RESPIRATORY DISTRESS IN THE NEWBORN
Proper diagnosis and management of respiratory distress in the neonate is extremely important. For medical-legal evaluations of complications of these types of cases the reviewer should have speciality training in areas such as pediatrics and otolaryngology and extensive clinical experience in treatment of the neonate with respiratory compromise.
In evaluating neonates with respiratory distress one should attempt to divide the causes of distress into upper airway abnormalities, lower airway abnormalities and extrapulmonary disorders. When the lesions are secondary to upper or lower airway abnormalities the abnormalities may be either congenital or acquired in nature. Regardless of the cause of obstruction, patients with neonatal respiratory distress may present with certain characteristic signs and symptoms including a respiratory rate of greater than 80 breathes per minute, hypoxia in room air (visible cyanosis, PaO2 less than 50) dyspnea associated with grunting, flaring, retractions and poor air exchange.
Determination Of Respiratory Distress:
Evaluation should include a careful history and physical examination, taking care to question the primary caregiver thoroughly, possibly an arterial blood gas, a complete blood count and a chest radiograph. If one proceeds in this manner, one will be able to localize the potential etiology of airway obstruction to a particular region of the airway. In this way it will be unnecessary to memorize a long list of etiologies of airway obstruction as long as one understands the process for assessment. It is imperative for the otolaryngologist to work in concert with a neonatologist in the diagnosis and management of infants with respiratory distress in order to recognize the extrapulmonary causes of respiratory distress, including phrenic nerve paralysis, congenital heart disease, anemia, polycythemia, metabolic disorders, central nervous system disorders and abdominal masses and distention.
Stridor, the production of noisy respiration secondary to partial airway obstruction may be described as inspiratory, expiratory or biphasic (two-way). In general obstructive lesions above the level of the vocal cords leads to the production of inspiratory noise whereas tracheobronchial lesions generally produce stridor during the expiratory phase of respiration. When lesions are in the upper trachea or subglottis, stridor may be present in both inspiration and expiration, hence leading to the term biphasic stridor. Neonates and infants will develop stridor more quickly than older patients. This phenomenon takes place because of the intrinsic small size of the neonatal airway. As an example while one mm of edema will lead to a doubling of resistance in the adult with a decrease in cross-sectional area of 30%, the same amount of edema will cause tripling of resistance and adolescents of 44% decrease in cross-sectional area, but the neonate will have his resistance increased by 16 with a decrease of 75% in the cross-sectional area of the subglottis with the same amount of edema. When evaluating children with airway obstruction, auscultation of the chest will demonstrate prolonged inspiration in children with a high obstruction and prolongation of expiration when the obstruction lies within the lower trachea or bronchi.
Once it has been established that a child has stridor, as much historical data as possible should be gathered from the family as well as the physicians and nursing staff managing the patient primarily. If the child is doing well clinically and has normal airway films and a normal flexible laryngoscopy, observation is appropriate. If these are abnormal, or if the patient demonstrates progression marked by symptoms such as increasing stridor, weight loss, or feeding difficulties, a more complete evaluation is appropriate, including the use of airway fluoroscopy, barium esophogram, microlaryngoscopy, bronchoscopy, esophagoscopy, echocardiography, electrocardiography, arterial blood gases and an evaluation for gastroesophegal reflux (GERD). In general, nasal or nasopharyngeal obstruction is marked by whistling, snorting or stertor. This is contrasted with oropharyngeal obstruction in which children typically present with gurgling, choking and snoring and laryngeal obstruction where patients usually have stridor, hoarseness and aphonia. Definitive therapy obviously is based on the diagnosis and may include intubation, laser therapy, observation, epiglottoplasty, cricoid split and tracheotomy.
Factors which must be elicited during history-taking include the time of onset, quality of the cry and voice, whether or not aspiration is present, any history of cyanosis, any history of intubation and whether a foreign body could be present. This information is supplemented by the physical examination. One of the most important aspects of this examination is observation. The physician should make the effort to simply sit and watch the baby during sleep and, if possible, while feeding. One can evaluate the child for fatigue and certain characteristics of stridor, including pitch, phase and timing. Auscultation is appropriate to ascertain these properties as well as those enumerated previously.
Localization Of Obstruction:
By doing these things, one is capable of localizing the region of obstruction to the nasopharynx, oropharynx, supraglottic larynx, glottis, subglottic larynx and tracheobronchial tree. In addition to localizing the site of obstruction one is capable of categorizing the potential etiology of obstruction into five specific groupings: congenita
It is useful to evaluate the different regions of the airway in regards to the characteristic features which may be present when airway obstruction exists. This is accomplished best when one proceeds in a logical manner, sequentially evaluating voice, stridor, retractions, ability to feed, position of the mouth and the presence or absence of cough.
In children with nasal obstruction the voice is generally normal but may be hyponasal when obstruction exists. True stridor is absent but stertor does exist when there is significant narrowing. The child generally feeds well and has no retractions unless the airway obstruction is severe. Mouth breathing is obligatory and cough generally is absent.
In contrast, children with oropharyngeal obstruction present in a very different manner. The voice is usually unaffected but it may be full. The child usually has course inspiratory stridor associated with sternal and intracostal retractions early and total chest retractions with increased obstruction. Because of the physical blockage present in the oropharynx, feeding is almost impossible and children often times drool. The mouth is held open with the jaw forward and cough is absent. Similarly patients with supraglottic laryngeal obstruction have almost an identical clinical presentation.
This is decidedly different from children with glottic obstruction who usually present with marked hoarseness and may be aphonic. Their stridor is usually inspiratory but may become expiratory with increased observation. Retractions are usually intercostal and xiphold. Patients generally are able to eat well and their mouth is usually closed during respiration. Nasal flaring is common with increased obstruction and no cough is present. Patients with sublglottic obstruction present in a very similar manner to those with glottic obstruction. However, their voice may be normal and these children often times have a barking cough. On the other hand patients with tracheobronchial obstruction usually have a normal voice. Their stridor is generally expiratory and by be described as "wheezing". These children frequently have a cough that has been described as "brassy".
If a mass is noted in the mediastinum on chest radiography, the physician must be aware of the potential problems this lesion may cause. Specifically evaluation of the patient under general anesthesia may precipitate an acute respiratory event secondary to airway collapse. Though evaluation by advanced imaging techniques such as computed tomography or magnetic resonance imaging is necessary. The physician must be prepared to do a bronchoscopy in order to secure the airway when anesthesia is introduced for imaging of these patients. The use of endoscopy is essential when patients present with stridor which is severe, progressive or unexplained following one's initial history and physical examination, airway films and flexible laryngoscopy. Similarly one should proceed with endoscopy if parents, grandparents or physicians are excessively worried. The examination can reduce anxiety, provide diagnostic information and prevent further testing. Depending on one's orientation, rigid or flexible bronchoscopy may be chosen for examination. Though both techniques have advantages and disadvantages, rigid endoscopy is preferred by most otolaryngologists because of the ability to assess the subglottic region superiorly. Objective data may be obtained in addition by the use of polysomnography. In this manner one may quantify the amount of oxygen desaturation which occurs during sleep in addition to evaluation numbers of apneic episodes. During endoscopy one is able to quantify the degree of airway utilizing endotracheal tubes in order to determine the degree of narrowing compared to a known standard. This is helpful in planning operative intervention as well as on a prognostic basis.
By following a standard protocol for the assessment of neonates with stridor one can develop a workable differential diagnosis which allows appropriate treatment to be initiated. Organization remains the key when dealing with respiratory compromise in the newborn.