Final answer:
Controlling external stimuli is the most effective nursing intervention to prevent seizures in clients with severe preeclampsia, as it helps maintain a calm environment that reduces neurological irritability.
Step-by-step explanation:
The most effective nursing intervention in preventing a seizure in a client with severe preeclampsia is b. Controlling external stimuli. Preeclampsia can lead to seizures, a condition known as eclampsia, which can be life-threatening for both the mother and the baby. To prevent seizures, the environment should be kept quiet and calm, with limited exposure to bright lights and loud noises, as these can increase neurological irritability and potentially trigger a seizure.
While other options such as having emergency equipment available and keeping calcium gluconate at the bedside are important for responding to a seizure should it occur, they do not prevent the onset of a seizure. Additionally, while anticonvulsants like diazepam are used to manage a seizure, they are not necessarily preventive and are used during active seizure management.