Measurement of capillary refill time is thought of a quick and reproducible method for assessing circulatory status. A refill time less than 2 cm has been considered as normal. Refill has also been shown to be a value in measuring the degree of dehydration and rehydration in children. However, no study has attempted to correlate capillary refill time with limb perfusion. This study attempted to compare and contrast refill time with arterial flow in healthy children.
The cohort was small, consisting of 10 pediatric patients between the age of 8 and 18 years. A Doppler ultrasound was performed to assess arterial flow of the radial and ulnar arteries. A variety of measurements were then calculated. Arterial perfusion was decreased with the use of a blood pressure cuff that was elevated to various pressures. The Peak systolic velocity and vessel diameter of radial and ulnar arteries were measured during cuff inflation. An attempt was made to correlate capillary refill time with these measures.
The results indicate that at various pressures, different total flow volumes and capillary refill times were measured. However, when plotting capillary refill time vs. total flow volume from the Doppler ultrasound measurements a lack of correlation was found. Initially a slightly delayed capillary refill time was associated with higher blood pressure cuff measurements. However, with even higher pressure values arterial flow and capillary refill time did not appear correlated.
The lack of correlation between the measurements on ultrasound and capillary refill time lends questions as to its usefulness clinically to assess perfusion. A large confounding factor is that when the blood pressure cuff was raised to 75mm Hg, there was an increase in arterial flow rather than a decrease. This may be secondary to a reactive hyperemia induced by the increasing cuff pressure. This makes the results of this study very confusing and difficult to interpret. The take home point is that capillary refill time can not be taken in isolation to demonstrate adequate perfusion. Capillary refill time should be a part of the examination to assess perfusion, but should not be used in isolation.