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Dr.Wahid Helmy pediatric consultant. Basics of Mechanical Ventilation in Neonates. Ventilator care requires a team effort. Everyone involved has to get along and trust one another !. Prevention of alveolar collapse.
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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!
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).
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 .
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 = 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 • Volumev- cycled ventilators.لمجرد المعرفة • Pressure ventilators . لمجرد المعرفة • Pressure-limited, time-cycled, continuous-flow ventilators .هام جدا • Patient–triggered ventilators (PTV).هام جدا
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.
(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 مقاومةof 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),thus CO2 elimination.
Minute alveolar ventilation Minute alveolar ventilation = (Tidal volume – Dead space) X Frequency. • Tidal volume,is determined mainly with pressure gradient between inspiration and expiration i.e. (PIP) minus (PEEP).
Ti and Te ●(Ti)is .3 - . 5 seconds for LBW and .5 - .6 seconds for larger infants ●Depends on the pulmonary mechanics: – Compliance . – Resistance . –Time constant. 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 theCommander?
A)Non-triggeredModes. 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) 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.
PTV is used in two modes • Assist Control Mode (A/C) or sippv • All breath initiated by patient is triggered= Assist. • Back up rate = ippv = ControL MV. • If apnea occur at any time baby will be ventilated. • Synchronized Intermttent Mandatory Ventilation (SIMV): • Preset rate that is triggered, • other patient breath is not assisted.
Indications of Mechanical Ventilation • hypoxemia→ with PaO2 less than 50 mmHg despite FiO2 of 0.8. • Respiratory acidosis → pH of less than 7.20 to 7.25, or PaCO2 above 60 mmHg. • Severe prolonged apnea. • Frequent intermittent apnea unresponsive to drug therapy. • Relieving work of breathing in an infant with signs of respiratory difficulty.
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.