What do systematic reviews say?

Drain vs No drain

Drains showed no clear difference in mortality compared with no drains (low certainty).

• External drains versus no drains after burr‐hole evacuation for the treatment of chronic subdural haematoma in adults 2016 · Cochrane Headline outcomes only
  RR 0.78 [0.45, 1.33]
  5 studies · 539 participants
  Low