Arterial Blood Gases (ABGs) and Acid-Base Balance

A set of vocabulary flashcards reviewing arterial blood gas interpretations, normal parameters, acid-base regulation systems, compensation rules, clinical signs, and underlying clinical causes.

Normal Blood pH Range

$$7.35 - 7.45$$

Normal $PaCO_2$ Range

$$35 - 45\,\text{mmHg}$$

Normal $HCO_3^-$ Range

$$22 - 26\,\text{mEq/L}$$

Normal $PaO_2$ Range

$$80 - 100$$

Normal $SpO_2$ Range

$94\%$ to $99\%$

Acidosis (pH Threshold)

$$pH < 7.35$$

Alkalosis (pH Threshold)

$$pH > 7.45$$

Buffer System

A regulatory mechanism that acts chemically to change strong acids to weak acids or bind acids, including carbonic acid–bicarbonate, phosphate, protein, and hemoglobin buffers.

Respiratory System Acid-Base Regulation

Regulation controlled by the medulla in which increased respirations increase $CO_2$ elimination, while decreased respirations lead to $CO_2$ retention.

Renal System Acid-Base Regulation

Regulation where the kidneys conserve bicarbonate ($HCO_3^-$) and excrete acid by secreting free hydrogen ($H^+$), combining $H^+$ with ammonia ($NH_3$), and excreting weak acids.

ROME Mnemonic

Respiratory Opposite (Alkalosis: $\uparrow pH$ $\downarrow PaCO_2$; Acidosis: $\downarrow pH$ $\uparrow PaCO_2$) and Metabolic Equal (Acidosis: $\downarrow pH$ $\downarrow HCO_3^-$; Alkalosis: $\uparrow pH$ $\uparrow HCO_3^-$).

Kussmaul Respirations

Fast, deep breathing that occurs as a compensatory response in metabolic acidosis (such as DKA) to eliminate excess $CO_2$.

Clinical Manifestations of Acidosis

Central nervous system (CNS) depression, confusion, drowsiness, weakness, lethargy, headache, Kussmaul respirations, slow/shallow breathing, and hyperkalemic state ($\uparrow K^+$).

Clinical Manifestations of Alkalosis

Central nervous system (CNS) irritability, anxiety, restlessness, seizures, tetany, muscle cramps/twitching, tingling/numbness, Chvostek's sign, Trousseau's sign, hypocalcemia, and hypokalemia.

Uncompensated Acid-Base Imbalance

An acid-base state where the $pH$ is abnormal, one respiratory or metabolic parameter ($PaCO_2$ or $HCO_3^-$) is abnormal, and the other parameter remains normal.

Partially Compensated Acid-Base Imbalance

An acid-base state where both $PaCO_2$ and $HCO_3^-$ are abnormal and the $pH$ remains outside the normal range.

Fully Compensated Acid-Base Imbalance

An acid-base state where both $PaCO_2$ and $HCO_3^-$ are abnormal, but the $pH$ has returned to the normal range ($7.35 - 7.45$).

Causes of Respiratory Acidosis

Conditions causing $CO_2$ retention, including COPD, pneumonia, respiratory failure, and overdose.

Causes of Respiratory Alkalosis

Conditions causing excessive $CO_2$ elimination, including hyperventilation, anxiety, and pain.

Causes of Metabolic Acidosis

Conditions leading to loss of base or retention of acid, including DKA, renal failure, and diarrhea.

Causes of Metabolic Alkalosis

Conditions leading to loss of acid or gain of base, including vomiting, NG suction, and diuretics.