Acid–Base Balance CCRN Practice Questions – Study Review

Comprehensive vocabulary flashcards covering normal arterial blood gas (ABG) reference values, the systematic first-middle-last naming method, compensation patterns, underlying etiologies, and advanced clinical calculation pearls for CCRN exam preparation.

Normal arterial pH

The normal physiological arterial blood pH range is $7.35\text{--}7.45$, where values below $7.35$ are acidic and values above $7.45$ are alkaline.

Normal $\text{PaCO}_2$

The arterial partial pressure of carbon dioxide, functioning as a respiratory acid, with a normal range of $35\text{--}45\,\text{mm Hg}$; values above $45\,\text{mm Hg}$ are acidic and values below $35\,\text{mm Hg}$ are alkaline.

Normal $\text{HCO}_3$

The serum bicarbonate concentration, functioning as a metabolic base, with a normal range of $22\text{--}26\,\text{mEq/L}$; values below $22\,\text{mEq/L}$ are acidic and values above $26\,\text{mEq/L}$ are alkaline.

First Name (Compensation)

The component of the naming method determined by whether the pH is normal (compensated) or abnormal (uncompensated or partially compensated).

Middle Name (System Origin)

The component of the naming method indicating which value moves in the same direction as the pH: matching $\text{PaCO}_2$ indicates respiratory, matching $\text{HCO}_3$ indicates metabolic, and both matching indicates combined.

Last Name (Acid-Base Status)

The component of the naming method that identifies whether the overall state is acidosis (pH below $7.35$) or alkalosis (pH above $7.45$), or which side of normal the pH leans toward if it is within range.

Uncompensated Imbalance

An acid–base state characterized by an abnormal pH while the non-causative system value remains within its normal reference range.

Partially Compensated Imbalance

An acid–base state where the pH is abnormal and the opposing system's value is abnormal in the opposite direction, indicating the body is attempting to compensate but has not normalized the pH.

Compensated (Fully) Imbalance

An acid–base state where the pH has returned to the normal range ($7.35\text{--}7.45$), but both $\text{PaCO}_2$ and $\text{HCO}_3$ are abnormal and point in opposite directions.

Combined (Mixed) Disorder

An acid–base disturbance where the pH is abnormal and both $\text{PaCO}_2$ and $\text{HCO}_3$ are abnormal in the same direction (both acidic or both alkaline).

Respiratory Acidosis

An imbalance driven by hypoventilation and retained $\text{CO}_2$ leading to $\text{PaCO}_2 > 45\,\text{mm Hg}$; common causes include late respiratory failure, oversedation, drug overdose with respiratory depression, severe obesity, and Guillain-Barré.

Respiratory Alkalosis

An imbalance driven by hyperventilation blowing off $\text{CO}_2$ leading to $\text{PaCO}_2 < 35\,\text{mm Hg}$; common causes include early respiratory failure, anxiety, severe pain, fever, sepsis, or ventilator tidal volume/rate set too high.

Metabolic Acidosis

An imbalance caused by excessive acid production or renal failure to clear acid, resulting in $\text{HCO}_3 < 22\,\text{mEq/L}$; common causes include DKA, AKI, aspirin (salicylate) overdose, other drug or alcohol overdoses, lactic acidosis, hyperkalemia, and hyperchloremia.

Metabolic Alkalosis

An imbalance caused by acid loss or excess bicarbonate, resulting in $\text{HCO}_3 > 26\,\text{mEq/L}$; common causes include vomiting, NG suction, antacid overuse, excess sodium bicarbonate, loop and thiazide diuretics, hypokalemia, and hypovolemia.

Renal Compensation

A slow physiological compensatory process by the kidneys occurring over hours to days, wherein $\text{HCO}_3$ rises in response to respiratory acidosis and falls in response to respiratory alkalosis.

Respiratory Compensation

A rapid physiological compensatory process by the lungs occurring within minutes, wherein $\text{PaCO}_2$ falls via hyperventilation (e.g., Kussmaul breathing in DKA) during metabolic acidosis and rises via slower breathing during metabolic alkalosis.

Anion Gap

A diagnostic calculation formulated as $\text{Na} - (\text{Cl} + \text{HCO}_3)$ with a normal value of about $8\text{--}12$; an elevated gap points to added acids (ketoacidosis, lactic acidosis, kidney failure, salicylates, methanol, ethylene glycol), while a normal gap indicates bicarbonate loss (such as diarrhea or large-volume saline).

Winter's Formula

A formula used to determine the expected $\text{PaCO}_2$ in metabolic acidosis: $\text{expected PaCO}_2 = (1.5 \times \text{HCO}_3) + 8 \pm 2$; a value higher than expected indicates a concurrent respiratory acidosis.

$7.40$ Midpoint Rule

A clinical guideline for interpreting compensated ABGs with normal pH: values from $7.35\text{--}7.39$ lean acidic, whereas values from $7.41\text{--}7.45$ lean alkaline.

$$\text{PaO}_2$$

The arterial partial pressure of oxygen with a normal range of $80\text{--}100\,\text{mm Hg}$; it evaluates oxygenation rather than acid–base status and is excluded from acid–base naming.