When she turns blue from lack of oxygen and only seconds separate life and death. When your sense of certainty in her outcome is shattered by the cries of a parent. To hold a dying child in your hands is to experience both the greatest responsibility and the greatest power in medicine. This is when we are needed most. This is when we change lives.

Fluid accumulated in her lungs. The odds were stacked against her from birth—born with a failing heart in a country without a surgeon, without options. Her oxygen levels fell like a stone. As her heart slowed, my heart raced. My world became the child—background commotion faded into oblivion. For a brief moment, the blistering sun shining through metal bars on the window and casting a checkered shadow over the room, time stood still. A thousand thoughts ran through my mind. Could we resuscitate her? Should we resuscitate her? Even if we succeed, we have no way to treat her. She’ll drown in her own secretions. What if she were my child? Is this what it feels like to be God?

As physicians we regularly confront mortality—the process, the motions, how it looks, smells and feels are all part of our repertoire. But for our patients and their families, mortality ranges from familiar to foreign, an experience for them which, as physicians, we cannot just witness, but rather we must define. We guide our patients during their darkest hours, at their most vulnerable times as they probe the limits of their own humanity. We listen to what they say, we interpret what we see, and we provide direction. It has long been said that with great power comes great responsibility. Perhaps, more appropriate to medicine, it is with great responsibility that comes great power.

How do you measure the responsibility of navigating between life and death? There is no course in medical school that teaches you, no credentials that one must acquire. Is one a failure? Is one a success? A point exists though which we pass in our care for the dying where hope and reality diverge—where idealism yields to reality. It is here where our patients are most vulnerable, and our responsibility to them the greatest. It is here, in the heat of the moment, where human emotion melds with the realities and limitations, the known and the unknowns of medicine, and a patient live or dies.

Almost a decade ago I wheeled a stretcher carrying a young man toward the operating room. A family gathered in the hallway, and as our convoy of monitors and infusion pumps shuffled through, I made eye contact with the patient’s mother. It was only hours earlier that we stood together at the bedside in the ICU as his family struggled to accept that further medical care was futile—that he was dead. Although the outcome was expected and they were prepared, the floodgates of emotion that opened were an appropriately raw and visceral response to the mercilessness of watching their child die. In the hours before his death I had learned who he was—his hobbies, his interests, his aspirations. I listened, I observed, and in some tacit way I contributed to the family’s acceptance of the inexorable outcome, and the decision that organ donation was the best way to honor him. So, as the sun rose on a crisp Thanksgiving morning, I guided him past his family on the way to the operating room, his final journey to donate his life to others.

For as much as we know about death and dying, it remains the ultimate of frontiers and the epitome of unknowns. And for this very reason, our choices and actions as physicians during out patients’ final moments may be based as much in our own emotions and beliefs as they are in science. Although some things in medicine may be virtually assured, results sometimes depend as much on the stars aligning as choosing the proper medication, and we have a responsibility to our patients and ourselves to acknowledge the shortcomings of our predictive powers—our lack of crystal ball. For our baby, as her heart rate slowed and her lips changed from pink to purple, the act of resuscitation seemed nothing more than a pantomime to me, her demise fated at birth from heart failure in a country that could not treat her. Yet few motivations are as powerful as the cries of a father, and we began chest compressions. It would have been impossible to know that not only would her heart rate increase and her color return, but that weeks later, on Thanksgiving Day to be precise, her heart would be repaired by a visiting surgical team and her life would begin anew.

Our responsibility as physicians is never greater than when we care for patients in the face of death. It is here, in the fertile grounds of uncertainty and emotion that we have the power to change lives—sometimes our patient’s, sometimes their family’s, sometimes our own. It is here where we must question our limitations and capabilities, decipher reality from hope. It is here, in the final act, where we define mortality.