Respiratory disease in its various forms remains the most common cause of pediatric and neonatal morbidity and mortality. One of the most common reasons for admission to pediatric or neonatal intensive care units is the need for ventilatory support for acute or impending respiratory failure. The major challenge for these units is to deal with a very heterogeneous population of patients who are characterized by enormous differences in age and size and marked developmental changes in organ physiology during growth. In particular, the pediatric intensive care unit population is characterized by a wide variety of rare and unique medical problems that make large clinical trials, even on general topics such as ventilator support, very difficult to conduct.1,2 Despite worldwide daily use of mechanical ventilation in pediatric and neonatal intensive care units, many clinical and practical questions remain unresolved. Answers are often extrapolated from the results of adult studies. This may seem sensible for older children but is dangerous when applied to neonates, infants, and children up to the age of 12 years, because of developmental alterations in the physiology of their organ systems, particularly (but not only) their respiratory system.
The considerable differences in respiratory physiology and anatomy between infants and adults3 explain why infants and young children have a higher susceptibility to more severe manifestations of respiratory diseases, and why respiratory failure is a common problem in neonatal and pediatric intensive care units (Table 23-1). The appreciation of the peculiarities of pediatric respiratory physiology is essential for correct management of critically ill and/or ventilated infants and children.
Table 23-1: Physiologic Reasons for the Increased Susceptibility for Respiratory Compromise of Infants in Comparison to Adults ||Download (.pdf)
Table 23-1: Physiologic Reasons for the Increased Susceptibility for Respiratory Compromise of Infants in Comparison to Adults
|Cause||Physiologic or Anatomic Basis|
|Metabolism ↑||↑ O2 consumption|
|Risk for apnea ↑||Immaturity of control of breathing|
|Resistance to breathing ↑|
|Upper airway resistance ↑||Nose breathing|
|Airway size ↓|
|Pharyngeal muscle tone ↓|
|Compliance of upper airway structures ↑|
|Lower airway resistance ↑||Airway size ↓|
|Airway wall compliance ↑|
|Elastic recoil ↓|
|Lung volume ↓||Numbers of alveoli ↓|
|Lack of collateral ventilation|
|Efficiency of respiratory muscles ↓||Efficiency of diaphragm ↓|
|Rib cage compliance ↑|
|Horizontal insertion at the rib cage|
|Efficiency of intercostal muscles ↓|
|Endurance of respiratory muscles ↓||Respiratory rate ↑|
|Fatigue-resistant type I muscle fibers ↓|
The basal metabolic rate is approximately twofold higher in infants than in adults (7 mL/kg/min at birth vs. 3 to 4 mL/kg/min in the adult). Hence, the normal resting state in infants is ...