Blood Flow: Life’s Quintessential Vital Sign?
The four universally recognized vital signs (body temperature, blood pressure, pulse, and respiratory rate) are regularly used to measure the body’s basic functions to help assess the general physical health of a person, give clues to possible diseases, and show progress toward recovery.
Yet, it is blood flow that delivers oxygen and nutrients to cells for metabolism and removes metabolic wastes. Blood flow is life giving. When blood flow ceases, life ends. Might blood flow also be considered a vital sign or life’s quintessential vital sign?
Whether CABG is performed minimally-invasively, off-pump, on-pump, or robotically-assisted, the end point is the same: to deliver sufficient blood to the myocardial territories so that the heart can pump effectively. To know how much blood flow is reaching the myocardium, one must also know how much flow is moving through a newly created anastomosis. The quality of a bypass graft is defined by its flow.
Measurements take only seconds to perform, but they are a key component in a surgeon’s decision-making armamentarium that includes standard clinical observations and measurements such as quality of the heart’s contractions, MAP, EKG, CO, and BP. Could a quantitative measurement of direct graft flow be the single parameter that helps the surgeon identify a problem’s source more effectively and efficiently than any other parameter?
Unfortunately, direct intraoperative blood flow measurements were not possible until the mid-twentieth century when precise flow measurement devices and technologies were first developed. In their stead, surrogate modalities took and continue to take precedence. Pressure, used by the body to control flow, became the standard parameter to assess hemodynamics. Pulses are felt. Doppler technology displays velocity of blood flow, not true flow. All are surrogates for knowing absolute volume flow, most precisely measured by transit-time ultrasound technology. It might well be the time to recognize that blood flow is life’s quintessential vital sign.