Intraoperative Multimodal Monitoring as a Means in Reducing the Duration of Mechanical Ventilation in High-Risk Patients Undergoing Major Abdominal Procedures - A Pilot Study

This study will include patients aged 50 years or older who are scheduled for elective abdominal oncologic surgery, specifically those classified as ASA II and ASA III due to their elevated anaesthetic and surgical risk profiles. Sex distribution will not serve as a stratification variable. Exclusion criteria encompass patient refusal; cognitive impairment; psychosis; known or suspected electroencephalographic disorders (including epilepsy or prior neurosurgical procedures); chronic use of psychoactive medications; urgent or emergent surgeries; body mass index (BMI) less than 18 kg/m² or greater than 35 kg/m²; persistent arrhythmias, including atrial fibrillation and undulation; documented NYHA class III-IV heart failure or preoperative left ventricular ejection fraction below 30%; significant valvular disease involving aortic or mitral stenosis or regurgitation; liver conditions such as decompensated cirrhosis and coagulopathies; and anticipated operative duration exceeding six hours. Eligible participants must provide written informed consent one day preceding surgery. Demographic information for both intervention and control groups will include age, sex, planned procedure type, comorbidities, ASA classification, height, weight, and BMI. Randomisation will be conducted prior to study initiation using https://www.random.org/ with a total sample size of 100 subjects. A pilot study was performed involving five patients in each group to inform sample size calculations.

Premedication will be administered to all patients according to institutional protocol and consists of intramuscular midazolam, with optional addition of atropine. Intraoperative monitoring will follow randomisation assignments. The control group will receive standard monitoring, including invasive pressure measurements, ECG, SpO2, IBP, and, when indicated, central venous pressure. Designated team members are responsible for data collection and archiving copies of the anaesthesia chart. In both groups, following intubation, patients will be connected to an anaesthesia machine (Dräger Perseus, Drägerwerk AG & Co. KGaA, Lübeck, Germany) and ventilated at 6-8 ml/kg of predicted body weight. Fresh gas flow will be maintained at 1 L/min, with FiO2 adjusted to ensure expiratory oxygen concentration remains between 30-40%. Upon completion of surgery, the attending anaesthesiologist will determine whether to continue mechanical ventilation and administer antidotes based on clinical judgement.

In the intervention group, patients will be monitored through radial artery cannulation performed under local anesthesia before induction. Monitoring devices used include LiDCOrapid®, Rainbow®, and an Hb module connected to the Root® monitor. Baseline measurements for mean arterial pressure (MAP) and cardiac output (CO) will be taken, with oxygen delivery (DO2) automatically calculated from the baseline CO and hemoglobin values detected by the Masimo Rainbow sensor. Prior to pre-oxygenation, SedLine® and O3® adult sensors will be attached to the patient's forehead to measure anaesthetic depth and regional oxygen saturation (rSO2), respectively. A low-dose infusion of noradrenaline (Noradrenalin Ligula Pharma, Laboratorios Normon S.A., Madrid, Spain; 1mg/50ml at 5 ml·hr-¹) will be started to help maintain venous tone.

Anaesthesia will be both induced and maintained using a target-controlled infusion (TCI) method with propofol (Propofol MCT Fresenius, Fresenius Kabi, Graz, Austria) and sufentanil (Sufentanil Altamedics, Altamedics GmbH, Cologne, Germany), delivered via the Braun Perfusor® Space system (B. Braun SE, Melsungen, Germany). The goal is to keep SedLine® values within a range of 30 to 50. Sufentanil dosing for intravenous induction will follow the Gepts effect-site model: for patients under 68 years, concentrations will be 0.5 ng/ml for induction, 0.3 ng/ml for maintenance, and 0.25 ng/ml for extubation. For those aged 69-79 years, the protocol calls for 0.35 ng/ml during induction, 0.25 ng/ml during maintenance, and 0.20 ng/ml at extubation. Patients over 79 years will receive 0.30 ng/ml for induction, 0.20 ng/ml for maintenance, and 0.17 ng/ml for extubation. Propofol will be administered according to the Schnider model, with 3 mcg/mL used for induction and 2-3 mcg/mL for maintenance.

The primary objective is to maintain rSO2 by ensuring adequate haemoglobin concentration and DO2 at or above 85% of baseline. Should rSO2 fall below this threshold, the at-tending anaesthesiologist will implement a DO2 optimization protocol: con-firming adequate anaesthetic depth, maintaining SpO2, and administering a 250 ml crystalloid bolus if stroke volume variation (SVV) exceeds 12%, repeated as needed until SVV drops below 12% or no further increase in stroke volume index (SVI) occurs. When SVV is below 12%, the PPV to SVV ratio will be assessed; if >0.7, crystalloid boluses will continue. Otherwise, systemic vascular resistance index (SVRI) will be evaluated, and a norepinephrine bolus (2-10 mcg) administered if SVRI is less than 1600 dynes·s·m²/cm⁵. If a significant MAP increase (>10%) follows, a norepinephrine infusion will be started and titrated to maintain MAP >65 mmHg. If not, the CI will be observed, and dobutamine infusion (Dobutamin Panpharma, Panpharma, Luitré, France) commenced if CI is below 2.4 L/min/m². If all measures fail to optimize rSO2, head position adjustments and increases in FiO2 and/or PEEP will be made until adequate rSO2 is achieved. For hypertension (systolic BP >180 mmHg) during appropriate anaesthetic depth, noradrenaline infusion will be discontinued. Maintenance fluids will be administered as balanced crystalloid (Iono-lyte, Fresenius Kabi Deutschland GmbH, Friedberg, Germany) at 4 mL/kg/h, aiming for urine output (UO) ≥0.5 mL/kg/h. Neuromuscular blockade will be achieved using rocu-ronium bromide (Esmeron, Merck Sharp & Dohme B.V., Haarlem, Netherlands) at 0.6 mg/kg lean body weight (LBW) for intubation and maintained with 6 mcg/kg/min LBW. At the conclusion of surgery, neuromuscular blockade will be reversed with sugammadex (Sugammadex Mylan, Mylan Pharmaceuticals Ltd., Dublin, Ireland).