Table 2.

A summary of nine studies that met the inclusion criteria and were included for analysis.

Reference	Study design	Study setting location	Number of participants	Condition
Kliempt et al., 1999	Randomised controlled trial	Hospital, UK	76	Surgery requiring general anaesthesia
Lewis et al., 2004	Randomised controlled trial	Hospital, USA	60	Bariatric or lumbar surgery
Dabu-bondac et al., 2010	Randomised controlled trial	Hospital, USA	60	Surgery requiring general anaesthesia
Zampi., 2015	Randomised repeated measures crossover controlled trial	Laboratory, USA	32	Chronic pain
Ecsy et al., 2017	Randomised repeated measures crossover controlled trial	Laboratory, UK	64	Healthy
Ecsy et al., 2018	Randomised repeated measures controlled trial	Laboratory, UK	32	Healthy
Arendsen et al., 2020	Randomised repeated measures crossover controlled trial	Laboratory, UK	20	Chronic pain
Gkolias et al., 2020	Double-blind randomised repeated measures crossover controlled trial	Pain unit and patient homes, Greece	21	Chronic pain
Olcucu et al., 2021	Randomised controlled trial	Hospital, Turkey	352	Cystoscopy and ureteral stent removal surgery patients