A comparison of the rate of rise of transcutaneous carbon dioxide during apnoeic oxygenation in microlaryngoscopy using transnasal humidified rapid insufflation ventilatory exchange (THRIVE) versus low flow tracheal insufflation: a randomised control trial

INTERVENTION: This study will involve patients undergoing elective microlaryngoscopy procedures under care of ENT and anaesthetics. These patients will be randomised on day of surgery using simple randomisation, assigning patients to one of two anaesthetic techniques; ARM 1: Trans‐nasal Humidified Rapid Insufflation Ventilatory Exchange (THRIVE) Those patients enrolled into the THRIVE arm will be induced with high flow nasal cannula attached but not yet turned on. As surgery begins, they will have their face masks removed and high flow O2 at 100% 70L started via Optiflow THRIVETM apparatus (Fisher and Paykel Healthcare Ltd, Auckland, New Zealand). OR ARM 2: Low Flow Intra‐tracheal Oxygen Insufflation (Lo‐Flo) Those patients enrolled into the Lo‐Flo arm will be induced. After face mask ventilation and waiting suitable time for paralysis, a low flow oxygen catheter will be passed through the glottic opening to sit mid tracheal level using standard intubating equipment (direct or indirect laryngoscopy). After this oxygen catheter has been place, the patient will be ventilated using face mask ventilation until the surgical start point. At this point, face mask will be removed and oxygen catheter attached to oxygen wall outlet will be started at 0.5L/min. The maximal allowable time for either apnoea technique will have a 30 minute cut off point. There will be 45 patients will be randomised into each trial arm. As the patient arrives in the holding bay prior to their operation, the transcutaneous carbon dioxide (TcCO2) monitor will be connected to the patient. Upon entering the operating room, routine anaesthetic monitoring will be established. The patient will be pre‐oxygenated using an appropriately size face mask until the end tidal oxygen (EtO2) CONDITION: Anaesthesiology ‐ Anaesthetics laryngeal pathology;carbon dioxide rate of rise; ; laryngeal pathology ; carbon dioxide rate of rise Respiratory ‐ Other respiratory disorders / diseases PRIMARY OUTCOME: Rate of rise of TcCO2 per unit time [Time zero will be the moment that the surgical laryngoscope first enters the patient’s oral cavity. TcCO2 is recorded continuously and electronically by the Sentec TcCO2 device. The TcCO2 will be measured every minute. The rate of CO2 rise will be calculated over the operative time period.] INCLUSION CRITERIA: All patients over the age of 18 years undergoing microlaryngoscopy procedure SECONDARY OUTCOME: Maintenance of oxygenation[Oxygen saturation (SpO2) at time zero; and at the completion of surgery will be recorded. The times at which SpO2 falls to 95% and 92% will also be recorded, should these events occur. ] Oral, nose or throat discomfort as reported by patient[Discomfort defined by patient complaining of mucosal dryness or pain immediately post operatively and at day 3 ‐5 post operatively by telephone will be recorded on a scale of none, mild, moderate or severe. ] Surgical conditions ‐ this will seek the opinion of the surgical conditions from our otolaryngologist performing the microlaryngoscopy. This will be recorded immediately after surgery on a proforma describing quality surgical field as poor, adequate or excellent, with a free text comments section. [To be documented by consultant surgeon immediately after procedure]