Mechanical ventilation in pediatrics and neonatal units

PEDIATRIC VENTILATION
6/3/23
Dr. M. Waka

Pulmonary Physiology-Micro level

Pulmonary Physiology

Ventilation is the movement of air into and out of the
alveoli of the lung.

During gas exchange (diffusion);
Oxygen(O2) moves from the alveolar space into the
pulmonary capillary
Carbon dioxide (CO2) moves from the pulmonary capillary
into the alveolar space for exhalation.

Pulmonary perfusion; flow of blood through the pulmonary
capillaries that surround the alveolar spaces.

After diffusion, oxygen is predominately bound to
hemoglobin within the red blood cells. As hemoglobin
gives up oxygen to the tissues it is able to pick up
carbon dioxide.

Pulmonary Physiology

Oxygen content in the arterial blood is the sum of the amount of oxygen
dissolved in the plasma and the amount bound to hemoglobin.

Approximately 3% of the oxygen content is dissolved in the plasma, with the
remaining 97% bound to hemoglobin.

Pao2; partial pressure of oxygen dissolved in arterial plasma. Ranges from 6–
10 kPa (45–75 mmHg)

Oxygen saturation (Sao2 ) is the percentage of oxygen bound to hemoglobin.

PaCO2; partial pressure of carbon dioxide dissolved in arterial blood. Ranges
from 5–7.5 kPa (37.5–56.0 mmHg)

PaCO2 is raised in respiratory acidaemia

In preterms hyperventilation lowers levels of PaCO2. Levels of 3 kPa
(20mmHg) causes increased incidence of periventricular leukomalacia
(PVL). This predisposes them to white matter injury.

Pulmonary Physiology-W

Each hemoglobin molecule can carry 4 O2 molecules. Each
reduced hemoglobin molecule can carry four carbon dioxide
molecules.

Cerebral blood flow increases by about 10% for each rise of 1
kPa in PaCO2. This causes an increased risk of Germinal
matrix–intraventricular haemorrhage (GMH-IVH)

Fetal hemoglobin has a higher affinity for oxygen than does
adult hemoglobin; therefore, at any given Pao2, more oxygen
is bound to adult hemoglobin. This makes it more difficult to
assess hypoxaemia clinically, since cyanosis occurs at a lower
PaO2 than in the adult.

Pulmonary Physiology-W
Carbon dioxide values fluctuate as needed to maintain the hydrogen ion
concentration, or pH, within a normal range. Carbon dioxide combines reversibly
with water to yield hydrogen (H + ) and bicarbonate (HCO 3- ) ions. The formula is
CO 2 + H 2 O H 2 CO 3 H + + HCO 3-
↔ ↔
Some values to use: While on at least 5 cmH 2 O of positive pressure ventilation, the
ratio of PaO 2 to FiO 2 (expressed as a decimal, such as 0.7) must be <300.
Mild ARDS is a PaO 2 /FiO 2 ratio of 200–300.
Moderate ARDS is 100–199.
Severe ARDS is <100.
The FiO 2 should be lowered, targeting a PaO 2 75–100, for a corresponding O 2
saturation of 95–99%, depending upon the individual oxygen-hemoglobin
dissociation curve.
Pulse Oximetry estimates the percentage oxygen saturation of haemoglobin in
arterial blood (SpO 2 ), not the partial pressure of oxygen (PaO 2 );

Pulmonary Physiology-Macro level


Airway resistance refers to the resistive forces encountered during the
mechanical respiratory cycle. The normal airway resistance is 5 cmH2O.
≤

Lung compliance refers to the elasticity of the lungs, or the ease with
which they stretch and expand to accommodate a change in volume or
pressure.

Lungs with a low compliance, or high elastic recoil, tend to have
difficulty with the inhalation process and are colloquially referred to
as “stiff” lungs. e.g. restrictive lung disease, e.g. pulmonary fibrosis.

Highly compliant lungs, or ones with a low elastic recoil, tend to have
more difficulty in the exhalation process; e.g. obstructive lung
diseases.
•


Derecruitment is the loss of gas exchange surface area due to
atelectasis. It commonly causes gradual hypoxemia in intubated
patients.

Recruitment is the restoration of gas exchange surface area by applying
pressure to reopen collapsed or atelectatic areas of lung.

Predicted body weight(PBW) is the weight that should be used in
determining ventilator settings, never actual body weight.

Lung volumes are determined largely by sex and height, and therefore,
these two factors are used in determining predicted body weight. The
formula;
▪ for men is PBW (kg) = 50 + 2.3 (height (in) – 60),
▪ for women is: PBW (kg) = 45.5 + 2.3 (height (in) – 60).

Indications for Ventilation-Clinical

Apnea and bradycardia requiring resuscitation in infants with lung disease

Unresponsive infant to CPAP

Requiring theophylline therapy in preterm infants with normal lungs

Respiratory distress/ Inefficient respiratory effort;

Rate > 60 min

Narcosis, or primary cardiopulmonary disease

Chest wall recession, grunting, Gasping

Sternal retraction, intercostal and subcostal recession

“See-saw” breathing; the diaphragm moves down on inspiration,
pushing the abdominal wall out, but rather than expanding, the
compliant chest moves in. On expiration, the reverse happens, there is
no air movement, and breathing becomes ineffective.

Tracheal tug


Respiratory distress/ Inefficient respiratory effort;

Stridor in laryngospasm, unilateral abductor paralysis,
postextubation edema and vocal cord weakness

Shock and asphyxia with hypo-perfusion and
hypotension;

HR > 180/min or < 80/min (< 5yr)

HR > 160/min or < 60/min (> 5yr)

Absent peripheral pulses / Cold peripheries

Capillary refill > 3 seconds

Systolic blood pressure < 70 + (age in years × 2) mmHg

Mean blood pressure < (postconceptual age in weeks) mmHg


RDS in infants weighing <1000 g, frequently making them incapable of
maintaining ventilation

Premature infant with minimal respiratory distress and low supplemental
oxygen requirement (to prevent atelectasis)

Respiratory distress and requirement of FiO2 above 0.30 by hood

Initial stabilization in the delivery room for spontaneously breathing, extremely
premature infants (25–28 weeks’ gestation)

Premature infants with moderately severe respiratory distress

Clinically significant retractions and/or distress after recent extubation

Administration of surfactant

Indications for Ventilation;
Reading Blood Gases

Severe hypoxemia;

Pao2 <50-60 mmHg with Fio2 ≥0.60

Severe hypoxemia;

Pao2 <60 mm Hg with Fio2 >0.40

infant weighing <1250 g

Severe hypercapnia;

Paco2 >55-65 mmHg with pH <7.20-7.25

Ventilation

Mechanical ventilation is a procedure often performed in
patients who present in respiratory distress.

The indications include airway protection, Rx of
hypoxemic/hypercapnic respiratory failure, or a combination
of both

Intubation and initiation of mechanical ventilation requires a
great degree of vigilance, as committing to this therapy can
affect the patient’s overall course.

Ventilation could be invasive or noninvasive in type.

Ventilation-Definitions
Peak inspiratory pressure (PIP or Ppeak)

The maximum pressure in the airways at the end of the
inspiratory phase.

Reflects the effects of the underlying mechanical properties of
the lungs & amount of gas delivered to the lungs in a given
breath;

Tidal volume: 4 to 6 ml/kg in preterms;

Tidal volume; 8 to 10 ml/kg in term infants) and the .

PIP is a determined by both airway resistance and compliance.

Evidence strongly suggests that lung injury results from
excessive tidal volume (excessive PIP).

Positive End Expiratory Pressure (PEEP)

Positive end-expiratory pressure (PEEP) is the positive pressure that remains
at the end of exhalation.

Helps prevent atelectasis by preventing the end-expiratory alveolar collapse.

PEEP is usually set at 5 cmH2O or greater

AutoPEEP or intrinsic PEEP (iPEEP) is when air is trapped in the alveoli at the
end of exhalation

autoPEEP exerts a pressure above and beyond the set PEEP and can be
quantified on the ventilator by pressing the expiratory pause button,
allowing the ventilator to briefly equilibrate the pressure at the end of
expiration.

Higher PEEP may interfere with cardiac output and must be used only if
indicated.

Tidal Volume (TV / VT)

Tidal volume (TV or VT) is the volume of gas delivered to the
patient with each breath.

Expressed in both milliliters (e.g. 450mL) and milliliters/kilogram
(e.g. 6 mL/kg) of predicted body weight

Every mode of ventilation delivers a tidal volume.

If under-ventilated or under-oxygenated, increase the tidal
volume in 0.5 mL/kg increments to a maximum of 6 mL/kg

Do not decrease Vt below 3.5 mL/kg as this is likely to be less
than the baby’s spontaneous tidal volume

Most babies can be extubated from a Vt of 4–4.5 mL/kg.

Minute ventilation (VĖ, Vė, or MV)

Is the ventilation the patient receives in 1 min

Calculated as the tidal volume multiplied by the respiratory
rate (TV x RR)

Expressed in liters per minute (L/min).

Most healthy adults have a baseline minute ventilation of 4–6
L/min

To help reduce the PaCO2 levels, if on volume control,
increase the tidal volume

Noninvasive Respiratory
Support

Assess whether the patient has an oxygenation problem or a
ventilation problem. Many patients will have both simultaneously.
Oxygen Support

Many patients who present with hypoxemia can be well
supported by supplemental oxygen.

Patients should be given only the minimal support they need to
maintain their desired oxygen level

Hyperoxia is increasingly appreciated as a risk factor for poor
outcomes

Noninvasive Respiratory
Support
High Flow Nasal Cannula

Heated, humidified, high-flow (greater than 1 L/min) nasal cannula
(HHHFNC) therapy as primary support for;

preterms with RDS, apnea of prematurity, and postextubation
respiratory care, including weaning from nasal continuous positive
airway pressure (NCPAP)

A typical nasal cannula can provide up to 6 L/min of supplemental oxygen.

HFNC also provides a small level of positive pressure, given the high flows.

Comparing HFNC to CPAP as postextubation support suggests that HFNC
may be an acceptable alternative to CPAP in many infants.

Data suggest that the failure of HFNC may be higher than of conventional
CPAP in infants <26 weeks’ gestation.

Nonnvasive Ventilation
Noninvasive Intermittent Mandatory Ventilation (NIPPV)

NIPPV refers to two noninvasive modes of ventilation, in which the
patient’s airway is not secured with an endotracheal tube.

Rather, ventilation are delivered through a tight-fitting face mask or
nasal prongs.

14 RCTs involving 1052 preterm and term neonates with RDS and apnea
of prematurity compared NIPPV to NCPAP found the following benefits
of NIPPV:

Reduction in endotracheal tube ventilation

Increased rate of successful extubation

Lower mortality and BPD/CLD rates

Fewer apneic episodes

Noninvasive Ventilation-CPAP
Continuous Positive Airway Pressure(CPAP)

CPAP helps infants with RDS to maintain forced residual capacity (FRC).

Can be delivered by ETT, double nasal prongs are now the most widely used
and safest technique. Other modes include nasal mask, or face mask.

The patient receives a constant airway pressure throughout the respiratory
cycle

Enables spontaneously breathing infants to gradually recruit atelectatic air
spaces while maintaining alveolar patency at end expiration despite the
absence of surfactant.

Early CPAP reduces the need to intubate and give surfactant and has
potential in decreasing the incidence of bronchopulmonary dysplasia (BPD).
The neonate must have a respiratory drive.

Noninvasive Ventilation - CPAP
How to use

Start with PEEP of 4-8 cm H2O.

Very difficult to get > 8 cmH2O using nasal prongs

Titrate oxygen to keep saturation between 90 to 94%.

Use gas flow at lowest effective level to achieve desired pressure.
Weaning:

Successful application of CPAP is defined by achieving and maintaining a normal
FRC

Gradually reduce the pressure by 1–2 cmH2O at a time.

Can be stopped using trial periods (initially 1 hour) off CPAP twice a day.

Initiated only after reduction of oxygen requirements (FiO2 )to <25% - <30%

Signs of unsuccessful weaning include increases in O2 requirement, RR, chest
retractions.

Complications of using prong CPAP include:

Nasal trauma leading to nostril deformity;

Feeding problems because the gas flow distends the
stomach;

Pneumothorax;

Over distension of lungs as atelectatic regions are
recruited and supported, esp. after administration of
surfactant

Failure, with a need for IPPV.

Invasive Respiratory
Support
Intubation process

Tube size choice is important for adequate ventilation

Rough guide for ETT size for infants is Gestation age/10 (e.g.
28weeks/10 == 2.8)

Older child tune size: [age/4] + 4

Tube length (oral); [age/2] + 12

Tube length (nasal); [age/4] + 15

Confirm tube position; look for symmetrical chest wall movement,
auscultate, and use colorimetric end-tidal CO2
detectors/capnography.

Support
Intubation process

Awake intubation is painful and associated with a stress response.

Drugs; which is

fentanyl 2–5 μg/kg, atropine 10 μg/kg and suxamethonium 1 mg/kg OR

Morphine 50–100 μg/kg and 0.5 mg/kg of atracurium

Non cuffed tubes recommended over cuffed ones

Immobilize the tube to prevent it from slipping out or traumatizing the larynx
by sliding up and down.

Keep the baby’s head in a constant degree of slight extension on his trunk.
Flexing and extending his neck causes vast differences in ETT position and
traumatizes the laryngeal mucosa.

Have a small a dead space between the ventilator circuit and the baby about
an extra 2 cm of ETT.

Support
Intubation process

Support
Intubation process


Ensure that the inspiratory gas temperature is kept at 37.0°C, and humidify to
achieve 100% relative humidity.

In RDS airway secretions are rarely increased so no need to suck out the ETT
routinely in the first 36–48 hours.

ETT sucking risks hypoxaemia, hypercapnia, hypertension and bradycardia, an
increased risk of Germinal matrix–intraventricular haemorrhage (GMH-IVH)

Suction should not be done for at least 4 hours after surfactant is given unless
the ETT is blocked

Suctioning time should be kept to 15 seconds and is ideally carried out with a
closed circuit system to prevent disconnection from the ventilator.

Modes of ventilation
Intubation process


Ensure that the inspiratory gas temperature is kept at 37.0°C, and humidify to
achieve 100% relative humidity.

In RDS airway secretions are rarely increased so no need to suck out the ETT
routinely in the first 36–48 hours.

ETT sucking risks hypoxaemia, hypercapnia, hypertension and bradycardia, an
increased risk of Germinal matrix–intraventricular haemorrhage (GMH-IVH)

Suction should not be done for at least 4 hours after surfactant is given unless
the ETT is blocked

Suctioning time should be kept to 15 seconds and is ideally carried out with a
closed circuit system to prevent disconnection from the ventilator.

Modes of ventilation
Types

SIMV

PC

VC

SIMV Combine;
– With PC
– With VC

Complications

Intubation complications

Barotrauma/Over distension of lungs as
atelectatic/pneumothorax

Infections-VAP

Tube issues; blockage, bleeding, extubation

Feeding problems because the gas flow distends the stomach

Mechanical ventilation in pediatrics and neonatal units

More Related Content

Similar to Mechanical ventilation in pediatrics and neonatal units

Recently uploaded

Mechanical ventilation in pediatrics and neonatal units