From the Guidelines
In adults with unrepaired Tetralogy of Fallot, an acceptable oxygen saturation level is typically considered to be in the range of 70-90%, which is lower than the normal range due to the underlying cardiac defects. This range is considered acceptable because patients with unrepaired Tetralogy of Fallot often develop compensatory mechanisms, such as polycythemia, to improve oxygen-carrying capacity despite lower saturation levels 1. The severity of cyanosis and oxygen desaturation varies depending on the degree of pulmonary stenosis and the size of the ventricular septal defect.
According to the BTS guideline for oxygen use in adults in healthcare and emergency settings, the desirable target saturation range for most acutely ill patients is 94-98% 1. However, in the context of unrepaired Tetralogy of Fallot, this target range may not be applicable due to the underlying cardiac defects. Instead, management typically focuses on maintaining adequate hydration, preventing anemia, and avoiding situations that increase right-to-left shunting rather than targeting specific oxygen saturation values.
It is essential to note that acute drops in oxygen saturation below a patient's baseline should prompt medical evaluation, as they may indicate worsening of the condition or development of complications. The BTS guideline also recommends checking blood gases in situations where there is an unexpected or inappropriate fall in SpO2 below 94% in patients breathing air or oxygen 1. However, in the context of unrepaired Tetralogy of Fallot, the threshold for concern may be lower due to the underlying hypoxemia.
In general, the goal is to maintain an oxygen saturation level that is consistent with the patient's baseline and to avoid acute drops in saturation. Therefore, an oxygen saturation level in the range of 70-90% is considered acceptable in adults with unrepaired Tetralogy of Fallot, as long as the patient is asymptomatic and there are no signs of worsening hypoxemia or other complications.
From the Research
Acceptable O2 Saturation Levels
- The acceptable oxygen saturation (O2 sat) level in an unrepaired adult with Tetralogy of Fallot is not explicitly stated in the provided studies.
- However, a study on repair of Tetralogy of Fallot in or beyond the fourth decade of life 2 mentions that preoperative oxygen saturation was negatively correlated with inotropic score, mechanical ventilatory support, intensive care unit stay, and hospital stay.
- The same study 2 reports that patients with lower oxygen saturation had a prolonged postoperative course, but it does not provide a specific acceptable O2 sat level.
- Another study 3 reports a case of a 3-month-old girl with unrepaired Tetralogy of Fallot who presented with an initial oxygen saturation of 56% and improved to 78% after treatment, but this is not directly applicable to adults.
- A study on aerobic capacity in adults with Tetralogy of Fallot 4 does not provide information on acceptable O2 sat levels.
- A study on early assessment of hemodynamic status after repair of Tetralogy of Fallot 5 mentions that pulmonary artery oxygen saturation of 80% or greater in the intensive care unit was associated with a pulmonary to systemic flow ratio greater than 1.5 at catheterization, but this is not directly relevant to unrepaired adults.
Key Findings
- Repair of Tetralogy of Fallot in adulthood is feasible with acceptable results 2.
- Patients with high hematocrit, lower oxygen saturation, right ventricular dysfunction, aortopulmonary collaterals, and high preoperative right ventricular outflow tract gradients have a prolonged postoperative course 2.
- Adult patients who have undergone surgical repair of Tetralogy of Fallot have lower peak uptake of oxygen and peak heart rate compared to predicted values 4.