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Three Part Question

[In children attending hospital with an emergency] is [a simple formula better than reference tables] at [identifying hypotension]?

Clinical Scenario

You are attending a paediatric patient in the Emergency Department. You note from the triage observations that the patient, a normally healthy 6-year-old, has a blood pressure of 80/40mmHg. You wonder if this is a little low, but cannot recall what the normal blood pressure for a child should be. You ask your registrar, who insists that you should use reference tables, while an eavesdropping consultant suggests using the formula from the APLS course - though he can't remember what it is. You wonder how best to ascertain the normal value.

Search Strategy

OVID interface on the worldwide web. 1996 - July 2010.
[child.kw OR paed.kw OR ped$ OR paediatric.kw OR pediatric.kw] AND [formula.af OR reference tables.af OR reference.af OR calculation.af OR estimation.af] AND [blood pressure.kw OR systolic.kw OR mean arterial pressure.kw OR MAP.kw or BP.kw or SBP.kw)

Search Outcome

33 papers, of which one was relevant to the search question.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Haque, Ikram U. & Zaritsky, Arno L. March 2007 USA	Normal healthy children; data obtained from 1999-2000 National Health and Nutrition Examination Survey of >32,000 boys and >31,000 girls aged 1-17 years of age.	Mathematical analysis of clinical database. Derivation of percentile values, stratified by height percentiles. Linear regression analysis to create simple formulae for 5th percentile SBP and 5th and 50th perentile MAP for different age groups at the 50th height percentile.	5th percentile SBP as representative of hypotension at 50th height percentile. 5th percentile & 50th percentile MAP at 50th height percentile for definition of hypotension and target for resuscitation .	5th percentile SBP: (2 x age in years) + 65mmHg. 5th percentile MAP: (1.5 x age in years) + 40mmHg. 50th percentile MAP: (1.5 x age in years) + 55mmHg.	Definition of hypotension as SBP below 5th percentile is not evidence-based. Considers normal values in healthy children as target end-point in resuscitation; in critically ill/injured children desired target is likely to be higher. Considerable difference within age groups by height percentile.

Comment(s)

Blood pressure alone cannot be used to assess the need for resuscitation. Formulae should be used as a guide to identify hypotension and it should be remembered that formulae are determined from reference tables of healthy children. Children with co-morbidities may have significantly different normal values. Children above 75th percentile or below 25th percentile in height may have a variation in SBP of 2mmHg for boys and 1.5mmHg for girls above or below values for children at the 50th height percentile.

Clinical Bottom Line

Hypotension as defined by systolic blood pressure in a child of average height can be estimated with the formula (2 x age in years) + 65mmHg and systolic blood pressure below this value should be considered carefully, however signs of end organ perfusion and thorough clinical assessment should be used in conjunction with measurement of blood pressure to determine those children in need of resuscitation.

References

1. Haque, Ikram U.; Zaritsky, Arno L. Analysis of the evidence for the lower limit of systolic and mean arterial pressure in children. Pediatric Critical Care Medicine March 2007; 8(2):138-144.