O2ER & SvO2 Clinical Case

Changes in SvO2 are an early indicator of

Early indicator of changes in patient's C(a-v)O2, VO2, and, O2ER

What is the normal value for Mixed Venous Oxygen Saturation (SvO2)?

75% (greater than 65% is acceptable).

Pulmonary Shunting (True Shunt)

Portion of the cardiac output (Blood) that enters the L side of the heart without gas exchange.

Shunt-like effect

Blood that exchanges gases but does not obtain a normal PaO2 (gas exchange was really bad).

Physiologic effect of shunt

Hypoxemia (caused by both true shunt and shunt-like effect).

Anatomic Shunt

2-5% of cardiac output (When alveoli can't do gas exchange)

Anatomic Shunt Venous Sources

Bronchial, Pleural and Thebesian veins

Causes of Anatomic Shunting

Congenital heart disease, Intrapulmonary fistula (Hole), Vascular lung tumors

Capillary Shunt

When capillaries can't do gas exchange; caused by Alveolar collapse or atelectasis, Alveolar fluid accumulation and Alveolar consolidation

True or Absolute Shunt

Sum of anatomic and capillary shunts = Refractory to O2 Therapy (Refractory = oxygen can't fix shunt)

Venous Admixture

It is the end result of pulmonary shunting

Shunt-Like Effect is when

Capillary perfusion exceeds alveolar ventilation

-Diffusion not effective so we get some gas but not enough

Shunt-Like Effect Causes

Hypoventilation, Bronchospasm or mucus plugging and ACM diffusion defects

Shunt-Like Effect Oxygen Response

Conditions corrected with oxygen therapy

Shunt Equation

Qs/Qt (Perfuion shunt/Perfusion total): CcO2-CaO2/CcO2-CvO2

PAO2

(PB - PH20) FIO2 - (PaCO2 x 1.25) if fio2 less than 60

CvO2

(Hb x 1.34 x SvO2) + (PvO2 x 0.003)

Normal Shunt

<10%

Shunt 10-20%

Abnormal but not clinically significant

Shunt 20-30%

Significant intrapulmonary shunting

Shunt >30%

Potentially life threatening