Acid-Base & Renal Tubular Acidosis: Step 1 review notes and self-test
Notes for the Acid-Base & Renal Tubular Acidosis rapid review: the clue that separates each of its 4 confusion pairs, with timestamps and a self-test.
October 21, 2026
This video covers acid-base disorders, potassium ECG changes, and renal tubular acidosis. Watch the video, then use these notes to test yourself.
Hyperkalemia ECG vs Hypokalemia ECG
Hyperkalemia causes peaked T waves that can progress to a widened QRS, while hypokalemia causes flattened T waves with prominent U waves. Both can cause weakness and arrhythmias, so do not rely on symptoms alone. Scan T-wave height, P-wave visibility, QRS width, and then U waves.
Hyperkalemia ECG vs Hypokalemia ECG Hyperkalemia: peaked T waves progressing to a widened QRS; hypokalemia: flattened T waves with prominent U waves. Open the comparison and video →High anion gap metabolic acidosis vs Normal anion gap metabolic acidosis
A high anion gap means added unmeasured acid, while a normal anion gap means bicarbonate loss or impaired renal acid secretion with chloride replacement. Low bicarbonate alone does not identify the cause. Calculate the anion gap as sodium minus the sum of chloride and bicarbonate, with 8 to 12 mEq/L as normal.
High anion gap metabolic acidosis vs Normal anion gap metabolic acidosis High-gap means added acid; normal-gap means bicarbonate loss or renal acid-handling failure with chloride replacement. Open the comparison and video →Respiratory acidosis vs Metabolic acidosis
Respiratory acidosis starts with increased PaCO2 from CO2 retention, while metabolic acidosis starts with decreased bicarbonate from acid gain or bicarbonate loss. Both can cause dyspnea and low pH, so identify whether PaCO2 or bicarbonate moved first.
Respiratory acidosis vs Metabolic acidosis Respiratory acidosis is CO2 retention; metabolic acidosis is bicarbonate loss or acid gain. Open the comparison and video →Distal / proximal renal tubular acidosis vs Type 4 renal tubular acidosis
Type 1 distal and type 2 proximal renal tubular acidosis are hypokalemic, while type 4 is hyperkalemic from aldosterone deficiency or resistance. All can cause normal-gap acidosis, so check potassium first. Then use urine pH and Fanconi clues to separate the subtypes.
Distal / proximal renal tubular acidosis vs Type 4 renal tubular acidosis Type 1 and type 2 RTA are hypokalemic; type 4 RTA is the hyperkalemic one, from aldosterone deficiency or resistance. Open the comparison and video →Quick self-test
Name the diagnosis from the clue, then tap to check.
Flattened T waves, ST depression, prominent U waves, and apparent QT/QU prolongation.
Hypokalemia ECG · Hyperkalemia ECG vs Hypokalemia ECG
Primary PaCO2 elevation from hypoventilation, COPD exacerbation, sedatives, neuromuscular weakness, or airway obstruction, with renal bicarbonate retention as compensation.
Respiratory acidosis · Respiratory acidosis vs Metabolic acidosis
Tall peaked T waves can progress to PR prolongation, P-wave flattening/disappearance, QRS widening, sine-wave rhythm, ventricular arrhythmia, and arrest.
Hyperkalemia ECG · Hyperkalemia ECG vs Hypokalemia ECG
Primary bicarbonate decrease from acid gain or bicarbonate loss, with hyperventilation lowering PaCO2 as compensation.
Metabolic acidosis · Respiratory acidosis vs Metabolic acidosis
Keep going
Every pair in this review has a free page in the library with a side-by-side comparison and a practice question. Work through the ones you missed in the self-test first.