Validation of bioelectrical impedance analysis for body composition assessment in children with obesity aged 8-14y.

BACKGROUND & AIMS: The aim was to generate a predictive equation to assess body composition (BC) in children with obesity using bioimpedance (BIA), and avoid bias produced by different density levels of fat free mass (FFM) in this population. METHODS: This was a cross-sectional validation study using baseline data from a randomized intervention trial to treat childhood obesity. Participants were 8 to 14y (n = 315), underwent assessments on anthropometry and BC through Air Displacement Plethysmography (ADP), Dual X-Ray Absorptiometry and BIA. They were divided into a training (n = 249) and a testing subset (n = 66). In addition, the testing subset underwent a total body water assessment using deuterium dilution, and thus obtained results for the 4-compartment model (4C). A new equation to estimate FFM was created from the BIA outputs by comparison to a validated model of ADP adjusted by FFM density in the training subset. The equation was validated against 4C in the testing subset. As reference, the outputs from the BIA device were also compared to 4C. RESULTS: The predictive equation reduced the bias from the BIA outputs from 14.1% (95%CI: 12.7, 15.4) to 4.6% (95%CI: 3.8, 5.4) for FFM and from 18.4% (95%CI: 16.9, 19.9) to 6.4% (95% CI: 5.3, 7.4) for FM. Bland-Altman plots revealed that the new equation significantly improved the agreement with 4C; furthermore, the observed trend to increase the degree of bias with increasing FM and FFM also disappeared. CONCLUSION: The new predictive equation increases the precision of BC assessment using BIA in children with obesity.

Five-component model validation of reference, laboratory and field methods of body composition assessment.

This study reports the validity of body fat percentage (BF%) estimates from several commonly employed techniques as compared with a five-component (5C) model criterion. Healthy adults (n 170) were assessed by dual-energy X-ray absorptiometry (DXA), air displacement plethysmography (ADP), multiple bioimpedance techniques and optical scanning. Output was also used to produce a criterion 5C model, multiple variants of three- and four-component models (3C; 4C) and anthropometry-based BF% estimates. Linear regression, Bland-Altman analysis and equivalence testing were performed alongside evaluation of the constant error (CE), total error (TE), se of the estimate (SEE) and coefficient of determination (R2). The major findings were (1) differences between 5C, 4C and 3C models utilising the same body volume (BV) and total body water (TBW) estimates are negligible (CE ≤ 0·2 %; SEE < 0·5 %; TE ≤ 0·5 %; R2 1·00; 95 % limits of agreement (LOA) ≤ 0·9 %); (2) moderate errors from alternate TBW or BV estimates in multi-component models were observed (CE ≤ 1·3 %; SEE ≤ 2·1 %; TE ≤ 2·2 %; R2 ≥ 0·95; 95 % LOA ≤ 4·2 %); (3) small differences between alternate DXA (i.e. tissue v. region) and ADP (i.e. Siri v. Brozek equations) estimates were observed, and both techniques generally performed well (CE < 3·0 %; SEE ≤ 2·3 %; TE ≤ 3·6 %; R2 ≥ 0·88; 95 % LOA ≤ 4·8 %); (4) bioimpedance technologies performed well but exhibited larger individual-level errors (CE < 1·0 %; SEE ≤ 3·1 %; TE ≤ 3·3 %; R2 ≥ 0·94; 95 % LOA ≤ 6·2 %) and (5) anthropometric equations generally performed poorly (CE 0·6- 5·7 %; SEE ≤ 5·1 %; TE ≤ 7·4 %; R2 ≥ 0·67; 95 % LOA ≤ 10·6 %). Collectively, the data presented in this manuscript can aid researchers and clinicians in selecting an appropriate body composition assessment method and understanding the associated errors when compared with a reference multi-component model.

Automatic unsupervised respiratory analysis of infant respiratory inductance plethysmography signals.

Infants are at risk for potentially life-threatening postoperative apnea (POA). We developed an Automated Unsupervised Respiratory Event Analysis (AUREA) to classify breathing patterns obtained with dual belt respiratory inductance plethysmography and a reference using Expectation Maximization (EM). This work describes AUREA and evaluates its performance. AUREA computes six metrics and inputs them into a series of four binary k-means classifiers. Breathing patterns were characterized by normalized variance, nonperiodic power, instantaneous frequency and phase. Signals were classified sample by sample into one of 5 patterns: pause (PAU), movement (MVT), synchronous (SYB) and asynchronous (ASB) breathing, and unknown (UNK). MVT and UNK were combined as UNKNOWN. Twenty-one preprocessed records obtained from infants at risk for POA were analyzed. Performance was evaluated with a confusion matrix, overall accuracy, and pattern specific precision, recall, and F-score. Segments of identical patterns were evaluated for fragmentation and pattern matching with the EM reference. PAU exhibited very low normalized variance. MVT had high normalized nonperiodic power and low frequency. SYB and ASB had a median frequency of respectively, 0.76Hz and 0.71Hz, and a mode for phase of 4o and 100o. Overall accuracy was 0.80. AUREA confused patterns most often with UNKNOWN (25.5%). The pattern specific F-score was highest for SYB (0.88) and lowest for PAU (0.60). PAU had high precision (0.78) and low recall (0.49). Fragmentation was evident in pattern events <2s. In 75% of the EM pattern events >2s, 50% of the samples classified by AUREA had identical patterns. Frequency and phase for SYB and ASB were consistent with published values for synchronous and asynchronous breathing in infants. The low normalized variance in PAU, was consistent with published scoring rules for pediatric apnea. These findings support the use of AUREA to classify breathing patterns and warrant a future evaluation of clinically relevant respiratory events.

Utility of published skinfold thickness equations for prediction of body composition in very young New Zealand children.

Measurement of body composition is increasingly important in research and clinical settings but is difficult in very young children. Bioelectrical impedance analysis (BIA) and air displacement plethysmography (ADP) are well-established but require specialist equipment so are not always feasible. Our aim was to determine if anthropometry and skinfold thickness measurements can be used as a substitute for BIA or ADP for assessing body composition in very young New Zealand children. We used three multi-ethnic cohorts: 217 children at a mean age of 24·2 months with skinfold and BIA measurements; seventy-nine infants at a mean age of 20·9 weeks and seventy-three infants at a mean age of 16·2 weeks, both with skinfold and ADP measurements. We used Bland-Altman plots to compare fat and fat-free mass calculated using all potentially relevant equations with measurements using BIA or ADP. We also calculated the proportion of children in the same tertile for measured fat or fat-free mass and tertiles (i) calculated using each equation, (ii) each absolute skinfold, and (iii) sum of skinfold thicknesses. We found that even for the best equation for each cohort, the 95 % limits of agreement with standard measures were wide (25-200 % of the mean) and the proportion of children whose standard measures fell in the same tertile as the skinfold estimates was ≤69 %. We conclude that none of the available published skinfold thickness equations provides good prediction of body composition in multi-ethnic cohorts of very young New Zealand children with different birth history and growth patterns.

Development of a dual-energy X-ray absorptiometry-derived body volume equation in Hispanic adults for administering a four-compartment model.

The purpose of the present study was: (1) to develop a new dual-energy X-ray absorptiometry (DXA)-derived body volume (BV) equation with the GE-Lunar prodigy while utilising underwater weighing (UWW) as a criterion and (2) to cross-validate the novel DXA-derived BV equation (4C-DXANickerson), Wilson DXA-derived BV equation (4C-DXAWilson) and air displacement plethysmography (ADP)-derived BV (4C-ADP) in Hispanic adults. A total of 191 Hispanic adults (18-45 years) participated in the present study. The development sample consisted of 120 females and males (50 % females), whereas the cross-validation sample comprised of forty-one females and thirty males (n 71). Criterion body fat percentage (BF %) and fat-free mass (FFM) were determined using a four-compartment (4C) model with UWW as a criterion for BV (4C-UWW). 4C-DXANickerson, 4C-DXAWilson and 4C-ADP were compared against 4C-UWW in the cross-validation sample. 4C-DXANickerson, 4C-DXAWilson and 4C-ADP all produced similar validity statistics when compared with 4C-UWW in Hispanic males (all P > 0·05). 4C-DXANickerson also yielded similar BF % and FFM values as 4C-UWW when evaluating the mean differences (constant error (CE)) in Hispanic females (CE = -0·79 % and 0·38 kg; P = 0·060 and 0·174, respectively). However, 4C-DXAWilson produced significantly different BF % and FFM values (CE = 3·22 % and -2·20 kg, respectively; both P < 0·001). Additionally, 4C-DXAWilson yielded significant proportional bias when estimating BF % (P < 0·001), whereas 4C-ADP produced significant proportional bias for BF % and FFM (both P < 0·05) when evaluated in Hispanic females. The present study findings demonstrate that 4C-DXANickerson is a valid measure of BV in Hispanics and is recommended for use in clinics, where DXA is the main body composition assessment technique.

The Accuracy of Respiratory Calibration Methods for Estimating Lung Volume During Speech Breathing: A Comparison of Four Methods Across Three Adult Cohorts.

Purpose This study evaluated the accuracy of respiratory calibration methods for estimating lung volume during speech breathing. Method Respiratory kinematic data were acquired via inductance plethysmography in 32 young adults, 22 older adults, and 13 older adults with Parkinson's disease (PD). Raw rib cage (RC) and abdomen (AB) signals (V) were calibrated to liters using 4 correction methods: (a) isovolume maneuvers, (b) a constant 2:1 RC-to-AB ratio, (c) least squares method with RC correction only (LsqRC), and (d) least squares method with both RC and AB corrections (LsqRC/AB). Mean percent error, the absolute difference between estimated and actual lung volumes then normalized to each speaker's vital capacity, was calculated for each method. Results For young adults, the LsqRC/AB method significantly reduced mean percent error compared to all other methods. Although LsqRC/AB also resulted in smaller errors for older adults and adults with PD, LsqRC/AB and LsqRC were not significantly different from one another in these groups. Conclusion The LsqRC/AB method reduces errors across all cohorts, but older adults and adults with PD also have reduced errors when using LsqRC. Further research should investigate both least squares methods across larger age and disease severity ranges.

Comparison of Forced and Slow Vital Capacity Maneuvers in Defining Airway Obstruction.

BACKGROUND: Obstructive lung disease is diagnosed by a decreased ratio of FEV1 to the vital capacity (VC). Although the most commonly used VC is FVC, American Thoracic Society guidelines suggest alternative VCs, for example, slow VC (SVC), may offer a more-accurate evaluation of breathing capacity. There is recent evidence that using only FEV1/FVC underrecognizes obstruction in subjects at high risk and who are symptomatic. Previous studies have indicated that healthy individuals show a minimum difference between FVC and SVC; however, testing of individuals with asthma and who are symptomatic indicates that SVC can be markedly larger than FVC. OBJECTIVE: To evaluate the differences among SVC, FVC, and SVC-based measurements in the diagnosis of symptomatic obstructive lung disease. METHODS: A retrospective analysis was performed of spirometry and plethysmography measurements from studies conducted between 2011 to 2015. We established a pulmonary function database that incorporated predictive equations from the National Health and Nutrition Examination Survey III (NHANES III). The SVC to FVC difference was calculated. FEV1/SVC was compared with FEV1/FVC by using NHANES III lower limit of normal values. RESULTS: A total of 2,710 studies with 2,244 subjects were reviewed. Spirometric obstruction, as defined by NHANES III, was identified in 26.1% of the studies (707/2,710). The mean (± SD) difference between SVC and FVC was 375.0 ± 623.0 mL and 258.8 ± 532.5 mL in those with and those without obstruction, respectively. Subgroup and multivariate analysis demonstrated age, body mass index, and FEV1 associated contributions to the difference between SVC and FVC. By using FEV1/SVC, the prevalence of obstruction increased from 26.1 to 45.0% (1,219/2,710) and identified 566 additional studies of subjects with obstruction. Fifty-four percent of the subjects with newly-identified obstructive lung disease (305/566) had smoking histories, and 67.4% (345/512) received medications for obstructive lung disease. CONCLUSIONS: The isolated use of FVC-based diagnostic algorithms did not recognize individuals with symptomatic obstructive lung disease. Recognizing the difference between SVC and FVC measurements in subjects will improve testing and diagnosis of obstructive lung disease.

Fat mass estimation in neonates: anthropometric models compared with air displacement plethysmography.

Newborn adiposity, a nutritional measure of the maternal-fetal intra-uterine environment, is representative of future metabolic health. An anthropometric model using weight, length and flank skinfold to estimate neonatal fat mass has been used in numerous epidemiological studies. Air displacement plethysmography (ADP), a non-invasive technology to measure body composition, is impractical for large epidemiological studies. The study objective was to determine the consistency of the original anthropometric fat mass estimation equation with ADP. Full-term neonates were studied at 12-72 h of life with weight, length, head circumference, flank skinfold thickness and ADP measurements. Statistical analyses evaluated three models to predict neonatal fat mass. Lin's concordance correlation coefficient, mean prediction error and root mean squared error between the predicted and observed ADP fat mass values were used to evaluate the models, where ADP was considered the gold standard. A multi-ethnic cohort of 468 neonates were studied. Models (M) for predicting fat mass were developed using 349 neonates from site 1, then independently evaluated in 119 neonates from site 2. M0 was the original anthropometric model, M1 used the same variables as M0 but with updated parameters and M2 additionally included head circumference. In the independent validation cohort, Lin's concordance correlation estimates demonstrated reasonable accuracy (model 0: 0·843, 1: 0·732, 2: 0·747). Mean prediction error and root mean squared error in the independent validation was much smaller for M0 compared with M1 and M2. The original anthropometric model to estimate neonatal fat mass is reasonable for predicting ADP, thus we advocate its continued use in epidemiological studies.

Practical measurement of body composition using bioelectrical impedance, air displacement plethysmography and ultrasound in stable outpatients with short bowel syndrome receiving home parenteral nutrition: comparison of agreement between the methods.

BACKGROUND: People diagnosed with intestinal failure (IF) as a result of short bowel syndrome are dependent on home parenteral nutrition (HPN). Measuring nutritional status is essential for monitoring treatment. The present study aimed to determine the agreement and feasibility of three methods bioelectrical impedance analysis (BIA), ultrasound and air displacement plethysmography (ADP) for measuring body composition in people receiving HPN. METHODS: Body composition data were collected from patients attending an IF clinic. RESULTS: There were 50 participants recruited and data were collected for BIA (n = 46), ultrasound (n = 49) and ADP (n = 9). Numbers for ADP were much lower because of a lack of participant uptake. Fat-free mass (FFM) measured by BIA and ultrasound in comparison to ADP was found to have good intraclass correlation (ICC) 0.791 (95% confidence interval (CI) CI  -0.21 to 0.96) and a moderate ICC 0.659 [95% (CI) -0.27 to 0.92], respectively. Fat mass (FM) measured by both BIA and ultrasound in comparison to ADP was found to have moderate ICC 0.660 (95% CI -0.28 to 0.92) and poor ICC -0.005 (95% CI -0.73 to 0.65), respectively. CONCLUSIONS: Compared to ADP, BIA indicated moderate to good agreement for measuring body composition, whereas ultrasound indicated far less agreement, particularly when measuring FM. The lack of uptake of ADP suggests that participants found the Bodpod (COSMED Srl, Shepperton, UK) unfavourable. Considering that ultrasound has limited agreement and ADP was not the preferred option for participants, BIA shows some potential. However, the difference between ADP and BIA was larger for FM compared to FFM, which needs to be considered in the clinical setting.

Quantitative Analysis of Thoracoabdominal Asynchrony in Pediatric Polysomnography.

STUDY OBJECTIVES: Objective measurements of thoracoabdominal asynchrony (TAA), such as average phase angle (θavg), can quantify airway obstruction. This study demonstrates and evaluates use of θavg for predicting obstructive sleep apnea (OSA) in pediatric polysomnography (PSG). METHODS: This prospective observational study recruited otherwise healthy 3- to 8-year-old children presenting for PSG due to snoring, behavioral problems, difficulty sleeping, and/or enlarged tonsils. Respiratory inductance plethysmography (RIP) was directly monitored and data were collected during each PSG. θavg and average labored breathing index (LBIavg) were calculated for earliest acceptable 5-minute periods of stage N3 sleep and stage R sleep. Associations between θavg and obstructive apnea index (OAI) and obstructive apnea-hypopnea index (OAHI), as well as between LBIavg and OAI and OAHI, were examined. RESULTS: Forty patients undergoing PSG were analyzed. Thirty percent of patients had OSA, 57.5% had enlarged tonsils, and 17.5% were obese. θavg during stage N3 sleep and stage R sleep had significant positive correlations with OAI (Spearman r = .35 [P = .03] and .40 [P = .01], respectively) and θavg during stage N3 sleep with OAHI (r = .35 [P = .03]). LBIavg showed lower correlations. Median θavg during stage R sleep (33.1) was significantly greater than during stage N3 sleep (13.7, P = .0005). CONCLUSIONS: Association of θavg with OAI and OAHI shows that θavg reflects airway obstruction and has potential use as a quantitative indicator of OSA. RIP provides valuable information that is readily available in PSG. The significant difference between θavg in stage N3 sleep and stage R sleep confirms the clinical observation that there is more asynchrony during rapid eye movement sleep than non-rapid eye movement sleep.

Comparison of Total Lung Capacity Determined by Plethysmography With Computed Tomographic Segmentation Using CALIPER.

PURPOSE: Traditionally, determination of total lung capacity (TLC) by plethysmography (TLCpleth) has been important in the diagnosis of lung diseases. Alternatively, data acquired from computerized tomography (CT) can be utilized to calculate a measure of TLC (TLCCT). The clinical utility of TLCCT is not certain. We sought to determine, in a clinical setting, whether TLCCT correlates with TLCpleth across a range of lung diseases and scanning techniques. In addition, we determined whether TLCCT affects the interpretation of pulmonary function tests. SUBJECTS AND METHODS: Records of 118 of 148 consecutive lung transplant recipients were reviewed and determined to have coinciding pulmonary function tests, including plethysmography as well as volumetric chest CT performed supine during full inspiration. CT images acquired with a wide range of scanning protocols were analyzed using CALIPER, a software program for lung and trachea extraction from a CT volume and volumetric tissue characterization of the lung. Segmentation of the lung was achieved by using completely automated dynamic thresholding and region-growing techniques developed to extract the relatively low-density lung and tracheal anatomy from the CT data set without user intervention. RESULTS: TLCpleth and TLCCT were strongly related with a correlation coefficient of 0.88 (P<0.001). The efficacy of the CT-derived measure was not influenced by specific lung diagnoses, age, height, body mass index, or spirometric parameters. TLCCT did not misidentify any diagnosis of restrictive lung disease, nor hyperinflation. CONCLUSIONS: In a clinical setting, CT segmentation analysis provides a favorable determination of TLC compared with traditional plethysmography. The technique has general applicability across varying CT data acquisition protocols, lung diseases, and patient characteristics. TLCCT may substitute for TLCpleth in pulmonary function interpretation and may be preferable for some patients in whom plethysmography is difficult to perform, such as transplant subjects with severe pulmonary fibrosis.

Intraoperative Pleth Variability Index Is Linked to Delayed Graft Function After Kidney Transplantation.

BACKGROUND: Delayed graft function (DGF) is an early postoperative complication of kidney transplantation (KT) predisposing to acute rejection and lower graft survival. Intraoperative arterial hypotension and hypovolemia are associated with DGF. Central venous pressure (CVP) is used to estimate volemia but its reliability has been criticized. Pleth variability index (PVI) is a hemodynamic parameter predicting fluid responsiveness. The aim of this study was to examine the relationship between intraoperative PVI and CVP values and the occurrence of DGF. METHODS: This was a prospective, noninterventional, observational, single-center study. All consecutive patients with KT from deceased donors were included. Recipients received standard, CVP, and PVI monitoring. Intraoperative hemodynamic parameters were recorded from recipients at 5 time points during KT. RESULTS: Forty patients were enrolled. There was a poor correlation between PVI and CVP values (r2 = 0.003; P = .44). Immediate graft function and DGF patients had similar hemodynamic values during KT, with the exception of PVI values, which were significantly higher in the DGF group. In particular, a PVI >9% before unclamping of the renal artery was the only predictive parameter of DGF in our multivariate analysis (P = .02). CONCLUSIONS: This study suggests that PVI values >9% during KT are associated with the occurrence of DGF.

Predicted versus measured thoracic gas volumes of collegiate athletes made by the BOD POD air displacement plethysmography system.

Measured (TGVm) and predicted (TGVp) thoracic gas volumes from the BOD POD were compared in 33 lean, university athletes. On average, TGVp (3.529 L) was not significantly different (p = 0.343) from TGVm (3.628 L); however, there was a bias (r = -0.703, p < 0.001). The difference in the percentage of body fat (BF) was within ±2% BF for 76% of the sample, but athletes at the extremes of height should have TGV measured.

The influence of supine posture on chest wall volume changes is higher in obese than in normal weight children.

The objective of this study was to analyze thoraco-abdominal kinematics in obese children in seated and supine positions during spontaneous quiet breathing. An observational study of pulmonary function and chest wall volume assessed by optoelectronic plethysmography was conducted on 35 children aged 8-12 years that were divided into 2 groups according to weight/height ratio percentiles: there were 18 obese children with percentiles greater than 95 and 17 normal weight children with percentiles of 5-85. Pulmonary function (forced expiratory volume in 1 s (FEV1); forced vital capacity (FVC); and FEV1/FVC ratio), ventilatory pattern, total and compartment chest wall volume variations, and thoraco-abdominal asynchronies were evaluated. Tidal volume was greater in seated position. Pulmonary and abdominal rib cage tidal volume and their percentage contribution to tidal volume were smaller in supine position in both obese and control children, while abdominal tidal volume and its percentage contribution was greater in the supine position only in obese children and not in controls. No statistically significant differences were found between obese and control children and between supine and seated positions regarding thoraco-abdominal asynchronies. We conclude that in obese children thoraco-abdominal kinematics is influenced by supine posture, with an increase of the abdominal and a decreased rib cage contribution to ventilation, suggesting that in this posture areas of hypoventilation can occur in the lung.

Non-invasive blood haemoglobin and plethysmographic variability index during brachial plexus block.

BACKGROUND: Plethysmographic measurement of haemoglobin concentration ([Formula: see text]), pleth variability index (PVI), and perfusion index (PI) with the Radical-7 apparatus is growing in popularity. Previous studies have indicated that [Formula: see text] has poor precision, particularly when PI is low. We wanted to study the effects of a sympathetic block on these measurements. METHODS: Twenty patients underwent hand surgery under brachial plexus block with one Radical-7 applied to each arm. Measurements were taken up to 20 min after the block had been initiated. Venous blood samples were also drawn from the non-blocked arm. RESULTS: During the last 10 min of the study, [Formula: see text] had increased by 8.6%. The PVI decreased by 54%, and PI increased by 188% in the blocked arm (median values). All these changes were statistically significant. In the non-blocked arm, these parameters did not change significantly. CONCLUSIONS: Brachial plexus block significantly altered [Formula: see text], PVI, and PI, which indicates that regional nervous control of the arm greatly affects plethysmographic measurements obtained by the Radical-7. After the brachial plexus block, [Formula: see text] increased and PVI decreased.

Pleth variability index predicts fluid responsiveness in mechanically ventilated adults during general anesthesia for noncardiac surgery.

OBJECTIVE: To investigate whether the pleth variability index (PVI), derived noninvasively from a pulse oximeter probe, would predict fluid responsiveness in patients undergoing noncardiac surgeries. DESIGN: A clinical, prospective, observational study. SETTING: Operating room of a tertiary care hospital. PARTICIPANTS: Twenty-nine adult patients undergoing a range of noncardiac surgeries, requiring general anesthesia, tracheal intubation, and mechanical ventilation. INTERVENTIONS: Intravenous volume expansion with 500 mL of colloid following induction of general anesthesia and after a period of hemodynamic stability before the start of surgery. MEASUREMENTS AND MAIN RESULTS: Baseline values for PVI and stroke volume index, derived from an esophageal Doppler monitor, were compared with final values after the volume expansion. Patients were classified into fluid responders and nonresponders based on a stroke volume index increase of ≥ 10%. The optimal cut-off value for baseline pleth variability index for predicting fluid responsiveness was determined. There were 17 responders (59%) to the 500-mL volume expansion. Baseline PVI value was significantly different between responders and nonresponders (16.5 ± 6.4% v 10.3 ± 2.7%; p = 0.004). Receiver operating characteristic analysis demonstrated significant predictive ability of an increase in stroke volume index for PVI with area under the curve of 0.84 (95% confidence interval = 0.69-0.99). The optimal cut-off value for baseline PVI was 10.5%, with a sensitivity of 88% and a specificity of 67%. CONCLUSIONS: Pleth variability index is predictive of fluid responsiveness in adult patients undergoing noncardiac surgery.

Evaluation of cardiac output in intensive care using a non-invasive arterial pulse contour technique (Nexfin(®)) compared with echocardiography.

In this prospective study, cardiac output was measured in 38 intensive care unit patients before and after a fluid challenge, using both pulse contour analysis (Nexfin(®); BMEYE, Amsterdam, the Netherlands) and transthoracic echocardiography. The ability of the Nexfin device to detect significant changes in the velocity-time integral was evaluated. The pulse wave could not be detected by the Nexfin device in five patients (13%), leaving 33 patients for analysis. The Nexfin device adequately tracked changes in the velocity-time integral in 20 (61%) patients. Using a cut-off of a 10% increase in cardiac output estimated by the Nexfin or by echocardiography, the sensitivity of the Nexfin device to detect a response to fluid challenge was 47%, with specificity 81% and accuracy 64%. The percentage error between the Nexfin and echocardiography was 448%; lower limit of agreement -48% (95% CI -62 to -36%) and upper limit of agreement, 32% (95% CI 20-45%). We conclude that the Nexfin device does not adequately track changes in cardiac output in critically ill patients.

Poor asthma control in obese children may be overestimated because of enhanced perception of dyspnea.

BACKGROUND: Although studies in adults have shown a non-TH2 obese asthma phenotype, whether a similar phenotype exists in children is unclear. OBJECTIVE: We hypothesized that asthmatic children with obesity, defined as a body mass index above the 95th percentile for age and sex, would have poorer asthma control as well as decreased quality of life, increased health care utilization, and decreased pulmonary function measures as a function of increased TH1 versus TH2 polarization. METHODS: This study involved a post hoc analysis of cross sectional data from 269 children 6 to 17 years of age enrolled in the National Heart, Lung, and Blood Institute Severe Asthma Research Program. Children answered questionnaires and underwent spirometry, plethysmography, exhaled nitric oxide determination, and venipuncture for TH1/TH2 cytokine determination. Asthma control was defined according to national asthma treatment guidelines that are based on prespecified thresholds for lung function and symptom frequency. RESULTS: Fifty-eight children (22%) were overweight and 67(25%) were obese. Obese children did not have poorer asthma control but were more likely to report nonspecific symptoms such as dyspnea and nocturnal awakenings. Obese children did have decreased asthma-related quality of life and increased health care utilization, but this was not associated with airflow limitation. Instead, obese children had decreased functional residual capacity. A unique pattern of TH1 or TH2 polarization was not observed. CONCLUSIONS: Poor asthma control in obese children with asthma may be overestimated because of enhanced perception of nonspecific symptoms such as dyspnea that results from altered mechanical properties of the chest wall. Careful assessment of physiologic as well as symptom-based measures is needed in the evaluation of obese children with respiratory symptoms.

Plethysmographic variability index (PVI) accuracy in predicting fluid responsiveness in anesthetized children.

INTRODUCTION: Plethysmographic Variability Index (PVI) has been shown to accurately predict responsiveness to fluid loads in adults. The goal of this study was to evaluate PVI accuracy when predicting fluid responsiveness during noncardiac surgery in children. MATERIAL AND METHODS: Children aged 2-10 years scheduled for noncardiac surgery under general anesthesia were included. PVI was assessed concomitantly with stroke volume index (SVI). A response to fluid load was defined by an SVI increase of more than 15%. A 10 ml·kg(-1) normal saline intravenous fluid challenge was administered before surgical incision and after anesthetic induction. After incision, fluid challenges were administered when SVI values decreased by more than 15% or where judged necessary by the anesthesiologist. Statistical analyses include receiving operator characteristics (ROC) analysis and the determination of gray zone method with an error tolerance of 10%. RESULTS: Fifty-four patients were included, 97 fluid challenges administered and 45 responses recorded. Area under the curve of ROC curves was 0.85 [0.77-0.93] and 0.8 [0.7-0.89] for baseline PVI and SVI values, respectively. Corresponding gray zone limits were [10-17%] and [22-31 ml·m(-2)], respectively. PVI values exhibited different gray zone limits for pre-incision and postincision fluid challenges, whereas SVI values were comparable. PVI value percentages in the gray zone were 34% overall and 44% for challenges performed after surgical incision. DISCUSSION: This study found both PVI and prechallenge SVI to be accurate when used to predict fluid load response during anesthetized noncardiac surgery in children. However, a third of recorded PVI values were inconclusive.

Pleth variability index is a weak predictor of fluid responsiveness in patients receiving norepinephrine.

BACKGROUND: In patients receiving an infusion of norepinephrine, the relationship between the amplitude of the oximeter plethysmographic waveform and stroke volume may be variable and quality of the waveform might be reduced, compared with patients not receiving norepinephrine. We assessed the reliability of the pleth variability index (PVI), an automatic measurement of the respiratory variation of the plethysmographic waveform, for predicting fluid responsiveness in patients receiving norepinephrine infusions. METHODS: We measured the response of cardiac index (transpulmonary thermodilution) to i.v. fluid administration in 42 critically ill patients receiving norepinephrine. Patients with arrhythmias, spontaneous breathing, tidal volume <8 ml kg(-1), and respiratory system compliance <30 ml cm H(2)O(-1) were excluded. Before fluid administration, we recorded the arterial pulse pressure variation (PPV) and pulse contour analysis-derived stroke volume variation (SVV, PiCCO2) and PVI (Masimo Radical-7). RESULTS: In seven patients, the plethysmographic signal could not be obtained. Among the 35 remaining patients [mean SAPS II score=77 (sd=17)], i.v. fluid increased cardiac index ≥15% in 15 'responders'. A baseline PVI ≥16% predicted fluid responsiveness with a sensitivity of 47 (inter-quartile range=21-73)% and a specificity of 90 (68-99)%. The area under the receiver operating characteristic curve was significantly lower for PVI [0.68 (0.09)] than for PPV and SVV [0.93 (0.06) and 0.89 (0.07), respectively]. Considering all pairs of measurements, PVI was correlated with PPV (r(2)=0.27). The fluid-induced changes in PVI and PPV were not significantly correlated. CONCLUSIONS: PVI was less reliable than PPV and SVV for predicting fluid responsiveness in critically ill patients receiving norepinephrine. In addition, PVI could not be measured in a significant proportion of patients. This suggests that PVI is not useful in patients receiving norepinephrine.