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68 Intensive Care
Respiratory insufficiency is generally recognised by an early
Respiratory failure is inadequate exchange of oxygen and carbon increase in respiratory rate, which may be followed by a decrease in
dioxide resulting in failure to meet metabolic demands. respiratory rate as the child’s clinical condition worsens. Apnoea
22
in the small infant is worrying and requires immediate intervention.
Cyanosis and tachycardia are early findings, and as hypoxia worsens,
Anatomically, the respiratory system structure comprises the lungs progression to bradycardia and cardiac arrest may occur. 23
and respiratory pump. The lungs include the airways, alveoli, and Supplemental oxygen can be delivered via many different delivery
pulmonary circulation. Failure in any of these elements may result in devices. The choice of device will be dictated by clinical situation
abnormal gas exchange, which is manifested by hypoxia; this condition and local availability as well as by which device is best tolerated by
is termed hypoxic respiratory failure. The respiratory pump refers to the the child.
thorax, respiratory muscles, and nervous innervations. The inability to Nonrebreathing face mask
effectively pump air into and out of the lungs results in hypoventilation A nonrebreathing face mask is the most effective way of delivering
and thus hypercarbia; this condition is termed hypercarbic respiratory oxygen by face mask. It consists of a face mask connected by a uni-
failure. Although the two systems can be described separately, the two directional valve to an oxygen reservoir bag. The unidirectional valve
interact significantly with each other. Failure in one of these systems delivers all inhaled gas from the oxygen reservoir and prevents exhaled
often results in failure of the other. air from entering the reservoir. The mask must fit snugly over the nose,
To achieve adequate gas exchange, several conditions must be met:
and the fresh gas flow rate must be maintained to ensure the reservoir
• Adequate gas must reach the alveoli. remains distended by at least half its volume at all times. In ideal con-
• Inspired gas in the alveoli must match the blood distribution within ditions, these masks can provide 100% oxygen; however, it is often
the pulmonary capillaries. slightly less than this in practice.
• The alveolar-capillary membrane must permit gas exchange. Venturi masks
The Venturi mask works on Bernoulli’s principle, which states that as
A child with a decreased level of consciousness due to any cause—
including the postoperative patient under the influence of anaesthetic, the velocity of gas increases the pressure surrounding that gas decreas-
analgesic, or sedating drugs—may have inadequate respiratory drive, es. Oxygen is introduced through a tapered inlet into the device. As
resulting in an inadequate respiratory rate (see Table 12.1). Acute the oxygen flows through the narrowed inlet the velocity increases and
respiratory distress may result from disease in the large or small a resultant decrease in pressure surrounding the stream of gas causes
airways, the lung parenchyma, the pleural space, or a combination of room air to be entrained into the device through side ports in the device.
all of these. Disease in other organ systems, such as cardiac failure The concentration of oxygen delivered with these devices remains rela-
or metabolic acidosis associated with diabetic ketoacidosis or toxin tively constant. These masks can deliver 24–40% oxygen.
ingestion, may give rise to increased respiratory effort. Should any of Nasal cannulae
these disease processes result in inadequate gas exchange, respiratory Nasal cannulae consist of two protruding prongs that are placed into
failure ensues. the child’s nares. The delivered concentration of oxygen depends on
the flow rate as well as the child’s minute ventilation and the volume of
Table 12.1: Normal respiratory rate in children.
the nasopharynx as these determine the amount of entrained room air.
Age Breaths per minute Generally, children accept flow rates of up to 2 litres per minute; flow
Birth–1 year 20–30 rates in excess of this are uncomfortable and poorly tolerated. Correctly
2–5 years 20–25 fitted and at appropriate flow rates, nasal cannulae are often better toler-
ated than face masks in most children, but they are less suitable when
>5 years 16–20
oxygen needs are high.
Oxygen hood, tent, and head box
In addition to the above factors, gas exchange may be affected Oxygen hoods, tents, or head boxes are clear plastic systems that
by systemic processes such as the systemic inflammatory response enclose either the head, upper body, or entire body. The child breathes
syndrome (SIRS) seen in sepsis and following cardiac bypass, as well as fresh gas supplied into the enclosure. The concentration within the
nonpulmonary factors, including acute blood loss, poor cardiac output enclosure can be monitored by using a gas analyser. High oxygen deliv-
(CO), increased oxygen demand, and chronic anaemia. Nutritional ery is difficult to maintain with this system because gas is lost through
deficiencies may contribute to an inability to meet the demands of acute leakage; this system may thus be most suitable for small infants. If this
medical or surgical illness. system is used, a minimum fresh gas flow of 2–3 l/kg per minute should
The most serious manifestation of respiratory insufficiency is be used to prevent carbon dioxide retention.
hypoxia. Initial compensatory hyperventilation may cause an early
drop in PaCO ; however, as these compensatory mechanisms fail, Bag-mask ventilation
2 Some children require positive pressure ventilation, either to overcome
hypercapnia ensues.
a degree of upper airway obstruction or to provide breathing support.
Effective bag-mask ventilation requires a good seal between the mask
Oxygen should be administered to all critically ill or injured and face to provide adequate inflation pressures as well as the ability
children in the highest possible concentration until the assessment to compress the gas-containing bag in a coordinated manner, which
of cardiorespiratory status is complete. is sometimes better achieved by two health care providers. It is often
necessary to gently move the child’s head and neck to determine the
optimum position to provide effective ventilation. Excessive flexion or
The early goal of administering the highest possible oxygen extension of the head and neck should be avoided, however, as this often
concentration to the acutely unwell patient remains the highest priority, results in airway obstruction. As mentioned previously, for all children
as oxygen delivery to the tissues may be suboptimal in the child with who have a potential cervical spine injury, the spine should be adequate-
decreased circulating volume or abnormalities in microcirculation, such ly immobilised and unnecessary manipulation should be avoided.
as may be seen in sepsis, hypovolaemia, or haemorrhage.