The challenge of exploring organ function: knowledge is not care, but care needs knowledge!

Abstract

The medical strategies of various diseases are not a straightforward process but are rather the result of complex development. These strategies are generally described as a backand-forth approach between the basic knowledge of disease pathophysiology and observations of symptoms. Results of clinical investigations or monitoring tools are often surrogates of collection of symptom, and therefore, this approach is renewed when an innovative tool becomes available. The respective role of each component, i.e., the basic knowledge, the new technique, and the clinical approach, varies according to the pathology or organ involved in the considered illness, but the rationale stays the same. However, this simplified pattern of medical approach does not fully describe the actual way of medical thinking. Indeed, this later is made more complex as the path of thinking from basic knowledge to symptom is not the same that the one required to discover the cause of a symptom. In other words, the pathways of the mind from basic knowledge to symptom and its reverse are not the same. In the present issue, the review article from Dr Sakka is an interesting opportunity to illustrate this huge difficulty [1].The present author presents the current position of the use of indocyanine green (ICG) in assessing liver perfusion and function. This molecule has a twofold property that makes it of interest in the liver exploration. First, the transcutaneous spectrophotometric determination of ICG allows the ICG kinetics to be measured in a non-invasive manner, and it can be performed easily at the bedside. Second, due to the particular pharmacodynamics of ICG, which is exclusively taken up by the liver and lacks entero-hepatic recirculation, its elimination rate is exclusively dependent on the liver. As all molecule cleared by the liver, its elimination depends on the liver blood flow and extraction rate, this later being very high in physiological conditions, the elimination is mainly dependent on the liver blood flow.As the factors leading to change in ICG kinetics are clearly known, it becomes reasonably easy to anticipate the effect of a variation in any of them. For example, a decrease in liver blood flow is expected to decrease ICG elimination and vice versa. If the blood flow remains stable, a change in extraction rate, which is assumed to be equivalent to liver function, leads to a change in the same direction in ICG kinetics. This deduction is a forward way of thinking, leading from physiological knowledge to the clinical effect. Conversely, the clinician faces the opposite position where he knows the result of ICG kinetics and must infer the factor or factors involved in the observed change. ICG kinetics is a warning signal arising from a systematic assessment of liver function or the result of a targeted investigation to quantify a liver injury. Regardless of the demand, the clinician faces a backward process of reasoning, which is far more challenging than the forward process is.Taking once more the example of ICG kinetics given by...