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CONOSCERE I VENTILATORI. Andrea Vianello Fisiopatologia Respiratoria Ospedale-Università di Padova. RESPIRATORY FAILURE. LUNG FAILURE. PUMP FAILURE. GAS EXCHANGE FAILURE. VENTILATORY FAILURE. HYPERCAPNIA. HYPOXEMIA. What’s the point of ventilation? Deliver O 2 to alveoli
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CONOSCERE I VENTILATORI Andrea Vianello Fisiopatologia Respiratoria Ospedale-Università di Padova
RESPIRATORY FAILURE LUNG FAILURE PUMP FAILURE GAS EXCHANGE FAILURE VENTILATORY FAILURE HYPERCAPNIA HYPOXEMIA
What’s the point of ventilation? • Deliver O2 to alveoli • Hb binds O2 (small amount dissolved) • CVS transports to tissues to make ATP - do work • Remove CO2 from pulmonary vessels • from tissues - metabolism
Why ventilate?- purposes • To maintain or improve ventilation, & tissue oxygenation. • To decrease the work of breathing & improve patient’s comfort.
When ventilate?- indications • Failure of pulmonary gas exchange • Hypoxaemia: low blood O2 • “Mechanical” failure • Hypercarbia: high blood CO2 • Respiratory muscle fatigue • Need to intubate eg patient unconscious • Others eg • need neuro-muscular paralysis to allow surgery • cardiovascular reasons
Definition: What is it? • Mechanical Ventilation =Machine to ventilate lungs = move air in (+ out) • Several ways to..move air in (IPPV vs others) Intermittent Positive Pressure Ventilation
Definition: What is it? • Mechanical Ventilation =Machine to ventilate lungs = move air in (+ out) • Several ways to..move air in (IPPV vs others) Intermittent Positive Pressure Ventilation • Several ways to connect the ventilator to the patient
Several ways to connect the machine to patient • Oro-tracheal Intubation • Tracheostomy • Non-Invasive Ventilation
Normal breath Normal breath inspiration, awake Lung @ FRC= balance Diaphragm contracts -2cm H20 Chest volume Pleural pressure -7cm H20 Alveolar pressure falls Air moves down pressure gradient to fill lungs
La pompa diaframmatica genera Pgarantendo la ventilazione polmonare, regolata da: • Equazione di moto del Sistema Respiratorio: Pmusc = V / C + V’ x R
Normal breath Normal breath expiration, awake -7cm H20 Diaphragm relaxes Pleural / Chest volume Pleural pressure rises -2cm H20 Alveolar pressure rises Air moves down pressure gradient out of lungs
Ventilator breath Portableventilator ICU ventilator ICU ventilator
Ventilator breath Ventilator breath inspiration Air blown in 0 cm H20 lung pressure Air moves down pressure gradient to fill lungs +5 to+10 cm H20 Pleural pressure
Il ventilatore sostituisce totalmente o parzialmente la pompa muscolare: • Equazione di moto del Sistema Respiratorio: Pappl (+ Pmusc) = V / C + V’ x R
Ventilator breath Ventilator breath expiration Similar to spontaneous…ie passive Ventilator stops blowing air in Pressure gradient Alveolus-trachea Air moves out Down gradient Lung volume
Practicalities • Ventilator settings: • Pressure vs volume • ‘Assist’ vs ‘Control’ • PEEP?
Practicalities Ventilator settings: Pressure vs volume ‘Assist’ vs ‘Control’ PEEP?
Details: Inspiration Pressure or Volume? • Do you push in.. • A gas at a set pressure? = ‘pressure…..’ • A set volume of gas? = ‘volume….’
Pressure Ventilators • The use of pressure ventilators is increasing in critical care units. • A typical pressure mode delivers a selected gas pressure to the patient early in inspiration, and sustains the pressure throughout the inspiratory phase. • By meeting the patient’s inspiratory flow demand throughout inspiration, patient effort is reduced and comfort increased.
Details: Inspiration Pressure or Volume? Pressure cm H20 Time Pressure cm H20 Time
Although pressure is consistent with these modes, volume is not. • Volume will change with changes in resistance or compliance • Therefore, exhaled tidal volume is the variable to monitor closely. • With pressure modes, the pressure level to be delivered is selected, and with some mode options, rate and inspiratory time are preset as well.
Volume Ventilators • The volume ventilator has been historically used in critical care settings • A respiratory rate, inspiratory time, and tidal volume are selected for the mechanical breaths. • The basic principle of this ventilator is that a designated volume of air is delivered with each breath. • Theamount of pressure required to deliver the set volume depends on : - Patient’s lung compliance - Patient–ventilator resistance factors
Peak Inspiratory Pressure (PIP ) must be monitored in volume modes because it varies from breath to breath 30 Peak Inspiratory Pressure P aw Time (s) cmH2O 1 2 3 -10
Details: Pressure vs Volume in the Acute Setting Secretions hypoventilation Vt preserved partial compensation hypoventilation sensitive insensitive Schönhofer ERS Monograph 2001; 16: 259-73, mod
small leak huge leak Details: leak compensation without leakage with leakage Pressure Vol Pressure Vol Pre-set Mehta et al. Eur Respir J 2001; 17: 259-267
Hybrid modes combine the advantages of pressure pre-set and volume pre-set VAPS Volume Assured Pressure Support • Automatic adjustment of inspiratory pressure (range setting) • Target volume set • Measurement of inspiratory pressure and expiratory volume • Calculation of missing inspiratory volume • Increase of inspiratory pressure Assurance of tidal volume + comfort of pressure pre-set
VAPS Volume Assured Pressure Support
VAPS Volume Assured Pressure Support
Efficacy and comfort of Volume-Guaranteed Pressure Support (PSV-VTG) in patients with chronic ventilatory failure of neuromuscular origin
Efficacy and comfort of Volume-Guaranteed Pressure Support (PSV-VTG) in patients with chronic ventilatory failure of neuromuscular origin
Four types of asynchronies: • Ineffective inspiratory effort (IE): thoraco-abdominal displacements not assisted by the ventilator positive pressure boost; • Inspiratory trigger delay: a time lag between the initiation of the patent’s IE and the onset of inspiratory support; • Prolonged inspiration or late expiratory cycling (hang-up): prolongation of mechanical insufflation beyond the end of patient inspiration; • Autotriggering: rapid succession of at least three pressurizations at a RR of >40 br/min. Efficacy and comfort of Volume-Guaranteed Pressure Support (PSV-VTG) in patients with chronic ventilatory failure of neuromuscular origin
Efficacy and comfort of Volume-Guaranteed Pressure Support (PSV-VTG) in patients with chronic ventilatory failure of neuromuscular origin
Practicalities Ventilator settings: Pressure vs volume ‘Assist’ vs ‘Control’ PEEP?
Interaction Ventilator Respiratory muscle pump
. . Ventilator Respiratory muscle pump work of breathing spontaneous assisted controlled
Noninvasive mechanical ventilation in acute exacerbation of restrictive thoracic disease Eur Respir Mon 2001; 6:70-73
Practicalities Ventilator settings: Pressure vs volume ‘Assist’ vs ‘Control’ PEEP?
RESPIRATORY FAILURE LUNG FAILURE PUMP FAILURE GAS EXCHANGE FAILURE VENTILATORY FAILURE HYPERCAPNIA HYPOXEMIA
Compliance of the Respiratory System ‘over-distended’ alveoli Compliance= Volume Pressure Volume • energy needed to open alveoli • damaged during open/closing? • - abnormal forces Pressure
Regional ventilation Spontaneous, standing Compliance= Volume Pressure Volume Pressure
Abnormalities of CRS Compliance= Volume Pressure Volume Pressure
What is PEEP? A constant positive pressure applied to the RS throughout the respiratory cycle Constant pressure → does not generate flow, does not increase volume !! Cannot be considered a form of ventilation in a strict sense!!however: It exerts important effects on RS mechanics: it may increase lung volume in order to correct acute lung restriction contributing to hypoxemia Pressure cm H20 PEEP Time Positive End Expiratory Pressure