Hemodynamic Effects of Apnoeic Oxygenation With High-flow Nasal Oxygen in Adults Undergoing Laryngeal Surgery

During apnoeic oxygenation there is a continuous raise in carbon dioxide with subsequent respiratory acidosis. The hypercapnia and respiratory acidosis have several dose-related effects on both the systemic and the pulmonary circulation and the heart that ultimately, if unrecognised, can result in cardiovascular collapse and fatal arrhythmias. In our knowledge, no studies have investigated the haemodynamic effects of apnoeic oxygenation with HFNO.

The general purpose of this project is to investigate haemodynamic alternations during apnoeic oxygenation with HFNO compared to mechanical ventilation in relatively healthy patients under general anaesthesia during laryngeal surgery.

This study aims to investigate and observe the circulatory effects in a patient undergoing apnoeic oxygenation with HFNO during shorter elective laryngeal surgery compared to mechanical ventilation. 20 patients scheduled for elective laryngeal surgery, eligible for apnoeic oxygenation at the Karolinska University Hospital, will be recruited. If eligible, the patient will receive oral and written study information by one of the investigators well in advance of the planned surgery. After a signed consent, the subject will be enrolled and randomised to either apnoeic oxygenation with HFNO or mechanical ventilation.

Patient characteristics such as age, sex, weight, height, ASA classification, other comorbidities and airway-related parameters will be documented. A preoperative transthoracic echocardiographic examination and routine perioperative monitoring, will be performed together with a 12-lead ECG. Preoperatively, an arterial catheter will be inserted in the radial artery and an arterial blood gas, measuring PaCO2, PaO2, pH, HCO3 and blood samples of stress markers including catecholamines and other cardiac biomarkers will be collected. The FloTrac system will be connected to the arterial catheter and baseline values will be registered. A peripheral venous catheter is placed prior to anaesthesia and the patient is placed supine.

In the apnoeic oxygenation group the HFNO nasal prongs (Optiflow, Fisher \& Paykel Healthcare, Auckland, New Zealand) is placed in the nostrils and used for pre-oxygenation, 100 % O2, 40 L/min during 3 min. Thereafter, anaesthesia is induced by intravenous Propofol and Remifentanil administration. Rocuronium for full neuromuscular blockade is administered and a jaw thrust is used to keep an open airway. The start of apnoea is noted, defined as 1 minute after Rocuronium administration. The airway will be kept patent throughout the procedure using a suspension laryngoscope, placed by the ENT surgeon.

During apnoea the flow of oxygen is increased to 70 L/min, 100% O2. Apnoea will be discontinued if any of the criteria SpO2 \< 90%, PaCO2 \>11 kPa, pH \<7.15 or arrhythmias with haemodynamic effects occur. In the mechanical ventilation group pre-oxygenation is performed by a tight-fitting facemask, 100 % O2, for three minutes. After anaesthesia induction using intravenous Propofol and Remifentanil and Rocuronium for full neuromuscular blockade, tracheal intubation is performed and mechanical ventilation is started. The start of apnoea is noted. The ventilator is set to PEEP 5 cmH2O, tidal volume (TV) 7 ml/kg ideal body weight, FiO2 0.4, and the respiratory frequency adjusted to reach a PaCO2 of 5,0 -5,3 kPa. Standard perioperative monitoring will be registered (peripheral oxygen saturation, heart rate and MAP). Arterial blood gases will be collected and ECG performed repeatedly. Data from the FloTrac system will be monitored throughout the procedure. Transthoracic echocardiography will be performed regularly. Blood samples to analyse stress markers including catecholamines and cardiac biomarkers will be collected at specific timepoints.

At the end of the procedure, any neuromuscular blockade is reversed by Sugammadex. The end of apnoea is defined as reoccurrence of spontaneous breathing or start of mask ventilation. In the mechanically ventilated group, subjects are extubated when awake and responsive.

After the procedure and when fully awake, the patient is transferred to the post-operative unit. The FloTrac monitoring will be continued during the postoperative period and the TTE, ECG evaluation, arterial blood gases, stress markers including catecholamines and cardiac biomarkers will be repeated during the post-operative period. Routine postoperative monitoring will be performed for a minimum of 60 minutes.

Eligibility Criteria:
Inclusion criteria

* Adult, ≥18 years old
* ASA 1-2
* BMI \< 30
* Planned for elective laryngeal surgery

Exclusion criteria

* NYHA-class \>1
* Pregnancy
* Severe gastric reflux
* Neuromuscular disease
* Any pulmonary disease
* Smokers or former smoker, last finished 6 months before inclusion
* Not capable of understanding study information and signing a written consent