The effect of nitrous oxide in comparison to oxygen combined with fentanyl on the hospitalization time and pain reduction in renal colic patients at emergency department

Background: renal colic is a painful medical emergency, needs urgent intervention to reduce pain. nonsteroidal anti‑inflammatory drugs, opioids, and entonox are pain‑relieving agents. this study was aimed to compare fentanyl + entonox (nitrous oxide + o_2) versus fentanyl + oxygen. materials and methods: one hundred and twenty patients with acute renal colic presenting to the emergency department were enrolled. first, 50 μg fentanyl was infused for all patients. then, patients divided into two groups receiving masks of entonox and oxygen, respectively. quantitative measurement of pain was performed by visual analog scale, before the intervention, after 3, 5, 10, and 30 min of that. if the pain was not relieved after 30 min, 50 μg fentanyl was infused. if the pain was still continued, ketorolac and ketamine were used. hospitalization duration and severity of pain at specified times were compared between patients in two groups. results: the mean (standard deviation) time of hospitalization was 211 (59) and 236 (61) min in fentanyl + entonox and fentanyl + o_2 groups, respectively (p = 0.024). the decrease in pain severity after 10 and 30 min in fentanyl + entonox group were significantly greater than fentanyl + o_2 group (p = 0.002 and 0.001, respectively). mean (standard error) of needed time for renal colic pain to get better was 11.27 (1.23) and 20.47 (1.71) min in fentanyl + entonox and fentanyl + o_2 groups, respectively (p < 0.001). proportion of patients relief from pain in fentanyl + entonox in the second, third, and fourth measurements were significantly more than fentanyl + o_2 group (p = 0.036, p < 0.001, and p < 0.001, respectively). conclusion: entonox is more effective to decrease the duration of hospitalization and reduction of pain than o_2 in renal colic patients.