Which situation would require an amniotomy according to a charge nurse's teaching?

An amniotomy, which is the artificial rupture of the membranes, is indicated when there is a need to facilitate monitoring of the fetus, such as when placing a fetal scalp electrode. This procedure allows for more accurate assessment of the fetal heart rate and other parameters, particularly when external monitoring is insufficient or impractical due to the position of the fetus or maternal body habitus.

In this context, using a fetal scalp electrode can provide continuous and reliable fetal heart rate readings, which are crucial for assessing fetal well-being during labor. By rupturing the membranes, access to the fetal scalp is gained, allowing for better placement of the electrode.

The other situations listed do not necessitate an amniotomy. Monitoring maternal blood pressure is a routine procedure that does not require any intervention with the membranes. Performing a manual rotation of the fetus may involve clinical judgment but does not directly link to the need for rupturing membranes. Administering pain relief medications likewise does not relate to the condition of the membranes. Therefore, out of the options provided, the situation requiring an amniotomy is certainly when placing a fetal scalp electrode to improve fetal monitoring accuracy.