Andrea Vianello S.C. Fisiopatologia Respiratoria Ospedale-Università di Padova CONCETTI GENERALI SUI VENTILATORI PNEUMOTRIESTE 2016

RESPIRATORY FAILURE LUNG FAILURE PUMP FAILURE GAS EXCHANGE FAILURE VENTILATORY FAILURE HYPOXEMIA HYPERCAPNIA

What’s the point of ventilation? –Deliver O 2 to alveoli Hb binds O 2 (small amount dissolved) CVS transports to tissues to make ATP - do work –Remove CO 2 from pulmonary vessels from tissues - metabolism

To maintain or improve ventilation, & tissue oxygenation. To decrease the work of breathing & improve patient’s comfort. Why ventilate?- purposes

When ventilate?- indications Failure of pulmonary gas exchange –Hypoxaemia: low blood O 2 “Mechanical” failure –Hypercarbia: high blood CO 2 – 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 inspiration, awake Diaphragm contracts  Chest volume  Pleural pressure Air moves down pressure gradient to fill lungs -2cm H cm H20 Alveolar pressure falls Normal breath FRC= balance

La pompa diaframmatica genera  P garantendo la ventilazione polmonare, regolata da:  Equazione di moto del Sistema Respiratorio: Pmusc = V / C + V’ x R

Normal breath expiration, awake Diaphragm relaxes Pleural / Chest volume  Pleural pressure rises Normal breath Alveolar pressure rises Air moves down pressure gradient out of lungs -7cm H20 -2cm H 2 0

Portable ventilator ICU ventilator Ventilator breath

Ventilator breath inspiration Air blown in  lung pressure Air moves down pressure gradient to fill lungs  Pleural pressure 0 cm H to+10 cm H 2 0 Ventilator breath

Il ventilatore sostituisce totalmente o parzialmente la pompa muscolare:  Equazione di moto del Sistema Respiratorio: Pappl (+ Pmusc) = V / C + V’ x R

Ventilator breath expiration Similar to spontaneous…ie passive Ventilator stops blowing air in Pressure gradient Alveolus-trachea Air moves out Down gradient  Lung volume Ventilator breath

Practicalities Ventilator settings: Pressure vs volume ‘Assist’ vs ‘Control’ Trigger sensitivity PEEP?

Practicalities Ventilator settings: Pressure vs volume ‘Assist’ vs ‘Control’ Trigger sensitivity PEEP?

Details: Inspiration Pressure or Volume? Do you push in.. –A gas at a set pressure? = ‘pressure…..’ –A set volume of gas? = ‘volume….’

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. Pressure Ventilators

TimePressure cm H 2 0 TimePressure cm H 2 0 Details: Inspiration Pressure or Volume?

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.

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. The amount of pressure required to deliver the set volume depends on : - Patient’s lung compliance - Patient–ventilator resistance factors Volume Ventilators

Details: Inspiration Pressure or Volume?

30 Time (s) aw P cmH 2 O Peak Inspiratory Pressure 3 Peak Inspiratory Pressure (PIP ) must be monitored in volume modes because it varies from breath to breath

Schönhofer ERS Monograph 2001; 16: , mod hypoventilation partial compensation sensitiveinsensitive Secretionshypoventilation Vt preserved Details: Pressure vs Volume in the Acute Setting

Vol Pressure without leakagewith leakage small leak huge leak Mehta et al. Eur Respir J 2001; 17: Pre-set Details: leak compensation

Practicalities Ventilator settings: Pressure vs volume ‘Assist’ vs ‘Control’ Trigger sensitivity PEEP?

Respiratory muscle pump Ventilator Interaction

Respiratory muscle pump Ventilator work of breathing spontaneous assistedcontrolled..

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’ Trigger sensitivity PEEP?

Nilsestuen et al. Respir Care 2005; 50: Inspiratory triggering 2.Inspiration 3.Termination of inspiration 4.Expiration 4 Phases Pressure Flow Volume Time

trigger asynchrony insensitive trigger sensitive trigger auto- triggering trigger sensitivity to low high level of PSV hypercapnic encephalopathy sedation sleep intrinsic PEEP (COPD) tubing obstruction trigger sensitivity to high resistance changes tubing leakage cardiac oscillation Details: trigger sensitivity

Trigger poco sensibile: allo sforzo inspiratorio non segue l’atto meccanico del respiratore

Pao Pes patient 1 patient 2 patient 3

Trigger troppo sensibile: l’atto meccanico si innesca spontaneamente

Asynchrony between patient and ventilator Problems: Increased work of breathing Need for sedation „Fighting the ventilator“ Ventilation-Perfusion-Mismatch Dynamic hyperinflation Consequences: Insufficient ventilation Withdrawal from NIV Weaning failure Prolonged ICU stay Costs Prognosis !

L’operatore imposta: L’operatore imposta: PSV Caratteristiche: - pressure-controlled - flow-cycled - patient-triggered - pressione inspiratoria - sensibilità trigger - eventuale “rampa” (tempo di raggiungimento PS) - > sincronismo paziente-ventilatore  > comfort - possibile graduazione sforzo inspiratorio 

lenta media rapida Diversi tipi di rampa

PSV PSV Problemi: - difficoltà di impostazione - livello PS  V T : 6-8ml/Kg; RR: 20-35b/min P 0.1 : 2-4 cm H 2 O abolizione dissincronismi toraco- addominali - possibile sovrassistenza

L’operatore imposta: L’operatore imposta: A-CV Caratteristiche: -volume-controlled -time-cycled -machine e/o patient-triggered (assistito) -pressure-limited (eventuale) -volume corrente -frequenza respiratoria -rapporto I/E -sensibilità del trigger Problemi: - possibile sovrassistenza  alcalosi respiratoria - insorgenza di PEEP intrinseca  - volume corrente insufflato garantito - rapporto I/E variabile

A-CV

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

Storre et al. Chest 2006;130:

AVAPS provides elegant adjustments of inspiratory pressures according to a pre-set target volume AVAPS improves quality of ventilation Improvements of sleep quality and quality of life are comparable to BiPAP-S/T However: Sleep quality is not completely normalized Further studies are needed

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

Practicalities Ventilator settings: Pressure vs volume ‘Assist’ vs ‘Control’ Trigger sensitivity PEEP?

RESPIRATORY FAILURE LUNG FAILURE PUMP FAILURE GAS EXCHANGE FAILURE VENTILATORY FAILURE HYPOXEMIA HYPERCAPNIA

Compliance of the Respiratory System Volume Pressure Compliance=  Volume  Pressure energy needed to open alveoli ?damaged during open/closing - abnormal forces ‘over-distended’ alveoli

Regional ventilation Volume Pressure Compliance=  Volume  Pressure Spontaneous, standing

Abnormalities of C RS Volume Pressure Compliance=  Volume  Pressure

V/Q mismatching (shunt effect)

CPAP/PEEP to improve oxygenation

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 Time Pressure cm H 2 0 PEEP Positive End Expiratory Pressure

A, The stiff lungs and increased shunt result in a drop in FRC and PaO 2. B and C, as PEEP is increased, C S and PaO 2 improve as the FRC increases, resulting in a lowering of the shunt effect. D, Too much PEEP has been used, and C S and cardiac output decrease as the FRC is increased above the optimum level. Effect of PEEP on respiratory mechanics and gas exchanges

ZEEP With CPAP Effect of CPAP on lung expansion

Vent settings to improve Vent settings to improve PEEP Increases FRC Prevents progressive atelectasis and intrapulmonary shunting Prevents repetitive opening/closing (injury) Recruits collapsed alveoli and improves V/Q matching Resolves intrapulmonary shunting Improves compliance Enables maintenance of adequate P a O 2 at a safe FiO 2 level Disadvantages Increases intrathoracic pressure (may require pulmonary a. catheter) Rupture: PTX, pulmonary edema

Indications for PEEP/CPAP Bilateral infiltrates on CXR Recurrent atelectasis with low FRC Reduced lung compliance PaO PaO 2 /FiO 2 ratio <200 for ARDS and <300 for ALI Refractory hypoxemia: PaO 2 increases 10mmHg with FiO 2 increase of 0.2

Dynamic hyperinflation and PEEPi Normal subjectCOPD

Details: cardiovascular effects

Details: Cardiovascular effects Compresses Pulmonary vessels Reduced LV inflow –  Cardiac Output: Stroke Volume –Blood Pressure = CO x resistance –  Blood Pressure –Neurohormonal Reduced RV outflow- backtracks to body –Head-  Intracranial Pressure –Others -  venous pressure

Contraindications for PEEP Hypovolemia Untreated or significant pneumothorax Elevated Intracranial Pressure Pre-existing hyperinflation – emphysema Unilateral lung disorders

PEEP Ranges Minimum or Low PEEP –3-5cmH 2 O –Preserves normal FRC Therapeutic PEEP –>/= 5cmH 2 O –Used to treat refractory hypoxemia –High levels are only beneficial to a small % –Associated with cardiopulmonary complications Optimum or Best PEEP –Level at which the maximum beneficial effects of PEEP occur and is not associated with profound cardiopulmonary side effects

NIV treatment: summary The ventilator management of NIV is continuously evolving; New ventilators are introduced, offering novel features; Clinical applications have been expanding; Clinicians must make selections that best match the ventilator with the patient’s requirements.