Mechanical Ventilation Éva Zöllei University of Szeged Department of Anaesthesia and Intensive...

Mechanical Ventilation

Éva Zöllei

University of Szeged

Department of Anaesthesia and Intensive Care

Medical Intensive Care Unit

Mechanical Ventilation

1952-53 polio outbreak in Copenhagen

Bjorn Ibsen proposed the use of positive pressure ventilation

mortality decreased from 87% to 15%

the birth date of modern mechanical ventilation

mechanical ventilation is the main supportive therapy to re-establish oxygen supply in acute respiratory failure

Mechanical Ventilation

1. indications for mechanical ventilation

2. haemodynamic consequences of positive-pressure ventilation

3. design and function of ventilators

4. the different modes of mechanical ventilation

5. how to set the respiratory parameters

6. ventilator-induced lung injury (VILI)

7. lung-protective ventilatory strategy

8. weaning from mechanical ventilation

Acute Respiratory Failure

- is not a single clinical entity but represents the final common pathway of many diseases

- can be either the consequence of mechanical pump failure and/or alveolar/capillary dysfunction

pump failure primarily results in alveolar hypoventilation, hypercapnia and respiratory acidosis

lung failure involves impaired oxygenation and impaired CO2 elimination

1. Indications for mechanical ventilation

- hypercapnia with respiratory acidosis pH 7,2

- hypoxaemia PaO2 60 mmHg, SaO2 90%

- reduction of the work of breathing, decrease VO2

Mechanical Ventilation

1. indications for mechanical ventilation

2. haemodynamic consequences of positive-pressure ventilation

3. design and function of ventilators

4. the different modes of mechanical ventilation

5. how to set the respiratory parameters

6. ventilator-induced lung injury (VILI)

7. lung-protective ventilatory strategy

8. weaning from mechanical ventilation

2. Haemodynamic consequences of positive pressure ventilation

- decreasing venous return, decreasing cardiac output

- decreasing intrathoracic blood volume

- decreasing left ventricular afterload

- alterations in pulmonary vascular resistance

- reversing hypoxic pulmonary vasoconstriction

- compressing alveolar vessels when lung overdistension occurs

2. Haemodynamic consequences of positive pressure ventilation

may cause hypotension at the start of ventilation in hypo- and normovolemic patients

can improve hemodynamics in congestive heart failure by unloading the left ventricle

causes alterations in remote organ perfusion and function by altered cardiac output, different flow distribution, and consequent neural and humoral compensatory mechanisms

Mechanical Ventilation

1. indications for mechanical ventilation

2. haemodynamic consequences of positive-pressure ventilation

3. design and function of ventilators

4. the different modes of mechanical ventilation

5. how to set the respiratory parameters

6. ventilator-induced lung injury (VILI)

7. lung-protective ventilatory strategy

8. weaning from mechanical ventilation

3. Design and function of ventilators

- gas supply apparatus

- respiratory circuit

with heated- humidifier or HME, inspiratory and exspiratory valves

- microprocessor control

- control panel,

- monitoring system

- alarm system

- triggering system

3. Design and function of ventilators

initiation of mechanical insufflation- automatically by the mashine (volume or pressure controlled)

- in synchrony with spontaneous inspiration (volume or pressure support)

- gas flow triggering system

- pressure triggering system

3. Design and function of ventilators

termination of mechanical insufflation

- volume-cycled

- time-cycled

- flow-cycled (ETS)

- pressure cycled (safety precaution)

3. Design and function of ventilators

inspiratory phase- volume targeted mode - modulates flow to reach the preset tidal volume during the inspiratory time variable pressure

- pressure targeted mode - modulates flow to maintain the preset inspiratory pressure during the inspiratory time variable tidal volume

3. Design and function of ventilators

exspiratory phase- exspired gas is rapidly vented to ambient

- rapid pressure reduction to preset end-exspiratory (PEEP) level

Mechanical Ventilation

1. indications for mechanical ventilation

2. haemodynamic consequences of positive-pressure ventilation

3. design and function of ventilators

4. the different modes of mechanical ventilation

5. how to set the respiratory parameters

6. ventilator-induced lung injury (VILI)

7. lung-protective ventilatory strategy

8. weaning from mechanical ventilation

CMVCMVCMVCMV

BIPAPBIPAPBIPAPBIPAP

SIMVSIMVSIMVSIMVAPRVAPRVAPRVAPRV

ASBASBASBASBVAPSVAPSVAPSVAPS

PAVPAVPAVPAV

PSVPSVPSVPSV

PCVPCVPCVPCV

4. The jungle of today

ASVASVASVASVHFJVHFJVHFJVHFJV

4. Non-invasive ventilation

4. Non-invasive ventilation

advantages and disadvantages- avoids complications associated with endotracheal tube

- lower rate of nosocomial infections and pneumonias

- shorter duration of mechanical ventilation

but- high workload on personnel

- patient selection and tolerance are critical

4. Non-invasive ventilation

criteria for patient selection- alert and cooperative (except COPD with CO2 coma)

- haemodynamic stability

- no need for endotracheal intubation to

protect airways

remove excessive secretions

- no need for high PEEP

- no acute facial trauma, skull base fracture, recent upper GI surgery

4. Non-invasive ventilation

criteria for discontinuing NIPPV- inability to tolerate the mask

- inability to improve gas exchange and dyspnoe

- need for endotracheal intubation

- haemodynamic instability

- signs of ischaemia on ECG

- failure to improve mental status within 30 min in CO2 coma or in hypoxaemic agitated patients

4. Volume controlled mode CMV

- volume targeted modes garantee flow and consequently tidal volume during the allowed inspiratory time, at the expense of variable airway pressures

- you can select: tidal volume or minute volume

flow pattern

respiratory rate, I:E

pop-off pressure alarm

PEEP

FiO2

4. Volume controlled mode

- breath initiation: automatic (due to preset respiratory rate)

- breath termination: volume-cycled (with safety pop-off pressure cycling)

- advantages:- tidal volume/minute ventilation garantee

- disadvantages: - often needs deep sedation

- high pressures can be generated

Flow

Pressure

Volume

4. Volume controlled mode

4. Assist control mode ACV

- patient triggered, volume targeted mode

- you can select: tidal volume or minute volume

flow pattern

trigger sensitivity

back-up respiratory rate

pop-off pressure alarm

PEEP

FiO2

4. Assist control mode

- breath initiation: triggered (pressure or flow)

- breath termination: volume cycled (with safety pop-off pressure cycling)

- advantages: - allows spontaneous breathing

- garantees tidal volume

- disadvantages: - pressure is not controlled

- often results in patient-ventilator dissynchrony

4. Pressure controlled mode PCV

- pressure targeted ventilation delivers preset pressure, and the tidal volume and flow will be dependent on respiratory system compliance and airway resistance

- you can select: inspiratory pressure

respiratory rate, I:E

PEEP

FiO2

4. Pressure controlled mode

- breath initiation: automatic (due to preset respiratory rate)

- breath termination: time cycled

- advantages: - control of peak pressures

- potencially improved distribution of flow

- usually better tolerated, less need for sedation

- disadvantages: - no tidal volume garantee!

4. Pressure controlled mode

flow

pressure

volume

4. Pressure support mode PSV

- patient triggered, pressure targeted mode, so the tidal volume and flow will depend on the mechanical characteristics of the respiratory system

- you can select: inspiratory pressure

trigger sensitivity

PEEP

FiO2

apnoe back-up settings

4. Pressure support mode

- breath initiation: patient triggered

- breath termination: flow cycled - ETS

- advantages: - flexible to patient needs

- better synchronization between the patient and the ventilator

- disadvantages: - no tidal volume/minute ventilation garantee

- the need for close monitoring with appropriate back-up and alarm settings

flow

pressure

volume

4. Pressure support mode

4. Other modes of mechanical ventilation

- CPAP - simply means Continous Positive Airway Pressure, the patient breathes spontaneously

- BIPAP - Bi-Level Positive Airway Pressure

- APRV - Airway Pressure Release Ventilation

- SIMV - Synchronized Intermittent Mandatory Ventilation, different levels of control and assistance

- ASV - Adaptive Support Ventilation

4. Novel modes of improving gas exchange

- high frequency ventilation - 60-600/min

- partial liquid ventilation - uses perfluorocarbon mixed with oxygen

- ECMO - ExtraCorporeal Membrane Oxygenation

- ECCO2R - ExtraCorporeal CO2 Removal

are intended to "keep the lung rest" to avoid further damage

Mechanical Ventilation

1. indications for mechanical ventilation

2. haemodynamic consequences of positive-pressure ventilation

3. design and function of ventilators

4. the different modes of mechanical ventilation

5. how to set the respiratory parameters

6. ventilator-induced lung injury (VILI)

7. lung-protective ventilatory strategy

8. weaning from mechanical ventilation

5. How to set the respiratory parameters

- correct hypoxaemia

- acceptable PaCO2 - pH of the arterial blood

- permissive hypercapnia!

- do not allow dynamic hyperinflation

- patient comfort - do not allow fighting the ventilator

- do not destroy the lung!

Mechanical Ventilation

1. indications for mechanical ventilation

2. haemodynamic consequences of positive-pressure ventilation

3. design and function of ventilators

4. the different modes of mechanical ventilation

5. how to set the respiratory parameters

6. ventilator-induced lung injury (VILI)

7. lung-protective ventilatory strategy

8. weaning from mechanical ventilation

6. Ventilator Induced Lung Injury (VILI)

mechanical ventilation itself can damage the lung

- high pressure

- high volume

- repetitive opening and closing of the alveoli

6. Ventilator Induced Lung Injury (VILI)

- volotrauma (high volume injury): alveolar damage caused by high volume, with or without high pressure (1974 Webb, Tierney) (1988 Dreyfuss)

- atelectotrauma (low volume injury): lung injury caused by increased shear stress, the consequence of repetitive opening and closing of the alveoli (Mead 1970)

- biotrauma: local or systemic inflammatory response due to abnormal mechanical forces

6. Ventilator Induced Lung Injury (VILI)

Dreyfuss, Saumon: Ventilator-induced lung injury. Am J Respir Crit Care Med. 1998;157:294-323.

Paw: 45 vízcm

5 min later

20 min later

Mechanical forces

Fung: A model of the lung structure and its validation. J Appl Physiol. 1988;64(5):2132-2141.

Abnormal mechanical forces

Mead: Stress distribution in lungs: a model of pulmonary elasticity. J Appl Physiol. 1970;28(5):596-608.

Stress and strainstress is defined as tension of the lung sceleton fibre system, an indicator for the stress applied to the lung parenchyma is transpulmonary pressure (Ptp = Palv-Ppl)

strain is defined as the elongation of the lung structure compared with its resting position, an approximate surrogate for it is Vt/EELV

in the diseased lung the distribution of stress and strain which are the triggers of VILI is not homogenousGattinoni: Physical and biological triggers of ventilator-induced lung injury and its prevention. Eur Respir J. 2003;22:Suppl 47:15s-25s.

6. Ventilator Induced Lung Injury (VILI)

Halbertsma: Cytokines and biotrauma in ventilator-induced lung injury: a critical review of the literature. The Netherlands Journal of Medicine. 2005;63:382-392.

Stress failure

Marini, Hotchkiss, Broccard: Microvascular and airspace linkage in ventilator-induced lung injury. Critical Care. 2003;7:435-444.

Mechanical Ventilation

1. indications for mechanical ventilation

2. haemodynamic consequences of positive-pressure ventilation

3. design and function of ventilators

4. the different modes of mechanical ventilation

5. how to set the respiratory parameters

6. ventilator-induced lung injury (VILI)

7. lung-protective ventilatory strategy

8. weaning from mechanical ventilation

ALI/ARDShealthy regions - non-dependent areas, can be overdistended by ventilation

atelectatic

- collapsed, consolidated, dependent areas, open it!

injured, but recruitable - opens and collapses at every breath, keep it open!

Gattinoni L. J Thorac Imag 1986; 1(3): 25

7. Lung protectiv ventilatory strategy

ensures oxygenation without causing further damage to the lung or other organs

it's always a priority!

- low tidal volume (6 ml/kg in ALI/ARDS)

- limited alveolar pressure (< 30-35 cmH2O)

- recruitment maneuvers

- optimal PEEP

"Open the lung and keep it open"

SuperimposedPressure

OpeningPressure

Inflated 0

Alveolar Collapse(Reabsorption) 20-60 cmH2O

Small AirwayCollapse 10-20 cmH2O

Consolidation

(modified from Gattinoni)

7. Lung protectiv ventilatory strategy

7. Lung protectiv ventilatory strategy

- pv curve- compliance- oxygenation - CT scan

Pelosi P et al, AJRCCM 2001;164:122-130Pelosi P et al, AJRCCM 2001;164:122-130

CT at end-expiration

7. Lung protectiv ventilatory strategy

Ventilation with lower tidal volumes as compared with traditional tidal

volumes for ALI/ARDSARDS network

N Engl J Med 2000;342:1301-8

ARDSnet low tidal volume study

traditional ventilation group- 12 ml/kg tidal volume- plateau pressure below 50 cmH2O

low tidal volume group- 6 ml/kg tidal volume

- plateau pressure below 30 cmH2O

N Engl J Med 2000;342:1301-8.

ARDSnet low tidal volume study

where do we go from here?

N Engl J Med 2000;342:1301-8

ARDSnet low tidal volume study

- inhospital mortality 31 vs 39,8 %- fewer

days on ventilator remote organ failure

- greater decrease in IL6 level

N Engl J Med 2000;342:1301-8.

Mechanical Ventilation

1. indications for mechanical ventilation

2. haemodynamic consequences of positive-pressure ventilation

3. design and function of ventilators

4. the different modes of mechanical ventilation

5. how to set the respiratory parameters

6. ventilator-induced lung injury (VILI)

7. lung-protective ventilatory strategy

8. weaning from mechanical ventilation

8. Weaning from mechanical ventilation

- criteria:

- major improvement in the cause of respiratory failure

- haemodynamic stability

- stable neurological status

- de-escalation: involves stepwise reduction of FiO2, PEEP and mechanical support

- weaning: the final step, deliberation from the ventilator

8. Weaning from mechanical ventilation

use weaning protocols with daily weaning trial

- in PSV mode - reduction in pressure support level

- in SIMV mode - reduction the number of controlled breaths

- CPAP trial

- T-piece trial - unassisted breathing

- automatic modes

are used on empirical basis,

important to allow adequate time for rest and sleep

8. Weaning from mechanical ventilation

ventilator dependency may be a serious problem

- weaning is an exercise

failure to wean may be due to inaquate cardiovascular reserve, which limits blood flow

or inadequate ventilatory reserve, which limits alveolar ventilation

- markedly increased work of breathing (normally ventilation at rest consumes 5% of oxygen delivery, this may increase to 25-30%)

8. Weaning from mechanical ventilation

causes of weaning failure:

1. unresolved underlying disease

2. poor respiratory muscle capacity

impaired central respiratory drive

respiratory muscle atrophy and fatigue

myopathies and neuropathies (e.g. critical illness neuropathy and myopathy)

rapid shallow breathing (high respiratory rate, low tidal volume)

8. Weaning from mechanical ventilation

causes of weaning failure:

3. inadequate nutrition

4. excessive inspiratory load

breathing circuit, tube, humidifier

intrinsic PEEP

5. left ventricular dysfunction

6. severe agitation and delirium

lung protective strategy is always a priority!