Mechanical ventilation

Mechanical ventilationMechanical ventilation

Mech. Ventilation is an Mech. Ventilation is an invasive life support invasive life support procedure .procedure .

The goal is to optimize both The goal is to optimize both gas exchange and clinical gas exchange and clinical status at a minimum FiO2 & status at a minimum FiO2 & ventilator pressures .ventilator pressures .

Indications for respiratory Indications for respiratory support:support:

(1) Relative indications(1) Relative indications:: frequent intermittent apnea frequent intermittent apnea

unresponsive to drug therapy.unresponsive to drug therapy. Early treatment when use of mech. Early treatment when use of mech.

Vent. Is anticipated bec. Of Vent. Is anticipated bec. Of deterioration of bl.gases.deterioration of bl.gases.

Relieving "work of breathing" in an Relieving "work of breathing" in an infant with signs of resp. difficulty.infant with signs of resp. difficulty.

Initiation of exogenous surfactant Initiation of exogenous surfactant therapy in infants with RDS. therapy in infants with RDS.

(2)(2) Absolute Absolute indicationsindications::

prolonged apneaprolonged apnea PaO2 < 50 mm Hg on FiO2PaO2 < 50 mm Hg on FiO2 0.800.80 PaCO2 > 60 mm Hg with persistent PaCO2 > 60 mm Hg with persistent

acidemia (art.PH 7.).acidemia (art.PH 7.). CNS insult with affection of resp.CNS insult with affection of resp. General anaesthesia General anaesthesia

* *Continuous positive air way Continuous positive air way pressur (CPAP)pressur (CPAP)..

Acont. Flow of heated, humidified gas in Acont. Flow of heated, humidified gas in circulated post the infant's airway at a set circulated post the infant's airway at a set pressure of 3-8 cm H2Opressure of 3-8 cm H2O

Maintaining an elevated end – expiratory lung Maintaining an elevated end – expiratory lung volume while the infant breaths spontaneously.volume while the infant breaths spontaneously.

The air oxygen mix. and airway pressure can be The air oxygen mix. and airway pressure can be adjusted.adjusted.

CPAP is usually delivered by means of nasal CPAP is usually delivered by means of nasal pronges or nasopharyngeal tube.pronges or nasopharyngeal tube.

N.B: prolonged ET CPAP is not used bec. The N.B: prolonged ET CPAP is not used bec. The high resistence of the ET tube increases the high resistence of the ET tube increases the work of breathing esp. in small infants.work of breathing esp. in small infants.

Advantages of CPAP:Advantages of CPAP:

Less invasive, less barotrauma.Less invasive, less barotrauma. When used in infants with RDS, When used in infants with RDS,

it can help and prevent alveolar it can help and prevent alveolar and airway collapse, which and airway collapse, which might result in deterioration of might result in deterioration of PO2.PO2.

CPAP decreased frequency of CPAP decreased frequency of obstructive & mixed apnaeic obstructive & mixed apnaeic spells in some infants.spells in some infants.

Disadvantages:Disadvantages: does not improve ventilation & may does not improve ventilation & may

worsen it.worsen it. In adequate resp. support in In adequate resp. support in

cases of severe RDS.cases of severe RDS. Maintaining nasal or nasophary. Maintaining nasal or nasophary.

CPAP in large active infants may CPAP in large active infants may technically be difficult .technically be difficult .

Swallowed air can elevate the Swallowed air can elevate the diaphragm & must be removed diaphragm & must be removed by a gastric tube.by a gastric tube.

Indications of CPAP:-Indications of CPAP:-

Early treatment of mild Early treatment of mild RDS.RDS.

Moderately frequently Moderately frequently apnaeic spells.apnaeic spells.

Weaning chronically Weaning chronically ventilator-dependent ventilator-dependent infantsinfants..

I.M.V:I.M.V:Pressure limited, time cycled, cont. flow Pressure limited, time cycled, cont. flow

ventilator:ventilator: cont. flow of heated & humidified gas cont. flow of heated & humidified gas

is circulated past the infant's air way.is circulated past the infant's air way. The gas is a selected mixture of air The gas is a selected mixture of air

with oxygen.with oxygen. Max. insp. Pressure (PIP) and positive Max. insp. Pressure (PIP) and positive

end exp. Pr. (PEEP) are selected.end exp. Pr. (PEEP) are selected. Resp. timing (rate & duration of insp. Resp. timing (rate & duration of insp.

& exp.) is selected:& exp.) is selected:

Advantages:Advantages:

1.1. the continuous flow of fresh gas allows the continuous flow of fresh gas allows the infants to make spont. resp. efforts the infants to make spont. resp. efforts between vent. breaths. (intermittent between vent. breaths. (intermittent mandatory ventilation (IMV).mandatory ventilation (IMV).

2.2. Good control is maintained over resp. Good control is maintained over resp. pressures.pressures.

3.3. Insp. and exp. Time can be controlled.Insp. and exp. Time can be controlled.

4.4. System is relatively simple & in System is relatively simple & in expensive.expensive.

Disadvantages:Disadvantages:

1.1. Tidal vol. is poorly controlled.Tidal vol. is poorly controlled.2.2. The system does not respond to changes in The system does not respond to changes in

resp.system compliance.resp.system compliance.3.3. The patient can take breaths on his or her The patient can take breaths on his or her

own but the vent. May cycle on during a own but the vent. May cycle on during a patient breath patient breath asynchrony. asynchrony.

4.4. Spont. breathing infants who breath out of Spont. breathing infants who breath out of phase with to many IMV breaths (Bucking' or phase with to many IMV breaths (Bucking' or fighting the ventil). May receive inadequate fighting the ventil). May receive inadequate vent. & are at increased risk for air leak.vent. & are at increased risk for air leak.

Indications: Useful in any form of lung Indications: Useful in any form of lung disease in infants.disease in infants.

SIMV SIMV Synchronized IMVSynchronized IMV Adaptation of conventional Adaptation of conventional

pressure limited ventilator.pressure limited ventilator. These vent. Combine the features These vent. Combine the features

of pressure limited, time cycled. of pressure limited, time cycled. Contin. Flow ventilators with Contin. Flow ventilators with

air way pressureair way pressure

air flow air flow SensorSensor

Or Or resp. movement resp. movement

By measuring insp. Flow or By measuring insp. Flow or movement, these ventilators deliver movement, these ventilators deliver intermittent positive pressure intermittent positive pressure breaths at a fixed rate in synchrony breaths at a fixed rate in synchrony with the baby's inspiratory effort with the baby's inspiratory effort and allows the patient to finish and allows the patient to finish expirat. Before cycling on expirat. Before cycling on (synchronized IMV, or SIMV) :(synchronized IMV, or SIMV) :

During apnea, SIMV ventilators During apnea, SIMV ventilators continue to deliver the set of IMV continue to deliver the set of IMV rate.rate.

Pressure support ventilator Pressure support ventilator (patient triggered (patient triggered ventilation).ventilation). Insp. Effort opens a valve allowing air Insp. Effort opens a valve allowing air

flow at preset +ve pi.flow at preset +ve pi. In patient triggered vent., a +ve pi breath In patient triggered vent., a +ve pi breath

is delivered with every insp. Effort.is delivered with every insp. Effort. Patient determines rate & insp. Time.Patient determines rate & insp. Time. As a result, the ventilator delivers more As a result, the ventilator delivers more

frequent +ve Pi breaths, usually allows frequent +ve Pi breaths, usually allows decrease in PIP needed for adeq. Gas decrease in PIP needed for adeq. Gas exchange.exchange.

During apnea, the vent. In patient During apnea, the vent. In patient triggered mode delivers an operator – triggered mode delivers an operator – selected IMV (control) rate (Assisst – selected IMV (control) rate (Assisst – control) control)

Advantages of SIMV & Advantages of SIMV & PSV :PSV : synchronizing the delivery of +ve pr synchronizing the delivery of +ve pr

breaths with the infant insp. effort breaths with the infant insp. effort reduces the phenomena of breathing out reduces the phenomena of breathing out of phase with IMV breaths (Fighting the of phase with IMV breaths (Fighting the ventilator), this may decreased the need ventilator), this may decreased the need for sedative medications & aid in for sedative medications & aid in weaning mechanically ventilated infants.weaning mechanically ventilated infants.

Pronounced asynchrony with ventilator Pronounced asynchrony with ventilator breaths during conventional IMV has breaths during conventional IMV has been associated with the development of been associated with the development of air leak & IV he.air leak & IV he.

Disadvantages:Disadvantages:

The ventilator may The ventilator may inappropriately trigger a inappropriately trigger a breath bec. Of artifactural breath bec. Of artifactural signal or fail to trigger signal or fail to trigger bec. Of problems with the bec. Of problems with the sensorsensor . .

Indications:Indications:

SIMV & PSV. Can be used SIMV & PSV. Can be used when a conventional pressure when a conventional pressure limited ventilator is indicated.limited ventilator is indicated.

If available, it may be the If available, it may be the preferable mode of ventilator preferable mode of ventilator therapy in infants who are therapy in infants who are breathing spontaneously on breathing spontaneously on IMV.IMV.

Ventilator parameters:Ventilator parameters:

(1) Peak insp. Pressure (PIP):(1) Peak insp. Pressure (PIP): Max. insp. Pressure attained Max. insp. Pressure attained

during the resp. .during the resp. . Main determinant of tidal volume Main determinant of tidal volume

when using pressure control V.when using pressure control V. Set at minimum pressure required Set at minimum pressure required

to achieve chest movement with to achieve chest movement with adequate air entry on adequate air entry on auscultation, in order to reduce auscultation, in order to reduce complication from barotrouma.complication from barotrouma.

(2) Positive end. Exp. Pressure (PEEP):(2) Positive end. Exp. Pressure (PEEP):

air way pressure maintained bet. Insp. air way pressure maintained bet. Insp. & exp. Phases.& exp. Phases.

- Prevent alveolar collapse during - Prevent alveolar collapse during expiration.expiration.

- Decreased work of reinflation.- Decreased work of reinflation. Improve gas exchange.Improve gas exchange. Minimum physiological PEEP is2 Minimum physiological PEEP is2

cmH2OcmH2O Start at level of 4-7 cm H2OStart at level of 4-7 cm H2O PCO2 may rise with increasing PEEP.PCO2 may rise with increasing PEEP.

(3) Rate : Number of mech. Breaths delivered (3) Rate : Number of mech. Breaths delivered per minute (in IMV.) or freq: rate of per minute (in IMV.) or freq: rate of oscillation in HFOV :oscillation in HFOV :

Major effect on minute volume and thus PCO2Major effect on minute volume and thus PCO2 Initial settings may vary from 20-100 Initial settings may vary from 20-100

depending or gestational age & underlying depending or gestational age & underlying diseased.diseased.

(4) Inspired oxygen concentration (FiO2):(4) Inspired oxygen concentration (FiO2): Fraction of O2 present in inspired gas.Fraction of O2 present in inspired gas. Select FiO2 0.05 higher than before ventilation.Select FiO2 0.05 higher than before ventilation. High FiO2 > 60-70 carries risk of lung toxicity.High FiO2 > 60-70 carries risk of lung toxicity. FiO > 80% leads to resorption collapse which FiO > 80% leads to resorption collapse which

may worsen the condition.may worsen the condition.

(5) Inspiratory time (Ti):(5) Inspiratory time (Ti): Length of time spent in the insp. Length of time spent in the insp.

phase of resp. cycle.phase of resp. cycle.

(6) I:E ratio:(6) I:E ratio: Ratio of insp. to exp. Time.Ratio of insp. to exp. Time. Normal ratio 1:1 to 1:3 are used.Normal ratio 1:1 to 1:3 are used. Reversed ratio with prolonged insp. Reversed ratio with prolonged insp.

Time e.g 3:1 result in improved Time e.g 3:1 result in improved oxygenation, but rarely used bec. Of oxygenation, but rarely used bec. Of risk of air leak as result of air risk of air leak as result of air trapping.trapping.

(7) Flow rate :(7) Flow rate :

normal setting of 6-12 L/min.normal setting of 6-12 L/min. start at 5-7L/min & increased to start at 5-7L/min & increased to

achieve higher pressure achieve higher pressure settings – always use minimum settings – always use minimum flow rate to achieve PIP as high flow rate to achieve PIP as high flow increased air way flow increased air way resistance & may overdistend resistance & may overdistend with lung.with lung.

(8) Mean air way pressure (MAP):(8) Mean air way pressure (MAP):

average pressure over entire resp. average pressure over entire resp. cycle.cycle.MAP = MAP = (PIP X Ti) + (PEEP X Te )(PIP X Ti) + (PEEP X Te )

(Ti + TE)(Ti + TE) changes in flow, PEEP, PIP, Ti, VR changes in flow, PEEP, PIP, Ti, VR

will alter MAP.will alter MAP. Correlates directly with oxygenation.Correlates directly with oxygenation. High MAP is associated with High MAP is associated with

increased risk of barotraumas & air increased risk of barotraumas & air leak.leak.

N.B:N.B: Main ventilator determinats for PaO2 are Main ventilator determinats for PaO2 are

FiO2 & MAPFiO2 & MAP - Main ventilator determinats for PCO2 - Main ventilator determinats for PCO2

are PIP & VR.are PIP & VR.

Initial suggested Initial suggested settings:settings:

setting should be altered to obtain setting should be altered to obtain synchrony of the infants resp. effort with synchrony of the infants resp. effort with ventilator by : decrease Ti , increased ventilator by : decrease Ti , increased rate.rate.

If this fails, ms relaxation may be used If this fails, ms relaxation may be used (rarely used for babies < 1000 gm).(rarely used for babies < 1000 gm).

Table 9.3. Suggested initial Table 9.3. Suggested initial

ventilator settingsventilator settings Infant with

normal lungs

RDS infant< 2000 g

RDS infant > 2000 g

FIO2As indicated by oximetry

As indicated by oximetry

As indicated by oximetry

PIP (cdmH2O)14-1818-2520-30

PEEP (cmH2O)2-33-53-6

Rate (bpm)15-2560-10040-60

Inspiratory time (Ti) (S)

0.4=0.50.3-0.50.4-0.6

Monitoring during mechanical Monitoring during mechanical ventilation:ventilation: ABC should be checked within 20 min of ABC should be checked within 20 min of

starting mech. Ventilation.starting mech. Ventilation. Ventilator settings adjusted to obtain Ventilator settings adjusted to obtain

satisfactory bl. Gases satisfactory bl. Gases Aim:Aim: Pa CO2Pa CO2 35-45 mmHg35-45 mmHgPa O2Pa O2 53-75 mmHg53-75 mmHgPH > 7.25PH > 7.25

Repeat bl. Gases with in 30 min. of Repeat bl. Gases with in 30 min. of alterations of ventilator setting.alterations of ventilator setting.

Where ventilation is stable, check bl. Where ventilation is stable, check bl. Gases at a minimum of 4 hr interval.Gases at a minimum of 4 hr interval.

Oxygenation should be monitored Oxygenation should be monitored continuously with pulse oxy.. continuously with pulse oxy..

How ventilator changes affect How ventilator changes affect

blood gasesblood gases

(A) Oxygenation:(A) Oxygenation:

(1) FIO2 : increasing the FiO2 (1) FIO2 : increasing the FiO2 is the simplest & most direct is the simplest & most direct means of improving means of improving oxygenation.oxygenation.

In preterm infants, the risk of In preterm infants, the risk of retinopathy & pulmonary toxicity retinopathy & pulmonary toxicity are present.are present.

(2) MAP : increased by :(2) MAP : increased by : PEEP , PIP, Ti, R, flow RPEEP , PIP, Ti, R, flow R All these changes lead to higher PO2, All these changes lead to higher PO2,

but each has different effect on PCO2..but each has different effect on PCO2.. Optimum MAP results from a balance Optimum MAP results from a balance

between optimizing PO2, minimizing between optimizing PO2, minimizing direct O2 toxicity, minimizing direct O2 toxicity, minimizing barotraumas adeq. Ventil.barotraumas adeq. Ventil.

MAP as low as (5) may be sufficient in MAP as low as (5) may be sufficient in infants with normal lung.infants with normal lung.

Where as (20) cm H2O may be Where as (20) cm H2O may be necessary in severe RDS. necessary in severe RDS.

Excessive MAP may impede V.R. & Excessive MAP may impede V.R. & adversely affect C.O.P.adversely affect C.O.P.

(B) Ventilation(B) Ventilation CO2 elimination depends on minute ventilation.CO2 elimination depends on minute ventilation. Since M. vent. Is the product of R.R. & T.V., Since M. vent. Is the product of R.R. & T.V.,

increased in ventilatory rate will lower PCO2.increased in ventilatory rate will lower PCO2. Increased tidal vol. can be achieved by Increased tidal vol. can be achieved by

increased PIP.increased PIP. Decreased PEEP will also improve ventilation.Decreased PEEP will also improve ventilation. Optimal PCO2 varies according to disease state.Optimal PCO2 varies according to disease state.

* For very immature infants or infants with air * For very immature infants or infants with air leak PCO2 leak PCO2 50-60 may be tolerated to minimize barotrauma 50-60 may be tolerated to minimize barotrauma provided PH > 7.25.provided PH > 7.25.* When hyperventilation is used to reduce * When hyperventilation is used to reduce pulmonary resist. PCO2 as low as 30 mmHg pulmonary resist. PCO2 as low as 30 mmHg may bemay be required. required.

Complications of Mech. Complications of Mech. VentilationVentilation

AC complicationsAC complications -: -:

1-1- Tube problems:- Tube problems:- trauma to nose, palate, larynx trauma to nose, palate, larynx trachea.trachea.Infection.Infection.Displacement, blockage, kinking.Displacement, blockage, kinking.

2-2- Circuit tubing problems: gas leak, Circuit tubing problems: gas leak, water obst. Or inhalation, kinking.water obst. Or inhalation, kinking.

3-3- Humidi fier: gas leakes, overheating, Humidi fier: gas leakes, overheating, infection, esp. pseudomon.infection, esp. pseudomon.

4-4- Gas supply: Failure, air / oxygen mix. Gas supply: Failure, air / oxygen mix.5- 5- Ventilator failure: raised pressure Ventilator failure: raised pressure

pneumoth. Interstial emphysema.pneumoth. Interstial emphysema.

CH. Complication:-CH. Complication:-Airway:Airway:* Trauma with deformities of nose.* Trauma with deformities of nose.

* Subglottic stenosis.* Subglottic stenosis.

* Tracheal ulceration.* Tracheal ulceration.

* Palatal groove.* Palatal groove.

LungsLungs : - broncho pulm. : - broncho pulm. Dysplasia.Dysplasia.

- post extubation collapsed. - post extubation collapsed.

Main causes of sudden deterioration Main causes of sudden deterioration Mech.Mech. Ventilator: Ventilator: Mech. Failure.Mech. Failure. Tube blockage or displacement.Tube blockage or displacement. Preumothorax.Preumothorax. Perivent ricular hge.Perivent ricular hge.

Check ventilator is working, Check ventilator is working, disconnect, and manually ventilate disconnect, and manually ventilate infant.infant.

If improvement occurs mech failure If improvement occurs mech failure is likely.is likely.

If no improvement assess potency of If no improvement assess potency of tube & exclude pneumo thorax.tube & exclude pneumo thorax.

Causes of gradual Causes of gradual eleterioration:eleterioration:Infection Infection

- PDA - PDA - slowly progressive interstitial emphysema.- slowly progressive interstitial emphysema.

Weaning from ventilation:Weaning from ventilation: This is as important as ventilation therapy itself since This is as important as ventilation therapy itself since

the condition of the baby may be worsen by poor the condition of the baby may be worsen by poor weaning.weaning.

It is made easier by use of intermittent mandatory It is made easier by use of intermittent mandatory ventilator (IMV).ventilator (IMV).

This allows ventilatory R. to be reduced & the infant to This allows ventilatory R. to be reduced & the infant to breath between each mech. Vent.breath between each mech. Vent.

SIMU more valuable in weaning from ventilator >SIMU more valuable in weaning from ventilator >Indication::- Bl. Gases : Indication::- Bl. Gases : PCO2 < 50PCO2 < 50

PH > 7.3PH > 7.3PO2 > 53PO2 > 53

Ventilator:Ventilator: FiO < 0.5FiO < 0.5PIP < 25 cmH2OPIP < 25 cmH2O

Technique:Technique:1.1. before weaning ensure ms. Relaxant before weaning ensure ms. Relaxant

have been discontinued, sedation have been discontinued, sedation reduced & max. coloric in take reduced & max. coloric in take obtained.obtained.

2.2. When start weaning, make small When start weaning, make small changes. Readucing PIP 1st by 1-2 changes. Readucing PIP 1st by 1-2 cmH2OcmH2O

3.3. Reduce insp. O2 content by 5% at Reduce insp. O2 content by 5% at time & VR by 5 breath / min at a time & VR by 5 breath / min at a time.time.

N.B:N.B:

When lowering V.R, remember to When lowering V.R, remember to adjust IE ratio so that, Ti remains to about adjust IE ratio so that, Ti remains to about 0.4 – 0.5 Sec.0.4 – 0.5 Sec.

1-1- Check bl. Gases with in 60 min of each Check bl. Gases with in 60 min of each change to ensure that pa CO2 is not rising.change to ensure that pa CO2 is not rising.

3-3- Endotracheal CPAP can be employed Endotracheal CPAP can be employed when :when :

PIP < 15 , FIO2 < 40, VR < 10 PIP < 15 , FIO2 < 40, VR < 10

3-3- Give resp. stimulants such as Give resp. stimulants such as aminophylline or caffeine during weaning aminophylline or caffeine during weaning to improve chance of successful extubationto improve chance of successful extubation

Extubation:Extubation: usually attempted only after a successful usually attempted only after a successful

period of hrs. on endotracheal CBAB.period of hrs. on endotracheal CBAB. An exception to this rule is the very An exception to this rule is the very

immature infant who has been ventilated immature infant who has been ventilated through 2.5 cm tube, since breathing is through 2.5 cm tube, since breathing is difficult due to high resistance in this difficult due to high resistance in this narrow tube.narrow tube.

A very immature infants may be A very immature infants may be successfully extubated when they have successfully extubated when they have tolerate IMV of 10 breaths/min.tolerate IMV of 10 breaths/min.

Technique:Technique:1.1. Avoid feeding infant before extubation or Avoid feeding infant before extubation or

empty stomach to prevent vomiting.empty stomach to prevent vomiting.2.2. Suction nasoph. Well.Suction nasoph. Well.3.3. Remove tube on inflation to achieve adeq. Remove tube on inflation to achieve adeq.

Inflation & prevent post extubation collapse.Inflation & prevent post extubation collapse.4.4. Place infant on well humidified O2 hood with Place infant on well humidified O2 hood with

FiO2 concent. The same as before FiO2 concent. The same as before extubation.extubation.If this infant less than 1500 gm place on If this infant less than 1500 gm place on nasal pronge CPAP to decreased incidence of nasal pronge CPAP to decreased incidence of collapse.collapse.

5-5- ABG 30 min after extubation. ABG 30 min after extubation.6-6- X-ray chest 4 hr later to look for collapse if X-ray chest 4 hr later to look for collapse if

FiO2 .FiO2 .7-7- Physiotherapy & gentle suctioning of u. air Physiotherapy & gentle suctioning of u. air

way are helpful.way are helpful.

Table 6-3. CAUSES OF WEANING Table 6-3. CAUSES OF WEANING

FAILUREFAILURE Slow resolution of

underlying disease.Inspiratory muscle

loadingPersistent atelectasisAsynchrony with ventilator

Pulmonary edemaMuscle injury or disease

Lower airway obstructionPphrenic nerve injury.

Ineffective ventilationIncreased work of breathing

- Decreased ventilatory driveAbdominal distension

SedationLower airway obstruction

Brainstem dysfunctionCirculatory failure

Metabolic alkalosisFever

- Vgentilator pump failureMetabolic acidosis

Muscle weaknessOther system diseaseProlonged paralysisCirculatory failure.MalnutritionMultiple organ system

failureFatigue from excessive work