Accuracy of height estimation and tidal volume setting using anthropometric formulas in an ICU Caucasian population

Abstract

Background: Knowledge of patients' height is essential for daily practice in the intensive care unit. However, actual height measurements are unavailable on a daily routine in the ICU and measured height in the supine position and/or visual estimates may lack consistency. Clinicians do need simple and rapid methods to estimate the patients' height, especially in short height and/or obese patients. The objectives of the study were to evaluate several anthropometric formulas for height estimation on healthy volunteers and to test whether several of these estimates will help tidal volume setting in ICU patients.

Methods: This was a prospective, observational study in a medical intensive care unit of a university hospital. During the first phase of the study, eight limb measurements were performed on 60 healthy volunteers and 18 height estimation formulas were tested. During the second phase, four height estimates were performed on 60 consecutive ICU patients under mechanical ventilation.

Results: In the 60 healthy volunteers, actual height was well correlated with the gold standard, measured height in the erect position. Correlation was low between actual and calculated height, using the hand's length and width, the index, or the foot equations. The Chumlea method and its simplified version, performed in the supine position, provided adequate estimates. In the 60 ICU patients, calculated height using the simplified Chumlea method was well correlated with measured height (r = 0.78; ∂ < 1 %). Ulna and tibia estimates also provided valuable estimates. All these height estimates allowed calculating IBW or PBW that were significantly different from the patients' actual weight on admission. In most cases, tidal volume set according to these estimates was lower than what would have been set using the actual weight.

Conclusion: When actual height is unavailable in ICU patients undergoing mechanical ventilation, alternative anthropometric methods to obtain patient's height based on lower leg and on forearm measurements could be useful to facilitate the application of protective mechanical ventilation in a Caucasian ICU population. The simplified Chumlea method is easy to achieve in a bed-ridden patient and provides accurate height estimates, with a low bias.

Keywords: Height estimation; ICU; Mechanical ventilation.

Figures

Fig. 1

Limb segment measurements. All measurements were performed using precision callipers on the right limbs. 1 index distal phalange; 2 hand length, from the IIIrd finger extremity to the wrist; 3 hand maximal width; 4 ulna, from the olecranon to the styloïd process; 5 tibia length, from the upper articular line to the extremity of the medial malleolus; 6 standard Chumlea measurement, the patient is positioned recumbent, knee raised vertically with a 90° angle between femur and tibia, and the caliper is positioned under heel and over femoral condyle of the leg; 7 simplified Chumlea measurement, the patient stays supine and the caliper is positioned under heel and over patella’s upper line; 8: foot length, from the extremity of the Ist toe to the posterior part of the heel

Fig. 2

Comparison of different methods for height evaluation in healthy volunteers. The left column represents the regression diagram of the two tested methods. The independent variable (reference value = measured height in the erect position) defines the vertical axis, and the dependent variable (tested method) defines the horizontal axis. Dark line represents the regression line; r = correlation coefficient; P value ≤0.05 was considered significant. The right column displays the scatter diagram of the differences of the two methods (Bland and Altman plot). Dark line represents the mean difference (estimation bias = ∂) between the two methods; dotted line represents the limit of agreement (plus and minus 1.96 SD) of the differences. For healthy volunteers, measured height in the upright position (reference) was well correlated with measured height in the supine position. This measured height may induce errors of 9.2 cm (2/60 volunteers with an error >10 cm). Chumlea height estimation, using either the standard or the simplified method in the supine position, was well correlated with actual height, with a low estimation bias. It may, however, induce errors from 8.9 to 11.8 cm

Fig. 3

Bland and Altman plot for tidal volume in ICU patients, using various measures and estimates. VT tidal volume, PBW predicted body weight, ABW actual body weight, VT Measured tidal volume set using the measured height, VT Chumlea S tidal volume set using the Simplified Chumlea height estimate. Tidal volume setting grandly vary while using either PBW or ABW, with as much as a 3.7 mL/kg range, whereas the mean bias remains low (−0.9 mL/kg). VT settings using either the measured PBW or its estimate (visual height estimation) are consistent. The simplified Chumlea method is consistent with the one using the measured value, generally providing a 1.1 mL/kg lower value