Measurement of the forearm to warrant low-tidal-volume ventilation in the acute respiratory distress syndrome

Introduction

Acute respiratory distress syndrome (ARDS) is a life-threatening situation in patients on the ICU. Most patients have to be ventilated mechanically to provide adequate oxygenation. Reduction of tidal volumes as low as 6 ml/kg adjusted bodyweight has been convincingly shown to reduce ARDS and mortality in the ARDSnet trial [1] and is now recommended in treating such patients. In the ARDSnet trial, body weight has been calculated by a formula implementing the body height [1]. We suggest that in most patients on ICUs the correct height is not known or is at best estimated, but very seldom correctly measured. We searched for both an easily obtainable and reproducible body mark to correctly predict body height. Anthropological and forensic data have shown a close correlation between the ulna length and body size. We prospectively measured body height and right and left ulna length in ventilated ICU patients.

Methods

In a 2-month period, 39 men and 42 women from four ICUs in a teaching hospital were included consecutively (mean age 62 years, range 23 to 87 years). Body height was measured following a standardized protocol, ulna length was measured from the edge of the olecranon to the caput ulnae.

Results

Eighty-one patients were included. Thirty-nine men: height 145 to 199 cm (mean 178.5 cm), right ulna 25 to 32 cm (mean 28.3 cm), left ulna 24.5 to 32 cm (mean 28.3 cm). Forty-two women: height 142 to 185 cm (mean 165.7 cm), right ulna 21 to 29 cm (mean 25.0 cm), left ulna 21 to 28 cm (mean 24.9 cm). Regression analyses were made in SAS 9.1 and showed a significant correlation between the body height (men and women) and the length of the ulna. Regression analyses for men: body height in cm = 3.9314 × (right ulna; in cm) + 67.059 cm (r² = 53.25%; SD = 6.79) and body height in cm = 3.9786 × (left ulna; in cm) + 65.824 cm (r² = 52.50%; SD = 6.84). Regression analyses for women: body height in cm = 4.88 × (right ulna; in cm) + 43.76 cm (r² = 55.53%; SD = 6.61) and body height in cm = 5.41 × (left ulna; in cm) + 30.95 cm (r² = 60.67%; SD = 6.21).

Conclusion

Ulna length is an easily obtainable estimate of total body height. It may aid in implementing low-tidal-volume ventilation. Anthropological data correlate reasonably with a contemporary ventilated ICU population. Whether ulna-derived estimates of body height may improve adherence to established guidelines has to be studied.