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Dr.Wahid Helmypediatric consultant.

Basics of Mechanical Ventilation in Neonates

Ventilator care requires a team effort. Everyone involved has to get along

and trust one another!

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Prevention of alveolar collapse ◘Functional residual capacty (FRC).

◘Surfactant.

◘ Elatic-recoil ( compliance).

◘Intrapleural pressure(-4mmHg) during inspiration and (+4mmHg) during inspiration.

◘If surfactant is absent , Intrapleural pressure negativity may be increased up to (-20mmHg) .

What is it?

Pulmonary Mechanics

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1)Tidal Volume (Vt)

◘ (Vt) = 6-10 mL/kg/Breath.

◘ RR is usually 30-60 BPM.

2) minute volume

= (Vt- Dead space)x RR.↑ (PIP)→↑ Tidal Volume →↑ minute volume .

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3 (Compliance = 0.004 L/cmH2O.

= Change in volume (mL) = 0.004 L/cmH2O.

Change in pressure(cmH2O)

4(Resistance = 30cm H2O/L/sec

Change in pressure (cmH2O) = 30cm H2O/L/sec

Change in flow (L/sec)

NB., Resistance X Compliance Resistance X Compliance = 1Time constant 1Time constant

1Time constant 1Time constant = 0.004 L/cmH2O. X 30cm H2O/L/sec =12

4)one Time constant = Resistance X Compliance

◘ one time constant → 63% equilibration of pressure inside & outside the alveoli.

◘ we need 3 time constant →97% equilibration of pressure inside & outside the alveoli.

• If resistance =30cm H2O/L/sec • compliance = 0.004 L/cmH2O.• One time constant =30 X 0.004 = 0.12 seconds.• We need 3time constant to inflate and deflate the lung

(3 X 0.12 seconds = 0.36 seconds=Ti ).• as aresult Te= 2 or 3 X 0.36seconds.• So I/E ratio = 1:2 or 1:3 .

Types of Mechanical Ventilators

Types of Mechanical Ventilators

• Volumev- cycled ventilators. المعرفة لمجرد• Pressure ventilators . المعرفة لمجرد• Pressure-limited, time-cycled, continuous-flow Pressure-limited, time-cycled, continuous-flow

ventilators .ventilators . جدا جدا هام هام

• Patient–triggered ventilators (PTV).Patient–triggered ventilators (PTV). جدا جدا هام هام

What is it?

Pressure-limited, time-cycled, continuous-flow ventilators Ventilators• You select (PIP)→ (pressure-limited).

• You select inspiratory time → (time-cycled).

• (Continuous flow) →Fresh heated humidified gas is delivered to the patient throughout the respiratory cycle.

Parameters of mechanical ventilation

)PIP (minus(PEEP)

• (PIP) → The maximum pressure reached during inspiration. If PIP is too low → low VT. If PIP too high → high VT → Hyperinflation and air leak → Impedance مقاومة of venous return.

• (Optimum (PEEP) is 4-6 cmH2O).• High PEEP >8 cmH2O .,→

–Reduces gradient between PIP & PEEP→ (↓ VT) .–Decreases venous return .–Increases pulmonary air leaks .

–Produces CO2 retention .

)FiO2( • why Increase in FiO2 improves oxygenation ?

↑ oxygen tension inside the alveoli→ ↑ r diffusion gradient → good oxygenation.

• Why Oxygen and Paw balance is essentiaL ? to minimize lung damage.

• Why Paw should be ↓ before a very low FiO2 is reached During weaning. to avoid a high incidence of air leak is observed.

RR, secrets• ↑ RR → ↑ (CO2 wash).

• RR(60 BPM) allows for PIP reduction in PIP → ↓ incidence of pneumothorax with about 50% .

• Most neonates have short time constants so they can tolerate (RR60-70 Bpm) and short (Te) without marked gas trapping .

• RR Determinesيحدد minute ventilation(RR×VT),thusCO2 elimination.

Minute alveolar ventilationMinute alveolar ventilation

Minute alveolar ventilationMinute alveolar ventilation

= (Tidal volume – Dead space) X Frequency.= (Tidal volume – Dead space) X Frequency.

• Tidal volume,is determined mainly with Tidal volume,is determined mainly with pressure gradient betweenpressure gradient between inspiration and inspiration and expiration expiration i.e. (PIP) minus (PEEP).

Ti and Te

● Depends on the pulmonary mechanics: – Compliance .– Resistance .–Time constant.

●(Ti)is .3 - . 5 seconds for LBW

and .5 - .6 seconds for larger infants

I:E ratio

● It should NOT be reversed

● I:E ratio should NOT be less than 1:1.2

mean airway pressure

• MAP + FiO2 → determines oxygenation.why?• An ↑ in PIP and PEEP→ ↑ MAP → ↑ oxygenation more than ↑ in the

I:E ratio.

• NB., ↑ ↑ ↑ Paw →alveolar over distension with right to left shunt.

Flow

Flow rates of 6-10 liter/min are usually sufficient.

Modes of venilation

Who is the Commander?

A)A) Non-triggeredNon-triggered Modes.Modes.

1.Controlled Mandatory Ventilation (CMV) or IPPV: – IPPV (intermittent positive pressure ventilation ).

–Ventilator rate is set > infant's spontaneous.

– RR (usually 50-80 breaths/min).

2.Intermittent Mandatory Ventilation (IMV):– Ventilator rate is set < infant's spontaneous breaths.

– RR (<30 breaths/min).

– spontaneous breaths above the set rate are not assisted.

B)B) Patient–Triggered Ventilators (PTV)

• Modification of conventional ventilation ( IMV or IPPV) by adding synchorinization (S).

• ASensor detect the Inspiratory efforts of the baby by so triggering ( the ventilator setting.

• the patient is able to initiate (trigger) ventilator breaths.

Assist Control Mode (A/C) or sippvAssist Control Mode (A/C) or sippv All breath initiated by patient is triggered= All breath initiated by patient is triggered=

Assist.Assist. Back up rate = ippv = ControL MV.Back up rate = ippv = ControL MV. If apnea occur at any time baby will be If apnea occur at any time baby will be

ventilated.ventilated.

Synchronized Intermttent Mandatory Synchronized Intermttent Mandatory Ventilation (SIMV):Ventilation (SIMV): Preset rate that is triggered, Preset rate that is triggered, other patient breath is not assisted.other patient breath is not assisted.

PTV is used in two modesPTV is used in two modes

Indications of Mechanical Ventilation 1. hypoxemia→ with PaO2 less than 50 mmHg despite

FiO2 of 0.8.

2. Respiratory acidosis → pH of less than 7.20 to 7.25, or PaCO2 above 60 mmHg.

3. Severe prolonged apnea.

4. Frequent intermittent apnea unresponsive to drug therapy.

5. Relieving work of breathing in an infant with signs of respiratory difficulty.

Blood Gases Changes by Ventilator Setting

Effect

Ventilator setting changes

PaCO2 PaO2

Increase PIP Decrease Increase

Increase PEEP Increase Increase

Increase rate Decrease Increase

Increase I:E ratio ------- Increase

Increase FiO2 ------- Increase

Increase flow Decrease Increase

ET Size

Infant weight(gm)Infant weight(gm) Endotracheal tube Endotracheal tube internal diameterinternal diameter

< 1,000gm 2.5mm

1,000 - 2,000 3.0mm

2,000 - 3,000 3.5mm

> 3,000 3.5 - 4.00mm

Initial Setting of Mechanical Ventilation

Initial settingsInitial settings

Fio2Fio2 As indicatedAs indicated

Systemic flowSystemic flow 6-10l/min6-10l/min

RateRate 60 breaths / min60 breaths / min

Ti/TeTi/Te 1:2 - 1:31:2 - 1:3

PIPPIP 18 - 22cm H2018 - 22cm H20

Good breath soundsGood breath sounds

PEEPPEEP 3 - 5cm H203 - 5cm H20

Subsequent settingsSubsequent settings PEEPPEEP PIPPIP

Low PaO2 ,Low PaO2 ,

Low PaCo2Low PaCo2Increase

Low PaO2 ,Low PaO2 ,

High PaCo2High PaCo2

Increase

High PaO2 ,High PaO2 ,

High PaCo2High PaCo2

Decrease

High PaO2 ,High PaO2 ,

Low PaCo2Low PaCo2

Decrease

Monitoring The Infant during Mechanical Ventilation

• (ABG)) .,– Obtain a blood gas within 15-30 minutes of any

change in ventilator settings. – Obtain a blood gas every 6 hours unless a sudden

change in the infant's condition occurs.

– Continuous monitoring of the O2 saturation level as

well as the HR and RR is necessary.

Paralysis and Sedation It is not routinely indicated. It may be used in irritable infants with their

spontaneous respiration is out of phase with the ventilator( as in modes with preset rates as in ippv and imv) .

in infants with RDS→ ↓dynamic lung compliance →↑ airway resistance, the removal of the infant’s respiratory effort contribution to tidal breathing.

after initiation of neuromuscular blockadeit is necessary to increase ventilator pressure

Weaning• Parameters gradually decreased (PIP 2 cm H2O, FiO2 5%,

Rate 5 BPM).• 1. Reduce FiO2 to 80% before changing PIP, I:E or PEEP.• 2. Reduce PIP as clinically indicated.• 3. Reduce FiO2 to less than 60%• 4. Reduce inspiratory time.• 5. Reduce PIP to 10-14 cm H2O (Larger babies may be

extubated with PIP 14-18)• 6. Reduce rate to 20 -40 /BPM then Te should be

prolonged.

Weaning (cont.)

• 7.preterm infants → Use of nasal CPAP → to avoid atelectasis.

• 8.prolonged intubation or previous failure of extubation → a short course of steroids may facilitate extubation.

• 9.If stridor caused by laryngeal edema develops after extubation, →nebulization with adrenaline.