What must be the minimum flow rate for a simple face mask to prevent CO2 rebreathing?

The minimum flow rate for a simple face mask to prevent carbon dioxide (CO2) rebreathing is generally recognized as 5 liters per minute. This flow rate ensures that enough fresh gas is delivered to dilute and wash out the exhaled CO2 that can accumulate within the mask. When higher flow rates are used, they help to maintain an adequate concentration of oxygen and reduce the risk of rebreathing CO2, which can occur if the flow is too low.

In the context of a simple face mask, initiating flow at 5 liters per minute helps to establish a positive pressure that effectively flushes out CO2 and prevents it from being inhaled again. This is particularly important during procedures involving sedation, as the patient's respiratory status must be carefully monitored to ensure safety and effectiveness.

Higher flow rates, such as those above 5 L/min, might still provide added safety by increasing the clearance of CO2, but the minimum threshold to prevent rebreathing is firmly established at 5 L/min.