Size matters: An observational study investigating estimated height as a reference size for calculating tidal volumes if low tidal volume ventilation is required

A prospective study on the precision of height data from electronic medical records in tidal volume calculation for lung-protective ventilation

Lung-protective ventilation is now the norm for all patients, regardless of the presence of acute respiratory distress syndrome (ARDS), owing to the mortality associated with higher tidal volumes (TV). Clinicians calculate TV using recorded height from medical records and predicted body weight (PBW); however, the accuracy remains uncertain. Our study aimed to validate accurate TV settings for lung-protective ventilation by examining the correlation between the charted height and bedside measurements. In a single-center study, we compared PBW-based TV calculated from recorded height to PBW-based TV from measured height and identified factors causing height overestimation during charting. Our team measured patient height within 24 hours of admission using metal tape. TV calculated from recorded height (6-8 mL/kg PBW) was significantly larger (391.55 ± 65.98 to 522.07 ± 87.97) than measured height-based TV (162.62 ± 12.62 to 470.28 ± 89.64) (P < .01). In the height overestimated group, 57.7% were prescribed TV by healthcare provider, which was more than TV of 8 mL/kg of PBW, as determined by measured height. Negative predictors for height overestimation were male sex (OR: 0.45 [95% CI: 0.25-0.82]; P = .008) and presence of driver's license information (OR: 0.45 [95% CI: 0.25-0.80]; P = .007), whereas Asian ethnicity was a positive predictor (OR: 4.34 [95% CI: 1.09-17.27]; P = .04). The height overestimation group had a higher in-patient mortality rate (38.5%) than the matched/underestimation group (20%) (P < .01). In stadiometer-limited hospitals, the PBW-based TV is overestimated using the recorded height instead of the measured height. In the group where heights were overestimated, over half of the patients received TV prescriptions from healthcare providers that surpassed the TV of calculated 8 mL/kg PBW based on their measured height. The risk factors for height overestimation include female sex, Asian ethnicity, and missing driver's license data. Alternative height measurement methods should be explored to ensure precise ventilation settings and patient safety.

Person-Specific Template Matching Using a Dynamic Time Warping Step-Count Algorithm for Multiple Walking Activities

This study aimed to develop and evaluate a new step-count algorithm, StepMatchDTWBA, for the accurate measurement of physical activity using wearable devices in both healthy and pathological populations. We conducted a study with 30 healthy volunteers wearing a wrist-worn MOX accelerometer (Maastricht Instruments, NL). The StepMatchDTWBA algorithm used dynamic time warping (DTW) barycentre averaging to create personalised templates for representative steps, accounting for individual walking variations. DTW was then used to measure the similarity between the template and accelerometer epoch. The StepMatchDTWBA algorithm had an average root-mean-square error of 2 steps for healthy gaits and 12 steps for simulated pathological gaits over a distance of about 10 m (GAITRite walkway) and one flight of stairs. It outperformed benchmark algorithms for the simulated pathological population, showcasing the potential for improved accuracy in personalised step counting for pathological populations. The StepMatchDTWBA algorithm represents a significant advancement in accurate step counting for both healthy and pathological populations. This development holds promise for creating more precise and personalised activity monitoring systems, benefiting various health and wellness applications.

Sex and gender differences in intensive care medicine

Despite significant advancements in critical care medicine, limited attention has been given to sex and gender disparities in management and outcomes of patients admitted to the intensive care unit (ICU). While "sex" pertains to biological and physiological characteristics, such as reproductive organs, chromosomes and sex hormones, "gender" refers more to sociocultural roles and human behavior. Unfortunately, data on gender-related topics in the ICU are lacking. Consequently, data on sex and gender-related differences in admission to the ICU, clinical course, length of stay, mortality, and post-ICU burdens, are often inconsistent. Moreover, when examining specific diagnoses in the ICU, variations can be observed in epidemiology, pathophysiology, presentation, severity, and treatment response due to the distinct impact of sex hormones on the immune and cardiovascular systems. In this narrative review, we highlight the influence of sex and gender on the clinical course, management, and outcomes of the most encountered intensive care conditions, in addition to the potential co-existence of unconscious biases which may also impact critical illness. Diagnoses with a known sex predilection will be discussed within the context of underlying sex differences in physiology, anatomy, and pharmacology with the goal of identifying areas where clinical improvement is needed. To optimize patient care and outcomes, it is crucial to comprehend and address sex and gender differences in the ICU setting and personalize management accordingly to ensure equitable, patient-centered care. Future research should focus on elucidating the underlying mechanisms driving sex and gender disparities, as well as exploring targeted interventions to mitigate these disparities and improve outcomes for all critically ill patients.

Depth-Based Measurement of Respiratory Volumes: A Review

Depth-based plethysmography (DPG) for the measurement of respiratory parameters is a mobile and cost-effective alternative to spirometry and body plethysmography. In addition, natural breathing can be measured without a mouthpiece, and breathing mechanics can be visualized. This paper aims at showing further improvements for DPG by analyzing recent developments regarding the individual components of a DPG measurement. Starting from the advantages and application scenarios, measurement scenarios and recording devices, selection algorithms and location of a region of interest (ROI) on the upper body, signal processing steps, models for error minimization with a reference measurement device, and final evaluation procedures are presented and discussed. It is shown that ROI selection has an impact on signal quality. Adaptive methods and dynamic referencing of body points to select the ROI can allow more accurate placement and thus lead to better signal quality. Multiple different ROIs can be used to assess breathing mechanics and distinguish patient groups. Signal acquisition can be performed quickly using arithmetic calculations and is not inferior to complex 3D reconstruction algorithms. It is shown that linear models provide a good approximation of the signal. However, further dependencies, such as personal characteristics, may lead to non-linear models in the future. Finally, it is pointed out to focus developments with respect to single-camera systems and to focus on independence from an individual calibration in the evaluation.

Disparities in Lung-Protective Ventilation in the United States

Background The objective of our study was to determine whether disparities exist in the use of lung-protective ventilation for critically ill mechanically ventilated patients in the United States based on gender, race/ethnicity, or insurance status. Methods This was a secondary data analysis of a prospective multicenter cohort study conducted from 2010 to 2012. The outcome of interest was the proportion of patients receiving tidal volume > 8 mL/kg predicted body weight (PBW). Results There were 1,595 patients in our primary analysis (710 women, 885 men). Women were more likely to receive tidal volumes > 8 mL/kg PBW than men (odds ratio [OR] = 3.42, 95% confidence interval [CI] = 2.67-4.40), a finding largely but not completely explained by gender differences in height. The underinsured were significantly more likely to receive tidal volume > 8 mL/kg PBW than the insured in multivariable analysis (OR = 1.54, 95% CI = 1.16-2.04). The prescription of > 8 mL/kg PBW tidal volume did not differ by racial or ethnic categories. Conclusions In this prospective nationwide cohort of critically ill mechanically ventilated patients, women and the underinsured were less likely than their comparators to receive lung-protective ventilation, with no apparent differences based on race/ethnicity alone.

Calculated Plasma Volume Status Is Associated With Mortality in Acute Respiratory Distress Syndrome

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The optimal method to assess fluid overload in acute respiratory distress syndrome is not known, and current techniques have limitations. Plasma volume status has emerged as a noninvasive method to assess volume status and is defined as the percentage alteration from ideal plasma volume. We hypothesized that plasma volume status would suggest the presence of significant excess volume and therefore correlate with mortality in acute respiratory distress syndrome.

Impact of sex on use of low tidal volume ventilation in invasively ventilated ICU patients-A mediation analysis using two observational cohorts

Background

Studies in patients receiving invasive ventilation show important differences in use of low tidal volume (V_T) ventilation (LTVV) between females and males. The aims of this study were to describe temporal changes in V_T and to determine what factors drive the sex difference in use of LTVV.

Methods and findings

This is a posthoc analysis of 2 large longitudinal projects in 59 ICUs in the United States, the ‘Medical information Mart for Intensive Care III’ (MIMIC III) and the ‘eICU Collaborative Research DataBase’. The proportion of patients under LTVV (median V_T < 8 ml/kg PBW), was the primary outcome. Mediation analysis, a method to dissect total effect into direct and indirect effects, was used to understand which factors drive the sex difference. We included 3614 (44%) females and 4593 (56%) males. Median V_T declined over the years, but with a persistent difference between females (from median 10.2 (9.1 to 11.4) to 8.2 (7.5 to 9.1) ml/kg PBW) vs. males (from median 9.2 [IQR 8.2 to 10.1] to 7.3 [IQR 6.6 to 8.0] ml/kg PBW) (P < .001). In females versus males, use of LTVV increased from 5 to 50% versus from 12 to 78% (difference, –27% [–29% to –25%]; P < .001). The sex difference was mainly driven by patients’ body height and actual body weight (adjusted average causal mediation effect, –30% [–33% to –27%]; P < .001, and 4 [3% to 4%]; P < .001).

Conclusions

While LTVV is increasingly used in females and males, females continue to receive LTVV less often than males. The sex difference is mainly driven by patients’ body height and actual body weight, and not necessarily by sex. Use of LTVV in females could improve by paying more attention to a correct calculation of V_T, i.e., using the correct body height.

Impact of Height Estimation on Tidal Volume Calculation for Protective Ventilation-A Prospective Observational Study

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.

Impact of Providing a Tape Measure on the Provision of Lung-protective Ventilation

INTRODUCTION

Emergency department (ED) patients are frequently ventilated with excessively large tidal volumes for predicted body weight based on height, which has been linked to poorer patient outcomes. We hypothesized that supplying tape measures to respiratory therapists (RT) would improve measurement of actual patient height and adherence to a lung-protective ventilation strategy in an ED-intensive care unit (ICU) environment.

METHODS

On January 14, 2019, as part of a ventilator-associated pneumonia prevention bundle in our ED-based ICU, we began providing RTs with tape measures and created a best practice advisory reminding them to record patient height. We then retrospectively collected data on patient height and tidal volumes before and after the intervention.

RESULTS

We evaluated 51,404 tidal volume measurements in 1,826 patients over the 4 year study period; of these patients, 1,579 (86.5%) were pre-intervention and 247 (13.5%) were post-intervention. The intervention was associated with a odds of the patient's height being measured were 10 times higher post-intervention (25.1% vs 3.2%, P <0.05). After the bundle was initiated, we observed a significantly higher percentage of patients ventilated with mean tidal volumes less than 8 cubic centimeters per kilogram (93.9% vs 84.5% P < 0.05).

CONCLUSION

Patients in an ED-ICU environment were ventilated with a lung-protective strategy more frequently after an intervention reminding RTs to measure actual patient height and providing a tape measure to do so. A significantly higher percentage of patients had height measured rather than estimated after the intervention, allowing for more accurate determination of ideal body weight and calculation of lung-protective ventilation volumes. Measuring all mechanically ventilated patients' height with a tape measure is an example of a simple, low-cost, scalable intervention in line with guidelines developed to improve the quality of care delivered to critically ill ED patients.

Lung-Protective Ventilation Over 6 Years at a Large Academic Medical Center: An Evaluation of Trends, Adherence, and Perceptions of Benefit

The main objective of this study was to evaluate trends in set tidal volumes across all adult ICUs at a large academic medical center over 6 years, with a focus on adherence to lung-protective ventilation (≤ 8-cc/kg ideal body weight). A secondary objective was to survey providers on their perceptions of lung-protective ventilation and barriers to its implementation.

DESIGN

Retrospective observational analysis (primary objective) and cross-sectional survey study (secondary objective), both at a single center.

PARTICIPANTS

Mechanically ventilated adult patients with a set tidal volume (primary objective) and providers rotating through the Medical and Neurosciences ICUs (secondary objective).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

From 2013 to 2018, the average initial set tidal volume (cc/kg ideal body weight) decreased from 8.99 ± 2.19 to 7.45±1.34 (p < 0.001). The cardiothoracic ICU had the largest change in tidal volume from 11.09 ± 1.96 in 2013 to 7.97 ± 1.03 in 2018 (p < 0.001). Although the majority of tidal volumes across all ICUs were between 6.58 and 8.01 (interquartile range) in 2018, 27% of patients were still being ventilated at volumes greater than 8-cc/kg ideal body weight. Most surveyed respondents felt there was benefit to lung-protective ventilation, though many did not routinely calculate the set tidal volume in cc/kg ideal body weight, and most did not feel it was easily calculable with the current electronic medical record system.

CONCLUSIONS

Despite a trend toward lower tidal volumes over the years, in 2018, over a quarter of mechanically ventilated adult patients were being ventilated with tidal volumes greater than 8 cc/kg. Survey data indicate that despite respondents acknowledging the benefits of lung-protective ventilation, there are barriers to its optimal implementation. Future modifications of the electronic medical record, including a calculator to set tidal volume in cc/kg and the use of default set tidal volumes, may help facilitate the delivery of and adherence to lung-protective ventilation.

A quantitative approach for the analysis of clinician recognition of acute respiratory distress syndrome using electronic health record data

IMPORTANCE

Despite its efficacy, low tidal volume ventilation (LTVV) remains severely underutilized for patients with acute respiratory distress syndrome (ARDS). Physician under-recognition of ARDS is a significant barrier to LTVV use. We propose a computational method that addresses some of the limitations of the current approaches to automated measurement of whether ARDS is recognized by physicians.

OBJECTIVE

To quantify patient and physician factors affecting physicians' tidal volume selection and to build a computational model of physician recognition of ARDS that accounts for these factors.

DESIGN, SETTING, AND PARTICIPANTS

In this cross-sectional study, electronic health record data were collected for 361 ARDS patients and 388 non-ARDS hypoxemic (control) patients in nine adult intensive care units at four hospitals between June 24 and December 31, 2013.

METHODS

Standardized tidal volumes (mL/kg predicted body weight) were chosen as a proxy for physician decision-making behavior. Using data-science approaches, we quantified the effect of eight factors (six severity of illness, two physician behaviors) on selected standardized tidal volumes in ARDS and control patients. Significant factors were incorporated in computational behavioral models of physician recognition of ARDS.

RESULTS

Hypoxemia severity and ARDS documentation in physicians' notes were associated with lower standardized tidal volumes in the ARDS cohort. Greater patient height was associated with lower standardized tidal volumes (which is already normalized for height) in both ARDS and control patients. The recognition model yielded a mean (99% confidence interval) physician recognition of ARDS of 22% (9%-42%) for mild, 34% (19%-49%) for moderate, and 67% (41%-100%) for severe ARDS.

CONCLUSIONS AND RELEVANCE

In this study, patient characteristics and physician behaviors were demonstrated to be associated with differences in ventilator management in both ARDS and control patients. Our model of physician ARDS recognition measurement accounts for these clinical variables, providing an electronic approach that moves beyond relying on chart documentation or resource intensive approaches.

Demographics, management and outcome of females and males with acute respiratory distress syndrome in the LUNG SAFE prospective cohort study

Rationale

We wished to determine the influence of sex on the management and outcomes in acute respiratory distress syndrome (ARDS) patients in the Large Observational Study to Understand the Global Impact of Severe Acute Respiratory Failure (LUNG SAFE).

Methods

We assessed the effect of sex on mortality, intensive care unit and hospital length of stay, and duration of invasive mechanical ventilation (IMV) in patients with ARDS who underwent IMV, adjusting for plausible clinical and geographic confounders.

Findings

Of 2377 patients with ARDS, 905 (38%) were female and 1472 (62%) were male. There were no sex differences in clinician recognition of ARDS or critical illness severity profile. Females received higher tidal volumes (8.2±2.1 versus 7.2±1.6 mL·kg−1; p<0.0001) and higher plateau and driving pressures compared with males. Lower tidal volume ventilation was received by 50% of females compared with 74% of males (p<0.0001). In shorter patients (height ≤1.69 m), females were significantly less likely to receive lower tidal volumes. Surviving females had a shorter duration of IMV and reduced length of stay compared with males. Overall hospital mortality was similar in females (40.2%) versus males (40.2%). However, female sex was associated with higher mortality in patients with severe confirmed ARDS (OR for sex (male versus female) 0.35, 95% CI 0.14–0.83).

Conclusions

Shorter females with ARDS are less likely to receive lower tidal volume ventilation, while females with severe confirmed ARDS have a higher mortality risk. These data highlight the need for better ventilatory management in females to improve their outcomes from ARDS.

Adoption of low tidal volume ventilation in the emergency department: A quality improvement intervention

BACKGROUND

Ventilator tidal volumes of >8 mL/kg of predicted body weight (PBW) may increase the risk of lung injury. We sought to evaluate the impact of a quality improvement intervention among intubated Emergency Department (ED) patients to protocolize the prescription of low tidal volume ventilation.

METHODS

In this before-and-after study, the average tidal volume delivered to ED patients receiving volume assist-control ventilation was compared before (2007-2014) and after (2015-2016) implementation of a ventilator initiation protocol (the quality improvement intervention). The intervention emphasized 1) measurement of the patient's height to calculate PBW and therefore tailor the tidal volume to estimated lung size (<8 mL/kg PBW), and 2) focused education and reference materials for ED physicians and respiratory therapists.

RESULTS

Among ventilated ED patients meeting inclusion criteria in the before (N = 2185) and after (N = 774) cohorts, the mean (±SD) tidal volume decreased from 9.0 ± 1.4 mL/kg to 7.2 ± 0.9 mL/kg PBW following the intervention (absolute difference 1.8 mL/kg, 95% confidence interval 1.7 to 1.9 mL/kg, p < 0.001). The proportion of patients receiving low tidal volume ventilation increased after the intervention (72%), as compared to before (23%). Low tidal volume ventilation continued to be utilized at 24 h after ICU admission in patients who remained intubated in the cohort following the intervention (mean tidal volume 7.3 mL/kg PBW).

CONCLUSIONS

Pairing a ventilator initiation protocol with focused education and resources for emergency physicians and respiratory therapists was associated with a significant reduction in tidal volume delivered to ED patients.

Relationship between height and outcomes among critically ill adults: a cohort study

PURPOSE

Many diagnostic and therapeutic interventions for critically ill adult patients are not performed according to patient size, but are standardized for an idealized 174-cm man (ideal body weight 70 kg). This study aims to determine whether critically ill patients with heights significantly different from a standardized patient have higher hospital mortality or greater resource utilization.

METHODS

Retrospective cohort study of consecutive patients admitted to 210 intensive care units (ICUs) in the United Kingdom participating in the Intensive Care National Audit and Research Centre's Case Mix Programme Database from April 1, 2009, to March 31, 2015. Primary outcome was hospital mortality, adjusted for age, comorbid disease, severity of illness, socioeconomic status and body mass index, using hierarchical modeling to account for clustering by ICU. Data were stratified by sex, and the effect of height was modeled continuously using restricted cubic splines.

RESULTS

The cohort included 233,308 men and 184,070 women, with overall hospital mortality of 22.5% and 20.6%, respectively. After adjustment for potential confounders, hospital mortality decreased with increasing height; predicted mortality (holding all other covariates at their mean value) decreased from 24.1 to 17.1% for women and from 29.2 to 21.0% for men across the range of heights. Similar patterns were observed for ICU mortality and several additional secondary outcomes.

CONCLUSIONS

Short stature may be a risk factor for mortality in critically ill patients. Further work is needed to determine which unmeasured patient characteristics and processes of care may contribute to the increased risk observed.