| Parameter | Reference Interval | Clinical Notes |
|---|---|---|
| pH | 7.35-7.45 | Measure of blood acidity/alkalinity |
| PaCO₂ | 35-45 mm Hg | Partial pressure of CO₂ in arterial blood |
| Bicarbonate (HCO₃⁻) | 22-26 mEq/L (mmol/L) | Primary buffer system |
| PaO₂ | 80-100 mm Hg | Decreases above sea level and with increasing age |
| SaO₂ | >95% | Arterial O₂ saturation |
| Base Excess | ±2.0 mEq/L | Metabolic component assessment |
Normal Arterial Blood Gas Values
Clinical Manifestations of Alkalosis
Respiratory Alkalosis (↓ PaCO₂)
Neurologic
- Dizziness
- Light-headedness
- Confusion
- Headache
Cardiovascular
- Tachycardia
- Dysrhythmias (related to hypokalemia from compensation)
Gastrointestinal
- Nausea, vomiting, diarrhea
- Epigastric pain
Neuromuscular
- Tetany
- Numbness
- Tingling of extremities
- Hyperreflexia
- Seizures
Respiratory
- Hyperventilation (compensatory if metabolic)
Metabolic Alkalosis (↑ HCO₃⁻)
Neurologic
- Irritability
- Lethargy
- Confusion
- Headache
Cardiovascular
- Tachycardia
- Dysrhythmias (related to hypokalemia from compensation)
Gastrointestinal
- Nausea, vomiting
- Anorexia
Neuromuscular
- Tetany
- Tremors
- Tingling of fingers and toes
- Muscle cramps, hypertonic muscles
- Seizures
Respiratory
- Hypoventilation (compensatory action by lungs)
Clinical Manifestations of Acidosis
Respiratory Acidosis (↑ PaCO₂)
Neurologic
- Lethargy
- Confusion
- Dizziness
- Headache
- Coma
Cardiovascular
- Decreased BP
- Ventricular fibrillation (related to hyperkalemia from compensation)
- Warm, flushed skin
Gastrointestinal
- No significant findings
Neuromuscular
- Seizures
Respiratory
- Hypoventilation with hypoxia
Metabolic Acidosis (↓ HCO₃⁻)
Neurologic
- Lethargy
- Confusion
- Dizziness
- Headache
- Coma
Cardiovascular
- Decreased BP
- Dysrhythmias (related to hyperkalemia from compensation)
- Cold, clammy skin
Gastrointestinal
- Nausea, vomiting, diarrhea, abdominal pain
Neuromuscular
- Muscle weakness
Respiratory
- Deep, rapid respirations
Causes, Pathophysiology, and Laboratory Findings
| Condition & Causes | Pathophysiology | Laboratory Findings |
|---|---|---|
|
Respiratory Acidosis • Chronic respiratory disease (COPD) • Barbiturate or sedative overdose • Chest wall abnormality • Severe pneumonia • Atelectasis • Respiratory muscle weakness • Mechanical hypoventilation • Pulmonary edema |
• ↑ CO₂ retention from hypoventilation • Compensatory response is ↑ HCO₃⁻ retention by kidney |
↓ Plasma pH ↑ PaCO₂ HCO₃⁻ normal (uncompensated) ↑ HCO₃⁻ (compensated) Sample ABG Uncompensated: pH 7.31 PaCO₂ 54 mm Hg HCO₃⁻ 25 mEq/L |
|
Respiratory Alkalosis • Hyperventilation (hypoxia, anxiety, fear, pain, exercise, fever) • Stimulated respiratory center (septicemia, stroke, meningitis, encephalitis, brain injury, salicylate poisoning) • Liver failure • Mechanical hyperventilation |
• ↑ CO₂ excretion from hyperventilation • Compensatory response is ↑ HCO₃⁻ excretion by kidney |
↑ Plasma pH ↓ PaCO₂ HCO₃⁻ normal (uncompensated) ↓ HCO₃⁻ (compensated) Sample ABG Uncompensated: pH 7.52 PaCO₂ 27 mm Hg HCO₃⁻ 24 mEq/L |
|
Metabolic Acidosis • Diabetic ketoacidosis • Lactic acidosis • Starvation • Diarrhea • Renal tubular acidosis • Renal failure • Gastrointestinal fistulas • Shock |
• Gain of fixed acid, inability to excrete acid or loss of base • Compensatory response is ↑ CO₂ excretion by lungs |
↓ Plasma pH PaCO₂ normal (uncompensated) ↓ PaCO₂ (compensated) ↓ HCO₃⁻ Sample ABG Uncompensated: pH 7.29 PaCO₂ 38 mm Hg HCO₃⁻ 18 mEq/L |
|
Metabolic Alkalosis • Vomiting • Nasogastric suctioning • Diuretic therapy • Hypokalemia • Excess NaHCO₃ intake • Mineralocorticoid use |
• Loss of strong acid or gain of base • Compensatory response is ↑ CO₂ retention by lungs |
↑ Plasma pH PaCO₂ normal (uncompensated) ↑ PaCO₂ (compensated) ↑ HCO₃⁻ Sample ABG Uncompensated: pH 7.50 PaCO₂ 40 mm Hg HCO₃⁻ 34 mEq/L |
Clinical Note: PaO₂ decreases above sea level and with increasing age. Always consider patient-specific factors when interpreting arterial blood gas results. Compensation mechanisms help maintain physiological pH but rarely completely normalize values.