VOLUME OF AIR REQUIRED TO INFLATE THE ENDOTRACHEAL CUFF TO ACHIEVE INTRACUFF PRESSURE OF 25cmH2O - AN PROSPECTIVE OBSERVATIONAL STUDY

After obtaining approval from the Institutional Ethics Committee, participants satisfying the inclusion criteria will be enrolled after obtaining informed written consent. A thorough pre-anaesthetic evaluation will be done a day prior to surgery according to standard anaesthetic protocol followed in hospital.

On the previous day thorough airway examination will be done during pre-anaesthetic check up and premedications will be prescribed as per standard protocol followed in hospital.

Once the patient is shifted to the operation theatre, standard preparations such as attaching of routine monitoring devices (electrocardiogram, pulse oximetry (SpO2), noninvasive blood pressure) will be performed. Intravenous (iv) fluids will be started after securing a suitable intravenous cannula as per standard institutional practice.

Consultant will select size of the ETT for intubation which will be recorded.

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All the patients will be preoxygenated with 100% oxygen for 3 minutes with a close-fitting mask followed by intravenous (iv) injection of Fentanyl (2 mcg/kg) . Standard Intravenous induction will be done with Propofol (2.0 mg/kg) as per standard anaesthetic protocol followed in hospital. After confirming adequate mask ventilation, muscle paralysis will be achieved with Succinylcholine (2 mg/kg) or a non depolarizing muscle relaxant as per standard institutional practice.

Male patient trachea will be intubated with an 8 or 8.5 mm internal diameter ETT and female patient trachea will be intubated with a 7.0 or 7.5 mm internal diameter ETT as per the standard institutional practice. The endotracheal intubation is done by anaesthesiologist under direct laryngoscopy.

Before cuff inflation, airway ultrasonography will be done using a 38 mm 6–13 MHz, linear ultrasound probe (L4 – 12t, GE Logique e, GE Healthcare, Chicago). The ultrasound probe will be placed transversely on the neck perpendicular to the skin. The probe will be moved cranially or caudally until the true vocal cords could be identified and transverse tracheal diameter (inter mucosal diameter and inter cartilaginous diameter) will be measured at the level just above sternal notch and transverse tracheal diameter will be noted.

In longitudinal view, at the midcuff level the distance between outer layer of ETT Cuff and the inner layer of trachea will be measured and same will be noted. Cuff will be inflated using a 10cc syringe according to manometer (PORTEX cuff pressure monitor, Germany) readings and intracuff pressure will be titrated to 25 cmH2O. Cuff will be inflated in such a way that with every ml of air intracuff pressure will be checked using manometer. Cuff will be inflated with air until the intracuff pressure 25 cmH2O is achieved. Once cuff is inflated to a pressure of 25 cmH2O, anterior part of the neck over trachea will be auscultated to note any audible leak around the ETT cuff.

After cuff inflation, airway ultrasonography will be done using a 38 mm 6–13 MHz, linear ultrasound probe (L4 – 12t, GE Logique e, GE Healthcare, Chicago). The ultrasound probe will be placed transversely on the neck perpendicular to the skin. The probe will be moved cranially or caudally until the true vocal cords could be identified and transverse tracheal diameter (inter mucosal diameter and inter cartilaginous diameter) will be measured at the level just above sternal notch and will be noted.

In longitudinal view, at the midcuff level the distance between outer layer of ETT cuff and the inner layer of trachea will be measured and same will be noted.Anaesthesia will be maintained with Isoflurane or Sevoflurane, a volatile anaesthetic agent, in

a combination of nitrous oxide and oxygen as per standard protocol followed in hospital.

Serial monitoring of intracuff pressure will be done every hourly and intracuff pressure

adjusted according to readings in the manometer by inflating or deflating the cuff. The

amount of air removed or amount of air added to maintain intracuff pressure of 25 cmH2O

will be noted.

Once patient is shifted to postoperative ward, presence of sore throat will be looked for and

will be recorded at zero, sixth and twenty fourth hour.

Sore throat will be evaluated while resting using a four-point scale (severe, moderate, mild,

or none), which is defined as follows:

1. Severe sore throat (hoarseness or change in voice that was considered to be throat

distress).

2. Moderate sore throat (patient-volunteered complaints of sore throat.

3. Mild sore throat (complaints of sore throat reported only after enquiring).

4. None.

Total duration of the procedure and intraoperative positional changes if any will be recorded.