Nigerian Journal of Paediatrics 2012;39(1): 35 - 43

SYMPOSIUM

Ahmed G,

Ventilatory support of the newborn

Mohammed SS,

Abdulkadir MB,

Adesiyun OO

DOI: http://dx.doi.org/10.4314/njp.v39i1.8

Received: 3rd November 2011

Abstract

Respiratory disorders

The goal of treatment is safe and

Accepted: 3rd November 2011

are a frequent cause of admission

effective assistance to oxygen

in the newborn. Respiratory

delivery and carbon dioxide

Adesiyun OO

( )

diseases have unique physiologic,

removal from the tissues. Inspired

Ahmed G,

a n a t o m i c

a n d

c l i n i c a l

oxygen should be administered in a

Mohammed SS,

characteristics during this period

controlled manner to provide

Abdulkadir MB,

necessitating special management.

adequate but not excessive blood

K n o w l e d g e

o f

t h e

oxygen tension levels. Mechanical

Department of Paediatrics and

pathophysiology of pulmonary

ventilation may be required to treat

Child Health, University of Ilorin

diseases and their differential

metabolic abnormalities. There is

Teaching Hospital,

impact on the lungs of differing

the need for continuous monitoring

P.M.B.1459, Ilorin, Nigeria.

stages of maturity is essential to the

and re- evaluation. This article is

Email: omotayoadesiyun@yahoo.com,

safe and efficacious applications of

intended to present an overview of

Tel: +2347087621125

special techniques of treatment.

the embryology of the respiratory

P r i n c i p l e s o f r e s p i r a t o r y

system, pulmonary physiology in

m a n a g e m e n t

i n c l u d e

the newborn, the principles of

establishment of the airway,

oxygen therapy and mechanical

ensuring oxygenation, assisted

ventilation. It also discusses the

ventilation, assessing adequacy of

complications that can follow.

ventilation, correction of

metabolic abnormalities and

Key words: Ventilatory support,

alleviation of cause of distress.

oxygen delivery, newborn

Introduction

The development of the lung is divided into 5

overlapping stages.

Embryology of the Respiratory System

Embryonic stage (3-7week) branching of

the

primitive bud to form terminal

The respiratory system is an outgrowth of the ventral

bronchioles.

wall of the foregut. While the epithelium of the

Pseudo glandular stage (5-17weeks) further

larynx, tracheal, bronchi, and the alveoli originate in

division of the terminal bronchiole into 2 or

the endoderm, the cartilaginous, muscular, and

more respiratory bronchioles.

connective tissue component are mesodermal in

Canalicular stage (16-26week) terminal sacs

origin. By the 4

th

week of gestation, the

are form and the capillaries establishes close

tracheoesophageal septum separates the tracheal

network. The type II alveoli cells are well

from the foregut, with the foregut gut dividing as the

delineated.

lung bud anteriorly and the esophagus posteriorly.

Saccular stage (26-36week) thinning of the

Contact between the two is maintain through the

interstitium and fusion of type I cells, and the

larynx, which is formed by the tissues of the 4 and

th

capillary basement in preparation for the lung

6 pharyngeal arches.The lung bud develop into 2

th

function as an organ of gas exchange.

main bronchi, while the right forms 3 secondary

Alveolar stage (36week -3-8yrs of age)

bronchi and 3 lobes, the left forms 2 bronchi and 2

secondary septal formation, further sprouting of

lobes.

the capillary network & development of true

alveoli.

36

Towards the end of the 6 month, type II alveoli

th

of the air inside the lung alveoli. When no air is

cells produce surfactant a phospholipids rich fluid

flowing into or out of the lungs, the pressures in all

capable of lowering surface tension at the alveoli

parts of the respiratory tree, all the way to the alveoli,

surface.

are equal to atmospheric pressure, that is, 0 cmH O

2

pressure. Transpulmonary pressure is the difference

Clinical importance

between the alveolar pressure and the pleural

pressure. It is the pressure difference between that in

Abnormalities in stage I

lung aplasia,

the alveoli and that on the outer surfaces of the lungs,

tracheoesophageal fistula and pulmonary cysts.

and it is a measure of the elastic forces in the lungs that

Abnormalities in stage II - pulmonary

tend to collapse the lungs at each instant of respiration,

s e q u e s t r a t i o n ,

c y s t i c

a d e n o m a t o i d

called the recoil pressure .

malformations, congenital diaphragmatic

hernia.

Compliance describes the elasticity or distensibility

Abnormalities in stage III - Respiratory distress

(e.g., of the lungs, chest wall, respiratory system) and

syndrome (RDS) and lung hypoplasia.

is calculated from the change in volume per unit

Before birth, the lungs are filled with fluid that

change in pressure as follows:

has a high chloride content, little protein, some

Compliance =

! Volume

mucus from bronchi gland. Fetal breathing

! Pressure

movement begins before birth and these

movements are important for stimulating the

The higher the compliance, the larger the delivered

development and conditioning of respiratory

volume per unit changes in pressure. Normally, the

muscles.

chest wall is compliant in newborns and does not

impose a substantial elastic load compared to the

Pulmonary Physiology in the Newborn

lungs. The range of total respiratory system

compliance (lungs + chest wall) in newborns with

The goals of respiration are to provide oxygen to the

healthy lungs is 0.003-0.006 L/cm H O, while

2

tissues and to remove carbon dioxide. To achieve

compliance in babies with RDS may be as low as

these goals, respiration occurs through four major

0.0005-0.001 L/cm H O. The alveolar surface tension

2

functions:

is an important factor affecting the compliance of the

lungs is the surface tension of the film of fluid that

Pulmonary ventilation which involves the inflow

lines the alveoli. If the surface tension is not kept low

and outflow of air between the atmosphere and

when the alveoli become smaller during expiration,

the lung alveoli;

they collapse in accordance with the law of Laplace.

Diffusion of oxygen and carbon dioxide between

the alveoli and the blood gas exchange.

The law states that in spherical structures like the

Transport of oxygen and carbon dioxide in the

alveoli, the distending pressure equals 2 times the

blood and body fluids to and from the body's

tension divided by the radius (P = 2T/r). The low

tissue cells.

surface tension when the alveoli are small is due to the

Regulation of ventilation and other facets of

presence in the fluid lining the alveoli of surfactant, a

respiration.

lipid surface-tension-lowering agent. Surfactant is a

mixture of dipalmitoylphosphatidyl-choline (DPPC),

Mechanics of Pulmonary Ventilation

other lipids, and proteins. Surfactant also helps to

prevent pulmonary edema.

The lungs can be expanded and contracted in two

ways: Either by downward and upward movement

Resistance describes the inherent capacity of the air

of the diaphragm to lengthen or shorten the chest

conducting system (e.g, airways, endotracheal tube

cavity or via elevation and depression of the ribs to

[ETT]) and tissues to oppose airflow and is expressed

increase and decrease the anteroposterior diameter

as the change in pressure per unit change in flow as

of the chest cavity.

Normal quiet breathing is

follows:

accomplished almost entirely by the first method

Resistance =

! Pressure

while the second method occurs during heavy

! Flow

breathing and involves the use of muscles of

Airway resistance depends on the radii of the

inspiration and expiration.

airways (total cross-sectional area), the length of

airways, the flow rate, and the density and viscosity

Pleural pressure is the pressure of the fluid in the thin

of gas. Resistance is governed by Poiseuille's law

space between the lung pleura and the chest wall

stated as:

pleura. This is normally a slight negative pressure.

R = 8 l η ÷ π r ( where R - resistance, η - viscosity, l

4

On the other hand, alveolar pressure is the pressure

- length, and r - radius).

37

Thus, airway resistance is inversely proportional to

Volumes and Capacities

its radius raised to the 4 power. If the airway lumen

th

is decreased in half, the resistance will increase 16-

Tidal volume (V _T ) is the amount of air moved in

fold. Newborns and young infants with their

and out of the lungs during each breath. At rest, it

inherently smaller airways are especially prone to

is usually 67 mL/kg body weight.

marked increase in airway resistance from inflamed

Inspiratory capacity (IC) is the amount of air

tissues and secretions. In diseases in which airway

inspired by maximum inspiratory effort after tidal

resistance is increased, flow often becomes

expiration.

turbulent. Distal airways normally contribute less to

Expiratory reserve volume (ERV) is the amount of

airway resistance because of their larger cross-

air exhaled by maximum expiratory effort after

sectional area, unless bronchospasm, mucosal

tidal expiration.

edema, and interstitial edema decrease their lumen.

Residual volume (RV) is the volume of gas

Small endotracheal tubes that may contribute

remaining in the lungs after maximum expiration.

significantly to airway resistance also are important,

Vital capacity (VC) is defined as the amount of air

especially when high flow rates that lead to turbulent

moved in and out of the lungs with maximum

flow are used. The range for total airway plus tissue

inspiration and expiration.

respiratory resistance values for healthy newborns is

20-40 cm H O/L/s; in intubated newborns this range

Total lung capacity (TLC) is the volume of gas

2

occupying the lungs after maximum inhalation.

is 50-150 cm H O/L/s.

2

Functional residual capacity (FRC) is the amount

of air left in the lungs after tidal expiration.

Time constant , measured in seconds, is a product of

compliance and resistance.

The VC, IC, and ERV are decreased in lung pathology

but are also effort dependent. The FRC represents the

Time constant = Resistance X Compliance

environment available for pulmonary capillary blood

for gas exchange at all times. A decrease in FRC is

It is a measure of how quickly the lungs can inflate or

often encountered in alveolar interstitial diseases and

deflate, and also a measure of how quickly the

thoracic deformities.

The major pathophysiologic

alveoli get into equilibrium with the air passages.

consequence of decreased FRC is hypoxemia.

Thus, the time constant of the respiratory system is

Reduced FRC results in a sharp decline in P _A O ₂ during

proportional to the compliance and the resistance.

exhalation because a limited volume is available for

For example, the lungs of a healthy newborn with a

gas exchange.

compliance of 0.004 L/cm H O and a resistance of 30

2

cm H O/L/s have a time constant of 0.12 seconds.

2

Gaseous exchange in the respiratory system occurs

When a longer time is allowed for equilibration, a

only in the terminal portions of the airways. The gas

higher percentage of airway pressure equilibrates

that occupies the rest of the respiratory system that is

throughout the lungs. The longer the duration of the

not available for gas exchange with pulmonary

inspiratory (or expiratory) time allowed for

capillary blood dead space. This space can be divided

equilibration, the higher the percentage of

as the anatomic dead space (respiratory system

equilibration.

volume exclusive of alveoli) and the physiologic

(total) dead space (volume of gas not equilibrating

For practical purposes:

with blood, i.e, wasted ventilation). In healthy

individuals, the two dead spaces are identical; but in

One time constant = 63% equilibrium.

disease states, there may be no exchange between the

2 time constant = 86% equilibrium.

gas in some of the alveoli and the blood, and some of

3 time constant = 95% equilibrium.

the alveoli may be overventilated.

5 time constant = 100% equilibrium.

Ventilation

perfusion (V/Q) mismatch usually is

Lungs with decreased compliance (such as in RDS)

caused by poor ventilation of alveoli relative to their

have a shorter time constant. Lungs with a shorter

perfusion. A V/Q mismatch is a major cause of

time constant will complete inflation and deflation

hypoxemia in infants with respiratory distress

faster than normal lungs. Patients with shorter time

syndrome (RDS) and other causes of respiratory

constants are best ventilated with relatively smaller

failure.

tidal volumes and faster rates to minimize peak

inflation pressure. In patients with increased airway

Gas exchange

resistance, a fast respiratory rate (and, therefore, less

time) does not allow enough pressure equilibration

The minute volume is a product of V _T and respiratory

to occur between the proximal airway and the

rate. Alveolar ventilation is the volume of

alveoli.

atmospheric air entering the alveoli and is calculated

as:

38

(V _T - dead space) × respiratory rate

the affinity of hemoglobin for O . The greater affinity

2

Gas exchange occurs by the process of diffusion and

of fetal hemoglobin (hemoglobin F) than adult

equilibration of alveolar gas with pulmonary

hemoglobin (hemoglobin A) for O ₂ facilitates the

capillary blood.

movement of O ₂ from the mother to the fetus.

Diffusion depends on the alveolar capillary barrier

O ₂ Hb dissociation curve

and amount of available time for equilibration. In

health, the equilibration of alveolar gas and

pulmonary capillary blood is complete for both

oxygen and carbon dioxide. In diseases in which

alveolar capillary barrier is abnormally increased

(alveolar interstitial diseases) and/or when the time

available for equilibration is decreased (increased

blood flow velocity), diffusion is incomplete.

Because of its greater solubility in liquid medium,

carbon dioxide is 20 times more diffusible than

oxygen. Significant elevation of CO ₂ does not occur

as a result of a diffusion defect unless there is

coexistent hypoventilation.

Oxygen transport

Control of Respiration

Oxygen (O ₂ ) diffuses through the respiratory

membrane from the alveoli to the blood from where

The control and maintenance of normal breathing

it is transported to the tissues for utilization. O ₂ is

largely reside within the respiratory control centers

transported in the blood combined with the O -

2

of the bulbopontine region of the brainstem.

carrying protein- hemoglobin. O ₂ delivery to a

Neurons within this area of the brain efferent output

particular tissue depends on the amount of O ₂

to the respiratory control muscles. Multiple afferent

entering the lungs, the adequacy of pulmonary gas

inputs induce modulation of the central respiratory

exchange, the blood flow to the tissue, and the

center efferent outputs to the respiratory and airway

capacity of the blood to carry O _2. The reaction is

muscles and lungs.

rapid, requiring less than 0.01 s. The deoxygenation

(reduction) of Hb O

4

8

is also very rapid. The

Among these inputs are signals from central and

transition from one state to another (i.e deoxyHb →

peripheral chemoreceptors, pulmonary stretch

OxyHb → deoxyHb) has been calculated to occur

receptors, and cortical and reticuloactivating system

about 10 times in the life of a red blood cell.

8

neurons. Theophylline and caffeine have been shown

to increase the central chemoreceptor ventilatory

2

The oxygen-hemoglobin dissociation curve, the

response to CO and decrease the number of apneic

curve relating percentage saturation of the O -

spells in premature babies.

2

carrying power of hemoglobin to the PO ₂ has a

Physiologic Response to Respiratory Diseases

characteristic sigmoid shape. Combination of the

first heme in the Hb molecule with O ₂ increases the

Tachypnea (RR > 60/min): Rapid and shallow

affinity of the second heme for O , and oxygenation

2

respirations are characteristic of parenchymal

of the second increases the affinity of the third, etc,

pathology, in which the elastic work of breathing is

so that the affinity of hemoglobin for the fourth O ₂

increased disproportionately to the resistive work of

molecule is many times that for the first.

breathing.

Retractions: Subcostal, intercostal, and suprasternal

Three important conditions affect the oxygen-

are most striking, with increased negative

hemoglobin dissociation curve: the pH, the

intrathoracic pressure during inspiration. This occurs

temperature, and the concentration of 2, 3-

in extrathoracic airway obstruction as well as diseases

diphosphoglycerate (DPG; 2, 3-DPG). A rise in

of decreased compliance.

temperature or a fall in pH shifts the curve to the

right. When the curve is shifted in this direction, a

Inspiratory stridor is a hallmark of extrathoracic

higher PO ₂ is required for hemoglobin to bind a

airway obstruction .

given amount of O . A convenient index of such

2

shifts is the P , the PO at which hemoglobin is half

50

2

Expiratory wheezing is characteristic of intrathoracic

saturated with O .Thus, the higher the P , the lower

2

50

airway obstruction, either extrapulmonary or

intrapulmonary.

39

Grunting is produced by expiration against a

is needed to prevent CO ₂ build up.

partially closed glottis and is an attempt to maintain

Non-rebreather face mask: Delivers highest FiO ₂

positive airway pressure during expiration for as

at 70-100%

long as possible. Such prolongation of positive

pressure is most beneficial in alveolar diseases that

Venturi mask: This works based on the Venturi

produce widespread loss of FRC, such as in

principle. It is the best method for delivering a

pulmonary edema, RDS and pneumonia.

specific and consistent FiO . The mask can deliver

2

Respiratory Support in the Neonate

FiO ₂ of 24-55% at flow rate of 4-10L. The masks

are usually colour coded at 24%, 28%, 31%, 35%,

The aim of respiratory support in the neonate is to

40% and 50%

maintain adequate gas exchange, minimize risk of

Oxygen hood/ tent: has the added advantage of easy

lung injury, minimize haemodynamic impairment,

visualization.

avoid injury to other organs, and to reduce work of

breathing.

Monitoring Oxygen Therapy

Oxygen and issues regarding use

Clinical indices used include:

Oxygen saturation (spO )

2

Oxygen as a drug provided in the neonate can be

Transcutaneous PO2(tcPO )

2

used to improve arterial oxygenation, cause

Transcutaneous CO2(tcPCO )

2

pulmonary vasodilation, and to enhance systemic

Arterial blood gases

oxygen delivery.

Central mixed venous PO 2

2

Oxygen therapy works by increasing the fractional

End tidal CO

inspired concentration of oxygen (FiO ) and the

2

Complications of Oxygen Therapy: These include

oxygen flow rate. The FiO ₂ determined by the

retinopathy of prematurity, bronchopulmonary

concentration of supplemental oxygen, the flow rate

dysplasia, absorption atelectasis, respiratory

of oxygen, oxygen delivery device, and the patient

acidosis, ventilatory depression, suppression of

respiratory effort.

erythropoeisis. Others are the complications related

to the delivery device.

The concentration of oxygen varies depending on

the source as follows: Room air 21%, oxygen tank

Continuous Positive Airway Pressure

100%, and oxygen concentrator >90% (varies with

the oxygen concentrator indicator).

The application of end-expiratory pressure is

intended to prevent alveoli and/or terminal airways

Oxygen delivery device that can be used include

from collapsing to airlessness. Continuous positive

nasal cannula, nasal catheter, face mask, oxygen

airway pressure (CPAP) may be applied during

hood, oxygen tent, endotracheal/nasotracheal

spontaneous breathing or as positive end-expiratory

tube/tracheostomy

pressure (PEEP) during mechanical ventilation. This

usually requires pressures between 4 to 6 cm H O for

2

Nasal cannula: This is a low flow device that can

CPAP and 3 to 8 cm H O for PEEP. The physiologic

2

deliver distending pressure. It is the least expensive

effects of CPAP/PEEP may vary depending on the

and the FiO ₂ delivered is 24-40%.

underlying pulmonary pathology, although the

primary goal is to prevent alveolar collapse.

Nasal catheter: It is inserted into the oropharynx,

and delivers a FiO2 similar to nasal cannula

In the surfactant-deficient state, alveoli will collapse

It could easily be clogged by secretions.

at end-expiration unless a minimum distending

pressure is maintained. CPAP of 3 to 4 cm H O will

2

Face mask: There are various type which include

prevent alveolar collapse but will not recruit

the simple, partial rebreathing, non-rebreathing and

atelectatic alveoli. Opening pressures of 12 to 15 cm

theVenturi face mask.

H O are required to inflate collapsed alveoli. The

2

infant will need to create a large distending airway

Simple face mask: Allows unregulated flow of

pressure in the absence of CPAP. The shear forces

room air, and the FiO ₂ delivered is 35-50%.

from opening and closing of small airways may

However an increase flow rate is needed to

contribute to alveolar epithelial damage. CPAP

prevent rebreathing.

theoretically could stimulate surfactant secretion.

Partial rebreather mask: Is a simple mask with an

Also, maintenance of alveolar volume will reduce

attached reservoir. Oxygen flow rate of 6-10L

right-to-left shunting of blood through atelectatic

required to deliver 40-70% FiO ₂ and a high flow

alveoli, hence reducing oxygen needs.

40

Indications: Its initial use was directed at RDS.

S y n c h ro n i z e d

I n t e r m i t t e n t

M a n d a t o r y

However, can be used to reduce the need for

Ventilation (SIMV): Is a ventilatory mode in which

ventilatory care in extreme preterms, and is used for

the mechanically delivered breaths are synchronized

the INSURE technique. It is also useful in recurrent

to the onset of spontaneous patient breaths, but at a

apnoea of prematurity, and when weaning off

lower rate. The patient may breathe spontaneously

conventional ventilation.

between mechanical breaths from the continuous

flow in the ventilatory circuit.

Benefits:

It effectively maintains Functional

Residual capacity, helps reduce infant work of

Pressure Support Ventilation (PSV): It is a mode of

breathing, reduces the need for intubation and

ventilation that has no set rate and only supports the

mechanical ventilation, and reduces the incidence of

patient's own spontaneous effort. It is primarily a

chronic lung disease. It results in improved non-

weaning mode. The patient controls RR, Ti and peak

pulmonary outcomes (increase mean weight gain,

insp. Flow, while the ventilator controls only PIP.

mean length and head circumference at 36weeks

This system synchronizes inspiration by sensing

post menstrual age).

patient effort, and also synchronizes expiration by

terminating inspiration in response to a decline in

Complications: This includes overinflation leading

airway flow. This results in complete synchronization

to increased work of breathing, air leak syndromes,

of the functioning of the baby and the ventilator

carbon dioxide retention, decreased cardiac output

throughout the entire respiratory cycle.

with high values, complications from delivery

device, and gastric distension.

Flow Sensitive Ventilation (FSV): Inspiration is

triggered by changes in flow and ends not according

Mechanical Ventilation

to time but according to airway flow changes. During

inspiration, the ventilator records the peak expiratory

This is an invasive life support procedure. The goal

flow rate and subsequently terminates inspiration

is to optimise both gas exchange and clinical status at

when the inspiratory flow decreases to 5-10% of peak

minimum FiO ₂

and ventilatory pressures/ tidal

flow. This enables both inspiratory and expiratory

volumes.

synchrony. Benefits of FSV include total breath

synchronization, decreased work of breathing, less

Conventional Ventilation

sedation, more efficient tidal volume delivery,

improved gas exchange, and fewer complications.

Ventilatory modes: Untriggered or triggered.

Untriggered

Mode:

Consists of intermittent

Newer modalities of Mechanical Ventilation

mandatory ventilation (IMV) and intermittent

positive pressure ventilation (IPPV).

Volume guaranteed (VG)

Volume associated pressure support (VAPS)

Intermittent Mandatory Ventilation: Provides

Pressure regulated volume control (PRVC)

fixed rate of mechanical ventilation and allows

Proportional assist ventilation (PAV)

spontaneous breathing between mechanical breathes

from continuous flow of oxygen.

Volume Guaranteed (VG)

Triggered ventilation: Consists of flow trigger and

This is a pressure-limited, time or flowcycled,

pressure trigger

volume-targeted form of ventilation. The

microprocessor compares exhaled tidal volume of the

Triggered modes: Types are the assist/control

previous breath to the desired target and adjusts the

mode, synchronized intermittent mandatory

working pressure up or down to try to achieve the

ventilation, pressure support ventilation, flow

target tidal volume. There is limit of pressure

sensitive ventilation, and volume timed ventilation.

increment from one breath to the next to a maximum

of 3cm H O to avoid overcorrection. Thus, several

2

Assist/Control

(A/C):

This modality involves

breaths may be needed to reach the target tidal

either the delivery of a synchronized mechanical

volume after a sudden change. The VG mode cannot

breath each time a spontaneous patient breath is

increase pressure higher than set pressure limit.

detected (ASSIST), or in the event that the patient

Benefits of VG

fails to exhibit spontaneous resp. effort , the

ventilator delivers a mechanical breath at a regular

Maintenance of constant tidal volumes in the

rate (CONTROL).

face of changing compliance, resistance and

changing ET- tube leak

Prevention of overdistention and volutrauma

41

Automatic lowering of pressure support level

1. Ventilatory strategy in RDS Ensure an inspiratory

during weaning (auto-weaning). As the

flow rate 7-12 L/min, peak inspiratory pressure

patient's lungs improve and compliance

20-25cmH ₂ O and positive end expiratory

increases, peak inspiratory pressure is weaned

pressure 4-5cmH O. The inspiratory time should

2

automatically.

be 0.5s while the expiratory time is set at 1.0s.

Trigger volume mode preferred. Alternative

Indications for VG: Virtually any infant requiring

strategy is with high frequency ventilation.

mechanical ventilation especially when lung

2. Ventilatory strategy in MAS

mechanics are likely to change, or in patients with

There is a high risk of pneumothorax because of

heterogenous lung disease because of differing time

ball valve effect, thus a low PEEP should be

constant throughout lung parenchyma

utilized to splint the airways. If airway resistance

is high, a slow rate, moderate pressure strategy

High Frequency Ventilation

should be utilized. If pneumonitis is more

prominent, more rapid rates can be utilized. HFV

HFV is a form of mechanical ventilation that uses

can be used with failed conventional ventilation

small tidal volumes, sometimes less than anatomic

or air leaks.

dead space, and extremely rapid ventilator rates.

3. Ventilatory strategy in air leaks

Goal is to reduce the mean airway pressure (MAP)

HFV in comparison to conventional IMV

to as low as possible and rely on FiO ₂ to improve

HFV delivers at high frequency: 300-1200/min=5-

oxygenation. HFOV is the modality of choice.

20 HzU and utilizes very small tidal volumes and can

Maintain MAP, do not use sigh maneuver. Use

detect incomplete inspiration and expiration. Causes

low PEEP

dampening of the oscillations along the airways and

4. Ventilatory strategy in apnoea with normal lungs

2

ensures a nearly constant alveolar pressure. Also,

Ensure low gas flow, low PIP 10-18cmH O, low

HFV has the ability to independently manage

PEEP 3-4cmH ₂ O, and normal rates 30-

ventilation and oxygenation, while ensuring the safe

40breaths/min

use of mean airway pressure that is higher than that

generally used during conventional mechanical

Oxygenation Index: This is an index of disease

ventilation.

severity

OI =

PAWx FiO2

Types of HFV

PaO2

An index greater than 15 indicates severe respiratory

HFFI (Higher-Frequency Flow interrupting

compromise, while an index greater than 40 on

Ventilation)

multiple occasions indicate mortality > 80%

HFJV(High- Frequency JetVentilation)

HFOV(High-Frequency OscillatoryVentilation)

Complications of Mechanical Ventilation

Indications for HFOV: Rescue therapy and air leak

syndromes.

This includes ventilation induced lung injury,

ventilation induced pneumonia, air leak syndromes,

Clinical Applications of Mechanical Ventilation

traumatic injury to large airways and endotracheal

tube complications.

CPAP: Mildly affected neonates with RDS: start

at 4-6cm H O and increase gradually to a maximum

Ventilator Induced Lung Injury (VILI)

2

of 7-8cm H O. It is titrated by: clinical assessment of

2

retractions, respiratory rates, and oxygen saturation.

There are four mechanisms of VILI: Barotrauma

(high airway pressure), volutrauma (large tidal

Neonatal Pulmonary Physiology By Disease State.

volume), atelectotrauma (alveolar collapse and re-

expansion), and biotrauma (increased inflammation).

Strategies need to be developed for the various

disease states requiring ventilation in the neonate.

Volutrauma caused by mechanical overdistension

leads to alveolar epithelial cell damage, alveolar

Setting parameters are required for the inspiratory

protein damage, altered lymphatic flow, hyaline

flow rate, peak inspiratory pressure, positive end

membrane formation, and inflammatory cell influx in

expiratory pressure, oxygen concentration,

the lungs. The precise tidal volume required to

inspiratory time, expiratory time, trigger volume.

minimize volutrauma is not known. Therefore efforts

Derived parameters are the FiO2, mean airway

to limit tidal volume may be a beneficial practice in

pressure, flow parameters, tidal volume, and the

the neonatal intensive care unit.

respiratory rate.

42

Ventilator Associated Pneumonia (VAP)

Retinopathy of prematurity is a vaso-proliferative

retinal disorder that decreases with gestational age.

This is defined as pneumonia in mechanically

Approximately 65% of infants with a birth weight

ventilated patients that develops ≥ 48 h after the

less than 1250g and 80% of those with a birth weight

patient has been placed on mechanical ventilation.

less than 1000g will develop some degree of

VAP is the second most common hospital acquired

retinopathy of prematurity.

infection among neonatal intensive care unit (NICU)

patients. This is often caused by organisms such as

Extracorporeal Membrane Oxygenation

Pseudomonas aeruginosa (the most common),

Staphylococcus aureus, Enterobacter species, and

This can be defined as a mechanical means of

Klebsiella pneumoniae

providing oxygen delivery and carbon dioxide

removal for patients who have cardiac and/or

Diagnostic criteria forVAP

respiratory failure. May be veno-arterial or veno-

Worsening gas exchange (oxygen desaturation or

venous.

increased oxygen or ventilatory requirements)

and 3 of the following:

Indication

Temperature instability with no obvious cause.

Critically ill term and late preterm newborns with

Leukopenia or leukocytosis with left shift.

reversible respiratory and/or cardiac failure who

Increased pulmonary secretions or greater need

have failed appropriate maximal medical

for suctioning.

management.

In conditions such as meconium aspiration

Examination reveals apnea, tachypnea, nasal flaring

syndrome, respiratory distress syndrome,

with chest retractions, grunting. Wheezing, rales,

persistent pulmonary hypertension of the

rhonchi may be present, with either bradycardia or

newborn, pneumonia, sepsis, severe rhythm

tachycardia.

disturbances, neonatal cardi0myopathies

Strategies to reduce VAP will include to prevent

Specific indications

contamination of equipment, ensure endotracheal

Respiratory criteria: OI >30-40 for 4 hours, acute

tube care, and to minimize duration of intubation.

deterioration with intractable hypoxaemia,

barotrauma with severe air leak not responsive to

Air-leak syndromes

HFOV

Cardiovascular/oxygen delivery criteria:Cardiac

T h e s e

i n c l u d e :

P n e u m o t h o r a x ,

arrest, plasma lactate >45mg/dl with metabolic

pneumomediastinum, pneumopericardium,

acidosis not improving or escalating with despite

pulmonary interstitial emphysema, and

adequate medical care, mixed venous saturation

subcutaneous emphysema.

<55% for 1 hour

Risk factors for air-leak syndromes in neonates are

Contraindications

extreme low birth weight, endotracheal tube

These include: Gestational age less than 32 weeks

displacement, using long inspiratory time (> 0.5

and/ or birth weight less than1800g, mechanical

sec), ↑

PIP, ↑

Vt. Also, increase in clinical

ventilation beyond 10-14 days due to likely

interventions including suction procedures, chest

irreversible lung disease, intraventricular

radiography, reintubation, bag & mask ventilation

hemorrhage greater than grade I, and coagulopathy

and chest compressions are risk factors. Other risk

unlikely to resolve with transfusion. Others are

factors are MAS, RDS, pulmonary hypoplasia.

severe congenital anomalies, uncorrectable cardiac

lesions, CDH with OI>45, hypoxic ischaemic

Tracheal

injury

and

endotracheal

tube

related

encephalopathy, and plasma lactate >225mg/dl.

complications

Complications

These include subglottic stenosis, tracheal

These are acute renal failure, hypertension,

perforation, palatal deformities, vocal cord avulsion,

haemolysis, seizures, hypotension, CNS infarction,

laryngeal oedema, subglottic cysts, necrotizing

intracranial haemorrhages, sepsis, surgical bleeding,

tracheitis and septal injury.

pulmonary haemorrhage, disseminated intravascular

coagulopathy (DIC), and brain death. Others are

Chronic lung disease is defined as the need for

cannula problems, air embolism, pump failure, and

supplemental oxygen beyond 28days of postnatal

clot formation.

age or oxygen dependency at 36weeks

postmenstrual age.

Supportive Care: This involves the use of surfactant

therapy, inhaled nitric oxide, heliox, ensuring

43

adequate tissue perfusion by optimizing

Arterial blood gas analyzers, flow sensors, oxygen

cardiovascular function and total parenteral

sensors, surfactant, total parenteral nutrition (TPN),

nutrition.

and disposable supplies (endotracheal tubes,

catheters, chest tubes, etc).

To be more practical where do we stand?

There is the need to establish mechanical ventilatory

care in our centers. Requirements are:

Acknowledgement

Manpower: Nursing staff, doctors, laboratory staff,

radiographers, need for training.

Reproduced with kind permission of the department

of Paediatrics and Child Health of the University of

Materials: Functioning ventilators, regular oxygen

Ilorin Teaching Hospital, Ilorin Nigeria owners of the

supply, regular power supply, regular water supply, a

Ilorin Paediatric Digest 2010.

mobile x-ray machine, pulse oximeters, complete

patient monitors (BP, HR,Temp, O ₂ saturation),

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