Acute respiratory failure 68 Postop 21 Pneumonia 14

Συχνότερες Ενδείξεις – Acute respiratory failure 68% • Post-op (21%) • Pneumonia 14% • CHF 10% • Sepsis 9% • Trauma 8% • ARDS 4. 5% • Aspiration 2. 5% • Cardiac arrest 1. 9% – Acute on chronic respiratory failure • COPD 10% • Asthma 1. 5% • Chronic respiratory disease (non_COPD) 1. 8% – Coma 16. 7% – Neuromuscular disease 1. 8%

Ventilator Modes Used Each Day During the Course of Mechanical Ventilation Esteban, A. et al. JAMA 2002; 287: 345 -355. Copyright restrictions may apply.

Kaplan-Meier Curves of the Probability of Survival Over Time of Mechanical Ventilation Esteban, A. et al. JAMA 2002; 287: 345 -355. Copyright restrictions may apply.

Mechanical ventilation • Physiology: – Positive pressure ventilation versus naturanl negative pressure ventilation • Effects: – Heterogeneous ventilation • Preferential ventilation of the non-dependent regions – Increased physiologic dead space – Improvement of physiologic shunt causes by atelectasis and/or alveolar filling – Rapid disuse atrophy of the diaphragm – Impairment of mucociliary clearance

Mechanical ventilation • Cardiovascular effects: – Decreased venous return • Exacerbated by: – – Auto-PEEP Applied PEEP Intravascular volume depletion Cardiac tamponnade – Increased right ventricular afterload: • Compression of the pulmonary vascular bed Increased PVR – May decrease left ventricular afterload • Lung exansion decreased extramural pressure

“…. An opening must be attempted in the trunk of the trachea, into which a tube or cane should be put; You will then blow into this so that lung may rise again…. And the heart becomes strong…. ” - Andreas Vesalius (1555)

Mechanical ventilation • Benefits – Improves gas exchange by improved V/Q matching predominantly be decreasing shunt – Decreased work of breathing

Κυματομορφές πίεσης, ροής και όγκου στα βασικά μοντέλα αερισμού Flow ~ Flow=ct Tidal Vol ~ Tidal Vol=ct Paw ~ Paw=ct Volume Control Pressure Control

Volume Control

Respiratory System Compliance C= tidal volume Pplat - PEEP Total PEEP Decreased with: • • • congestive heart failure ARDS atelectasis consolidation fibrosis hyperinflation • • • tension pneumothorax pleural effusion abdominal distension chest wall edema thoracic deformity normal 100 m. L/cm H 2 O

Inspiratory Resistance Ri = Increased with: Ppeak - Pplat flow measure with 60 L/min (1 L/s) constant flow • Secretions • Bronchospasm • Small endotracheal tube Normal: 5 - 10 cm H 2 O/L/s for intubated ventilated adults

Cstat = Vt/(Pplateau - PEEPtotal) (ml/cm. H 2 O) Rin = (Ppeak - Pplateau)/Inspiratory flow (cm. H 2 O/Lps)

FLOW Ppeak / Pmax P 1 Pao P 2/Ppl PEEP Ti Tpl Te

ΜΕΙΩΣΗ ΔΙΑΤΑΣΙΜΟΤΗΤΑΣ FLOW Ppeak Pao Ppl PEEP Ti Tpl Te

ΑΥΞΗΣΗ ΑΝΤΙΣΤΑΣΕΩΝ FLOW Ppeak Pao Ppl PEEP Ti Tpl Te

ΥΠΑΡΞΗ auto-PEEP FLOW Ppeak Pao Ppl = VΤ /Ctp Ti Tpl Te

Ti decreases

Compliance decreases

Ti increases, pressure falls, PEEPi develops, overdistention develops

Pressure Control

Pressure-Controlled Ventilation Increasing airways resistance Decreasing lung compliance Lucangelo, Respir Care 2005; 50: 55

Assisted modes Assist volume/pressure control SIMV Pressure support CPAP

Triggering

Pressure or Flow Trigger

Synchronized Intermittent Mandatory Ventilation

Pressure Support Ventilation

Pressurization Rate

Expiratory threshold 100% flow 75% FLOW 50% Time 25 %

Expiratory threshold 50% 100% Flow 75% FLOW 50% 25% Time T. I.

Expiratory treshold 75% 100% Flow FLOW 75% 50% 25% Time T. I.

Expiratory threshold 25% 100% Flow 75% FLOW 50% 25% Time T. i.

Pressure support cycling off

Pressure support cycling off

PSV με SIMV

PRVC (Pressure regulated volume control) A control mode, which delivers a set tidal volume with each breath at the lowest possible peak pressure. Delivers the breath with a decelerating flow pattern that is thought to be less injurious to the lung…… “the guided hand”.

Decelerating inspiratory flow pattern (square wave pressure build up) Flow Pressure automatically adjusted according respiratory mechanics to deliver set tidal volume Volume PRVC Set tidal volume

PRVC Automatically Adjusts To Compliance Changes

Advantages of volume targeted ventilation A significant increase in lung compliance, such as following exogenous surfactant administration will lead to a proportional increase in delivered VT unless the inflating pressure is reduced As the VT increases due to improving compliance after surfactant administration, the ventilator automatically drops the PIP. Volume Guarantee: New Approaches in Volume Controlled Ventilation for Neonates. Ahluwalia J, Morley C, Wahle HG. Dräger Medizintechnik Gmb. H. ISBN 3 -926762 -42 -X

PRCV: Advantages Decelerating inspiratory flow pattern Pressure automatically adjusted for changes in compliance and resistance within a set range Tidal volume guaranteed Limits volutrauma Prevents hypoventilation

PRVC: Disadvantages Pressure delivered is dependent on tidal volume achieved on last breath Volume Flow Pressure Intermittent patient effort variable tidal volumes Set tidal volume

PRVC: Disadvantages Pressure delivered is dependent on tidal volume achieved on last breath Volume Flow Pressure Intermittent patient effort variable tidal volumes Set tidal volume

Mechanical Ventilation Assessment of Weaning Readiness A method for Screening (Spontaneous Breathing Trial = SBT) A method for Weaning Difficult-to-wean patients (i. e. , patients who fail SBT)

Which mode? T piece PSV How long? Esteban et al, AJRCCM 1997 A) Esteban et al, AJRCCM 1999 B) Perrin et al, Intensive Care Med 2002

The Difficult- to-Wean Patients

14 Intensive Care Units: -12 months prospective study -546 patientts meeting weaning criteria Esteban et al. , N Engl J Med 1995, 332: 345 -50

3 Intensive Care Units: Creteil, Rome, Barcelona -18 months prospective study -456 patientts meeting weaning criteria Brochard et al. , AJRCCM 1994, 150: 896

PSV T-piece Am J Respir Crit Care Med 2001; 164: 225 -230.