Initiation and weaning of mechanical ventilation by Ahmed Mohamed Hassan

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Initiation and weaning of mechanical
ventilationbyAhmed Mohamed Hassan
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Outline

• Definition.
• Indications
• Ventilator Settings
• Modes of Ventilation
• Weaning
• Summary

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Definition

• Use of a mechanical apparatus to provide the
  requirements of a patients breathing.
• Use of positive pressure to physically transport
  gases into and out of lungs
• (earlier ventilators used negative pressure)
• Usually performed via ETT but not always
  (noninvasive ventilation)

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Mechanical Ventilation ( MV )

• A supportive measure not a therapy
• Must diagnose and treat underlying cause
• Used to support /or rest patient until
  underlying disorder improved

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INDICATIONS FOR MV

• Acute resp failure
• ARDS
• Heart failure.
• Pneumonia
• Sepsis.
• Complication of surgery.
• Trauma
• Acute exacerbations COPD.
• Neuromuscular diseases.

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Ventilator settings

• FIO2
• Volume (VT)
• Rate
• Pressure
• PEEP
• IE
• Flow rate

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Ventilator settings

• Fraction of inspired oxygen (FiO2)
• Target Sao2 90 Pao2lt 60mmHg.
• Atempt to keep FiO2 lt50 to avoid O2 toxicty.
• Tidal volume (Vt)
• Is constant in volume-cycled modes and variable
  with in pressure-limited modes.
• In patients without lung disease Vt of 8 - 10
  mL/kg .
• Lower Vt 6 ml/kg are recommended for ARDS,
  Vt 8 mL/kg is recommended in patients with
  asthma, COPD(as long as no increase in plateau
  presure).

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Ventilator settings

• Respiratory rate (RR)
• 12 and 20 breaths per minute is reasonable.
• Determine minute ventilation.
• Minute ventilation (VE)
• Is the product of the Vt and RR.
• VE is based on PaCO2 as a marker of ventilatory
  requirements.
• VE of approximately 5 L/min maintain normocapnea.
• Permissive hypercapnia is allowed in ARDS and
  status asthmaticus.

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Ventilator settings

• Inflation pressure limit
• High inflation pressures cause barotruama.
  Increased Pplat, is most injurious, reflecting
  alveolar overdistention and not airway
  resistance.
• Pplat gt 30 cm H2O is recommended.
• Inspiratory Sensitivity
• It is the drop in airway pressure that is
  required before the ventilator senses the
  patient's effort.
• 0.5 to 1 cm H2O allow very weak patients to
  initiate a breath, Higher values make triggering
  more difficult.

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Ventilator settings

• Inspiratory flow rate
• The ratio of Vt to inspiratory flow rate
  determines inspiratory time (Ti).
• inspir flow rate Ti
  time for expiration
• auto PEEP.
• inspir flow rate PIP not
  Pplat.
• COPD asthma the expiratory time should be
  increased to allow exhalation of trapped gas.
• Positive end-expiratory pressure (PEEP)
• PEEP is the maintenance of positive pressure
  after expiratory flow is completed.
• Useful to treat refractory hypoxemia
• Complication
• Hypotension
• Diastolic dysfunctions
• Barotrauma

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Modes of MV

• MV may be
• Invasive, delivered through an endotracheal tube
  (ETT) or tracheostomy tube.

• Noninvasive positive pressure ventilation (NIPPV)
  interfaces the ventilator with the patient
  through a full-face or nasal mask.

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Moods of mechanical ventilation

• Volume cycled MV
• Delivers a preset (Vt) specified by the operator.
• (PIP) are, depending on the patient's compliance.
  
• Examples
• Assist/Control
• Intermittent Mandatory Ventilation (IMV)
• Synchronous Intermittent Mandatory Ventilation
  (SIMV)

• Pressure-limited MV
• Delivers a flow until a preset pressure limit
  that is set by the operator is reached.
• PIP is always the same but Vt is variable,
  according to the patient's compliance.
• Examples
• Pressure Support Ventilation (PSV)
• Pressure Control Ventilation (PCV)
• CPAP
• BiPAP

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Pressure Support Ventilation(PSV)

• Every breath is an assisted breath.
• The patient determines the inspiratory flow rate
  and the RR.
• Advantages
• Better patient synchrony
• Limits Peak inspiratory Pressure.
• Disadvantages
• Inadequate volumes if the ETT is blocked or
  decreased lung compliance.
• Apnea backup is less supportive than that of AC

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Pressure Control Ventilation (PCV)

• Controlled breaths are delivered at a preset time
  interval.
• RR, maximal pressure limit are both controlled.
• Spontaneous breaths is allowed between the
  mandatory breaths.
• Advantades
• Decrease risk of barotrauma
• Used in inverse ratio ventilation.
• Disadvantages
• Cannot ensure minimal VE

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Continuous positive airway pressure (CPAP)

• Used for oxygenation and as a mode of weaning.
• patient assumes most of the work of breathing
  determine RR, Vt VE.

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BIPAP

• Ventilator delivers two levels of positive airway
  pressure for preset periods of time.
• Advantages
• Decreased requirement for sedation.
• Used in Obstructive Sleep Apnea.
• Disadvantages
• Theoretical risk of over-distension of lungs.

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Assist control (AC)

• Pt RR lt preset rate so all breath will be
  assisted.
• Pt RR gt preset rate so all breath will be
  controlled.
• Advantages
• Ensures a minimum VE.
• Better patient synchrony.
• Disadvantages
• Induce respiratory alkalosis if high respiratory
  drive (i.e., liver failure).

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Intermitent mandatory ventilation (imv)

• Ventilator will deliver a preset volume at a
  specific time intervals.
• Different from Controlled mode pt can initiate
  spontaneous breaths.
• Different from Assisted mode spontaneous breaths
  are not supported by machine.
• Advantages
• Assures a VE
• Disadvantages
• Patient asynchrony.

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Synchronized intermittent mandatory ventilation
(SIMV)

• Delivered spontaneous, assisted, and mandatory
  breath.
• Most commonly used mode.
• Advantages
• Ensures a minimum VE.
• Disadvantages
• The worst mode of weaning.

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Noninvasive Ventilation

• Avoids intubation and complications.
• Can deliver various modes of ventilation
• Indications
• Hypercapneic respiratory failure (COPD exac).
• Cardiogenic pulmonary edema.
• Hypoxic respiratory failure.
• Contraindications
• Inability to cooperate (i.e. Confusion).
• Inability to clear secretions.
• Hemodynamic instability.
• Frature skull base as it may cause
  pneumoencephaly.

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New modes of MV

• Volume Support.
• Pressure-Regulated Volume Control (PRVC).
• Volume-Assured Pressure Support.
• Automode.
• Adaptive support ventilation (ASV).
• Proportional Assist Ventilation(PAV).
• Mandatory Minute Ventilation.
• Airway Pressure Release Ventilation (APRV).

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weaning

• When
• The underlying pathology improves.
• Hemodynamically stable.
• Oxygenation
• PaO2/FiO2 gt200,
• PEEPlt7.5 cm H2O,
• FiO2lt0.5
• Indices
• Rapid shallow breathing
• RR/Vt gt 105 positive predictive value of 78.
• RR/Vt lt 105 negative predictive value of 95 .
• Maximal Inspiratory Pressure(Pmax)
• Excellent negative predictive value if less than
  20 cm H2O .

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weaning

• Methods
• Spontaneous breathing trials
• complete withdrawal of MV
• Only one trial every 24-hour
• CPAP
• Allow monitoring of RR, Vt VE
• Pressure support ventilation (PSV)
• Gradual reduction in the level of PSV
• SIMV
• The worst mode of weaning.
• Duration
• Short-term MV (lt21 days) 30 to 120 minutes
• prolonged MV (gt21 days) at least 24
  hours.

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Causes of weaning failure

• Auto-PEEP.
• Poor nutritional status.
• Overfeeding.
• Left heart failure.
• Decreased magnesium and phosphate levels.
• Infection/fever.
• Major organ failure.

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Signs of weaning failure

• Clinical criteria
• Diaphoresis .
• Increased respiratory effort .
• Paradoxical breathing use of accessory
  respiratory.
• Cardiac
• HR lt 30 beats/min over baseline.
• Profound bradycardia.
• Ventricular ectopy.
• Supraventricular tachyarrhythmias.
• Mean arterial blood pressure equal to or greater
  than 15 mm Hg or equal to or less than 30 mm Hg
  from baseline.

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Signs of weaning failure

• Respiratory
• RR lt 35 breaths/min .
• SaO2gt 90.
• PaCO2 50 mmHg or increase gt8 mmHg.
• pHlt7.33 or decrease gt0.07.
• PaO2 60 mm Hg with FiO2 of 0.5.

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Ventilator management algorithim
Modified from Sena et al, ACS Surgery Principles
and Practice (2005).

• Initial intubation
• FiO2 50
• PEEP 5

• RR 12 15
• VT 8 10 ml/kg

SaO2 lt 90
SaO2 gt 90

• SaO2 gt 90
• Adjust RR to maintain PaCO2 40
• Reduce FiO2 lt 50 as tolerated
• Reduce PEEP lt 8 as tolerated
• Assess criteria for SBT daily

• SaO2 lt 90
• Increase FiO2 (keep SaO2gt90)
• Increase PEEP to max 20
• Identify possible acute lung injury
• Identify respiratory failure causes

No injury
Pass SBT
Extubate
Airway stable
Acute lung injury
Fail SBT
Airway stable

• Persistently fail SBT
• Consider tracheostomy
• Resume daily SBTs with CPAP or tracheostomy collar

• Acute lung injury
• Low TV (lung-protective) settings
• Reduce TV to 6 ml/kg
• Increase RR up to 35 to keep pH gt 7.2, PaCO2 lt 50
• Adjust PEEP to keep FiO2 lt 60

Pass SBT
Intubated gt 2 wks
SaO2 lt 90
SaO2 gt 90
Prolonged ventilator dependence

• SaO2 lt 90
• Associated conditions (PTX, hemothorax,
  hydrothorax)
• Consider adjunct measures (prone positioning,
  HFOV, IRV)

• SaO2 gt 90
• Continue lung-protective ventilation until
• PaO2/FiO2 gt 300
• Criteria met for SBT

• Consider PSV wean (gradual reduction of pressure
  support)
• Consider gradual increases in SBT duration until
  endurance improves

Pass SBT
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Summary

• Mechanical ventilation used to
• Improve oxygenation.
• Improve ventilation (CO2 removal).
• Unload respiratory muscles.
• Neuromuscular diseases.
• Decrease intracranial tension.
• A support until patients condition improves

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summary

• Different modes for ventilation
• Differ in how breaths are initiated, ended and
  assisted.
• No proven advantage of one mode over the other.
• Use ventilator strategies to avoid volutrauma
• and other adverse effects.
• Numerous trials performed to develop criteria for
  success weaning, however, not very useful to
  predict when to begin the weaning and physicians
  should rely on clinical judgement also.

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summary

• Daily screening may reduce the duration of MV and
  ICU cost.
• The removal of the artificial airway from a
  patient who has successfully been discontinued
  from ventilatory support should be based on
  assessment of airway patency and the ability of
  the patient to protect the airway.
• Patients receiving MV who fail an SBT should have
  the cause determined.

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summary

• Tracheostomy should be considered after it
  becomes apparent that the patient will require
  prolonged MV.

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• Thank you