Risk factors for critical care admission following routine upper airway surgery in otolaryngology

Introduction

Unplanned critical care (CC) admissions in the perioperative period represent a logistical challenge for hospitals when predicting staffing, bed allocation, and distribution of other limited resources (1,2). Nonetheless, unplanned events that require perioperative CC admission do occur. However, resource allocation can be optimized if a patient’s preoperative risk of requiring CC can be identified early and potential intensive care unit (ICU) or high dependency unit (HDU) care planned ahead of the procedure if needed (3).

In otolaryngology, routine surgeries that involve the upper airway and have risk of ICU/HDU issues include sinonasal airway procedures, tonsillectomy, and uvulopalatopharyngoplasty (UPPP). While post-operative CC might be electively booked for complex head and neck procedures, such as head & neck tumor resections with free flap reconstruction, it is uncommonly arranged for routine otolaryngological operations of the upper airway. However, otolaryngologists are familiar with the increased risks of post-operative complications in upper airway procedures, especially in patients who are obese or with significant obstructive sleep apnea (OSA) (4-7). The risk of missing early identification impacts more than just resource planning, as patients who undergo indirect admission to CC, in the post-operative period, have poorer outcomes than those with planned admissions (3). Improved identification of patients potentially at high risk of CC may allow for better perioperative outcomes and reduce variation in practice.

Whilst there is a consensus statement that identifies children at risk from respiratory complications following oropharyngeal airway surgery, the statement is based on level V evidence (8).

The aim of this study is to review the reported risk factors predisposing an otolaryngology patient undergoing a routine upper airway procedure to CC admission or CC resource use. Such synthesized data would assist otolaryngologists in planning post-operative care for patients undergoing these surgeries.

Methods

This systematic review was structured according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines (available at https://www.theajo.com/article/view/10.21037/ajo-25-8/rc) (9). The aim of this systematic review was to analyze the literature on risk factors for unplanned critical (intensive or higher dependency) care after routine upper airway surgery. This review was registered with Research Registry (London, UK) with Unique Identifying Number: reviewregistry1188. A protocol was not prepared.

Inclusion criteria

Prospective and retrospective case-control studies, cohort studies, and randomized controlled trials were included. Studies assessing adult and/or pediatric patients undergoing routine upper airway surgery were included. Studies were included that assessed procedures where CC would not ordinarily be anticipated, including adenotonsillectomy, tonsillectomy, sinonasal surgery, tongue channeling, UPPP, pharyngoplasty, and minor tongue base surgery. Studies reported in English or with an English translation were included.

Exclusion criteria

Studies of complex surgery where CC admission may be expected were excluded. Examples of these include head & neck surgery, including total or subtotal maxillectomy, partial or total glossectomy, laryngeal procedures, and tracheobronchial surgery; and endonasal anterior skull base surgery. Non-airway procedures, such as otologic surgery, were also excluded. Case reports and case series were excluded.

Outcomes

The primary outcome sought was the need for ICU/HDU level care within 24 hours of surgery. Secondary outcomes included events or triggers, within 24 hours of surgery, for interventions that might be associated with or precipitate the need for ICU/HDU level care, referred to hereafter as CC. These surrogate markers for CC included: airway compromise with need for intervention, desaturation or acute respiratory deterioration with need for intervention, need for ventilatory support, re-admission to hospital within 24 hours of surgery, mortality, primary hemorrhage with or without need for intervention (as this often activates the intensity of nursing care usually provided in an ICU), cardiac arrest and circulatory compromise requiring inotropic support. Long-term outcomes were not included in this study.

Risk factors assessed

Relevant risk factors to include in the literature search were identified based on existing literature on ICU admission after major surgery, including extremes of age, American Society of Anesthesiologists (ASA) physical status, body mass index (BMI), OSA, and operative duration (3). Further risk factors identified included: smoking, diabetes, lung disease, difficult intubation, high opioid requirement, vascular disease, polypharmacy, chromosomal abnormalities, and syndromes. This list was expanded upon after completion of the systematic review, prior to the meta-analysis, to include all risk factors reported upon within the studies.

Databases

Databases searched included Medline and Embase, both via Ovid and including studies from 1 January 1996 to 17 January 2021, the search date. The Cochrane Library was also searched for existing reviews. A 25-year cutoff was chosen so that the results may accurately reflect modern practice. Appendix 1 shows the search strategies utilized for Medline and Embase.

Data extraction

The review author independently reviewed the abstract, title, or both, of every record retrieved, to determine which reports met the inclusion criteria and should be assessed further. All potentially relevant articles were investigated as full text. Included reports were categorized based on the type of surgery studied (oropharyngeal, sinonasal, or both) and their population (adult, pediatric, or both). Data was extracted from the reports in multiple passes to minimize errors in data extraction. A senior surgeon (R.J.H.) reviewed the data extraction process and participated in the resolution of eligibility.

Quality and bias assessment

Quality and bias of studies were assessed using the following factors: cohort size; study design; number of centers; definitive inclusion and exclusion criteria; possibility of selection bias; description of cohort characteristics; and type of statistical analysis performed (10).

Where available, total study population mean age and standard deviation (SD), number of subjects studied (n), and number of subjects who satisfied criteria for a primary or secondary outcome were recorded. Data imputation was used where necessary and appropriate to convert median and range or interquartile range data into mean and SD (11). Synthesized population mean ages among included studies within each category were calculated from reported and imputed data.

Meta-analysis

The variables assessed by each article as potential risk factors for CC were also recorded. The ten most studied risk factors, by number of studies reporting on each, formed the basis for meta-analysis. Meta-analysis was performed within the demographic groupings of either adult or pediatric and either oropharyngeal or sinonasal. Studies falling into multiple groups were analyzed separately within each group. Data was extracted and meta-analysis was performed on eligible studies assessing the ten most studied risk factors. The overall rate of CC requirement across studies of consecutive populations (which were deemed to have reduced risk of selection bias) was calculated for each demographic grouping.

Statistics

In addition to the number of subjects studied (n) and number of patients meeting outcome criteria, meta-analysis of each risk factor involved the collection of the total number of participants with the risk factor, and the number with the risk factor who met outcome criteria for CC. These numbers were also imputed where necessary and appropriate, either from reported statistics or from odds ratios (ORs). Where both univariate and multivariate analysis had been performed within an individual study, the multivariate results were preferentially used. These risk factors, as categorical variables, were then used to compute ORs with 95% confidence intervals (CIs) for each study assessing individual risk factors. The ORs were synthesized in Mix 2.0 (BiostatXL, Mountain View, CA, USA) using a fixed effects model into a summary OR and CI for each risk factor.

Where a risk factor was only studied in severity as an ordinal variable and reported as a summary statistic, the mean and SD for the CC and non-CC groups were extracted or imputed from the studies.

Throughout this study, 95% CIs were used to indicate statistical significance and have been reported in their standard scientific notation.

Results

Systematic review

The literature searches of Medline and Embase databases were performed on 17 January 2021, yielding 6,235 records to be screened. Results of the screening process were summarized in Figure 1. A total of 69 studies, representing n=356,180 patients, were suitable for inclusion in the systematic review. Five studies related to adult sinonasal surgery (n=12,717) and 64 studies related to oropharyngeal surgery (n=343,372), 53 pediatric (n=258,585), and 11 adults (n=84,878). Appendix available at https://cdn.amegroups.cn/static/public/10.21037ajo-25-8-1.docx shows the characteristics of the included studies and their formal bias assessments. Most studies included in this review had potential sources of bias (58/69 studies). Typically, selection bias in the inclusion/exclusion criteria and single-center studies were the main sources of this bias, as highlighted in appendix available at https://cdn.amegroups.cn/static/public/10.21037ajo-25-8-1.docx.

Figure 1 Flow diagram of search results for studies of risk factors for CC in patients undergoing routine upper airway surgery, categorized by type of surgery and age. CC, critical care.

Risk factors assessed

The risk factors with the highest number of studies assessing them, their definitions, and total numbers of patients studied are listed in Table 1. These risk factors and the number of studies assessing them are: (I) OSA severity (n=27); (II) obesity (n=13); (III) young age (n=24); (IV) cardiac disease (n=9); (V) asthma (n=7); (VI) concomitant surgery (n=5); (VII) neuromuscular disorders or cerebral palsy (n=9); (VIII) chromosomal abnormality (n=8); (IX) underweight (n=7); and (X) ethnicity (n=5).

The following risk factors were also assessed, each by four or less included studies: (I) perioperative factors, including duration, timing or urgency of surgery, intra-operative complication, time spent or complications in recovery unit, estimated blood loss, extubation depth and surgeon training level; (II) disease factors, including pathology or indication for surgery; and (III) patient factors, including concurrent viral infection, gastro-esophageal reflux, gender, lower respiratory disorders, medications, medical device dependence including long-term gastrostomy, airway anomaly, haemoglobinopathy, alcohol dependence, ASA physical status >2, attention deficit disorder, autism, chronic kidney disease, coagulopathy, diabetes, gastrointestinal comorbidities, mucopolysaccharidoses, multiple comorbidities, nutritional deficiency, pulmonary hypertension, seizure disorders, severe systemic disorder or syndrome and smoking.

Baseline demographics

The mean age for pediatric oropharyngeal studies was 5.23 (95% CI: 5.08–5.38) years. The mean age for adult oropharyngeal and sinonasal studies was 37.83 (95% CI: 29.40–46.26) and 38.20 (95% CI: 22.91–53.50) years, respectively.

Synthesized overall rate of CC requirement

Across six studies (12-17) of pediatric oropharyngeal surgery (226,531 patients), 0.52% (95% CI: 0.49–0.55%) rate of CC was seen. Across three studies (7,18,19) of adult oropharyngeal surgery (3,834 patients), 0.87% (95% CI: 0.58–1.17%) rate of CC was seen. In two studies (20,21) of adult sinonasal surgery (2,190 patients), 1.38% (95% CI: 0.89–1.87%) rate of CC was seen.

Risk factors

OSA

Apnea hypopnea index (AHI) and lowest oxygen saturation (LSAT) were the most reported measures of OSA severity in the included studies. Ordinal AHI and/or LSAT data was reported or imputed as mean and SD for the CC and non-CC groups in 16 of 27 studies (5-7,15,22-33), all on oropharyngeal surgery. All syntheses showed, with statistical significance, that those patients requiring CC had more severe OSA using both measures compared to the non-CC groups, in both adults and pediatrics. The CC group in adults had mean AHI 51.09 (95% CI: 45.76–56.42) (SD: 30.14) events/h, compared with the non-CC group in adults, which had mean AHI 41.65 (95% CI: 40.08–43.22) (SD: 25.90) events/h. The synthesized mean difference between these groups was 6.13 (95% CI: 5.11–7.14) events/h.

Severe OSA as a risk factor for CC in pediatric studies was also commonly reported as categorical data with cut-offs as AHI ≥10 events/h (26,34,35), LSAT <80% (22,36,37), or symptomatic determination (≥10 second-long hypopneic episodes) (14,15,38,39). OR =2.14 (95% CI: 1.43–3.20) (n=1,276), OR =3.25 (95% CI: 1.52–6.96) (n=249), and OR =3.01 (95% CI: 2.21–4.10) (n=3,077) were conferred for CC by diagnosis of OSA by AHI, LSAT, and symptomatic definitions, respectively. A combined meta-analysis (Figure 2A) using data from 10 studies (14,15,22,26,34-39) of patient outcomes using these definitions of severity revealed OR =2.70 (95% CI: 2.14–3.41) for CC amongst patients meeting any of those OSA severity criteria.

Figure 2 Meta-analysis of odds of CC in pediatric patients undergoing routine oropharyngeal surgery with (A) severe OSA (AHI ≥10 events/h, LSAT <80%, symptomatic diagnosis with ≥10 second-long hypopneic episodes) and (B) obesity (BMI >95^th or 97^th centile for age). AHI, apnea hypopnea index; BMI, body mass index; CC, critical care; CI, confidence interval; LSAT, lowest oxygen saturation; OSA, obstructive sleep apnea.

Obesity

Obesity was defined in adult studies as BMI ≥30 kg/m² and in pediatric studies as BMI >95^th or 97^th centile for age. Using these thresholds, from nine studies (16,24,31,40-45), pediatric obesity in patients undergoing oropharyngeal surgery confers OR =1.82 (95% CI: 1.59–2.07) of CC (Figure 2B). The two adult studies (21,46) (both sinonasal surgery) that assessed BMI ≥30 kg/m² as a threshold found that obesity was not a statistically significant risk factor for CC in adults undergoing sinonasal surgery, with OR =1.54 (95% CI: 0.96–2.47).

Young age

A threshold for younger age as a risk factor for CC was studied in 12 of 24 studies (14,23,31,32,34,38,39,47-51) on pediatric oropharyngeal surgery. A cut-off of 2 years of age was used in three studies (23,34,50), with a synthesized OR =3.62 (95% CI: 2.29–5.73) for CC in those aged below 2 years. A cut-off of 3 years of age was assessed in nine studies (14,31,32,38,39,47-49,51), resulting in an OR of 4.31 (95% CI: 3.34–5.55). A combined synthesis using both cut-offs for “young age” from the 12 studies showed OR =4.14 (95% CI: 3.32–5.18) for CC for patients below 3 years of age (Figure 3).

Figure 3 Meta-analysis of odds of CC in young (age ≤2–3 years) patients undergoing routine oropharyngeal surgery. CC, critical care; CI, confidence interval.

Cardiac disease

Documented history of congestive heart failure was assessed in one adult study (46) on sinonasal surgery. This showed OR =3.47 (95% CI: 2.14–5.60) for CC. Cardiac disease, congenital heart disease, or cardiac anomaly were assessed in eight studies (15,16,33,34,39,48,50,52) on pediatric participants undergoing oropharyngeal surgery. Seven (15,16,33,34,48,50,52) of these studies, including one (52), which had two datasets, showed a synthesized OR =3.15 (95% CI: 2.34–4.24) for CC (Figure 4A). One study (39) was excluded from this analysis because there were no patients with cardiac disease in the non-CC group, resulting in an undefined OR.

Figure 4 Meta-analysis of odds of CC in pediatric patients undergoing routine oropharyngeal surgery with (A) cardiac disease, congenital heart disease, or cardiac anomaly, and (B) asthma. CC, critical care; CI, confidence interval.

Asthma

In seven studies (34,36,42,45,53-55) of pediatric oropharyngeal surgery, a diagnosis of pediatric asthma conferred OR =3.21 (95% CI: 2.20–4.68) for CC (Figure 4B).

Concomitant surgery

Three studies (7,27,56) on concomitant adult sinonasal and oropharyngeal surgery, which found OR =1.51 (95% CI: 0.96–2.39) for CC, suggested there is not a statistically significant increase in risk of CC conferred by the concomitant surgeries (Figure 5).

Figure 5 Meta-analyses of odds for increased risk of CC in adult patients undergoing concomitant surgery. CC, critical care; CI, confidence interval.

Neuromuscular disorders and cerebral palsy

Documented diagnosis of a neuromuscular disorder or cerebral palsy was assessed in nine pediatric studies (12,15,16,22,33,34,38,51,57) of oropharyngeal surgery. It was found to confer OR =3.54 (95% CI: 2.74–4.59) for CC.

Chromosomal abnormality

Across eight studies (4,12,14-16,22,33,38), diagnosed chromosomal abnormalities in pediatric patients undergoing oropharyngeal surgery conferred OR =4.32 (95% CI: 3.37–5.54) for CC.

Underweight

Of the seven studies (12,14,15,34,39,49,58) of pediatric patients undergoing oropharyngeal surgery assessing underweight as a risk factor for CC, five (12,14,15,39,49) used exact weights as cut-offs ranging from 10 to 20 kg, irrespective of age, with no two studies using the same threshold. The other studies (34,58) assessed weight-for-age using centile and z-score. Given the heterogeneity of thresholds used and the obvious correlation between weight as a single threshold for all patients and other factors (e.g., age and OSA status), it was deemed inappropriate to synthesize data of questionable validity. It should also be noted that four (14,34,49,58) of the seven studies found underweight patients to be statistically indifferent in risk for CC as normal weight patients.

Ethnicity

Three studies (34,59,60) of pediatric patients undergoing oropharyngeal surgery found through multivariate analysis that African American ethnicity conferred OR =1.72 (95% CI: 1.53–1.94) for CC.

Discussion

This systematic literature review and meta-analysis showed that the risk factors for CC in pediatric patients undergoing oropharyngeal surgery are severe OSA (AHI ≥10 events/h, LSAT <80%, or 10 second-long hypopneic episodes), young age (under 3 years), obesity (BMI ≥95^th centile for age), neuromuscular disorder or cerebral palsy, cardiac disease or anomaly, chromosomal abnormality, asthma diagnosis and African American ethnicity. This aligns well with the existing literature (8). It also showed that the overall risk of CC in these patients is 0.52% (95% CI: 0.49–0.55%).

The common risk factors for CC in adults undergoing sinonasal or oropharyngeal surgery are congestive heart failure and very severe OSA (with AHI >50 events/h). The overall risk of CC in adults is 0.87% (95% CI: 0.58–1.17%) for oropharyngeal surgery and 1.38% (95% CI: 0.89–1.87%) in sinonasal surgery. Importantly, adult obesity (OR =1.54; 95% CI: 0.96–2.47), when defined as BMI ≥30 kg/m², and concomitant surgery (OR =1.51; 95% CI: 0.96–2.39) were not risk factors for CC in isolation.

This review highlights the paucity of high-quality studies published on this topic. Most studies included in this review had potential sources of selection bias (58/69 studies, appendix available at https://cdn.amegroups.cn/static/public/10.21037ajo-25-8-1.docx). Typically, the exclusion or exclusive inclusion of high-risk age-groups or those with risk factors for CC admission were the source of selection bias, particularly in those studies that were single-center (appendix available at https://cdn.amegroups.cn/static/public/10.21037ajo-25-8-1.docx). This had a variable effect on the odds of CC in each study—for example, some studies selectively excluded populations with risk factors for CC according to this review, while others selected higher risk populations to study. Pooling of numerous studies in most of the risk factor syntheses, however, reduces the overall variability due to these differences in criteria. Fully eliminating all studies with potential selection bias would result in the exclusion of most of the studies used in the meta-analyses.

Another weakness identified by this review was the high proportion of univariate analyses performed (33/69 studies, appendix available at https://cdn.amegroups.cn/static/public/10.21037ajo-25-8-1.docx). This increased the risk of overestimated odds due to confounding variables. Though the meta-analysis favors larger studies with lower variance, resulting in blunting of effects from confounders, it is important to note that the magnitude of the strengths of association may still be overestimated due to confounding variables. This risk becomes compounded when multiple risk factors are combined in the use of data (e.g., a 2-year-old with severe OSA and chromosomal abnormality may have a grossly overestimated odds of CC should the ORs be multiplied).

Whilst this review analyzed risk factors for CC in routine upper airway surgery, it did not include risk factors that would be deemed background risks for CC in all surgeries (e.g., abdominal, cardiothoracic, neurosurgery, etc.), due to their omission from the search strategy. Furthermore, this review selected risk factors based on number of studies providing evidence about their link to CC requirement. Other risk factors were identified that may confer risk for CC but have not been studied outside the ten most frequently reported and were thus excluded from meta-analysis.

It should be noted that this review does contain some sources of potential bias, including the use of fixed-effects modelling rather than random-effects. Another potential source of bias is the decision to impute missing data to increase the power of the meta-analysis. Additionally, imputation was only performed where the relevant data were available and documented clearly, minimizing the consequent risk of bias. Finally, the screening of the titles and abstracts from the search by the review author independently confers a risk of bias. This was minimized by the utilization of a senior author to resolve all questions about eligibility.

Amongst the risk factors mentioned, all but OSA severity can be readily identified from history and examination. Only about 10% of paediatric otolaryngologists obtain a preoperative polysomnogram before tonsillectomy for sleep-disordered breathing (61). Alternatively, parents could report loud snoring or pauses, but there are suggestions that history is not consistently confirmed by polysomnogram (62). Symptoms may therefore fail to reveal a diagnosis of severe OSA. Interestingly, the meta-analysis suggests that a symptomatic diagnosis of OSA confers a similar OR for CC utilization to using the LSAT cut-off of 80%, and even higher (but still similar) than the AHI ≥10 events/h cut-off. It was therefore felt that patients meeting any one of these definitions of OSA diagnosis could be considered higher risk for CC, resulting in a combined meta-analysis being performed.

The pathophysiology behind the finding of African American ethnicity as a risk factor for CC has been discussed and may even be multifactorial (34,60). The proposed inheritable mechanisms involve reduced airway cross-sectional area, increased frequency of ultrarapid codeine metabolizers, and decreased lung function due to decreased birth weight. There are also several environmental and socioeconomic variables that have been proposed to be confounding factors, though the three studies from which this result is derived all performed multivariate analyses. However, all three studies are possibly subject to selection bias. The generalizability of this particular result is therefore questionable without further focused study and analysis.

The implication of the results of this review for practice and policy is that a model could be prospectively created to pre-operatively predict increased risk of CC requirement in the appropriate cohort of patients, similar to but more comprehensive than those proposed by current literature (63). This would be beneficial for clinical outcomes, patient safety, and standardized care, as well as logistical planning and resource allocation. In addition, the review has identified risk factors that can be studied in more depth and detail to identify delineating thresholds.

Conclusions

This systematic review identifies likely risk factors for CC in routine upper airway surgery, subject to significant confounders and selection bias. In pediatric patients undergoing oropharyngeal surgery, these include age below 3 years, severe OSA (defined as AHI ≥10, LSAT<80%, or ≥10 second-long hypopneic episodes), obesity (BMI ≥95^th centile for age), neuromuscular disorders, cerebral palsy, chromosomal abnormality, cardiac disease, asthma diagnosis, and African American ethnicity. In adults undergoing either sinonasal or oropharyngeal surgery, risk factors include severe OSA (AHI >50 events/h) and congestive heart failure. Obesity (when defined by BMI ≥30 kg/m²) and concomitant sinonasal and oropharyngeal surgery in adults are not associated with increased odds of CC.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the PRISMA reporting checklist. Available at https://www.theajo.com/article/view/10.21037/ajo-25-8/rc

Peer Review File: Available at https://www.theajo.com/article/view/10.21037/ajo-25-8/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://www.theajo.com/article/view/10.21037/ajo-25-8/coif). P.M. serves as an unpaid editorial board member of Australian Journal of Otolaryngology from January 2019 to December 2027. J.C. serves as an unpaid editorial board member of Australian Journal of Otolaryngology from January 2019 to December 2027. R.G.C. serves as an unpaid editorial board member of Australian Journal of Otolaryngology from January 2019 to December 2027. R.J.H. serves as an unpaid editorial board member of Australian Journal of Otolaryngology from April 2024 to December 2027. R.J.H. is consultant with Medtronic, Stryker, Novartis, Meda, and NeilMed pharmaceuticals. Research grant funding received from Glaxo-Smith-Kline, Sanofi and Stallergenes. He has been on the speakers’ bureau for Glaxo-Smith-Kline, Sanofi, P&G, Meda Pharmaceuticals, and Seqirus. The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This review was registered with Research Registry (London, UK) with Unique Identifying Number: reviewregistry1188. A protocol was not prepared.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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