Target-controlled infusion achieves smoother autonomic modulation than manual bolus during propofol induction: Evidence from wavelet-based spectral analysis.

BACKGROUND: Anesthesia induction involves rapid autonomic shifts that may compromise hemodynamic stability. Propofol administered via target-controlled infusion (TCI) produces a more gradual onset, whereas rapid manual bolus (MB) administration often triggers abrupt autonomic disturbances. Thus, the propofol delivery method is critical to autonomic stability; however, conventional monitoring lacks sufficient temporal resolution to capture transient fluctuations during early induction. To address this gap, we compared TCI and MB using high-temporal-resolution wavelet-based spectral analysis (WBSA) of heart rate variability (HRV) and pulse photoplethysmography amplitude (PPGA) to characterize real-time autonomic dynamics.

METHODS: This prospective, single-center observational study included adult patients undergoing elective surgery who received propofol induction via TCI or MB administered over 10 seconds. HRV and PPGA were continuously recorded and analyzed using WBSA. High-frequency power and low-to-high frequency ratio assessed parasympathetic tone and sympathovagal balance, while PPGA served as a surrogate for peripheral sympathetic tone. Simulated effect-site concentrations (CeP) were calculated to examine relationships between concentration dynamics and autonomic responses.

RESULTS: Forty-four patients were analyzed. Compared with MB, TCI produced significantly more gradual and attenuated changes in high-frequency, low-frequency, and low-to-high frequency ratio (all p < 0.05), along with slower and smaller increases in PPGA, indicating better preservation of autonomic balance and milder peripheral sympatholysis. Simulated CeP reached 5.5 μg·mL - 1 at 117 seconds with TCI vs 36 seconds with MB. Greater transient autonomic disturbance was associated with a faster rise in CeP, rather than absolute CeP values, indicating that delivery mode and rate were primary determinants of autonomic modulation.

CONCLUSION: TCI provided smoother autonomic modulation than did MB during the physiologically unstable induction phase. By enabling real-time detection of short-lived fluctuations, WBSA revealed mechanistic differences not captured by conventional analyses, supporting TCI as a potentially more stable and physiologically balanced induction strategy, particularly for patients at risk of peri-induction instability.