Respiratory Failure

Published on 24/03/2015 by admin

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Chapter 3 Respiratory Failure

Mark D. Joffe, MD

1 Why is it so important to know about respiratory failure in children?

Children are at greater risk of respiratory failure than adults. Respiratory symptoms are one of the most common reasons children are taken to emergency departments (EDs) and the most frequent cause of cardiopulmonary arrest. The potential for progression of respiratory distress to respiratory failure necessitates prompt evaluation of children with respiratory symptoms. Much of the morbidity and mortality from respiratory disease in children can be prevented by competent pediatric emergency care.

2 Why are children at greater risk for respiratory failure?

Children have greater metabolic requirements and greater need for oxygen on a per-kilogram basis when compared to adults. Anatomic factors put infants, in particular, at high risk for respiratory failure. Infants breathe almost exclusively through their noses because the nasopharynx is in close proximity to the more cephalad glottis and the infant tongue fills most of the oropharynx. Nasal obstruction, therefore, can cause significant respiratory signs and symptoms in infants. The caliber of infant airways is small, so respiratory resistance is much higher in infants, especially when they have inflammation of the respiratory tree. Alveoli have less collateral ventilation in infants. Thus, obstruction of small, peripheral airways is more likely to lead to atelectasis and hypoxemia. A compliant chest wall facilitates passage through the birth canal but leads to respiratory problems when airway resistance is increased. The diaphragm of infants is weaker and more easily fatigued compared with the diaphragm of older children and adults. Also, the inability of younger children to verbalize their symptoms may cause delayed presentations of respiratory problems.

3 What are the clinical features of respiratory failure?

image Poor color (ashen or central cyanosis)

image Obtunded mental status

image Decreased chest wall movement, with or without signs of respiratory distress

image Bradypnea or marked tachypnea

American Heart Association, Subcommittee on Pediatric Resuscitation: Recognition of respiratory failure and shock. In Zritsky AL (ed): Pediatric Advanced Life Support Provider Manual, Dallas, American Heart Association, 2002, p 81.

4 Why does respiratory resistance increase so significantly with inflammation of the respiratory tree?

The resistance to laminar air flow through a tube is inversely related to the radius to the fourth power (Poiseuille’s law). Modest decreases in the radius of the lumen of the airway can lead to dramatic increases in respiratory resistance when airway caliber is small (Fig. 3-1).

image

Figure 3-1 Comparison of the effects of 1 mm of mucosal edema on airway resistance in an infant versus an adult. Resistance is inversely proportional to the fourth power of the radius for laminar flow and the fifth power for turbulent flow. Airway resistance increases sixteenfold in the infant for laminar flow. In a crying infant with turbulent air flow, resistance increases thirty-twofold.

From Cote CJ, Todres ID: The pediatric airway. In Cote CJ, Ryan JF, Todres ID, Groudsouzian NG [eds]: A Practice of Anesthesia for Infants and Children, 2nd ed. Philadelphia, W.B. Saunders, 1993.

5 Why do children get respiratory infections so frequently?

The immature immune system puts infants at risk for respiratory infections. Children have less immunologic memory, so exposure to a particular respiratory pathogen is more likely to be a child’s first. Young children playing together in a group tend to exchange contaminated respiratory secretions with particular aplomb. They do not know that frequent handwashing can dramatically reduce the spread of respiratory infections. Many adult caregivers do not recognize this as well.

6 Are there different types of respiratory failure?

Some clinicians divide respiratory failure into two categories. The first type is generally caused by mismatch of ventilation and perfusion resulting from problems in the lung. This type of respiratory failure is characterized by hypoxemia with normal or low PCO2. Other patients with respiratory failure have an overall decrease in alveolar ventilation that is usually the result of upper airway obstruction, neuromuscular disease, thoracic trauma, or muscle fatigue. These patients have relatively proportional decreases in PO2 and increases in PCO2. The physiology in most children with respiratory failure is a combination of these two types because one type often leads to the other. For instance, an infant with bronchiolitis initially may have hypoxemia from atelectasis and ventilation–perfusion mismatch, but may progress to inadequate alveolar ventilation when airway resistance is high and respiratory muscle fatigue supervenes.

7 How do I know which of the numerous children with respiratory symptoms will progress to respiratory failure?

Predicting the future is difficult, but many clinical skills can be employed. A detailed history can give information about the vulnerability of the child to respiratory decompensation. Children who are very young, were born prematurely, have chronic pulmonary or cardiac diseases, or have immunodeficiencies are at particular risk. Recent medical advances, including the development of home nursing capabilities, have resulted in many “graduates” of intensive care nurseries living in our communities. EDs are confronted with these medically fragile children more than ever before.

Diseases have a natural history that must be considered. If a child is evaluated early in the course of respiratory infection, you can anticipate that the child is likely to worsen before improvement will be noted. Intervention may vary depending upon the stage in the natural history of the disease a child is in at the time of the visit. Children with significant respiratory distress may worsen as their disease process progresses or as they become fatigued.

Young children are more difficult to assess for respiratory problems. Histories are obtained secondhand, as the parent interprets behaviors and relays observations that have been made. Young children with significant respiratory distress may remain happy and playful until fatigue suddenly sets in. A careful clinical assessment of the current degree of respiratory distress is necessary to identify those sicker patients who are more likely to develop respiratory failure.

8 How do I assess respiration in a baby who screams every time I approach him?

“Stranger anxiety” normally develops in the second half of the first year of life. The child’s alertness to your presence is certainly a positive sign. Observing the child from across the room provides valuable information. General appearance, state of hydration, respiratory rate, nasal flaring, retractions, paradoxical respirations, and grunting can be appreciated without close proximity to the child. In many cases, the child is more cooperative if your approach is delayed, slow, and accompanied by soothing speech.

9 What are paradoxical respirations? Why do they occur?

Infants who have increased airway resistance need to generate high negative intrathoracic pressures to inflate their lungs. As the diaphragm moves downward and intrathoracic pressure becomes negative, the cartilaginous bones and weak intercostal musculature cannot maintain the thoracic circumference. As the abdomen moves outward, the chest collapses inward (rather than the normal expansion) on inspiration; hence the terms paradoxical respirations, thoracoabdominal asynchrony, or see-saw breathing. Paradoxical respirations are often a sign of impending respiratory failure.

10 How can one tell if the respiratory failure is caused by an upper airway disease or by lower airway disease?

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