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).

Control group patients Sufentanil and propofol target-controlled infusion (TCI) dosing will be administered according to established protocols. The anaesthesiologist will monitor the effect-site concentration (Ce) of propofol during induction, adjusting the dosage until loss of eyelash reflex, absence of response to verbal stimuli, and onset of apnoea are observed; subsequently, Ce will be increased by 20% and maintained throughout the duration of surgery. Following intubation, 0.03 mg/kg midazolam (Midazolam Hameln, Hameln, Germany) will be administered to ensure amnesia in case of inadvertent awareness. If the patient's heart rate or mean blood pressure exceeds preoperative values by more than 20%, the propofol Ce will be increased by 0.3 mcg/ml. Signs suggestive of intraoperative awareness-including lacrimation, sweating, limb movement, or spontaneous respiration-will prompt administration of an additional 0.03 mg/kg midazolam and 0.2 mg/kg esketamine (Esgamda, G.L. Pharma GmbH, Lannach, Austria). Rocuronium bromide will be given at 0.6 mg/kg lean body weight for intubation, with supplemental 10 mg doses provided as necessary based on inadequate muscle relaxation (propofol Ce > 4.5 mcg/ml, as determined by the surgeon). Intravenous fluids (crystalloids and colloids), blood transfusions, vasopressors, and inotropes will be managed at the discretion of the attending anaesthesiologist.

Data Recording Masimo Root® monitors equipped with LiDCO®, Hb module, Sedline®, and O3® will be employed for the intervention group. All relevant data-including times of induction, incision, and intraoperative remarks-will be documented either on the Root® monitor or recorded separately when appropriate. Upon completion of each procedure, data will be extracted using Trace® software for the Root® system. As the anaesthesia record is maintained in a non-digital format, copies of the anaesthesia sheet containing all essential details must be produced and submitted together with the corresponding digital records. Following surgery, patients will be transferred to the ICU.

Laboratory Analysis Blood samples for routine laboratory investigations will be collected at three specific time points: prior to surgery, upon ICU admission, and 24 hours post-admission. Analyses will include complete blood count, electrolyte assessment, prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen concentration, blood gas parameters, lactate concentration, troponin I, and N-terminal pro-brain natriuretic peptide (NTproBNP).

The same parameters will be systematically monitored for both the control and intervention groups. Monitored variables include duration of anaesthesia (in minutes), administered medications, volume and type of infusions, quantity and type of blood components, intraoperative urine output, ICU length of stay, duration of mechanical ventilation, incidence of significant postoperative complications (e.g., cardiovascular events, acute kidney injury, cerebrovascular events), frequency of postoperative surgical complications (including re-operations), mortality rates at 7 and 30 days, as well as overall hospital length of stay.

Continuous variables are presented as either mean and standard deviation (SD) for descriptive statistics, or median and interquartile range (tables), and mean with 95% confidence interval (graphs) for inferential analysis. Normality of distribution was assessed using the Shapiro-Wilk test. Categorical variables are reported as counts and percentages.

Statistical significance of differences in continuous variables was evaluated using the Mann-Whitney U test, while repeated measurements between groups were analysed via repeated measures analysis of variance (RM-ANOVA) with post-hoc Holm-Šidák correction. Differences in categorical variables between groups were assessed using the chi-squared test or Fisher's exact test, as appropriate.

Analysis of covariance (ANCOVA), incorporating patient age as a covariate, was employed to compare clinical outcomes between groups. All statistical analyses, power calculations, and data visualizations were performed using the jamovi software package version 2.5.3. A p-value less than 0.05 was considered statistically significant.