High Frequency Variability Index as an Early Indicator of Fluid Resuscitation During Gynecologic Surgery: A Case Report

Author(s): Mitsutaka Edanaga, Motonobu Kimizuka, Mako Doumi, Akihiro Miyazaki, Michiaki Yamakage

Background: High Frequency Variability Index (HFVI), derived from heart rate variability (HRV), is an indicator of parasympathetic nervous activity. Recently, HFVI has been used as an objective marker of analgesia, with values above 50 generally indicating adequate pain relief. In this report, we present the first case in which HFVI served as a prompt indicator for initiating fluid resuscitation during intraoperative hemorrhage.

Case: A woman in her 40s was scheduled to undergo a radical abdominal hysterectomy. In addition to standard vital signs monitoring, HFVI was used to adjust the dosage of remifentanil. Following epidural catheterization, general anesthesia was induced. Anesthesia was maintained with 1.3 L/min of Air, 0.7 L/min of O2 and 1.5% of sevoflurane (end-tidal concentration: 1.0%). Only the remifentanil dosage was modified based on HFVI readings. Approximately 150 minutes after the start of surgery, the systolic blood pressure frequently dropped below 80 mmHg, and phenylephrine was administrated several times. HFVI values fell below 50, followed by a gradual increase in heart rate. In response to suspected hypovolemia, fluid resuscitation was performed using crystalloid solution and Voluven®. After treatment, HFVI values rose above 50 and remained stable. Notably, vital sign may not change until significant blood loss has occurred, whereas parasympathetic withdrawal may appear earlier in the course of hemorrhage.

Conclusion: HFVI may serve as a useful early indicator for initiating fluid resuscitation during intraoperative hemorrhage.