basic mechanical ventilation

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Slide 1: 

1/26/2012 1 Basics of mechanical ventilation Dr Nabeel

Indications for intubation? : 

All three problems may coexist 1/26/2012 2 Indications for intubation?

Oxygenation failure : 

Oxygenation failure 1/26/2012 3 Oxygenation failure most often occurs at pulmonary capillary-alveolar interface. Classically injuries are divided up into Diffusion defects and Ventilation Perfusion mismatch Diffusion abnormality thickening of the alveoli (pulmonary fibrosis) or increased extracellular fluid (Pulmonary edema) Ventilation/Perfusion Mismatch Dead Space Ventilation  Shunt

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1/26/2012 4

Slide 5: 

Air (Ventilation) Blood (Perfusion) Normal Gas Exchange Collapsed Alveoli Decreased Ventilation Normal Ventilation Normal Perfusion Decreased Perfusion Shunt (Wasted Perfusion) Dead Space (Wasted Ventilation) Ventilation/perfusion mismatch 1/26/2012 5

Ventilatory Failure : 

Ventilatory Failure 1/26/2012 6 Load compliance+resistance Insp. muscle performance Reduced central drive Impaired inspiratory muscle performance Excessive respiratory workload

Slide 7: 

Principles : Oxygenation The primary goal of oxygenation is to maximize O2 delivery to blood (PaO2) Alveolar-arterial O2 gradient (PAO2 – PaO2) Equilibrium between oxygen in blood and oxygen in alveoli A-a gradient measures efficiency of oxygenation PaO2 partially depends on ventilation but more on V/Q matching Oxygenation in context of ICU V/Q mismatching Patient position (supine) Pulmonary parenchymal disease, small-airway disease V/Q Matching. Zone 1 demonstrates dead-space ventilation (ventilation without perfusion). Zone 2 demonstrates normal perfusion. Zone 3 demonstrates shunting (perfusion without ventilation). Adjustments: PEEP/I:E/ FiO2 1/26/2012 7

Slide 8: 

Principles : Ventilation The goal of ventilation is to facilitate CO2 release and maintain normal PaCO2 Minute ventilation (VE) VE = (RR) x (TV) VE comprised of 2 factors VA = alveolar ventilation VD = dead space ventilation VD/VT = 0.33 Ventilation in context of ICU Increased CO2 production fever, sepsis, injury, overfeeding Increased VD atelectasis, lung injury, ARDS, pulmonary embolism V/Q Matching. Zone 1 demonstrates dead-space ventilation (ventilation without perfusion). Zone 2 demonstrates normal perfusion. Zone 3 demonstrates shunting (perfusion without ventilation). Adjustments: RR and TV 1/26/2012 8

Slide 9: 

Initiation of invasive mechanical ventilation 1/26/2012 9

0utline of ventilator classification system : 

0utline of ventilator classification system 1/26/2012 10 1) INPUT POWER electric Pneumatic Combined 2)Positive or negative pressure generators 3) CONTROL systems and circuits Open/closed loop Control subsystems (circuit /control valves) Power transmission or drive mechanism (eg. compressors, piston) Control panel(user interface) 4) OUTPUT Waveforms (pressure/volume/flow) Displays 5) ALARMS

Slide 11: 

Expiration line inspiration line ventilator Y connector Exhalation valve 1/26/2012 11

Control : 

Control 1/26/2012 12 Control: Primary variable adjusted by ventilator to deliver inspiration. The ventilator can control only one variable at a time. Types: Volume Controlled (volume limited, volume targeted) and Pressure Variable Pressure Controlled (pressure limited, pressure targeted) and Volume Variable Dual Controlled (volume targeted (guaranteed) pressure limited)

Slide 13: 

Pressure ventilation vs. volume ventilation Pressure-control modes deliver a fixed pressure at variable volume. Volume-control modes deliver a fixed volume at variable pressure. 1/26/2012 13

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1/26/2012 14

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1/26/2012 15

4 phases of breath : 

4 phases of breath 1/26/2012 16 Change from exhalation to inspiration Inspiration Change from inspiration to exhalation Exhalation

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1/26/2012 18

Trigger : 

Trigger 1/26/2012 19 Trigger: What causes the ventilator to begin inspiration? Types: Time trigger: the ventilator cycles at a set frequency as determined by the controlled rate. Pressure trigger: the ventilator senses patient's inspiratory effort by way of a decrease in the baseline pressure. Flow trigger

Trigger : 

Trigger 1/26/2012 20

Limit : 

Limit 1/26/2012 21 LIMIT: A variable(pressure, volume, flow) is ‘limited’ if it increases to to a preset value before inspiration ends. inspiration is NOT terminated when a variable has reached its limit volume flow Flow limited volume flow Flow limited Volume limited Volume cycled

Cycling : 

Cycling 1/26/2012 22 Cycling: How the ventilator switches from inspiration to expiration: the flow has been delivered to the volume or pressure target - how long does it stay there? Types: Time cycled - such in in pressure controlled ventilation Flow cycled - such as in pressure support Volume cycled - the ventilator cycles to expiration once a set tidal volume has been delivered (volume control)

Slide 23: 

1/26/2012 23

Slide 24: 

1/26/2012 24 Flow limited Volume cycled

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1/26/2012 25

Slide 26: 

1/26/2012 26 limit Flow Pressure Cycle Volume/ time Pressure flow Volume control

Slide 27: 

1/26/2012 27 limit Flow Pressure Cycle Volume time Pressure flow pressure control

Slide 28: 

1/26/2012 28 limit Flow Pressure Cycle Volume Time Pressure/ /flow Pressure support

Slide 29: 

1/26/2012 29 limit Flow Pressure Cycle Volume Time Pressure flow Volume targeted Pressure Control (dual control)

Flows : 

Flows 1/26/2012 30 Sinusoidal = flow pattern seen in spontaneous breathing and CPAP Decelerating = flow pattern seen in pressure targeted ventilation: inspiration slows down as alveolar pressure increases (there is a high initial flow). Most intensivists and respiratory therapists use this pattern in volume targeted ventilation also, as it results in a lower peak airway pressure than constant and accelerating flow, and better distribution characteristics Constant = flow continues at a constant rate until the set tidal volume is delivered.

Advantages of descending ramp flows : 

Advantages of descending ramp flows 1/26/2012 31 Inspiration slows down as alveolar pressure increases (there is a high initial flow). lower peak airway pressure than constant and accelerating flow, and better distribution gas characteristics Reduced dead space Improves oxygenation by increasing the mean airway pressures Lower peak pressures Most intensivists use this pattern in volume targeted ventilation also.

Pressure vs Volume controlled mode : 

Pressure vs Volume controlled mode 1/26/2012 32 Pressure control is better

Expiratory support : 

Expiratory support 1/26/2012 33 Expiratory support is almost always PEEP/CPAP, which elevates the baseline airway pressure. CPAP

Slide 34: 

. Expiratory support 1/26/2012 34

Slide 35: 

1/26/2012 35 Ventilator settings

Ventilator settings : 

Ventilator settings 1/26/2012 36 Ventilator mode Respiratory rate Tidal volume or pressure settings Inspiratory flow I:E ratio PEEP FiO2 Inspiratory trigger

Main controls : 

Main controls 1/26/2012 37 To improve oxygenation: increase FIO2 increase mean alveolar pressure increase mean airway pressure increase PEEP increase I:E ratio To improve CO2 elimination: respiratory rate tidal volume


INSPIRATORY TIME (Ti), I:E ratio 1/26/2012 38 INSPIRATORY TIME (Ti), I:E ratio, Inspiratory Pause Time the time over which the tidal volume is delivered or the pressure is maintained (depending on the mode) I:E ratio=(inspiratory time + inspiratory pause time):expiration usually set 1:2 to mimic usual pattern of breathing Inspiratory pause time is only set in modes where a fixed tidal volume is set and delivered (volume control) EXPIRATORY TIME is whatever time is left over before the next breath

What long inspiratory times do? : 

What long inspiratory times do? 1/26/2012 39 improve oxygenation by: Increasing mean airway pressure (longer period of high pressure increases mean airway pressure over the entire respiratory cycle) allowing re-distribution of gas from more compliant alveoli to less compliant alveoli decrease peak pressure by decreasing inspiratory flow increase risk of gas trapping, intrinsic PEEP and barotrauma by reducing expiratory time less well tolerated by the patient, necessitating a deeper level of sedation

Slide 40: 

1/26/2012 40 In pressure control modes, either inspiratory time or I:E ratio is set (flow is adjusted to ensure that the set tidal volume is delivered in that time). These modes include: pressure control volume control (Siemens and Drager ventilators) pressure regulated volume control In volume-control modes, either inspiratory time/I:E ratio is set or the flow is set and inspiration ends when the set tidal volume has been delivered. These modes include: volume control (Puritan-Bennett and Bear ventilators) In pressure support (flow cycled) mode, the patient determines the duration of inspiration . M A N D A T O R Y

Relation between Ti, flow and tidal volume (VT) VT = flow× Ti : 

Relation between Ti, flow and tidal volume (VT) VT = flow× Ti VOLUME CONTROL PRESSURE CONTROL 1/26/2012 41

Rise time or %rise time : 

Rise time or %rise time 1/26/2012 42

Slide 43: 

1/26/2012 43

Alarm settings : 

Alarm settings 1/26/2012 44 Set the alarm settings for: Rates Minute ventilation Airway pressures PEEP Apnea time Sound level

Basic modes of ventilation(Inspiratory Support) : 

Basic modes of ventilation(Inspiratory Support) 1/26/2012 45 The description of the mode of ventilation refers to the method of inspiratory support - how the patient is helped up the volume /pressure curve. MANDATORY Continuous mandatory ventilation (CMV) Assist/control (A/C) ventilation Intermittent mandatory ventilation (IMV) Synchronized intermittent mandatory ventilation (SIMV) ± PSV (Pressure/volume control) SPONTANEOUS SPONTANEOUS BREATHING CPAP ± PSV PSV

Slide 46: 

1/26/2012 46 Mandatory modes

For eg; CMV/VC or PC : 

For eg; CMV/VC or PC 1/26/2012 47 pressure/flow

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1/26/2012 48

Slide 49: 

1/26/2012 49 Or volume Pressure or flow

IMV(pressure/volume control) : 

IMV(pressure/volume control) 1/26/2012 50

Slide 51: 

1/26/2012 51 For eg; IMV(volume control)

Slide 52: 

SYNCHRONIZED BREATHS 1/26/2012 52 /volume Pressure or flow

Slide 53: 

1/26/2012 53

Slide 54: 

1/26/2012 54 Flow limited Volume cycled For eg; SIMV/VC

Slide 55: 

1/26/2012 55 For eg; SIMV/PC

Slide 56: 

1/26/2012 56 Spontaneous modes

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1/26/2012 57

Slide 58: 

1/26/2012 58

Slide 59: 

1/26/2012 59 Supported breath

Slide 60: 

1/26/2012 60 Supported breath

Slide 61: 

1/26/2012 61 Non-Invasive ventilation

Setting up an acute non-invasive ventilation : 

Setting up an acute non-invasive ventilation 1/26/2012 62

Overview : 

Overview 1/26/2012 63 Patient selection Knowing our equipment Set initial ventilator parameters and initiate NIV Assess improvement and deterioration Recognise and solve problems that limit effectiveness of NIV

Mechanism of action of NIV in COPD : 

Mechanism of action of NIV in COPD 1/26/2012 64 Supra-atmospheric pressure in airways Increased transpulmonary pressure Augments tidal volume Partial unloading of respiratory muscles In COPD , NIV counteracts autopeep

Mechanism of action of NIV in CHF : 

Mechanism of action of NIV in CHF 1/26/2012 65 preload reduction After load reduction more less Improved cardiac output in patients with poor contractility

Slide 66: 

1/26/2012 66 Patient selection

CPAP/BiPAP Indications : 

CPAP/BiPAP Indications 1/26/2012 67 Acute cardiogenic pulmonary edema “Severe” COPD Exacerbations Acute Respiratory Failure in the Immunosuppressed To Facilitate Early Extubation in COPD Note: NOT for extubation failures HOWEVER DO NOT DELAY INTUBATION IF INDICATED!!!

Recommendations NIV in ARF : 

Recommendations NIV in ARF 1/26/2012 68 Strong Evidence – (multiple controlled trials) Acute hypercapnic COPD Acute cardiogenic Pulmonary edema Immunocompromised patients Less strong – (single controlled trials, multiple case series) Asthma Community Acquired Pneumonia in COPD patients Facilitation of weaning in COPD Avoidance of extubation failure Post Operative Respiratory Failure Do not intubate patients

Recommendations for NIV in ARF : 

Recommendations for NIV in ARF 1/26/2012 69 Weak Evidence – (few case series, no benefit in controlled trials) ARDS Community acquired pneumonia - non COPD Cystic fibrosis Weaning – non COPD OSA/ obesity hypoventilation Trauma Post op – upper airway, oesophageal surgery

When NIV is not an Option : 

When NIV is not an Option 1/26/2012 70 Decreased level of consciousness Unprotected airway Excessive secretions Persistent vomiting Facial or neurosurgical trauma Circulatory instability Upper GI anastomosis Severe acidaemia Inability to interface High IAP Too sick or can't protect airway

Setting - NIV : 

Setting - NIV 1/26/2012 71

NIV masks / Interfaces : 

NIV masks / Interfaces 1/26/2012 72

Using of the Sizing Gauge for Nasal Mask : 

Using of the Sizing Gauge for Nasal Mask 1/26/2012 73

Slide 74: 

1/26/2012 74

Nasal Masks Vs Facial masks : 

Nasal Masks Vs Facial masks 1/26/2012 75 Advantages Easier secretion clearance Less claustrophobia Easier speech Easy to fit and secure Less dead space Disadvantages Mouth leak Higher resistance through nasal passages Less effective with nasal obstruction Nasal irritation and rhinorrhea Mouth dryness

Equipment-Checklist : 

Equipment-Checklist 1/26/2012 76

Application to patient : 

Application to patient 1/26/2012 77 Key points Patient sitting in upright position Explain to patient what will happen Apply face mask without straps at first Allow patient to get used to machine and then apply straps Assess mask fit and leak by using hand to feel for air escaping around mask.

Application to patient : 

Application to patient 1/26/2012 78 Observe that each patient effort is synchronised to ventilator breaths Recognise ventilation cycle by sound from exhalation port or by observing pressure gauge/waveform. Poor synchronisation usually due to incorrect mask fit with excessive leak . If inspiratory time pre-set ensure that it matches patient efforts

Initial prescription : 

Initial prescription 1/26/2012 79

Slide 80: 

. Techniques of NIV 1/26/2012 80

Monitoring : 

Monitoring 1/26/2012 81 Check ABG after one hour If pH and PaCO2 improving continue with current settings Increase IPAP if pH and PaCO2 not improving Titrate oxygen for SaO2. 88% -92% EPAP can also be increased to improve SaO2 Usually those patients who respond to NIV will have significant improvement in ABG in first 1-2 hours. ABG recommendations are at 1 hr, 2hrs,4hrs and 12 hrs [A] Continuous Pulse oximetry, ECG,HR,BP, Sensorium [B] BTS Guidelines

Factors associated with success : 

Factors associated with success 1/26/2012 82 Chest 2007

Slide 83: 

1/26/2012 83 THANK YOU

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