Acid & Base Disorders and Calculations – Core Vocabulary

Vocabulary flashcards covering definitions, causes, clinical signs, normal values, calculations, and compensatory mechanisms for the four primary acid–base disorders and related concepts.

Respiratory Acidosis

Acid–base disorder caused by inadequate ventilation relative to CO₂ production; characterized by pH < 7.35 and PaCO₂ > 44 mmHg.

Hypercapnia

Elevated arterial carbon dioxide tension (PaCO₂ > 44 mmHg), typically seen in respiratory acidosis.

Common Causes of Respiratory Acidosis

Oversedation, brain-stem trauma, respiratory-muscle paralysis, chest-wall disorders, lung-parenchyma disease, airway obstruction.

Clinical Signs of Respiratory Acidosis

Headache, restlessness, blurred vision, lethargy, muscle twitching, tremors, convulsions, coma.

Metabolic Acidosis

Disorder due to excess non-carbonic acids or loss of HCO₃⁻; defined by pH < 7.35 and HCO₃⁻ < 24 mEq/L.

Kussmaul Respirations

Deep, rapid breathing characteristic of severe metabolic acidosis (e.g., diabetic ketoacidosis).

High-Anion-Gap Acidosis

Metabolic acidosis where the calculated anion gap exceeds 16 mEq/L, indicating the presence of unmeasured acids such as lactate or ketoacids.

Anion Gap (AG) Formula

AG = ([Na⁺] + [K⁺]) – ([Cl⁻] + [HCO₃⁻]); normal range 8–16 mEq/L.

Common Causes of Metabolic Acidosis

Lactic acidosis, renal failure, diabetic ketoacidosis, ingestion of methanol/ethylene glycol, severe diarrhea.

Respiratory Alkalosis

Disorder from excessive ventilation; pH > 7.45 and PaCO₂ < 38 mmHg.

Hypocapnia

Reduced arterial carbon dioxide tension (PaCO₂ < 38 mmHg), typical of respiratory alkalosis.

Common Causes of Respiratory Alkalosis

Fever, anemia, thyrotoxicosis, anxiety, panic disorder, excessive mechanical ventilation.

Clinical Signs of Respiratory Alkalosis

Dizziness, confusion, paresthesia, carpopedal spasms, tachypnea, possible convulsions or coma.

Metabolic Alkalosis

Acid–base disorder from HCO₃⁻ retention or acid loss; pH > 7.45 and HCO₃⁻ > 26 mEq/L.

Common Causes of Metabolic Alkalosis

Prolonged vomiting, gastric suction, excessive bicarbonate intake, hyperaldosteronism with hypokalemia, diuretic use.

Clinical Signs of Metabolic Alkalosis

Weakness, muscle cramps, hyperreflexia, paresthesias, tetany, seizures, slow shallow respirations, dysrhythmias.

Potassium Shift in Acidosis

H⁺ moves into cells and K⁺ shifts to extracellular fluid, often causing hyperkalemia.

Potassium Shift in Alkalosis

H⁺ exits cells while K⁺ moves intracellularly, leading to hypokalemia.

Normal Arterial pH

7.35 – 7.45.

Normal PaCO₂

35 – 45 mmHg.

Normal HCO₃⁻

22 – 26 mEq/L (some sources 21–27).

Normal Anion Gap

8 – 16 mEq/L.

Simple Four-Step ABG Analysis

1) Check pH; 2) Examine PaCO₂; 3) Assess HCO₃⁻ and other values; 4) Decide if disorder is compensated.

Renal Compensation for Respiratory Acidosis

Kidneys increase HCO₃⁻ reabsorption and H⁺ excretion to raise pH.

Respiratory Compensation for Metabolic Acidosis

Hyperventilation lowers PaCO₂ to raise pH (e.g., Kussmaul breathing).

Renal Compensation for Respiratory Alkalosis

Kidneys excrete more HCO₃⁻ and retain H⁺ to decrease pH.

Respiratory Compensation for Metabolic Alkalosis

Hypoventilation retains CO₂ (PaCO₂ > 40 mmHg) to lower pH.

Mixed Acid-Base Disorder

Presence of more than one primary acid-base abnormality simultaneously (e.g., metabolic acidosis with respiratory alkalosis).

Diabetic Ketoacidosis (DKA)

High-anion-gap metabolic acidosis caused by accumulation of ketoacids due to insulin deficiency; often shows compensatory hyperventilation.

Case of David Mandel

Type I diabetic with pH 7.22, HCO₃⁻ 8 mEq/L, PaCO₂ 20 mmHg: diagnosed with metabolic acidosis (DKA) with respiratory compensation.