open lung approach concept of mechanical ventilation

OUTLINE• Introduction• Goals & Indications of Mechanical Ventilation• Physiology/Pathophysiology of MechanicalVentilation• Recruitment strategies/Open Lung concept• Choosing an Appropriate Ventilatory Strategy• Monitoring; Adverse Effects• Non-Conventional Approaches

WARNING/CAUTION• Do not attempt this if you have never seen amechanical ventilator• Some of the principles may be harmful inNeonates• Learning and responsible practice will getyou with the programme!• Use strategy that suits your patient and youbest!

• HistoryINTRODUCTION• Vivisection work; PolioEpidemics• Conventional Ventilation• Principal mode in criticallyill patients• Initially for totally apnoeicpatients• Ventilator design• From Iron Lung to TotalSophistication• No ideal ventilator

INTRODUCTION• One of the key measures of patient outcome and thequality of care in ICU is ventilator-free days.• Ventilatory protocols for acutely ill patients in the ICUhave improved favourably over time.• Strategies have changed from optimizing convenientphysiology variables, such as O2 and CO2 levels, toprotecting the lung from injury and↓cytokinemodulation of the lung

PHYSIOLOGY OF MECHANICALVENTILATION• Positive pressure via ETT• Large pressures applied• Increase in Mean Intrathoracic Pressure• Decreased venous return and CO :– Compensated for by normal vascular reflexes– Pronounced in hypovolaemic patients and atextremely high mean airway pressures

PATHOPHYSIOLOGY OFMECHANICAL VENTILATION• The cycle of continuous expansion and collapseof alveoli in respiratory cycle structuralchanges by barotrauma and volutrauma, as wellas surfactant function and cytokinereleaseAlveolar collapse with impropermechanical ventilation(↓PEEP↑VT) activation of SIRS• Disruption of Alveolar gas membrane• Surfactant system dysfunction• The lung is an important causative part of aninflammation-induced systemic disease state MOF,not only a pulmonary disease process.

ARDS• Catastrophic pulmonary or non-pulmonary• event resulting in ALI & respiratory failure• Increased intrapulmonary shunt• Hypoxaemia• Decreased pulmonary compliance• Diffuse pulmonary infiltrates• Exclusion of left heart failure• Need for mechanical ventilation

Goals of Mechanical Ventilation• Optimise oxygen delivery and ventilation• Oxygenation• Carbon dioxide Removal• Minimise toxicity• Barotrauma• Volutrauma• Cardiorespiratory Interractions• Optimise patient work of breathing

VOLUTRAUMA:Stretch Injury-alters capillarytransmural pressures-causes breaks incapillary endothelium& epithelium-increases leakof proteinaceousmaterial

BAROTRAUMA-air-leak intopleural orinterstitialspace-tearing at bronchoalveolarjunction aslung is recruited &allowed to collapse-most occurs independent lung attransition zone

OPTIMISED LUNG VOLUMEhigh lung volumeventilation overdistendsresultingin volutraumalow lungvolumeventilation tearsadhesivesurfaces

OPEN LUNG CONCEPT• The strategy of lung recruitment or openlung concept (OLC) refers to the dynamicprocess of opening previously collapsedlung units by ↑transpulmonary pressure.• The OLC may play an important role inpreventing ventilator-induced lung injury

LUNG RECRUITMENT Recruitment maneouvre controlled positive ventilatorypressure necessary to expand alveoli. In true alveolar collapse, the pressure needed foralveolar recruitment may reach above 70 cmH2O Alveolar bed may be opened best using the deceleratingwave pattern of Methods vary: Sustained inflation with 30cmH2O for 30 -60 seconds High PEEP 20-40 cmH2O- then titrate down Proning + Higher PEEP Initial High Paw on HFOV for 60 seconds then back to transitioning Paw

LUNG RECRUITMENT ↑initial inspiratory pressure recruit collapsealveoli, then minimal pressure prevent lungfrom collapsing Intrapulmonary suction renewed collapse of alveoli PaO2↓,secretion management must be balance withalveolar recruitment Early OLC ( < 72hrs ) higher response rate, thisprobably related to the change from exudate to afibroproliferative process

Appropriate Ventilatory StrategySystematic Evaluation• Identify the pathophysiology of the patient• Evaluate available modes based on physiology,advantages, & disadvantages• Pathophysiology directed therapy:– hypothesis testing– “take your best guess”• Monitor for effects / side-effects of therapy– non-invasive: exam, CXR, graphics– invasive: ABG, SVO2, lactates

Practical Clinical GuideInitiating Ventilation• Open lungs first: Recruit!!!• Sustained Inflation; PEEP Titration; High Paw on HFOV• Volume limited:• TV = 4-6 ml/kg ; PEEP = 8-10 ; FIO2 =1.0• Rate: physiological limits for age• Pressure Limited• PIP = 20 ; PEEP = 8-10 ; FIO2 = 1.0• Rate: physiological limits for age• PSV: PEEP = 8-10; PS to give TV 6-8ml/kg

Monitoring Ventilatory TherapyClinical EvaluationBlood GasesPulse OximetryEnd Tidal CO2Airway GraphicsRadiologic studies

WeaningMeet weaning criteria• Primary condition reversed/improved• ideally no other organ support• Normal metabolic profile• Decreased need for sedatives/relaxants• A-aDO2 less than 100• OI less than 13• Transitioning devises• What is comfortable for the patient

LUNG PROTECTIVE STRATEGIES• UNDERSTAND MODES OF VENTILATION• OPEN LUNG APPROACH• LOW TIDAL VOLUME STRATEGY• HIGH PEEP LOW PIP• PERMISSIVE HYPERCAPNIA IF POSSIBLE• LOW FIO 2 ASAP!

Consider Non Conventional Modes• High Frequency Oscillation• Partial Liquid Lung Ventilation• ECMO• Negative Pressure Ventilation

NON CONVENTIONAL MODES

CONCLUSION• Conventional Ventilation:• Tried & tested- still mainstay of vent support• Familiar with it• Adverse effects; Failure• Quest for “Zero” Lung Damage• Smarter ventilatory protocols• Don’t chase normal physiologic values in adiseased lung

ADIOS: I WILL BE BACK• L’HITRAOT• SIZOBONANA FUTHI• TILL WE MEET AGAIN• GO YA KA MAGORO GA SE GOTSWANA• LATER DUDES AND DUDDETTES• Au Revoir• RI do VHONANA• HASTA LA VISTA