Lecture 03 Acid Base Balance and Arterial Blood Gas (ABG) Interpretation

Question 1

What are purposes of ABGs? (5)

Answer 1

1. žPrecisely measure oxygenation and ventilation status
2. žReflective of lung & kidney function
3. žDetect acid-base imbalances that can occur with heart, lung and kidney failure, uncontrolled diabetes, severe infections, and drug overdose
4. žTypically ordered in the setting of worsening respiratory distress
5. žArterial blood preferred in order to measure the levels of O2 and CO2 in the blood prior to the gases entering and being modified by body tissues

Question 2

In what settings are ABGs done the most?

Answer 2

ICUs, ED, and operating room when patient is on heart-lung bypass machine

Arterial blood is preferred because you want to know what the levels of O2 and CO2 are prior to the gases entering and being modified by the body tissues which is what would be reflected on a venous or capillary sample, however venous or capillary blood can be used if necessary, keeping in mind that different ranges exist for normal values.

Question 3

Who typically performs arterial sticks for ABGs?

Answer 3

Nurses do not typically perform arterial sticks to obtain ABGs unless they have received advanced training. However, if a patient has an arterial line, nurses are allowed to access the line and draw samples of blood from the arterial line to evaluate blood gases. Respiratory therapists are the ones who run the blood gases in their respiratory lab in the ICUs.

Question 4

What is the ratio for acid to base? Why is this important? What maintains this ratio?

Answer 4

The goal is not for the amount of acid in the blood to equal the amount of base in the blood, the goal is to keep the ratio the same. The normal acid-base ratio is 1:20 representing 1 part carbon dioxide (CO2) to 20 parts bicarbonate (HCO3). The respiratory and renal systems work together to maintain this ratio and when this ratio is maintained then the pH will be normal and when the pH is normal, then cellular function and homeostasis will be optimized.

Question 5

How is CO2 regulated?

Answer 5

Regulated by the respiratory system

the lungs are primarily responsible for accomplishing this by regulating the RATE and depth of respiration. An increase in respiratory rate = increase in CO2 elimination = a decreased amount of CO2 present in the blood. A decrease in respiratory rate = a decrease in CO2 elimination = an increased amount of CO2 present in the blood.

Question 6

What is Bicarb regulated by?

Answer 6

žRegulated by the renal system and metabolic processes

Question 7

What are normal values for:

pH?

PaCO2?

HCO3

Answer 7

pH 7.35~7.45

PaCO2 35~45 mmHg

HCO3 21~28 mEq/L

Question 8

What are normal values of

PaO2?

SaO2?

Answer 8

PaO2 80~100mmHg

SaO2 (Oxygen saturation) 96%~100%