ABSTRACT
Background
Optimal initial laryngoscope blade selection for paediatric emergency intubation is uncertain. We examined whether Miller or Macintosh blades are associated with differences in first‐pass success (FPS) and adverse events in children < 5 years.
Methods
Prospectively collected data from the Australia and New Zealand ED Airway Registry (ANZEDAR) between March 2010 and March 2024 were analysed for children under 5 years of age. We report demographics, FPS and adverse events by initial blade type. Multivariable models examined factors associated with FPS and hypoxia.
Results
Among 201 children, 88 (43.8%) were intubated with a Miller blade and 113 (56.2%) with a Macintosh blade. In unadjusted analyses, children intubated with Miller blades were younger (median 0.4 years, IQR 0.08–1.35 vs. median 1.6 years, IQR 0.75–2.00), p < 0.001), had lower FPS (63.6% vs. 80.5%; OR 0.42, 95% CI 0.22–0.80; p = 0.008) and had a higher incidence of hypoxia (33.0% vs. 17.7%; OR 2.28, 95% CI 1.19–4.46; p = 0.01) compared with children intubated with Macintosh blades. Hypotension rates did not differ.
Conclusion
In this cohort of young children intubated in the ED, Macintosh blade use was associated with higher FPS and fewer hypoxic events compared with Miller blade. Age was a significant confounder and should be considered when choosing which laryngoscope blade to use in young children.
Keywords: airway management, airway registry, emergency department, first pass success, hypoxia, intubation, laryngoscopy
1. Introduction
Emergency tracheal intubation in young children is a high‐acuity, low‐occurrence procedure, demanding careful attention to technique and equipment choice [1, 2, 3]. Data from the Australia and New Zealand Emergency Department Airway Registry (ANZEDAR) show that children account for about 5% of emergency department (ED) intubations, with first‐pass success (FPS) around 80% and complications, most often desaturation, occurring in one third of cases [1, 3]. Infants under 1 year of age experience the highest risk, whilst video laryngoscopy, bougie use and experienced operators improve outcomes [1, 3]. In this context, uncertainty regarding the optimal direct laryngoscopy blade for children under 5 years persists, despite growing evidence on factors that improve intubation success. Considerable variation in airway practise across the region highlights the need for context‐specific evidence to guide device selection [2].
Successful first‐pass intubation in paediatric emergency medicine represents a critical clinical skill that can significantly impact patient outcomes. The choice between Miller and Macintosh blades for children under 5 years of age remains an important consideration for emergency physicians, as failed intubation attempts increase the risk of complications, hypoxaemia and other adverse events [4].
Both Macintosh and Miller blades have been used for paediatric laryngoscopy for more than 80 years [5]. Traditionally the Miller blade, a straight blade, is favoured for infants and neonates, as it directly lifts the epiglottis to visualise the vocal cords whereas the Macintosh blade, a curved blade, is more commonly used in older children and adults to elevates the epiglottis via the vallecula. However, recent evidence suggests that either blade can be used to directly or indirectly lift the epiglottis, depending on operator preference and technique [6].
Anatomical differences between paediatric and adult airways create unique challenges for emergency intubation. Children have proportionally larger heads and tongues, more anterior larynges and distinct epiglottal characteristics. These features have historically guided blade selection preferences, but contemporary practise increasingly recognises that technique and operator experience may be as important as blade type in determining intubation success [7].
Blade selection is particularly relevant in emergency settings, where laryngoscopic view and ease of visualisation directly influence FPS and the likelihood of adverse events. Despite its clinical importance, the evidence comparing Miller and Macintosh blades in paediatric ED settings is limited. Existing research including studies by Varghese and Kundu was conducted primarily in controlled anaesthesia environments rather than in emergency contexts [7, 8]. These studies reported no significant difference in laryngoscopic view or intubation success between the two blade types; however, the Miller blade was not used with its intended paraglossal technique, potentially limiting the validity of the comparison [9].
No studies to date have specifically examined the characteristics of children intubated in the ED using Miller versus Macintosh blades, nor have adverse events associated with each blade type been described outside of the operating theatre. The aim of this study is to describe the demographics of children intubated in the ED with Miller and Macintosh laryngoscope blades and to report the associated adverse events and FPS rates for each blade type. Understanding the comparative effectiveness of these blades in paediatric emergency intubation is essential for developing evidence‐based protocols and improving patient safety outcomes in paediatric airway management.
2. Methods
We conducted a retrospective analysis of prospectively collected data from the Australian and New Zealand Emergency Department Airway Registry (ANZEDAR) between March 2010 and March 2024. The study dataset was contributed to by 37 EDs across Australia and New Zealand, including dedicated paediatric tertiary children's hospitals (n = 3), major tertiary referral centres (n = 14), urban district hospitals (n = 11) and regional, rural or remote mixed EDs (n = 9), reflecting a broad spectrum of clinical settings within the ANZEDAR network. The Australia and New Zealand Emergency Department Airway Registry project is approved by the Northern Sydney Local Health District Human Research Ethics Committee (ID: 1209–318 M) and is registered with the Australia and New Zealand Clinical Trials Registry and operated under a waiver of informed consent model. No written consent has been obtained from the patients as there is no patient‐identifiable data included. The clinical study registration number is ACTRN12613001054707.
Children younger than 5 years who underwent ED tracheal intubation using either a Miller or Macintosh laryngoscope blade on the first intubation attempt were included. Patients were excluded if unable to ascertain the intubating blade used. Intubation episodes using video‐assisted devices (CMAC/Video laryngoscope/glidescope) were excluded for analysis (Figure 1). This was due to the different visualisation mechanics and operator technique using video‐assisted laryngoscopy, and due to limitations of the ANZEDAR database (which does not record the blade type for video‐assisted intubations). Demographic data, indication for intubation, intubation technique, success rates and adverse event rates were recorded. FPS and adverse event rates between children intubated using a Miller blade were compared with those using a Macintosh blade. Second and subsequent attempts and overall success by blade type were not reported due to the increasing influence of cross‐over and rescue strategies, which introduce confounding and heterogeneity.
FIGURE 1.
Cohort enrolment diagram.
2.1. Outcomes and Covariates
Definitions for variables are consistent with previously reported ANZEDAR research [1, 3, 10, 11]. In brief, FPS was defined as successful tracheal intubation following the first insertion of the laryngoscope blade into the mouth. Desaturation was defined as SpO2 < 93% when SpO2 was ≥ 93% at the end of pre‐oxygenation, or a decrease in SpO2 of > 10 percentage points when SpO2 was < 93% at the end of pre‐oxygenation. Hypotension was defined as a systolic blood pressure < 90 mmHg at any time, or if a hypotension complication was recorded.
Age was included as a continuous variable. Some covariates were categorised to allow for meaningful groups including laryngoscopic view (Cormack–Lehane grade dichotomised as good I–II vs. poor III–IV, site category, team leader and intubator specialty (ED or other) and seniority (specialist or other)). Indications for intubation are reported although were dichotomised for modelling (trauma or medical).
2.2. Statistical Analysis
We summarised baseline characteristics overall and by first‐attempt blade type (Miller or Macintosh). Continuous variables were reported as medians (IQR) and compared using Wilcoxon rank‐sum. Categorical variables as n (%) and compared using χ 2 or Fisher's exact tests as appropriate. We estimated unadjusted ORs (95% CI) for associations between blade type and outcomes (FPS, hypoxia, hypotension).
Multivariable regression modelling using age, FPS, hypoxia and hypotension as covariates was undertaken. All analyses were conducted in R (v3.6.1).
3. Results
A total of 201 emergency intubation episodes in children under 5 years of age were included, with 113 (56.2%) performed using a Macintosh blade and 88 (43.8%) using a Miller blade on the first attempt (See Table S1 for all scope use patterns). Children in the Miller group were significantly younger (median age 0.4 years) compared with those intubated with a Macintosh blade (median age 1.6 years; p < 0.001). Most intubations were performed by clinicians reporting more than 100 prior intubations (56.3%), although experience levels differed between groups: 70% of Macintosh intubations were conducted by experienced operators compared with 39.1% in the Miller group (p < 0.001). Clinical seniority was similar between blade types, with specialists performing approximately 41% of procedures.
Emergency physicians conducted nearly half of all intubations (49%), though they accounted for a larger proportion in the Miller group (58.8%) than the Macintosh group (41.3%) (p = 0.023). Baseline clinical characteristics, including trauma status, GCS category and Cormack–Lehane grade, were comparable between groups. However, site category showed significant variation (p = 0.026), with a higher proportion of Miller intubations occurring in major referral centres. Predicted difficult airways also differed, with a greater proportion of predicted difficult intubations in the Miller group (30.4% vs. 14.3%; p = 0.014). Use of adjuncts varied significantly (p = 0.011), with Miller intubations more frequently employing a stylet, whereas bougie use was more common in the Macintosh group (Table 1). Overall, the majority of intubations were for medical indications (84.1%), whilst trauma accounted for 15.9%. The Macintosh blade was used more often in trauma cases (22 of 113; 19.5%), whereas the Miller blade was predominantly used for medical indications (78 of 88; 88.6%) (Figure 2).
TABLE 1.
Patient demographics and characteristics of intubation and team by blade type.
| Characteristic | Overall n = 201 | Macintosh 113 (56.2) | Miller 88 (43.8) | p |
|---|---|---|---|---|
| Age, years a | 1.2 (0.2–2.00) | 1.6 (0.8–2.0) | 0.4 (0.1–1.4) | < 0.001 |
| Indication for intubation | 0.173 | |||
| Trauma | 32 (15.9) | 22 (19.5) | 10 (11.4) | |
| Medical | 169 (84.1) | 91 (80.5) | 78 (88.6) | |
| Site category | 0.026 | |||
| Major referral | 108 (53.7) | 53 (46.9) | 55 (62.5) | |
| Rural | 43 (21.4) | 24 (21.2) | 19 (21.6) | |
| Urban district | 50 (24.9) | 36 (31.9) | 14 (15.9) | |
| Intubator experience b | < 0.001 | |||
| 0–9 intubations | 11 (5.6) | 4 (3.6) | 7 (8.0) | |
| 10–99 intubations | 75 (38.1) | 29 (26.4) | 46 (52.9) | |
| > 100 intubations | 111 (56.3) | 77 (70.0) | 34 (39.1) | |
| Intubator seniority b | 0.368 | |||
| Specialist | 81 (40.9) | 49 (44.1) | 32 (36.8) | |
| Other grade | 117 (59.1) | 62 (55.9) | 55 (63.2) | |
| Intubator specialty b | 0.023 | |||
| Emergency | 95 (49.0) | 45 (41.3) | 50 (58.8) | |
| Other specialty | 99 (51.0) | 64 (58.7) | 35 (41.2) | |
| Glasgow Coma Scale | 0.655 | |||
| Severe (3–8) | 131 (74.9) | 78 (77.2) | 53 (71.6) | |
| Moderate (9–12) | 18 (10.3) | 10 (9.9) | 8 (10.8) | |
| Mild (13–15) | 26 (14.9) | 13 (12.9) | 13 (17.6) | |
| Predicted difficult intubation | 0.014 | |||
| No | 145 (78.8) | 90 (85.7) | 55 (69.6) | |
| Yes | 39 (21.2) | 15 (14.3) | 24 (30.4) | |
| Cormack and Lehane grade | 0.463 | |||
| I–II | 160 (86.5) | 93 (88.6) | 67 (83.8) | |
| III–IV | 25 (13.5) | 12 (11.4) | 13 (16.2) | |
| Adjuncts | 0.011 | |||
| Bougie | 21 (10.8) | 15 (13.8) | 6 (7.1) | |
| Stylet | 63 (32.5) | 26 (23.9) | 37 (43.5) | |
| None | 100 (56.7) | 68 (62.4) | 42 (49.4) | |
Note: Values are n (%) unless stated. p < 0.05 (in bold).
Abbreviation: IQR, interquartile range.
Median (IQR) for age.
On first attempt at intubation; p values from Wilcoxon rank sum (continuous) and χ 2/Fisher's exact tests (categorical).
FIGURE 2.
Clinical Indication for Intubation using different types of laryngoscopes. LOC; level of consciousness; Other; intubation performed for patient transport or for computed tomography scan.
Overall, FPS was achieved in 73.1% of cases. FPS was significantly more frequent with the Macintosh laryngoscope compared with the Miller laryngoscope (80.5% vs. 63.6%, OR = 0.42, 95% CI = 0.22–0.79; p = 0.008) (Table 2). Hypoxia occurred in 49 of 201 intubations (24.4%). In unadjusted analyses, hypoxia was more frequent among children intubated using a Miller blade compared with a Macintosh blade (33.0% vs. 17.7%; unadjusted OR = 2.28, 95% CI = 1.18–4.40; p = 0.01). Blade choice demonstrated strong age dependence (Table 3). Miller blades were used predominantly in infancy (Median = 0.4 years, IQR = 0.08, 1.35, p < 0.001), with the probability of use declining steeply with increasing age, whilst Macintosh blades predominated beyond the first year of life (Median = 1.6 years, IQR = 0.75, 2.00, p < 0.001) (Figure 3). Figure 4 demonstrates that although fewer incidences of Macintosh use in infant patients is noted, a higher FPS was still displayed. This age‐dependent exposure pattern resulted in limited overlap between blade type and age, such that inclusion of both variables in adjusted models led to unstable estimates and poor model identifiability. All candidate adjusted models (FPS, hypoxia and hypotension) had events‐per‐variable (EPV) values below accepted thresholds (EPV ~4–5 for FPS and hypoxia; EPV ~7 for hypotension), indicating high risk of overfitting and poor model identifiability. These resulted in model instability or non‐convergence and offered no meaningful improvement in model performance. Accordingly, blade type is reported in unadjusted analyses only (Tables S2, S3 and Figure S1).
TABLE 2.
Intubation outcomes: first pass success and adverse events by blade.
| Patient outcomes | Overall n = 201 | Macintosh 113 (56.2) | Miller 88 (43.8) | p |
|---|---|---|---|---|
| Successfully intubated on first attempt | ||||
| No | 54 (26.9) | 22 (19.5) | 32 (36.4) | 0.012 |
| Yes | 147 (73.1) | 91 (80.5) | 56 (63.6) | |
| Adverse events | ||||
| Hypoxia (yes) | 49 (24.4) | 20 (17.7) | 29 (33.0) | 0.020 |
| Hypotension (yes) | 23 (11.4) | 12 (10.6) | 11 (12.5) | 0.848 |
TABLE 3.
Attempts and FPS by blade type, categorised by age of patient.
| Age category | Overall n = 201 | Macintosh n = 113 | Miller n = 88 | Overall FPS | FPS/Macintosh | FPS/Miller |
|---|---|---|---|---|---|---|
| Age, median [25th, 75th percentile] | 1.2 [0.17, 2] | 1.6 [0.75, 2] | 0.424 [0.08, 1.35] | |||
| 0–3 months | 62 (30.8%) | 20 (17.7%) | 42 (47.7%) | 39/62 (62.9%) | 16/20 (80%) | 23/42 (54.8%) |
| 4–12 months | 36 (17.9%) | 16 (14.2%) | 20 (22.7%) | 27/36 (75%) | 13/16 (81.2%) | 14/20 (70%) |
| 13–23 months | 41 (20.4%) | 29 (25.7%) | 12 (13.6%) | 34/41 (82.9%) | 24/29 (82.8%) | 10/12 (83.3%) |
| 2 years | 30 (14.9%) | 23 (20.4%) | 7 (8%) | 23/30 (76.7%) | 18/23 (78.3%) | 5/7 (71.4%) |
| 3 years | 25 (12.4%) | 20 (17.7%) | 5 (5.7%) | 19/25 (76%) | 17/20 (85%) | 2/5 (40%) |
| 4 years | 7 (3.5%) | 5 (4.4%) | 2 (2.3%) | 5/7 (71.4%) | 3/5 (60%) | 2/2 (100%) |
FIGURE 3.
Age distribution by FPS and blade type.
FIGURE 4.
First pass success by age and blade type.
4. Discussion
Emergency intubation of a young child is a critical intervention, and maximising FPS is a key factor in reducing adverse physiological events. In this multi‐centre observational study of children under 5 years intubated in EDs across Australia and New Zealand, we found that the Macintosh blade was used more frequently than the Miller blade, particularly among older children and trauma cases. In unadjusted analyses, Macintosh blade use was associated with a higher FPS rate and lower hypoxic events.
Traditional teaching favours straight blades for infants because a floppy, omega shaped epiglottis can be directly lifted to expose the glottis. Comparative work in controlled elective settings has shown similar glottic visualisation with Miller and Macintosh in children under 2 years, whilst neonatal data suggest an advantage for Miller size 0 over Macintosh size 0, findings that collectively emphasise age and anatomy over any universal blade hierarchy [12, 13].
We were unable to disentangle age‐related anatomical, physiological and contextual factors from intrinsic device performance when interpreting the lower FPS observed with the use of Miller blades compared with Macintosh blades in this cohort of patients. Infants represented the majority of Miller blade intubations, and airway visualisation in this group may be inherently more challenging, regardless of blade choice. Additionally, emergency clinicians, particularly those trained primarily in adult airway management, may have greater familiarity with the Macintosh blade, potentially improving procedural efficiency during high‐acuity resuscitations.
Additionally, though hypoxia occurred more frequently in children intubated with Miller blades in unadjusted counts, factors such as patient age, laryngoscopic view and FPS may play an important role in hypoxic risk. These findings reinforce the central importance of FPS as a modifiable target for improving paediatric airway safety.
From a clinical perspective, the Macintosh blade appears to perform well across most of the under‐five age range in ED in unadjusted analyses. Given the observed variability in blade use by age, structured training in both blades remains important, with an emphasis on clinician familiarity and reducing cognitive load during emergencies.
These findings highlight the need for prospective comparative simulation or patient‐based studies to determine optimal blade selection by age and clinical context. Integration of video laryngoscopy data, operator‐level analysis and objective grading of glottic view would help disentangle device from experience effects.
A strength of this study is the real‐world, multi‐centre ED setting across Australia and New Zealand, capturing contemporary practise in a high acuity, low occurrence paediatric procedure. This study's primary limitation is the choice of blades was not randomised and may have been influenced by patient age, anticipated difficult laryngoscopy, clinical urgency and operator preference. Accordingly, blade comparisons were confined to descriptive and unadjusted analyses. We were unable to report FPS by blade type for those patients intubated using video‐assisted laryngoscopy due to limitations in the data captured by the ANZEDAR.
5. Conclusion
In children under five intubated in the ED, Macintosh use was associated with higher FPS and fewer hypoxic events, but these differences occurred alongside systematic age and difficulty related selection of blades. Disentangling the interrelated effects of blade type, age and achieved glottic view‐ and determining how best to achieve a high, complication free FPS rate in this cohort‐ will likely require a randomised study. The findings in this study suggest but cannot conclude that Macintosh blade use is not inferior to Miller in all age groups for intubations in the ED and should not preclude the possibility of a potential randomised future study. Regular training should be encouraged in this emergency procedure to build familiarity and confidence in the airway equipment of choice of the intubator.
Supporting Information provided describe all reported laryngoscope patterns described in the airway registry including those that were excluded from the study. There is also the description and data of attempted regression modelling of airway registry data; this includes the explanation of why only unadjusted analysis was included in the study.
Author Contributions
A.W., E.L., H.A. and H.B. drafted the manuscript. H.A. is the ANZEDAR coordinator and conceived the study. H.B. provided data and statistical analysis. All authors revised the manuscript and approved the final draft. T.F. is Principal Investigator of the ANZEDAR.
Funding
The project was funded by the Emergency Care Institute (ECI) through the Agency of Clinical Innovation research funding scheme.
Ethics Statement
The ANZEDAR project was approved by the Northern Sydney Local Health District Human Research Ethics Committee in 2012 (ID: 1209‐318M).
Conflicts of Interest
The authors declare no conflicts of interest.
Supporting information
Table S1: All laryngoscope patterns used in children < 5 years.
Table S2: Events per variable (EPV) for candidate adjusted models.
Table S3: Linear multicollinearity diagnostics (GVIF).
Figure S1: Age related probability of use of Miller and Macintosh blades.
Acknowledgements
The authors H.A., E.L. and T.F. are part of the ANZEDAR investigator group and with A.W. and H.B. thank the ANZEDAR investigators and all site investigators and clinicians who contributed through data collection.
Data Availability Statement
The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Table S1: All laryngoscope patterns used in children < 5 years.
Table S2: Events per variable (EPV) for candidate adjusted models.
Table S3: Linear multicollinearity diagnostics (GVIF).
Figure S1: Age related probability of use of Miller and Macintosh blades.
Data Availability Statement
The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.