MECHANICAL VENTILATION IN PEDIATRICS

PRESENTED BY DR.MAYSA ABDULHAQModerator DR.NADWA AL-ZOHLOF

Contents

Basics of ventilators/ control pattern and modes.

Indications /aims . Initial settings/adjusting of ventilator settings Problems during ventilation and

complications Weaning stratigies

The Basics of Mechanical Ventilation

Depending on connecting prosthesis, mechanical ventilation is defined:

non-invasive ventilation when inferior airways are not invaded to introduce external gases into lungs. Prostheses largely used are nasal and facial masks to perform non-invasive.

invasive ventilation when tracheal intubation or tracheostomy are used to connect patient to ventilator.

There are two ways to give a breath

Volume Controlled Pressure Controlled

Ventilator’s Modes& control variables Control Variables The control variables\independent variables,

determined by the clinicians and include pressure, flow, or volume.

must overcome the elastic and resistive forces to allow gas delivery to the patient.

During expiration, the elastic and resistive elements of the respiratory system are passive, and expiratory waveforms are not directly affected by the modes of ventilation or the controller.

volume controller

When the clinician presets a volume pattern, it operates as a volume controller: Volume is an independent variable and pressure is a dependent variable. pressure then varies with compliance. Expiration is passive, and the expiratory profile is not directly affected by the mode of ventilation but rather by compliance and resistance

Volume Control The patient is given a specific volume of air during

inspiration.

The PIP observed is a product of the lung compliance, airway resistance and flow rate. The ventilator does not react to the PIP unless the alarm limits are violated.

The PIP tends to be higher than during pressure control ventilation to deliver the same volume of air.

Volume Controlled

What do you set?

You set:Tidal volume

Peak flowRateFiO2PEEP

Volum Control Ventilation

Controlling pH and pCO2 is done by controlling minute ventilation. You can set both the respiratory rate and the tidal volume.

Controlling pO2 you can adjust the FiO2, the PEEP and, indirectly, the PIP by adjusting the tidal volume (bigger TV yields bigger Pmax) although we don’t do this so much in practice

Pressure Controller

when the clinician presets the pressure pattern, the ventilator operates as a pressure controller: Pressure is the independent variable, and volume is the dependent variable determined by the level of pressure.and is the function of lung compliance and airways resistance.

Pressure Control

The pressure is constant throughout inspiration. The ventilator adjusts the flow to maintain the pressure. Flow decreases throughout the inspiratory cycle.

Volume delivered depends upon the inspiratory pressure, I-time, pulmonary compliance and airway resistance.

The delivered volume can vary from breath-to-breath depending upon the above factors. MV not assured.

Good mode to use if patient has large air leak, because the ventilator will increase the flow to compensate it.

You set:Pressure

limitTime spent in

inspiration (Itime)Rate

You set:FiO2PEEP

Pressure Controlled

What do you set in PC?

Pressure Control Ventilation

Controlling the pH and pCO2 is done by controlling the minute ventilation. You can set the RR, but the TV is managed indirectly.

Controlling the pO2, again you can adjust the FiO2 and the PEEP, in addition you control the PIP.

Volume vs. Pressure

Modes of Ventilation

the mode of ventilation is a description of the way a mechanical breath is delivered.

In general we are trying to accomplish one of two things for a patient using mechanical ventilation: either to control their ventilation and oxygenation, which they are unable to do, or to support them as they wean from ventilatory support. Hence, we can look at ventilator modes as either Control Modes, or Support Modes.

Modes of Ventilation

Mechanical ventilation can be applied both invasively or non-invasively in the following ways:

Controlled mechanical ventilation: Pressure controlled Ventilation PC, Volume Controlled Ventilation VC, , Pressure Regulated Volume     Controlled Ventilation PRVC , High Frequency Ventilation ,CMV and IMV.(which are rarely , if ever, used today),

Supported spontaneous breathing: Pressure Support Ventilation and     Volume Support Ventilation

Mixed respiratory support: (SIMV)Synchronized Intermittent Mandatory Ventilation .SIMV/PS

Assisted spontaneous breathing: Continuous Positive Airway Pressure (CPAP

AC (assist control) or VC (Volume Control)

Characteristics: preset rate and tidal volume (sometimes PIP), full mechanical breath is delivered either triggered by patient’s respiratory efforts, or –if not sufficient- the preset mechanical rate is maintained automatically.

Uses: for patients who have a very weak respiratory effort, allows synchrony with the patient but maximal support. Not a weaning mode, as at any rate they are getting complete mechanical support.

Advantages: a fairly comfortable mode, providing a lot of support.

Disadvantages: can lead to hyperventilation if not closely monitored, not able to wean in this mode.

Patient efforts recognized by ventilator

Assist Control (A/C)

Characteristics: a volume control assist control mode, In this mode, a target minute ventilation is set.

The ventilator will adjust the flow to deliver the volume without exceeding a target inspiratory pressure.

Uses: in patients with high airway pressures, although it can be used in any patient.

Contraindications: none in particular Advantages: No change in minute ventilation if pulmonary

conditions change. The desired TV can be guaranteed at the lowest PIP necessary to achieve it thus minimizing the barotrauma. Disadvantages: new, Hard to use on a spontaneously breathing patient or one with a large air leak. Not a “weaning” mode.

PRVC (Pressure Regulated Volume Control)

IMV (Intermittent Mandatory Ventilation)

Characteristics: set breath delivered at a fixed interval. No patient interaction, but allow the patient to breath through the ventilator circuit by providing gas flow( unlike CMV). pressure or volume control,

Contraindications: none really, unfriendly to older patients Advantages: regular guaranteed breath

Disadvantages: does not allow patient to breath with the ventilator except by chance..Does not work with the patient

Intermittent Mandatory Ventilation (IMV)

Ventilator lets patient breathe spontaneously BUT does not change its

plan of ventilation.

PS /Pressure Support

Characteristics: supports each spontaneous breath with supplemental flow to achieve a preset pressure.

1. All the breaths are triggered by the patient2. Prest value : PIP, PEEP, FiO2.3. the patint determine: rate, Ti, I:E ratio, TVi.4. Needs intact resp. drive.

Uses: In the spontaneously breathing patient this helps overcome the airway resistance of the endotracheal tube. Can be very helpful for weaning.

Contraindications: patient who is not spontaneously breathing, i.e. on muscle relaxants

Advantages: helps overcome resistance of tube, making spontaneous breathing easier

VS/Volume Support

Characteristics: variable level of pressure support is delivered on each spontaneous patient-triggered breath in order to achieve preset tidal volume.

All breaths are triggered by the patient. The clinician pre set: iTV, FiO2, PEEP, The patient determine the RR, Ti, I:E ratio. Uses: a weaning mode. The concept is that as the patient becomes

stronger, or more awake they will make more respiratory effort on their own. The more effort they make the less support they will need from the ventilator and hence the level of pressure delivered will get smaller.

Contraindications: patient who is not spontaneously breathing, as there is no back-up rate.

Advantages: greatly decreases the number of interventions needed to wean patient from a ventilator versus traditional weaning

Weaning by Support Ventilation

Ventilators workof breathing

Weaning by Support Ventilation

Ventilators work ofbreathing

Weaning by Support Ventilation

Ventilators workof breathing

The following modes fall into both Control and Support categories in that they have set rates, but the spontaneous breaths are not controlled, so they can be used in weaning.

SIMV (Synchronous IMV)

Characteristics: Derived from Intermittent mandatory ventilation (IMV)Preset mechanical breath delivered within an interval based on the preset respiratory

rate. Ventilator spends part of the interval waiting for spontaneous breath from the patient, which it will use as a trigger to deliver a full breath. If not sensed it will automatically give a breath at the end of the period. Any other breaths during the cycle are not supplemented.

Patient does ALL work of breathing on the spontaneous breaths.Plus some work on the SIMV breaths. (Tries to synchronize to patient’s efforts)

TV on the spontaneous breaths depends entirely upon patient effort and lung mechanicsCan be pressure or volume controlled

Uses: commonly used in many settings. Can be a weaning mode (see also with PS) Contraindications: none in particular Advantages: allows work with the patient, somewhat more friendly. Disadvantages: Any other breaths during the cycle are not supplemented/ not good for

fighting patients.

SIMV

SIMV divides Tb into Mandatory periods (Tm) and Spontaneous periods (Ts)

SIMV

If patient tries to breathe during Tm, the ventilator gives a FULLY ASSISTED BREATH

SIMV

If patient tries to breathe during Ts, the ventilator allows the patient to take the breath.

Assistance may or may not be provided with PRESSURE SUPPORT (coming soon)

Triggering the Ventilator

SIMV/PS

Characteristics: combination of the previous two modes. Extra breaths in the cycle are supplemented with pressure support.

Uses: useful in most circumstances, including weaning. Contraindications: none in particular. Advantages: allows both synchrony with the patient and help in

overcoming the resistance in the endotracheal tube, to allow easier spontaneous breathing

Disadvantages: none in particular. PS does not add anything in the patient who is not spontaneously breathing.

Assisted Spontaneous Breathing Continuous Positive Airway

Pressure :CPAP is a mode of ventilation, the pressure above the atmospheric pressure maintained throught out the resp. cycle during spontaneous breathing, thus pressure in the airway is always positive

CPAP

This method presents several advantages because of:

increased lung volume and FRC and improve in ventilation/perfusion ratio.

preventing and resolving atelectasis. reduced work of breathing and prevention of

muscle fatigue . Applied by invasive and noninvasive methods

CPAP is not advisable in

high risk patients. severe respiratory effort to maintain ventilation

any patient without spontaneous respiratory effort.

Not a good idea in a patient with obstructive pulmonary disease (like asthma).

hypercapnia

CPAP is indicated in:

for patients with upper airway soft tissue obstruction

or tendency for airway collapse. As a final mode prior to extubation in some

patients.

CPAP

This is very similar to PEEP, except that the inspiratory pressure is also maintained at the CPAP level, leading to support on inspiration and resistance on exhalation.

So what is PEEP?PEEP is the residual pressure above atmospheric pressure maintained at end of expiration.

PEEP can be added to any mode of mechanical ventilation

A/C – PC or VCSIMV – PC or VC

PEEP

Good…. Recruits Alveoli FRC Redistributes

Pulmonary Edema Fluid

intrapulmonary shunt

PaO2

Bad…. ’d Venous Return /

C.O. May ICP,/ intensify

cerebral ischemia Overdestention/’s

Risk of Barotrauma May impair

oxygenation????

Figure 6 - Tracheo-bronchial distention due to PEEP application leads to a progressive recruitment of alveoli. On the left, 2 PEEP;

on the right, 10 cm H2O PEEP.

What is “Auto-Peep?”

FLOW

INSP

EXP

Expiratory flow ends before next breath

Next breath begins before

exhalation ends

Obstructive lung disease (pursed lip)

Rapid breathing (breath stacking)

Forced exhalation (anxiety)

Conditions associated with auto-PEEP

Patients with obstructive lung disease( sever Asthma)

Kinked or obstructed ETT with secretions. In adequate Te in mechanically ventilated

patients

Signs of air trapping (auto-PEEP):

Over expansion of the chest Decreased chest wall expansion. CO2 retention. Cardiovascular dysfunction.

Ventilator settings in auto-PEEP:

Low or Zero PEEP Long Te( as possiple) Low RR

Relieve underlying causes( bronchospasm, secretions, position of ETT)

Who needs a ventilator?

“If you don't know where you are going, you might wind up someplace else.”

Try to figure out ‘why’ the patient is requiring intubation.

Who needs a ventilator?

Can’t oxygenate (low PaO2/SPO2) Can’t ventilate (high PaCO2) Can’t participate or protect airway (low GCS) If you’re not sure whether or not the patient needs a

ventilator, the patient needs a ventilator.

Assessment of the need for mechanical ventilation Symptoms Dyspnea

OrthopneaIncreased cough or wheezeSomnolence

Signs Stridor

TachypneaUse of accessory muscles of respirationRetractionsProlonged expiratory phaseParadoxical abdominal motion on inspirationCyanosis

Laboratory tests Arterial blood gas measurement

Pulse oximetric studiesChest radiographMeasurements of pulmonary mechanics

Aims of mechanical ventilation

Always remember assisted ventilation is a supporitive technique; it’s NOT a curative

Aims of mechanical ventilation

Provide ventilation( CO2 removal) Optimal systemic oxygenation Decrease the work of breathing

Ventilator Settings

There is no optimum mode of ventilation for any disease state optimum method of weaning patients from mechanical ventilation.

Mechanical ventilation is associated with a number of diverse consequences include volutrauma, barotrauma, oxygen toxicity.

To Minimize side effects, the physiologic targets need not to be in normal range.

Initial Ventilator Settings Rate: 20-24 for infants and preschoolers

16-20 for grade school kids 12-16 for

adolescents TV: 10 -15ml/kg PEEP: 3-5cm H2O

FiO2: 100% I-time: 0.7 sec for higher rates, 1sec for lower

rates PIP (for pressure control): about 24cm H2O.

Adjusting The Ventilator

Obtaining a blood gas early after intubation (15-20 minutes after being on the ventilator) will help you decide if you are moving in the right direction.

It’s better to accept a certain degree of resp. acidosis and possibly even hypoxemia to avoid ventilator induced lung injury. (pemisive haypercapnia and relative hypoxia)

It may be better to risk O2 toxicity than to use high pressure.

Adjusting The Ventilator

pCO2 too high

pCO2 too low

pO2 too high

pO2 too low PIP too high

pCO2 Too High

Patient’s minute ventilation is too low. Increase rate or TV or both. If using PC ventilation, increase PIP. If PIP too high, increase the rate instead. If air-trapping is occurring, decrease the rate

and the I-time and increase the TV to allow complete exhalation.

Sometimes, you have to live with the high pCO2, so use bicarbonate to increase the pH to >7.20.

pCO2 Too Low

Minute ventilation is too high. Lower either the rate or TV. Don’t need to lower the TV if the PIP is <20. TV needs to be 8ml/kg or higher to prevent

progressive atelectasis If patient is spontaneously breathing, consider

lowering the pressure support if spontaneous TV >7ml/kg.

pO2 Too High

Decrease the FiO2.

When FiO2 is less than 40%, decrease the PEEP to 3-5 cm H2O.

Wean the PEEP no faster than about 1 every 8-12 hours. Sudden decease in PEEP may lead to precipitous decrease in oxygenation and FRC.

While patient is on ventilator, don’t wean FiO2 to <25% to give the patient a margin of safety in case the ventilator quits.

pO2 Too Low Increase either the FiO2 or the mean airway

pressure (MAP). Try to avoid FiO2 >70%. Increasing the PEEP is the most efficient way

of increasing the MAP in the PICU. Can also increase the I-time to increase the

MAP (PC). Can increase the PIP in Pressure Control to

increase the MAP, May need to increase the PEEP to over 10,

but try to stay <15 if possible.

PIP Too High

Decrease the PIP (PC) or the TV (VC). Increase the I-time (VC). Change to another mode of ventilation.

Generally, pressure control achieves the same TV at a lower PIP than volume control.

If the high PIP is due to high airway resistance, generally the lung is protected from barotrauma unless air-trapping occurs.

Permissive Haypercapnia and Relative Hypoxia(

Attempts to maintain normal values during treatement of acute lung injury expose airways to ventilator-induced lung injury:

Barotrauma Volutrauma Oxygen toxicity

Permissive Haypercapnia and Relative Hypoxia(

So permissive haypercapnia and relative hypoxia are treatment strategies to prevent the development of ventilator-induced injury.

Used in the acute or recovery phase of acute lung injury or ARDS

Allows for respiratory acidosis with metabolic compensation

Progressinve increase in PaCO2 to 60-100 and may be higher.

Rate of development of hypercapnia is 5-10mmHg/hr will allow renal compensation. But rapid increase in PCO must be avoided.

Permissive Haypercapnia and Relative Hypoxia(

To avoid oxygen toxicity: Keep FiO2 < 50% Maintain low PaO2 near 50 mm Hg with fairly adequate O2sat > 85%

The tow strategies may be used separately to or together depending on the clinical

conditions.

Contraindications for permissive hypercapnia and hypoxia:

Suspected intracranial hypertention Cerebrovasculer disease Cardiac arrhythmias Sever pulmonary hypertension Sever systemic hypertension Sever cardiac failure Sickle cell disease

Indication for permissive hypercapnia and hypoxia:

Acute lung injury or ARDS. Weaning from mechanical ventilator. Patients with air leak syndrom Status asthmaticus in resp. failure. Post operative recovery.

Inverse ratio ventilation

The clinician must increase the Ti to greater than Te for I:E ratio more than.1:1

Benefit in refractory hypoximic ARDS that not responding to other strategies.

Can be used in both volume and pressure control ventilation, but volume control is not preferred

Effects of inverse ratio:

This maneuver will recruits the alveoli by: 1-Prolonged time constant will increase the

mean airway pressure. 2- increasing the Te will increase the Paw

by causing auto-PEEP.

Alveolar recruitment will improve V/Q and enable the clinician to decrease PIP, PEEP, and FiO2

During inverse ratio:

Provide adequate sedation and neuromuscular blockade

Small tidal volum 5-8 ml/kg PIP < 35 mmHg PEEP< 10 cm H2O

Side effects: decrease cardiac out put/ may need pulmonary art.

catheter for close haemodynamic monitring . Increase risk of barotrauma and volutrauma

Complications of Mechanical Ventilation

Pulmonary Barotrauma Ventilator-induced lung

injury Nosocomial pneumonia Tracheal stenosis Tracheomalacia Pneumothorax

Cardiac Myocardial ischemia Reduced cardiac output

Gastrointestinal Ileus Hemorrhage Pneumoperiteneum

Renal Fluid retention

Nutritional Malnutrition

Acute Deterioration

DIFFERENTIAL DIAGNOSES Pneumothorax Pneumonia Malposition of the ETT Pulmonary edema Airway occlusion Ventilator malfunction Mucus plugging Air leak

Physical Exam

Tracheal shift Pneumothorax

Wheezing Bronchospasm Mucus plugging Pulmonary edema Pulmonary

thromboembolism

Asymmetric breath sounds Pneumothorax Mainstem intubation Mucus plugging with

atelectasis Decreased breath

sounds bilaterally Tube occlusion Ventilator malfunction

Weaning from Mechanical Ventilation Weaning from mechanical ventilatory support

has traditionally been a mix of science and art

It requires waiting until the disease process that caused the patient to need assisted ventilation reverses and then successfully decreasing ventilator support to a level that allows for extubation.

Weaning Priorities

Wean PIP to <35cm H2O

Wean FiO2 to <60% Wean I-time to <50% Wean PEEP to <8cm H2O

Wean FiO2 to <40% Wean PEEP, PIP, I-time, and rate towards

extubation settings. Can consider changing to volume control

ventilation when PIP <35cm H2O.

Extubation Criteria

Neurologic Cardiovascular Pulmonary

Neurologic

Level of sedation should be low enough that the patient doesn’t become apneic once the ETT is removed.

No apnea on the ventilator. Patient must be able to protect his airway,

e.g, have cough, gag, and swallow reflexes. Must be strong enough to generate a

spontaneous TV of 5-7ml/kg Being able to follow commands is preferred.

Cardiovascular

Patient must be able to increase cardiac output to meet demands of work of breathing.

Patient should have evidence of adequate cardiac output without being on significant inotropic support.

Patient must be hemodynamically stable. includes good perfusion ,age-appropriate blood pressure.

Pulmonary Patient should have a patent airway. Pulmonary compliance and resistance should

be near normal. Patient should have normal blood gas and

work-of-breathing on the following settings:

CPAP/PS for 1hr for older children and adolescents FiO2 <40%

PEEP 3-5cm H2O Spontaneous TV of 5-7ml/kg