Capillary refill time (CRT) is defined as the time taken for colour to return to an external capillary bed after pressure is applied to cause blanching. It was first described in 1947 and has since become widely adopted as part of the rapid structured circulatory assessment of ill children. Capillary refill time (CRT) is a simple bedside measurement that is undertaken as part of the ABCDE approach to assess cardiac output and peripheral circulation especially in neonates. Capillary refill time (CRT) is a simple and quick test requiring minimal equipment or time to perform. There are only few studies describing normal values and the correct method of recording CRT.
The value of CRT is affected by various factors like ambient or skin temperature, age, site of measurement, duration as well as amount of pressure and inter observer variation. However, none of these have been standardized. Hence, we conducted this study to establish the normal value and factors affecting Capillary Refilling Time (CRT) in healthy neonates in Varanasi.
Recommended measurement method for CRT in children
- Use the finger as the preferred measurement site.
- Press for 5 seconds using moderate pressure.
- Ideally, measure at room temperature (20–25°C) irrespective of the child’s body temperature. Allow time for skin temperature to acclimatise if the child has recently been moved from a warmer or colder environment.
- Use a timer (for example, a watch) to count the seconds it takes for the finger to regain its original colour.
- An abnormal CRT in infants and children over 7 days of age is 3 seconds or more; a normal CRT is 2 seconds or less. A CRT measurement of between 2 and 3 seconds may be considered ‘borderline abnormal’, but some healthy children may have CRT as long as 2.5 seconds.
- Record measurements using the actual number of seconds (for example, ‘4 seconds’ or ‘2 seconds or less’) rather than using terms such as ‘prolonged’ or mathematical symbols.
Note: This procedure should be undertaken only after approved training, supervised practice and competency assessment, and carried out in accordance with local policies and protocols.
External factors which may affect the accuracy of capillary refill time (CRT) in children and neonates
- Temperature: Gorelick et al measured the CRT of 32 healthy children who had been assigned to either a warm (mean temperature 25.7°C) or cool environment (mean temperature 19.4°C) for 15 min. Children who had been in the cool environment had a significantly prolonged CRT compared with those in the warm environment. Only 31% in the cool environment had a CRT <2 s, whereas, those in the warm environment all had a CRT of <2 s. It is debatable whether fever has an effect on CRT. CRT has been shown to decrease in adults as core temperature increases.22 However, the only study in children showed that patient temperature had no effect on CRT.
- Ambient light: A study in 309 adult participants compared the measurement of CRT in daylight conditions to the measurement of CRT in dark conditions. In dark conditions, CRT was unable to be accurately assessed in 66.7% of the subjects compared with 3.9% in daylight conditions.
- Site of measurement: CRT has been shown to be longer if it is measured at the heel than the head or sternum in neonates. Paradoxically, the only study which has examined the effect of site on CRT in older children concluded that fingertip CRT was significantly faster than CRT measured at the sternum.
- Pressure application: There is no clear consensus on exactly how long pressure should be applied to measure CRT, with most guidelines stating between 3 and 5 s. However, in neonates, it has been shown that applying pressure for a prolonged time (3–4 s) compared with a brief time (1–2 s), can significantly increase CRT.
- Interobserver reliability: Initial rapid partial refilling of the capillaries may be followed by a slower complete filling, and defining when this has finished is subjective. In general, the literature suggests that there is not good agreement when different observers measure CRT. In a study of 46 nurses and nursing assistants who were shown a video of adults having CRT measured, there was only moderate agreement for the exact value of CRT and what constituted normal. Otieno et al also showed that there was not good agreement between four different observers when measuring CRT in 100 children admitted consecutively to a hospital in Kenya. However, agreement between observers did improve when the CRT was short (<1 s) or long (>4 s).