Non-invasive ventilation

The idea behind

Non-invasive ventilation (NIV) includes a range of ventilation modes to support the paediatric patient in acute or chronic respiratory failure without the use of an invasive airway such as an endotracheal tube (ETT) or tracheostomy. 

Every effort should be made to advocate and optimise its use among paediatric ICU patients in order to minimise the risks associated with invasive ventilation (IV) such as:

- Manipulation of critical airway structures (Pharynx, tongue, teeth, larynx, glottis, subglottic area and trachea)

- Need for sedation to allow tube tolerance and its associated complications (Withdrawal, delirium, neuromyopathy, cardiovascular compromise)

- Nosocomial infection, namely ventilator-associated pneumonia (VAP)

- Need to remain in PICU (ability to ambulate and even receive the support at home)

NIV has clearly defined contraindications and less well-defined indications as well as a set of potential side effects.

The body of evidence for the use of NIV in children is growing while some of the data remains extrapolated from adult studies. 

What is CPAP?

CPAP (Continuous Positive Airway Pressure) refers to the application of a certain amount of positive airway pressure during the entirety of the respiratory cycle. 

The patient can breathe spontaneously at any point in time but does not receive any additional support during inspiration. 

CPAP causes an increase in functional residual capacity (FRC) which leads to increased oxygenation. 

By re-inflating previously collapsed areas of lung and avoiding re-collapse (atelectasis) CPAP causes an increase in compliance and therefore indirectly reduces the work of breathing (WOB).

CPAP can be successfully applied in patients with adequate respiratory drive, muscle strength and airway patency.

What is NIV?

NIV (Non-invasive ventilation) includes different modes that apply two separate levels of pressure with a variety of triggers ultimately generating a pressure gradient that allows for increased flow into the lungs, greater tidal volumes and reduced work of breathing (WOB). 

The lower pressure level (PEEP or EPAP) is responsible for an increase in FRC which improves oxygenation while the high pressure level (IPAP or PIP) supports the generation of larger tidal volumes thereby increasing minute ventilation, CO2 clearance and assisting re-recruitment while decreasing the WOB.

While the EPAP recruits collapsed lung areas and helps avoid re-collapse, the IPAP assists the patient in overcoming the opening pressure of the lung tissue.

indications

INFANTS

CHILDREN

  • Type I or Type II respiratory failure

  • Asthma

  • Bronchiolitis

  • Pulmonary oedema

  • Congenital heart disease / Congestive heart failure

  • Respiratory failure secondary to chronic lung disease

  • Cystic fibrosis (CF)

  • Neuromuscular disease

  • Neurological state with depressed respiratory drive

  • Chest-Wall deformities

  • Post extubation

  • Obstructive airway disease   (Laryngo-, Tracheo-, Bronchomalacia)

Contra-indications

INFANTS

  • Frequent and severe apneas

  • Unrepaired congenital diaphragmatic hernia (CDH)

  • Gastric overdistension

  • Tracheo-esophageal fistula

  • Cranio-facial abnormality

  • Untreated pneumothorax (PTx)

  • Neurological disorders with severe respiratory depression

CHILDREN

  • Severe pARDS

  • Untreated PTx

  • Facial injuries including burns and mid-facial fractures

  • Risk of aspiration

  • Cardiovascular instability

  • Upper gastro-intestinal tract surgery

  • Oral surgery (eg. cleft palate) - check with surgeon

  • Patients with increased intracranial pressure

side effects

  • Facial pressure necrosis

  • Eye irritation

  • Delay in definitive treatment (ETT)

  • Difficult transport

  • Risk of aspiration

  • Poor tolerance

  • Poor tracheal toilet 

  • Hypoxemia if disconnected

  • Masks causing increased dead space

requirements

1. NIV compatible ventilator

2. Patient alert & comfortable

3. Adequate respiratory drive

4. Well-fitted interface

5. Absence of contraindications 

6. Skilled / trained staff

Ventilators used for NIV

Bilevel Ventilator

- Single limb circuit

- Passive exhalation port

- Leaks either intentional through passive exhalation port or unintentional in the circuit or at the interface

- Dedicated NIV ventilators allow better patient-ventilator synchrony than ICU ventilators, even with their NIV algorithm engaged

Critical Care Ventilator

-  Separate in- and expiratory limbs

- Active exhalation valve

Traditionally more leak intolerant - improving with newer modes / software

ICU ventilators’ NIV algorithms efficiency is however highly variable among ventilators. 

Interfaces

Choice of interface is a major determinant of NIV success as it significantly affects patient comfort! 

MOUTHPIECE

NASAL MASK

ORO-NASAL MASK

FULL FACE MASK

HELMET

  • The helmet volume is larger than the tidal volume. This leads to CO2 rebreathing depending on the amount of fresh-gas flow potentially increasing the patient's CO2 levels causing an increase in respiratory drive, dyspnea, air hunger, asynchrony and energy expenditure

  • Helmets seem to have the worst synchrony if compared to full-face mask and ETT 

Interfaces

  • Mouthpiece: placed between the patients lips and held in place by lip-seal

  • Nasal mask: covers the nose but not the mouth

  • Oronasal mask: covers the nose and mouth

  • Full-face mask: covers the mouth, nose, and eyes

  • Helmet: covers the whole head and all or part of the neck

Be aware of which interface you use with which ventilator as this potentially creates an interface-ventilator mismatch in which the ventilator does not work optimally because it has been set to work with ​a manufacturer's specific interfaces. A ventilator may let you choose the interface (such as the V60). Make sure you are aware of whether your unit's NIV capable ventilators offer this option! 

When switching to a different mask:

  • Adjust trigger sensitivity

  • Adjust pressure settings

  • Assure absence of rebreathing (gases)

The pressure required to seal the mask to the skin and prevent leaks (mask-face seal pressure) is the difference between the airway pressure and the mask pressure against the face. With mask-face seal pressure > 2 cm H2O the air leaks were negligible and nearly constant, whereas with mask-face seal pressure < 2 cmH2O air leaks became relevant.

Higher mask pressure against the face decreases air leaks, as does decreasing the airway pressure applied by the ventilator. However, if the mask pressure against the face exceeds the skin capillary pressure and therefore impairs tissue perfusion, this can cause skin damage.

Interfaces and Humidification for Noninvasive Mechanical Ventilation, Nava S et al., Respiratory Care Jan 2009, 54 (1) 71-84;

Effect of Interface on Dead Space 

Spontaneous Ventilation

ETT

Oro-Nasal Mask

Dead Space Fraction during NIV

The VD/VT fraction is reduced more in the case of Bilevel and CPAP than pressure-support ventilation.

Bilevel and CPAP have constant pressure throughout the expiratory phase as opposed to pressure support ventilation. This decreases dead space through creating positive pressure during expiration forcing exhaled gas out of the main stream, thus moving the so called "elimination point" nearer to the patient. In other words, the effect of fresh gas flow during expiration is directly related to good flushing of the face mask.

Circuits

SINGLE LIMB

  • Depends on leak port within the set-up

  • The leak port provides the resistance against which the ventilator generates pressure and allows for exhaled gases to escape

  • Can ONLY be used with either vented masks or nasal interfaces to avoid CO2-retention and asphyxia!

  • Does not allow for expiratory tidal  volume or CO2 measurement

DUAL LIMB

  • Closed circuit

  • Encompasses in- and expiratory limb

  • Depends on tight seal 

  • Allows for expiratory tidal volume and CO2 measurements

  • Allows for more sophisticated ventilation modes

Single limb set-ups

Circuit: Single limb

Interface: Nasal Mask

Interface Vented: YES

Leak Port: NO

Comment: Expiration also through mouth

Circuit: Single limb

Interface: Nasal Mask

Interface Vented: NO

Leak Port: YES

Comment: Expiration also through mouth

Circuit: Single limb

Interface: Oro-Nasal Mask

Interface Vented: YES

Leak Port: NO

Circuit: Single limb

Interface: Oro-Nasal Mask

Interface Vented: NO

Leak Port: YES

double limb set-up

Circuit: Double limb

Interface: Oro-Nasal Mask / Full-face mask

Interface Vented: NO

Leak Port: NO

Comment: In- and expiratory limbs have valves to control flow

Initiation

What triggers the initiation of a breath?

- Time

- Flow

- Pressure

- Edi

Limitation

What limits the breath?

- Pressure

Cycling

What cycles from in- to expiration?

 

- Time

- Flow

Assist

Does the ventilator allow for assisted breaths on top of the mandatory breaths?

 

- Yes

- No

Modes of ventilation during NIV

CPAP (COntinuous Positive Airway Pressure)

CPAP + Pressure support

Contact/Suggestions

Juerg Burren, MBBS MD FMH (CH) EPIC FCICM

Paediatric Intensivist and Ventilation Enthusiast

​​

Tel: +61 (0) 481 751 073

info@pivares.com

© 2019-2020 by Juerg Burren for PIVARES

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