Physiology Regarding Apnoeic Oxygenation During Nasal Cannula Therapy at Different Flow Rates

Study Overview
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Brief Summary
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This study compares under controlled conditions if different flow rates affect apnoea time after induction of anaesthesia and how CO2 clearance is influenced. Furthermore, this study enables to quantify the effects of increased pCO2 on vital parameters (e.g. blood pressure, cardiac output, cerebral perfusion, etc.) The investigators will enroll patients undergoing elective surgery at the University Hospital of Bern, Switzerland. Once anesthesia has been induced, apnoea will set it. During this period, the investigators will compare different methods of apnoeic oxygenation for a maximum of 15 or 30 minutes. Before discharge, an interview will be conducted, assessing complications and patient satisfaction.

Detailed Description
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Eligible, consenting adults will be prepared for general anaesthesia in the usual way consisting of ECG, pulse-oximetry, NarcotrendTM, a venous cannula and an arterial line for continuous blood pressure monitoring. They will receive additional monitoring such as transcutaneous measurement of pCO2 and O2, NIRS, and thoracic electrical impedance tomography (EIT, PulmoVista® 500, Draeger, Luebeck, Germany). Normal pre-oxygenation (until etO2 is > 90% or time > 3 minutes) will occur. Anaesthesia will be started (= induction) using Propofol and Fentanyl, 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. If necessary, additional dosage of neuromuscular blockage will be administered. After administration of Rocuronium, possibility of mask ventilation will be confirmed and the sealed envelope with the randomization will then be opened. As a study intervention, the assigned method (HFNCT 70 l/min with either jaw thrust or laryngoscopy, or 10 l/min or 2l/min with the standard nasal canula, or 0.25l/min delivery of oxgen via a tracheal tube) will be installed and mask ventilation discontinued starting the apnoea period. Nasopharyngoscopy (EF-N slim, Acutronic, Hirzel, Switzerland) will confirm upper airway patency. Blood gas analysis will be conducted: baseline awake, start of apnoea, first minute after apnoea start, and every 2 minutes thereafter with a maximum of 75ml 150 ml in total. Other measurements (ECG, pulse-oximetry, blood pressure, NIRS, thoracic EIT, NarcotrendTM, PtcO2, PtcCO2) will be measured continuously over the study period The study intervention will end when one of the following criteria (study end-points) is met: SpO2 <92%, PtcCO2 > 100 mmHg or time > 30 minutes. When any of the end points is reached, patient-centred standard anaesthesia care will be continued, as planned for the case. A post-operative interview will be conducted before discharge to evaluate injuries during airway management (bleeding, sore throat, hoarseness), pain, postoperative nausea and vomiting.

Official Title
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Physiology Regarding Apnoeic Oxygenation During Nasal Cannula Therapy at Different Flow Rates

Conditions
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Apnoeic Oxygenation

Intervention / Treatment
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* Drug: Oxygen 70l/min
* Drug: Oxygen 10 l/min
* Drug: Oxygen 2l/min
* Procedure: Jaw thrust
* Procedure: Videolaryngoscopy
* Drug: oxygen 0.25l/min


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 Exclusion Criteria: Any Indication for fibre optic intubation Expected impossible mask ventilation Known coronary heart disease Known heart failure, NYHA classification ≥ 2 Therapy including β-receptor antagonists Arrhythmias in need of anti-arrhythmic therapy (e.g. implanted cardio defibrillator) Peripheral occlusive arterial disease, Fontaine ≥ 2b Known stenosis of the (common or internal) carotid or vertebral arteries BMI > 35kg/m2 and BMI < 16kg/m2 Hyperkalaemia (K > 5.5 mmol/l) Known COPD Gold classification ≥ 2 Known pulmonary arterial hypertension, systolic > 35mmHg Known obstructive sleep apnoea syndrome in need of therapy High risk of aspiration (requiring rapid sequence induction intubation) Increased intracranial pressure Intracranial surgery Limited knowledge of German language Absent power of judgement Anaemia, Hb < 100 g/l Pregnancy (pregnancy test in all female patients) 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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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Treatment
Allocation: Randomized
Intervention Model: Single Group Assignment
Interventional Model Description: single centre, prospective, randomized-controlled trial
Masking: Single


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Active Comparator: Control<br>These patients will receive HFNCT with oxygen 70l/min after induction of general anesthesia. Throughout the entire measurement period of 15 or 30 minutes, continuous videolaryngoscopy will be performed. | Drug: Oxygen 70l/min<br>* HFNCT will be provided using OptiFlow by Fisher&Paykel.<br>* Other names: high flow;Procedure: Videolaryngoscopy<br>* Continuous<br>|
| Experimental: High flow<br>These patients will receive HFNCT with oxygen 70l/min after induction of general anesthesia. Throughout the entire measurement period of 15 or 30 minutes, jaw thrust will be performed. | Drug: Oxygen 70l/min<br>* HFNCT will be provided using OptiFlow by Fisher&Paykel.<br>* Other names: high flow;Procedure: Jaw thrust<br>* Continuous<br>|
| Experimental: medium flow<br>These patients will receive oxygen 10l/min after induction of general anesthesia. Throughout the entire measurement period of 15 or 30 minutes, jaw thrust will be performed. | Drug: Oxygen 10 l/min<br>* Medium flow will be applied with a humidifier (Hudson RCI) and a standard nasal cannula.<br>* Other names: medium flow;Procedure: Jaw thrust<br>* Continuous<br>|
| Experimental: low flow<br>These patients will receive oxygen 2l/min after induction of general anesthesia. Throughout the entire measurement period of 15 or 30 minutes, jaw thrust will be performed. | Drug: Oxygen 2l/min<br>* Low flow will be applied with a humidifier (Hudson RCI) and a standard nasal cannula.<br>* Other names: low flow;Procedure: Jaw thrust<br>* Continuous<br>|
| Experimental: minimal flow<br>These patients will receive a standard tracheal tubes after induction of general anesthesia, with 100% Oxygen and Minimum-flow 0.25l/min. The measurement period is 15 or 30 minutes. | Drug: oxygen 0.25l/min<br>* 0.25l/min of oxygen via an endotracheal tube<br>* Other names: minimal flow;|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| pCO2 increase in kPa/min | pCO2 will be measured transcutaneously throughout the apnea period | 15 or 30 minutes (maximum apnea time) | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Lowest Saturation | Lowest SpO2 in % | During apnea period (until end-point is met or max. 15 or 30 minutes) | 
| Change in PaO2 in kPa | Blood gas analyses as well as transcutaneous measurement | During apnea period (until end-point is met or max. 15 or 30 minutes) | 
| Change in cardiac output in L/min | Cardiac output will be measured using pulse pressure measurement | During apnea period (until end-point is met or max. 15 or 30 minutes) | 
| Change in cerebral perfusion in % | Near infrared spectroscopy will be measured continuously | During apnea period (until end-point is met or max. 15 or 30 minutes) | 
| Changes in end-expiratory lung impedance | To quantify atelectasis during apnoeic oxygenation | During apnoea time (until end-point is met or max. 15 or 30 minutes) | 
| Change in invasive blood pressure | Measurement of change due to hypercarbia | During apnoea time (until end-point is met or max. 15 or 30 minutes) | 
| Standard monitoring | 3 pole ECG | During apnoea time (until end-point is met or max. 15 or 30 minutes) | 
| Depth of anaesthesia | Using Narcotrend-EEG | During apnoea time (until end-point is met or max. 15 or 30 minutes) | 
| Bilateral brain oxygenation | Using NIRS | During apnoea time (until end-point is met or max. 15 or 30 minutes) | 
| Arterial blood gas analyses | pH | At 0, 1, 3, 5, 7, 9, 11, 13 and 15 minutes of apnoea or 0,1,3,5,7,9,13,15,17,19,21,23,25,27,29 and 30 min of apnoea. | 
| Arterial blood gas analyses | pCO2 in mmhg | At 0, 1, 3, 5, 7, 9, 11, 13 and 15 minutes of apnoea or 0,1,3,5,7,9,13,15,17,19,21,23,25,27,29 and 30 min of apnoea. | 
| Arterial blood gas analyses | pO2 in mmhg | At 0, 1, 3, 5, 7, 9, 11, 13 and 15 minutes of apnoea or 0,1,3,5,7,9,13,15,17,19,21,23,25,27,29 and 30 min of apnoea. | 
| Arterial blood gas analyses | SaO2 in % | At 0, 1, 3, 5, 7, 9, 11, 13 and 15 minutes of apnoea or 0,1,3,5,7,9,13,15,17,19,21,23,25,27,29 and 30 min of apnoea. | 
| Arterial blood gas analyses | Potassium in mmol | At 0, 1, 3, 5, 7, 9, 11, 13 and 15 minutes of apnoea or 0,1,3,5,7,9,13,15,17,19,21,23,25,27,29 and 30 min of apnoea. | 
| Arterial blood gas analyses | Bicarbonate in mmol | At 0, 1, 3, 5, 7, 9, 11, 13 and 15 minutes of apnoea or 0,1,3,5,7,9,13,15,17,19,21,23,25,27,29 and 30 min of apnoea. | 
| Postoperative questionnaire | Visual analogue scale (VAS) : pain, nausea, vomiting, feeling worried or anxious, feeling sad or depressed, injuries, discomfort, any complications | Morning of first postoperative day | 
| Standard monitoring | Pulse oximetry SpO2 in % | During apnoea time (until end-point is met or max. 15 or 30 minutes) |