CLASSIFICATION OF ACUTE RESPIRATORY DISORDERS: DISCUSSION
The most surprising finding of this investigation was that most neonates with respiratory symptoms were not classifiable by standard diagnostic criteria for textbook pulmonary disorders, even applying the broadest definitions. To our knowledge, this is the first attempt to classify acute respiratory disorders in the newborn in three decades in North America. Interestingly, similar to the findings of Hjalmarson in Sweden 21 years ago, a large proportion of infants with respiratory symptoms fail to meet any diagnostic criteria for the respiratory conditions as defined in standard textbooks. Nevertheless, they are ill and in many cases present with frank respiratory failure.
As previous authors have observed, no classification system is perfect. There is always an overlap between various disorders, and some infants may have more than a single disease process causing their illness. Borderline clinical pictures also are seen, such as infants presenting as relatively severe TTN or mild surfactant deficiency (RDS), requiring neither intubation nor surfactant replacement but with persistent symptoms. Nevertheless, classification of all newborns in an ongoing, consistent manner can be useful, especially for comparing disease patterns over time. The particular problem addressed by our revised classification scheme is the need to categorize all newborns with respiratory disorders, even if the underlying pathophysiology of some classes of patients is still unknown. More explicit discussion of diagnostic criteria in the literature could lead to better comparability between institutions and might help focus research on gaps in current knowledge. The system of classification we used did not require any specialized procedures other those commonly used in neonatal units all over the country and could thus be readily adapted to most settings. tadacip 20
The 21% incidence of respiratory disorders we report is much higher than that quoted in other studies, typically in the range of 2 to 3%. This is due in large part to the greater number of high-risk deliveries in perinatal centers such as ours. Our study was institution based while Hjalmarson’s analysis was population based. This skew in population risk is reflected in high incidence of low birth weight in our referral center: 16.8% compared with 4% in the Swedish study. This difference alone could account for a four-fold increase the incidence of respiratory disorders even if birth weight-specific incidences were equal. Radiological interpretation may also influence the outcome because the chest film was an important part of diagnosis. However, differences in x-ray interpretation would affect final diagnosis, not overall prevalence of symptoms. The influence of antenatal steroids and intrapartum antibiotics were not assessed, but such treatments, which should lower disease frequency, are more widespread now than at the time of Hjalmarson’s study, tending to narrow rather than widen the observed gap in incidence.
The infant with TTN has been described as having early onset of symptoms, an x-ray picture suggestive of retained fluid (fluid in the minor fissure, increased markings), oxygen requirement usually less than 40%, and a self-limiting condition lasting from two to five days. Only 51 infants in our series came close to these criteria, leaving many others unclassified. Hjalmarson chose to substitute two new terms to describe infants with non-specific self-limited conditions. The more severe cases he called “pulmonary mal-adaptation” or PMA. These infants had abnormal lung fields on x-ray, no evidence of infection and spontaneous improvement during the first days of life and made up 32% of his symptomatic infants. The milder self-limited cases, some 38% of symptomatic newborns, he classified as “mild respiratory disorder” or MRD. These infants’ symptoms generally resolved in less than six hours and diagnostic tests were not routinely carried out on them. Apparently, some of his “pulmonary maladapta-tion” infants required mechanical ventilation. Thus the two categories of self-limited illness in Hjalmarson’s classic population study accounted for 70% of all infants with pulmonary signs. His system left less than 0.5% of infants unclassified.
However, the categories Hjalmarson introduced in 1981 have never become widely adopted. buy antibiotics amoxicillin
Rather than use Hjalmarson’s two novel categories, we chose to use the widely used term of transient tachypnea of the newborn (TTN), but with an expanded definition. However, we felt that infants with respiratory failure, because of the more severe nature of their transitional difficulties, should be kept separate. These infants, with respiratory failure but no pulmonary diagnosis, were sick enough to need assisted ventilation and yet did not meet minimal diagnostic criteria for any established disease. We introduced the term transient respiratory insufficiency of the newborn or TRIN for this group.
We see TTN as an empirical classification, which should be conceptualized, as a spectrum of disturbances in pulmonary transition at birth, ranging from very mild to more severe, and including multiple contributing etiologies. In the mildest form, the infant gets well within few hours and the chest film, if obtained, is normal. These infants may have little or no oxygen requirement. At the other end of the spectrum are those with high oxygen requirement or prolonged duration, sometimes lasting more than a week. Somewhere between these extremes we find the classical TTN with its typical history, radiographic findings and clinical course. It is likely that over time, with diagnostic and therapeutic innovations, subsets of these “TTN” patients will be identified having a particular disease with specific pathophysiology and a narrower range of presenting clinical picture. At present, designating them all as TTN (modified by “mild,” “moderate” and so forth, if desired) should clearly communicate the transient and non-specific nature of the disorder without making any claims concerning etiology, as implied by such terms as “wet lung” or “amniotic fluid aspiration.”
In our series, the spectrum of TTN accounted for 61% of our total symptomatic population. Infants with more severe transitional problems, that is, requiring assisted ventilation and designated TRIN, made up an additional 6%. The sum of these two categories of self-limited and nonspecific transitional disorders, 67%, is similar to the analogous total in Hjalmarson’s series mentioned above of 70%. canadian discount drugs
The etiology of TRIN is presumably diverse. Seventy-two percent were of low birth weight, including 28% with weights below 1500 grams. In fact, one subgroup could correspond to Hjalmarson’s “immaturitas pulmonum.” Those infants were quite immature with birth weights under 1000 grams; their X-ray did not suggest hyaline membrane disease and most of them died in an era when modern ventilators and exogenous surfactant therapy did not exist. These days many more of these infants survive. Of the larger infants, antenatal magnesium was given in some instances, and some of them were depressed at birth, making inadequate respiratory efforts. Most, however, made strong efforts, indeed were tachypnic and retracting, but nevertheless, could not maintain adequate ventilation in the period of adaptation to extrauterine life. The common denominator was that they were sick enough to need assisted ventilation.
In conclusion, most infants with acute respiratory disorders at birth are not easily classified when previously published diagnostic criteria are rigorously applied. We propose a revised classification system which categorizes all cases of neonatal respiratory illness. In this system TTN is broadened considerably to include infants with very transient disease, as well as those with normal chest films and those with any degree of 02 requirement short of respiratory failure. Also, for infants who are ventilated but do not meet diagnostic criteria for any of the recognizable diseases, such as RDS, MAS or PPHN, we propose to use the term transient respiratory insufficiency of newborn (TRIN). In addition, we suggest that response to surfactant be used along with more established features as a diagnostic criterion of RDS. tadalis sx 20
