Nasotracheal intubation is usually required in patients undergoing oromaxillofacial, otolaryngological or plastic surgery under general anaesthesia as it provides a clear operating field for the surgeons. Epistaxis is the most common complication of the procedure with a reported incidence ranging from 9.6 to 70% without an endoscopic examination of the nasal passages1,2; even if both nostrils are patent, as observed with a nasal endoscope, an incidence of up to 44.4% is observed.3 Numerous methods have been proposed to reduce epistaxis, including the application of a mucosal vasoconstrictor, a smaller size of tube, a gastric tube or suction tube to guide the tracheal tube and heating the tube to soften it, but none of these methods completely prevents epistaxis.4 It may be helpful to select the more patent nostril to resolve this issue. Several studies on the topic have been published recently but the evidence is still conflicting.3,5–9 Some textbooks advocated that the left nostril be used for nasotracheal intubation because of less damage to the turbinate from the sharp tube tip,10,11 some recommend the right nostril because of less epistaxis and shorter intubation times,3,5,6 and some studies showed no difference in the incidence of epistaxis between the nostrils. 7,9,12 The purpose of this meta-analysis of randomised controlled trials (RCTs) was to try and determine, which nostril is more suitable for nasotracheal intubation when using a tube with a left-facing bevel at the tip in adult surgical patients undergoing general anaesthesia.
The article was prepared in accordance with the Preferred Reporting Items for Systematic reviews and Meta- Analysis Statement guidelines.13 The study protocol was registered on PROSPERO (http://www.crd.york.ac.uk/prospero), registration number CRD42020169949.
Literature search and selection criteria
Two investigators (YT and ZW) independently searched PubMed, Embase and the Cochrane Register of Controlled Trials for articles published from the start of the database until 1 March 2020. The electronic search terms used were ‘nostril AND (nasotracheal intubation OR nasal intubation) AND random∗’. No language restriction was imposed. The reference lists of the screened full-text studies and previous review articles were hand-searched to identify other potentially eligible trials. Studies meeting the following criteria were included: adult surgical patients undergoing nasotracheal intubation under general anaesthesia; right nostril compared with left nostril for nasotracheal intubation; epistaxis as an outcome measure and an RCT study design.
Data extraction and outcome assessed
Data were entered on a specially designed data-extraction sheet: first author, year of publication, country of origin, number of patients, tube type, intubation instrument, the experience of the operator and the outcomes. The data were extracted independently by two investigators (YT and BZ) and any discrepancy was resolved by consensus with two other investigators (YN and YD). The original authors were contacted if data needed clarification or were not presented in the publication. The median was used as an estimate of the mean if it was not provided. Standard deviation (SD) was calculated using the interquartile range (IQR) with the formula: SD = IQR/1.35, as described in the Cochrane Handbook for Systematic Reviews of Interventions.14 The primary outcome was the incidence of epistaxis, and secondary outcomes included incidence of severe epistaxis, the time to pass the tube through the nasal passage and total intubation time.
The risk of bias was assessed using the Cochrane Collaboration tool.15 Two authors (YT and BZ) independently classified the risk of bias for the studies as ‘high’, ‘low’ or ‘unclear’ in the following domains: random sequence generation, allocation concealment, blinding of participants and personnel, blinding of outcome assessment, incomplete outcome data, selective reporting and other bias. Trials with high risk of bias in one or more domains were considered at high risk of bias. Trials with low risk of bias in all domains were considered at low risk of bias. Otherwise, they were considered as unclear risk of bias.16
Data analysis was performed by two authors (YT and ZW) and checked by two authors (YN and YD). Dichotomous variables and continuous variables are presented as relative risks (RRs) with 95% confidence intervals (95% CI) and mean difference with 95% CI, respectively. Heterogeneity was quantified using I2 statistic. When I2 less than 50% and P value more than 0.1, the heterogeneity was considered acceptable. In the meta-analysis, a random-effects model was used regardless of heterogeneity. Potential publication bias was assessed by visually inspection of the Begg's funnel plots in which the log RRs were plotted against their standard errors (SEs). The presence of publication bias was also evaluated by using Begg's and Egger's tests. All statistical analyses were conducted using Review Manager 5.3 by the Cochrane Collaboration.17P less than 0.05 was considered significant.
Study selection and characteristics
A detailed flowchart of the literature search and selection results is shown in Fig. 1. The search of the databases yielded 113 citations, 7 RCTs3,5,6,8,9,18,19 were included after 106 citations were excluded based on their title or abstract, improper intervention/control, duplicate studies and nonrelevant topic. Three additional RCTs7,20,21 were identified from references within manuscripts, thus 10 RCTs met the inclusion criteria and were included in the present meta-analysis.3,5–9,18–21
The main characteristics of the included studies are shown in Table 1. These ten studies were published from 2001 to 2019, with sample sizes ranging from 35 to 434 patients and included a total of 1658 patients. All ten 10 RCTs enrolled adult patients with normal airways undergoing oral or maxillofacial surgery under general anaesthesia. Nine studies reported the intubation instrument and tube type,3,5–9,18–20 and six studies reported the experience of the operators as residents or expert anaesthesiologists (2 or more years’ experience).3,5,6,8,9,19 All 10 studies reported the incidence of epistaxis,3,5–9,18–21 and five studies reported the severity of epistaxis.3,6,19–21 Two studies reported the time to pass the tube through the nasal passage,6,9 and three studies reported the total intubation time.5,6,9
Table 1 -
Characteristics of the 10 included randomised controlled trials
|Ahmed-Nusrath et al., 200818
|Arslan and Turkyilmaz, 20195
||Anaesthesiologists with at least 4 years’ experience
||Epistaxis and intubation time
|Boku et al., 20146
||‘Ivory’ cuffed tube
||Anaesthesiologists with more than 7 years’ experience
||Epistaxis, severe epistaxis, nasal passage time and intubation time
|Chi et al., 20167
||Nasal RAE tube
|Coe et al., 200120
||‘Ivory’ cuffed tube
||Epistaxis, severe epistaxis
|Kim et al., 20008
||Nasal RAE tube
||Residents who trained for at least 2 years
|Lim et al., 201219
||Epistaxis, severe epistaxis
|Sanuki et al., 20103
||Nasal RAE tube
||Anaesthesiologists with less than 3 years’ experience
||Epistaxis, severe epistaxis
|Seo et al., 200521
||Epistaxis, severe epistaxis
|Wang et al., 20199
||Polar preformed tube
||Anaesthesiologists with 5 years’ experience
||Epistaxis, nasal passage time and intubation time
The details for risk of bias are summarised in Fig. 2. Random sequence generation and allocation concealment were conducted adequately in most trials except for one trial where the nostril selection was determined by operating site after discussion with the surgeon, so both domains in this trial were evaluated at high risk of bias.8 Blinding of participants and personnel and blinding of outcome assessment were judged to be at low risk of bias for all the trials, since it was inevitable that the operators who inserted the nasotracheal tube could see which nostril was used and what the epistaxis was like during intubation.
All trials (1658 patients)3,5–9,18–21 reported the incidence of epistaxis. For the left nostril, the incidence of epistaxis was 25.2% (207/823), and for the right nostril 19.4% (162/835). Nasotracheal intubation via the right nostril was associated with a decreased incidence of epistaxis with a RR (95% CI) of 0.78 (0.62 to 0.99) (P = 0.04), with low heterogeneity (P = 0.12, I2 = 37%) (Fig. 3).
Five trials (923 patients)3,6,19–21 were included in the analysis of the severity of epistaxis, described as either mild, moderate, or severe. The incidence of severe epistaxis when using the right nostril was 3.0%, (14/463), significantly lower than the 8.3% (38/460) with the left nostril, RR = 0.40 (0.22 to 0.75) (P = 0.004), with low heterogeneity (P = 0.40, I2 = 2%) (Fig. 3).
Two RCTs (310 patients) reported the time required to pass the tube through the nasal passage6,9: this was not significantly different between the two sides, mean difference (95% CI) −0.59 (−1.95 to 0.77) s (P = 0.40), with low heterogeneity (P = 0.17, I2 = 47%) (Fig. 4). Intubation time was reported in three studies (345 patients).5,6,9 Although the definition of the intubation time was not the same in the three trials, there was a tendency for a reduced time to intubation when using the right nostril compared with the left nostril: mean difference −7.28 (−14.40 to −0.16) s (P = 0.05), with high heterogeneity (P = 0.0008, I2 = 86%) (Fig. 4).
Assessment of publication bias was performed using Begg's funnel plot and Begg's tests. The result showed no potential publication bias among the included 10 trials (Begg's Test, P = 0.592) (Fig. 5).
The present meta-analysis suggests that the right nostril is more appropriate for nasotracheal intubation when using a tube with a left-facing bevel, with a lower incidence and severity of epistaxis and a shorter intubation time compared with left nostril. To date, there have been neither guidelines nor consensus on nostril selection for nasotracheal intubation. This meta-analysis is important as it provides the first such evidence that, when both nostrils are patent, intubation via the right nostril is not only faster but also reduces the incidence and severity of epistaxis in patients under general anaesthesia.
Epistaxis is the most common complication of nasotracheal intubation and it not only tends to obscure the view during intubation but may also cause airway obstruction or a life-threatening condition.12,22 A retrospective analysis on the risk factors for epistaxis during nasotracheal intubation showed epistaxis was most likely to occur if transit of the tube through the nasal passage was difficult: there was no relation with nostril selection.23 However, the present meta-analysis indicated a significant difference in epistaxis between the two nostrils. According to Boku et al.,6 epistaxis generally resulted from mucosal laceration of the turbinates or nasal septum. The mucosal tissue of the nasal septum is more fragile than that of the turbinates, and so is more susceptible to trauma from the sharp tube tip. In addition, Kiesselbach's plexus on the antero-inferior part of the nasal septum, a superficial arterial plexus supplied by the posterior septal artery, the greater palatine artery and septal branches of the superior labial and anterior ethmoidal arteries, is the most common bleeding site in the nasal cavity.24,25 A tube with a left-facing bevel at the tip is more likely to scrape against Kiesselbach's plexus when inserted via the left nostril than right. This may be one of the reasons for the reduced incidence and severity of nasal bleeding when intubating via the right nostril. In addition, the meta-analysis demonstrated that the incidence of epistaxis between both nostrils, whether in seven trials from the Far East (China, Japan and Korea) or in two trials from the UK, is not remarkably different (data not shown), indicating that epistaxis related to nostril selection during nasotracheal intubation may have no ethnic variation.
Although the time required to pass the tube through the right or left nasal passage was not significantly different in the current meta-analysis, the total intubation time was longer via the left nostril, suggesting that the difference lies in the tube passage time from the posterior naris and onwards through the glottis. The reason may correlate with the anatomical features of the nasal cavity and the left-facing bevel of the tube tip.5,26 Briefly, when the tube tip is inserted into the right nostril and passing through the nasal cavity and posterior pharynx, the tube tip is usually dislocated to the right side of glottis and does not entirely align toward the glottis and vice versa. The right dislocation requires an anticlockwise rotation to make alignment of the tube tip toward the glottis whereas the left dislocation usually requires a clockwise rotation. When rotating clockwise via the left nostril, the tube tip with the left-facing bevel is more likely to be obstructed by the tissues around the glottis and arytenoid cartilage, thus preventing a smooth entrance through the glottis.26 Furthermore, a dislocation of the tube to the left makes it difficult for Magill's forceps to assist because of a limited oral field and deeper position. However, the fact that most anaesthetists are right-handed cannot be ignored and that they select the right nostril (nearer to the right hand) more often, thus greater practice with the right nostril may contribute to the apparent easier intubation through the right nostril.
Although nasotracheal intubation is a well tolerated and effective technique, it is also a difficult procedure to learn, so a lack of experience may affect the incidence and severity of epistaxis and the intubation time. The experience of operators in the included studies was poorly described, or not at all, which may result in bias. The different anaesthetic methods (local vs. general) and the patient setting (emergency vs. nonemergency) were not relevant in this meta-analysis as all the patients underwent elective surgery with general anaesthesia. The haemostatic status of the patients was not clear in the included trials but again this may not be relevant as a coagulation disorder is a contraindication to nasotracheal intubation.
There are several limitations in the present meta-analysis. First, most RCTs included had only a small-to-medium sized sample (n<100), and the effect of nostril selection on nasotracheal intubation can be overestimated in small samples. Second, most studies included were not blind as the operator who performed the intubation knew which nostril had been used, and thus assessing the epistaxis may have resulted in bias. Third, the equipment used for intubation and the type of tube was not identical, which may have a potential impact on our results. Fourth, some clinically meaningful indicators including intubation success rate, haemodynamics or other complications other than epistaxis were not assessed because of limited descriptive data across the studies. Finally, the 10 RCTs enrolled only patients with normal airways, and more attention should be paid to patients with difficult airways as nasal intubation in such patients is more challenging.
In conclusion, the current available evidence suggests that the right nostril is a safer and faster option for nasotracheal intubation under general anaesthesia, with a lower incidence and severity of epistaxis and a shorter intubation time. On the basis of such evidence, when both nostrils are patent the right nostril is recommended for nasotracheal intubation under general anaesthesia using a left-facing bevel tube.
Acknowledgements relating to this article
Assistance with the study: none.
Financial support and sponsorship: this work was supported by National Natural Science Foundation of China (No. 81772880) and Jiangsu Provincial Medical Youth Talent, the project of Invigorating Healthcare though Science, Technology and Education (No. QNRC2016117).
Conflicts of interest: none.
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