Question

A nurse checks the client's arterial blood gas results which are as follows: \(\mathrm{pH}, 7.38 ; \mathrm{PO}_2, 88 \mathrm{~mm} \mathrm{Hg} ; \mathrm{PCO}_2\), \(33 \mathrm{~mm} \mathrm{Hg} ; \mathrm{HCO}_3, 24 \mathrm{mEq} /\); and \(\mathrm{O}_2\) saturation, \(96 \%\). Which is the correct interpretation of these results? a. Metabolic acidosis b. Metabolic alkalosis c. Normal values d. Respiratory alkalosis

Short answer

d. Respiratory alkalosis

Step-by-step solution

Check the pH level

First, look at the pH value. The pH value given is 7.38, which is within the normal range (7.35 to 7.45). Since the pH is within the normal range, it indicates that the blood gas is either normal or compensated.

Evaluate the PCO₂ level

Next, examine the PCO₂ (partial pressure of carbon dioxide) level. The normal range for PCO₂ is 35 to 45 mm Hg. In this case, the PCO₂ is 33 mm Hg, which is lower than the normal range indicating a tendency towards alkalosis due to respiratory factors.

Analyze the HCO₃ level

Check the bicarbonate (HCO₃) level. The normal range for HCO₃ is 22 to 26 mEq/L. In this case, the HCO₃ is 24 mEq/L, which is within the normal range.

Determine the overall interpretation

Given that the pH is normal but the PCO₂ is low, this suggests that there is a compensated respiratory alkalosis. The normal HCO₃ indicates that there is no metabolic compensation needed.

Key concepts

pH Levels

The pH level in the blood is crucial for determining the acid-base balance. It measures the hydrogen ion concentration, reflecting how acidic or basic the blood is. A normal pH range is between 7.35 and 7.45. If the pH level is below 7.35, it indicates acidosis, meaning the blood is too acidic. If the pH is above 7.45, it suggests alkalosis, where the blood is too basic. In the given exercise, the pH level is 7.38, which falls within the normal range, indicating that the blood’s acid-base balance is normal or possibly compensated.

PCO₂ Analysis

PCO₂, or the partial pressure of carbon dioxide, is another important factor in arterial blood gas (ABG) interpretation. It indicates how well carbon dioxide is able to move out of the body. The normal range for PCO₂ is 35 to 45 mm Hg. Lower levels of PCO₂ (below 35 mm Hg) suggest respiratory alkalosis, where the body is exhaling too much CO₂. Higher levels (above 45 mm Hg) suggest respiratory acidosis, indicating CO₂ retention. In the given scenario, the PCO₂ level is 33 mm Hg, which is lower than the normal range, suggesting a tendency towards respiratory alkalosis.

HCO₃ Levels

HCO₃, or bicarbonate, is a buffer that helps maintain the pH balance in your blood. The normal range for HCO₃ is between 22 to 26 mEq/L. If the HCO₃ level is higher than normal, it indicates metabolic alkalosis, where the blood is too basic due to a metabolic cause. If it's lower than normal, it means metabolic acidosis, where there is too much acid or not enough base in the blood. In the provided blood gas result, the HCO₃ level is 24 mEq/L, which is within the normal range, suggesting there is no metabolic component altering the blood pH.

Respiratory Alkalosis

Respiratory alkalosis is a condition where the blood pH is elevated above 7.45 due to excessive exhalation of CO₂. Common causes include hyperventilation due to anxiety, fever, or other conditions. In the given case, although the pH is within the normal range at 7.38, the lower-than-normal PCO₂ of 33 mm Hg signals that the body is excreting too much CO₂, suggesting respiratory alkalosis. The normal pH signifies that the condition has been compensated, typically by adjusting other components like HCO₃.

Compensated Blood Gas

When the body experiences an imbalance in pH due to respiratory or metabolic issues, it attempts to compensate to normalize the pH. This compensatory mechanism involves changes in either breathing rate, which affects CO₂, or kidney function affecting HCO₃. A compensated blood gas means that the pH has returned to normal levels despite underlying issues. In the provided example, the normal pH of 7.38, along with the low PCO₂ of 33 mm Hg, indicates respiratory alkalosis. The fact that pH is within normal range suggests that compensation has occurred, typically by reducing the bicarbonate (HCO₃) levels to balance the low PCO₂ and maintain a normal pH.