Criteria abstracted from The Users' Guide to Medical Literature, from the Health Information Research Unit and Clinical Epidemiology and Biostatistics, McMaster University

Highlighted lines and questions below provide links to the pertinent description of criteria in The EBM User's Guide, now available at the Canadian Centres for Health Evidence

Article Reviewed:

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Possible risk factors associated with moderate or severe airway injuries in children who underwent endotracheal intubation.

Gomes Cordeiro AM, Fernandes JC, Troster EJ.

Pediatr Crit Care Med. 2004 Jul;5(4):364-8. [abstract]

Reviewed by Angela Wratney MD MHSc, Children's National Medical Center, Washington, DC

Review posted November 25, 2005

I. What is being studied?

Study objective:

Evaluate the risk factors associated with moderate or severe airway injuries in infants and children who underwent endotracheal intubation.

Study design

Prospective cohort study.

Methods:

Patients: All infants and children who required endotracheal intubation during a 25-month period from October 1999 to October 2001 were prospectively evaluated. Patients were excluded if death occurred before extubation or if the weight was <1250 grams. Informed consent was obtained for all enrolled patients.

Setting: Pediatric intensive care unit of the Hospital Universitario da Universidade de Sao Paulo.

Study Protocol: All patients were intubated by rapid sequence intubation and received a standardized sedation regimen. The attending physician had the discretion to choose an orotracheal or nasotracheal intubation. All extubations were elective. A PICU staff physician performed airway endoscopy for all patients at the time of extubation and at re-intubation for those patients who required re-intubation. A sample of 50 endoscopic examinations was video-recorded for blinded review by a second reviewer.

The outcomes assessed:

Visual assessment/classification of minor, moderate, or severe airway injury associated with endotracheal intubation.

II. Are the results of the study valid?

Note: These questions follow from Randolph AG et al. Understanding articles describing clinical prediction tools. Crit Care Med 1998;26:1603-1612. [abstract]

1. Was a representative and well-defined sample of patients at a similar point in the course of the disease? Was follow-up sufficiently long and complete?

1. Was a representative and well-defined sample of patients at a similar point in the course of the disease?

   Yes. 215 newborns, infants and children were enrolled in the study. 61 (28.4%) patients were newborns (average age 7.8 ± 6.3d) and 154 (71.6%) patients were infants and children (average age 13.2 ± 24.8 mos). The age of the population ranged from 1d to 14 years. This study excluded premature infants weighing <1250g and any intubated patient who died prior to an extubation trial.

   In the 25-month study period, there were a total of 1,435 patients admitted to the PICU with 313 (21.8%) requiring endotracheal intubation. Nearly 100 patients were excluded due to: 35 who died without airway examination; 11 pts weighed <1250g; and 12 families refused consent; 40 additional patients did not have airway examination (8-no consent; 14-technical problems; 10-unplanned extubation; 8-pts transferred to another facility).

   The main indication for intubation was respiratory distress/failure in 134 pts, cardiovascular instability in 18 pts, a combination of respiratory and cardiovascular instability in 38 pts, neurologic instability in 7 pts, and other etiologies (not further described) in 18 pts.

   These demographic data compare with the US report by Randolph et al which screened mechanically ventilated children over six consecutive months from nine large pediatric intensive care units across North America. This report found a total of 6,403 ICU admissions and 1,096 (17.1%) patients requiring mechanical ventilatory support for a minimum of 24 hours (1).

2. Was follow-up sufficiently long and complete?

   Uncertain. The time frame for the development of airway injury after intubation has not been well-described in the literature. The authors report that no further trauma occurs after the removal of the endotracheal tube, but the repairing process could last 2 weeks (2). Therefore, it is unclear if endoscopic examination of airway injury upon endotracheal tube removal (rather than a more remote period of time) would over- or underestimate the severity and/or clinical importance of these injuries. Furthermore, the authors chose to re-evaluate only those patients who required re-intubation. New findings, as compared with the patient's prior examination, were recorded. This may lead to bias by finding children with more moderate or severe airway injury. They do not report the follow-up parameters. Therefore the significance of the stated re-intubation rate and the consequences of their findings on endoscopy are difficult to interpret.

   Complete follow-up could not be obtained because airway endoscopy was not performed on 40 patients due to procedural problems such as lack of consent, technical problems, unplanned extubations, or transfer of the patient to another facility. They report an analysis of those not lost to follow-up with those lost to follow-up, but that data is not presented anywhere.

2. Were all potential predictors included?

No. Risk factors evaluated were age (newborn vs infants and children); sex; organ failure; indication for intubation; level of difficulty of intubation; endotracheal tube size; need for reintubation; tube changes; and duration of intubation. Difficulty of intubation was based on the need of two or more laryngoscopies necessary to achieve a successful intubation. Endotracheal tube size was assessed by whether the internal diameter conformed within ± 0.5mm to published pediatric advanced life support and neonatal resuscitation standards [3]. Reintubation was the term used when a patient was electively extubated but required reintubation. A tube change was recorded when the endotracheal tube was changed due to accidental extubation, tube block, or because the tube internal diameter was considered inappropriate. Potential predictors not included in this analysis, but which may have been pertinent, include: skill level of personnel performing the intubation; time of day for the intubation; location of intubation within the hospital, operating room, or outside facility; naso- vs. oro-tracheal intubation; administration of systemic steroids during mechanical ventilation; leak around the endotracheal tube; and the presence of endotracheal tube cuff.

3. Did the investigators test the independent contribution of each predictor variable?

Yes. The relative risk for airway injury and the 95% confidence intervals for each predictor were calculated. Univariate analysis using the chi squared test identified risk factors which discriminate among those patients who had moderate or severe airway injury. Logistic regression was then performed to identify the independent role of each variable.

4. Were outcome variables clearly and objectively defined?

Perhaps. Airway injury was identified by airway endoscopies performed using a rigid bronchoscope connected to 0- or 30-degree telescopes or a flexible bronchoscope prior to all extubations or after reintubation. Endoscopic findings were classified as minor, moderate, or severe based upon the proposed classification schema of Benjamin (4). Minor lesions were defined as edema, hyperemia, and erosion. Moderate lesions included: subglottic edema, vocal folds edema, ulcerations, tongues of granulation tissue, cartilage exposure, cartilage dislocation, ulcerated troughs, laceration and bleeding. Severe injuries included: glottic or subglottic stenosis, interarytenoid adhesion, healed fibrous nodules, intubation granuloma, healed furrows, fixed cricoarytenoid joint, and vocal fold paralysis. However, the reliability/reproducibility of these findings is questionable as the kappa statistic was only 0.48.

III. What are the results?

1. What is(are) the prediction tool(s)?

Normal endoscopic airway findings were present in only 10.2% of the patients; 55% had minor airway injury; 24.2% had moderate lesions; and 10.7% had severe airway injury. Age was not statistically associated with the occurrence of moderate or severe airway injury. Those risk factors which were identified in univariate analysis to be associated with the risk of developing moderate or severe airway injury included: gender, indication for intubation, reintubation, tube changes, and duration of intubation.

Using stepwise forward regression in the logistic regression model, only two risk factors, reintubation and tube changes, were found to be independent predictors of moderate or severe airway injuries in this group of patients. A stratified analysis of these variables found: among those patients reintubated, the RR of airway injury was 45 (95% CI 14.7, 137.8) with no tube changes, compared to a RR of 1.5 (95% CI 1.1, 1.9) for those who underwent tube changes. Among those who underwent tube changes, the RR of airway injury was 30.6 (95% CI 9.7, 96.7) for those who did not undergo reintubation, compared to those who underwent reintubation (reference group).

2. How well does the model categorize patients into different levels of risk?

For patients who were reintubated, the risk for moderate or severe airway injury is 45x higher (95% CI, 14.7 to 137.8) than for those patients who do not require reintubation. For those patients who have their endotracheal tube changed during the course of mechanical ventilation due to an inappropriately sized endotracheal tube and accidental extubation or tube occlusion, yet go on to extubate successfully, the relative risk of moderate or severe airway injury in these patients is still very high at 30.6 (95% CI, 9.7 to 96.7).

Clinically, 73.3% of patients with moderate or severe endoscopic airway injury required reintubation. However, the need for reintubation was not be entirely due to the airway injuries identified; only one third of these could be attributed to the airway injury. Reintubation was due to: (1) instability of the underlying disease in 46.2% of infants and children and in 56.3% of the newborn patients (p=0.70); (2) upper airway obstruction in 25.6% of the infants and children and 31.2% of the newborns (p=0.74); and (3) due to the need for surgical procedures. No statistical interactions among age, duration of intubation and post-extubation upper airway obstruction or the need for reintubation could be identified.

3. How confident are you in the estimates of risk?

95% CI are presented for the relative risk (RR) of airway injury related to reintubation and tube changes are provided above. The confidence intervals are always greater than 1 indicating there is always additional risk for the development of airway injury for the patient if they require a tube change or reintubation, but the risk may be as small or as large as indicated by the boundaries of the confidence limits, and for the high risk categories, the confidence intervals are very wide.

IV. Will the results help me in caring for my patients?

1. Does the tool maintain its prediction power in a new sample of patients?

Unknown. The authors did not test their results in a new study population. It is unknown how much these endoscopic findings are user dependent.

2. Are your patients similar to those patients used in deriving and validating the tool(s)?

Probably. The age range for study patients was 1d to 14yrs and most of the patients averaged 13.2 ± 24.8 mos of age. Premature infants <1250 grams were excluded. This is the population found in many PICUs within the US. A large clinical study by Randolph et al, screened patients who were mechanically ventilated in nine large PICUs across the US and found the average age range for mechanically ventilated patients in the PICU was 327 days, with an interquartile range of 68 days to 7.3 years. Of this population, 13% were neonates, 40% were infants <1 yr, 34% were children between 1 yr and 12 years of age, and 14% were > 12 yrs of age (1).

The present study by Cordeiro et al presents an unusual population in that only 16.4% of patients were ventilated < 7 days, while 73.6% of patients were intubated >7 days. Furthermore, 55 patients (25.6%) required reintubation. The US study by Randolph et al reported the mean duration of mechanical ventilation was 9.5 days ± 8.8 days, range 2 to 64 days) (1). Only 17% of patients were mechanically ventilated >24 hrs. Extubation failure rates range from 2.7-22% depending upon the population studied and the way in which outcomes are defined (5-8,11). A large multi-center observational study in the US reported an extubation failure rate for the typical ICU patient population of 6.2% (95% CI 5.3-7.1) (8). Patients intubated > 48 hours had a higher extubation failure rate of 8% (8).

3. Does the tool improve your clinical decisions?

Possibly. Although this study identifies airway injury commonly occurs after endotracheal intubation, clinically important sequelae such as post-extubation stridor, reintubation, or need for tracheostomy cannot be directly correlated with the presence of airway injury. Of the 55 patients reintubated, the most common etiology for reintubation was instability of the underlying disease (27 pts). Upper airway obstruction was identified in 10 pts, a combination of upper airway obstruction and instability in 13 pts, and the need for surgical procedures requiring reintubation occurred in 5 pts.

However, the data make a strong argument to prevent elective endotracheal tube changes and to reduce the need for reintubation, when clinically possible, as these are independent risk factors for the development of moderate or severe airway injury. These data may reinforce the clinical decision to attempt non-invasive forms of ventilation (such as high-flow nasal cannula, continuous positive airway pressure, or biphasic airway pressure) to avoid reintubation (9,10).

4. Are the results useful for reassuring or counseling patients?

Yes. Parents of infants and children within the PICU should receive counseling about the risk of airway injury associated with extubation failure requiring reintubation and the risks associated with tube changes. These injuries may include vocal cord paralysis, subglottic stenosis and granulation tissue that may require later surgical intervention. These injuries may also increase the risk of airway obstruction post-extubation and the need for reintubation. To reduce the risk of reintubation after failed elective extubation, several authors have tried to identify patient or intubation risk factors, which may be amenable to clinical intervention. However, no such risk factors have been identified (5-8,11). Therefore, parents may be counseled on the inability to accurately predict the probability of extubation failure for any one patient. From this data, we may also counsel parents that a greater number of endotracheal tube changes (through re-intubation or tube changes) increases the risk for airway injury. However, the duration of intubation itself does not lead to greater risk for airway injury.

References

1. Randolph AG, Meert KL, O'Neil ME, Hanson JH, et al. The feasibility of conducting clinical trials in infants and children with acute respiratory failure. American Journal of Respiratory and Critical Care Medicine. 2003; 167: 1334-1340. [abstract]
2. Gomes Cordeiro AM, Fernandes JC, Troster EJ. Possible risk factors associated with moderate or severe airway injuries in children who underwent endotracheal intubation. Pediatr Crit Care Med. 2004 Jul;5(4):364-8. [abstract]
3. Niermeyer S, Kattwinkel J, Van Reempts P, et al. International guidelines for neonatal resuscitation: An excerpt from the guidelines 2000 for cardiopulmonary resuscitation and emergency cardiovascular care. International consensus conference on science. Pediatrics 2000; 106: e29. [abstract]
4. Benjamin B. Laryngeal trauma from intubation: endoscopic evaluation and classification. In: Otolarngology Head and Neck Surgery. 2nd edition. Cummings CW, Fredrickson LM, Harker LA, et al (eds). St. Louis, Mosby-Year Book, 1993, pp 1875-1896.
5. Hubble CL, Gentile MA, Tripp DS, et al. Deadspace to tidal volume ration predicts successful extubation in infants and children. Critical Care Medicine 2000; 28(6):2034-2040. [abstract]; [PedsCCM EBJC Review]
6. Baumeister BL, el-Khatib M, Smith PG, et al. Evaluation of predictors of weaning from mechanical ventilation in pediatric patients. Pediatr Pulmonol 1997; 24(5):344-352 [abstract]; [PedsCCM EBJC Review]
7. Mhanna MJ, Yaacov BZ, Tichy CM, et al. The "air leak" test around the endotracheal tube, as a predictor of postextubation stridor, is age dependent in children. Critical Care Medicine 2002; 30:2639-2643. [abstract]
8. Kurachek SC, Newth CJ, Quasney MW, et al. Extubation failure in pediatric intensive care: a multiple-center study of risk factors and outcomes. Critical Care Medicine 2003; 31(11):2657-64. [abstract]; [PedsCCM EBJC Review]
9. Fortenberry JD, Del Toro J, Jefferson LS, Evey L, et al. Management of pediatric acute hypoxemic respiratory insufficiency with bilevel positive pressure (BiPAP) nasal mask ventilation. Chest 1995. 108: 1059-1064. [abstract]
10. Hertzog JH, Siegel LB, Hauser GJ, Dalton HJ. Noninvasive positive-pressure ventilation facilitates tracheal extubation after laryngotracheal reconstruction in children. Chest 1999; 116(1):260-263. [abstract]
11. Farias JA, Alia I, Esteban A, et al. Weaning from mechanical ventilation in pediatric intensive care patients. Intensive Care Medicine 1998; 24:1070-1075. [abstract]; [PedsCCM EBJC Review]

 

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