A Comparison of Three Methods of Height Estimation and Their Impact on Low Tidal Volume Ventilation in a Mixed Ethnicity Intensive Care Unit: A Real-World Experience.

Keevan Singh,Natalia Gocool

doi:10.7759/cureus.9221

Abstract

BackgroundHeight measurement is crucial for calculating predicted body weight (PBW) and establishing low tidal volume ventilation (LTVV). However, standing height is usually unavailable in critically ill patients and supine height may be difficult to obtain.ObjectiveWe investigated whether there were any significant differences in tidal volumes (VT) obtained using PBW derived from supine, forearm, and lower leg lengths in an intensive care unit (ICU) setting.MethodsSupine, forearm and lower leg lengths were measured in 100 mechanically ventilated patients. Limb lengths were converted to height and PBW calculated using published formulae. The 6 mL/kg VT for the supine (sVT), forearm (fVT), and lower leg (lVT) methods were compared to each other and to visually estimated VT (estVT).ResultsForearm length produced the greatest height estimate, leading to a significantly greater tidal volume fVT (437.6 ± 62.1 mL) compared with sVT (385.5 ± 63.8 mL) and lVT (369.1 ± 66.4 mL), (p < .001). There was no significant difference between lVT and sVT, (p = .169). On Bland Altman analysis, the lowest bias was found between lVT and sVT (−16.4 ± 36.0 mL, 95% limits of agreement (LOA) [−86.9, 54.1]), whereas fVT had a bias of 52.1 ± 41.5 mL, 95% LOA [−29.1, 133.4] compared to sVT. The fVT was significantly greater than sVT and lVT in all sexes and ethnic groups (p < .05).ConclusionLower leg length may be a suitable alternative to supine height to facilitate the application of LTVV in an ICU setting.

Highlights

Mechanical ventilation carries the risk of precipitating and exacerbating pre-existing lung injury [1]
We investigated whether there were any significant differences in tidal volumes (VT) obtained using predicted body weight (PBW) derived from supine, forearm, and lower leg lengths in an intensive care unit (ICU) setting
On Bland Altman analysis, the lowest bias was found between leg derived VT (lVT) and sVT (−16.4 ± 36.0 mL, 95% limits of agreement (LOA) [−86.9, 54.1]), whereas Forearm derived VT (fVT) had a bias of 52.1 ± 41.5 mL, 95% LOA [−29.1, 133.4] compared to sVT

Summary

Introduction

Mechanical ventilation carries the risk of precipitating and exacerbating pre-existing lung injury [1]. The pathophysiological mechanisms involved in ventilator-associated lung injury (VALI) include alveolarcapillary barrier disruption and inflammation secondary to volutrauma, barotrauma, atelectrauma and biotrauma. The traditional use of high tidal volumes (VTs) between 10 to 15 mL/kg predicted body weight (PBW) has been shown to be a critical mediator of VALI [2,3,4], which is associated with increased morbidity and mortality [5]. A key component of a lung-protective ventilatory strategy, involves the use of low tidal volume ventilation (LTVV) between 4 to 8 mL/kg PBW [6,7,8,9]. Height measurement is crucial for calculating predicted body weight (PBW) and establishing low tidal volume ventilation (LTVV). Standing height is usually unavailable in critically ill patients and supine height may be difficult to obtain

Methods

Results

Conclusion