- shunt fraction, normally < 5%, represents the mismatch of ventilation to perfusion; - it is ratio to non-ventilated alveoli to perfused pulmonary capillaries; - alteration in the ventilation to perfusion ratio results from either relative obstruction of ventilation or relative obstruction of perfusion; - rising shunt fraction is usually associatted with progressive respiratory failure or ARDS; Decreased Ventilation: Decreased Perfusion: - ARDS (See Resp. Failure) - Massive PE - Pulmonary Edema - Micro Pulmonary Emboli - Atelectasis Calculation: Qs/Qt = (
Aa grad * 0.003) / (AVo diff + Aa grad * 0.003) Cco2 - Cao2 = ----------------- Cco2 - Cvo2 Cco2 = (Hgb * 1.34) + Pco2 (0.003) = pulm. capillary O2 content Cao2 = (Hgb * 1.34) (Sao2/100) + Pvo2 * 0.003 = art. O2 content Cvo2 = (Hgb * 1.34)
Causes of Increased Shunt in the Post Resusitation Period: - cardiogenic pulmonary edema - aspiration pneumonia - non aspiration penumonitis - pulmonary bone marrow emboli from trauma to the sternum during CPR - ARDS (associatted w/ sepsis) - atelectasis - toxic chemical aspiration; - Rx: - begin therapeutic
PEEP to decrease
Shunt (inorder to incr PaO2) - however, ensure that the apparent decrease in Shunt is not due to a decrease in
Mixed Venous O2 thru the usual 5% shunt; - this sends markedly desaturated blood thru the normal shunt making it appear as if the shunt were actually larger;
