The effect of colonoscopy on optic nerve sheath diameter

Colonoscopy is widely used for the diagnosis and treatment of colorectal diseases and is considered the gold standard for colorectal cancer screening. Air insufflation during colonoscopy may increase intra-abdominal pressure, which may influence intracranial physiology. Colonoscopy was associated with increased ONSD measurements, a noninvasive surrogate marker related to intracranial pressure. Ultrasonographic measurement of optic nerve sheath diameter (ONSD) is a noninvasive method that has been shown to correlate with ICP. The aim of this study was to investigate changes in ONSD during colonoscopy under sedation as a noninvasive surrogate marker related to ICP. Written informed consent was obtained from all participants before enrollment in the study. Sixty patients aged 18–65 years with American Society of Anesthesiologists (ASA) physical status I–III who were scheduled for colonoscopy were included in this prospective observational study. Patients with ocular diseases, previous ocular surgery, chronic obstructive pulmonary disease, elevated ICP, congestive heart failure, or obesity (body mass index > 30 kg/m²) were excluded. ONSD measurements were performed using ultrasonography before anesthesia induction (T0), 1 min after induction (T1), 10 min after induction (T2), and after completion of the colonoscopy procedure (T3). Hemodynamic parameters, including heart rate, mean arterial pressure, systolic blood pressure, diastolic blood pressure, and peripheral oxygen saturation, were recorded simultaneously. Sixty patients completed the study. No significant differences were observed between patients with and without increased ONSD regarding demographic characteristics, propofol dose, or procedure duration. Compared with baseline values, ONSD measurements at T1, T2, and T3 were significantly increased ( p < 0.001). Pairwise comparisons showed significant differences between T1 and T2 and between T2 and T3, whereas T1 and T3 did not differ significantly after Bonferroni correction. Mean arterial pressure, systolic blood pressure, and heart rate significantly decreased during the procedure ( p < 0.001), whereas peripheral oxygen saturation remained unchanged. Colonoscopy performed under sedation was associated with a significant increase in ONSD. However, as ICP was not measured directly, these findings should be interpreted as transient changes in ONSD rather than evidence of clinically significant intracranial hypertension. ONSD monitoring may be useful in patients at risk for elevated ICP.