Evaluation of changes in airway parameters using Point of Care Ultrasonography in patients undergoing spine surgery in prone position: A prospective observational study

Following enrollment, after pre-anaesthesia evaluation, patients posted for spine surgeries in the prone position will be brought to the preoperative area, and we will assess the MMC during airway examination, neck circumference will be assessed using standard measuring tape at the level of cricoid cartilage. An ultrasound machine (Sonosite) Fujifilm Inc. USA) with a low-frequency convex array probe (1–15 MHz) and a high-frequency linear array probe (6–15 MHz) will be used for sonography. A low-frequency ultrasound probe will be placed beneath the chin, along the midline and will be adjusted to obtain a clear visualization of the entire outline of the tongue, as well as the border between the mandible and the hyoid bone on the screen. Once the desired image is achieved, it will be frozen and saved. This frozen image will then be used to measure the cross-sectional area of the tongue by outlining the tongue’s trajectory. Subsequently Tongue Thickness (TT), Tongue width (TW) and Tongue cross-sectional area (TCSA) will be measured.  Finally, a high-frequency ultrasound probe will be placed transversely at the level of the thyrohyoid membrane and adjusted to obtain a clear view of the epiglottis. The epiglottis will appear as a curved, hypoechoic structure, and its image will be frozen and saved. (22)

After shifting the patient inside the operation theatre (OT), we will attach American Society of Anaesthesiologists (ASA) standard monitors i.e., Non-invasive Blood Pressure (NIBP), pulse oximetry (SpO2) and the Electrocardiography ECG electrodes, intravenous fluids (i.v.) will be connected through i.v. lines by securing 2 large bore i.v. cannulas simultaneously. Once the vitals are visualized on the monitors, pre-oxygenation will be started using appropriate size mask for 3 minutes followed by induction with standard induction agents. Patients will be premedicated with injection midazolam 0.01mg/kg. General anaesthesia will be induced with a suitable opioid- fentanyl (2mcg/kg), titrated doses of propofol (1.5 – 2.5mg/kg) and vecuronium 0.1mg/kg. Intubation will be done using an appropriate size cuffed endotracheal tube (8mm for males and 7.5mm for females). Once the airway is secured, bilateral air entry will be confirmed by 5-point chest auscultation and End-Tidal Carbon dioxide (ETCO2) graph. General anaesthesia will be maintained with isoflurane at titrated doses in a mixture of oxygen and nitrous oxide (50:50) and vecuronium. The patients will be ventilated with a tidal volume of 6-8 ml/kg, positive end expiratory pressure (PEEP) will be set at 5 cms of H2O, an inspiratory: expiratory (I:E) ratio of 1:2, and the respiratory rate will be adjusted to maintain an end-tidal carbon dioxide concentration (ETCO2) of 35-40 mm of Hg. Strict temperature monitoring will be done in order to maintain normothermia throughout the surgical procedure. Preloading with deficit fluid (body weight X 1.5ml X hours fasted) will be done to maintain euvolemia before turning the patient to prone position. The mean arterial blood pressure (MAP) will be maintained at more than 60 mm of Hg. After induction on the transport trolley, the patient will be carefully turned to prone position on the operation theatre (OT) table over 2 bolsters, one for the shoulder and other for the iliac crests. The abdomen will be set free. A horse-shoe shaped head support will be used which will ensure a straight head and neck alignment to avoid neck compression, it will provide adequate venous drainage and will reduce kinking of the endotracheal tube. Axilla and knees will be cushioned appropriately with cotton padding to avoid brachial plexus traction or peripheral nerve injuries. All pressure points will be appropriately padded in order to prevent pressure injuries. Eye padding will be used to reduce pressure effects on the eyes and prevent any ocular injuries. The arms will be positioned at < 90 oangles at shoulder and axilla. The table will be positioned such that the heart lies above the level of tragus in order to improve cerebral venous drainage.  This position will be maintained throughout the surgery. After the surgery is done, extubation of trachea will be done if the extubation criteria is met using i.v. reversal agents- i.v. neostigmine 0.05 mg/kg and i.v. glycopyrrolate 0.01mg/kg. Monitors will be detached along with the i.v. lines. Within 20 minutes of extubation of trachea, we will measure following parameters using POCUS: ANS-VC, TT, TW AND TCSA and the frozen images will be stored. Next, we will measure neck circumference at the level of cricoid cartilage using standard measuring tape. The duration of anaesthesia and duration of surgery will be noted. The total volume of intravenous fluids used intraoperatively will be noted.