High Flow Oxygen During Operative Hysteroscopy

High‐flow nasal cannula (HFNC) oxygen therapy represents an open circuit ventilationsystem that uses flows up to 70 L/min of 100% oxygen through Optiflow THRIVETM(transnasal humidified rapid‐insufflation ventilatory exchange) device (Fisher and PaykelHealthcare Ltd, Auckland, New Zealand).Compared to conventional low‐flows oxygen therapy systems, the heating and humidificationof the flow facilitate tolerability by the patient, ensure an efficient muco‐ciliaryfunction and allow to reach higher and more stable inspiratory fractions of oxygen.The system produces a flow‐dependent effect of continuous positive airway pressure ofabout 1 cmH20 for every 10L/min increase in oxygen flow and a reduction of the deadspace, having the potential to increase the alveolar volume thus improving gas exchanges.The resulting reduction in respiratory rate and the improvement of thoracoabdominalsynchrony minimize the onset of respiratory fatigue in the patient.Initially introduced for the treatment of acute hypoxemic respiratory failure, HFNCoxygen therapy is increasingly used also in anesthesia as the only airways managementtechnique during short‐term procedures performed under sedation (e.g. digestiveendoscopy) or under general anesthesia (such as microlaryngoscopies).Compared to low‐flows oxygen systems, the greater CO2 elimination capacity could reducethe incidence of hypoventilation and apnea episodes potentially associated with patientsedation.Operative hysteroscopy is a brief procedure, normally lasting <30 minutes, usuallyperformed in a day‐hospital regime under procedural analgo‐sedation, with conventionalventilatory support through a face mask/laryngeal mask.The primary objective of this study is the comparison of the rate of success in airwaysmanagement via the THRIVE system versus positive pressure ventilation by I‐gel laryngealmask during 180 hysteroscopies performed under general anesthesia.Secondary objectives are: the comparison of intraoperative and postoperativecomplications between the two groups.Materials and methods Patient monitoring throughout the procedure will include automaticnoninvasive, intermittent (every 5 minutes) blood pressure monitoring, 3‐leadselectrocardiogram, peripheral oxygen saturation (SpO2), bispettral index (BIS),transcutaneous capnography with TCM5 Radiometer monitor.Upon arrival in the operating room, the patient will assume the lithotomic position; aperipheral venous cannula will be placed at the level of the hand or forearm and it willbegin the infusion of Ringer Lactate solution 3 ml/kg/h. Omeprazole 40 mg anddexamethasone 4 mg will be administered before the procedure as standard internalpractice.In the THRIVE group, dedicated Optiflow THRIVETM nasal cannulas will be positioned for100% high flow oxygen therapy at an initial flow of 30 L/min. After induction ofanesthesia and throughout the procedure the flow of oxygen will be increased to 70 L/min.In the control group (CONTROL) after induction of anesthesia the patient will bemechanically ventilated through an I‐Gel laryngeal mask.General anesthesia, as per normal clinical practice, will be induced and maintained bytarget‐controlled infusion (TCI) of propofol (7 mcg/Kg) by Orchestra Infusion system(Fresenius Kabi) and fentanyl 1.5 mcg/kg and in both groups. Propofol infusion rate willbe between 3‐4 mcg/ml for propofol, so to maintain a level of sedation monitored via BISbetween 40‐50. Paracetamol 1g, ondansetron 4 mg and ketorolac 30 mg will also beadministered as per normal clinical practice.In case of desaturation episodes, defined as a SpO2< 94% or increases in tcCO2 above 65mmHg, the patient will be assisted with positive pressure ventilation through a facial orlaryngeal mask or oro‐tracheal intubation based on clinical judgment of theanesthesiologist.At the end of the hysteroscopy the patient will be transferred to the Post‐AnesthesiaCare Unit (PACU) for 3 hours of post‐procedural monitoring as required by internalprotocol for day‐surgery procedures. Standard monitoring will include non‐invasive,intermittent (every 15 minutes) blood pressure monitoring, 3‐leads electrocardiogram andperipheral oxygen saturation (SpO2).One hour after the end of the procedure and before discharge from the PACU the patientwill be asked to quantify the perceived degree of dyspnea with the Borg dyspnoea scoreand the degree of comfort using a Visual Numeric Scale (VAS) ranging from 0 to 10. Incase of SpO2<94%, additional oxygen will be administered by means of a Venturi‐type facemask with FiO2 40%. Discharge from the PACU will require an Aldrete score of 9‐10.Statistics The data will be analyzed according to an intention‐to‐treat principle.Clinical and demographic characteristics of the sample will be described throughdescriptive statistical techniques. Continuous quantitative variables with normaldistribution will be reported as mean and standard deviation; as median and interquartilerange the non‐normal variables.Categorical variables and missing data will be presented as absolute values andpercentage, n (%).Continuous variables will be compared with the Student t‐test in case of normaldistribution or, if not, with the Mann‐Whitney test for independent samples. Thenormality of the distribution of the variables will be verified graphically by histogramsand with the Shapiro‐Wilk test.Continuous variables with repeated measurements will be compared with a mixed‐effectlinear regression model. The type of airway management used and the timing at which themeasurements will be performed will be considered as fixed effects; a random effectrelated to the patient will also be added.The assumption of normality of the residues of the model will be graphically verified byhistograms and Q‐Q plots. The P‐values will be obtained with the likelihood ratio test ofthe complete model with the effect in question with respect to the model without theeffect. The estimates of the predictors used in the model will be reported with therelative 95% confidence intervals and P‐values obtained with the Wald test.In case of failure of the technique, defined as a transcutaneous concentration of carbondioxide (tcCO2) > 65 mmHg and/or SpO2 < 94% in any of the study groups, a time‐to‐event(Kaplan‐Meier) analysis will be carried out that takes into account the differentduration of the procedures and therefore the different risk ranges for the possible onsetof hypercapnia and / hypoxemia.Differences between categorical data will be reported in terms of relative risk or riskdifferences, 95% confidence intervals and p‐values based on the Χ2 test or fisher's exacttest.The significance level will be set for α < 0.05. All analyses will be performed with thestatistical software R version 4.1.2 (R Foundation for Statistical Computing, Austria).Continuous variables with repeated measurements will be compared with a mixed‐effectlinear regression model. Normality of distribution will be verified with the Shapiro‐Wilktest. Continuous variables will be compared with Student t ‐ or Mann Whitney test;categorical variables with the Chi‐square test.Sample size calculation In 2021, Kim et al. compared the safety of high flow oxygentherapy to conventional low‐flow oxygen support for gastrointestinal endoscopicprocedures performed under sedation reporting minimum values of peripheral saturationdetected by pulse‐oximeter higher in the high‐flow group (99.8%) compared to low‐flowoxygen therapy (95.1%).To our knowledge, no study has compared these two methods during operative hysteroscopiesunder procedural sedation.Based on literature and on the results from an internal registered pilot study in whichwe investigated the success rate of THRIVE as unique airway management technique in thissetting, assuming a similar success rate of 95% for THRIVE and laryngeal maskventilation, for a unilateral confidence interval of 95% and a 90% test power, weestimated a minimum sample of 82 patients per group to test a non‐inferiority limit of10%. The sample was increased to 90 patients for group to take into account any dropouts.