From the Guidelines
The patient is critically ill and requires immediate oxygen supplementation to address the severe hypoxemia, with a target saturation of 94-98%. The blood gas results indicate a severe metabolic acidosis with a pH of 7.39 not being the case here, but rather a pH of 7, and a low PCO2 of 2.30 kPa, suggesting respiratory alkalosis, and a critically low PO2 of 19.9 kPa, indicating severe hypoxemia. The bicarbonate level is reduced at 16 mmol/L and the base excess is markedly negative at -11.9, indicating metabolic acidosis. According to the BTS guideline for oxygen use in adults in healthcare and emergency settings 1, the patient should be commenced on 15 L/min oxygen via reservoir mask or bag-valve mask and managed as advised in Table 1. The patient's SpO2 should be titrated to maintain a target range of 94-98% and repeat blood gases should be obtained at 30-60 minutes to assess the response to oxygen therapy. If the patient is at risk of hypercapnic respiratory failure, the target saturation should be adjusted to 88-92% 1.
- Key points to consider in management:
- The patient's respiratory rate and heart rate should be carefully measured, as tachypnoea and tachycardia are more common than cyanosis in hypoxaemic patients 1.
- Appropriate changes should be made to any 'track and trigger' system used to allow for a lower target range in patients at risk of hypercapnic respiratory failure 1.
- The underlying cause of the respiratory alkalosis and metabolic acidosis should be identified and treated promptly.
- The patient should be closely monitored for signs of respiratory deterioration, such as increased respiratory rate, decreased oxygen saturation, or decreased level of consciousness, and immediate senior review should be sought if there is any concern about the patient's condition 1.
From the Research
Blood Gas Analysis
- The given blood gas values are: pH 7.39, pCO2 2.30, PO2 19.9, bicarbonate (HCO3-) 16, and base excess (BE) -11.9.
- These values indicate a state of metabolic acidosis, as evidenced by the low bicarbonate level and negative base excess 2, 3.
- The low pH value (7.39) also supports the diagnosis of metabolic acidosis, although it is not severely acidic 4, 5.
Diagnosis of Metabolic Acidosis
- Metabolic acidosis can be classified into two main categories: anion gap acidosis and non-anion gap acidosis 4, 3.
- The calculation of the serum anion gap can aid in diagnosis, with a gap of 12 ± 4 mmol/L considered normal 3.
- However, without the serum electrolyte values (e.g., sodium, chloride), it is difficult to determine the anion gap and classify the type of metabolic acidosis.
Treatment and Management
- Treatment of metabolic acidosis is aimed at addressing the underlying cause, such as removing toxins or treating the underlying disease process 2, 4.
- The use of bicarbonate to normalize the pH is controversial, and its administration should be considered on a case-by-case basis 3, 5.
- In some cases, such as severe metabolic acidosis, mechanical ventilation or extracorporeal therapies may be necessary to manage the condition 4, 5.