stridor

Introduction

stridor is a clinical sign of upper airway obstruction, and if it is acute, should be regarded as a life threatening emergency
when the site of the obstruction is outside the thoracic cage, the obstruction typically becomes worse during inspiration as negative intra-tracheal airway pressures in inspiration further narrow the airway and thus an inspiratory stridor occurs initially but may become biphasic as it becomes more severe
when the site of obstruction is within the thoracic cage, inspiration tends to open the tracheal airways, while in forced expiration the airways within the thorax tend to become smaller, thus the stridor may occur primarily during expiration as with bronchospasm and wheeze
most cases in neonates and infants are due to benign laryngomalacia
most acute cases in children with a barking cough are due to croup and these patients generally settle with adrenaline nebulisers and steroid therapy, and rarely need intubation

BEWARE the child who is drooling with stridor and a minimal cough as epiglottis may rapidly progress to complete airway obstruction if the child is upset with attempts at iv cannulation or inspection of oropharynx with a tongue depressor - these children should have an anaesthetist gas them down to enable intubation to protect the airway
compromised patients will often signal the posture which best provides respiration - do not ignore this

Aetiology

supraglottic (obstruction above the larynx):
- the unconscious patient in supine position is not able to protect their airway from obstruction from the tongue falling posteriorly
  - this is usually easily remedied by jaw thrust maneuver
- foreign body within upper airway eg. bolus of meat
- angioedema
- epiglottitis
  - now rare in children vaccinated for HiB
  - most common in unvaccinated children aged 2-7yrs and present with drooling, fever and minimal cough
  - may occur in adults
- other oropharyngeal pathologies:
  - retropharyngeal abscess
    - more common in children under 6yrs age and usually follows bacterial pharyngitis and presents as sore throat, high fever, dysphagia, refusal to eat and child maintaining head in hyperextension
  - peritonsillar abscess (quinsy)
glottic (laryngeal) obstruction:
- laryngospasm
- laryngeal trauma
- laryngomalacia
  - causes chronic stridor in neonates and early infancy and is usually benign and self-limiting
- vocal cord dysfunction
  - infantile unilateral vocal cord paralysis:
    - second most common cause of stridor in infants presenting as weak cry and biphasic stridor which improves with lying affected side down
    - congenital
    - birth trauma
    - post-op cardiothoracic procedures
  - bilateral vocal cord paralysis is more serious
    - present with aphonia and high pitched biphasic stridor and high risk of severe respiratory distress
    - in infants it is usually due to raised intracranial pressure / Arnold-Chiari malformation
- laryngeal webs
- laryngeal cysts and rarely, haemangiomas
- laryngeal papillomas
  - vertical transmission of human papilloma virus (HPV)
- laryngeal tumours
- patients with rheumatoid arthritis - crycoarytenoid arthritis
subglottic (tracheal) obstruction:
- intraluminal obstruction:
  - inhaled foreign body
  - tracheal secretions
- inflammation within the tracheal wall:
  - croup usually presents in children in Autumn as a barking cough and stridor
    - viral tracheobronchitis
    - spasmodic croup
  - bacterial tracheitis
    - uncommon, mainly children under 3yrs but can occur in adults
  - inhaled hot gases causing burns
- subglottic stenosis
  - congenital subglottic stenosis
    - due to an incomplete canalization of the subglottis and cricoid rings causes a narrowing of the subglottic lumen
  - acquired:
    - scarring from prolonged intubation
- extrinsic tracheal compression
  - congenital vascular rings, pulmonary artery slings and double aortic arch
  - thyroid mass:
    - goitre
    - post thyroidectomy haematoma
  - massive swelling
  - mediastinal mass eg. thymoma, lymphoma
    - these are rare causes, and may also cause signs of superior vena cava (SVC) obstruction