• Juan Mariano Aguilar Mulet, Virginia Álvarez Rodríguez, Alberto M Borobia Pérez, Rafael Velayos Rubio, María Dolores Ochoa Mazarro, and Carmen Del Arco Galán.
• Servicio de Urgencias, Hospital Universitario de la Princesa, Instituto de Investigación Sanitaria del Hospital de la Princesa (IIS-IP), Madrid, España.
• Emergencias. 2016 Oct 1; 28 (5): 305-312.

ObjectivesTo assess the efficacy of a nitrous oxide and oxygen mixture (N2O/O2 50/50) for reducing pain and increasing satisfaction in patients with an initial clinical diagnosis of renal colic in the emergency department.Material And MethodsMulticenter, triple-blind randomized placebo-controlled trial. We randomized 147 patients with a clinical diagnosis of renal colic to an experimental group to receive the N2O/O2 50/50 mixture (n = 70) or a control group to receive 50% oxygen in air (n = 77). Both groups also received conventional analgesia with dexketoprofen plus metamizol and opiates administered sequentially until pain was brought under control; rescue doses of opioids were also available. The endpoints were the reduction in pain intensity expressed on a visual analog scale (VAS) 5 minutes after the start of treatment and the patient's level of satisfaction with treatment on discharge.ResultsThe mean (SD) reduction in pain 5 minutes after starting analgesic treatment was 1.84 (2.05) VAS points in the intervention group and 1.67 (1.91) in the placebo group. The difference was not significant (P = .603). Neither were between-group differences significant at other pain evaluation times (10, 15, 30, and 60 minutes). Treatment was considered satisfactory (􀀀 9 on a VAS) by 53 of the 70 intervention-group patients (75.7%) and 56 of the 77 (72.7%) placebo-group patients (P = .412). Adverse effects appeared in 33 of the 70 patients (48.5%) who received the N2O/O2 mixture and in 19 patients (24.7%) who received the placebo (P = .003).ConclusionThe addition of N2O/O2 50/50 to standard analgesic therapy does not enhance the efficacy of pain control or the satisfaction of patients treated for renal colic in the emergency department.

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