Postextubation Stridor

Introduction

Stridor is a high-pitched breathing sound caused by turbulent airflow in a narrowed airway. The obstruction or airway narrowing typically occurs in the larger airways. It is usually inspiratory and is often best heard over the front of the neck. It can be distinguished from wheezing and bronchiolitis, which usually occur during expiration and are best heard lower in the chest.

Stridor can be caused by croup, epiglottitis, foreign body aspiration, airway abscesses (retropharyngeal or peritonsillar), anaphylaxis, anatomic issues (e.g., vascular ring, airway hemangiomas) or iatrogenic events such as postextubation.

PES is a sign of acute upper airway narrowing or obstruction that occurs immediately postextubation. PES in children typically represents laryngeal edema in the subglottic area. Most children with PES are intubated for a medical or surgical procedure with anesthesia. Historically, the incidence of PES in this population was 1%. The incidence is decreasing due to the increased use of cuffed endotracheal tubes (ETT).¹ The incidence of PES in children after prolonged endotracheal intubation in the ICU ranges from 4-37%.²

Resistance to Airflow

According to the Hagen-Poiseuille equation, resistance to airflow is inversely proportional to the fourth or fifth power of the radius. Resistance to laminar flow is inversely proportional to the fourth power of the radius, whereas resistance to turbulent airflow is inversely proportional to the fifth power of the radius.³

In an infant, 1 mm of circumferential edema in the subglottis decreases the cross-sectional area of the airway by approximately 75% and increases the resistance to airflow (which is usually turbulent) by about 32-fold (Table 1).³

Risk Factors for PES

A retrospective study in the 1970s reported the following risk factors for PES.⁴

• Age (1-4 years)
• Traumatic intubation or multiple laryngoscopy attempts
• Large ETT or minimal leak around ETT
• Duration of surgery longer than 1hr
• Coughing while intubated
• Position change during surgery

Historically, uncuffed ETTs were used in children younger than 8 years. Due to the narrow cricoid cartilage, there was a concern that cuffed ETTs cause subglottic edema, postextubation stridor, and possibly subglottic stenosis in the long term.

Of note, both cuffed and uncuffed ETTs can cause postextubation stridor. The incidence of PES may be decreasing as the need to exchange the ETT for a different size is decreased when a cuffed ETT is used.

Management

A scoring system for the severity of infectious croup has been developed to guide treatment.⁵

Patients with mild symptoms, a stable airway and a score of 2 or lower can be treated with humidified air or oxygen. Caregivers can also be encouraged to sit with the child in a steam-filled bathroom. While these are treatments traditionally for infectious croup, they can also be used for PES.

Caregivers should be encouraged to watch for nasal flaring, difficulty breathing, cyanosis, retractions and advised to seek medical attention if these occur after discharge.

In a meta-analysis, corticosteroids were found to decrease the rate of PES, upper airway obstruction, and extubation failure in pediatric patients.² Intravenous dexamethasone may be given prophylactically in the operating room if there were known issues with intubation. Dexamethasone can also be given to treat PES symptoms that occur postoperatively. As it may take some time to work, humified air or oxygen should also be considered until symptoms improve.

Nebulized racemic epinephrine is often recommended in cases of significant stridor. It is thought to work on the ⍺-receptors in the subglottis, causing vasoconstriction and decreasing edema. It works quickly to decrease stridor symptoms and can allow other treatments, such as corticosteroids, time to act. Racemic epinephrine is typically administered as a nebulizer and the dose is 0.05 mL/kg (maximum of 0.5 mL) of a 2.25% solution diluted to 3 mL total volume with normal saline.

The effect of racemic epinephrine often lasts for an hour clinically and is gone in 2 hours. There is a concern for “rebound hyperemia” after the epinephrine wears off and that swelling might be worse than before, necessitating observation for at least 4 hour after nebulizer administration.1 However, a recent study of infectious croup showed that symptoms might recur after the epinephrine wears off, but the symptoms were no worse than before treatment with racemic epinephrine.⁶