Predictors for failure of supraglottic superimposed high‐frequency jet ventilation during upper airway surgery in adult patients; a retrospective cohort study of 224 cases

Supraglottic Superimposed High Frequency Jet Ventilation (SSHFJV) maximizes surgical field during endoscopic upper airway surgery. In our retrospective series of 224 cases, there was a low incidence (12%) of failure with the use of SSHFJV in upper airway surgery. Positive history of pulmonary pathology (OR=4.91) and high BMI (OR=1.15) were found to be significant independent factors for failure of SSHFJV in adult patients undergoing upper airway surgery. Converting ventilation techniques could be safely performed when SSHFJV failed. SSHFJV is a safe ventilation technique during upper airway surgery, even in combination with the application of CO2 laser.

Predictors for failure of supraglottic superimposed highfrequency jet ventilation during upper airway surgery in adult patients; a retrospective cohort study of 224 cases

| INTRODUC TI ON
During endoscopic upper airway surgery, anaesthetists and surgeons have to share the airway. Therefore, alternative ventilation techniques have been developed in the past decades. To optimise the surgical field high-frequency jet ventilation (HFJV) was developed. A "tubeless" HFJV method has been introduced in the late 90s: supraglottic superimposed HFJV (SSHFJV). 1 Other, frequently used tubeless technique is spontaneous breathing with propofol-remifentanil anaesthesia with or without high-flow nasal oxygenation. 2,3 During SSHFJV, surgery is performed through a laryngoscope which has integrated jet stream nozzles enabling ventilation and no catheter is needed, in contrast to conventional HFJV. Using SSHFJV, there is completely free access of the surgical field and adequate oxygenation and ventilation can be achieved during surgery. SSHFJV also lowers the chance of airway burn during laser surgery, as no flammable tube or catheter is needed. As no disposables (like catheters in conventional HFJV) are used during SSHFJV, it seems to be a cheaper technique; however, a cost-effectiveness study has not been performed yet. The only disadvantage of SSHFJV seems to be obligatory visualisation of the airway through the ventilating laryngoscope during the whole procedure, otherwise the ventilation of the patient is not possible, which makes it not suitable, for instance, for intervention in the hypopharynx. According to previous reports, SSHFJV is a safe ventilation method, even in patients with severe cardiovascular and pulmonary comorbidities. 4,5 However, sometimes ventilation has to be temporarily or definitively converted into endotracheal tube ventilation because of drop in O 2 saturation and accumulation of CO 2 . 6 The aim of the present study was to identify factors which can predict failure of SSHFJV in upper airway surgery.

| Ethical considerations
Data were retrospectively collected and the anonymity of the patients has been guaranteed; therefore, no approval of the Institutional Review Board is needed in accordance with Dutch Medical Research Law legislation.

| Patients
This retrospective study included 163 adult patients who underwent 224 upper airway procedures with SSHFJV between November 2007 and November 2017 at our tertiary referral centre.

| Supraglottic superimposed high-frequency jet ventilation
Under general anaesthesia, after pre-oxygenation through a mask, a modified laryngoscope (Jet Laryngoscope; Carl Reiner GmbH) was inserted and the SSHFJV was connected (TwinStream™ Multi Mode Respirator; Carl Reiner GmbH). (Figure 1) During SSHFJV, two jet streams with different frequencies are being used at the same time. One jet stream fires at a high frequency and is continuous, the low frequency is biphasic, providing an inspiratory and expiratory phase.

| Variables
Relevant data from the electronic patients' files were extracted and retrospectively analysed. Clinical imaging data were available in all cases and were reassessed to estimate the severity of the airway stenosis.
The following variables were extracted from the electronic patients' files: age, sex, weight, smoking status, comorbidity status This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

| Outcome measure
When the saturation drops during ventilation with SSHFJV the anaesthesiologist may choose to intubate with endotracheal tube for a short period of time to reoxygenate. When the saturation of the patient is normalised, the operation with SSHFJV can be continued (temporary conversion); however, sometimes it is not possible (definitive conversion). Failure of SSHFJV was defined as temporary and/or definitive conversion.

| Statistical analysis
Patient characteristics and other variables were compared between the converted and non-converted patients using chi-square test (or Fisher's exact test). The t test was used in case of continuous variables.
The potentially predictive variables for conversion of ventilation were analysed using univariable logistic regression. Odds ratios with corresponding 95% confidence intervals and P-values were calculated.
Statistically significantly variables were included in the multivariable logistic regression model and analysed using the backward stepwise method. All statistical analyses were performed using ibm spss statistics 23.0 (IBM, Armonk).

| Patients characteristics
In 198 (88%) cases, satisfactory ventilation by SSHFJV was achieved; however, during 26 interventions (12%) ventilation had to be definitively or temporarily converted to endotracheal tube ventilation.
The main reason for conversion was desaturation of the patient (25/26 cases).
A detailed rendering of the patient characteristics, including age, sex, weight, smoking status, laryngological history, anatomical level of the pathology, diagnosis, treatment and comorbidities, are described in Table 1. Of the converted cases, 14 had a history of pulmonary diseases: six had chronic obstructive pulmonary disease (COPD), two had bronchial asthma, three patients suffered from sarcoidosis involving the lungs and two had obstructive sleep apnoea (OSA). The mean BMI was 34 in the converted group, vs 28 in the non-converted group (P = <.001). In the converted group, the percentage of obstruction was estimated at 51% compared with 33% in the non-converted group (P = .011). There was no difference in CO 2 laser use between conversion and nonconversion groups (77% and 71%, respectively; P = .543). No complications due to use of SSHFJV were observed in any of patients.

| Multivariable analysis
Multivariable model, containing BMI, pulmonary pathology, ASA class and percentage of obstruction after backward stepwise elimination, included BMI and pulmonary pathology only (Table 3). In

| Synopsis
This is the first study investigating the predictors of unsuccessful SSHFJV. In this retrospective analysis of 224 adult cases, we confirmed that SSHFJV is applicable in the vast majority of the cases. The risk of conversion to endotracheal intubation is higher in patients with a history of pulmonary disease or elevated BMI.

| Complications during SSHFJV
We found no severe complications, like barotrauma, subcutaneous emphysema, endotracheal fire or death in our series. This is in line with other, larger studies including 500 and 1515 cases. 4,5

| Pulmonary pathology and SSHFJV
We found a significantly increased chance of conversion SSHFJV to endotracheal intubation in patients with a positive history of pulmonary pathology; however, a notable percentage (41/55; 74.5%) of patients with pulmonary pathology could undergo surgery with SSHFJV. In another study, high-risk patients including patients with COPD, emphysema, bronchial asthma or pulmonary metastases were reported to be adequately ventilated; however, in that series two of three converted cases had pulmonary comorbidities. 5

| Obesity and SSHFJV
Obese patients have impaired oxygen reserve, respiratory mechanics and often diverse comorbidities 7 ; therefore, HFJV is expected to be more often difficult. Indeed, we found a higher chance of conversion in patients with a higher BMI. None of the above-mentioned studies shared that conclusion. 4,5

| Stenosis and SSHFJV
In line with other studies, we experienced no correlation in the multivariable analysis between the severity of the stenosis and the chance

| Strengths and limitations
The study included a consecutive series of patients without any selection; therefore, our database includes high-risk patients, too. We used validated scoring systems in our analysis which makes our results comparable with other studies. Furthermore, beyond reviewing clinical charts, we have reassessed the clinical photographs in order to minimise missing data and to avoid incorrect data that may come from inaccurate registration.
Of course, the study suffers from its retrospective nature with some missing data and also some bias in the inclusion, as anaesthetists might have contraindicated SSHFJV ahead of the procedure, for instance based on comorbidities. Furthermore, the point of conversion is also strongly depending on the anaesthesiologist: some anaesthesiologists convert earlier, some later.

| CON CLUS IONS
Upper airway surgery ventilated with SSHFJV is possible in the vast majority of the patients. However, clinicians have to be alert in patients with positive history of pulmonary pathology and with higher BMI, as these patients have higher risk for failure.