Fluid Electrolyte and Acid Base Balance

Question 1

pH (important)

Answer 1

7.35-7.45
pH is a negative logarithm of the free H+ concentration, a measure of how acid or alkaline the blood is. Values below 7.35 indicate abnormally acid, and above 7.45 indicate abnormally alkaline. Small changes in pH denote large changes in H+ concentration and are clinically important.

Question 2

PaCO2 (important)

Answer 2

35-45 mm Hg (4.7-6 kPa)
PaCO2 is partial pressure of carbon dioxide (CO2), a measure of how well the lungs are excreting CO2 produced by cells. Increased PaCO2 indicates CO2 accumulation in blood (more carbonic acid) caused by hypoventilation; decreased PaCO2 indicates excessive CO2 excretion (less carbonic acid) through hyperventilation.

Question 3

HCO3- (important)

Answer 3

22-26 mEq/L (22-26 mmol/L)
is concentration of the base (alkaline substance) bicarbonate, a measure of how well the kidneys are excreting metabolic acids. Increased indicates that the blood has too few metabolic acids; decreased indicates that the blood has too many metabolic acids.

Question 4

PaO2

Answer 4

80-100 mm Hg (10.7-13.3 kPa)
PaO2 is partial pressure of oxygen (O2), a measure of how well gas exchange is occurring in the alveoli of the lungs. Values below normal indicate poor oxygenation of the blood.

Question 5

SaO2

Answer 5

95%-100%
SaO2 is oxygen saturation, the percentage of hemoglobin that is carrying as much O2 as possible. It is influenced by pH, PaCO2, and body temperature. It drops rapidly when PaO2 falls below 60 mm Hg (8 kPa).

Question 6

Base excess

Answer 6

−2 to +2 mmol/L
Base excess is observed buffering capacity minus the normal buffering capacity, a measure of how well the blood buffers are managing metabolic acids. Values below −2 (negative base excess) indicate excessive metabolic acids; values above +2 indicate excessive amounts of bicarbonate.