Blood Gas Analysis: Indications, Normal Values, and Acid-Base Disorders

What are the indications for blood gas and oximetry analysis?

Indications include abnormalities in respiratory status suggested by symptoms, medical history, physical examination, or lab data.

What is the significance of arterial blood gases compared to venous blood gases?

Arterial blood gases are independent of metabolism , while venous blood gases vary widely based on local metabolism.

What are the normal values for pH in blood gas analysis?

Normal pH ranges from 7.35 to 7.45.

What is the normal range for PaCO2 in blood gas analysis?

Normal PaCO2 ranges from 35 to 45 torr.

What is the normal range for PaO2 in blood gas analysis?

Normal PaO2 ranges from 80 to 100 torr.

What is the normal range for HCO3- in blood gas analysis?

Normal HCO3- ranges from 22 to 26 mEq/L.

What is the normal range for SpO2 in adults?

Normal SpO2 is greater than 92%.

Acidosis

increase in PCO2 and decrease in pH

Alkalosis

decreased PCO2 and increased pH

Symptoms seen in acidosis

drowsiness, lethargy, coma, and death

Symptoms seen in alkalosis

irritability, arrhythmias, convulsions, and death

What are acute blood gas changes characterized by?

Acute changes are characterized by abnormal pH with at least one abnormal value (CO2 or HCO3-).

What defines chronic blood gas changes?

Chronic changes are defined by normal (or normal-ish) pH with two abnormal values (CO2 and HCO3-).

Acute on chronic

patient with chronic respiratory failure becomes acutely ill with worsening gas exchange

How does the body compensate for poor respiratory conditions

the kidneys will retain bicarbonate to increase the pH to normals levels

What is 'combined acidosis' in blood gas interpretation?

Combined acidosis occurs when both CO2 and HCO3- contribute to a decrease in pH.

What is 'combined alkalosis' in blood gas interpretation?

Combined alkalosis occurs when both CO2 and HCO3- contribute to an increase in pH.

What is the predicted PaO2 based on FiO2?

Predicted PaO2 is calculated as 5 times FiO2.

Hyperoxemia

greater than 100 mmHg

Normoxemia

80-100 mmHg

mild hypoxemia

60-79 mmHg

moderate hypoxemia

40-59 mmHg

severe hypoxemia

less than 40 mmHg

What are common causes of respiratory acidosis?

Common causes include hypoventilation and conditions like COPD.

What is a common cause of respiratory alkalosis?

hyperventilation

What conditions can lead to metabolic acidosis?

Conditions include diabetic ketoacidosis (DKA), severe diarrhea, shock and renal failure.

What are common causes of metabolic alkalosis?

GI suction, vomiting, diuretics, NaHCO3- administration

What is the role of a pulmonary artery catheter in blood gas monitoring?

A pulmonary artery catheter is used for invasive blood gas monitoring to assess cardiac output and pressures.

What is the normal range for EtCO2?

Normal EtCO2 ranges from 35 to 45 torr or 3-5%.

What is an intracardiac shunt?

An intracardiac shunt is a condition where blood flows abnormally within the heart, leading to either left-to-right or right-to-left shunting.

What are the characteristics of a left-to-right cardiac shunt?

Left-to-right shunts are more common and typically have better outcomes, with left heart pressures exceeding right heart pressures.

What are the characteristics of a right-to-left cardiac shunt?

Right-to-left shunts are less common and can cause profound hypoxemia, with right heart pressures exceeding left heart pressures.