Positive Airway Pressure Under Apnoeic Oxygenation With Different Flow Rates in Nasal Cannula Therapy

Study Overview
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Brief Summary
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The main objective of this explorative observational study is to investigate the pressures in infraglottic airway and the pharynx provided by THRIVE , using flows ranging from 1l/min to 80 l/min, in patients hospitalized for elective surgical procedure; to investigate the correlation between airway pressure and nasal oxygen flow.

Detailed Description
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Eligible adults with written informed consent will be monitored for general anaesthesia according standard operating procedure of the Bern University Hospital's anaesthesia department. Additional non-invasive monitoring for this study are transcutaneous measurement of carbon dioxide and oxygen (TCM 5®, Radiometer, Krefeld, Germany), NarcotrendTM ( Narcotrend-Group, Hannover, Germany)and thoracic electrical impedance tomography (EIT, PulmoVista® 500, Draeger, Luebeck, Germany). Normal pre-oxygenation (until end expiratory carbon dioxide is > 90% or time > 3 minutes) will occur. Anaesthesia will be started using a target -controlled infusion system for Propofol and Remifentanil, using NarcotrendTM to measure depth of anaesthesia. All patients will receive a standard dose of neuromuscular blockage to facilitate airway management and total intravenous anaesthesia will be installed. Using the train of four measurement (TOF) full neuromuscular blockage with Rocuronium will be confirmed every 30 seconds. After administration of rocuronium, proper bag-mask ventilation will be confirmed. Intratracheal pressure will be measured by 11 Fr. catheter (Cook Medical, Bloomington, IN, USA), connected to a CODAN Xtrans®-transducer (CODAN ARGUS Ag, Baar, Switzerland). A 11 Fr. catheter (Cook Medical, Bloomington, IN, USA) will be introduced oral in the trachea facilitated by video-laryngoscopy. To ensure patency of the upper airway jaw thrust via Esmarch manoeuvre will be applied and flexible bronchoscopy will confirm upper airway patency. Initially this 11 Fr. catheter will be positioned in the right main bronchus (2 cm below the carina). The first measurement will be performed with a randomized sequence of flow rates of 80, 60, 40, 20 or 1 l/min with opened and closed mouth. Each pressure measurement will be performed after a stable pressure plateau of 10 seconds will be observed. The catheter will then be retracted and the pressure quantification are performed with the same sequence, defined above, in different positions (50% of trachea length and pharyngeal pressures 10 cm from upper front teeth). The order of flow and mouth opening will be randomized. The study intervention will end when all measurements are taken or upper airway patency cannot be ensured under direct endoscopy view. If one of the following criteria is met: peripheral oxygen saturation (SpO2) <92% or transcutaneous carbon dioxide (PtCO2) >80mmHg, immediately bag mask ventilation will be initiated, until normal values of SpO2 and PtCO2 are reached. When any of the end points is reached, normal anesthesiologic care will be established as planned. A safety interview will be conducted on the first post-operative day to evaluate injuries during airway management (e.g. bleeding, sore throat, hoarseness, lip injuries), pain, postoperative nausea and vomiting.

Official Title
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Positive Airway Pressure Under Apnoeic Oxygenation With Different Flow Rates

Conditions
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Apnoeic Oxygenation

Intervention / Treatment
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* Drug: Oxygen


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: > 18 years Written informed consent Undergoing elective surgery Requiring general anesthesia ASA 1-3 (American Society of Anesthesiologists) Exclusion Criteria: Any Indication for fibre optic intubation Expected impossible mask ventilation Known coronary heart disease Known heart failure, NYHA classification( New York Heart Association ) ≥ 2 Peripheral occlusive arterial disease, Fontaine ≥ 2b BMI > 30kg/m2 and BMI < 16kg/m2 Hyperkalaemia (K > 5.5 mmol/l) Known COPD (Chronic obstructive pulmonary disease) Gold classification ≥ 2 Known pulmonary arterial hypertension, systolic > 35mmHg Known obstructive sleep apnoea syndrome in need of therapy High risk of aspiration Increased intracranial pressure Intracranial surgery Limited knowledge of German language Absent power of judgement Pregnancy (pregnancy test before inclusion) Neuromuscular disorder Known or suspected cervical spine instability Nasal obstruction, impossibility of nasal ventilation (both sides patent) Allergies or contra-indications to one or more of the used anaesthesia agents

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Treatment
Intervention Model: Sequential Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: High-flow-nasal-cannula-therapy (HFNCT)<br>100% Oxygen at 80 l/min with flow reductions of 20 l/min, jaw thrust, with opened and closed mouth, using different flow rates (80l/min, 60l/min, 40l/min, 20l/min, 1l/min) within each subject. | Drug: Oxygen<br>* HFNCT (high flow nasal cannula therapy) will be provided using OptiFlow by Fisher&Paykel.<br>* Other names: High flow Oxygen;|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Mean positive airway pressure during Apnoea (approx.10 min) with HFNCT (High-Flow-Nasal-Cannula-Therapy) | Measurement of the mean positive airway pressure in cm H2O during apnoea time in the pharynx (10cm distal upper front teeth), in the trachea (50% length) and in the right main bronchus (2cm distal carina), with different flow-rates (80l/min, 60l/min, 40l/min, 20l/min, 1l/min), with opened and closed mouth | After induction of anaesthesia; Each pressure measurement (main bronchus,trachea, pharynx) will be performed after a stable pressure plateau of 10 sec. will be observed; until all measurements are taken or upper airway patency cannot be ensured | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Changes in ptcO2 and ptcCO2 in mmHg/min | Transcutaneous measurement | After induction of anaesthesia, during apnoea period; until all pressure measurement (main bronchus,trachea, pharynx) are taken or upper airway patency cannot be ensured | 
| Upper airway patency | Flexible bronchoscopy will confirm upper airway patency: Open or closed | After induction of anaesthesia, during apnoea period; until all pressure measurement (main bronchus,trachea, pharynx) are taken or upper airway patency cannot be ensured | 
| Changes in electrical impedance tomography. (EIT) | EIT will be continuously measured using PulmoVista® 500 visualizing possible atelectasis formation. | After induction of anaesthesia, during apnoea period; until all pressure measurement (main bronchus,trachea, pharynx) are taken or upper airway patency cannot be ensured |