Related Experiment Video
Updated: Nov 3, 2025
Combining Volumetric Capnography And Barometric Plethysmography To Measure The Lung Structure-function Relationship
Published on: January 8, 2019
Impact of Height Estimation on Tidal Volume Calculation for Protective Ventilation-A Prospective Observational Study
André R Alexandre1, Filipa R Rocha1, Luís Landeiro1
1All authors: Department of Intensive Care, Hospital da Luz - Lisboa, Lisboa, Portugal.
Objectives:
The current standard of care to deliver invasive mechanical ventilation support is the protective ventilation approach. One pillar of this approach is the limitation of tidal volume to less than 6 mL/Kg of predicted body weight. Predicted body weight is calculated from patient's height. Yet, little is known about the potential impact of errors arising from visual height estimation, a common practice, to calculate tidal volumes. The aim of this study was to evaluate that impact on tidal volume calculation to use during protective ventilation.
Design:
Prospective observational study.
Setting:
An eight-bed polyvalent ICU.
Patients:
Adult patients (≥ 18 yr).
Interventions:
None.
Measurements And Main Results:
Tidal volumes were calculated from visual height estimates made by physicians, nurses, and patients themselves and compared with tidal volumes calculated from measured heights. Comparisons were made using the paired t test. Modified Bland-Altman plots were used to assess agreement between height estimates and measurements. One-hundred patients were recruited. Regardless of the height estimator, all the mean tidal volumes would be greater than 6 mL/Kg predicted body weight (all p < 0.001). Additionally, tidal volumes would be greater than or equal to 6.5 mL/Kg predicted body weight in 18% of patients' estimates, 25% of physicians' estimates, and 30% of nurses' estimates. Patients with lower stature (< 165 cm), older age, and surgical typology of admission were at increased risk of being ventilated with tidal volumes above protective threshold.
Conclusions:
The clinical benefit of the protective ventilation strategy can be offset by using visual height estimates to calculate tidal volumes. Additionally, this approach can be harmful and potentially increase mortality by exposing patients to tidal volumes greater than or equal to 6.5 mL/Kg predicted body weight. In the interest of patient safety, every ICU patient should have his or her height accurately measured.
More Related Videos
Related Concept Videos
01:15Respiratory Volumes
Tidal Volume (TV) Tidal volume (TV) is the air inhaled or exhaled in a...
01:20Assessment of Ventilation I: Respiratory Rate
A Ventilation assessment is critical for monitoring a patient's health status. Respiration, one of the most accessible vital signs, provides insights into the function of numerous body systems and can indicate serious health issues, such as brainstem injuries from head trauma.
Critical Guidelines for Assessing Ventilation:
01:22Respiratory Volumes and Capacities
01:19Factors Affecting Pulmonary Ventilation
Alveolar Surface Tension
The alveolar fluid lines the luminal surface of the alveoli and exerts a force called surface tension. This force is caused by the polar water molecules in the liquid being more strongly attracted to each...
01:29Assessment of Ventilation II: Respiratory Depth and Rhythm
Respiratory depth measures the volume of air inhaled or exhaled during a breath. It can vary from shallow to deep and typically remains consistent when a person is at rest or asleep. Occasionally, individuals will automatically inhale deeply, known as sighing, which inflates the lungs with more air than normal breathing.
To assess respiratory depth, observe the degree of chest excursion or movement:
01:26Respiratory Volumes and Capacities I