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Correspondence |

Method of Height Determination Used in Predicted Body Weight Equations FREE TO VIEW

Christopher D. Hingston, MB BCh; Matt P. Morgan, PhD; Ann Smith, PhD; Matt P. Wise, DPhil
Author and Funding Information

FINANCIAL/NONFINANCIAL DISCLOSURES: None declared.

CORRESPONDENCE TO: Christopher D. Hingston, MB BCh, Department of Adult Critical Care, University Hospital of Wales, Heath Park, Cardiff CF14 4XW, Wales


Copyright 2016, American College of Chest Physicians. All Rights Reserved.


Chest. 2016;149(2):605. doi:10.1016/j.chest.2015.09.041
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Linares-Perdomo and colleagues describe significant differences among three predicted body weight (PBW) equations in both men and women. The PBW is widely used to determine tidal volume during mechanical ventilation, to deliver a lung-protective ventilation strategy. Linares-Perdomo and colleagues concluded that variation in calculated PBW as determined by these formulas might be an important confounder when comparing studies. This may well be true because even minor changes in the tidal volume may have significant clinical consequences. A retrospective study by Gajic and colleagues suggested that overventilation by even a small amount might be harmful. Patients admitted without acute lung injury had an OR of 1.3 (P < .01) of developing lung injury for every 1 mL/kg above 6 mL/kg tidal volume delivered.

However, an additional confounding variable must be considered as it has the potential to introduce further significant error. PBW equations all use patient height, and it is our experience and that of others that accurate measurement of this parameter in critically ill patients often can be extremely difficult. Current practice is frequently to use head-to-heel length, measured while the patient is supine in the bed; however, this method has been shown to overestimate height significantly. Significant variation also exists among health-care professionals performing measurements. Numerous alternative methods of deriving height have been described and validated, particularly in the elderly population. Researchers use formulas that require measuring arm span, arm demi-span, knee height, or ulnar length,, which may be easier to perform. Not all of these methods have been validated in patients who are receiving critical care, and the optimal method of height measurement in this patient group remains to be determined.

We believe it is important for the methods of determining both patient height and ascertaining PBW to be transparent to allow comparison between studies and, more significantly, to allow the reliable clinical application of any relevant findings.

References

Linares-Perdomo O. .East T.D. .Brower R. .Morris A.H. . Standardizing predicted body weight equations for mechanical ventilation tidal volume settings. Chest. 2015;148:73-78 [PubMed]journal. [CrossRef] [PubMed]
 
Gajic O. .Dara S.I. .Mendez J.L. .et al Ventilator-associated lung injury in patients without acute lung injury at the onset of mechanical ventilation. Crit Care Med. 2004;32:1817-1824 [PubMed]journal. [CrossRef] [PubMed]
 
Gray D.S. .Crider J.B. .Kelley C. .Dickinson L.C. . Accuracy of recumbent height measurement. JPEN J Parenter Enteral Nutr. 1985;9:712-715 [PubMed]journal. [CrossRef] [PubMed]
 
Dennis D.M. .Hunt E.E. .Budgeon C.A. . Measuring height in recumbent critical care patients. Am J Crit Care. 2015;24:41-47 [PubMed]journal. [CrossRef] [PubMed]
 
Hickson M. .Frost G. . A comparison of three methods for estimating height in the acutely ill elderly population. J Hum Nutr Diet. 2003;16:13-20 [PubMed]journal. [CrossRef] [PubMed]
 

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References

Linares-Perdomo O. .East T.D. .Brower R. .Morris A.H. . Standardizing predicted body weight equations for mechanical ventilation tidal volume settings. Chest. 2015;148:73-78 [PubMed]journal. [CrossRef] [PubMed]
 
Gajic O. .Dara S.I. .Mendez J.L. .et al Ventilator-associated lung injury in patients without acute lung injury at the onset of mechanical ventilation. Crit Care Med. 2004;32:1817-1824 [PubMed]journal. [CrossRef] [PubMed]
 
Gray D.S. .Crider J.B. .Kelley C. .Dickinson L.C. . Accuracy of recumbent height measurement. JPEN J Parenter Enteral Nutr. 1985;9:712-715 [PubMed]journal. [CrossRef] [PubMed]
 
Dennis D.M. .Hunt E.E. .Budgeon C.A. . Measuring height in recumbent critical care patients. Am J Crit Care. 2015;24:41-47 [PubMed]journal. [CrossRef] [PubMed]
 
Hickson M. .Frost G. . A comparison of three methods for estimating height in the acutely ill elderly population. J Hum Nutr Diet. 2003;16:13-20 [PubMed]journal. [CrossRef] [PubMed]
 
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