Frequently, neonates hospitalized in neonatology units require anesthesia for surgery. The drugs used for this purpose are opioids and other anesthetics, such as propofol.

Currently, the administration of anesthesia is difficult in neonates due to the neurological immaturity of these patients, the scarcity of adequate pharmacological studies, the prolonged use of one or more sedatives prior to surgery and the limited usefulness of current anesthetic monitoring devices in this population.

Electroencephalography (EEG), which has allowed estimation of anesthetic depth in other populations, has been less explored in neonates. To date, there are no EEG markers, correlated with a given dose of anesthesia, that allow an adequate administration in this kind of patients. In this context, a better understanding of the anesthetic effect in the neonatal brain would allow defining characteristic EEG patterns, improving the estimation of anesthetic depth and anesthetic dosage in neonates.

As a consequence of the cerebral immaturity of newborns (1,2), together with the fact that in the NICU it is common to find patients requiring surgery who are sedated with multiple drugs, it is necessary to define characteristic EEG patterns that allow estimation of the anesthetic depth and adequate dosage of anesthetics, avoiding the the risk of under- or overdosing of anesthetics (3).

The investigators will conduct an exploratory study. The aim of the study is to determine, by frontal electroencephalography, markers of brain electrical activity associated with the administration of propofol in term newborns requiring surgery in the NICU. A sample of 20 term neonatal patients admitted to the NICU UC with a diagnosis of surgical pathology will be included.

General objective:

To describe the characteristics of the frontal electroencephalographic pattern associated with increasing doses of propofol, in term neonates, requiring surgery in the NICU and its correlation with a clinical response, to the surgical stimulus.

Specific objectives:

• Identify the association between electroencephalographic parameters and different levels of sedation prior to surgery.
• To identify the association between electroencephalographic parameters and increasing doses (plasma concentration) of propofol administered in a previously sedated patient.
• To relate the clinical response observed to the surgical stimulus and increasing doses (plasma concentration) of propofol in a previously sedated patient (dose (concentration) - response curve).
• To describe the temporal profile of propofol anesthesia, based on the changes in electroencephalographic parameters observed over time, during the period of administration and suspension of the anesthetic.

On the scheduled day of surgery in the NICU and prior to anesthetic induction, in sedated and standardly monitored patients (ECG, SpO2, PAI, temperature, diuresis). A four-channel SedLine® monitor (Masimo Corporation, Irvine, CA, USA) will be used to monitor frontal brain electrical activity 10 minutes before the induction of anesthesia. At the end of this period, the level of sedation will be evaluated with the N-PASS clinical scale (4) and the types, doses and duration of sedative drugs administered up to that time will be recorded. Then, patients will be randomized into 4 groups, of 5 patients each, to receive manual total intravenous anesthesia, with different propofol infusion rates: Group 1, Propofol 2.0 mg/kg/hr; Group 2, Propofol 4.0 mg/kg/hr; Group 3, Propofol 6.0 mg/kg/hr; Group 4, Propofol 8.0 mg/kg/hrs. At 10 and 20 minutes after the start of the propofol infusion, arterial blood samples will be taken to determine the plasma concentration of propofol reached during the anesthetic induction. In case of hemodynamic alteration (heart rate and/or blood pressure drop by 20%) during the propofol infusion, a 25% decrease of the original dose will be performed. At the end of this period, surgery will be initiated. The hemodynamic and motor response to the surgical stimulus will be observed and recorded. If there is hemodynamic response (increase in heart rate and/or blood pressure by 20%) and/or motor response, after the surgical stimulus, fentanyl rescue 5 mcg/kg/iv will be administered. Subsequent anesthesia will be in the hands of the treating anesthesiologist in the doses and forms he/she deems convenient. Electroencephalographic tracing will be maintained continuously throughout the procedure (from 10 minutes before and up to 10 minutes after surgery). Changes and adjustments to the anesthesia and analgesia given, hemodynamic changes occurring during the procedure and anesthetic and surgical times will be recorded.

Inclusion Criteria:

• Term newborns (>37 weeks) admitted to the NICU
• Diagnosis of surgical pathology, non-neurological, to be resolved in the NICU, in the next hours or days.
• Need for continuous sedation-analgesia prior to surgery.

Exclusion criteria:

• Perinatal asphyxia
• Evidence of severe neurological injury.
• Suspected or diagnosed brain malformations
• Uncontrolled metabolic and hemodynamic instability at the time of surgery.