Brief Answer:
you need pleural fluid drainage first.

Detailed Answer:
Hello dear, thanks for your question on HCM.
I want to ask you few questions first.
1. Are you smoker?
2. How much pleural effusion is present? Approximately amount and side of effusion (left or right)
3. What symptoms you are having? And since how many days?
4. Is there any lung parenchymal lesion or pleural lesion on CTthorax?
5. Do you have any cardiac disease?

In any case of pleural effusion, pleural fluid aspiration is must. And tests of fluid should be undergo to reach the diagnosis.
Since your age is 80 (old age) I can think of following common causes.
1. Infection like TB
2. Cardiac anx hepatic causes.
3. Malignant pleural effusion.
So we need to do following tests with fluid
1. Pleural fluid routine and microscopy.
2. Pleural fluid cytology
3. Pleural fluid ADA (Adenosine DeAminase)
4. Pleural fluid culture and sensitivity.
If not conclusive from above tests, pleural biopsy is needed.
So we need to search the cause first and than start the treatment accordingly.

Hope I have solved your query.
I will be happy to help you further.
Wish you good health.
Thanks.

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