A normal capillary refill time predicts adequate superior vena cava oxygen saturation

Article Outline

• Question
• Design
• Setting
• Participants
• Intervention
• Outcomes
• Main Results
• Conclusions
• Commentary
• Copyright

Raimer PL, Han YY, Weber MS, Annich GM, Custer JR. A Normal Capillary Refill Time of ≤ 2 Seconds is Associated with Superior Vena Cava Oxygen Saturations of ≥ 70%. J Pediatr 2011;158:968-72.

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Question 

Among critically ill children, how accurately does having a normal capillary refill time (CRT) ≤ 2 seconds predict a superior vena cava oxygen saturation (ScvO₂) ≥ 70%?

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Design 

Two-year, prospective study.

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Setting 

Tertiary-level pediatric intensive care unit, Ann Arbor, Michigan.

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Participants 

Twenty-one critically ill children, average age 45 months, 12 of whom had septic shock and 6 who had respiratory failure/pneumonia.

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Intervention 

Whenever ScvO₂ measurements were obtained, central (forehead/sternum) and peripheral (finger/toe) CRTs were concomitantly assessed.

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Outcomes 

Sensitivity and specificity of the CRT ≤ 2 seconds as a diagnostic test.

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Main Results 

Central and peripheral CRTs ≤ 2 seconds were both associated with ScvO₂ ≥ 70% (P < .01). Sensitivity/specificity analyses revealed that central CRT ≤ 2 seconds demonstrated a sensitivity of 84.4%, specificity of 71.4% (positive likelihood ratio 2.95; negative likelihood ratio 0.22) in predicting ScvO₂ ≥ 70%. Peripheral CRT ≤ 2 seconds had a sensitivity of 71.9%, specificity of 85.7% (positive likelihood ratio 5.03, negative likelihood ratio 0.33) in predicting ScvO₂ ≥ 70%.

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Conclusions 

A normal CRT ≤ 2 seconds can be predictive of ScvO₂ ≥ 70%. This corroborates the recommendations of the Pediatric Advanced Life Support curricula targeting a normal CRT ≤ 2 seconds as a therapeutic endpoint for goal-directed shock resuscitation. This clinical target remains particularly relevant in community hospitals when the ability to obtain central venous catheter access may be limited and ScvO₂ data unavailable.

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Commentary 

Goal-directed therapy (GDT) for septic shock in pediatric and neonatal patients targets a ScvO₂ of ≥ 70%. ScvO₂ closely approximates mixed venous saturation and is therefore an indicator of adequate tissue oxygen delivery, relative to tissue metabolism (ie, oxygen extraction). Given the technical challenges of obtaining a ScvO₂, CRT could permit application of GDT earlier and in a greater number of patients. Importantly, the population in this study included patients with septic shock, which might be expected to diminish CRT (due to vasodilation) even in settings of inadequate tissue oxygenation. If the goal is to minimize the misclassification of any patients who remain with a ScvO₂ < 70% (ie, do not prematurely discontinue resuscitation), one can analyze the statistical results of the study. The sensitivity and specificity (which are independent of the pre-test probability) of central CRT ≤ 2 seconds were 84.4% and 71.4%, respectively. However, what we seek clinically from this test is a high positive-predictive value (PPV) (ie, in any given patient with a CRT ≤ 2 seconds we want to know that the ScvO₂ is > 70). In the study group, the PPV was 93.1%, which would be considered quite good by most clinicians. It is important to remember that, unlike sensitivity and specificity, which are intrinsic to the test, PPV depends on the prevalence of the condition within the study population. In a group of very sick children, it is likely that there would be more patients with a ScvO₂ > 70, which would give a lower PPV. Clearly, the sickest patients would benefit from actual monitoring of the ScvO₂, as the authors readily admit. However, this study certainly lends support to the idea of using CRT as a predictive tool until ScvO₂ access can be obtained.