06 Ventilation

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Fibrosis

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• deposition of fibrous tissues in lungs, destroys alveoli

• barrier created by fibrous tissue

Shunt

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V/Q < 1

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• 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

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• 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

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• water resulting in less ventilation V/Q < 1

• distinct from shunt/dead space

Diagnosis

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100% O2

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• 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

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• increased dead space causes hypercapnia

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

• less ventilation to left side

Lung Zones

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

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

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• 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 )