Laparoscopic surgery is common alternative for open surgery. Laparoscopic surgeries are minimally invasive. Laparoscopic procedures offer better cosmesis, associated with lower postoperative pain scores, enhanced recovery and hence, reduced length of stay at hospital. ¹ The pneumoperitoneum for abdominal laparoscopy is created using carbon dioxide (CO₂). Pneumoperitoneum increases intra-abdominal pressure. The elevated intra-abdominal pressure results in an elevated intracranial pressure (ICP). ^{2, 3} Multiple physiological changes are associated with pneumoperitoneum: elevated airway pressure, reduced lung compliance, increased mismatch in ventilation/perfusion, decreased venous return, elevated systemic vascular resistance, hypercapnia and respiratory acidosis. ^{4, 5}

Gold standard technique to measure the ICP is external ventricular drain (EVD) placement. Although being the most accurate method for measuring ICP, it is invasive and can cause neurological injury, intracranial haemorrhage, and infection. ⁶ The use of these high-risk invasive procedures to measure ICP during routine laparoscopic surgery is not needed. Compared to EVD, the ultrasound measurement of ONSD offers a simpler, non-invasive, and convenient method for bedside ICP monitoring. It allows for the observation of changes in ICP at any point during the surgery. ⁷ Anaesthetic agents have variable effects on ICP. Volatile anaesthetic agents are potent cerebral vasodilators and alter the ICP in a dose-dependent manner. ⁵ Dexmedetomidine is highly specific and potent alpha-2 adrenergic receptor agonist. Dexmedetomidine stimulates postsynaptic alpha-2 adrenergic receptors on the cerebral blood vessels that causes cerebral vasoconstriction and decreased cerebral blood flow. ^{4, 5} Propofol is a gamma-aminobutyric acid agonist. Propofol exhibits a dose-dependent effect on the contraction of cerebral blood vessels, as well as the inhibition of cerebral metabolic oxygen rate and reduction of ICP.

Hansen et al, in their research, discovered a robust association between intracranial pressure and ONSD. Maissan et al, suggested that the optic nerve sheath diameter (ONSD) could potentially serve as a real-time indicator of ICP. After a review of the relevant literature, the authors found contradictory findings, highlighting the need for additional research. This work may provide additional evidence to understand the changes in ICP during laparoscopic procedures. ^{5, 6, 8, 9, 7, 10}

Therefore, we aimed to evaluate the impact of dexmedetomidine and propofol on potential alterations in intracranial pressure by monitoring ONSD in patients undergoing laparoscopic surgery, which is a valuable non-invasive technique for evaluating intracranial pressure.

This was a prospective double-blind randomized controlled study. Approval from the institutional ethical committee (IEC No. 03 dated 12 Sep 2022) was taken. The study was registered with CTRI (clinicaltrials.gov) with registration number CTRI/2022/10/046896. The study was conducted at a tertiary care hospital in Mumbai, between September 2022 to December 2023. While conducting the research all guidelines as per declaration of Helsinki and good clinical practice were followed.

Sample size was calculated with the formula [n=Z^2-p(1-p)/E²], with a confidence interval of 95%, estimated prevalence of 4% and margin of error 5%. Sample size calculated was 60. Simple randomization technique was used to make two group of patients: propofol group and dexmedetomidine group. Thirty patients were allocated in each group. Concealment of allocation to either group was ensured by serially numbered opaque sealed envelope technique. Patient and observer were blinded about the drug being used for the study. All adult patients between 18 to 65 years of age, American Society of Anesthesiologists (ASA) physical status I and II, undergoing laparoscopic surgery and consented for participation were enrolled in the study. Patients with neurological, endocrine and psychiatric disorders, patients with pre-existing ophthalmic diseases and ocular injuries, ASA physical status III and above, patients with known allergies to drugs used in the study were excluded.

Written and informed consent was taken from the participants. Patients who met the criteria were included in the study. In operation theatre monitors were attached and baseline readings of heart rate, non-invasive blood pressure (NIBP), respiratory rate, pulse oximetry (SpO₂), and electrocardiography (ECG) tracings were recorded. Preoxygenation with 100% oxygen was done. The patients were premedicated with injection fentanyl (2mcg/kg) intravenously (iv). Patients were induced with propofol (2mg/kg) iv and intubated with non-depolarising muscle relaxants (vecuronium-0.1mg/kg). Intraoperative monitoring: ECG, NIBP, SpO₂, pulse rate, respiratory rate, end-tidal CO₂ (ETCO₂) and anaesthesia gas monitor (AGM) for minimum alveolar concentration (MAC) were recorded. Depth of anaesthesia was maintained using 50% O₂ + 50% air, nondepolarizing muscle relaxants (vecuronium) and inhalational agents (sevoflurane). ETCO₂ was maintained within the range of 30–40 mmHg by adjusting the ventilatory settings. ONSD was measured by observer who was blind for the drug used, after intubation but before pneumoperitoneum and labelled as ‘A’ (Basal value). ONSD was again measured after pneumoperitoneum and labelled as ‘B’. The drug used in the study was prepared as an infusion in 50 ml syringes. Rate of infusion of Dexmedetomidine was 0.5 mcg/kg/h and propofol was 100 mcg/kg/min for 15 to 30 min. During this phase the target MAC was 0.6-0.9. Fifteen to thirty minutes later, when all the physiological changes related to pneumoperitoneum are plateaued, third reading of ONSD was taken by the observer and labelled as ‘C’. Fourth reading of ONSD was taken after desufflation of pneumoperitoneum and labelled as ‘D’. The difference between ‘B’ and ‘C’ reading was calculated. ONSD readings ‘A’ and ‘D’ were taken to confirm whether the ICP reaches to normal values after desufflation.