mechanical ventilation & respiratory support therapy

8/2/2019 Mechanical Ventilation & Respiratory Support Therapy

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Mechanical ventilation &Respiratory supporttherapy

DR.REZWANUL HOQUE BULBULMBBS, MS, FCPS, FRCSG, FRCS EdASSOCIATE PROFESSORDEPARTMENT OF CARDIAC SURGERYBSMMU, DHAKA, BANGLADESH


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DEFINITION

It refers to the gamut of artificial means usedto support ventilation and oxygenation.

They encompass all forms of PositivePressure Ventilation and those modes used to

increase airway pressure above atmosphericduring spontaneous ventilation


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GOALS OF VENTILATION

Increase efficiency of breathingIncrease oxygenationImprove ventilation/perfusion

relationshipsDecrease work of breathing


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Types of Systems

Negative Pressure VentilatorIron lung Allows long-term ventilation withoutartificial airwayMaintains normal intrathoracichemodynamicsUncomfortable, limits access topatient


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Types of Systems

Positive Pressure VentilatorUses pressures above atmospheric

pressure to push air into lungsRequires use of artificial airwayTypes

Pressure cycledTime cycledVolume cycled


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Positive Pressure VentilatorsPressure Cycled

Terminates inspiration at preset pressureSmall, portable, inexpensiveVentilation volume can vary with changes inairway resistance, pulmonary complianceUsed for short-term support of patients withno pre-existing thoracic or pulmonaryproblems


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Positive Pressure VentilatorsVolume cycled

Most widely used systemTerminates inspiration at preset volumeDelivers volume at whatever pressure isrequired up to specified peak pressureMay produce dangerously high intrathoracicpressures


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Positive Pressure VentilatorsTime cycled

Terminates inspiration at preset timeVolume determined byLength of inspiratory time

Pressure limit setPatient airway resistancePatient lung complianceCommon in neonatal units


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CLASSIFICATION / On the basis of three functions

INITIATION CONTROL Initiation triggered by machine at a

predetermined time set regardless of patienteffort

ASSIST Supported breath is triggered when patientinitiates a breath that develops negativepressure below a threshold termed sensitivity

LIMIT VOLUME Tidal volume is preset while peak airwaypressure is variable

PRESSURE Airway pressure is preset while tidal volumeis variable

CYCLE OFF VOLUME Tidal volume delivered then converted toexpiration

TIME May be prolonged by inspiratory pause

FLOW RATE Converted to expiration when flow rate

declines to predetermined level


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VENTILATOR MODES

Defined by inspiratory events while expiration istreated as independent entity


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CONTROLLED MECHANICAL VENTILATION(CMV)Initiation is time dependent with a fixed rate

Tidal volume is delivered along with inspiratory pauseTidal volume is delivered regardless of airway pressureIf pressure limit is set delivery will stop once the limit isreached

Eliminates patients work of breathingRequires an anaesthetized and paralyzed patientUseful when inspiratory effort contraindicated (flailchest)

Patient must be incapable of initiating breathsRarely used


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ASSISTED MECHANICAL VENTILATION

Initiation is assisted when sensitivity is reachedOtherwise similar to CMVBetter tolerated in light sedationCannot be used in sedated or paralyzedWork of breathing is greaterCan predispose to alkalosis if resp. rate is high


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Assist ModeAssist/Control (A/C )

Patient triggers machine to deliver breaths butmachine has preset backup ratePatient initiates breath--machine delivers tidalvolumeIf patient does not breathe fast enough, machinetakes over at preset rateTachypnea patients may hyperventilatedangerously


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A/C mode


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Assist Mode

INTERMITTENT MANDATORY VENTILATION(IMV)

Combination of CMV and Spontaneousmodified circuit allows continuous flow that allows patient tobreathe between machine delivered breath with minimal workof breathing

Delivery is regardless of the stage of respirationPatient breathes on ownMachine delivers breaths at preset intervalsPatient determines tidal volume of spontaneous breathsUsed to wean patients from ventilators patient machine dyssynchrony may lead to lung overdistension or fighting with the ventilatorPatients with weak respiratory muscles may tire frombreathing against machines resistance Largely abandoned in favor of SIMV


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Assist modeSYNCHRONISED INTERMITTENT MANDATORENTILATION(SIMV)

IMV in assist modeMachine timed to delay ventilations until end of spontaneous

patient breathsAvoids over-distension of lungsDecreases barotrauma risk

However if patient does not breathe then IMV deliversRelative work of breathing is lessDoes not contribute to central hyperventilationsyndromeDoes not require sedation or paralysisIn COPD patients, hypercarbia is preservedPopular mode for weaning of patients


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SIMV mode


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PRESSURE SUPPORT VENTILATIONApplicable in spontaneous ventilation

Initiation of respiration cause rapid flow of gas untilselected pressure is crossed and continues untilinspiration drive is stoppedAdvantage over SIMV being support is provided foreach breathRequires spontaneous ventilation but spontaneous

breath in SIMV mode are also supportedCannot be used in low pulmonary complianceCentral hyperventilation syndrome along with

resp.alkalosis may developMonitoring of tidal volume is required


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Pressure support ventilation


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Volume control vs. pressurecontrol

There are, effectively, two ways of assisting inspiration by using positivepressure to deliver a certain amount of volume (volume control ventilation),or by delivering a certain amount of pressure (pressure control ventilation).Volume control means volume constant and pressure variable.Pressure control means pressure constant (or limited) volume variable

ventilation.The mode of ventilation, is the way in which the ventilator uses volume orpressure to bump the patient up the pressure-volume curve.Patients may be given mandatory breaths (controlled ventilation) or may

have their spontaneous breaths assisted (assist control ventilation).An alternative mode (which is often used with controlled modes) is pressuresupport, which allows a patient breath spontaneously, start and finishbreaths and determine the tidal volume.Mechanical ventilation that is achieved regardless of the patient's

spontaneous breathing, but that uses pressure as the major determiningvariable, along with rate and time, of how much air the patient receives.


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High Frequency Ventilation (HFV)

Small volumes, high ratesAllows gas exchange at low peak pressures

Mechanism not completely understood

High frequency positive pressure ventilation--60-120 breaths/min

High frequency jet ventilation--up to 400 breaths/min High frequency oscillation--up to 3000 breaths/min


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High Frequency Ventilation (HFV)

Useful in managing:Tracheobronchial or bronchopleural fistulas Severe obstructive airway disease Patients who develop barotrauma or decreased cardiac output with more conventional methods Patients with head trauma who develop increased ICP with conventional methods Patients under general anesthesia in whom ventilator movement would be undesirable


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Alternative modes of ventilation

Non-invasive positive pressure ventilation using specialized faceor nasal maskNegative pressure ventilation using special apparatus in COPDpatientAirway pressure release ventilation- Lung is kept inflated atconstant pre-set pressure to achieve alveolar recruitment andinflation, intermittent release of pressure to allow exhalationMandatory minute ventilation- Pre-set minute ventilation either byspontaneous or by supplemental breath by machineInverse ratio ventilation- normal I:E ratio is reversed from 1:2/1:3to 1:1-3:1Partial liquid ventilation- Perfluorocarbon liquid instilled into lungfollowed by standard mechanical ventilationECMO


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POSITIVE END EXPIRATORY PRESSURE

commonly kept at 3 5 cm of water as a substitute forphysiological PEEP provided by closed glottis

primary goals include:

1. increase functional Residual Capacity2. distends patent alveoli3. recruits previously collapsed alveoli4. In pulmonary edema, may redistribute extra vascular

lung water from alveolar capillary interstitium toperibronchial and perihilar interstitium


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Disadvantages

1. Alveolar distention and pulmonary dead spaceincreases air trapping, CO2 retention andhypercapnia

2. Not useful in diseased lung3. Not tolerated in awake patients

4. Increased work of breathing5. Increased chances of barotraumaContraindications

1. Severe hemodynamic instability2. Acute bronchospasm3. Severe Emphysema4. Pneumothorax Suspected or present


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Continuous Positive Airway Pressure(CPAP)

PEEP without preset ventilator rate or volume Physiologically similar to PEEP May be applied with or without use of a ventilator or artificial airway Requires patient to be breathing spontaneously Does not require a ventilator but can be performed with some ventilators


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RATIONALE FOR MECHANICAL VENT.

Provides the time to reverse the adverse effects onlung function induced by anaesthesia and surgery

Allows aggressive pain control without concern forrespiratory depression

Reduces the work of breathing and saves energy atthe critical period

In patients who are hemodynamically unstable,ensures effective ventilation reducing the number ofvariables in management


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INDICATION OF MECHANICAL VENTILATION

PLANNED POST OPERATIVEBased on Surgical procedures

1. Cardiac Surgery2. Major Vascular Surgeries3. Procedures with major blood loss4. High risk Surgical Incisions

Planned- other diseases1. Neuromuscular and Mechanical dysfunction2. Parenchymal lung diseases3. Acute lung injury4. Multi System Organ FailureUnplanned

1. Depressed CNS response to hypoxia and hypercapnia

upper abdominal reduces FRC by 60% thoracotomy reduces FRC by 40%


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INDICATION (CONTD CARDIO PULMONARY COMPLICATION

Acute Myocardial Infarction

ArrhythmiasPulmonary edemaSevere bronchospasmLobar Atelectasis

SURGICAL COMPLICATIONSHemorrhageCardiac contusion following TEE, Phrenic Nerve injury

OPERATIVE CATASTROPHECardiac arrest, Malignant hyperthermia, ABO mismatchGastric Acid aspiration, Major anaphylactic reaction

INADEQUATE REVERSAL OF ANAESTHESIAinadequate elimination of anaesthetic agentsinadequate reversal of opioid analgesicsinadequate reversal of muscle relaxants


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Ventilator SettingsTidal volume--10 to 15ml/kg (std = 12 ml/kg)Respiratory rate--initially 10 to 16/minuteFiO 2--0.21 to 1.0 depending on disease process

100% causes oxygen toxicity and atelectasis in less than 24 hours40% is safe indefinitelyPEEP can be added to stay below 40%Goal is to achieve a PaO 2 >60I:E Ratio--1:2 is good starting pointObstructive disease requires longer expirationsRestrictive disease requires longer inspirations

Changes are made according to Arterial Blood Gas reports Maintain with ACV, use sedatives & muscle relaxants if needed Switch to Synchronized Intermittent Mandatory Ventilation (SIMV) mode, reduce respiratory rate gradually and finally switch to Spontaneous mode Extubate the patients when the criteria's are met.


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Ventilator SettingsAncillary adjustments

Inspiratory flow timeTemperature adjustmentsHumidityTrigger sensitivityPeak airway pressure limitsSighs


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Quick Guide to Setup

Self check and/or Calibration as needed

Check circuit and connectionsSet Mode: Usually Assist/Control

Adjust I time: Usually 1 second Set tidal volume: 10-12 ml/kg is standard

May need to set Flow based on I time Set ventilatory rate: Adult 12-16/min

WEANING FROM VENTILATOR


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WEANING FROM VENTILATORCriteria

1. Mental Alertness2. No active bleeding3. Haemodynamic stability4. Normothermic5. Satisfactory Arterial Blood Gas report

PaO2 > 70 mm of Hg on an FIO2 10 15ml / kgNegative Inspiratory Force > 25 cm waterSpontaneous Respiratory Rate < 30 / minD(A-a)O2


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Ventilator Complications

Mechanical malfunctionKeep all alarms activated at all timesBVM must always be availableIf malfunction occurs, disconnect ventilator and ventilatemanually


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Airway malfunctionSuction patient as neededKeep condensation build-up out of connecting tubesAuscultate chest frequentlyEnd tidal CO 2 monitoring

Maintain desired end-tidal CO 2Assess tube placement


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Ventilator ComplicationsPulmonary barotraumaAvoid high-pressure settings for high-risk patients (COPD)Monitor for pneumothorax

Anticipate need to decompress tension pneumothorax

low chance with peak airway pressure < 45 cm of waterhigh tidal volume may injure alveolar capillary membrane

Oxygen toxicityincidence and rapidity of oxygen related injury increases withFIO2 > 60%


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Renal malfunctionGastric hemorrhagePulmonary atelectasisInfectionOxygen toxicityLoss of respiratory muscle tone

increased intra cranial pressure

V il li i


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Ventilator complications

Acute Respiratory Insufficiencypresent when there is evidence of inadequate oxygenation (PaO2 50 mm Hg) duringmechanical ventilatory support.

Causes:

-Ventilator malfunction, improper setting- Endotracheal tube malfunction- Pulmonary Problems Atelectasis, Pulmonary

edema, Pneumonia, Pneumothorax,Haemothorax

- Low cardiac output states- Aspiration Pneumonia


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Management:

- Examine the ventilator setting and function, ETTube, ABGs, CXR

- Hand ventilate with 100% O2, increase FIO2 inventilator until problem is corrected

- May require repositioning of ET tube, insertion ofIntra thoracic tube

- Asses and optimise hemodyanmics- Add Inverse Ratio Ventilation with PEEP increment- Consider sedation and Paralysis in patient Ventilator

synchronicity- Treat identifiable causes


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Chronic Respiratory insufficiencyinability to wean from ventilator within 48-72 hours

caused by problems that primarily impair oxygenationor produce primary Ventilatory insufficiency

Causes: Hypoxia, ARDS, Sepsis, Metabolic

Abnormalities,Phrenic nerve paralysis

Management:

Treat the primary causePatients may even require Tracheostomy forfurther airway management


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Thank you

mechanical ventilation & respiratory support therapy

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