Patients undergoing cranial neurosurgery face a high-risk postoperative period, particularly during emergence from anesthesia and early recovery in the post-anesthesia care unit (PACU). Standard monitoring provides limited insight into brain and autonomic recovery processes. Heart rate variability (HRV) and processed electroencephalography (pEEG) may offer complementary markers of autonomic and cortical function, with potential to improve early detection of complications and guide individualized care.

Patients undergoing cranial neurosurgery face a particularly vulnerable postoperative course. The immediate hours after surgery represent a high-risk window, as the transition from anesthesia to recovery is marked by abrupt physiological shifts and the potential for neurological or systemic instability. As patients transition from deep anesthesia to consciousness, dynamic fluctuations in autonomic tone and cortical activity reflect the brain's ability to recover from surgical and anesthetic stress. Smooth emergence and extubation are therefore essential: coughing, hypertension, or surges in intracranial pressure (ICP) can endanger hemostasis and compromise brain protection. Most serious complications-such as intracranial bleeding, cerebral edema, ischemia, hydrocephalus, or herniation-tend to arise within the first hours after surgery.

The Post Anesthesia Care Unit (PACU) constitutes a important window of observation. At this critical phase many strategies have been developed to protect the brain from complication triggering events. For example, remifentanil infusion-whether manual or target-controlled at effect-site concentrations, like adopted at our institution, titrated to suppress airway reflexes and blunt cardiovascular responses-have been shown to promote safe and controlled awakening while preserving prompt neurological evaluation(1-6), facilitating the identification of surgical from anesthetic causes of delayed recovery. Any unrecognized or delayed deterioration early after surgery may herald potentially warning signs, highlighting the need for accurate, physiology-based monitoring to support timely detection and intervention.

Standard monitoring-focused largely on vital signs-offers limited insight into the underlying brain and autonomic processes that govern recovery. Heat rate variability (HRV) and processed electroencephalography (pEEG) features, may provide novel means to characterize patient vulnerability in the PACU, improving risk stratification and guiding individualized perioperative care.

Inclusion Criteria:

• Adult patients (≥18 years) scheduled for elective cranial neurosurgery.
• Planned extubation in the PACU after surgery.
• Ability to obtain high-quality ECG and EEG recordings intra- and postoperatively (≥60 min expected PACU monitoring).
• Written informed consent signed preoperatively.

Exclusion Criteria:

• Pre-existing severe cardiac arrhythmias (e.g., atrial fibrillation, frequent ectopy) or pacemaker dependence.
• Known severe autonomic neuropathy (e.g., advanced diabetes, Parkinson's disease with autonomic failure).
• Preoperative conditions associated with abnormal EEG (status epilepticus, uncontrolled seizures, sedative/hypnotic overdose).
• Intraoperative or immediate postoperative events necessitating continued mechanical ventilation or ICU admission (e.g., massive bleeding, intraoperative arrest).
• Inability to provide informed consent (e.g., cognitive impairment, language barrier without interpreter).
• Refusal of informed consent

Elective Cranial Neruosurgical Patients with planned extubation in the Post-Anesthesia Care Unit (PACU)