CHANGES IN HEMATOLOGY / ELECTROLYTES

Increases in RBC, hematocrit, and hemoglobin values are common due to chronic hypoxia stimulating RBC production. Chloride ion is excreted to facilitate retention of bicarbonate ion to balance retained CO2 and decreased pH - therefore patients may be hypochloremic.

CHANGES IN OXYGENATION INDICES

Oxygenation Saturation and Content-Based Indices

These values assess the transport and utilization of oxygen at the tissues, and are ways of quantifying whether or not the patient's tissue oxygenation needs are being met.

Most Common Oxygenation–Saturation and Content-Based Indices

Total oxygen delivery

Arterial-venous oxygen content difference

Oxygen consumption

Oxygen extraction ratio

Mixed venous oxygen saturation

Pulmonary shunting

Total Oxygen Delivery

DO2 = QT x (CaO2 x 10)

For example, if a patient has a cardiac output of 4 L/min and a CaO2 of 15 vol%, what is the DO2?

DO2  = QT x (CaO2 x 10)

  = 4 L/min x (15 ml/100 ml x 10)

  = 600 ml O2/min

Normally, about 1000 ml/min

Decreases if the following occur:

Low PaO2

Low SaO2

Low Hb

Low cardiac output (perfusion inadequate to meet tissue metabolic needs)

Increases if the following occur:

Increased PaO2

Increased SaO2

Increased Hb

Increased cardiac output

Arterial-Venous Oxygen Content Difference

*also referred to as the a-vDO2

For example, if a patient's CaO2 is 15 vol% and the CvO2 is 8 vol%, what is the C(a-v)O2?

C(a-v)O2 = CaO2 – CvO2

  = 15 vol% – 8 vol%

  =  7 vol%

          Normally, 5 vol%  

Increases (which means the tissues are pulling off larger amounts of oxygen) may be caused by:

Decreased cardiac output

Exercise

Seizures

Hyperthermia

Decreases (which means the tissues are using less oxygen) may be caused by:

Increased cardiac output

Skeletal relaxation

Peripheral shunting

Cyanide

Hypothermia

Oxygen Consumption

For example, if a patient has a cardiac output of 4 L/min and a C(a-v)O2 of 6 vol%, what is the total amount of oxygen consumed by the tissue cells in 1 minute?

VO2 = QT [C(a-v)O2] x 10

  = 4 L/min x 6 vol% x 10

  = 240 ml O2/min

Normal is 250 ml O2/min

Increases in consumption can occur with:

Seizures

Exercise

Hyperthermia

Body size

Decreases in consumption can occur with:

Skeletal muscle relaxation

Peripheral shunting

Certain poisons (e.g., cyanide)

Hypothermia

Oxygen Extraction Ratio

For example, if a patient's CaO2 is 15 vol% and the CvO2 is 10 vol%, what is O2ER?

  = 15 vol% – 10 vol%

             15 vol%

  = 5 vol%

     15 vol%

  = 0.33

      Normal is 0.25 or, when expressed as a percentage, 25%

Increases:

Decreased cardiac output

Periods of increased O2 consumption

Exercise, seizures, hyperthermia

Anemia

Decreased arterial oxygenation

↓Hb, ↓PaO2

Decreases:

Increased cardiac output

Skeletal muscle relaxation

Peripheral shunting

Certain poisons (e.g., cyanide)

Hypothermia

Increased arterial oxygenation

↑Hb, ↑PaO2

Mixed Venous Oxygen Saturation

Signals changes in the:

C(a-v)O2

VO2

O2ER

    Normally about 75%

Decreases:

Decreased cardiac output

Exercise

Seizures

Hyperthermia

Increases:

Increased cardiac output

Skeletal muscle relaxation

Peripheral shunting

Certain poisons (e.g., cyanide)

Hypothermia

Pulmonary Shunting

 

Qs = CcO2 – CaO2

QT    CcO2 – CvO2