Thyromental Height Test Versus Sternomental Displacement in Elderly

Thyromental Height Test (TMHT) : will be measured while a patient is lying supine with the head and neck are maintained in a neutral position using a pillow under the head. By using a digital depth gauge, the TMH is the vertical distance measured between the anterior border of the thyroid cartilage directly on the thyroid notch and the anterior border of the mentum.

Sternomental displacement (SMDD): While the patient is sitting with the head in a neutral position, SMD-neutral will be measured using a tape as the distance between upper borders of the manubrium sterni and the mentum. The SMD-extension will then be measured in the same way with the head extended on the neck. The difference between SMD-extension and SMD-neutral will then be calculated as SMDD.

patients will be pre-oxygenated with 100% oxygen for 3 minutes, anesthesia will be then induced intravenously using fentanyl 2 μg/kg, propofol 1 -1.5 mg/kg, and succinylcholine 1 mg/kg lean body weight. Mask ventilation will be maintained till complete muscle relaxation guided by a peripheral nerve stimulator. Using Macintosh laryngoscopy, an anesthetist who has at least three years experience and who will be blinded to the preoperative tests' results, determined the best laryngeal view by using Cormack-Lehane (CL) grading system from I-IV. External neck manipulation will be used when needed to obtain the best laryngoscopic view. Endotracheal intubation will then be accomplished. The number and duration of intubation attempts will be recorded.