From the Guidelines
The heart can continue to function after brain death due to its intrinsic electrical conduction system, but its stability is highly dependent on meticulous medical management, as outlined in the 24th Bethesda Conference: Cardiac Transplantation guidelines 1.
The key to maintaining heart function after brain death lies in careful management of hemodynamic stability, which includes monitoring of intraarterial pressure, central venous pressure, and urinary output, as well as the use of fluid resuscitation, dopamine for hypotension, and sodium nitroprusside for hypertension 1.
- Maintaining systolic blood pressure above 100 mm Hg through adequate fluid administration is crucial, with central venous pressure targeted at 10 to 12 mm Hg.
- The development of diabetes insipidus, characterized by urinary output exceeding 300 ml/h, should be treated with parenteral vasopressin to prevent excessive fluid loss.
- Electrolyte levels, acid-base balance, and oxygenation must also be closely monitored and managed, with hourly potassium supplementation often required to prevent hypokalemia.
- Ventilator-dependent donors require frequent blood gas analysis to correct inadequate oxygenation and alterations in pulmonary function, with measures such as endotracheal suctioning and positive end-expiratory pressure used to manage neurogenic pulmonary edema.
The independent beating of the heart after brain death is made possible by the sinoatrial node and the intrinsic cardiac pacemaker system, which can function without brain signals. However, the duration of this independent function is limited without the regulatory support of the brain stem for blood pressure, hormone production, and other vital functions. In clinical settings, interventions such as mechanical ventilation and the use of vasopressors can temporarily sustain heart function, particularly in the context of organ donation, as guided by the principles outlined in the 24th Bethesda Conference 1.
From the Research
Physiological Changes After Brain Death
The heart can still beat after brain death due to several physiological changes that occur in the body. Some of the key changes include:
- Breakdown of effective central regulatory mechanisms of cardiocirculatory stability 2
- Decrease in vasopressin levels, which can be treated with exogenous administration of vasopressin to maintain cardiocirculatory stability 2, 3
- Neuro-humoral changes, myocardial injury, and altered loading conditions that can contribute to cardiac dysfunction 4
- Reduced myocardial contractility due to decreased pre- and afterload and coronary perfusion 4
Persistence of Cardiac Function
Studies have shown that cardiac function can persist for a significant amount of time after brain death. For example:
- A study in Kuwait found that the mean persistence of cardiac function after brain death was 8.20 days, with a median survival time of 6 days 5
- Another study found that some patients who were diagnosed as brain dead continued to exhibit certain brain functions, including neuroendocrine functions 6
Management of Cardiac Function
The management of cardiac function after brain death is crucial for successful organ transplantation. Some of the strategies used to manage cardiac function include: