What are the diagnostic steps and treatment options for acidosis?

Diagnosis of Acidosis

Acidosis is diagnosed when arterial blood pH is <7.35, confirmed by arterial blood gas analysis showing reduced pH alongside assessment of PaCO2 and bicarbonate to determine if the acidosis is metabolic, respiratory, or mixed. 1

Diagnostic Steps

Initial Clinical Assessment

• Obtain focused history looking for precipitating causes: diabetes (ketoacidosis), shock states (lactic acidosis), renal disease, drug ingestions (salicylates, methanol, ethylene glycol), severe diarrhea, or respiratory compromise 2, 3

• Physical examination findings suggesting acidosis include: cold sweated extremities, oliguria, mental confusion, dizziness, narrow pulse pressure, and signs of hypoperfusion 1

• Respiratory pattern assessment: Look for compensatory hyperventilation (Kussmaul breathing) with respiratory rate >25 breaths/min, which indicates metabolic acidosis 1

Essential Laboratory Tests

Arterial blood gas analysis is mandatory and provides three critical parameters 1, 4:

• pH <7.35 confirms acidosis 1
• PaCO2 distinguishes respiratory (>45 mmHg) from metabolic causes 1
• Bicarbonate level (HCO3-) is reduced in metabolic acidosis 5

Calculate the anion gap immediately using: Anion Gap = [Na+] - ([Cl-] + [HCO3-]) 3, 6, 4

• Normal anion gap: 8-12 mEq/L
• High anion gap (>17 mEq/L) indicates presence of unmeasured anions from organic acids 5, 6
• Normal anion gap suggests bicarbonate loss or chloride retention 3, 7

Additional laboratory evaluation should include 5, 4:

• Plasma glucose (to detect diabetic ketoacidosis)
• Serum ketones (β-hydroxybutyrate preferred over nitroprusside method) 5
• Serum lactate (>2 mmol/L is elevated) 1
• Blood urea nitrogen and creatinine (renal function)
• Serum electrolytes including potassium
• Complete blood count
• Serum osmolality (if toxic ingestion suspected)

Categorization by Anion Gap

High anion gap metabolic acidosis (HAGMA) with anion gap ≥17 indicates 5, 6:

• Diabetic ketoacidosis
• Lactic acidosis (from shock, sepsis, tissue hypoperfusion)
• Renal failure (uremic acidosis)
• Toxic ingestions (methanol, ethylene glycol, salicylates)

Normal anion gap (hyperchloremic) acidosis suggests 3, 7:

• Gastrointestinal bicarbonate loss (severe diarrhea)
• Renal tubular acidosis
• Ingestion of acidifying chloride salts

Respiratory Acidosis Assessment

If PaCO2 >45 mmHg with pH <7.35, this indicates respiratory acidosis from alveolar hypoventilation 1, 7

Look for causes including 1:

• COPD exacerbation (47% have PaCO2 >45 mmHg)
• Severe kyphoscoliosis or chest wall disorders
• Neuromuscular weakness
• Drug-induced respiratory depression (opioids, benzodiazepines)
• Morbid obesity (BMI >40 kg/m²)

Assess severity of respiratory acidosis 1:

• pH <7.35 with PaCO2 >45 mmHg indicates acidosis
• pH <7.25 indicates severe acidosis requiring urgent intervention

Monitoring Parameters

In acute settings, monitor every 2-4 hours until stabilized 5:

• Arterial blood gases and pH
• Serum electrolytes (especially potassium)
• Glucose
• Lactate
• Renal function (BUN, creatinine)

Venous pH can substitute for arterial pH in stable patients (typically 0.03 units lower than arterial) 5

Treatment Approach

General Principles

Treatment must address the underlying cause while providing supportive care 2, 3, 8

The rate of correction matters: Rapid changes can cause complications, so stepwise correction over 4-8 hours is preferred for metabolic acidosis 2

Metabolic Acidosis Treatment

For diabetic ketoacidosis 1, 5:

• Administer regular insulin as continuous IV infusion at 0.1 units/kg/h after initial bolus of 0.1 units/kg
• Begin isotonic saline (0.9% NaCl) at 15-20 mL/kg/h during first hour
• Add potassium 20-30 mEq/L to infusion once renal function confirmed
• Continue until pH >7.3, bicarbonate ≥18 mEq/L, and anion gap normalized

For lactic acidosis from shock 2, 8:

• Restore tissue perfusion with volume resuscitation
• Treat underlying cause (sepsis, hemorrhage)
• Supportive care is primary; bicarbonate use remains controversial

Bicarbonate Therapy Indications

Bicarbonate is generally NOT recommended for pH >7.0 5, 2

Consider bicarbonate only for severe acidosis with pH <7.0 5, 2:

• Administer 50-100 mmol sodium bicarbonate diluted in 200-400 mL sterile water over 1-2 hours
• Dose: 1-2 mEq/kg over 1 hour for pH <7.0

Specific indications for bicarbonate 2:

• Hyperkalemia with metabolic acidosis
• Certain drug intoxications (salicylates, methanol, barbiturates)
• Hemolytic reactions requiring urine alkalinization

Avoid bicarbonate in ketoacidosis unless pH <6.9 due to risk of intracellular acidosis, reduced ionized calcium, and hyperosmolality 5, 8

Respiratory Acidosis Treatment

For COPD with respiratory acidosis 1:

• Target oxygen saturation 88-92% (not higher)
• Use controlled oxygen therapy (28% or 35% Venturi mask or 1-2 L/min nasal cannula)
• Avoid excessive oxygen which worsens CO2 retention
• If pH <7.35 with acidosis, step down oxygen delivery but don't discontinue abruptly

For severe respiratory acidosis 1:

• Consider non-invasive ventilation
• Escalate to invasive mechanical ventilation if patient deteriorating
• Treat underlying cause of hypoventilation

Critical Pitfalls to Avoid

Do not rely on nitroprusside method for ketone measurement as it misses β-hydroxybutyrate, the predominant ketoacid in DKA 5

Do not attempt full correction of acidosis in first 24 hours as this may cause rebound alkalosis due to delayed ventilatory adjustment 2

Do not give excessive oxygen to COPD patients as 30-35% received high-concentration oxygen inappropriately, worsening acidosis 1

Monitor for cerebral edema in pediatric DKA by avoiding osmolality reduction >3 mOsm/kg/h 5

In cardiac arrest, risks from acidosis exceed those of hypernatremia, so rapid bicarbonate infusion (44.6-100 mEq initially) is justified despite hypertonic nature 2