Comparison of usual and alternative methods to measure height in mechanically ventilated patients: potential impact on protective ventilation

Body Fat Percentage and Availability of Oral Food Intake: Prognostic Factors and Implications for Nutrition in Amyotrophic Lateral Sclerosis

Adequate nutritional support and high body mass index (BMI) are good prognostic factors for disease progression and survival in amyotrophic lateral sclerosis (ALS). However, whether the composition of body weight, such as body fat percentage, has an independent effect on ALS prognosis remains unclear. The clinical data of 53 ALS patients were collected by medical record review. The data included: disease onset, sex, age, time of diagnosis, survival duration, presence of percutaneous endoscopic gastrostomy (PEG), nasogastric tube, tracheostomy, and availability of oral intake throughout the course of the disease, and interval measurement values of body mass by bioelectrical impedance analysis (BIA). The interval change (∆) of the BIA parameters was calculated by subtracting the follow-up values from the baseline values. Change in body fat percentage/interval between BIA measurements (months) (hazard ratio [HR] = 0.374, p = 0.0247), and availability of oral food intake (HR = 0.167, p = 0.02), were statistically significant for survival duration in multivariate hazard proportional regression analysis. Survival analysis and Kaplan–Meier curves showed similar results. Higher average monthly change in body fat percentage and availability of oral food intake are prognostic factors in ALS survival.

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.

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

Background

Height 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.

Objective

We 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.

Methods

Supine, 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).

Results

Forearm 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).

Conclusion

Lower leg length may be a suitable alternative to supine height to facilitate the application of LTVV in an ICU setting.

Comparação dos métodos de estimativa de peso e altura em pacientes hospitalizados

O objetivo deste estudo foi comparar o peso e altura aferidos com métodos de estimativa correspondentes em pacientes internados em um hospital da cidade de Juiz de Fora. Estudo transversal realizado no período de maio a dezembro de 2016 com a coleta dos seguintes dados: gênero, idade, raça, motivo da internação, peso, altura, altura do joelho, circunferência do braço, abdominal e da panturrilha, comprimento do braço e da ulna, semi-envergadura do braço e dobra cutânea subescapular. Foi empregado teste t pareado para comparar os valores de peso e altura aferidos foram com aqueles obtidos a partir de fórmulas de estimativa, considerando nível de significância estatística o valor de p < 0,05. Foram avaliados 90 pacientes, sendo 53,3% mulheres, 67,7% adultos e 68,9% eutróficos. Para a estimativa de peso corporal, as fórmulas de CHUMLEA et al. (1985) e (1994), RABITO et al. (2008) e MARTÍN et al. (2013) não se diferenciaram da medida de peso aferido (p > 0,05). Para a estimativa de altura, as fórmulas que não se diferenciaram foram as de CHUMLEA et al. (1985), CHUMLEA et al. (1994) e SILVEIRA et al. (1994) (p > 0,05). Concluiu-se que as equações de estimativa de peso e altura que utilizaram medidas de circunferências e altura do joelho em suas fórmulas se demonstraram adequadas para a estimativa de peso e altura em adultos e idosos hospitalizados. A escolha do método deverá ser baseada conforme disponibilidade de equipamentos e avaliadores treinados para realização das medidas.

Weight and height documentation: Does ICU measure up?

BACKGROUND

Reliable assessment and documentation of weight and height are essential for the accurate delivery of many critical care interventions.

METHODS

We conducted a 3-month retrospective, cross-sectional, single-centre audit to determine the prevalence of weight and height documentation in the clinical records of patients admitted to the intensive care unit (ICU) for the period from 3 months prior to hospital admission up to hospital discharge.

RESULTS

One hundred forty-one index ICU admissions were identified from October-December 2015 with 138 medical records available for analysis. Median (interquartile range) age was 64.5 (50.8-75.3) years, the majority were male (60.9%, 84/138), and the ICU admission Acute Physiology and Chronic Health Evaluation II score was 19.0 (14.0-25.0). Overall, weight and height were recorded in 90 (65.2%) and 63 (45.6%) patients, respectively. For elective postoperative admissions (n = 20), weight and height were recorded in 20 (100%) and 19 (95%) patients. For emergency medical and surgical admissions, 70 (59.3%) and 44 (37.2%) patients had weight and height recorded in both the 3-month period prior to hospital admission and the in-hospital period. A moderate, positive correlation was shown, r = 0.55, P < 0.001, with a longer hospital length of stay being associated with a greater number of weight and height records for each patient. In the emergency patient cohort, 81.7% (n = 215/263) of weight- and/or height-based interventions occurred before or during the ICU admission, of which 69.9% (n = 184/263) required consideration of ideal body weight.

CONCLUSION

Measurement and medical record documentation of weight and height is infrequently performed in ICU patients. Given the clinical requirement for accurate measurement and documentation, further research to understand the barriers to perform and document this important process of care is necessary.

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

Purpose

Acute lung injury is a life threatening condition often requiring mechanical ventilation. Lung-protective ventilation with tidal volumes of 6 mL/kg predicted body weight (PBW, calculated on the basis of a patient’s sex and height), is part of current recommended ventilation strategy. Hence, an exact height is necessary to provide optimal mechanical ventilation. However, it is a common practice to visually estimate the body height of mechanically ventilated patients and use these estimates as a reference size for ventilator settings. We aimed to determine if the common practice of estimating visual height to define tidal volume reduces the possibility of receiving lung-protective ventilation.

Methods

In this prospective observational study, 28 mechanically ventilated patients had their heights visually estimated by 20 nurses and 20 physicians. All medical professionals calculated the PBW and a corresponding tidal volume with 6 ml/kg/PBW on the basis of their visual estimation. The patients’ true heights were measured and the true PBW with a corresponding tidal volume was calculated. Finally, estimates and measurements were compared.

Results

1033 estimations were undertaken by 153 medical professionals. The majority of the estimates were imprecise and resulting data comprised taller body heights, higher PBW and higher tidal volumes (all p≤0.01). When estimates of patients´ heights are used as a reference for tidal-volume definition, patients are exposed to mean tidal volumes of 6.5 ± 0.4 ml/kg/PBW. 526 estimation-based tidal volumes (51.1%) did not provide lung-protective ventilation. Shorter subjects (<175cm) were a specific risk group with an increased risk of not receiving lung protective ventilation (OR 6.6; 95%CI 1.2–35.4; p = 0.02), while taller subjects had a smaller risk of being exposed to inadequately high tidal volumes (OR 0.15; 95%CI 0.02–0.8; p = 0.02). Furthermore, we found an increased risk of overestimating if the assessor was a female (OR 1.74; 95%CI 1.14–2.65; p = 0.01).

Conclusion

The common practice of visually estimating body height and using these estimates for ventilator settings is imprecise and potentially harmful because it reduces the chance of receiving lung-protective ventilation. Avoiding this practice increases the patient safety. Instead, height should be measured as a standard procedure.

Predicted body weight relationships for protective ventilation - unisex proposals from pre-term through to adult

BACKGROUND

The lung-protective ventilation bundle has been shown to reduce mortality in adult acute respiratory distress syndrome (ARDS). This concept has expanded to other areas of acute adult ventilation and is recommended for pediatric ventilation. A component of lung-protective ventilation relies on a prediction of lean body weight from height. The predicted body weight (PBW) relationship employed in the ARDS Network trial is considered valid only for adults, with a dedicated formula required for each sex. No agreed PBW formula applies to smaller body sizes. This analysis investigated whether it might be practical to derive a unisex PBW formula spanning all body sizes, while retaining relevance to established adult protective ventilation practice.

METHODS

Historic population-based growth charts were adopted as a reference for lean body weight, from pre-term infant through to adult median weight. The traditional ARDSNet PBW formulae acted as the reference for prevailing protective ventilation practice. Error limits for derived PBW models were relative to these references.

RESULTS

The ARDSNet PBW formulae typically predict weights heavier than the population median, therefore no single relationship could satisfy both references. Four alternate piecewise-linear lean body-weight predictive formulae were presented for consideration, each with different balance between the objectives.

CONCLUSIONS

The 'PBWuf + MBW' model is proposed as an appropriate compromise between prevailing practice and simplification, while also better representing lean adult body-weight. This model applies the ARDSNet 'female' formula to both adult sexes, while providing a tight fit to median body weight at smaller statures down to pre-term. The 'PBWmf + MBW' model retains consistency with current practice over the adult range, while adding prediction for small statures.

A calibrated measuring tape accurately predicts tidal volumes from ulna length

BACKGROUND

Low tidal volume ventilation improves outcomes in acute respiratory distress syndrome. Calculation of this volume requires knowledge of a patient's gender, and height, which may not be available in emergency admissions, and the subsequent application of a nomogram. The objective of this study was to test the accuracy of a calibrated measuring tape that reads in mL of tidal volume when the ulna is measured.

METHODS

The measuring tape was used to obtain an estimate of a subject's tidal volume from their ulna length, and standing height was then measured (reference method).

RESULT

A total of 100 healthy volunteers were included. Mean tidal volume was 450 mL for males and 372 mL for females when calculated from the height. Comparing tidal volumes from the tape with those from the reference method, Bland Altman analysis showed a bias of -10 mL (limits of agreement (2SD) -74 mL to 54 mL) for males and a bias of -36 mL (limits of agreement (2SD) -88 mL to 16 mL) for females. Predicted mean tidal volumes were 5.7 mL/kg (95% CI: 5.1-6.3 mL/kg) for males and 5.8 mL/kg (95% CI: 5.3-6.2 mL/kg) for females.

CONCLUSIONS

Usage of a calibrated measuring tape produced accurate estimates of tidal volumes required for lung protective ventilation in healthy volunteers.