
  • CO2 up: ventilation wasted because CO2 not exchanged

V/Q Mismatch

  • water resulting in less ventilation V/Q < 1
  • distinct from shunt/dead space

Diagnosis

100% O2

  • O2 only goes to right side
  • nothing changes on left side, even if give 100% O2
  • hypoxemia persists

  • all blood pushed to right side, Q very high
  • hypoxemia if on room air, 21%

  • can fix hypoxemia if changed to 100% O2

Hypercapnia

  • increased dead space causes hypercapnia

  • when patient ventilates, none of the ventilation wasted on left side

  • less ventilation to left side

Lung Zones

  • apex least blood flow: blood has to push up against gravity

  • Tb has affinity for highly oxygenated part of body, upper lobe

  • more hydrostatic pressure at bottom

  • bottom blood vessels fully extended; blood flow normally
  • top: alveolar pressure higher, compress vessels, no blood flow
  • middle: compress veins, pulsatile flow when RV contract to push blood through but no flow in veins in diastole
  • in real life, most lungs are all zone 3
  • in pathologic state: more lungs in Zone 1, especially ventilator (pressure in alveoli very high )