From the Guidelines
The patient's oxygen saturation of 97% on room air takes precedence over the arterial blood gas results, suggesting that immediate oxygen therapy may not be necessary, and the focus should be on addressing the underlying cause of the metabolic acidosis and verifying the accuracy of the blood gas sample. The arterial blood gas results show a mixed acid-base disturbance with mild metabolic acidosis (pH 7.32, HCO3 20 mEq/L, base excess -5) and severe hypoxemia (PO2 27 mmHg, O2 saturation 46%), but the discrepancy with the oxygen saturation on room air indicates a potential pre-analytical error in the blood gas sample 1. According to the BTS guideline for oxygen use in adults in healthcare and emergency settings, blood gases should be checked in situations where there is an unexpected or inappropriate fall in SpO2, deteriorating oxygen saturation, or increasing breathlessness in a patient with previously stable chronic hypoxaemia 1.
Given the patient's stable oxygen saturation on room air, the initial approach should focus on verifying the accuracy of the blood gas sample and addressing the underlying cause of the metabolic acidosis, which could include renal dysfunction, diabetic ketoacidosis, lactic acidosis, or medication effects 1. The guideline recommends starting oxygen therapy with nasal cannulae at 2–6 L/min or simple face mask at 5–10 L/min unless the saturation is below 85%, in which case a reservoir mask at 15 L/min may be used 1. However, in this case, the patient's oxygen saturation on room air is 97%, which suggests that oxygen therapy may not be immediately necessary.
The metabolic acidosis should be addressed by identifying and treating the underlying cause, and intravenous fluids may be appropriate depending on the patient's volume status and the cause of the acidosis. It is essential to note that the BTS guideline emphasizes the importance of adjusting oxygen therapy based on the patient's individual needs and response to treatment, and that oxygen therapy should be titrated to achieve a target saturation range of 94–98% in most cases 1.
In summary, the patient's oxygen saturation on room air takes precedence, and the focus should be on addressing the underlying cause of the metabolic acidosis and verifying the accuracy of the blood gas sample, rather than initiating immediate oxygen therapy.
From the Research
Arterial Blood Gas Results Interpretation
The patient's arterial blood gas results show acidosis (pH 7.32), normal pCO2 (39), hypoxemia (pO2 27), base deficit (-5), low bicarbonate (HCO3 20), and low oxygen saturation (46%) on arterial blood. However, the oxygen saturation on room air is 97% 2.
Discrepancy between SaO2 and SpO2
The discrepancy between the patient's SaO2 (46%) and SpO2 (97%) can be attributed to various factors, including pseudohypoxemia, which is an artifactual condition that occurs in patients with extreme leukocytosis and thrombocytosis 3. Another possible explanation is the effect of supplemental oxygen on the detection of hypoventilation by pulse oximetry, which can mask the ability to detect abnormalities in respiratory function 4.
Treatment Approach
Given the patient's arterial blood gas results and the discrepancy between SaO2 and SpO2, the treatment approach should focus on addressing the underlying cause of the hypoxemia and acidosis. This may involve:
- Providing supplemental oxygen to improve oxygenation, but being aware of its potential to mask hypoventilation 4
- Managing the patient's acid-base status, including correcting the base deficit and normalizing the bicarbonate level
- Addressing any underlying respiratory or cardiac conditions that may be contributing to the hypoxemia and acidosis
- Considering the use of alternative monitoring methods, such as capnography and arterial blood gas analysis, to assess the patient's respiratory function and oxygenation status 5
Oxygen Delivery Capacity
In patients with severe metabolic acidosis, the oxygen delivery capacity of the blood may be impaired, even with a normal or elevated PaO2 6. Therefore, it is essential to monitor the patient's oxygenation status closely and adjust the treatment approach as needed to ensure optimal tissue oxygenation.