What is the interpretation of the arterial blood gas (ABG) results showing a pH of 7.38, partial pressure of carbon dioxide (pCO2) of 4.4, partial pressure of oxygen (pO2) of 8.9, lactate level of 2.6, base excess (BE) of -5.6, and bicarbonate (HCO3-) level of 21.1?

From the Guidelines

These blood gas results indicate a mild metabolic acidosis with respiratory compensation, and the patient's lactate level of 2.6 mmol/L suggests tissue hypoperfusion, which is a critical marker of shock severity, as evidenced by studies showing the value of serial lactate measurements for predicting survival in shock 1. The pH of 7.38 is at the lower end of normal (7.35-7.45), while the bicarbonate is reduced at 21.1 mmol/L (normal 22-26 mmol/L) with a negative base excess of -5.6, confirming the metabolic acidosis.

• Key points to consider in the interpretation of these results include:
  • The PCO2 of 4.4 kPa (33 mmHg) is slightly low, representing appropriate respiratory compensation through increased ventilation to help normalize the pH.
  • The PO2 of 8.9 kPa (67 mmHg) is below normal, suggesting mild hypoxemia.
  • The lactate level of 2.6 mmol/L is mildly elevated (normal <2.0 mmol/L), which may be contributing to the metabolic acidosis and is an important marker for tissue hypoperfusion, as highlighted in the European guideline on management of major bleeding and coagulopathy following trauma: sixth edition 1.
• The clinical management of this patient should prioritize identifying and treating the underlying cause of the acidosis, ensuring adequate oxygenation, and closely monitoring the lactate level for signs of worsening tissue hypoperfusion or shock, as lactate has been used as a diagnostic and prognostic marker of haemorrhagic shock since the 1960s 1. Given the importance of lactate as a marker of tissue hypoperfusion and its implications for patient outcomes, as noted in studies showing the value of serial lactate measurements for predicting survival in shock 1, it is crucial to address the elevated lactate level promptly and effectively.

From the Research

Interpretation of Arterial Blood Gas (ABG) Results

The given ABG results show a pH of 7.38, partial pressure of carbon dioxide (pCO2) of 4.4, partial pressure of oxygen (pO2) of 8.9, lactate level of 2.6, base excess (BE) of -5.6, and bicarbonate (HCO3-) level of 21.1. To interpret these results, we need to consider the following factors:

• The pH level is slightly alkalotic, indicating a respiratory alkalosis or a compensated metabolic acidosis 2.
• The pCO2 level is low, which supports the diagnosis of respiratory alkalosis 3.
• The lactate level is elevated, indicating tissue hypoxia or metabolic acidosis 4.
• The base excess (BE) is negative, indicating a metabolic acidosis 5.
• The bicarbonate (HCO3-) level is low, which supports the diagnosis of metabolic acidosis 6.

Acid-Base Disorder Diagnosis

Based on the ABG results, the patient has a mixed acid-base disorder, consisting of:

• Respiratory alkalosis (low pCO2)
• Metabolic acidosis (low HCO3-, negative BE, and elevated lactate)

Clinical Correlation

The diagnosis of mixed acid-base disorder should be correlated with the patient's clinical condition, including their medical history, physical examination, and other laboratory results 2. The patient's lactate level and base excess should be monitored closely to guide treatment and assess the effectiveness of interventions 4.

Key Points to Consider

• The anion gap should be calculated to determine if the metabolic acidosis is due to an increase in unmeasured anions 3.
• The patient's oxygenation and ventilation status should be assessed to determine if the respiratory alkalosis is due to hyperventilation or other factors 6.
• The patient's renal function and electrolyte levels should be monitored to determine if the metabolic acidosis is due to renal dysfunction or other factors 5.