It has been revealed staff at Concord hospital were forced to ventilate patients on life support by hand, during a power outage on the weekend.
Power generators failed to kick-in in the intensive care and emergency departments on Saturday morning - leaving the wards without power for around two hours.
NSW Opposition Leader Barry O'Farrell said Health Minister Reba Meagher needed to explain how such a "catastrophic failure" could occur in one of NSW's largest hospitals.
"How is it possible for a contingency electricity supply to fail in the most crucial parts of the hospital - the intensive care unit and the emergency department," Mr O'Farrell said in a statement.
"It's a tribute to the outstanding staff that no one died during this major failure."
The opposition wants the government to review all emergency back-up electricity generator systems in public hospitals statewide.