Is There a Contract Between Surgeons and Patients About the Use of Life Support?

Survey of over a thousand cardio thoracic surgeons, vascular surgeons and nerro surgeons to determine whether they negotiate with their patients pre operatively about the use of life supporting and sustaining treatments in the post operative period as a condition for performing surgery. Surgeons were asked to imagine that one of your patients requires non emergent surgery and is at moderate risk for long term vent support or ialysis. Would you negotiate a time period after which this life sustaining treatment could be withdrawn? And i'm really curious about the idea of this informal contract. So i wonder what that mean to the surgeon, versus what that means to the patient, and how exactly is that done?