SYMPOSIUM: INTENSIVE CARE
Respiratory support in
children
What’s new
Over the last few years, the mainstays of respiratory support in
children have remained the same. Characterizing the type of respiratory failure is crucial to choose the appropriate respiratory support.
New objective tools are emerging to help the bedside clinician with
assessment of the child with respiratory failure. Non-invasive modalities of respiratory support are also gaining popularity. The
response to the chosen method of support and underlying pathophysiology of the disease should guide decision making in a child
with respiratory failure.
Anoopindar K Bhalla
Christopher JL Newth
Robinder G Khemani
Abstract
Respiratory failure is defined by the inability of the respiratory system
to adequately deliver oxygen or remove carbon dioxide from the pulmonary circulation resulting in hypoxemia, hypercapnia or both. A
wide variety of disease processes can lead to respiratory failure in children. Multiple interventions can support the paediatric patient with respiratory failure, from simple oxygen delivery devices to high frequency
oscillatory ventilation and extracorporeal membrane oxygenation. This
article will review available devices to improve oxygenation and ventilation, their advantages and disadvantages, and help guide physicians
in the management of children with respiratory failure.
Overview of respiratory physiology
Gas exchange
The content of oxygen in the blood leaving the lungs depends on
several aspects of lung function; the partial pressure of oxygen in
the alveoli, diffusion of oxygen across the alveolar wall, and the
degree of pulmonary shunt. Pulmonary shunt is the blood flow
through the lungs that does not encounter areas of ventilation
and therefore does not participate in gas exchange.
The alveolar gas equation describes the partial pressure of
oxygen present in individual alveoli.
Keywords anoxia; artificial; hypercapnia; paediatrics; respiration;
respiratory insufficiency
PAO2 ¼ FiO2 (PB e PH20) e PACO2/RQ
Where PAO2 is the partial pressure of oxygen in the alveolus, FiO2
is the fractional concentration of inspired oxygen, PB is the
barometric pressure, PH20 is the partial pressure of water vapor,
PACO2 is the partial pressure of carbon dioxide in the alveolus
(assumed to equal the partial pressure of arterial CO2, the PaCO2)
and RQ is the respiratory quotient (represents the ratio of oxygen
consumption to carbon dioxide production and is usually
approximated at 0.8).
The difference between the PAO2 and the arterial partial
pressure of oxygen (PaO2) is minimal in healthy lungs (10
e15 mmHg). In diseased lungs, this Alveolar-Arterial (Aea) PO2
gradient represents the severity of pulmonary shunt and
ventilation-perfusion mismatch or rarely, a diffusion abnormality. Although an elevated PaCO2 from hypoventilation can lead to
hypoxemia as demonstrated by the alveolar gas equation, a
modest increase in FiO2 will easily increase the PaO2. On the
other hand, improving the hypoxemia related to pulmonary
shunt or severe ventilation-perfusion mismatch is generally
accomplished only with interventions that lead to resolution of
the shunt.
Carbon dioxide removal from the pulmonary circulation is
somewhat dependent on the minute ventilation (Minute ventilation ¼ Tidal Volume x Respiratory Rate). However, this tidal
volume includes alveolar volume as well as physiologic dead
space volume, (i.e. volume that is distributed to areas of the
respiratory system that are ventilated but do not receive perfusion and therefore do not participate in gas exchange). The
physiologic dead space volume is composed of both airway dead
space, the mouth and conducting airways, and alveolar dead
space, (alveoli that are ventilated but not perfused with blood).
Normally, physiologic dead space volume is approximately 30%
of each breath, with alveolar dead space being close to zero.
Respiratory support in children
Respiratory illness accounts for approximately 1 in 5 hospital
admissions and respiratory failure is the leading cause of cardiac
arrest in children. Specifically, respiratory failure is the inability
of the respiratory system to adequately oxygenate or remove
carbon dioxide from the pulmonary circulation, resulting in
hypoxemia, hypercapnia or both. Any abnormality of the respiratory system can lead to respiratory failure (Table 1). Due to
several anatomical and physiological considerations, in any
given medical situation infants and young children are at greater
risk of respiratory failure than older children or adults.
Anoopindar K Bhalla MD Assistant Professor, Department of
Anesthesiology and Critical Care Medicine, Children’s Hospital Los
Angeles, Los Angeles, CA, USA and Keck School of Medicine,
University of Southern California, Los Angeles, CA, USA. Conflicts of
interest: none declared.
Christopher J L Newth MD FRCPC FRACP Professor of Pediatrics,
Department of Anesthesiology and Critical Care Medicine, Children’s
Hospital Los Angeles, Los Angeles, CA, USA and Keck School of
Medicine, University of Southern California, Los Angeles, CA, USA.
Conflicts of interest: none declared.
Robinder G Khemani MD MsCI Associate Professor of Pediatrics,
Department of Anesthesiology and Critical Care Medicine, Children’s
Hospital Los Angeles, Los Angeles, CA, USA and Keck School of
Medicine, University of Southern California, Los Angeles, CA, USA.
Conflicts of interest: none declared.
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wall have a tendency to move in opposite directions, the lungs
collapse and the chest wall expands outward. The balance point
of these two forces occurs when the lung volume is at functional
residual capacity (FRC). At FRC, the compliance of the respiratory system is the greatest.
Common causes of respiratory failure in children
Site of respiratory failure
Examples of disease processes
Upper airway disorders
Anaphylaxis
Foreign body
Infection (croup, epiglottitis,
bacterial tracheitis)
Laryngotracheomalacia
Asthma
Obstructive lower
airways disease
Restrictive lung disease
Central nervous
system disorders
Disorders of the muscles of
Respiration and peripheral
nervous system
Compliance ðof the respiratory systemÞ ¼ DVolume=DPressure
Restrictive lung disease, such as pneumonia or a pleural effusion,
is characterized by decreased respiratory system compliance
with an end-expiratory lung volume that is below normal FRC.
These patients develop atelectasis and subsequent hypoxemia
predominantly due to intrapulmonary shunt. While minimal
atelectasis and shunt can be overcome with supplemental oxygen, patients with significant restrictive disease often require
additional support with positive pressure to re-expand areas of
lung collapse and consolidation.
In obstructive airways diseases, such as bronchiolitis or
asthma, patients develop air trapping with an end-expiratory
lung volume above normal FRC. They have mismatching between areas of ventilation and perfusion in the lung and are
prone to the development of regional atelectasis and over
distension. These patients may require assistance with ventilation secondary to muscle fatigue or less frequently due to hypoxemia related to shunt.
Bronchiolitis
Cystic fibrosis
Abdominal compartment
syndrome
Acute respiratory distress
syndrome
Chronic lung disease
Pleural effusion
Pneumonia
Pulmonary edema
Intracranial injury (hemorrhage,
hypoxic ischemic injury)
Metabolic encephalopathy
Pharmacologic agent (central
nervous system depressant)
Guillian Barre syndrome
Infant botulism
Muscular dystrophy
Myasthenia gravis
Scoliosis
Spinal cord injury
Respiratory support devices
The management of respiratory failure is largely based on
symptomatic support until the underlying disease process abates.
Therapies should be applied in a manner that addresses the
pathophysiology behind the respiratory failure (Table 2).
Oxygen delivery devices
Table 1
The initial support for hypoxemic respiratory failure is to increase the alveolar FiO2 through an oxygen delivery device. For
each child, the optimal oxygen delivery device depends on the
FiO2 it can deliver, the severity of hypoxemia, and the likelihood
the patient will tolerate the device.
However, in children with significant lung disease physiologic
dead space can approach 60e70% of each breath. Because the
physiologic dead space volume does not participate in gas exchange, it does not aid in carbon dioxide removal. Therefore, the
alveolar minute ventilation determines carbon dioxide removal.
Blow by or wafting oxygen
Blow by oxygen describes blowing or wafting oxygen near the
face of a patient. Generally this is used briefly in patients who are
unable or unwilling to tolerate other methods of oxygen delivery.
This is not a reliable method of oxygen delivery and should be
used only while preparing a more suitable device.
Alveolar Minute Ventilation ¼ (Tidal Volume e Physiologic
Dead Space Volume) x Respiratory Rate
It is important to note that in children, particularly infants,
airway dead space is larger than in adults due to differences in
the anatomy of the oropharynx. Methods to decrease airway
dead space, such as washout with high flow rates of air (for
example with high flow humidified nasal cannula), can preserve
alveolar minute ventilation whilst decreasing the minute ventilation and therefore reduce the effort of breathing required for
appropriate gas exchange. Carbon dioxide diffuses rapidly;
consequently abnormalities in alveolar diffusion do not generally
affect ventilation.
Oxygen hood or headbox oxygen
The oxygen hood is a clear plastic tent surrounding the head of
the patient into which oxygen is infused at a flow rate of 10e15
L/min. An oxygen hood can achieve up to 0.9 FiO2. Most hoods
are not suitable for patients greater than a year of age, as these
patients are likely to move causing disruption of the seal and
allowing oxygen to escape.
Nasal cannula
A simple nasal cannula delivers oxygen into the nares through
prongs. The oxygen mixes with room air in the nasopharynx
prior to entering the lungs. Similar to any oxygen delivery device,
Respiratory mechanics
Inspiration is an active process and exhalation in normal lungs is
passive. Given their elastic properties, the lungs and the chest
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Site specific treatments for respiratory failure in children
Site of respiratory failure
Pathophysiology
Treatment
Upper airway disorders
Turbulent flow
Upper airway collapse or narrowing
Medical therapy to improve obstruction
Obstructive lower airways disease
Air trapping with decreased compliance
Respiratory muscle fatigue causing
hypoventilation
Mismatching between ventilation and
perfusion
Restrictive lung disease
Lung atelectasis and consolidation causing
intrapulmonary shunt
Decreased lung compliance Respiratory
muscle fatigue
Decreased or absent drive to breathe
Loss of airway tone
Loss of airway protective reflexes
Respiratory muscle fatigue or paralysis
Loss of airway tone and ability to cough
Central nervous system disorders
Disorders of the muscles of respiration and
peripheral nervous system
Heliox to increase laminar flow
Bypass obstruction with an endotracheal tube
Medical therapy to improve obstruction
Supplemental oxygen for hypoxemia
In severe cases; mechanical ventilation either
non-invasive or invasive to improve
hypoventilation and decrease work of
breathing
Supplemental oxygen for mild hypoxemia
Hypercapnia or significant hypoxemia requires
positive pressure ventilation
Endotracheal intubation and mechanical
ventilation
Mechanical ventilation to unload respiratory
muscles, may be non-invasive or invasive
depending on weakness severity and
chronicity
Table 2
the FiO2 of oxygen delivered to the lungs depends on the minute
ventilation of the patient and the amount of oxygen lost to the
environment.
For example, a child breathing with a tidal volume of 120 ml
at a rate of 30 breaths per minute has a minute ventilation of 3.6
L/min. If that child is receiving nasal cannula oxygen at 1 L/min,
the FiO2 of air delivered to the lungs assuming complete nasal
breathing can be no more than:
Max FiO2 delivered ¼
Simple face mask
The simple face mask forms a reservoir for oxygen to collect.
Room air enters the mask reservoir and mixes with the oxygen
during inspiration. The flow of oxygen should be at least 5 L/min
to limit the rebreathing of exhaled carbon dioxide. Depending on
the mask fit, oxygen flow rate, and minute ventilation a simple
face mask can deliver an FiO2 from 0.35 to 0.5.
ðFiO2 x Oxygen Flow RateÞ þ ð0:21 x ðMinute Ventilation Oxygen Flow RateÞ
Minute Ventilation
The maximum FiO2 that can be delivered to this child by
simple nasal cannula ¼ ((1 x 1) þ (0.21 x 2.6))/3.6 ¼ 0.43. That
is, 43% inspired O2.
The majority of air entering the lungs in this child is entrained
room air, not oxygen. Moreover, the maximal FiO2 delivered to
the patient will decrease if minute ventilation increases, given
the same oxygen flow rate. Simple nasal cannulas are generally
not used at higher than 3 L/min in children due to irritation and
drying of the nares that can occur at higher flow rates. They are
well tolerated by patients and have the distinct advantage of
allowing patients to feed while receiving oxygen therapy. This is
a very important piece of simple physiology that should be understood by all those looking after children.
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Partial rebreather face mask/Non-rebreather face
mask
A partial rebreather mask is a simple face mask attached to a bag
reservoir (Figure 1). This maximizes the FiO2 of air drawn into the
lungs and limits entrained room air. At flow rates of 10e15 L/min,
a partial rebreather face mask can achieve an FiO2 of 0.5e0.6.
A non-rebreather face mask contains additional one way
valves on the mask and the bag reservoir which limit mixing of
the oxygen supply with room air or exhaled carbon dioxide
(Figure 2). Normally, one port on the mask does not have a
valve, allowing room air to enter and preventing suffocation if
the mask is disconnected from the oxygen source. Of all simple
oxygen delivery devices (no positive pressure), non-rebreather
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into the mask. The device functions based on Bernoulli’s principle, the increase in velocity of a gas as it travels through a
narrowed tube creates a fall in the pressure it exerts. Venturi
masks are advantageous when a specific FiO2 is required.
High flow heated humidified or vaporized nasal
cannula
High flow heated nasal cannula (HFNC) can be used at high flow
rates (from 3 to 20 L/min in children) without drying respiratory
mucus membranes due to the heating and humidification or
vaporization of the delivered gas. New evidence suggests that
HFNC can significantly decrease effort of breathing in children
with respiratory failure. Those who are likely to benefit the most
are infants and younger children receiving flow at the rate of 1.5 2 L/kg/min. The precise mechanism of this effect, while not
clear, is likely related to both the generation of positive pressure
and in small children the washout of airway dead space (see
above). Because of the high flow rates, HFNC can also deliver
higher FiO2 than simple nasal cannula. HFNC should be used
primarily in patients who may benefit from higher FiO2 than can
be delivered with simple nasal cannula or have mild to moderate
increased effort of breathing, but do not have a clear indication
for mechanical ventilation.
Figure 1 Partial rebreather face mask.
Ventilation and advanced oxygenation support
Indications
Children with respiratory failure require ventilation and
advanced oxygenation support for many reasons. Fundamentally, ventilation and advanced oxygenation support devices
provide different degrees of positive intrathoracic pressure. For
patients with decreased alveolar minute ventilation causing hypercapnic respiratory failure related to decreased tidal volume,
increased dead space, or decreased respiratory rate, mechanical
ventilation can guarantee a minimal respiratory rate and provide
positive pressure during inspiration to increase tidal volume and
decrease effort of breathing. Patients with significant hypoxemia
from intrapulmonary shunt require advanced oxygenation support with continuous positive airway pressure (CPAP) or mechanical ventilation to recruit atelectatic and consolidated lung,
improve lung compliance, and offer a delivery method for high
concentrations of FiO2. For patients with decreased tidal volume
due to muscle fatigue or weakness, positive end expiratory
pressure (PEEP) helps maintain lung expansion to optimize
compliance and inspiratory pressure assists the patient with lung
inflation to decrease the work of breathing. In obstructive airways disease where muscle fatigue can lead to hypoventilation,
applied PEEP can match the intrinsic PEEP associated with air
trapping decreasing the effort required to inhale.
Figure 2 Non-rebreather face mask. Note the one way valves limiting
the mixing of room air or exhaled carbon dioxide with the oxygen
supply.
face masks provide the highest concentration of oxygen (FiO2 up
to 0.95 at 15 L/min) to a spontaneously breathing patient.
Physiology
The forces generated to move air in and out of the lungs during
ventilation support are a combination of the muscular effort of
the patient and support from the positive pressure device. Flow
occurs during inspiration when the total force exceeds the elastic
and the resistive elements of the lungs and the chest wall.
Venturi (air entrainment) mask
Venturi masks deliver oxygen at a high flow rate, significantly
exceeding the minute ventilation of the patient, thereby
providing a constant FiO2. Venturi air entrainment devices attach
to a simple mask. The highest FiO2 that can be delivered through
a Venturi mask is 0.6. Oxygen is forced through a small jet orifice
on the device generating a high velocity stream leading to sub
atmospheric pressure that entrains a constant portion of room air
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Paw þ Pmus ¼ Volume/Compliance þ Flow x Resistance
where Paw is the pressure generated by the ventilation support
device, Pmus is the pressure generated by the patient, flow x
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Ventilation bags
Bag mask manual ventilation is the most immediate mechanism
for positive pressure ventilation support. Two main devices are
used for bag mask ventilation, a self-inflating bag and a flowinflating bag (Figure 3). Self-inflating bags re-inflate by a recoil
mechanism, allowing them to function without an external gas
source. When the self-inflating bag is used with oxygen, attaching an oxygen reservoir ensures that oxygen is the primary gas
entering the bag during expansion. Self-inflating bags usually
have a one way valve preventing re-breathing of exhaled air;
oxygen only reliably flows to the patient when the bag is
squeezed.
Flow-inflating bags on the other hand do require an external
gas source to inflate. An advantage of the flow-inflating bag is
the ability to provide oxygen or CPAP to spontaneously
breathing patients because a constant flow of oxygen is present
even without inflation or deflation of the bag. Flow-inflating
bags are more difficult to operate effectively as they require
skill in achieving a suitable mask seal and delivering appropriate airway pressure to the patient. Bag mask ventilation with
either type of bag is a temporary method of support while
preparations are made for endotracheal intubation and mechanical ventilation.
pressure (EPAP). Adding IPAP to the EPAP assists the patient in
the work of inflating the lungs and can increase the tidal volume
of each breath.
Although the indications for non-invasive ventilation in pediatric patients are not clearly defined, practitioners commonly
use it for post extubation support, pulmonary oedema, asthma
and long term nocturnal support for patients with chronic lung
disease, obstructive sleep apnoea, or neuromuscular disease.
Non-invasive ventilation should not be used for patients who
have suffered a cardiac or respiratory arrest, have severely
impaired consciousness, are unable to cooperate or protect their
airway, or are likely to require a prolonged period of continuous
support. Ideal candidates for non-invasive support are either
likely to improve quickly due to the initiation of a definitive
medical therapy or only need intermittent long term support
while sleeping. Other limitations of non-invasive ventilation
include skin breakdown at the site of the interface or gastric
distension with the inability to feed. Asynchrony between the
patient’s respiratory effort and the support delivered by the noninvasive ventilation device can be a common problem as triggering mechanisms are either absent or insensitive. New technologies such as Neurally Adjusted Ventilatory Assist (NAVA)
are improving this problem. NAVA uses an esophageal catheter
to obtain the neural respiratory signal as it is transmitted through
the phrenic nerve to the diaphragm in order to trigger the
ventilator, decreasing asynchrony.
Non-invasive mechanical ventilation
Non-invasive mechanical ventilation refers to any type of mechanical ventilation delivered through a non-invasive interface
(nasal mask, face mask, nasal prongs). Although a face mask
provides the most effective ventilation by ensuring no escape of
air through the mouth, a nasal mask is often most comfortable
for patients. A ventilator delivers either CPAP or bi-level positive
airway pressure (BiPAP), an inspiratory positive airway pressure
(IPAP) for each breath and a baseline expiratory positive airway
Conventional mechanical ventilation
Patients who are unresponsive to the interventions previously
discussed or those who present with severe hypoxemia or hypercapnia, cardiac or respiratory arrest, or loss of airway protective reflexes (cough, gag) require endotracheal intubation and
conventional mechanical ventilation.
Ventilator modes are classified by the one independent
inspiratory variable they control; pressure, volume, or flow. In
all control modes, the clinician sets a PEEP, an inspiratory time,
resistance are the resistive forces, and volume/compliance are
the elastic forces that the system must overcome.
Figure 3 There are two types of ventilation bags for bag mask manual
ventilation the self-inflating bag (a) and the flow-inflating bag (b).
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an FiO2, and a mandatory breath rate. Exhalation remains a
passive process in conventional mechanical ventilation, governed by the elastic and resistive forces of the respiratory system.
Airway pressure release ventilation
Airway pressure release ventilation provides a continuous
level of positive airway pressure that is terminated for brief
periods of time. The elevated pressure aids oxygenation while
the releases in pressure allow ventilation. The patient breathes
spontaneously during both phases with or without additional
pressure support. There is some evidence that oxygenation
and ventilation can be maintained at lower pressures using
this mode in comparison to pressure or volume control modes.
Pressure control modes
In pressure control modes the clinician sets the pressure, the
independent variable. Flow increases rapidly at the beginning
of inspiration to generate the set pressure, then decreases over
inspiration as alveolar volume increases. The volume delivered varies as a function of the compliance and resistance of
the respiratory system and patient effort. The constant pressure improves the distribution of ventilation from well opened
alveoli to more collapsed areas. This is theoretically helpful
when children have non-homogenous lung disease (such as in
pneumonia or Acute Respiratory Distress Syndrome). The
initial high flow is thought to be beneficial to open stiff alveoli
and is more comfortable for patients as it matches their initial
high flow demand. The peak inspiratory pressure (PIP) for the
same tidal volume is usually less during pressure control
ventilation than volume control ventilation. The largest limitation of pressure control ventilation is the variability in
delivered tidal volume as the compliance or resistance of the
respiratory system changes.
Patient ventilator asynchrony
Patient ventilator asynchrony can be caused by difficulty triggering the ventilator to deliver a breath, inadequacy of the flow
delivered, or delayed or premature breath termination. This can
lead to patient discomfort, increased sedation requirement, and
wasted patient effort. NAVA is also being used with conventional
ventilation allowing the ventilator to respond quickly to patient
attempts to breathe.
Patients with obstructive airways disease often develop
intrinsic PEEP (PEEPi). In order to trigger a breath, the patient
must lower their pleural pressure enough to overcome both the
PEEPi and the ventilator sensitivity triggering pressure or flow
threshold. If the patient is unable to reach this threshold, the
ventilator is not triggered, the breath is not delivered, and there is
wasted patient effort. If the PEEP set on the ventilator is
increased to match the PEEPi of the patient (judged clinically in
spontaneously breathing patients or with the assistance of tools
such as esophageal manometry) only the sensitivity threshold
must be met to trigger the ventilator, decreasing the effort of
breathing for the patient.
Flow control modes
Volume control modes are actually constant flow control modes.
Flow is the set independent variable and pressure is the dependent variable. Flow is delivered constantly throughout the set
inspiration time to achieve a specific volume target. The airway
pressure varies depending on the compliance and the resistance
of the system. The advantage of this mode is consistent minute
ventilation; however, the pressure delivered can vary significantly with changes in the compliance or resistance of the respiratory system.
High frequency oscillation ventilation
Children with severe restrictive lung disease and hypoxemia or
carbon dioxide retention refractory to management with conventional ventilation may have better oxygenation at lower peak
airway pressures with high frequency oscillatory ventilation
(HFOV). HFOV delivers very small tidal volumes of 1e3 ml/kg at
a rate of 180e1200 breaths/min. Inspiration and expiration are
pushed and pulled actively from the lungs by the force of a piston. The mean airway pressure (MAP) is generally set initially 5
e10 cm H2O higher than on the conventional ventilator due to
attenuation of the pressure in the airway and the general need for
improved alveolar recruitment. The MAP is then adjusted to
achieve appropriate lung expansion and oxygenation. The
amplitude, or driving pressure DP, and frequency, or the rate of
oscillations are adjusted to achieve appropriate ventilation. As
opposed to conventional ventilation, a lower frequency increases
the tidal volume and minute ventilation. HFOV can be very
effective at CO2 removal; however, because it is an active mode
of exhalation it should not be used in patients with significant
airway obstruction. Due to smaller tidal volumes and lower peak
airway pressures, HFOV may be helpful in limiting ventilator
associated lung injury and in the management of pneumothorax
(Figure 4).
Synchronized intermittent mandatory ventilation and
assist control (D)
Synchronized intermittent mandatory ventilation (SIMV) delivers
a preset number of breaths, controlled by the selected mode, in
coordination with the spontaneous effort breaths of the patient.
The ventilator attempts to synchronize all breaths to the spontaneous breaths of the patient, delivering both the preset number
of fully supported ventilator breaths and generally providing
some support, either pressure or volume support, to additional
spontaneous breaths. In contrast, in assist control ventilation
every spontaneous breath of the patient is fully supported by the
ventilator with the preset variables. In either mode, if the patient
is not triggering the ventilator, the ventilator will deliver breaths
at the preset rate.
Pressure regulated volume control
Pressure regulated volume control (PRVC) is a hybrid mode that
controls pressure and targets a set volume. The pressure is
adjusted from breath to breath to meet a set volume target. In
addition, there is a pressure limit above which no further volume
will be delivered. As each breath is pressure controlled, there is a
decelerating flow pattern during inspiration. The advantage of
PRVC is maintaining minute ventilation while limiting peak
pressures.
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Extracorporeal membrane oxygenation
Extracorporeal membrane oxygenation (ECMO) is considered
only in patients with respiratory failure when the strategies
outlined above have failed. During ECMO, venous blood is
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initiated by the patient with a set amount of pressure or volume
supplied for the breath. The patient may then be placed on a
CPAP mode where they must utilize their respiratory muscles to
generate the flow of air into their lungs. A T-piece trial, oxygen
supplied to the endotracheal tube with zero positive pressure,
may be indicated for some patients prior to extubation.
Respiratory support for other disorders
The management of patients with respiratory failure caused by
an abnormality besides a primary restrictive lung or obstructive
lower airways disease utilizes many of the treatments outlined
previously. There are also additional disease specific therapies
worth highlighting.
Respiratory support for upper airway disorders
The subglottic region is the narrowest area in the pediatric
airway, predisposing children to obstruction with any type of
airway swelling such as that caused by viral illness or endotracheal intubation.
Heliox
Figure 4 High frequency oscillatory ventilation uses smaller tidal volumes and lower peak airway pressures than conventional ventilation.
During mechanical ventilation, both conventional ventilation settings
and HFOV settings should avoid the upper inflection point (overdistension) and the lower inflection point (atelectasis) danger zones of
mechanical ventilation. In these danger zones, there is a small change
in volume for a given change in pressure.
Heliox is a combination of oxygen and helium (useful clinically
in mixes from 60/40% to 80/20% helium/oxygen) delivered
through a hood, nasal cannula, or face mask for upper airway
obstruction. The Reynolds number determines the tendency for
gas flow through a tube to be either laminar (lower number) or
turbulent (higher number).
extracted from the body, circulated outside the body to an
oxygenator which performs the main function of the lungs;
removing the carbon dioxide and fully saturating the blood with
oxygen. The oxygenated blood is then infused back into the body
in a central vein or artery. Although ECMO is considered
routinely as the last resort for the support of neonates with respiratory failure or for the post-operative support of congenital
heart disease, ECMO in pediatric respiratory failure is controversial. For this reason, criteria for ECMO vary significantly from
institution to institution. Due to the anticoagulation required for
the ECMO circuit, patients who are bleeding or at significant risk
for bleeding should not be placed on ECMO. Respiratory ECMO
should only be used in children with reversible conditions.
Another method of extracorporeal support is through extracorporeal CO2 removal (ECCO2). The goal of this approach is to
use extracorporeal CO2 removal through venousevenous bypass
while using lung protective ventilation settings, high airway
pressures with low tidal volumes, through either a conventional
ventilator or HFOV to oxygenate the lung. This method is
currently used infrequently in pediatric respiratory failure.
Reynolds Number ¼ (2 x airway radius x density of gas x velocity)/gas viscosity
By replacing nitrogen in the gas the patient breathes with helium,
a much lower density gas with similar viscosity, the Reynolds
number is decreased and flow becomes less turbulent through
areas of narrowing. Laminar flow has lower resistance and reduces the work of breathing for the patient. The minute ventilation of the patient should be mostly supplied from the heliox
flow; practitioners should ensure a good face mask seal or deliver
a high flow via the nasal cannula because any entrained room air
will increase the Reynolds number again. In addition, heliox
should not be used in patients with more than a minimal oxygen
requirement as higher percentages of oxygen also increase the
density of the gas mixture.
The proper treatment for patients with severe upper airway
obstruction is to bypass the obstruction with endotracheal intubation. Patients with croup commonly have some degree of
hypoxemia due to mismatching between ventilation and perfusion. Hypercapnia caused by decreased alveolar ventilation
related to either muscle fatigue or an absence of airflow is a late
sign in croup that follows the development of hypoxemia and
generally requires support with endotracheal intubation. Patients
with a non-reversible source of obstruction, such as a craniofacial abnormality, who require endotracheal intubation for upper
airway obstruction will generally need the subsequent placement
of a tracheostomy tube or a definitive airway procedure.
Assessing the severity of upper airway obstruction and if a
child improves with medical therapies can be difficult at the
Weaning from mechanical ventilation
As the indication for mechanical ventilation resolves, the patient
can be weaned from mechanical ventilation support. The main
objective in weaning from mechanical ventilation is to transition
the work of breathing from the ventilator to the patient. Normally, the patient is weaned to a mode of spontaneous breathing
or intermittently placed on a mode of spontaneous breathing
during periods of sprinting. Pressure support or volume support
(no set rate) is commonly attempted first where every breath is
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bedside. There are new methods being developed using respiratory plethysmography and esophageal manometry that may aid
with the objective assessment of these children.
Hamel DS, Klonin H. The role of noninvasive ventilation for acute
respiratory failure. Respir Care Clin 2006; 12: 421e35.
Heulitt MJ, Wolf GH, Arnold JH. Mechanical ventilation. In: Nichols DG,
ed. Rogers’ textbook of pediatric intensive care. Philadelphia:
Lippincott, Williams and Wilikins, 2008; 508e31.
Khemani RG, Bart III RD, Newth CJ. Respiratory monitoring during
mechanical ventilation. Paediatrics Child Health 2007; 17:
193e201.
Krishnan JA, Brower RG. High-frequency ventilation for acute lung
injury and ARDS. Chest 2000; 118: 795e807.
Kubicka ZJ, Limauro J, Darnall RA. Heated, humified high-flow nasal
cannula therapy: yet another way to deliver continuous positive
airway pressure? Pediatrics 2008; 121: 82e8.
Newth CJ, Levison H, Bryan AC. The respiratory status of children with
croup. J Pediatr 1972; 81: 1068e73.
Newth CJ, Venkataraman S, Wilson DF, et al. Weaning and extubation
readiness in pediatric patients. Pediatr Crit Care Med 2009; 10:
1e11.
Pilbeam SP. How a breath is delivered. In: Pilbeam SP, Cairo JM, eds.
Mechanical ventilation: physiological and clinical applications. St.
Louis: Mosby Elsevier, 2006; 45e62.
Rubin S, Ghuman A, Deakers T, Khemani R, Ross P, Newth CJ. Effort
of breathing in children receiving high-flow nasal cannula. Pediatr
Crit Care Med 2014; 15: 1e6.
Thompson AE. Pediatric airway management. In: Fuhrman BP,
Zimmerman JJ, eds. Pediatric critical care. Philadelphia: Mosby
Elsevier, 2006; 485e509.
Wratney AT, Hamel DS, Cheifetz IM. Inhaled gases. In: Nichols DG, ed.
Rogers’ textbook of pediatric intensive care. 4th ed. Philadelphia:
Lippincott, Williams and Wilikins, 2008; 532e43.
Respiratory support for central nervous system disorders
Patients with central nervous system dysfunction may have
respiratory failure related to the loss of upper airway tone with
upper airway obstruction, an insufficient or absent drive to
breathe, or the loss of airway protective reflexes. The proper
management of these patients is to ensure airway protection and
guarantee minute ventilation through endotracheal intubation
and mechanical ventilation. It is important to remember that in
some of these patients, such as a patient with hemiparesis after
head trauma, vocal cord paresis, both bilateral and unilateral,
can cause upper airway obstruction. Furthermore, patients with
decreased respiratory drive will require a set rate on the
ventilator.
Respiratory support for disorders of the muscles of
respiration or peripheral nervous system
Patients with muscle weakness may have respiratory failure due
to hypoventilation related to muscular fatigue, poor airway tone
with upper airway obstruction, or an inability to cough effectively and clear secretions leading to atelectasis. These patients
may benefit initially from intermittent non-invasive mechanical
ventilation (BiPAP) during sleep when their hypoventilation is
generally more pronounced. If the muscle weakness is progressive or if the patient has paralysis, invasive mechanical ventilation is generally required.
Summary
Although respiratory failure is common in children, there are a
multitude of options available for the respiratory support of these
patients. Understanding the advantages, disadvantages, and limitations of each respiratory support option is important in implementing the appropriate management plan for each child.
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Practice points
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FURTHER READING
Abboud P, Raake J, Wheeler DS. Supplemental oxygen and bagvalve-mask ventilation. In: Wheeler DS, Wong HR, Shanley TP, eds.
Resuscitation and stabilization of the critically Ill child. London:
Springer-Verlag, 2009; 31e6.
Argent AC, Newth CJ, Klein M. The mechanics of breathing in children
with acute severe croup. Intensive Care Med 2008; 34: 324e32.
Ghuman A, Khemani R, Newth CJ. Paediatric applied respiratory
physiology-the essentials. Paediatrics Child Health 2017; 23:
279e86. https://doi.org/10.1016/j.paed.2017.03.001.
Graham AS, Chandrashekharaiah G, Citak A, Wetzel RC, Newth CJL.
Positive end-expiratory pressure and pressure support in peripheral airways obstruction. Intensive Care Med 2007; 33: 120e7.
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Oxygen delivery devices vary significantly in the FiO2 they
can deliver and for non-invasive devices that do not provide
positive pressure, the non-rebreather face mask delivers
the highest concentration of oxygen to a spontaneously
breathing patient.
Patients with hypoxemic respiratory failure refractory to
supplemental oxygen or with hypercapnic respiratory failure
require aid with positive airway pressure.
Continuous non-invasive ventilation should be limited to
patients who require short term support while a definitive
medical therapy is implemented.
Patients with severe hypoxemia or hypercapnia, cardiac or
respiratory arrest, or a loss of airway protective reflexes
require endotracheal intubation and mechanical ventilation.
HFOV can be useful in patients with severe hypoxemic or
hypercarbic respiratory failure refractory to management
with conventional mechanical ventilation.
Ó 2019 Published by Elsevier Ltd.