Risk factors for desaturation after tonsillectomy: analysis of 4092 consecutive pediatric cases

Apnea-hypopnea index severity as an independent predictor of post-tonsillectomy respiratory complications in pediatric patients: A retrospective study

INTRODUCTION

Despite the presence of clinical practice guidelines for overnight admission of pediatric patients following adenotonsillectomy, variance in practice patterns exists between pediatric otolaryngologists. The purpose of this study is to examine severity of apnea-hypopnea index (AHI) as an independent predictor of postoperative respiratory complications in children undergoing adenotonsillectomy.

METHODS

Retrospective chart review of all children undergoing adenotonsillectomy at a large tertiary referral center between January 2015 and December 2019 who underwent preoperative polysomnography and were admitted for overnight observation. Charts were reviewed for total adverse events and respiratory events occurring during admission.

RESULTS

Overall, respiratory events were seen in 50.6% of patients with AHI ≥10 and in 39.6% of patients with AHI <10. The overall mean AHI was 19.2, with a mean of 28.1 in the AHI ≥10 subgroup vs 4.6 in the AHI <10 subgroup. There was no statistical correlation or increased risk between an AHI ≥10 and having a pure respiratory event, with a relative risk of 1.19 (.77-1.83, P = .43). There was a statistically significant difference between the mean AHI of those with any adverse event and those without (21.6 vs 13.4, P = .008). There is additionally an increased risk of any event with an AHI over 10, with a relative risk of 1.51 (1.22-1.88, P < .0001).

CONCLUSION

Preoperative AHI of 10 events per hour was not a predictor of postoperative respiratory complications. However, there was a trend for those with a higher AHI requiring additional supportive measures or a prolonged stay. Practitioners should always use their best judgment in deciding whether a child warrants postoperative admission following adenotonsillectomy.

Adenotonsillectomy for Obstructive Sleep Apnea in Children

Obstructed breathing is the most common indication for tonsillectomy in children. Although tonsillectomy is performed frequently worldwide, the surgery is associated with a number of significant complications such as bleeding and respiratory failure. Complication risk depends on a number of complex factors, including indications for surgery, demographics, patient comorbidities, and variations in perioperative techniques. While polysomnography is currently accepted as the gold standard diagnostic tool for obstructive sleep apnea, studies evaluating outcomes following surgery suggest that more research is needed on the identification of more readily available and accurate tools for the diagnosis and follow-up of children with obstructed breathing.

Socioeconomic and racial disparities in revisits, indication, and readmission or reoperation in pediatric tonsillectomy

INTRODUCTION

Pediatric tonsillectomy is a frequent otolaryngologic procedure. This study aimed to characterize disparities in post-tonsillectomy revisits, including emergency department evaluation, readmission, or reoperation as well as indication for revisit.

METHODS

Cases of inpatient and ambulatory pediatric tonsillectomy in New York and Florida in 2016 constituted the analytic sample. Patients were extracted from the State Ambulatory Surgery Databases (SASD) and State Inpatient Databases (SID) and linked to the SID and State Emergency Department Database (SEDD) and SASD. Outcomes include 3 types of revisits within 30 days: ED visits, hospital readmissions, and reoperation. Indication for revisit was also analyzed. Multivariable analysis determined the association of each outcome with gender, age, race/ethnicity, primary payer, urbanicity, and zip code median household income quartile. The Holm Bonferroni test was used to correct for multiple hypothesis testing.

RESULTS

15,264 pediatric tonsillectomies were included. The revisit rate was 6.77% (N = 1,034, 49.1% female; 6 years median age [interquartile range: 5]). The 30-day ED revisit rate was 4.85%, readmission rate was 1.27%, and reoperation rate was 0.65%. On multivariate analysis, Latinx patients (OR = 3.042, 95% CI = 1.393-6.803) and those who identify as other race/ethnicity (OR = 6.116, 95% CI = 1.989-19.245) have greater odds of requiring inpatient care for indications including pain, dehydration, nausea, and vomiting compared to white patients. No significant differences in tier of care for the management of post-tonsillectomy hemorrhage were identified.

CONCLUSION

Disparities in pediatric post-tonsillectomy ED presentation, readmission and reoperation demonstrate opportunities to improve patient safety and equity.

Pediatric obstructive sleep apnea: a prospective observational study of respiratory events in the immediate recovery period after adenotonsillectomy

BACKGROUND

Adenotonsillectomy is often curative for pediatric obstructive sleep apnea, yet children remain at high risk of respiratory complications in the postoperative period. We sought to determine the incidence and risk factors for respiratory depression and airway obstruction, as well as clinically apparent respiratory events in the post-anesthesia care unit (PACU) in high-risk children after adenotonsillectomy.

METHODS

In this prospective cohort study, we enrolled 60 high-risk children having adenotonsillectomy. Our primary outcome was respiratory depression and airway obstruction in the PACU measured using a noninvasive respiratory volume monitor (RVM) and defined by episodes of predicted minute ventilation less than 40% for at least 2 min. We measured clinically apparent respiratory events using continuous observation by trained study staff.

RESULTS

The median (range) age of our sample was 4 years (1, 16) and 27 (45%) were female. Black and Hispanic race children comprised 80% (n = 48) of our cohort. Thirty-nine (65%) had at least one episode of PACU respiratory depression or airway obstruction measured using the RVM, while only 21 (35%) had clinically apparent respiratory events. Poisson regression demonstrated the following associations with an increase in episodes of respiratory depression and airway obstruction: BMI Z-score less than -1 (estimate 3.91; [95%CI 1.49-10.23]), BMI Z-score 1-2 (estimate 2.04; [1.20-3.48]), and two or more comorbidities (estimate 1.96; [1.11-3.46]).

CONCLUSIONS

Respiratory volume monitoring in the immediate postoperative period after pediatric high-risk adenotonsillectomy identifies impaired ventilation more frequently than is clinically apparent.

The high-risk pediatric patient for ambulatory surgery

PURPOSE OF REVIEW

The aim of this article is to briefly review the pediatric ambulatory surgery landscape, identify two of the most common comorbidities affecting this population, examine the influence of pediatric obesity and sleep disordered breathing (SDB)/obstructive sleep apnea (OSA) on perioperative care, and provide information that can be used when formulating site specific criteria for ambulatory surgical centers.

RECENT FINDINGS

Most pediatric surgeries performed are now ambulatory, a majority of which take place outside of academic centers. Children with comorbidities such as obesity and SDB/OSA are undergoing surgical or diagnostic procedures which were previously deemed unacceptable for ambulatory surgery. The increase in pediatric ambulatory surgery coupled with a recent shortage of pediatric anesthesiologists means many children will receive anesthesia care from general clinicians who care for children intermittently and may be unfamiliar with the perioperative risks these comorbidities can present.

SUMMARY

Our pediatric ambulatory surgical population is anticipated to demonstrate increasing rates of obesity and SDB/OSA. Bringing attention to potential perioperative complications associated with these comorbidities provides a stronger foundation upon which to formulate criteria for individual ambulatory centers. It allows for targeted anesthetic management, influences provider assignments and/or staffing ratios, and informs scheduling times. For anesthesiologists who do not practice pediatric anesthesia daily, knowing what to anticipate plays a significant role in the ability to eliminate surprises and care for these patients safely.

Estimations of Inpatient and Ambulatory Pediatric Tonsillectomy in the United States: A Cross-sectional Analysis

OBJECTIVE

To estimate the incidence of inpatient and ambulatory pediatric tonsillectomies in the United States in 2019.

STUDY DESIGN

Cross-sectional analysis.

SETTING

Healthcare Cost and Utilization Project databases.

METHODS

We determined national incidences of hospital-based ambulatory procedures, inpatient admissions, and readmissions among pediatric tonsillectomy patients, ages 0 to 20 years, using the Kids Inpatient Database, Nationwide Ambulatory Surgery Sample, and Nationwide Readmission Database. We described the demographics, commonly associated conditions, complications, and predictors of readmission.

RESULTS

An estimated 559,900 ambulatory and 7100 inpatient tonsillectomies were performed in 2019. Among inpatients, the majority were male (59%) and the largest ethnic group was white (37%). Adenotonsillar hypertrophy (ATH), 79%, and obstructive sleep apnea (OSA), 74%, were the most frequent diagnosis and Medicaid (61%) was the most frequent primary payer. The majority of ambulatory tonsillectomy patients were female (52%) and white (65%); ATH, OSA, and Medicaid accounted for 62%, 29%, and 45% of cases, respectively, (all p < .001 when compared to inpatient cases). Common inpatient complications were bleeding (2%), pain/nausea/vomiting (5.6%), and postprocedural respiratory failure (1.7%). On the other hand, ambulatory complications occurred in less than 1% of patients. The readmission rate was 5.2%, with pain/nausea/vomiting and bleeding accounting for 35% and 23% of overall readmissions. All Patient Refined Diagnosis Related Groups severity of illness subclass predicted readmission (odds ratio = 2.18, 95% confidence interval = 1.73-2.73, p < .001).

CONCLUSION

A total of 567,000 pediatric ambulatory and inpatient tonsillectomies were performed in 2019; the majority were performed in ambulatory settings. The index admission severity of illness was associated with readmission risk.

Risk Factors for Post-Tonsillectomy Respiratory Events in Children With Severe Obstructive Sleep Apnea

OBJECTIVES/HYPOTHESIS

To identify risk factors for postoperative respiratory events in pediatric patients with severe obstructive sleep apnea (OSA).

METHODS

Retrospective single-institution retrospective cohort study of pediatric patients with severe OSA who were admitted postoperatively after tonsillectomy. Patients who experienced respiratory events after surgery were identified and differences between the respiratory event and no event groups were compared.

RESULTS

There were 887 patients included in this study. 14.8% (n = 131) experienced a documented respiratory event. The following risk factors were found to be most significant: %sleep time with O₂  < 90% (tb90) (95% CI = 1.07-1.14, OR = 1.10, p < 0.001), Black race (95% CI = 1.53-3.58, OR = 2.34, p < 0.001), primary neurologic co-morbidity (1.67-6.32, OR = 3.27, p < 0.001), Down syndrome (1.25-5.94, OR = 2.72, p = 0.01), and age (0.84-0.94, OR = 0.88, p < 0.001). Regression modeling demonstrated that the rate of respiratory events increased with tb90.

CONCLUSIONS

Our results demonstrate that there are other potential risk factors outside of AHI and O₂ nadir that are associated with respiratory events after tonsillectomy. Black race and prolonged desaturations during polysomnography (PSG) are independent risk factors. Measures of abnormal gas exchange on PSG may be better at identifying at risk patients.

LEVEL OF EVIDENCE

4 Laryngoscope, 2022.

Tonsillectomy for Obstructive Sleep-Disordered Breathing: Should They Stay, or Could They Go?

OBJECTIVES/HYPOTHESIS

Children who do not require oxygen beyond 3 hours after surgery and pass a sleep room air challenge (SRAC) are safe for discharge regardless of polysomnogram (PSG) results or comorbidities.

STUDY DESIGN

Cross-sectional prospective study.

METHODS

All children observed overnight undergoing an adenotonsillectomy for obstructive sleep-disordered breathing were prospectively recruited. Demographic, clinical, and PSG characteristics were stratified by whether the patient had required oxygen beyond 3 hours postoperatively (prolonged oxygen requirement [POR]) and compared using t test, chi-squared test, or Fisher's exact test depending on distribution. Optimal cut points for predicting POR postsurgery were calculated using receiver operating characteristic curves. The primary analysis was performed on the full cohort via logistic regression using POR as the outcome. Significant characteristics were analyzed in a logistic regression model, with significance set at P < .05.

RESULTS

A total of 484 participants met the inclusion criteria. The mean age was 5.65 (standard deviation = 4.02) years. Overall, 365 (75%) did not have a POR or any other adverse respiratory event. In multivariable logistic regression, risk factors for POR were an asthma diagnosis (P < .001) and an awake SpO2  <96% (P = .005). The probability of a POR for those without asthma and a SpO2  ≥ 96% was 18% (95% confidence interval: 14-22). Age, obesity, and obstructive apnea/hypopnea index were not associated with POR.

CONCLUSIONS

In conclusion, all children in our study who are off oxygen within 3 hours of surgery and passed a SRAC were safe for discharge from a respiratory standpoint regardless of age, obesity status, asthma diagnosis, and obstructive apnea/hypopnea index. Additional investigations are necessary to confirm our findings.

LEVEL OF EVIDENCE

3 Laryngoscope, 132:1675-1681, 2022.

Considerations in Surgical Management of Pediatric Obstructive Sleep Apnea: Tonsillectomy and Beyond

Obstructive sleep apnea (OSA) is an increasingly recognized disorder with a reported incidence of 5.7% in children. Tonsillectomy (with or without adenoidectomy) in pediatric OSA in otherwise healthy non-obese children has a success rate of approximately 75%. However, the cure rate reported for all children undergoing tonsillectomy varies from 51% to 83%. This article reviews the history of tonsillectomy, its indications, techniques, various methods, risks, and successes. The article also explores other surgical options in children with residual OSA post-tonsillectomy.

Risks and Benefits of Adenotonsillectomy in Children With Cerebral Palsy With Obstructive Sleep Apnea: A Systematic Review

OBJECTIVES/HYPOTHESIS

Assess the risks and benefits of adenotonsillectomy (AT) for obstructive sleep apnea (OSA) in children with cerebral palsy (CP).

STUDY DESIGN

Systematic review.

METHODS

We conducted a systematic review of Medline, Embase, and Cochrane Central Registry from 1946 to 2021. Broad search concepts included cerebral palsy, pediatric, tonsillectomy/adenoidectomy, and sleep. Additional articles were identified by searching reference lists. Studies on the safety and efficacy of AT for OSA management in children with CP were included.

RESULTS

Fifteen articles met inclusion criteria. Articles were classified into one or more of four themes: intraoperative risk (n = 1), postoperative risk (n = 3), postoperative care requirements (n = 6), and surgical outcomes (n = 7). No intraoperative anesthetic complications were reported. Postoperatively, respiratory complications including pneumonia were common and necessitated additional airway management. Following AT, children with CP required close postoperative observation, experienced increased lengths of stay, and had increased odds of unplanned intensive care unit (ICU) admission. Benefits following AT were improvement in OSA as measured by a reduction in obstructive apnea-hypopnea index (OAHI) as well as improved quality of life in some; however, many patients went on to require tracheostomy due to persistent OSA.

CONCLUSIONS

Children with CP who undergo AT have a significant risk of developing a postoperative respiratory complication. Realistic counseling of families around increased perioperative risks in this population is imperative and close postoperative monitoring is critical. Many children will obtain a reduction in OAHI, but additional surgical management is often required, including tracheostomy. Further research is needed to determine the best management strategy for OSA in children with CP. Laryngoscope, 2021.

Predictors of hypoxemia after general anesthesia in the early postoperative period in a hospital in Ethiopia: an observational study

BACKGROUND

Early postoperative hypoxemia is a common problem after general anesthesia. The identification of factors associated with an increased occurrence of it might help healthcare professionals to hypoxemia risk patients, therefore this study aims to assess the incidence and factors associated with early postoperative hypoxemia among surgical procedures.

METHODS

A prospective cohort study design was conducted from February 1, 2020 to June 30, 2020, on a total of 424 patients who underwent surgery under general anesthesia in Debre Tabor Comprehensive Specialized Hospital. The data was collected using a structured checklist. Bivariable and multivariable logistic regressions were used to check the association.

RESULTS

The incidence of early postoperative hypoxemia was 45.8%. Patients having a BMI of 25-29.9 kg/m2 and BMI of 30-39.9 kg/m2, patients having a chronic disease, current smokers, SPO2 reading before induction of less than 95%, emergency surgery, and the absence of oxygen therapy during the period of transfer and/or in the post anesthesia care unit were significantly associated with an increased risk of hypoxemia in the early postoperative period.

CONCLUSIONS

The incidence of early postoperative hypoxemia was high in Debre Tabor Comprehensive Specialized Hospital. Obese patients, patients having a chronic disease, current smokers, and lower oxygen saturations before induction, emergency surgery, and the absence of oxygen therapy were the main predictors of an increased occurrence of early postoperative hypoxemia.

Transcutaneous CO2 Monitoring in Children Undergoing Tonsillectomy for Sleep Disordered Breathing

OBJECTIVES/HYPOTHESIS

Children undergoing tonsillectomy for sleep-disordered breathing are at risk for respiratory compromise when narcotics are administered. Severe complications resulting from hypoxia can include neuro-devastation and death. The objective of this prospective study was to evaluate the feasibility, accuracy, and utility of transcutaneous carbon dioxide (tcPCO2) monitoring during and after adenotonsillectomy.

STUDY DESIGN

Prospective, Observational study.

METHODS

Twenty-nine children with sleep-disordered breathing scheduled for adenotonsillectomy were included in the study. Peri-operative measurements of tcPCO2 were compared against a single venous blood sample (PaCO2) and end-tidal (ET) CO2. The differences between ETCO2, tcPCO2 measures, and PaCO2 were examined using non-paired t-tests and linear regression. Parameters from PSG were recorded and associations with tcPCO2 values were performed using linear regression analysis. Group comparisons were made between pre-, intra-, and post-operative tcPCO2 measurements.

RESULTS

Similar to ETCO2, there was good correlation of tcPCO2 to PaCO2. Children with lower oxygen (O2) saturation nadirs had higher peak CO2 levels during surgery and spent a greater proportion of time with CO2 > 50 mmHg in the recovery room (P < .01 and P < .08). Other PSG measures (apnea-hypopnea index, O2 desaturation index, and peak CO2) did not have any significant correlation. Frequent episodes of hypercapnia were noted intra- and post-operatively and mean tcPCO2 values during both periods were significantly higher than baseline (P < .001).

CONCLUSIONS

tcPCO2 monitoring is viable in children undergoing adenotonsillectomy and can provide a good estimate of hypoventilation. tcPCO2 measurements may have particular benefit in the post-operative setting and may assist in identifying children at greater risk for respiratory complications.

LEVEL OF EVIDENCE

4 Laryngoscope, 131:1410-1415, 2021.

Respiratory complications after adenotonsillectomy in high-risk children with obstructive sleep apnea: A retrospective cohort study

BACKGROUND

Obstructive sleep apnea (OSA) occurs in 1%-4% of children; adenotonsillectomy is an effective treatment. Mortality/severe brain injury occurs among 0.6/10 000 adenotonsillectomies; in children, 60% are secondary to airway/respiratory events. Earlier studies identified that children aged <2 years, extremes of weight, with co-morbidities of craniofacial, neuromuscular, cardiac/respiratory disease, or severe OSA are at high risk for adverse post-operative respiratory events (AE). We aimed to: Firstly, investigate which risk factors were associated with AEs either in the post-anesthesia care unit (PACU), pediatric intensive care unit (PICU), or both in this population. Secondly, we investigated factors associated with post-operative PICU AE despite no event in the PACU in order to predict need of post-operative PICU after their PACU stay.

METHODS

Retrospective study of children admitted to the PICU after adenotonsillectomy between 08/2006-09/2015. Demographics, risk factors, and occurrence of AE (oxygen saturation <92, stridor, bronchospasm, pneumonia, pulmonary edema, re-intubation) were recorded.

RESULTS

During the studied time period 4029 tonsil/adenoid procedures were performed in 3997 children. 179, admitted to the PICU post-operatively, met criteria for analysis. PICU AEs occurred in 59%: 44%-83% in any particular risk category. PACU AEs occurred in 42%. Of those with PACU events: 92% suffered AEs in the PICU; however, 35% of those without a PACU AE still suffered a PICU AE.

CONCLUSIONS

Among high-risk children undergoing TA, absence of adverse events in PACU during a 2-hour observation period does not predict absence of subsequent AEs in the PICU.

Association Between Age and Weight as Risk Factors for Complication After Tonsillectomy in Healthy Children

Importance

The 1996 Tonsillectomy and Adenoidectomy Inpatient Guidelines of the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) Pediatric Otolaryngology Committee recommended that children younger than 3 years be admitted following tonsillectomy. Recommendations for hospital observation were not included as a key action statement in the 2011 AAO-HNS Clinical Practice Guidelines for Tonsillectomy in Children.

Objective

To examine the association between posttonsillectomy complication rate and the age and weight of the child at the time of surgery.

Design, Setting, and Participants

This was a multicenter case series study with medical record review of 2139 consecutive children ages 3 to 6 years who underwent tonsillectomy at 1 tertiary care academic center and 5 acute care centers in New Orleans, Louisiana, between 2005 and 2015. Children with moderate to severe developmental delay, bleeding disorders, and other major medical comorbidities were excluded.

Main Outcomes and Measures

Complications examined included respiratory distress, dehydration requiring intravenous fluids, and bleeding.

Results

Of the 2139 patients, 1817 met inclusion criteria. A total of 1011 (55.6%) were male. The mean (SD) age at the time of the procedure was 46 (14) months (range, 12-72 months). The mean weight at the time of the procedure was 17 (5) kg (range, 9-43 kg). A total of 95 patients (5.2%) had a postoperative complication. Of the 455 children younger than 3 years in the study, 32 (7.0%) had complications compared with 63 (4.6%) of the 1362 patients 3 years or older. The odds of having a complication in children younger than 3 years was 1.5 times greater than it was in children 3 years or older (odds ratio [OR], 1.56; 95% CI, 1.00-2.42). When examining total complications, children younger than 3 years were more likely to experience a complication within the first 24 hours after surgery than children 3 years or older (25% vs 9.5%; OR, 3.17; 95% CI, 1.00-10.11). The children admitted to the hospital had a greater risk of complication than those treated as an outpatient, independent of age (6.9% vs 93.0%; OR, 3.49; 95% CI, 2.0.18-6.05). No association between weight and complications was found on logistic regression (area under the curve = 0.5268; P = .66).

Conclusions and Relevance

Healthy children younger than 3 years may be at an increased risk for complication following tonsillectomy. Those children may also be at increased risk for complications within the first 24 hours after surgery compared with children 3 years or older. Our data suggest that complications are independent of weight in these patients. In our cohort, those patients selected for overnight observation were associated with an increased number of adverse events following tonsillectomy, suggesting that clinician judgment is crucial in determining which patients are safe for outpatient tonsillectomy.

Analysis of intensive care admissions among paediatric obstructive sleep apnoea referrals

Introduction The aim of this study was to identify the proportion of children referred to a paediatric tertiary referral centre who required admission to the paediatric intensive care unit (PICU) following surgery for obstructive sleep apnoea (OSA) and to establish risk factors for these admissions. Methods Retrospective review of case notes and the operative database was performed for all children undergoing adenotonsillectomy for sleep disordered breathing and OSA symptoms in Great Ormond Street Hospital over a 10-year period. Results Overall, 1,328 children underwent adenotonsillectomy for sleep disordered breathing and OSA. The mean age was 3.1 years (standard deviation [SD]: 1.7 years). A total of 37 (2.8%) were admitted to the PICU postoperatively (mean length of PICU stay: 1.2 days, standard deviation [SD]: 0.6 days) and 282 (21.2%) required nasopharyngeal airway (nasal prong) insertion intraoperatively. The mean length of stay on the ward following surgery was 1.4 days (SD: 0.8 days). Patients with severe OSA (apnoea-hypopnoea index [AHI] >10) and ASA (American Society of Anesthesiologists) grade ≥3 were more likely to require postoperative PICU admission (22/37 vs 381/1,291 [p<0.001] and 29/37 vs 660/1,291 [p=0.001] respectively). Severe OSA was also more common in children who required nasal prong insertion intraoperatively (186/282 vs 217/1,046, p<0.001). Conclusions Very few children referred to a paediatric tertiary referral centre actually require PICU admission following surgery. This may be in part due to the use of a nasopharyngeal airway in patients where postoperative obstruction is anticipated. In children with severe OSA (AHI >10) and an ASA grade of ≥3, nasopharyngeal airway insertion and potential admission to the PICU should be considered.

Obstructive Sleep Apnea and Surgery: Quality Improvement Imperatives and Opportunities

Obstructive sleep apnea (OSA) is more common in surgical candidates than in the general population and may increase susceptibility to perioperative complications that range from transient desaturation to catastrophic injuries. Understanding the potential impact of OSA on patients' surgical risk profile is of particular interest to otolaryngologists, who routinely perform airway procedures-including surgical procedures for treatment of OSA. Whereas the effects of OSA on long-term health outcomes are well documented, the relationship between OSA and surgical risk is not collinear, and clear consensus on the nature of the association is lacking. Better guidelines for optimization of pain control, perioperative monitoring, and surgical decision making are potential areas for quality improvement efforts. Many interventions have been suggested to mitigate the risk of adverse events in surgical patients with OSA, but wide variations in clinical practice remain. We review the current literature, emphasizing recent progress in understanding the complex pathophysiologic interactions noted in OSA patients undergoing surgery and outlining potential strategies to decrease perioperative risks.