Evaluation of optic nerve sheath diameter to transverse diameter ratio for predicting the neurological outcome in patients undergoing supratentorial craniotomy: Comparison of USG AND CT Measurements

METHODOLGYAfter Institutional Ethics Committee approval & Written Informed Consent, patients undergoing elective supratentorial craniotomy and tumour excision and fulfilling inclusion criteria will be included in the study.

During the preoperative period, optic nerve sheath diameter and eyeball transverse diameter will be measured by computed tomography.

CT GUIDED TECHNIQUEThe CT scans will be performed on a spiral scanner (64 row with a tube voltage of 120 kV, tube current of 200–300 mA, slice thickness of 2 mm, slice interval of 3 mm, and pitch of 1.

The ONSD and ETD will be measured at a fixed mediastinal window (width, 300; level, 35) for the same contrast and brightness. The direction of the optic nerve is identified by three-dimensional reconstruction of brain CT data, and the ONSD will be measured 3 mm behind the eyeball. ETD will be measured from one side of the retina behind the lens to the other for the maximum diameter. All of the measurements of ONSD and ETD will be performed bilaterally, and the mean value will be considered to calculate the ONSD/ETD ratio.

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As per institutional protocol, all patients will be examined on the night before surgery, and instruction regarding NPO, premedication will be given and all patients will be explained about USG-guided ONSD and ETD measurement for ICP assessment.

After taking the patient into the operation theatre, all standard monitors will be attached and IV-line will be secured. After making the patient comfortable and relaxed, we will measure the optic nerve diameter and eye ball transverse diameter with the help of USG machine before induction of anaesthesia

A linear 6-13 MHz probe of portable Sonosite Turbo-M ultrasonography (Fujifilm Sonosite, Bothell, USA) machine will be placed carefully on the gel over the closed (adhesive tape) upper eyelid without exerting pressure on the eye. In the two- dimensional mode, ONSD will be measured 3 mm below the junction site between the eyeball and optic nerve on a transverse line bilaterally, the values will be recorded for both the eyes. Average of three recordings for each eye will be taken separately for that par ticular point of time.

    The eyeball transverse diameter ETD (retina to retina) is defined as the maximal

transverse diameter of the eyeball obtained by scanning from the superior to the

inferior side. Average of three recordings for each eye will be taken separately for that

particular point of time.

Anaesthesia induction will be achieved with intravenous (IV) fentanyl 2µg/kg and propofol 2mg/kg. Patient will be intubated after adequate muscle relaxation with vecuronium 0.1mg/kg with appropriate size cuffed endotracheal tube. Maintenance of anaesthesia will be done with 60% air and 40% oxygen,1.5-2.0% sevoflurane with desired MAC up to 0.8-1.0 along with continuous infusion of vecuronium @0.03mg/kg/hr intravenously, supplemented with intravenous fentanyl 1.0 mcg/kg/hr. Patient will be ventilated with volume- controlled mode and end tidal carbon dioxide (ETCO2) will be maintained between 30-35mm Hg. Arterial catheter and central venous catheter (CVC) will be placed under USG guidance

The neurosurgeon will insert the intracranial pressure (ICP) catheter (subdural bolt) through the burr hole made on the contralateral side of craniotomy.

The catheter will be inserted into the subdural space for measurement of intracranial pressure and will be connected to the ICP monitor. The opening ICP will be recorded.

Cerebral perfusion pressure (CPP) will be measured as per below formulae:

 Formula: CPP = MAP – ICPWhere,

MAP = Mean arterial pressure.

ICP = Intra Cranial pressure.

 Brain relaxation score will be assessed by the operating surgeon immediately on opening the duramater on a four-point scale (1=adequately relaxed, 2=satisfactorily relaxed, 3=firm brain, 4=bulging brain). Heart rate (HR), MAP, EtCo2, CVP, will be monitored continuously and recorded at 30 minutes interval till end of surgery. Fluid intake, urine output and blood loss will be recorded at the interval of 1 hour till the end of surgery. ABG, serum electrolytes and osmolarity will be first recorded at the start of surgery and will be taken as base line value, thereafter it will be analyzed at the interval of 1 hour till the end of surgery.

During intraoperative period, patient will be looked for any complications like Hypotension, Hyponatremia, Hypernatremia, Hypokalemia, Hyperkalemia and will be treated accordingly.

At the end of surgery further course will be decided by the discretion of anesthesiologist (extubation/postoperative ventilation). Patients not fulfilling the criteria for extubation will be shifted to Intensive Care Unit (ICU) for ventilation and delayed extubation, whereas others will be extubated after reversal of neuromuscular blockade with injection neostigmine (0.05 mg/kg) and glycopyrrolate (0.01 mg/kg)

The time to extubation will be recorded. Neurological status of patients at the time of extubation and at the time of discharge will be recorded.

The patient will be followed till the discharge from the hospital and neurological outcome with

Extended Glasgow Outcome Scale (GOS- E) will be recorded over telephone at the end of 3

months