I'll look into the literature to determine whether increased endotracheal tube diameter is associated with a higher incidence of sore throat in adult patients. I'll prioritize randomized controlled trials (RCTs) as they provide higher-quality evidence but will also consider observational studies and meta-analyses if relevant. I'll update you once I have the findings.

Postoperative Sore Throat and Endotracheal Tube Diameter in Adults

Introduction

Postoperative sore throat (POST) is a common complication after general anesthesia with endotracheal intubation, with reported incidences ranging from about 21% up to 72%journals.plos.org. A variety of factors contribute to POST, including patient-related factors (female sex, younger age, smoking history, etc.) and procedural factors such as intubation technique, cuff pressure, and the endotracheal tube (ETT) itselfwww.frontiersin.org www.zora.uzh.ch. In particular, the size (internal diameter) of the ETT has a direct impact on mucosal trauma and ischemia in the airway; larger tubes can cause more pressure on the tracheal mucosa, leading to a higher risk of sore throat and hoarsenessjournals.plos.org www.dovepress.com. This answer reviews the evidence – prioritizing randomized controlled trials (RCTs) – on whether using a smaller-diameter ETT reduces the incidence of POST in adults, and summarizes key findings from RCTs, meta-analyses, and observational studies. Key details like study design, sample size, statistical significance, and confounding factors are highlighted, along with any recommendations on optimal tube sizing to minimize sore throat.

Evidence from Randomized Controlled Trials

Multiple RCTs have directly compared different ETT diameters in adult surgical patients, and most indicate that smaller tubes significantly reduce POST incidence:

Jaensson et al. (2010), Acta Anaesthesiol Scand – This was a single-center RCT in 100 healthy women undergoing elective surgerywww.metajournal.com. Patients were randomized to a 6.0 mm ID ETT (small) or a 7.0 mm ID ETT (standard for females). Sore throat severity was rated on a 4-point scale at 1–2 hours and 24 hours post-op. The 1–2 hour results showed a significantly higher proportion of patients with sore throat in the 7.0 mm group (51.1%) compared to the 6.0 mm group (27.1%, p = 0.006)www.metajournal.com. The difference remained significant when comparing changes from baseline throat discomfort (p = 0.002). The larger tube also caused more moderate–severe throat discomfort (39% vs 19%, p = 0.02)www.metajournal.com. By 24 hours, most sore throats had improved (only 11% still had symptoms by day 4 in either group), and there was no significant difference in hoarseness between groupswww.metajournal.com. This trial concluded that using a smaller 6.0 mm ETT “can alleviate sore throat and discomfort in women” in the immediate postoperative periodwww.metajournal.com www.metajournal.com. Notably, all patients were female to eliminate gender as a confounder, and anesthesia/intubation protocols were standardized across groups.
Ali et al. (2021), Cureus – This RCT in Pakistan focused on female breast surgery patients (n=110) randomized to ETT size 6.5 mm vs 7.5 mmwww.cureus.com. Both groups were managed identically except for tube size; cuff inflation and extubation were done carefully in a standard manner. The primary outcome was the presence of sore throat at 24 hours post-op. The smaller 6.5 mm ETT group had 14 of 55 patients (25%) report a sore throat at 24 h, compared to 33 of 55 (60%) in the 7.5 mm groupwww.cureus.com. This difference was statistically significant (χ² test, p 30 cm H₂O halved the incidence of sore throat (43% vs 66% at 24 h)www.frontiersin.org.
Duration of Intubation: Longer surgeries/intubation times raise the likelihood of sore throat (more prolonged pressure and drying on the mucosa)www.zora.uzh.ch. If larger tubes tend to be used in longer cases (or vice versa), duration could confound results. The RCTs addressed this by having similar case types and lengths in both groups (often elective short-to-moderate length surgeries). In Cho et al., all were laparoscopic abdominal cases of roughly comparable duration; in Jaensson’s trial, all were low-risk elective cases with mean anesthesia time ~1 hour (no difference between 6.0 and 7.0 groups reported). Moreover, randomization ensures that any slight variability in case length is evenly distributed on average. Some observational studies did find duration as a factorwww.zora.uzh.ch, so it’s an important consideration.
Lubrication and Other Preventive Measures: Using a water-soluble jelly or lidocaine gel on the ETT can reduce friction on mucosa. In the 1987 Stout study (and the 2005 Al-Qahtani study), they explicitly did not use any lubrication on the tubesforums.studentdoctor.net, in order to not mask the effect of diameter. Modern practice often uses a lubricant, so the absolute rates of POST in those older studies (48% etc.) might be higher than what we see today, but the relative difference with tube size remains meaningful. None of the RCTs with tube size differences used steroid ointments or topical anesthetics in one group and not the other – any such interventions (like intracuff lidocaine, topical sprays, etc.) were either avoided or applied uniformly so as not to skew the comparison. Essentially, researchers kept both groups on equal footing in terms of prophylactic measures against sore throat, isolating tube size as the variable. If anything, some studies were interested in combining strategies; for example, a trial in 2016 examined small tubes plus IV dexamethasone to see if that further reduced POSTwww.ijcmph.com. But for the purpose of determining the effect of size, we look at studies where no other preventive drug differed between groups.
Patient Factors (Age, Smoking, etc.): Randomization tends to equalize these. The Cureus study by Ali et al. explicitly checked that age and BMI did not skew their results by doing a post-stratified analysiswww.cureus.com. Biro et al.’s large study found smoking or pre-existing lung disease was associated with more sore throatwww.zora.uzh.ch – in an RCT, with sufficient sample, smokers should be roughly evenly split between small and large ETT groups. Similarly, most trials limited inclusion to ASA I–II adults (excluding those with recent respiratory infections, etc.), which controls major patient risk factors in the study population. In summary, the strongest studies controlled or accounted for confounders by design. They often limited the analysis to a homogeneous group (to reduce variability) or statistically adjusted for any differences. The consistency of findings across well-controlled trials gives confidence that increased ETT diameter itself is an independent contributor to postoperative sore throat, rather than merely a marker for other issues.

Recommendations on Optimal ETT Size

What tube size should one use to minimize sore throat? Based on the evidence, the general recommendation is to use the smallest ETT diameter that will still allow safe, effective ventilation and any necessary airway interventions. In practice, this means rethinking the “default” tube sizes for adults:

For adult female patients, an internal diameter of 6.0–7.0 mm is usually sufficient for routine surgerieswww.frontiersin.org. Traditionally, many anesthesiologists used 7.5 mm for women, but studies clearly show 6.0 or 6.5 mm tubes dramatically cut down throat irritationwww.metajournal.com www.cureus.com without causing ventilatory problems. Thus, a size 6.5 (or even 6.0 in smaller women) is often recommended as optimal for minimizing POST in females, unless there is a specific need for a larger tube.
For adult male patients, a size 7.0–8.0 mm is generally suitablewww.frontiersin.org. Many providers routinely use 8.0–8.5 mm for males, but sizing down to a 7.0 or 7.5 mm can reduce mucosal trauma. In Cho et al.’s RCT, men with a 6.5 mm had significantly less POST than those with 7.5 mm, and even that 6.5 mm tube did not hinder ventilation in a laparoscopic case (peak pressures ~15–20 cmH₂O in both groups)www.researchgate.net. Therefore, aiming for ~7.0 mm in an average male (or 6.5 mm in a smaller-framed male) is a reasonable approach if high airway pressures are not anticipated. These sizes align with textbook guidance to some degree – e.g. one anesthesia text (Butterworth 2013) suggests 6.5–7.5 for females and 7.0–8.0 for males as typical rangeswww.frontiersin.org. The difference now is an emphasis on using the lower end of those ranges when possible. The phrase “the smallest tube that will do the job” is apt. In practice, this means considering a 7.0 instead of 8.0 for a man, or a 6.5 instead of 7.5 for a woman, particularly for short or moderate cases where postoperative comfort is a priority and the slight increase in airway resistance with a smaller tube is inconsequential. Modern ventilators can compensate with a bit higher pressure if needed, and studies show no clinically significant impact on ventilation or CO₂ with these one-size decrementswww.researchgate.net.Of course, clinical context matters. If a patient will be on a ventilator in the ICU post-op, a larger tube (to facilitate pulmonary toilet or bronchoscopy) might be chosen despite the sore throat risk. In such cases, one might mitigate POST by other means (careful cuff management, steroids, etc.). But for the typical extubated-in-OR patient, there is a clear argument to err on the side of a smaller ETT to maximize comfort. As one clinician quipped, “use the smallest tube you can get away with” for an extubated caseforums.studentdoctor.net. This philosophy is increasingly reflected in practice; for instance, some hospitals have adopted protocols of defaulting to 7.0 for males and 6.5 for females, only upsizing if needed. The evidence reviewed here supports that practice: it should reduce the incidence of POST and hoarseness, thereby improving patient satisfaction without compromising safetyforums.studentdoctor.net.In conclusion, using a larger-diameter endotracheal tube is indeed associated with a higher incidence of postoperative sore throat in adults. High-level evidence from RCTs and meta-analyses demonstrates that downsizing the ETT by about 1 mm can significantly decrease sore throat rates both immediately post-op and at 24 hoursjournals.plos.org www.researchgate.net. These studies have robust designs and adequate sample sizes (ranging from 100 to 170+ patients in RCTs) and report statistically significant improvements (often p < 0.01–0.05). Observational data and clinical experience corroborate these findings, although they remind us that factors like intubation technique and cuff pressure are important co-determinants of throat symptoms. To minimize POST, clinicians should consider smaller tube sizes as part of a multi-faceted strategy (along with gentle technique and proper cuff management). Optimal sizing generally means ~6.0–6.5 mm internal diameter for most adult women and ~7.0–7.5 mm for most menwww.frontiersin.org, assuming no other contraindications. By prioritizing a smaller ETT when appropriate, anesthesiologists can significantly improve postoperative patient comfort, as evidenced by the reduced incidence and severity of sore throat in the studies reviewed.Sources: The analysis above is based on multiple studies including RCTswww.metajournal.com www.researchgate.net www.cureus.com, a meta-analysisjournals.plos.org, and observational researchforums.studentdoctor.net www.zora.uzh.ch that investigated the relationship between ETT diameter and postoperative sore throat in adult surgical patients. All findings consistently point toward smaller ETTs being advantageous in reducing POST, with careful control of confounders such as patient sex, intubation technique, and cuff pressure across these studies. The consensus recommendation is to select the smallest effective ETT size to minimize mucosal injury and sore throat riskwww.frontiersin.org.