Inaccuracies in calculating predicted body weight and its impact on safe ventilator settings ( Journal of the Intensive Care Society 2016;17: 191–195)

We read with interest your recent article on inaccuracies in height measurement in intensive care patients with its implications for lung protective ventilation. ¹

We are concerned that repeated measuring in the same eight volunteers to establish the accuracy of at the different methods might lead to results that are not applicable to the wider population. Some of the methods use anthropometric relationships between length of bones and total height and these may vary between individuals. A sample of only eight could easily give different results to that from a larger sample. Estimations of height from knee height ² and ulna length ³ in larger samples have been found in previous studies to provide good estimates of standing height.

A further important factor in achieving the end goal of tidal volumes of 6 ml/kg predicted body weight (PBW) is the ease of the measurement and its subsequent conversion. Even if you are able to accurately measure the recumbent length, you then have to convert this into a PBW and then a tidal volume. At our institution, we have developed a measuring tape for the ulna (Figure 1) that directly reads off estimated height, PBW, and tidal volume (previously reported in this journal). ⁴ We validated this in a sample of 100 volunteers. This tape can be rapidly used at the onset of ventilation by one person without need to alter patient position. Since introduction, it has become the standard method for tidal volume estimation in unplanned admissions for whom a standing height is unknown, and has been enthusiastically adopted by the medical and nursing staff, as it is simpler, quicker to use and easier than other methods. OPEN IN VIEWER

We think it has reduced the number of patients ventilated at higher than recommended tidal volume.