Final answer:
An endobronchial blocker is appropriate when isolation of small lung segments is needed or when there are anatomical changes in the left main bronchus, making it a better choice than a double-lumen endotracheal tube in such scenarios.
Step-by-step explanation:
An endobronchial blocker should be selected in lieu of a double-lumen endotracheal tube when isolation of small lung segments is needed, such as B) Isolation of small lung segments. Unlike the double-lumen endotracheal tube, which is more suitable for situations where differential ventilation of both lungs is needed or when only one lung needs ventilation, an endobronchial blocker allows for more precise control and is useful for procedures that require isolation within one lung, such as surgery on a bronchopulmonary segment. Additionally, the use of an endobronchial blocker may be preferable when there are significant changes to the anatomy of the left main bronchus, which could complicate the placement of a double-lumen tube.