Course no: Course 6 Title: Anaesthesia According to the Patient, Type of Surgery and Mode of Organization Sub-category: Ventilatory Support Topic:

Transcription

1 Course no: Course 6 Title: Anaesthesia According to the Patient, Type of Surgery and Mode of Organization Sub-category: Ventilatory Support Topic: Mechanical Ventilation in Infants and Neonates Date: Sep 01, 2018 Language: City: Country: Speaker: English Lahore Pakistan Dr Shahab Naqvi

2 Conflict of interest: None Disclosure

3 Plan Lung development Differences in anatomy and physiology Respiratory failure in infants Goal of Mechanical Ventilation Modes, popular in kids ventilation Protocols for HFV Word about ECMO Weaning

4 Lung Development Significant Milestones: At 3-4 wks. Lung bud from esophagus At wks. Segmentation of bronchi complete At wks. Type II pneumatocytes develop At 24 wks. Surfactant production At 34 wks. PG production Note : Lung maturity lags behind by 2-4 wks in maternal diabetes

5 Airway Anatomy and Physiology Upper and lower airways of infants are much smaller and tongue is proportionally very large Respiratory bronchioles, alveolar ducts and alveoli grow in number until 8 years of age, and continue to grow in size until adulthood Subglottic airway is much smaller and more compliant and may collapse during spontaneous inspiratory effort Ribs are very compliant and may fail to maintain the lung volume Limited oxygen reserve and high O2 consumption

6 Airway Anatomy and Physiology Pores of Kohn connecting alveoli are not developed until 1 year of age, and Channels of Lambert which connect alveoli to larger airways do not develop until 5 years of age Majority of airway resistance lies in lower airways as compared to adults where nasal passages alone may be responsible for 60% Due to softer cartilage supporting the airway, collapse of the airway is more common

7 Ventilation - Kids vs.. adults Positioning Preoxygentation -- critical -- lower FRC Mucous plugging more need of PT Air leaks -- around tube desirable High FiO2 very dangerous Irregular I:E ratio - Periodic breathing Reactive Airways Cannot reason with child

8 Respiratory Failure in Neonates Neonatal respiratory failure is not a single disease entity It is a condition of impaired gas exchange that can result from a number of lung parenchymal or vascular abnormalities. Five most common of them include: RDS Meconium Aspiration Syndrome Pneumonia Persistent Pulmonary Hypertension of Newborn Bronchopulmoary Dysplasia

9 Goal of Mechanical Ventilation To achieve and maintain adequate pulmonary gas exchenge To reduce patient work of breathing (WOB) To optimize patient comfort To minimize risk of lung injury Challenge: To identify the most appropriate device, technique, and strategy

10 Science and Art of Ventilation The science of mechanical ventilation is to optimize gas exchange The art is to achieve that without damaging the lung

11 Non Invasive Ventilation

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13 CPAP Takes the advantage of LaPlace s Law Increases TLC and FRC In addition, it produces regular breathing in preterm infants by: Reducing thoracic distortion and stabilizing the chest wall Splinting the upper airway thus preventing obstructive apnea Stimulate J receptors by stretching lung/pleura providing positive feedback to respiratory centre by Hering Breuer reflex Enhancing surfactant release from Type II Pneumocytes Resulting in better V/Q mismatch, improved minute ventilation and decreased work of breathing

14 CPAP with Facemask

15 CPAP with Nasal Mask

16 Disadvantages of IPPV Conventional IPPV of premature lungs results in inflation and deflation of alveoli at high pressure Barotrauma Few alveoli collapse and reopen from collapsed state resulting in atelectrauma In addition endotracheal tube as a foreign material may result in local inflammation and infection Biotrauma Use of IPPV results in rupture of interalveolar septa thus decreasing the surface area for gas exchange despite increasing lung volume

17 Alveolar Septa in mice after 72 hours of IPPV

18 IPPV

19 Initial Selection PCV FiO2 Rate I-time PEEP PIP VCV FiO2 Rate I time PEEP Tidal Volume Tidal Volume &( MV) Varies PIP & (MAP) Varies

20 Initial Settings Rate: start with 20-30/min for infant/small child FiO2: 1 and wean down to 0.5 PEEP: 3-5 PIP. Expect PIP in patients with healthy lungs, for moderate lung disease, in more severe disease. Watch for VT: 8-10 ml/kg Inspiratory time (I time): minimum 0.5 seconds, ranging up to 1 second in older kids Pressure support 5-10

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23 Modes Popular in Neonatal and Infant Ventilation

24 Closed Loop Ventilation in Kids ASV Auto mode PAV CLV SAVI Smart Care NAVA

25 SIMV + PS Partially Controlled Primary Mode SIMV provides graded levels of assistance Physician sets the number of mandatory breaths of fixed V T, between which patient can breathe spontaneously Avoids muscle atrophy & eliminates fighting WOB can be much more than desired PS is added to counter the increase in WOB

26 PSV Partially Closed Loop Ventilation Supports spontaneous breaths partially or fully, by inspiratory pressure assist above baseline pressure Decrease WOB caused by narrow ETT, ventilator circuit and demand valve Can be used alone or with SIMV

27 Contraindications: Partially Closed Loop Ventilation PSV Deep sedation and muscle paralysis Severe Neurological Disorders Hypoventilation syndromes Patients who may be unable to activate trigger demand valve

28 Partially Closed Loop Ventilation VSV Assists spontaneous breathing like PSV If patient generates pre-set V T, ventilator provides no VS and you can extubate If apnea occurs ventilator automatically switches to PRVC Indications and C/I are same as PSV

29 VSV vs. PSV Partially Closed Loop Ventilation The main advantages of VSV over PSV are: Ventilator adapts to changes in lung mechanics of patient to maintains stable V T Being protected should apnea occur Being able to recognize when the patient no longer requires PS to generate pre-set V T

30 Adaptive Pressure Control (APC) Pressure control ventilation cannot guarantee minimum minute ventilation in changing lung mechanics or patient s effort, or both. To overcome this APC was introduced. The APC mode delivers pressure controlled breaths with an adaptive targeting scheme. A machine in APC mode adjusts the inspiratory pressure to deliver the set minimal target tidal volume.

31 Adaptive Pressure Control (APC) No. Ventilator Adaptive Pressure Control 1. Dra ger Evita 4 and XL AutoFlow 2. Hamilton Galileo Adaptive Pressure Ventilation Adaptive Support Ventilation (ASV) 3. Maquette Servo-i Pressure Regulated Volume Control (PRVC) Volume Support Ventilation (VSV) 4. Puritan Bennett 840 Volume Control + 5. Newport E500 Volume Target Pressure Control 6. Viasys/Pulmonetics PalmTop Ventilator Pressure Regulated Volume Control (PRVC) 7. Viasys Avea Pressure Regulated Volume Control (PRVC) 8. Engstrom Controlled Volume Guaranteed

32 PRVC When lung compliance and resistance vary rapidly Siemens 300a ventilator Achieves volume support while keeping PIP at lowest possible level Done by altering peak flow and inspiratory time in response to changing airway resistance and compliance Partially Closed Loop Ventilation Breath to Breath Control

33 Pressure, Volume, Flow Time Graph in PRVC Mode

34 Completely Closed Loop Ventilation Automode Siemens 300A Combines PRVC with volume support If 2 consecutive breaths trigger mechanical breaths, Automode switches to VS If the patient stops breathing for a pre-determined period of time (5sec for neonate; 8sec for pediatric; 12sec for adult) ventilator automatically switches back to PRVC Eur J Cardiothorac Surg 2006;29:

35 VAPS Combines features of VCV and PSV Clinician has to set VT, PS and PIF As long as patient effort results in delivery of desired V T, breath is PS If breath delivers a V T below desired it shifts to VC breath Bird 8400 STi and T Bird ventilators Partially Closed Loop Ventilation Within Breath Control

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37 Partially Closed Loop Ventilation Within Breath Control VAPS - Advantages Major advantage is its immediate response, rather than using a breath-averaging methodology Decreased WOB Lower peak airway pressure Less need for sedation

38 Completely Closed Loop Ventilation ASV Used by Galileo, Raphel, G5 and C3 ventilators Closed loop controlled mode that switches from PCV to PC-SIMV to PSV modes Clinician enters IBW and % of MV Ensures early tracheal extubation Anesth Analg Dec;97(6): Anesthesiology Jul;109(1):81-7

39 Completely Closed Loop Ventilation SAVI Synchronised Assistance to Ventilation in Infants (SAVI) Synchronization is accomplished by modified thoracic impedance technology using standard neonatal cardiorespiratory monitors Output of the ventilation synchronizers triggering the exhalation solenoid valve Sechrist Ventilator

40 Completely Closed Loop Ventilation NAVA Neurally Adjusted Ventilator Assist Servoi Bipolar electrodes attached to NG tube Positioned in the esophagus at the level of and perpendicular to the crura of the diaphragm Catheter captures signals from resp centre travelling through phrenic nerve and feeds it to ventilator The ventilator responds by providing the requested level of support to the patient. C. Sinderby. Minerva Anesthesiol 2002;68:378-80

41 Completely Closed Loop Ventilation NAVA Measuring of electric diaphragm activity

42 Automatic Tube Compensation Evita 4 ventilator, PB840 Applied in All Ventilator Modes Offsets and compensates for the airflow resistance from the artificial airway Allows patient to have a breathing pattern as if breathing spontaneously without an artificial airway

43 High Frequency Ventilation HFV

44 HFV HFV is defined by the high frequency ( Hz) and low tidal volume (0.5-5 ml/kg) Characteristics: Continuous distending pressure Small V T (less than anatomic dead space) Rapid ventilation rates Three principal types: HFPPV: Rate /min HFJV: Rate /min HFOV: Rate /min

45 HFV: Examples in Nature Humming bird ~250 bpm while at rest One-way flow via parabronchi and air sacs (NOT tidal) Panting dog V T less than dead space Very high respiratory rate

46 High Frequency Ventilation Provides augmented gas distribution by means of numerous gas transport mechanisms: 1. Convection, transit time, direct ventilation 2. Pendelluft effect 3. Taylor dispersion 4. Asymmetric velocity 5. Cardiogenic Mixing 6. Molecular diffusion 7. Collateral Ventilation

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50 Comparative Pressure Profiles HFJV, HFOV and CV

51 Impedance HFV: Impediment to Gas Flow Airway frequency

52 impedance HFV: Impediment to Gas Flow Alveolae frequency

53 impedance HFV: Impediment to Gas Flow Airway Airway + Alveolae Alveolae frequency

54 impedance HFV: Resonant Frequency Sweet spot frequency

55 CV VS HFOV During CV, there are swings between the zones of injury from inspiration to expiration. During HFOV, the entire cycle operates in the safe window and avoids the injury zones. Zone of Overdistention Volume Safe window Zone of Derecruitment and atelectasis Pressure

56 HFV: The Design HFOV Diaphragm or piston Active expiration Single control of Paw Single device Optimum volume, low pressure Air trapping Fixed (rigid) circuit HFJV High pressure jet Passive expiration Multiple controls of Paw CMV in series Low volume, low pressure Air trapping Triple lumen ET tube

57 HFV: The Strategy HFOV Severe homogeneous lung disease RDS Early-onset pneumonia PPHN Target: RDS HFJV Severe heterogeneous lung disease MAS Late-onset pneumonia Air leak syndromes Pneumothorax PIE (Pulmonary Interstitial Emphysema) Target: barotrauma

58 HFV: Pitfalls and Complications HFV is a more effective ventilation mode, so the risk of hypocarbia is greater. Lung overdistention airleak Air trapping Hypercarbia Increased intrathoracic pressure Reduced systemic venous return Hypotension

59 Cochrane Review: Published: 16 October 2015 Authors: Rojas-Reyes M, Orrego-Rojas PA Primary Review Group: Neonatal Group Rescue high-frequency jet ventilation versus conventional ventilation for severe pulmonary dysfunction in preterm infants Question: In preterm infants with severe respiratory dysfunction despite attempts at conventional ventilator support, does use of rescue HFJV compared with ongoing conventional ventilation decrease the risk of lung injury (chronic lung disease) or death? Study characteristics: One study randomly assigned 166 preterm infants and reported data on 144 infants. The included study was completed before the introduction of surfactant and widespread use of antenatal steroids. Key Results: This trial demonstrated no differences in outcomes among infants who received high-frequency jet ventilation. Researchers reported no differences in the incidence of chronic lung disease among survivors at 28 days of age, and they found no differences in intraventricular haemorrhage, new air leaks, airway obstruction and necrotising tracheobronchitis. Conclusions: Existing evidence does not support the use of rescue highfrequency jet ventilation compared with conventional mechanical ventilation for treatment of preterm infants with severe pulmonary problems.

60 ECMO Venoarterial: RIJ Oxygenator RCCA Venovenous: RIJ Oxygenator RIJ Indications: Retractable, but potentially reversible RF not responding to IPPV or HFOV > 80% chance of death with an infant >2 kg and > 34 weeks of gestational age Oxygenation Index: > 40 Donn SM, Sinha SK, Respiratory Care, April 2003 Vol 48 No 4

61 Oxygenation Index OI = MAP x FiO 2 x 100 / PaO 2 Start with PC Ventilation If OI is > 20 give HFO If OI is > 40 use ECMO Reverse criteria is used for weaning

62 Weaning Techniques Gradual reduction of vent support. SIMV rate and PS VS weaning VAPS weaning Automode, ASV SBTs: PS Trial, CPAP, T-Tube ERTs: Leak test to assess NIF Role of steroids Newth CJL, Venkataraman S, Willson DF. Pediatr Crit Care Med. 2009;10(1):1-11

63 Summary Basic goals of Ventilatory support remain the same Use NIV as long as possible Use FiO2 as low as possible Low VT and open lung strategy to avoid VALI Always keep basic pathology in mind Wean as early as possible

64 Recent Advances in Pediatric Ventilatory Assistance F1000 Research 2017, 6(F1000 Faculty Rev): 290 Last updated: 20 MAR 2017 To limit ventilator-induced lung injury using transpulmonary pressure and volumetric capnography monitoring To limit diaphragmatic dysfunction by monitoring electrical activity of the diaphragm To better identify the timing of extubation with spontaneous breathing trials using CPAP mode or T-Tube Ventilation Mode: To consider NAVA to improve patient ventilator interaction To still consider HFOV in the most severe pediatric ARDS not adequately supported with optimally set CV To consider NIV as a first-line support in many pathologies To consider high- flow nasal cannula to improve comfort and tolerance of NIV

65 Nardi N, Mortamet G, Ducharme-Crevier L et al. Recent Advances in Pediatric Ventilatory Assistance [version 1; referees: 2 approved] F1000 Research 2017, 6(F1000 Faculty Rev): 290 (doi: /f1000research )

66 Thank You