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What do we know about this problem?
Ideal weight calculation requires accurate height measurement, a procedure which is not standardized in many intensive care units.
In intensive care, the reference equation used to calculate the ideal weight is the one proposed by the Acute Respiratory Distress Syndrome Network (ARDSnet) guideline which was designed on the basis of anthropometric measurements of the United States population.
INTRODUCTION
Ideal body weight (IBW) is similar to healthy body weight and is associated with good health condition. It is determined using equations that include anthropometric variables such as height, weight, sex and/or one or several body segments like the arm or leg; these predictive equations are used routinely by healthcare professionals 1.
Sometimes, body weight measurements - specifically in intensive care units - cannot always be made directly due to the lack of appropriate tools and the patient's condition and, therefore, subjective estimates influence the result. In such cases, equations that can be used to calculate ideal weight are needed 2. However, most equations have been designed using anthropometric variables that are not representative of the whole population spectrum, and their use overestimates ideal weight, with repercussions in critically ill patients 3.
IBW calculation is widely used in critical medicine for drug dosing, ventilator settings, glomerular filtration rate adjustments, and nutritional assessment 4. However, the equations suggested and used for the calculation originated in the United States and do not consider the very different anthropometric characteristics (weight/height) of the Latin American population.
In particular in adult intensive care units (ICUs), height measurement to estimate ideal weight is very important when it comes to determining tidal volume in patients on mechanical ventilation in order to obtain an objective, effective and preventive determination of lung ventilation and avoid and/or reduce events or complications related to inadequate tidal volume settings 5.
The Acute Respiratory Distress Syndrome Network (ARDS Network) guidelines suggest that low tidal volumes should be used in patients with acute lung injury and acute respiratory distress syndrome. Moreover, they propose an equation to calculate ideal body weight based on body height measurements. This equation, created on the basis of anthropometric measurements in the United States population, is still the gold standard for ideal weight calculation in the ICU 6.
The consequences of inadequate ideal weight estimation in critically ill patients include ventilation-related complications, considering that over or underestimations of this variable result in wrong tidal volume calculations for ventilator settings. This can result in lung trauma, such as volutrauma, barotrauma, atelectrauma, inflammatory cascade activation, longer mechanical ventilation, and increased ICU length of stay 7.
Because body height can be influenced by environmental factors, equations for estimating ideal weight that include this anthropometric variable must be designed and validated in accordance with the characteristics of the target population. Notwithstanding, there are no known studies that have designed and proposed other equations to calculate body height in the Latin American population 8. This exploratory review maps the evidence related to the equations used to calculate ideal weight in patients on mechanical ventilation in adult ICUs in Latin America.
METHODS
This review followed the guidelines contained in the checklist for the presentation of exploratory reviews of the PRISMA-ScR declaration and was based on the Joanna Briggs Institute (JBI) method initially developed by Arksey and O'Malley 9, which was based, in turn, on the methodological guidance set forth by Peters et al. 10 that suggests: formulation of the research question, identification of relevant studies, study selection, data extraction, summary and reports of the results, and conclusions.
Research question
The following PICO question was built to guide the exploratory review: Which are the equations used to calculate ideal weight in patients on mechanical ventilation in intensive care units in Latin America? The question was designed on the basis of population, intervention, comparison and results: P (Population): Adult patients on invasive mechanical ventilation. I (Intervention): Reference equations for ideal weight calculation. C (Comparison): Not relevant. O (Outcomes): Ideal weight calculation (Figure 1). Comparison/control was not taken into consideration as it was not considered relevant during the development of the research given that there was no control group for outcome comparisons.
SOURCE: Authors, from González-Seguel, et al. 11
FIGURE 1 Inclusion criteria used on the basis of population, intervention and context.
Selection of studies
Selected studies had to meet the following inclusion criteria: 1) Primary scientific studies, reviews, expert recommendations, lectures, guidelines or protocols published in Spanish, English and Portuguese. 2) Potentially relevant studies that answered the research question, whether published or not. 3) Studies carried out in adult Latin American population.
Studies that met the following criteria were excluded: 1) Studies that did not provide sufficient information about the equation used for calculating ideal weight. 2) Studies in which ideal weight was calculated but was used for calculations other than ventilation parameters
Types of participants
Selected studies described, in the methodology, the use of equations for estimating ideal weight in adult patients on mechanical ventilation in different intensive care units in Latin America.
Concepts
The relevant concepts for this review included the following:
Intensive care units (ICUs). Intensive care consists of providing automated monitoring of multiple parameters for the management of patients with multi-organ decline, supplementary testing, basic and advanced bedside support devices and a multidisciplinary clinical team 12. This services provides care to critically ill patients with any type of disease condition (multiple trauma, surgery, respiratory disease, coronary heart disease, among others), in close collaboration with all other hospital services, in particular the emergency service 13.
In Latin America, the first intensive care units were established in the late 1960s and early 1970s. It can be safely stated that intensive care units can be found in all Latin American countries, managed by intensive care physicians and equipped with sufficient technology to provide adequate management as needed 14.
Ideal weight. It refers to a similarity with the body weight associated with good health condition. For decades, multiple equations have been used to calculate ideal weight, taking into account different body measurements such as height, body weight, ulnar length and even body mass index 15.
Ideal weight is very useful in intensive care units and, specifically, in the area of mechanical ventilation, as an essential tool for calculating tidal volume settings for objective and effective ventilation as well as for preventing ventilation-related events such as volutrauma, barotrauma, atelectrauma, inflammatory cascade activation, length of mechanical ventilation, need for re-intubation and length of ICU stay 7.
Body height. More sensitive than weight, this parameter is used to determine growth in length; it is critical for anthropometric assessment and essential for creating indicators involved in nutritional diagnosis, and dietary and pharmacological prescriptions 16.
Mathematical equation. From the Latin word aequatio, it constitutes an equality in which there is at least one unknown quantity that needs to be revealed by the person solving the question. Each of the algebraic expressions that allow to discover linked data and unknown quantities through various mathematical operations are known as members.
Mechanical ventilation (MV). Therapeutic option which, based on the understanding of the pathophysiological mechanisms of respiratory function and with the help of technological advances, offers the opportunity to provide efficient life support to critically ill patients in respiratory failure 17.
Tidal volume (TV). Gas volume that circulates between normal inspiration and expiration. In mechanical ventilation, a volume between 6 and 8 mL per kilogram of ideal body weight may be programmed in patients without lung compromise 18.
Protective ventilation. It is defined as a mechanical ventilation strategy in which low tidal volume and minimum airway pressure are used in order to prevent associated complications 17. Meta-analysis reports and randomized studies have shown that protective mechanical ventilation reduces short-term mortality 19.
Identification of relevant studies
The literature search was conducted by two physical therapists with more than 4 years of intensive care experience, advised by a biomedical librarian. The process of study identification, review, eligibility and inclusion was carried out by consensus between the researchers. Studies conducted in any Latin American country in the context of adult ICUs were selected.
Search strategy
This review used primary sources in the form original published research articles, and secondary sources in the form of existing reviews on the topic described but which included studies carried out in the Latin American population. Unpublished evidence was also included, such as results of research that met the predefined selection criteria, conducted by specialization, master's and PhD programs.
A complete search was carried out in three phases to identify published and unpublished literature on the core theme of this review: a preliminary search in the BVS, LILACS, Ovid, and SciELO databases using the keywords artificial respiration, pulmonary ventilation volume, algorithms, body size, mathematical concepts, reference values, body weight, ideal body weight in Spanish, English and Portuguese without time or language restriction. Additional keywords most frequently used in the relevant studies that met the inclusion criteria for this review were identified from the analysis of the results of the preliminary search.
A second search was conducted using all the keywords derived from the previous phase, but this time expanded to other databases (Redalyc and Google Scholar). In the final phase, the references listed in the articles and reviews previously selected were reviewed in depth to identify other studies and key authors to contact in order to identify primary studies or reviews not yet published or in process of publication. Time limits were not taken into account for the search and articles published in Spanish, English and Portuguese were included.
Key words sorted according to the PIO question were defined, allowing to develop a search equation with the main structured descriptors and qualifiers, and leading also to a higher degree of accuracy to localize linked terms in the articles included in the literature database of interest for the review. The general search was as follows: P -Respiration, Artificial OR Tidal Volume-. I -Algorithms OR Size OR mathematical concepts OR Reference values-. O -Body Weight OR Ideal Body Weight-.
A search restriction was established as a specificity strategy with the aim of eliminating noise or the number of irrelevant studies, achieving thoroughness, and arriving at the maximum possible number of studies that contained the information relating to the research question.
To initiate the search, the concepts in the BVS and PubMed portal databases were normalized. An advanced literature search was then conducted in the databases listed in Table 1, using DeCS/MeSH terms in English, Spanish and Portuguese, and a specific search equation for each.
TABLE 1 Database-specific search strategy.
| Database | Search equation | Results | Number of studies that met the inclusion criteria |
|---|---|---|---|
| Regional BVS portal (MEDLI-NE-LILACS-IBECS) | * (tw:(Respiration, Artificial)) OR (tw:(Tidal Volume)) AND (tw:(Algorithms)) OR (tw:(Reference values)) OR (tw:(ma-thematical concepts )) OR (tw:(Body Size)) AND (tw:(Body Weight)) OR (tw:(Ideal Body Weight)) | English: 245 Spanish: 51 Portuguese: 62 | 0 |
| SciELO | (respiración artificial) OR (peso ideal) OR (volumen de ventilación pulmonar) AND subject_area:("Health Sciences") AND wok_subject_categories:("medicine, general & internal" OR "anesthesiology" OR "nutrition & dietetics" OR "nursing" OR "medicine, research & experimental") | 177 | 4 |
| OVID (MEDLINE, ACP Journal Club, Cochrane, Database of Abstracts of Review of Effects, Health Technology Assessment, NHS Economic Evaluation Database). | Respiration, Artificial OR Tidal Volume AND Algorithms OR Body Size OR Mathematical Concepts OR Reference Values AND Body Weight OR Ideal Body Weight | 68 | 0 |
| Google Scholar | EQUATION #1: care OR intensive "IBW" With all words: IBW With at least one word: Intensive Care EQUATION #2: mechanical ventilation, height ,"ideal body weight" | # 1: 344 #2: 162 | #1: 3 #2: 6 |
| Redalyc | "Tidal volume" + "Ideal body weightl" | 20 | 3 |
*A search was conducted with this equation in English, Spanish and Portuguese.
SOURCE: Authors.
The database search was completed manually with the review of the bibliographic references of the articles retrieved, in order to ensure a thorough search. This process was repeated several times in order to make sure no useful studies were overlooked.
A search of the grey literature was also conducted through the Opengrey.eu site, with no results.
Data extraction
Having completed the identification and selection phase, the researchers read the articles and prepared a descriptive table with the most relevant data. One team member removed duplicate articles and screened the remaining studies based on the information extracted from the title, the abstract and the full text, classifying it as relevant and not relevant in accordance with the pre-determined inclusion criteria. Quality control of the selection process was performed by the second researcher who assessed the excluded articles in order to ensure that no relevant information was lost. No discrepancies between researchers occurred. Table 2 describes the characteristics of the articles: author, year of publication, country of origin and context of the study, objectives, study population, sample size, methodology, variables, intervention description, and results.
TABLE 2 Summary of study findings.
| Author, year/ country | Diagnosis | Study design | Sample size | Ideal weight equation | Purpose of obtaining ideal weight | Results |
|---|---|---|---|---|---|---|
| Olvera Guzmán et al., 2004 20/México | Group A: ARFS and Group B: no ARFS connected to MV | Prospective cohort study | 203 patients | 50th percentile of the Hispanic Health and Nutrition Examinations Survey | TV setting | Adequate adherence to international recommendations regarding the use of MV in patients with ARFS |
| Domínguez Cherit et al., 2009 21/ México | Influenza A H1N1 connected to MV | Clinical practice guideline | N/A | M: 50+2,3 [Height (inches)-60]F: 45.5+2.3 [Height (inches)-60] | TV settings | MV strategies defined in critically ill patients with Influenza A H1N1 and respiratory failure |
| Tominic et al., 2010 22/Chile | ARDS connected to MV | Review article | N/A | M: 50+0,91 χ (height in cm-152,4) F: 45.5+0.91 χ (height in cm-152.4) | Tidal volume settings in patients with ARDS | Mechanical ventilation settings in patients with ARDS is still controversial |
| Paredes et al., 2010 23/Ecuador | ARDS connected to MV | Prospective cohort studies | 24 patients | H: 50+0,91 χ (altura In cm-152,4) M:45,5+0,91 χ (altura en cm-152,4) | TV settings | Over a 2-month period, 24 patients were admitted to the ICU with suspected influenza A H1N1. All of the patients presented with severe hypoxemia on admission; 100% required MV; mortality in this group of patients with invasive and noninvasive ventilation was 16.6% |
| Seiberlich et al., 2011 24/ Brasil | ALI and ARDS connected to MV | Review article | N/A | M:50+0.91 χ (height in cm-152.4) F:45.5+0.91 χ (height in cm-152,4) | TV settings | Protective ventilation could minimize end-expiratory stretching and potential inflation/alveolar collapse |
| Gutiérrez Muñoz, 2011 18/Perú | ARFS connected to MV | Review article | N/A | M:50+0.91 χ (height in cm-152.4) F:45.5+0.91 χ (height in cm-152.4) | Initial settings/TV change | Detailed description of the mechanical ventilator, use mode, ventilation parameters, indications and physiological effects |
| Bugedo et al., 2014 25/ Chile | Brain death connected to MV | Review article | N/A | M:50+0.91 χ (height in cm-152.4) F:45,5+0.91 χ (height in cm-152.4) | TV settings in the potential cadaver donor | It is essential to maintain adequate perfusion, protective ventilation strategy and metabolic/hormonal support of the potential cadaver donor |
| Rocha Rossi et al., 2014 26/Brasil | Obesity connected to MV | Review article | N/A | M:50+0.91 χ (height in cm-152.4) F:45.5+0.91 χ (height in cm-152.4) | TV settings | Existing data suggest protective ventilation strategy with low TV, recruitment maneuvers and higher PEEP in obese patients during surgery. |
| Gálvez Blanco et al., 2017 27/México | Patients subjected to NIMV | Retrospective observational study | 40 patients | H: (Height in cm-152.4) χ 0.91+50 M: (Height in cm-152.4) χ 0.91+45.5 | TV monitoring as predictor of NIMV failure | Initial TV and after 6 hours of NIMV is not a predictor of failure of this therapy |
ALI: acute pulmonary injury; ARDS: acute respiratory distress syndrome; ARFS: acute respiratory failure syndrome; MV: mechanical ventilation; NIMV: non-invasive mechanical ventilation; N/A: not applicable; PEEP: positive end-expiratory pressure: TV: tidal volume.
SOURCE: Authors.
Presentation of the results
The results of the review are presented in descriptive tables that show relevant aspects pertaining to the studies, including study type, type of population, sample size, country of origin of the study, equation used. Moreover, a flow diagram describing the search process and the final number of studies included is presented.
RESULTS
Overall, 1,126 studies were identified using the search equations. Following the initial selection, relevance in relation to the inclusion and exclusion criteria was assessed, resulting in 1,120 studies discarded, and 6 retained; 3 additional studies were identified through the manual search from the list of references that met the inclusion criteria. Ultimately, this review included a total number of 9 studies (Figure 2).
Of the selected studies, 56% were review articles, 22% were prospective cohort studies, 11% were clinical practice guidelines and 11% were retrospective observational studies.
The studies found were published over a 13-year period, between 2004 and 2017. In 100% of the studies, it was found that the ideal weight calculation was used for calculating tidal volume. Studies were carried out in Chile, Brazil, Mexico, Ecuador and Peru.
Various disease conditions were identified in the articles, the highest in percentage terms being acute respiratory distress syndrome (ARDS) (33.3%), followed by acute respiratory failure syndrome (ARFS) (22,2%), acute lung injury (11.1%), and influenza A H1N1 (11.1%). Of the included studies, 89% used the ARDSnet equation for ideal weight calculation. Only one study, carried out in Mexico, used the 50th percentile equation of the Hispanic Health and Nutrition Examinations Survey (Table 3).
TABLE 3 Summary and characterization of the studies.
| Author | Sample | Diagnosis | Year | Equation | Country |
|---|---|---|---|---|---|
| Olvera Guzmán et al. 20 | N/A | Group A: Patients with ARFS and Group B: patients without ARFS | 2004 | 50th percentile of the Hispanic Health and Nutrition Examinations Survey | México |
| Domínguez et al. 21 | N/A | Influenza A H1N1 | 2009 | ARDSnet | México |
| Tominic et al. 22 | N/A | ARDS | 2010 | ARDSnet | Chile |
| Paredes et al. 23 | 24 patients/ARDS | 2010 | ARDSnet | Ecuador | |
| Seiberlich et al. 24 | N/A | Patients without pulmonary injury, patients with ALI and ARDS | 2011 | ARDSnet | Brasil |
| Gutiérrez 18 | N/A | Patients with ARFS | 2011 | ARDSnet | Perú |
| Bugedo et al. 25 | N/A | Patients with brain death | 2014 | ARDSnet | Chile |
| Rocha et al. 26 | N/A | Obese patients | 2014 | ARDSnet | Brasil |
| Gálvez et al. 27 | 40 patients/Patients with hypoxemic ARFS | 2017 | ARDSnet | México |
ALI: acute lung injury; ARDS: acute respiratory distress syndrome; ARFS: acute respiratory failure syndrome; N/A: not applicable.
SOURCE: Authors.
DISCUSSION
This review explored the evidence related to the use of equations for estimating ideal weight in adult patients on mechanical ventilation in Latin American ICUs.
This evidence review found that in countries like Mexico, Ecuador, Chile, Peru and Brazil the ARDSnet equation is used for calculating ideal weight in critically ill patients. This equation, created in 2000 from the ARMA study 6 was the most widely reported despite the fact that it was created on the basis of anthropometric measurements and estimations in people with very different biotypes, ethnicity and race when compared to the Latin American population, potentially giving rise to over or understimations, thus affecting their specific use.
In terms of the design and methodology of the 9 studies included in the review, 56% were reviews, 22% prospective cohort studies, and none of them described in the methodology the height measurement protocol used for calculating ideal weight with the ARDSnet.
Research studies and clinical practice guidelines indicate ideal weight calculation in patients on mechanical ventilation using the ARDSnet calculation, which includes body height and gender as variables: males: 50+0.91X (height in cm-152.4) and females: 45.5+0.91 χ (height in cm-152.4). However, no standardized methods are described for accurate and reliable measurement of body height in critically ill patients. Similar to the results found in a survey conducted by García-Martínez et al. 28, it is the opinion of the authors of this review that units where no weighing tools are available (hanging scales or bed scales), continue to use visual and subjective estimates.
The studies in this review found that, in Latin America, the clinical conditions in which the ARDSnet equation was used for calculating ideal weight were ARDS (33%), acute respiratory failure (22%) and A H1N1 pneumonia (11%), perhaps due to the fact that the ARMA study, from which the equation was derived, proposed low-volume lung ventilation (6 mL/kg/ideal weight) as a strategy, showing that mortality was lower and there were fewer ventilation-related complications 6. However, although the equation requires measuring body height, none of the studies describe the technique or the standardization of the measurement protocol.
In the absence of predictive equations for calculating ideal weight in critically ill patients designed for the Latin American population, the ARDSnet equation continues to be the best option, which implies the need for accurate height measurement.
With this review, the authors highlight the importance of standardizing and/ or formalizing height measurements in critically ill patients, and the influence of the method utilized on the interpretation of the clinical outcomes; and, moreover, of creating interest regarding the design of predictive equations for the calculation of ideal weight based on anthropometric variables in the Latin American population. Future research should focus on the design and validation of equations in our population.
The strength of this review lies in the selection process guided by the Joanna Briggs Institute (JBI) tool. Difficulty searching the grey literature in an attempt at identifying relevant unpublished material was found to be a limitation.
In conclusion the equation proposed by the ARDSnet is the most widely used in adult intensive care units in Latin America for calculating ideal body weight.
ACKNOWLEDGEMENTS
Author's contributions
HAPS and JLEZ. Study planning, data collection, interpretation of the results, data analysis and initial and final drafting of the manuscript.
ECWL. Conception of the original project, study planning, interpretation of the results, and drafting and approval of the final manuscript.
