Impaired consciousness has various causes. One such cause includes hypoglycemia, which may be symptomatic or asymptomatic and is associated with high mortality. Autonomic abnormalities are also common in hypoglycemic patients. Early detection is critical for improving prognosis. In this study, we evaluated changes in vital signs and pupillary responses before and after glucose administration in patients with hypoglycemia managed in a prehospital emergency setting. : This retrospective observational study included 583 adult patients from the Tokyo Fire Department database. All patients were suspected by emergency medical technicians (EMTs) to have hypoglycemia-related impaired consciousness and showed improved consciousness after receiving intravenous glucose infusion at the scene. Vital signs, level of consciousness, and pupillary responses were assessed before and after glucose administration. : The mean patient age was 58.9 years, and approximately 90% had comorbid diabetes mellitus. Tachypnea was common at the scene, with 27% showing tachycardia, while blood pressure remained normal. Miosis and abnormal pupillary light reflexes were observed in 68% and 84% of cases, respectively. Anisocoria occurred in 7.6% of the patients. After glucose administration, both abnormal reflexes and anisocoria significantly decreased (both < 0.0001). Although vital signs did not consistently reflect autonomic responses, changes in pupillary findings were prominent. : Altered pupillary responses are common in hypoglycemic coma. Findings such as miosis and anisocoria can result from various causes, including central nervous system disorders and cholinergic toxicity; thus, careful differential diagnosis is essential. Normal blood pressure may help to distinguish hypoglycemic coma during prehospital care.