Adolf Fick was a German physician who is known for several things including the description of the law of diffusion of gas across a fluid membrane (1855), the invention of the contact lens (1887) and the description of cardiac function, oxygen delivery and consumption known as the Fick Principle (1870). The Fick principle describes oxygen delivery and oxygen extraction. But this only relates to the macrovascular function of perfusion. In reality the factors that determine tissue oxygenation and carbon dioxide removal at the microvascular level are just as relevant in determining the life or death of the patient.
Oxygen Pressure Field Theory (OPFT) describes the details of vital gas exchange at the capillary level. So for perfusionists, OPFT may explain why some patients with seemingly normalized cardiac output, hemodynamic pressure, arterial oxygen saturations and venous oxygen saturations may end up in organ failure or expire of an unexpected complication while other patients who seem to struggle with achieving normal cardiovascular parameters can recover miraculously.
The Fick principle is the foundation of goal directed therapy for the critical care of cardiopulmonary patients. The therapeutic goal for a patient with poor heart or lung function is to normalize hemodynamics and oxygen delivery. This is accomplished by the administration of oxygen and fluids using tools like a ventilator, inotropic drugs and even a heart/lung pump in the most severe cases. At times, successful goal directed therapy fails to reverse the increasing morbidity. Even the use of a heart/lung pump to maintain normal hemodynamics and oxygen delivery can fail to reverse multisystem organ failure or prevent other lethal complications such as stroke and hemorrhage. In these instances an understanding of OPFT can sometimes help to explain this treatment failure phenomenon and provide guidance to a more effective critical care strategy.
The theoretical concepts discussed in this seminar will be the oxygen pressure field, the Krogh cylinder, perfused capillary density, radial and axial gas transfer vectors, anoxic and hypercapnic lethal corners, the carbon dioxide pressure field and the fundamental basis of shock and organ failure. Associated clinical applications discussed will include new ways to assess perfusion, alternative interpretations of blood gases and electrolytes, the corrected anion gap, the venoarterial CO2 gradient, the Viability Index, base deficits on CPB, edema, ultrafiltration, hypothermic circulatory arrest, gaseous emboli, nitrogen off gassing, the use of normoxia/hyperoxia, oxygen toxicity, reperfusion injury, breaking the reperfusion barrier, reviving expired patients using the ECPR pump and case reports.
|Table top scenario: accidental gross blood splash to the face.|
Perfusion Theory is an educational platform for the Oxygen Pressure Field Theory (OPFT). August Krogh’s theoretical concept of the oxygen pressure field is explained and then applied to clinical applications in perfusion practice.