When using a glass oral thermometer, what is a necessary precaution?

The correct approach when using a glass oral thermometer is to always shake down the mercury before each use. This precaution is necessary because if the mercury column is not reset to a lower level, the thermometer may give an inaccurate reading. Shaking it down ensures that the mercury is at the correct starting point, typically below the normal body temperature range, allowing for a proper measurement.

By ensuring that the thermometer starts at an appropriate baseline, you can help guarantee that the resulting temperature reading will reflect the patient's actual body temperature accurately. This practice is critical for obtaining reliable readings that can inform appropriate care decisions.

In contrast, the other options present incorrect practices that could compromise the effectiveness and safety of thermometer use. For instance, leaving the thermometer in the patient's mouth for more than the recommended time or attempting to run it under hot water may not provide accurate readings and can pose risks to the patient. Keeping the thermometer intact is also important; therefore, being careful not to shake it unexpectedly ensures that it remains in good condition and continues to function effectively.