The ratio of means method as an alternative to mean differences for analyzing continuous outcome variables in meta-analysis: A simulation study

<p>Abstract</p> <p>Background</p> <p>Meta-analysis of continuous outcomes traditionally uses mean difference (MD) or standardized mean difference (SMD; mean difference in pooled standard deviation (SD) units). We recently used an alternative ratio of mean values (RoM) method, calculating RoM for each study and estimating its variance by the delta method. SMD and RoM allow pooling of outcomes expressed in different units and comparisons of effect sizes across interventions, but RoM interpretation does not require knowledge of the pooled SD, a quantity generally unknown to clinicians.</p> <p>Objectives and methods</p> <p>To evaluate performance characteristics of MD, SMD and RoM using simulated data sets and representative parameters.</p> <p>Results</p> <p>MD was relatively bias-free. SMD exhibited bias (~5%) towards no effect in scenarios with few patients per trial (n = 10). RoM was bias-free except for some scenarios with broad distributions (SD 70% of mean value) and medium-to-large effect sizes (0.5–0.8 pooled SD units), for which bias ranged from -4 to 2% (negative sign denotes bias towards no effect). Coverage was as expected for all effect measures in all scenarios with minimal bias. RoM scenarios with bias towards no effect exceeding 1.5% demonstrated lower coverage of the 95% confidence interval than MD (89–92% vs. 92–94%). Statistical power was similar. Compared to MD, simulated heterogeneity estimates for SMD and RoM were lower in scenarios with bias because of decreased weighting of extreme values. Otherwise, heterogeneity was similar among methods.</p> <p>Conclusion</p> <p>Simulation suggests that RoM exhibits comparable performance characteristics to MD and SMD. Favourable statistical properties and potentially simplified clinical interpretation justify the ratio of means method as an option for pooling continuous outcomes.</p

Early mobilisation in mechanically ventilated patients:A systematic integrative review of definitions and activities

From PubMed via Jisc Publications RouterHistory: received 2018-10-23, accepted 2018-12-11Publication status: epublishMechanically ventilated patients often develop muscle weakness post-intensive care admission. Current evidence suggests that early mobilisation of these patients can be an effective intervention in improving their outcomes. However, what constitutes early mobilisation in mechanically ventilated patients (EM-MV) remains unclear. We aimed to systematically explore the definitions and activity types of EM-MV in the literature. Whittemore and Knafl's framework guided this review. CINAHL, MEDLINE, EMBASE, PsycINFO, ASSIA, and Cochrane Library were searched to capture studies from 2000 to 2018, combined with hand search of grey literature and reference lists of included studies. The Critical Appraisal Skills Programme tools were used to assess the methodological quality of included studies. Data extraction and quality assessment of studies were performed independently by each reviewer before coming together in sub-groups for discussion and agreement. An inductive and data-driven thematic analysis was undertaken on verbatim extracts of EM-MV definitions and activities in included studies. Seventy-six studies were included from which four major themes were inferred: (1) , (2) , (3) and (4) . The first theme indicates that EM-MV is either not fully defined in studies or when a definition is provided this is not standardised across studies. The remaining themes reflect the diversity of EM-MV activities which depends on patients' characteristics and ICU settings; the negotiated decision-making process between patients and staff; and their interdependent relationship during the implementation. This review highlights the absence of an agreed definition and on what constitutes early mobilisation in mechanically ventilated patients. To advance research and practice an agreed and shared definition is a pre-requisite

Effect of prone positioning in patients with acute respiratory distress syndrome and high Simplified Acute Physiology Score II

Characterization of a new clinically more interpretable techniques to pool continuous outcomes in meta-analysis.Canadian Institutes of Health ResearchClinician Scientist - Phase

Utility of Gram stain in the clinical management of suspected ventilator-associated pneumonia. Secondary analysis of a multicenter randomized trial.

PURPOSE: Gram stains of endotracheal aspirates (EA) and bronchoalveolar lavages (BAL) may guide empiric antibiotic therapy in critically ill patients with suspected ventilator-associated pneumonia (VAP). Previous studies differ regarding the ability of the Gram stain to predict final culture results. The aim of the present study was to evaluate the relationship between EA or BAL Gram stains and final culture results in intensive care unit patients with a suspected VAP. MATERIAL AND METHODS: We retrospectively analyzed data from the Canadian multicenter VAP study to correlate EA or BAL Gram stain and final culture results. We categorized Gram stains as Gram positive (GP) and Gram negative (GN) if any GP or GN organisms respectively were seen on staining. Cultures were considered "positive" if they yielded pathogenic organisms on final results. RESULTS: Seven hundred forty patients were enrolled in the study; 35 did not have a Gram stain done leaving 350 BALs and 355 EAs from 705 patients. Pooling BAL and EA results, we found the overall agreement between Gram stain class and pathogenic bacteria culture results to be poor (kappa = 0.36; 95% CI, 0.31-0.40). Among specimens with Gram stains showing no organisms, 99 (30%) of 331 grew pathogenic organisms. Among specimens with Gram stains showing no GN organisms, 113 (25%) of 452 grew pathogenic GN organisms. Among specimens with Gram stains showing no GP organisms, 45 (11%) of 428 grew pathogenic GP organisms. CONCLUSIONS: Gram stains performed for clinically suspected VAP poorly predict the final culture result and thus have a limited role in guiding initial empiric antibiotic therapy in such patients.Characterization of a new clinically more interpretable techniques to pool continuous outcomes in meta-analysis.Canadian Institutes of Health ResearchClinician Scientist - Phase

Previous cultures are not clinically useful for guiding empiric antibiotics in suspected ventilator associated pneumonia: secondary analysis from a randomized trial.

Purpose: To examine the predictive validity of prior cultures at predicting the microorganism isolated at the time of suspicion of ventilator-associated pneumonia (VAP). Materials and Methods: We performed a retrospective analysis of a randomized controlled trial of different diagnostic and antibiotic strategies. In a subset of patients with pre-enrollment cultures, we examined agreement between cultures 1 to 3 days before suspicion of VAP and enrollment cultures performed on the day of suspicion of VAP and potential antibiotic error rates (estimated using the equation 1 − crude agreement). Results: Two hundred eighty-one (39%) of 739 patients had pre-enrollment culture. One hundred thirty (46%) of 281 yielded a pathogenic microorganism. In patients with positive pre-enrollment cultures, crude agreement was 0.63 (95% confidence interval, 0.55-0.71) for organism, 0.84 (0.77-0.89) for Gram class, and 0.61 (0.52-0.69) for species with sensitivity. Potential antibiotic error rates ranged from 16% (11%-33%) to 39% (31%-48%). Better agreement (P = .033) occurred in isolates from patients receiving new antibiotics during the surveillance period (0.78 [0.64-0.87]) compared to those not on antibiotics (0.58 [0.45-0.69]), or on no new antibiotics (0.50 [0.32-0.68]). Conclusions: There is poor agreement between prior cultures and cultures performed at time of suspicion of VAP. Prior cultures should not be used to narrow the spectrum of empiric antibiotics.Characterization of a new clinically more interpretable techniques to pool continuous outcomes in meta-analysis.Canadian Institutes of Health ResearchClinician Scientist - Phase