Preoxygenation With Optiflow™ in Morbidly Obese Patients is Superior to Face Mask

Preoxygenation With Optiflow™, a High Flow Nasal Cannula (HFNC), is Superior to Preoxygenation With Facemask in Morbidly Obese Patients Undergoing General Anesthesia

Optiflow™ may provide an opportunity to prolong apnea time in the morbidly obese patient population. This study will examine whether Optiflow can do this, and compare the pre-oxygenation with Optiflow to the pre-oxygenation achieved with face mask.

The use of high flow nasal cannula (HFNC) originated in neonatal care, and has become widespread in its application for patients that are high risk for hypoxemia, both in critical care and emergency settings. Therefore, high flow nasal oxygenation continues to be studied in airway management for preoxygenation, as well as maintenance of oxygenation in airway procedures. Optiflow™, a humidified high flow nasal cannula, has already been shown to be useful in preventing desaturation during intubation in ICU patients versus the non-rebreathing mask, in addition to, prolonging safe apnea time in patients with potential difficult airways. Additionally, preoxygenation with HFNC prior to intubation of patients in hypoxemic respiratory failure has also been shown to decrease desaturation during apnea compared to preoxygenation with traditional bag valve mask. The morbidly obese patient presents a separate group of challenges to the anesthesiologist in regards to mask ventilation and intubation. Obesity (along with other factors) has been shown to contribute to difficulty with mask ventilation. Obese patients have altered respiratory physiology, including decreased functional residual capacity, increased oxygen consumption and lower tidal volumes, as compared to the non-obese patient. These factors contribute to obese patients potentially having a shorter apnea time before desaturating during induction of general anesthesia, as compared to the non-obese patient. Weight is inversely correlated with safe apnea time. Optiflow™ may provide an opportunity to prolong apnea time in the morbidly obese patient population. If demonstrated to be efficacious as a method for preoxygenation and prolongation of apneic time, this could provide a safer environment for intubation in this particular patient population.

Standard preoxygenation with a mask will be performed for five minutes. Once preoxygenation is complete, patients will be induced with standard induction medications including lidocaine, midazolam, fentanyl and propofol. Once the patient is apneic, one breath will be given via facemask to confirm ventilation and then 0.6 mg/kg of rocuronium will be administered. The 5.5mm flexible intubation scope will be introduced into the oropharynx and advanced into the trachea with the assistance of the C-MAC video laryngoscope. Once the flexible intubation scope is in the trachea, the endotracheal tube (7.0 mm unless otherwise specified) will be advanced. Ventilation will not begin until the primary or secondary endpoints are reached.

The high flow nasal cannula (Optiflow) will be applied as soon as the patient is in the operating room. The patient will be preoxygenated with high flow nasal cannula at 50 L/min for 5 minutes. After induction, general anesthesia will be maintained with a propofol infusion. One breath will be given via facemask to confirm ventilation and then 0.6 mg/kg of rocuronium will be administered. Upon apnea, the Optiflow™ flow will be increased to 70 L/min and jaw thrust will be performed until the patient is adequately relaxed. The video laryngoscope (C-MAC) will then be introduced into the oropharynx and the flexible intubation scope advanced into the trachea with the assistance of the C-MAC. Once the flexible intubation scope is in the trachea, the endotracheal tube will be advanced.

Optiflow™ (Fisher & Paykel Healthcare Limited, East Tamaki, Auckland-New Zealand) offers the ability to comfortably deliver a complete range of oxygen concentrations and flows to extend the traditional boundaries of oxygen therapy. This will be placed on the patient immediately upon entering the operating room for 5 minutes, at 50 liters per minute then increased to 70 liters per minute after induction.

We will apply the facemask to the patient immediately upon entering the operating room to pre-oxygenate for five minutes.

Propofol infusion 50 micrograms to 150 micrograms will be administered immediately on induction to maintain sedation throughout apneic oxygenation.

After patient is induced, the 5.5mm flexible intubation video scope (C-MAC Premium Video Intubation Platform-KARL STORZ) will then be introduced into the oropharynx and advanced into the trachea with the assistance of the C-MAC video laryngoscope (3 or 4 blade based on anesthesiologist's discretion).

Intraoperatively, apneic time will be record from the time of administration of the muscle relaxant. The time until the first desaturation will be recorded. The maximum time of measurement will be 10 minutes.

The time until hypercarbia to more than 65 mmHg will be measured from the time of administration of the muscle relaxant. The time until transcutaneous CO2 is > 65 mmHg will be recorded, unless 10 minutes is reached before that level is reached.

Assessment of accurate correlation between transcutaneous CO2 monitoring, end tidal CO2, and/or PaCO2 will be performed up to 10 minutes.

Inclusion Criteria: Adult patients (≥ 18 years old) undergoing elective surgery requiring general anesthesia BMI > 40 kg/m2 American Society of Anesthesiology (ASA) Physical Status II-III Exclusion Criteria: Chronic hypoxemia (SpO2 <94% on room air or on home oxygen) Acute respiratory failure Coronary artery disease and/or congestive heart failure Moderate-Severe pulmonary hypertension and/or RV dysfunction Full stomach (recently eaten) Pregnancy Chronic pulmonary disease (specifically COPD or interstitial disease, NOT asthma) Respiratory tract pathology Facial Abnormality American Society of Anesthesiology (ASA) Physical Status IV-V

This is a collaborative study, so the information will be shared with the researchers in Texas. However, we do not plan to use this information for other studies.

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