Send letter to journal:
Re: Discrediting capillary refill - do we have evidence?

Tibby et al[1] have questioned the role of capillary refill time measurement in the evaluation of shock because it doesn't "correlate with more objective measure of haemodyanamic status" - namely the Cardiac Index (CI), Systemic Vascular Resistance Index (SVRI), and Stroke Volume Index (SVI). They err in their premise that CI, SVRI and SVI are individually good measures of shock.

Shock by definition is a clinical state of inadequate perfusion in which the demands of the body are incompletely met.[2] It may be broadly divided into two categories.

1. Hypovolemic shock resulting from intravascular hypovolemia due, either to vasodilation (increased capacitance) or loss of fluid. Here the cardiac output is often elevated. The systemic vascular resistance and central venous pressure are decreased.
2. Cardiogenic shock resulting from cardiac dysfunction. Here intravascular volume is normal or increased. The cardiac output and cardiac index are reduced in such cases.

Thus we see cardiac index is reduced or elevated depending on the type of shock, so by itself, it cannot be reckoned as an indicator of shock. It is not surprising that it does not correlate consistently with capillary refilling time. The same may be said of the other indicators (SVRI and SVI) used by authors.

How well a distal capillary bed is perfused, depends upon how well the cardiac pump is thrusting, blood volume and vascular capacitance, at what rate blood is travelling against the vis-a -fronte parameters like side-on and end on blood pressures, viscosity, the status of precapillary sphincters decided by local vasodilatory and vasoconstrictor influences (eg, temperature), amount of damming due to vis-a-turgo forces, eg, mean systemic filling pressure, among other factors.[3] Basic laws of proportionality stand to testify the fact that if capillary refill time (t) is proportional to an expression representing sum of the aforesaid factors (x+y+z+……), it does not follow that 't' has to be proportional to x or y or z or any other factor taken individually.

The absence of a correlation between capillary refill time and SVR or SVRI or CI individually, does not mean that the former does not vary directly with a parameter that represents their sum, which could represent presence of shock. It is therefore not surprising that the did not find a significant relation between capillary refill time and SVI, SVRI, or CI.

The issue has not been taken up in the correspondence columns of you esteemed journal. In an environment where more people are looking to practice evidence based medicine, it would be sad if a valuable clinical sign falls into disrepute on the basis of this paper.

References
(1) Tibby SM, Hatherill M, Murdoch I A Capilary refill and core-peripheral-temperature-gap as indicators of hemodynamic status in pediatric intensive care patients. Arch Dis Child 1999;80:163-6.

(2) O'Rorrke PP. Shock. In: Nelson Textbook of Pediatrics. Eds. Nelson WE, Behrman RE, Kleigman RM, Arwin AM. Philadelphia, WB Saunders Company, 1996:263-4.