2.2. Selection of studies and data extraction
Two investigators (WJX and HFC) reviewed all titles, abstracts, and then
full texts sequentially. Finally, eligible trials were determined and
eligibility, quality, and outcomes data were retrieved independently.
Disagreements on eligibility between two reviewers were resolved via
mutual discussion, when needed, a third reviewer (YCL) was requested for
final decision. Relevant data were extracted from eligible literature
with a standard extraction formula with subsequent cross-checking.
Data retrieved included: (1) first author, year of publication, study
location, study design, sample size, gender, age, ASA status, types of
surgery, premedication, anesthesia maintenance, intervention
description, control description, dose of opioids, postoperative
analgesic strategines, and (2) pain intensity in the form of the various
pain scores during the 0 to 24 postoperative hours, pain threshold or
normalized area of hyperalgesia during the 0 to 48 postoperative hours,
cumulative morphine consumption at 24h after surgery, time to first
rescue analgesic, and incidence of postoperative opioid-related
side-effects, such as postoperative nausea and vomiting (PONV),
shivering, dizziness and hypotension. Dichotomous data were extracted as
the number of patients (%). Continuous data were extracted in the form
of mean ± standard deviations (SDs).
When the target data in the article were incomplete, we attempted to
contact the author via e-mail twice, but no responses were received.
When the standard deviation was missing, range and median
estimation[15] were used for the conversion.