Simultaneous bispectral index and near-infrared spectroscopy monitoring to evaluate two induction protocols in elective cardiovascular surgery

Laryngoscopy and intubation provoke strong sympathetic activation and may cause hemodynamic instability in cardiovascular surgery patients. Maintaining adequate hypnotic depth and cerebral oxygenation during induction is essential. Although BIS and NIRS are widely used, their simultaneous behavior during induction in a homogeneous cardiovascular surgery population is not well established. To compare thiopental–low-dose fentanyl and midazolam–high-dose fentanyl induction protocols regarding their effects on BIS, regional cerebral oxygen saturation (rSO₂), and hemodynamic responses during the peri-intubation period. This prospective, randomized study included 30 adults undergoing elective cardiovascular surgery. Patients received thiopental (5–7 mg/kg) + fentanyl (1.5 µg/kg) or midazolam (0.1 mg/kg) + fentanyl (5 µg/kg). BIS, bilateral rSO₂, arterial pressures, heart rate, and end-tidal CO₂ were recorded at four time points: before induction (T0), two minutes after induction (T1), immediately after intubation (T2), and two minutes post-intubation (T3). Statistical comparisons were performed within and between groups (p < 0.05). Both protocols demonstrated similar BIS patterns: a marked decrease after induction, a rise at intubation, and a decline thereafter. rSO₂ increased significantly at T1–T2 and decreased at T3 in both groups. Hemodynamic responses showed parallel post-induction decreases and intubation-related increases. No significant intergroup differences were identified in BIS, rSO₂, or major hemodynamic variables. Thiopental–low-dose fentanyl and midazolam–high-dose fentanyl induction yield comparable effects on hypnotic depth, cerebral oxygenation, and hemodynamic stability. Combined BIS–NIRS monitoring provides complementary information and may enhance peri-intubation safety in cardiovascular surgery. WHAT IS KNOWN • Laryngoscopy and endotracheal intubation can induce significant sympathetic stimulation, leading to hemodynamic fluctuations that are particularly risky in cardiovascular surgery patients. • Bispectral index is widely used for objective assessment of anesthetic depth, while near-infrared spectroscopy allows continuous monitoring of cerebral oxygenation. • Previous studies have generally evaluated BIS and NIRS separately, and comparative data on different induction protocols in homogeneous cardiovascular surgery populations are limited. WHAT IS NEW • This study provides a focused peri-intubation comparison of BIS and bilateral rSO₂ trends under two commonly used induction protocols in elective cardiovascular surgery patients. • It highlights that thiopental–low-dose fentanyl and midazolam–high-dose fentanyl protocols produce closely similar monitoring trajectories during induction and intubation. • The findings reinforce the practical value of interpreting anesthetic depth and cerebral oxygenation together within the same peri-intubation time window.