Criteria abstracted from The Users' Guide to Medical Literature, from the Health Information Research Unit and Clinical Epidemiology and Biostatistics, McMaster University

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Article Reviewed:

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Capillary refill and core-peripheral temperature gap as indicators of haemodynamic status in paediatric intensive care patients

Tibby SM, Hatherill M, Murdoch IA.

Arch Dis Child 1999; 80: 163-166. [full-text for subscribers] [abstract]

Reviewed by Steven Cray, MBBS FRCA, Birmingham Children's Hospital, UK

Review posted January 14, 2000

I. What is being studied?

Study objective:

To assess the relationships between capillary refill time > 2 seconds and hypovolemia (measured by central venous pressure) and various indices of adequacy of systemic blood flow (cardiac output, stroke volume, systemic vascular resistance and blood lactate) in children receiving intensive care. A similar relationship was sought between core-peripheral temperature gap and the previously mentioned variables.

Study design:

Measurements of capillary refill time and core-peripheral temperature gap were performed concurrently with measurements of hemodynamic variables and blood lactate.

The patients investigated:

A total of 90 measurements were made in 55 mechanically ventilated children (aged 3 months to 7 years) in one intensive care unit. They were subdivided into those who had undergone cardiac surgery (n=27) and a "general" group (n=28), predominantly with septic shock (24 patients). Patients were excluded if they had conditions affecting the accuracy of measurement of cardiac output by thermodilution (anatomical shunts on echocardiography, arrhythmias or valvular regurgitation).

II. Are the results of the study valid?

Primary questions:

1. Was there an independent, blind comparison with a reference standard?

It is not clear if the comparison was independent or blinded. A single investigator performed the capillary refill time measurements in a standardized fashion. It is not stated whether the hemodynamic measurements were performed independently. It is not stated whether any method of blinding was used.

The reference standard was a technique used by the authors to measure cardiac output called femoral artery thermodilution, . The same group has compared cardiac output measurements by femoral artery thermodilution with the direct Fick method in children and shown that similar values were obtained. [1] Blood lactate was also used as an indicator of adequacy of the circulation although it's validity was not clearly stated.

2. Did the patient sample include an appropriate spectrum of patients to whom the diagnostic test will be applied in clinical practice?

The study group was typical of a large group of children who require intensive care and require frequent assessment of adequacy of the circulation. The study did not include some other important groups of PICU patients in whom capillary refill time might be useful, such as those with traumatic injuries or admitted after non-cardiac surgery

Secondary questions:

3. Did the results of the test being evaluated influence the decision to perform the reference standard?

No. Hemodynamic and blood lactate measurements were always measured.

4. Were the methods for performing the test described in sufficient detail to permit replication?

Yes.

III. What are the results?

1. Are likelihood ratios for the test results presented or data necessary for their calculation provided?

The authors present most of their findings as correlation coefficients. They found that capillary refill time and core-peripheral temperature gap were related (r = 0.58). However, in the post-cardiac surgery patients there was no relationship between capillary refill time or core-peripheral temperature gap and any of the measured hemodynamic variables or blood lactate. In the "general" group of patients prolonged capillary refill time (> 2 seconds) was associated with a reduction in stroke volume index (SVI) (r = -0.46) and blood lactate (r = 0.47). There was no correlation between core-peripheral temperature gap and the measured hemodynamic variables that met statistical significance.

A positive and strong correlation between capillary refill time and core-peripheral temperature gap should be expected as these are related values. It would be surprising to find no correlation. However, correlation is not a good measurement for prediction. Regression analysis is needed if one is trying to predict something in the future, and likelihood ratios or sensitivity or specificity are indicated if looking at diagnosing a current condition.

Liklihood ratios (LR) are not presented but may be calculated as sensitivity/(1-specificity). For example, the authors determined that, in the "general" group of patients, a capillary refill time 6 seconds predicted an abnormally low SVI (<30 ml/m2) with a sensitivity of 57% and specificity of 94%. Therefore, the LR of a positive test is 57/6 or 9.5. This means that in those patients with a positive test, i.e., delayed capillary refill 6 seconds, they are 9.5 times more likely to have an abnormally low SVI. In the "general" group of patients with capillary refill time 3 seconds the likelihood ratio for SVI <30 ml/m2 is 86/53 or 1.6. The test is thus unlikely to be useful for diagnosing abnormally low SVI at this level or by inference at the original cut-off point of > 2 seconds.

IV. Will the results help me in caring for my patients?

1. Will the reproducibility of the test result and its interpretation be satisfactory in my setting?

Unclear. The reliability of testing capillary refill across observers was not examined.

2. Are the results applicable to my patient?

Yes. The patients studied are representative of many children requiring intensive care. However it does not include some important groups of patients (e.g., trauma). It is likely that the widespread use of vasodilators post-cardiac surgery had a considerable influence on capillary refill time in these patients.

3. Will the results change my management?

This study casts considerable doubt on the validity of two commonly used tests for assessing the adequacy of the circulation in children requiring intensive care following cardiac surgery. The present study is in agreement with previous findings that core-peripheral temperature gap was not related to cardiac output or other hemodynamic parameters in children after cardiac surgery. [2,3]

It is less clear whether we should abandon the use of capillary refill time in patients with sepsis or in those groups of patients not included in the study. Delayed capillary refill time at the extremes (> 6 seconds) may be a strong indicator of low SVI. This may not be as useful, however, as the benefit of using this noninvasive indicator would be if it predicted problems earlier. By the time capillary refill is extremely delayed, it may be too late. The ability of a capillary refill time 3 seconds to predict abnormal hemodynamic values is poor.

4. Will patients be better off as a result of the test?

Perhaps this should be expressed in terms of some patients being better off if the test (capillary refill time or core-peripheral temperature gap) is ignored! This may prevent unnecessary intervention (e.g. administration of a fluid bolus) in children post-cardiac surgery in the absence of other evidence of circulatory insufficiency.

References

1. Tibby SM, Hatherill M, Marsh MJ, Morrison G, Anderson D, Murdoch IA. Clinical validation of cardiac output measurements using femoral artery thermodilution with direct Fick in ventilated children and infants. Intensive Care Med 1997 Sep;23(9):987-91. [abstract]
2. Ryan CA, Soder CM. Relationship between core/peripheral temperature gradient and central hemodynamics in children after open heart surgery. Crit Care Med 1989 Jul;17(7):638-40. [abstract]
3. Butt W, Shann F. Core-peripheral temperature gradient does not predict cardiac output or systemic vascular resistance in children. Anaesth Intensive Care 1991 Feb;19(1):84-7. [abstract]

 

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