What pH value and condition should the nurse expect when interpreting the laboratory findings of HCO-3- 18mEq/L and PaCO2: 28mmHg?

To interpret the laboratory findings of HCO3- at 18 mEq/L and PaCO2 at 28 mmHg, understanding the relationship between these values and pH is critical.

A bicarbonate level of 18 mEq/L indicates a decrease from normal bicarbonate (which is typically between 22-26 mEq/L), suggesting a form of metabolic acidosis. This condition occurs when there is an accumulation of acid or a loss of bicarbonate in the body. The low level of bicarbonate is indicative of compensation for acidosis, hence one would expect the pH to also be decreased, aligning with metabolic acidosis.

Furthermore, a PaCO2 of 28 mmHg is lower than normal, reflecting a respiratory compensation mechanism where the body is trying to eliminate carbon dioxide (an acid) to counter the acidosis. The respiratory alkalosis indicated by the low PaCO2 would not override the main problem, which is a primary metabolic acidosis indicated by the low bicarbonate.

Thus, with a decreased pH alongside the low bicarbonate level and low PaCO2, the interpretation is clear: the parameters affirm a state of metabolic acidosis. This is why the correct answer highlights a decreased pH and metabolic acidosis.