Mechanical ventilation is not futile if it succeeds in passing air into a patients lungs. CPR is not futile if it succeeds in moving blood out of the heart. Even the use of extra corporeal membrane oxygenation in terminally ill patients cannot be considered physiologically futile, since it can maintain circulation and ventilation. The immediate physiologic effect of these interventions differ from the broader and more uncertain question of prognosis. Another method of assessing futility is by statistical probability of a desirable outcome.
Futility seems almost always a matter of probability.
But the statistical cutoff point chosen as the threshold for determining futility is usually relative to opinion. No matter what point is selected, there is always a potential survivor not predicted to survive, prompting the public and the courts to spend vast quantities of scarce resources to avoid the possibility of that survivor expiring. Even if we could agree on a statistical cutoff point for determining futility, physicians are often highly unreliable in estimating the likelihood of success of a therapeutic intervention. Even in theory, statistical inferences about what might happen to groups of patients do not permit accurate predictions of what will happen to the next such patient. Another difficult issue of futility is it's impact on allocation of scarce resources.