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Original Research: Critical Care Medicine |

Standardizing Predicted Body Weight Equations for Mechanical Ventilation Tidal Volume SettingsStandard Equations for Predicted Body Weight FREE TO VIEW

Olinto Linares-Perdomo, PhD; Thomas D. East, PhD; Roy Brower, MD; Alan H. Morris, MD
Author and Funding Information

From the Pulmonary and Critical Care Division (Drs Linares-Perdomo and Morris), Department of Medicine, Intermountain Medical Center, Salt Lake City, UT; LCF Research (Dr East), New Mexico Health Information Collaborative, Albuquerque, NM; Pulmonary and Critical Care Medicine (Dr Brower), Johns Hopkins University School of Medicine, Baltimore, MD; and the University of Utah School of Medicine (Dr Morris), Salt Lake City, UT.

CORRESPONDENCE TO: Olinto Linares-Perdomo, PhD, Pulmonary/Critical Care Division, Sorenson Heart & Lung Center—6th Floor, Intermountain Medical Center, 5121 S Cottonwood St, Murray, UT 84157-7000; e-mail: Olinto.linares@imail.org


FOR EDITORIAL COMMENT SEE PAGE 3

FUNDING/SUPPORT: This work was supported by Agency for Healthcare Research & Quality [Grant HS06594], Siemens Inc, Emtek Inc, ACT/PC Inc, the Respiratory Distress Syndrome Foundation, the Deseret Foundation (LDS Hospital), and Intermountain Healthcare.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2015;148(1):73-78. doi:10.1378/chest.14-2843
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BACKGROUND:  Recent recommendations for lung protective mechanical ventilation include a tidal volume target of 6 mL/kg predicted body weight (PBW). Different PBW equations might introduce important differences in tidal volumes delivered to research subjects and patients.

METHODS:  PBW equations use height, age, and sex as input variables. We compared National Institutes of Health (NIH) ARDS Network (ARDSNet), actuarial table (ACTUARIAL), and Stewart (STEWART) PBW equations used in clinical trials, across physiologic ranges for age and height. We used three-dimensional and two-dimensional surface analysis to compare these PBW equations. We then used age and height from actual clinical trial subjects to quantify PBW equation differences.

RESULTS:  Significant potential differences existed between these PBW predictions. The ACTUARIAL and ARDSNet surfaces for women were the only surfaces that intersected and produced both positive and negative differences. Mathematical differences between PBW equations at limits of height and age exceeded 30% in women and 24% in men for ACTUARIAL vs ARDSNet and about 25% for women and 15% for men for STEWART vs ARDSNet. The largest mathematical differences were present in older, shorter subjects, especially women. Actual differences for clinical trial subjects were as high as 15% for men and 24% for women.

CONCLUSIONS:  Significant differences between PBW equations for both men and women could be important sources of interstudy variation. Studies should adopt a standard PBW equation. We recommend using the NIH National Heart, Lung, and Blood Institute ARDS Network PBW equation because it is associated with the clinical trial that identified 6 mL/kg PBW as an appropriate target.

Figures in this Article

Mechanical ventilation (MV) strategies for acute lung injury (ALI) and patients with ARDS can have different risks and benefits.13 Evidence from experimental models has demonstrated ventilator-induced lung injury from excessive volumes and pressures during inspiration and from low volumes and pressures during expiration.2 Many MV modes require a tidal volume setting (Vtset). Predicted body weight (PBW), rather than actual body weight, reflects lung size and is commonly used to estimate required tidal volume (Vt), because actual body weight could produce excessive Vt in obese patients or inadequate Vt in underweight patients. Although MV strategies comparing different Vt in patients with ALI/ARDS yielded inconsistent results, the best current evidence and practice emphasize lung protective MV with a Vt target of 6 mL/kg PBW in patients with ALI/ARDS.37 While we have no evidence that variation in PBW has an important influence on patient outcome, it seems reasonable to standardize PBW estimation to remove its potential impact on outcome.

Several clinical trials used different equations for estimating the PBW required for calculating Vt. While some investigators used different terms (eg, ideal body weight), we will refer to all predictions as PBW predictions. Stewart et al6 calculated PBW = 25 × (height in meters)2. Brochard et al8 calculated PBW = actual body weight − estimated weight gain due to water and salt retention. Brower et al9 calculated PBW = 50.0 + 0.905 × (height in cm − 152.4) for men and 45.5 + 0.905 × (height in cm − 152.4) for women.10 The PBW equations used by Brower et al9 used equations from Devine,11 supported by subsequent publications.12,13 Morris et al14 calculated PBW (from actuarial tables) as 24.881 × (height in meters)2 + 0.0957 × (age in years) − 3.508 for men and as 19.347 × (height in meters)2 + 0.1885 × (age in years) − 2.2575 for women.14,15 East et al16 used the same PBW equations as Morris et al.14 The National Institutes of Health/National Heart, Lung, and Blood Institute (NIH/NHLBI) ARDS Network (ARDSNet)4 used the same PBW equations as Brower et al.9 The PBW equations used in these trials, and Vt in the experimental groups, are summarized in Table 1. There is currently no standard for calculating PBW.

Table Graphic Jump Location
TABLE 1 ]  PBW Equations and Results in Different Clinical Trials

ARDSNet = ARDS Network; NIH/NHLBI = National Institutes of Health National Heart, Lung, and Blood Institute; PBW = predicted body weight; Vt = tidal volume.

a 

Control group only (extracorporeal group subjects ignored).

b 

Only for the 179 patients supported with the assist/control mechanical ventilation mode.

We examined the magnitude of the deviations in PBW from the NIH/NHLBI ARDSNet10 equation with two different PBW equations: from actuarial tables (ACTUARIAL)15 and Stewart et al6 (STEWART). We used actual clinical trial subject data16 to assess the magnitude of differences of PBW equations on Vtset in a clinical trial cohort.

PBW Mathematical Equations
We compared three PBW equations, ACTUARIAL, STEWART, and ARDSNet (Table 1), to evaluate the mathematical differences between them within all possible combinations of height and age for both sexes (Fig 1). We varied height from 152.4 to 210 cm because this range includes most adult patients with ARDS. We included ages from 18 to 98 years. We produced three-dimensional surfaces of PBW as a function of age and height using Matlab, version R12 (The MathWorks Inc). To quantify the difference between the surfaces produced by two PBW equations, we expressed the differences (Fig 2) as a percent of the average PBW (since neither of the surfaces can be considered a more valid representation)17 according to the following equations:
%PBWdifference=(ACTUARIALARDSNet0.5(ACTUARIAL+ARDSNet))×100% eq 1
%PBWdifference=(STEWARTARDSNet0.5(STEWART+ARDSNet))×100% eq 2
Figure Jump LinkFigure 1 –  A-D, ACTUARIAL,14,15 STEWART,6 and ARDSNet4,10 PBW equation surfaces for women and men. A, B, Mathematically derived surface of PBW as a function of age (18-98 y) and height (152.4-210 cm) for ACTUARIAL and ARDSNet. C, D, Mathematically derived surface of PBW as a function of age (18-98 y) and height (152.4-210 cm) for STEWART and ARDSNet. ARDSNet = ARDS Network; PBW = predicted body weight.Grahic Jump Location
Figure Jump LinkFigure 2 –  A-D, %PBW difference for women and men. A, B, ACTUARIAL − ARDSNet. C, D, STEWART − ARDSNet. STEWART PBW predictions are age independent. See Figure 1 legend for expansion of other abbreviations.Grahic Jump Location
PBW Differences in Clinical Trial Subjects

We collected data from 179 subjects ventilated with an assist/control mode in a multicenter, randomized clinical trial (115 men and 64 women) (Table 2).16 We generated two-dimensional plots of %PBW difference as a function of age and height for women and men (Fig 3).

Table Graphic Jump Location
TABLE 2 ]  Demographic Data of Clinical Trial Subjects ≥ 152.4 cm (5 ft) Tall, Supported With Assist/Controlled Mechanical Ventilation

Data presented as mean (± SD, range) unless otherwise indicated. See Table 1 legend for expansion of abbreviation.

Figure Jump LinkFigure 3 –  A-D, The %PBW differences from ARDSNet predictions (for the ACTUARIAL1 and STEWART2 predictions) for clinical trial subject data as a function of age and height for women and men.16 See Materials and Methods section for equations. See Figure 1 legend for expansion of other abbreviations.Grahic Jump Location
Mathematical Results
ACTUARIAL vs ARDSNet:

In women, these prediction equation surfaces intersect (Fig 1A) but not in men (Fig 1B). Differences for women (Fig 2A) were maximum between young and tall women and old and short women. %PBW difference varied from about −11.8% to about 30% for women (Figs 1A, 2A). In men, the ARDSNet PBW equations are consistently lower than ACTUARIAL PBW equations for all combinations of age and height (Fig 1B). The maximum %PBW difference occurs in older and shorter men (Fig 2B). %PBW difference varied from about 5% to about 24% (Figs 1B, 2B).

STEWART vs ARDSNet:

In women and men, the ARDSNet predictions were consistently lower than STEWART predictions for all heights (Figs 1C, 1D). The surface-plot differences reveal maximum PBW prediction equation differences in young and short women. The %PBW difference varied from about 12% to about 25% in women and about 7.5 to about 15% in men (Figs 1C, 1D, 2C, 2D).

Clinical Trial Subject Results

The clinical trial subjects16 had maximum (ACTUARIAL − ARDSNet) %PBW differences (Figs 3AD) between about −10% and about 24% for women and about 5% and about 16% for men. For example, an 80-year-old woman, 152.4 cm tall, had a PBW difference of about 24%, and a 20-year-old, 183 cm tall, woman had a %PBW difference of about −10% (Figs 3A, 3B). For (STEWART − ARDSNet), the maximum %PBW differences were between about 25% and about 15% for women, and between about 13% and about 7% PBW for men (Figs 3AD).

The PBW differences from ARDSNet predictions for the ACTUARIAL and STEWART predictions (Figs 13) could be clinically significant, although our study does not provide proof of this. However, we see no reason to continue to introduce variation in PBW calculations. Our results indicate that PBW calculation differences could be as high as about 30%. We do not know that these differences produce important changes in patient outcome, but we think continuing to allow this PBW variation is unwise.

These PBW differences will create unwarranted variation in the mechanical ventilator Vtset in different studies and in clinical practice. The PBW differences may contribute significantly to the inconsistent results from different MV clinical trials in patients with ALI/ARDS. Standardization of PBW for both clinical research and clinical practice seems the only reasonable response to the results we present. The ARDSNet PBW equations seem a reasonable choice, since the NIH/NHLBI ARDSNet study provided the results that have become a common clinical target for Vtset.4 The ARDSNet PBW equations are not new. They were first introduced by Devine11 and limited to patients 152.4 cm (5 ft) or taller, although they appear to be applicable to shorter adults.18

While it is not possible to identify a “true” or “correct” PBW, it is possible to choose a reasonable PBW equation that will eliminate this source of unwarranted variation in clinical research and practice. This will stabilize the choice of Vtset and likely improve results in both clinical research and practice, just as stabilization of process has improved products in industry.19

Significant differences between PBW equations for men and women could be important sources of interstudy variation. Studies should adopt a standard PBW equation. We recommend using the NIH/NHLBI ARDSNet PBW equation because it is associated with the clinical trial that identified 6 mL/kg PBW as an appropriate Vtset target.

Author contributions: O. L.-P., T. D. E., R. B., and A. H. M. had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. O. L.-P., T. D. E., and A. H. M contributed to the study concept and design; T. D. E. and A. H. M. contributed to data acquisition; O. L.-P., R. B., and A. H. M. contributed to data analysis and interpretation; O. L.-P. and A. H. M. contributed to writing the manuscript; O. L.-P., T. D. E., R. B., and A. H. M. contributed to revision of the manuscript and approved the final version

Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Role of sponsors: The sponsors had no role in the design of the study, the collection and analysis of the data, or in the preparation of the manuscript.

Other contributions: See Reference 16 for collaborating institutions and personnel in the clinical trial from which we extracted data.

ALI

acute lung injury

ARDSNet

ARDS Network

MV

mechanical ventilation

NIH/NHLBI

National Institutes of Health/National Heart, Lung, and Blood Institute

PBW

predicted body weight

Vt

tidal volume

Vtset

tidal volume set

Slutsky A. Mechanical ventilation. American College of Chest Physicians’ Consensus Conference. Chest. 1993;104(6):1833-1859. [CrossRef] [PubMed]
 
Dreyfuss D, Saumon G, Hubamyr R.. In:Lenfant C., ed. Ventilator-Induced Lung Injury. New York, NY: Taylor & Francis Group; 2006.
 
Slutsky AS, Ranieri VM. Ventilator-induced lung injury. N Engl J Med. 2013;369(22):2126-2136. [CrossRef] [PubMed]
 
The Acute Respiratory Distress Syndrome Network. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. N Engl J Med. 2000;342(18):1301-1308. [CrossRef] [PubMed]
 
Amato MB, Barbas CS, Medeiros DM, et al. Effect of a protective-ventilation strategy on mortality in the acute respiratory distress syndrome. N Engl J Med. 1998;338(6):347-354. [CrossRef] [PubMed]
 
Stewart TE, Meade MO, Cook DJ, et al; Pressure- and Volume-Limited Ventilation Strategy Group. Evaluation of a ventilation strategy to prevent barotrauma in patients at high risk for acute respiratory distress syndrome. N Engl J Med. 1998;338(6):355-361. [CrossRef] [PubMed]
 
Gajic O, Dara SI, Mendez JL, et al. Ventilator-associated lung injury in patients without acute lung injury at the onset of mechanical ventilation. Crit Care Med. 2004;32(9):1817-1824. [CrossRef] [PubMed]
 
Brochard L, Roudot-Thoraval F, Roupie E, et al. Tidal volume reduction for prevention of ventilator-induced lung injury in acute respiratory distress syndrome. The Multicenter Trail Group on Tidal Volume reduction in ARDS. Am J Respir Crit Care Med. 1998;158(6):1831-1838. [CrossRef] [PubMed]
 
Brower RG, Shanholtz CB, Fessler HE, et al. Prospective, randomized, controlled clinical trial comparing traditional versus reduced tidal volume ventilation in acute respiratory distress syndrome patients. Crit Care Med. 1999;27(8):1492-1498. [CrossRef] [PubMed]
 
Knoben JE, Anderson PO, Troutman WG, Davis LJ. Handbook of Clinical Drug Data.7th ed. Hamilton, IL: Drug Intelligence Publications; 1993.
 
Devine B. Gentamicin therapy. Drug Intell Clin Pharm. 1974;8(11):650-655.
 
Robinson JD, Lupkiewicz SM, Palenik L, Lopez LM, Ariet M. Determination of ideal body weight for drug dosage calculations. Am J Hosp Pharm. 1983;40(6):1016-1019. [PubMed]
 
Miller D, Carlson J, Loyd B, Day B. Determining ideal body weight (and mass). Am J Hosp Pharm. 1983;40(10):1622.
 
Morris A, Wallace C, Menlove R, et al. Randomized clinical trial of pressure-controlled inverse ratio ventilation and extracorporeal CO2removal for adult respiratory distress syndrome. Am J Respir Crit Care Med. 1994;149(2):295-305. [CrossRef] [PubMed]
 
Society of Actuaries and Association of Life Insurance Medical Directories of America. Build Study, 1979. Schaumburg, IL: Society of Actuaries and Association of Life Insurance Medical Directories of America; 1980:25-42.
 
East TD, Heermann LK, Bradshaw RL, et al. Efficacy of computerized decision support for mechanical ventilation: results of a prospective multi-center randomized trial. Proc AMIA Symp. 1999:251-255.
 
Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet. 1986;1(8476):307-310. [CrossRef] [PubMed]
 
Pai MP, Paloucek FP. The origin of the “ideal” body weight equations. Ann Pharmacother. 2000;34(9):1066-1069. [CrossRef] [PubMed]
 
Deming W. Out of the Crisis. Cambridge, MA: Massachusetts Institute of Technology, Center for Advanced Engineering Study; 1986.
 

Figures

Figure Jump LinkFigure 1 –  A-D, ACTUARIAL,14,15 STEWART,6 and ARDSNet4,10 PBW equation surfaces for women and men. A, B, Mathematically derived surface of PBW as a function of age (18-98 y) and height (152.4-210 cm) for ACTUARIAL and ARDSNet. C, D, Mathematically derived surface of PBW as a function of age (18-98 y) and height (152.4-210 cm) for STEWART and ARDSNet. ARDSNet = ARDS Network; PBW = predicted body weight.Grahic Jump Location
Figure Jump LinkFigure 2 –  A-D, %PBW difference for women and men. A, B, ACTUARIAL − ARDSNet. C, D, STEWART − ARDSNet. STEWART PBW predictions are age independent. See Figure 1 legend for expansion of other abbreviations.Grahic Jump Location
Figure Jump LinkFigure 3 –  A-D, The %PBW differences from ARDSNet predictions (for the ACTUARIAL1 and STEWART2 predictions) for clinical trial subject data as a function of age and height for women and men.16 See Materials and Methods section for equations. See Figure 1 legend for expansion of other abbreviations.Grahic Jump Location

Tables

Table Graphic Jump Location
TABLE 1 ]  PBW Equations and Results in Different Clinical Trials

ARDSNet = ARDS Network; NIH/NHLBI = National Institutes of Health National Heart, Lung, and Blood Institute; PBW = predicted body weight; Vt = tidal volume.

a 

Control group only (extracorporeal group subjects ignored).

b 

Only for the 179 patients supported with the assist/control mechanical ventilation mode.

Table Graphic Jump Location
TABLE 2 ]  Demographic Data of Clinical Trial Subjects ≥ 152.4 cm (5 ft) Tall, Supported With Assist/Controlled Mechanical Ventilation

Data presented as mean (± SD, range) unless otherwise indicated. See Table 1 legend for expansion of abbreviation.

References

Slutsky A. Mechanical ventilation. American College of Chest Physicians’ Consensus Conference. Chest. 1993;104(6):1833-1859. [CrossRef] [PubMed]
 
Dreyfuss D, Saumon G, Hubamyr R.. In:Lenfant C., ed. Ventilator-Induced Lung Injury. New York, NY: Taylor & Francis Group; 2006.
 
Slutsky AS, Ranieri VM. Ventilator-induced lung injury. N Engl J Med. 2013;369(22):2126-2136. [CrossRef] [PubMed]
 
The Acute Respiratory Distress Syndrome Network. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. N Engl J Med. 2000;342(18):1301-1308. [CrossRef] [PubMed]
 
Amato MB, Barbas CS, Medeiros DM, et al. Effect of a protective-ventilation strategy on mortality in the acute respiratory distress syndrome. N Engl J Med. 1998;338(6):347-354. [CrossRef] [PubMed]
 
Stewart TE, Meade MO, Cook DJ, et al; Pressure- and Volume-Limited Ventilation Strategy Group. Evaluation of a ventilation strategy to prevent barotrauma in patients at high risk for acute respiratory distress syndrome. N Engl J Med. 1998;338(6):355-361. [CrossRef] [PubMed]
 
Gajic O, Dara SI, Mendez JL, et al. Ventilator-associated lung injury in patients without acute lung injury at the onset of mechanical ventilation. Crit Care Med. 2004;32(9):1817-1824. [CrossRef] [PubMed]
 
Brochard L, Roudot-Thoraval F, Roupie E, et al. Tidal volume reduction for prevention of ventilator-induced lung injury in acute respiratory distress syndrome. The Multicenter Trail Group on Tidal Volume reduction in ARDS. Am J Respir Crit Care Med. 1998;158(6):1831-1838. [CrossRef] [PubMed]
 
Brower RG, Shanholtz CB, Fessler HE, et al. Prospective, randomized, controlled clinical trial comparing traditional versus reduced tidal volume ventilation in acute respiratory distress syndrome patients. Crit Care Med. 1999;27(8):1492-1498. [CrossRef] [PubMed]
 
Knoben JE, Anderson PO, Troutman WG, Davis LJ. Handbook of Clinical Drug Data.7th ed. Hamilton, IL: Drug Intelligence Publications; 1993.
 
Devine B. Gentamicin therapy. Drug Intell Clin Pharm. 1974;8(11):650-655.
 
Robinson JD, Lupkiewicz SM, Palenik L, Lopez LM, Ariet M. Determination of ideal body weight for drug dosage calculations. Am J Hosp Pharm. 1983;40(6):1016-1019. [PubMed]
 
Miller D, Carlson J, Loyd B, Day B. Determining ideal body weight (and mass). Am J Hosp Pharm. 1983;40(10):1622.
 
Morris A, Wallace C, Menlove R, et al. Randomized clinical trial of pressure-controlled inverse ratio ventilation and extracorporeal CO2removal for adult respiratory distress syndrome. Am J Respir Crit Care Med. 1994;149(2):295-305. [CrossRef] [PubMed]
 
Society of Actuaries and Association of Life Insurance Medical Directories of America. Build Study, 1979. Schaumburg, IL: Society of Actuaries and Association of Life Insurance Medical Directories of America; 1980:25-42.
 
East TD, Heermann LK, Bradshaw RL, et al. Efficacy of computerized decision support for mechanical ventilation: results of a prospective multi-center randomized trial. Proc AMIA Symp. 1999:251-255.
 
Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet. 1986;1(8476):307-310. [CrossRef] [PubMed]
 
Pai MP, Paloucek FP. The origin of the “ideal” body weight equations. Ann Pharmacother. 2000;34(9):1066-1069. [CrossRef] [PubMed]
 
Deming W. Out of the Crisis. Cambridge, MA: Massachusetts Institute of Technology, Center for Advanced Engineering Study; 1986.
 
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