Pulmonology ICD-10: E87.2

Arterial Blood Gas Disorders

Also known as: ABG Imbalances, Acid-Base Disorders

Dangerous imbalances in the blood's acidity and oxygen levels caused by severe lung, kidney, or metabolic diseases. Diagnosis requires drawing blood directly from an artery.

Source: ATS/ERS Guidelines on Respiratory Failure

Updated: Aug 18, 2026

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Red Flag Warning & Emergency Situations

A 'normal' pCO2 in a severe asthma exacerbation; this indicates impending respiratory muscle fatigue and respiratory arrest.
pH dropping below 7.15, portending imminent cardiovascular collapse.

Emergency Management: Acute hypercapnic respiratory failure with coma. Requires immediate bag-valve-mask ventilation followed by endotracheal intubation.

Core Definition:

Arterial Blood Gas (ABG) disorders refer to physiological derangements in blood pH, carbon dioxide (pCO2), and bicarbonate (HCO3-) levels. They are broadly categorized into four primary processes: metabolic acidosis, metabolic alkalosis, respiratory acidosis, and respiratory alkalosis. These disorders reflect underlying severe systemic illness, respiratory failure, or renal dysfunction.

Detailed Overview

The human body strictly maintains a blood pH between 7.35 and 7.45. The lungs regulate volatile acid (CO2), acting within minutes to hours via ventilation. The kidneys regulate metabolic acids by reabsorbing or excreting bicarbonate and secreting H+, a slower process taking days. An abnormality in one system triggers a compensatory response in the other. Proper interpretation of an ABG allows clinicians to diagnose life-threatening conditions like diabetic ketoacidosis (DKA), sepsis, opioid overdose, or acute respiratory distress syndrome.

Epidemiology & Demographics

Not a single disease but a consequence of numerous pathologies. Present in nearly all critically ill ICU patients, severely decompensated COPD patients, and uncontrolled diabetics.

Etiological Mechanism

Respiratory Acidosis: Hypoventilation (e.g., COPD, opioids, Guillain-Barré). Respiratory Alkalosis: Hyperventilation (e.g., panic attack, high altitude, early pulmonary embolism). Metabolic Acidosis: Acid accumulation (MUDPILES) or bicarb loss (diarrhea). Metabolic Alkalosis: Acid loss (vomiting) or bicarb retention (diuretics).

Primary Causes

Underlying conditions such as severe asthma/COPD, renal failure, severe vomiting/diarrhea, poisoning (salicylates, methanol), or massive infection/sepsis.

Chronic Lung Disease: COPD patients chronically retain CO2, risking acute-on-chronic respiratory acidosis.
Renal Failure: Inability to excrete daily metabolic acid load leads to chronic metabolic acidosis.
Diabetes Mellitus: Poorly controlled type 1 diabetes risks severe high-anion-gap metabolic acidosis (DKA).

Acidemia (pH < 7.35) depresses myocardial contractility, causes arterial vasodilation with venoconstriction, and increases the threshold for ventricular arrhythmias. Alkalemia (pH > 7.45) shifts the oxygen-hemoglobin dissociation curve to the left (decreasing tissue oxygen delivery) and causes acute hypocalcemia (tetany/seizures). The Anion Gap (Na+ - (Cl- + HCO3-)) helps differentiate the cause of metabolic acidosis: >12 mEq/L indicates unmeasured acids (e.g., lactic acid, ketones), while normal indicates HCO3- loss (e.g., diarrhea, RTA).

Characteristic Clinical Presentation

Kussmaul Respirations: Deep, rapid breathing serving as respiratory compensation for severe metabolic acidosis.
Altered Mental Status: CO2 narcosis in respiratory acidosis causes profound somnolence and coma.
Muscle Tetany: Tingling, carpopedal spasms, and cramps seen in acute alkalosis due to ionized hypocalcemia.

Physical Examination Signs

Asterixis (flapping tremor) in hypercapnic respiratory acidosis.
Chvostek and Trousseau signs positive in severe alkalosis.
Fruity breath odor in DKA-associated metabolic acidosis.

Clinical Risk: Uncontrolled or untreated conditions may progress to the following complications:

Fatal Arrhythmias: Severe acidemia (pH < 7.1) profoundly alters potassium balance, leading to V-Fib or asystole.
Cerebral Edema: Rapid shifts in pCO2 levels can severely alter cerebral blood flow.

Diagnostic Criteria & Guidelines

Arterial Blood Gas sampling via radial or femoral artery puncture. Normal values: pH = 7.35-7.45; pCO2 = 35-45 mmHg; pO2 = 80-100 mmHg; HCO3- = 22-26 mEq/L. Stepwise interpretation: 1. Identify acidemia or alkalemia. 2. Identify the primary driver (pCO2 or HCO3- matching the pH shift). 3. Calculate compensation (e.g., Winter's formula). 4. Calculate anion gap.

Differential Diagnosis

High Anion Gap Metabolic Acidosis: MUDPILES (Methanol, Uremia, DKA, Propylene Glycol, Isoniazid, Lactic acidosis, Ethylene glycol, Salicylates)
Non-Anion Gap Metabolic Acidosis: HARDUP (Hyperalimentation, Addison's, RTA, Diarrhea, Ureterosigmoidostomy, Pancreatic fistula)

Laboratory Tests & Biomarkers

Winter's Formula (Expected pCO2): (1.5 * HCO3-) + 8 +/- 2. Used to determine if metabolic acidosis is appropriately compensated.
Serum Lactate: Elevated (> 2 mmol/L) in tissue hypoperfusion/sepsis driving metabolic acidosis.
Urine Electrolytes: Urine chloride < 20 mEq/L indicates saline-responsive metabolic alkalosis (vomiting); > 20 indicates saline-resistant (Conn syndrome).

Imaging Modalities & Findings

Chest X-Ray:
Renal Ultrasound:

Uncompensated
Primary pH alteration has occurred, but the opposing system has not yet adjusted.
Partially Compensated
Opposing system is working to normalize pH, but pH remains outside 7.35-7.45.
Fully Compensated
Opposing system has brought the pH back within the normal range (though still leaning toward the primary disturbance).

First-Line Treatment:

Treat the underlying cause; ABG disorders are symptoms, not primary diseases. For severe respiratory acidosis (pH < 7.25, high pCO2), intubation and mechanical ventilation or non-invasive BiPAP is required to blow off CO2. For diabetic ketoacidosis (metabolic acidosis), aggressive IV normal saline and IV continuous insulin (0.1 U/kg/hr). For lactic acidosis, reverse shock with vasopressors and fluids.

Second-Line & Adjunctive Therapy

For profound, life-threatening metabolic acidemia (pH < 7.10) where hemodynamics are crashing, slow IV administration of Sodium Bicarbonate (NaHCO3) 1-2 mEq/kg may be used as a desperate temporizing measure. For saline-responsive metabolic alkalosis, administration of 0.9% NaCl IV corrects volume depletion and chloride deficit.

Surgical & Procedural Management

Not primarily surgical, though surgical source control (e.g., amputation of ischemic bowel) is critical to stop severe lactic acidosis.

Recommended Lifestyle Changes

Strict compliance with insulin therapy for patients with Type 1 Diabetes to prevent DKA.
Smoking cessation and medication adherence in COPD to prevent hypercapnic respiratory failure.

Patient Counseling & Advice

For COPD patients on home O2, instruct strictly not to increase flow rates beyond prescribed limits (usually 1-2 L/min), as this can dangerously increase pCO2 levels.

Follow-Up & Monitoring Schedule

Continuous pulse oximetry and serial ABG or VBG (venous blood gas) draws every 2-4 hours in the ICU until the acid-base derangement is resolved.

Preventive Strategies

Prompt recognition and treatment of sepsis to prevent lactic acidosis. Careful monitoring of electrolyte and fluid balance in patients receiving heavy diuretic therapy.

Highly variable based entirely on the etiology. Mild DKA has virtually 100% survival, whereas severe lactic acidosis from mesenteric ischemia carries a mortality >70%.

Frequently Asked Questions

Arteries are deeper, possess a thicker muscular wall with more nerve endings, and the puncture requires going through more sensitive tissue.

Yes, massive ingestion of calcium carbonate or baking soda can cause severe metabolic alkalosis and milk-alkali syndrome.

Authoritative Sources & Evidence References

ATS/ERS Guidelines on Respiratory Failure:
View Official Guideline

Key Literature & References:

Evidence Understanding Acid-Base Disorders