MECHANCAL VENTILATION

NUR AINA BINTI AB KADIR

MECHANCAL VENTILATION

CONTENTS

INTRODUCTIONThe fundamental operation of positive pressure ventilation is to create a pressure that moves a volume of gas into the lungs. 1. Volume-controlled ventilation , where the inflation volume (tidal volume) is preselected, and the ventilator automatically adjusts the inflation pressure to deliver the desired volume. The rate of lung inflation can be constant or decelerating.2. Pressure-controlled ventilation, where the inflation pressure is preselected, and the duration of inflation is adjusted (by the operator) to deliver the desired tidal volume. The rate of lung inflation is high at the onset of lung inflation (to achieve the desired inflation pressure), then rapidly decelerates (to maintain a constant inflation pressure).

TYPES

NON INVASIVEHave respiratory failure but no urgent need of intubationConscious and cooperativeNo risk of aspirationTightly fitted mask

CONTRAINDICATION

Contraindication :Cardiac and respiratory arrestSevere hypoxemiaHigh risk of aspirationFacial traumaInability to protect airwaysUpper GI bleed

COMPLICATIONSLeakage HypoventilationInconvenience and claustrophobiaIncrease chance of aspirationSkin breakdown, facial edema on prolonged use

INITIAL SETTING OF VENTILATORTidal volume : 6-8 mlI:E ratio : 1:2 Frequency : 10-12 breaths/minInspiratory flow rate : 60-80 liters/minPEEP : 3-5 cmH2OTrigger sensitivity : -1 to -2 cmH2OFIO2 : 0.5 (50%)

INDICATIONS

OTHERSExcessive fatigue of respiratory muscleLoss of protective airway reflexesInability to cough adequately

MODESControlled mode ventilation (CMV)Assisted controlled ventilation (AC)Synchronized intermittent mandatory ventilation (SIMV)Positive end expiratory pressure (PEEP)Continuous positive airway pressure (CPAP)Inverse ratio ventilation (IRV)Pressure support ventilation (PSV)Pressure controlled ventilation (PCV)Bi-level positive airway pressure (BIPAP)Airway pressure release ventilation (APRV) High frequency ventilation

CONTROLLED MODE VENTILATION(CMV)No spontaneous effort from patient.All breath are fully provided by ventilator.Control both pressure and volume

ASSISTED CONTROL VENTILATION (VC)Patients spontaneous breath is assisted.If spontaneous breath exceed preset rate, no control breath will be delivered and vise versa.

SYNCHRONIZED INTERMITTENT MANDATORY VENTILSTION (SIMV)Similar to control mode.Whatever the preset mode, it is consider mandatory.ventilator synchronize its breath with patients breath.

SYNCHRONIZED INTERMITTENT MANDATORY VENTILSTION (SIMV)Advantages over CMV :Less hemodynamic depression (less cardiac output)Less need of heavy sedation or muscle relaxantsLess V/Q mismatchMore rapid weaning

Disadvantages :Use lots work of breathing (leads to muscle fatiggue)Increase chance of hypocapnia (due hyperventilation)

POSITIVE END EXPIRATORY PRESSURE (PEEP)Positive pressure is given at end of expiratory :Prevent alveolar collapseLead to gas exchange during expiration

Used in :Pulmonary edemaARDSIn thoracic surgery to minimise bleedingPhysiological PEEP

SIDE EFFECTS OF PEEP hypotension and decrease cardiac outputIncrease pulmonary artery pressure and right ventricular strainIncrease dead spaceIncrease pleural pressureIncrease mediastinal pressureIncrease intracranial pressure

CONTINUOUS POSTIVE AIRWAY PRESSURE (CPAP)Continuously the positive pressure is given.Help prevent alveolar collapse.Used for spontaneously breathing patient

INVERSE RATIO VENTILATIONInverse the inspiration and expiration ratio from 1:2 to 2:1.It prolonged the gas exchange time as inspiration time is more

PRESSURE SUPPORT VENTILATIONPreset pressure is given to achieve desired tidal volume.The PEEP preset are 8 cmH2O and then titrated to achieve desired tidal volume.Can be used alone or combine with SIMV.Help in decrease work of breathing and overcome resistance offered by endotracheal tube and ventilator tubing.

PRESSSURE CONTROLLED VENTILATION(PCV)Similar to pressure support ventilation.Difference is :Ventilator will cycle to expiration once a predetermined time is elapse in the inspiration (time cycle).

Advantages :Less chance of barotraumaHave choice to extending the inspiratory time

Disadvantages :Tidal volume can vary with airway pressure

BI-LEVEL POSITIVE AIRWAY PRESSURE (BIPAP)Similar to continuous positive airway pressure.But it have typical setting :8-20 cmH2O on inspiration(IPAP)5 cmH2O on expiration(EPAP)

Combination of PEEP and CPAP.

AIRWAY PRESSURE RELEASE VENTILATION (APRV)Combine with PEEP and CPAP.Make a periodic release of pressure to decrease incidence of barotrauma and hypotension.

HIGH FREQUENCY VENTILATIONUsed in condition where exact tidal volume cannot be delivered.Thus minute volume is compensated by high frequency.

Indication : Bronchopleural fistulaBronchoscopiesMicrolaryngeal surgeryEmergency ventilation through cricothyroid membrane

HIGH FREQUENCY VENTILATIONHigh frequency ventilation may be :High frequency of positive pressure : 60-120 cycles/minHigh frequency jet ventilation : 100-300 cycles/min with gases at high pressureHigh frequency oscillations : 600-3000 cycles/min

DUAL MODE VENTILATIONCombine both pressure and volume ventilation.Modes used : Pressure controlled ventilation volume guaranteedBi-level volume guaranteed

COMPLICATIONSPulmonary barotraumaInfectionDue to prolonged intubationDue inadequate ventilationGITCardiovascularCNSLiver and kidney dysfunctionNeuromuscular weaknessOxygen toxicityPhysiologicalDue to prolonged bed rest

WEANINGDiscontinuing of ventilator support.Method :Shift from control/assist mode to SIMV.Decrease the rate of breathing till 1 to 2 breath/min.If tidal volume not sufficient give pressure support.Once tidal volume and frequency achieved, disconnected it.If normal cardiac and pulmonary functions maintained, extubation can be done.

WHEN??Initial setting in normal rangeRapid shallow breathing index (RSBI)Normal arterial pHNormal hemoglobinNormal cardiac statusNormal electrolyteAdequate nutritional status

REFERENCESShort textbook of Anaesthesia,Ajay Yaday,5th editionThe ICU Book, Paul L. Marino, 3rd Edition.