External validity limitations of randomized trials cited in adult critical care clinical practice guidelines: a systematic review of guidelines published from 2015 to 2020 - Weiting Chen; Li Zhong; Cheng Zheng; Wenyun Ding; Kai Zhang; Nanxia Xuan; Lanxin Cao; Baoping Tian; Wei Cui; Pingli Wang; Zhongheng Zhang; Gensheng Zhang (Frontiers in Medicine, 2026)