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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.
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