Arterial Blood Gas Analysis of Patients with Tramadol-induced Seizure; a Cross Sectional Study

Introduction: Tramadol is an active analgesic drug that is commonly used to treat moderate to severe pain. The present study aimed to assess the arterial blood gas (ABG) analysis of patients with tramadol-induced seizure (TIS).

Methods: This prospective cross-sectional study was performed on 50 TIS cases that were referred to emergency department within a maximum of one hour after their last episode of seizure. The results of ABG analysis on admission were collected and their association with dosage and time interval between ingestion and admission was assessed.

Results: 50 cases with the mean age of 35.10 ± 9.62 years were studied (80.0% male). The mean dosage of ingestion was 1122.00 ± 613.88 (400 to 3000) mg and the mean time interval between ingestion and admission was 7.16 ± 2.18 hours. ABG analysis on admission showed that 49 (98.0%) patients had pH < 7.35 and PaCO2 > 45 mmHg (respiratory acidosis). There was a significant association between ingestion to admission time interval and both PaCO₂ (r = -0.330, p = 0.019), and PaO₂ (r = 0.303, p = 0.032). The dose of ingestion was negatively associated with respiratory rate (r = -0.556, p = 0.001), arterial pH (r = -0.676, p = 0.001), and PaO₂ (r = -0.514, p = 0.001), but was positively associated with PaCO₂ (r = 0.461, p = 0.001). Higher doses of tramadol led to more severe hypercapnia and need for intubation (OR = 1.12, 95% CI: 0.88 - 1.26; p = 0.045). 5 (10.0%) cases needed mechanical ventilation. All patients improved after supportive care with no in-hospital death.

Conclusion: Based on the findings, 98% of TIS cases had respiratory acidosis. Higher doses of ingested drug and longer time interval between ingestion and admission were associated with severity of ABG disturbances.