In this prospective, randomized controlled study, we hypothesized that nociception level index monitoring reduced opioid administration during surgery. The secondary goals are to compare the total dose hypnotic drugs, as well as hemodynamic parameters, and to investigate the relationship between changes in the NOL index and HR change following severe noxious stimuli during effect site TCI of propofol and remifentanil in patients undergoing intracranial tumor surgery who are monitored using either standard monitors or the NOL monitor additionally.

The study will be conducted on 50 patients aged between 18-75 years, with the American Society of Anesthesiologists (ASA) classification II-III, who would undergo intracranial tumor surgery after ethics committee approval (08/09/2020, 2020-15/15) and written consent from the patients. Standard monitoring (invasive arterial monitoring, 5-lead ECG, peripheral oxygen saturation-SpO2) and Bispectral Index Score (BIS) monitoring will be performed in the standard care group (SC; n=25), and NOL index monitoring will be performed in addition to standard monitors in the NOL guided group (NOL-G; n=25).

During TCI, propofol (Schnider) effect-site concentration (Ce) will be titrated to BIS score between 40-60 and remifentanil (Minto) Ce to standard hemodynamic parameters in the SC group and NOL index between 10-25 in the NOL-G group.

In all patients, Systolic, Diastolic and Mean Arterial Pressure (SAP, DAP, MAP), Heart Rate (HR), SpO2, BIS scores will be recorded before induction, intubation, head holder pinning, skin incision, muscle and periosteal dissection, craniotomy, dural incision, tumor excision, dural suturation, muscle and periosteum suturation, skin suturation, and interruption of infusions. In addition, NOL index in the NOL-G group patients will be recorded in all that time.

Hemodynamic parameters, to be administered propofol and remifentanil doses will be compared in two groups. NOL index changes before and after intubation, head holder pinning, skin incision and craniotomy, which are determined as severe noxious stimuli, will be compared with changes in HR.

Traditionally, the hemodynamic reactivity such as increased HR and blood pressure (BP), and/or nocifensive movements in the absence of paralytic agents are clinically considered for the assessment of nociception. The response to nociceptive stimuli is monitored as an increase in sympathetic or a decrease in parasympathetic tone (Guignard, 2006). The sympathetic response generates physiological changes such as increased HR, increased peripheral vasoconstriction, pupillary dilation, and changes in galvanic skin conductance (Guignard, 2006). As the understanding of nociception has grown in the past two decades, the industry has developed various nociception detecting devices based on some of the mentioned parameters.The only multi-parameter device is the Nociception Level (NOL) index (Ledowski, 2019). Evidence suggests the multi-parameter approach may be superior to the single-parameter approach for the assessment of nociceptive pain induced by tonic heat stimuli among healthy volunteers (Treister et al., 2012)

The PMD-200 system (NOL device) consists of a display and computing unit, a reusable non-invasive finger probe and a single-use sensor.The proprietary signal acquisition sensor platform (the combination of the finger probe and the single-use sensor) acquires physiological signals. Using advanced algorithms, the system processes and analyses multiple nociception related physiological parameters and their various derivatives, which correspond with the sympathetic nervous system's response to noxious stimuli. The finger probe and single-use sensor continuously acquire four physiological signals through the following four sensors; photoplethysmograph (PPG), galvanic Skin Response (GSR), peripheral Temperature (Temp), accelerometer (ACC). From these four signals the NOL algorithm extracts and analyses nociception-related physiological parameters and derivatives: pulse rate, pulse rate variability, pulse wave amplitude, skin conductance level, peripheral temperature, movement, and their various derivatives. Then a patient's specific nociception signature is established and continuously monitored. Peripheral temperature and movement serve as guardrails supporting algorithm validity and do not contribute directly to the algorithm calculation.

In 2013, Ben-Israel et al., published the first study on the multiparametric Nociception Level index (NOL). The few validation studies to date allowed the preliminary conclusion that the NOL index presented as an accurate means to measure the level of nociception during general anesthesia (Edry et al., 2016) . On the other hand, there are studies showing that the NOL index monitor does not reduce opioid consumption, or even though it does, there is no significant difference (Espitalier et al., 2021; F. Meijer et al., 2020; Niebhagen et al., 2022; Renaud-Roy et al., 2022) In addition, many studies in the literature indicate that NOL index monitoring is a reliable monitor in the evaluation of nociception or in distinguishing noxius stimuli (Renaud-Roy et al., 2019) (Treister et al., 2012) (Edry et al., 2016) (Martini et al., 2015) (Bollag et al., 2018) .

Inclusion Criteria:

• İntracranial mass surgery
• Craniotomy
• ASA II-II
• elective surgery

Exclusion Criteria:

• pregnant or suspected of pregnancy
• receive antiarrhythmic therapy
• autonomic nervous system disease
• ASA IV
• emergency surgery
• patients with difficult airway features
• patients receiving chronic pain treatment