Table 1.

Best evidence papers.

Author, date and country	Patient Group	Study type and Level of evidence	Outcomes	Key results	Comments
Arora et al., 2015 [2], UK	Prospective analysis of 14 patients (13 male, 1 female): 4 had TORS BOT reduction alone while 10 had TORS BOT reduction in combination with epiglottoplasty (depending on DISE findings) Patient characteristics: -Mean age = 54.3 -Mean preoperative BMI = 28.7kgm-2 -Pre-operative AHI = 35.6h−1 -Mean pre-operative ESS = 14.9 -Mean pre-operative oxygen saturation level (SaO2) = 92.9% -9 patients had undergone previous oropharyngeal surgery for OSA Inclusion criteria: (1)Moderate to severe OSA (2)Intolerant to conventional treatment (CPAP and/or MAD) (3)BMI<35kgm-2 (4)Obstruction at the level of the tongue base and/or epiglottis as diagnosed via DISE Exclusion criteria: (1)Numerous comorbidities (2)Limited mouth opening (3)Inadequate follow-up	Level IIb prospective cohort study	Primary: -Post-operative AHI -Post-operative SaO2 -Post-operative ESS Secondary: -Operative time -Blood loss -Complications PROMs: -Voice (VHI-2) -Swallowing (MDADI) -QoL (EQ-5D)	Significant decrease in mean AHI post-TORS (21.2h−1+/−24.6 h−1 vs. 36.3 h−1+/−21.4 h−1, p = 0.026) Significant increase in mean SaO2 post-TORS (92.9% ±1.8% vs. 94.3% ±2.5%, p = 0.005) Significant decrease in mean ESS (p = 0.002) and normalised by 6 months Obese patients (BMI>30kgm-2) had significantly higher failure rates compared to non-obese (p < 0.01) One patient had a minor secondary haemorrhage, one patient had dysgeusia and two patients had odynophagia to solids Voice and swallowing worsened initially in first 2 week (p < 0.005) but returned to normal levels within 3 months Quality of life was improved 3 months after the procedure (p < 0.001)	TORS BOT reduction with or without wedge epiglottoplasty are clinically effective in non-obese OSA patients who have failed to tolerate conventional treatment Study strengths: -Prospective nature -Long follow-up -Both subjective and objective outcomes measured Limitations: -No control group -Small sample size
Chiffer et al., 2015 [11], USA	Prospective analysis of a mixed cohort of 19 patients (16 male, 3 female): All underwent TORS bilateral posterior hemiglossectomy with limited pharyngectomy and an uvulopalatopharyngoplasty Patient characteristics: -Mean age = 46.8 years, range 24–59 years -Mean preoperative BMI = 34.0kgm-2, range 26.6–55.0kgm-2 -Mean preoperative AHI = 52.9h−1, range 17-112h−1 Inclusion criteria: -At least 18 years old -AHI >5 -Informed consent Exclusion criteria: -Under 18 years old -Active infection that is not being treated -Pregnancy -Previous head and neck procedure that prevented transoral access -Comorbidities that prevented them from undergoing TORS or GA due to increased operative risk	Level IIb prospective cohort study	-Post-operative AHI -Volumetric outcomes (based on MRI measurements pre- and post-operatively)	61% of patients (11/18) were classified as surgical successes Patients in the surgical success group experienced a significant mean drop in AHI of 52.9 ± 29.0h−1 compared to 4.5 ± 33.5h−1 in those that did not meet the criteria for surgical success (p = 0.006) 67% were classified as surgical responders (12/18) There was an increase in airway volume following TORS at the retropalatal and total lateral wall levels	When comparing obese and non-obese patients, no statistically significant difference was found in terms of surgical response (56.3% vs. 50%, p > 0.1) The success rate in the non-morbidly obese patients (BMI = 30-35kgm-2) was 62.5% Study strengths: -Prospective study -Multiple outcome measures (based on both polysomnography and volumetric MRI) -Individual BMI values were presented which allowed further analysis Limitations: -Small sample size -Lack of standardization (pre-op MRI scans as well as pre- and post-op PSG studies were performed at different institutions) -BMI changes were not controlled for -Clinicians analysing the MRI scans were not blinded to post-op AHI values; may introduced bias
Hoff et al., 2014 [12], USA	Retrospective analysis of a mixed cohort of 121 patients (83 male, 38 female) with moderate to severe OSA that underwent TORS tongue base surgery ± multilevel surgery Patient characteristics: -Mean age = 54.5 years -Mean preoperative BMI = 28.4kgm-2 and mean postoperative BMI = 27.5kgm-2 -Mean preoperative AHI = 42.7h−1 and mean postoperative AHI = 22.2h−1 Inclusion criteria: (1)Moderate-to-severe OSA (2)Intolerance to CPAP therapy (3)Tongue base hypertrophy (DISE) (4)Good tongue base exposure during TORS (5)Complete preoperative and 3-month postoperative polysomnography (PSG) data Exclusion criteria: a)Mild OSA b)TORS lingual tonsillectomy not performed c)No postoperative PSG	Level III retrospective cohort study	Postoperative AHI Success if: AHI<20h−1 and AHI decreased by 50% Cure if AHI<5h−1	Mean post-operative AHI dropped from 42.7h−1 to 22.2kgm-2 84.3% of patients showed an improvement in their AHI In 51.2% of patients, TORS proved successful 14% of patients were cured Lingual tonsil volume resected correlated with drop in AHI The lower the pre-operative BMI, the higher the percentage of success following TORS (56.5% with BMI<30kgm-2 underwent successful TORS compared to 78.3% of patients with BMI<25kgm-2) No complications reported	Pre-operative BMI can be used as a marker of success in TORS for OSA Study strengths: Largest retrospective analysis of TORS procedures performed by a single surgeon Limitations: -Retrospective nature -Significant difference between mean preoperative and postoperative BMI, which could act as a cofounder The condition of 16% of patients worsened and this can be because for 6 of them PSG was done more than 5 years before TORS procedure (and thus not representative of pre-operative BMI) and also smaller lingual tonsil volume was resected in these patients
Lin et al., 2014 [13], USA	Retrospective analysis of 39 patients (24 male, 15 female) with moderate to severe OSA TORS procedures performed: -BOT reduction (11) -BOT reduction plus UPPP (2) -BOT reduction plus epiglottectomy (7) -BOT reduction, plus epiglottectomy, plus UPPP (19) Demographic data: -Mean age = 46.5 years -Race (26 Caucasian, 2 Hispanic and 11 African American) Clinical data: -Mean pre-operative BMI = 32.9 + 7.0kgm-2 -Mean neck circumference = 16.2 + 1.5 cm -Mean Friedman stage = 3.0 + 0.6) -DISE findings (most of the patients experienced collapse in the nasopharynx, BOT, and epiglottis) -Mean preoperative AHI = 43.9 + 32.3), -Mean pre-operative ESS = 15.6 + 5.4) -Mean pre-operative LO2sat = 81.6 + 8.1% -18 had a tonsillectomy done before, 8 a UPPP, 4 BOT reduction, 4 tracheostomy, and 21 other procedures Inclusion criteria: -Adult patients -Moderate to severe OSA -Have completed demographic and clinical data -Have completed 4 months of follow up	Level III retrospective cohort study	-Post-operative AHI -Post-operative ESS -Post-operative LO2sat	-Mean post-operative AHI = 21.9 + 23.5h-1 -Mean post-operative ESS = 5.7 + 4.3 -Mean post-op LO2sat = 83.4 + 7.3% Overall, 21 patients did have a positive surgical response as defined by >50% decrease in AHI and a post-op AHI <15 together with a post-op ESS less or equal to 9 Patients with BMI<30kgm-2 enjoyed an excellent surgical response rate of 88.2%, whereas patients with BMI≥40kgm-2 had a poor surgical response rate of only 16.7% Complications: -No airway or haemorrhage -3 patients experienced dysphagia due to oropharyngeal scarring that needed surgical/medical intervention -Most of the patients had dysgeusia and tongue numbness which resolved within 3 months following TORS except in 3 patients in whom it lasted for more than a year	Patients with BMI<30kgm-2 had the best response whereas those with BMI more or equal to 40kgm-2 had the worst (BMI<30kgm-2 88.2%, BMI ≥ 30kgm-2 but <40kgm-2 31.3%, BMI≥40kgm-2 16.7% p < 0.000) Patients with AHI<60h−1 had the best surgical response rate compared to those with AHI>60h−1 (67.9% vs. 18.2% p = 0.011) Study strengths: -Adequate number of patients -Specifically looked into the impact of BMI on surgical access Limitations: -Retrospective nature -Absence of long-term follow-up
Spector et al., 2016 [14], USA	Retrospective analysis of 118 patients (87 male, 31 female) with moderate to severe OSA All had TORS lingual tonsillectomy either alone or in combination with multilevel surgery: -epiglottectomy (60) -tonsillectomy (55) -partial midline glossectomy (40) -pharyngoplasty (39) -palatoplasty (37) -UPPP (30) -turbinate reduction (29) -uvulectomy (23) -septoplasty (2) -adenoidectomy (1). Patient characteristics: -Mean age = 54.6 years -Mean BMI = 29.0kgm-2 -Mean AHI = 43.0h-1 -Mean excised lingual tonsil volume = 8.0 ml Inclusion criteria: -Moderate-to-severe OSA -Failure to tolerate conventional treatment Exclusion criteria: -Previous TORS	Level III retrospective cohort study	Post-operative AHI	Mean post-op AHI was 22.6kgm-2 82.5% of the patients experienced an improvement in their post-op AHI In 63% of the patients the intervention was considered successful (AHI<20h−1 and 50% drop in pre-op AHI) 16.9% of the patients satisfied the cure criteria for 3 months post-surgery (AHI<5h−1) Patients with BMI<30kgm-2 had a success rate of 69.9% whilst for those with a BMI >30kgm-2 the success rate dropped to 51% (p = 0.041)	BMI can predict operative success of TORS for OSA As BMI increases, the chances of success of TORS for OSA decrease Study strengths: -Large sample size -Specifically evaluated predictive role of BMI Limitations: -Retrospective study -No control group

Abbreviations: OSA = obstructive sleep apnoea; TORS = transoral robotic surgery; AHI = apnoea-hypopnoea index; CPAP = continuous positive airway pressure; DISE = drug-induced sleep endoscopy; PSG = polysomnography; BOT = base of tongue; MAD = mandibular advancement device; ESS = Epworth Sleepiness Score; PROMs = patient reported outcome measures; QoL = quality of life; GA = general anaesthetic; LO₂sat = lowest oxygen saturation.