mechanical ventilation principles and practices
TRANSCRIPT
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Mechanical VentilationPrinciples and Practices
Dr LAU Chun Wing Arthur
Department of Intensive CarePamela Youde Nethersole Eastern Hospital6 October 2009
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In this lecture, you will learn
Major concepts in respiratory physiology General concepts of noninvasive and
invasive ventilation Different modes of mechanical
ventilation: VC, PC, CPAP + PS, SIMV Settings for different clinical scenarios:
COPD, asthma, APO, neuromuscular disease
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Four important equations in respiratory medicine
PaCO2 is measured in mm Hg, VCO2 in ml/min (STPD), and VA in L/mPaCO2 is measured in mm Hg, VCO2 in ml/min (STPD), and VA in L/min (BTPS); hence the in (BTPS); hence the units must be converted to mm Hg. This conversion is achieved byunits must be converted to mm Hg. This conversion is achieved by the constant, 0.863.the constant, 0.863.
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Four important concepts in assisted ventilation
Know the set of pathophysiology in your patient
Resistance = ∆Pressure/∆Flow High: COPD, asthma
Compliance = ∆Volume/∆Pressure Low (lung): ARDS, APO, pneumonia Low (chest wall): neuromuscular diseases High: emphysema
Know how to and how much to correct the pathophysiology (e.g. open lung approach, protective lung strategy, permissive hypercapnia)
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Invasive ventilation
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ICU ventilators
Viasys AveaSiemens Servo i
Puritan Bennett 840
Draeger Evita 4
Have to be equipped with a “noninvasive mode”: leak-tolerant, use only the essential alarms
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Hybrid ventilators
Viasys VelaBird VSO2
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Home ventilators
Respironics BiPAP VisionVersamed iVent Breas PV 102
Breas LTV 1000 Sirio NIV-S
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Heated Humidifier
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Heat and Moister exchanger (HME)
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Key terms in Mechanical Ventilation
Tidal volume Rate: breaths per minuteMinute ventilation PEEP FiO2 I:E ratio, Inspiratory flow rate Pressure control pressure CPAP, Pressure support
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Control mode 1Assist Control Ventilation
TV is set Rate is set Airway pressure varies with lung
compliance Ventilator delivers a fixed volume
(patient triggers or mandatory)
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Control mode 2Pressure control ventilation
PCV is set Rate is set Insp time is set Volume varies according to lung
compliance Ventilator delivers a fixed pressure
(patient triggers or mandatory)
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VC PC
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Support mode
Patient must be able to breathe spontaneously
1. Pressure support + CPAP: each spontaneous breath is supported on top of the CPAP (PEEP) level till the target pressure level is achieved
2. Volume support + CPAP: each spontaneous breath is supported on top of the CPAP (PEEP) level till the target volume is achieved
Backup: ventilator switches to control mode if there is apnoea for a set period
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Control + Support modeSynchronized Intermittent Mandatory Ventilation (SIMV)
PC + PS: each spontaneous breath is supported till the target pressure level is achieved
VC + PS: each spontaneous breath is supported till the target volume is achieved
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Non-invasive ventilation (NIV)
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Nasal
Nasal pillow
Facial
Total face
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Helmet
Nasal prong device
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Exhalation device (used if there is no decidated expiratory limb)
Whisper-Swivel II, RespironicsPlateau valve
1. In mask2. In circuit
a. Whisper-Swivelb. Whisper-Swivel IIc. Plateau valve
Whisper-Swivel
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Key terms in NIV
CPAP = continuous positive airway pressure
BiPAP = IPAP
(inspiratory) EPAP
(expiratory)
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Clinical conditions
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Scenario 1: COPD
M/80: 60 pack-year smoking history, c/o SOB for 3 days
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COPD: Ventilation requirements
NIV: very useful, start with this mode unless there is profuse sptum
IPPV Set a lower rate to allow for longer time for
expiration PEEP 5 or above, adjust according to
autoPEEP
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Scenario 2: Asthma
M/20: Non-smoker, c/o wheezing and SOB for 3 days
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Status asthmaticus: pathophysiology
Smooth muscle hypertrophy and spasm
Inflamed airway Thick bronchial cast
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Asthma: Requirements
NIV may not be useful IPPV setting:
High resistance Low freq and small volume Long expiratory time Zero PEEP Allow pCO2 to rise (permissive hypercapnia), allow
pH around 7.2 Muscle relaxation Manual assisted expiration
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Scenario 3: Acute pulmonary edema
M/60: DM, ECG: ST elevations
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APO requirements
NIV (both CPAP or BiPAP) useful IPPV
Low volume (6 – 8 ml/kg PBW) Higher freq High PEEP High FiO2
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Scenario 4: Neuromuscular disease
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Problems
Removal of secretions Ventilatory pump failure Progressive atelectasis Increasing oxygen requirement Decreasing MIP and VC
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Choice of ventilatory support
Noninvasive positive-pressure ventilation If reversibility is expected over hours to days, e.g.
mild LRTI in chronic neuromuscular disease as polymyositis or MG; Problem: secretion retention
Intermittent positive pressure ventilation via endotracheal tube Larger tidal volumes (12 – 14 ml) may be better
tolerated and maximize stimulaton of surfatantproduction
PEEP: use physiological PEEP (3- 5 cm H2O) MV adjusted for desired pH Tracheostomy for failure to wean within 3 weeks
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Summary
Major concepts in respiratory physiology General concepts of noninvasive and
invasive ventilation Different modes of mechanical
ventilation: VC, PC, CPAP + PS, SIMV Settings for different clinical scenarios:
COPD, asthma, APO, neuromuscular disease
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Invasive ventilatorysettings in various conditions
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Non-invasive ventilation
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Thank you