Statistical analysis
Statistical analyses were performed using the Statistica (TIBCO v.13.3)
software. Continuous variables are expressed as mean ± standard
deviation (SD) or median range as appropriate. Confidence intervals
(95% CI) for individual groups and the whole group were measured. For a
subset of studies with analyzable and comparable data, the results were
synthesized quantitatively by performing random-effects model
meta-analyses to compute absolute net changes in continuous variables
(for example, time to PNI or temperature to PNI) and pooled OR for
binary variables (for example, PNI with CMAP and no phrenic nerve
injury). All pooled estimates were displayed with a 95% CI. For PNI
resolution the Wilcoxon Peto’s log-rank test was used because higher
sensitivity at early survival times than late ones. The existence of
heterogeneity among effect sizes of individual studies was assessed
using an I2 of higher than 50% with p value of < 0.1,Q test, and the T 2 index with a value of
≥ 95%, indicating medium-to-high heterogeneity. A funnel plot and Begg
and Mazumdar’s test were used to investigate publication bias for the
primary clinical outcome.