Ventilator Management

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Ventilator Management

• Michael Schmitz, DO, MS
• Emergency Medicine/Internal Medicine
• October 10, 2007

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Objectives

• To review differences in ventilator modes
• To review how to interpret ventilator settings
  and readings
• To discuss the protocol for assessing a
  ventilated patient who is in distress
• To review the pathophysiology of the obstructive
  lung diseases
• To discuss guidelines for ventilator settings for
  patients with obstructive lung disease

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BUY EASY TIGER by RYAN ADAMS

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Nomenclature

• A/C 600/14/50/5

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Volume Cycled Ventilation

• A/C Ventilation
• SIMV

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Pressure Cycled Ventilation

• Pressure Support
• (PSV)
• Airway Pressure Release (APRV)

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Flow Rate / IE Ratio

• Flow Rate a measure of the rate of delivery of
  oxygen through the system to the patient.
• (usually 60 liters per minute)
• IE Ratio a measure of total inspiratory time to
  expiratory time. (13) is ideal
• Inspiratory time Tidal Volume / Inspiratory
  flow
• An increase in flow rate will shorten inspiratory
  time and decrease IE
• Insufficient flow rates contribute to patient
  dyspnea
• Insufficient expiratory time increases mean
  airway pressure, the likelihood of barotrauma and
  auto-PEEP.

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Trigger Mode/Sensitivity

• Trigger Mode- (A/C)
• Most common is pressure triggering the
  patient must generate a sufficient NET negative
  airway pressure in order to receive a breath
• Sensitivity- the set negative pressure the
  patient must overcome to open the demand valve
  and trigger a breath

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Flow Pattern

• Constant (square)
• Decelerating (ramp)
• -possibly better in COPD
• Sinusoidal

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PEAK VS. PLATEAU PRESSURES

• Peak Pressure Pressure at the end of
  inspiration. Determined by inflation volume,
  airway resistance and the elastic recoil of the
  lungs and chest wall
• Plateau Pressure Measured when airflow is
  stopped. It is directly proportional to the
  elasticity of the lungs and chest wall

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PEAK VS. PLATEAU PRESSURES

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Positive End-Expiratory Pressure

• PEEP an elevation in alveolar pressure above
  atmospheric pressure at the end of exhalation
• Extrinsic PEEP (ePEEP) applied through a
  mechanical ventilator

ACV without PEEP
ACV with PEEP
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Positive End-Expiratory Pressure
Physiologic (3-5 cm H20) overcomes the decrease
in functional residual capacity due to
endotracheal intubation (glottis has been
bypassed)

• improves gas exchange by opening small airways in
  the dependent lung zones and distributing
  inspired gas homogeneously.
• decreases expiratory flow limitation and dynamic
  hyperinflation.
• decreases oxygen consumption

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Positive End-Expiratory Pressure

• Supraphysiologic PEEP (gt 5 cm H20)
• Offsets auto-PEEP in patients with obstructive
  lung disease
• Improves oxygenation in patients with hypoxemic
  respiratory failure
• Improves oxygenation and cardiac performance in
  patients with cardiogenic pulmonary edema
• Caution in focal lung disease, pulmonary
  embolism, hypotension, patients with increased
  ICP, hypovolemia, bronchopleural fistula

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Positive End-Expiratory Pressure
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Auto-PEEP

• Intrinsic PEEP (iPEEP, aka occult,
  vent-associated) occurs because of incomplete
  ventilation Initiating a new breath prior to
  complete exhalation causes air-trapping

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Auto-PEEP

• Causes high minute volume ventilation,
  expiratory flow limitation or increased
  expiratory resistance
• Hypoxemia, hypotension and barotrauma can occur
  as a result

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Auto-PEEP
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PEEP

• Applying PEEP can decrease the magnitude of
  negative pressure that the patient must generate
  to trigger the ventilator, which reduces work
  done by the muscles of inspiration

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Consequences of MV

• Positive pressure ventilation preferentially
  inflates the more compliant, non-dependent upper
  lung zones
• Uneven gas distribution contributes to barotrauma
  and auto-PEEP, with a preference for damaging
  normal alveoli
• Occurs in ARDS, asthma and chronic interstitial
  lung disease

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Consequences of MV

• Barotrauma causes damage to adjacent alveoli via
  stretching and shearing forces.
• High peak airway pressures are directly
  correlated with barotrauma

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Consequences of MV

• Complications of alveolar rupture can be
  devastating
• Pulmonary interstitial emphysema
• Pneumomediastinum
• SQ Emphysema
• Pneumothorax
• Pneumoperitoneum

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Ventilator Synchrony

• Setting the ventilator to cycle with the
  patients respiratory rhythm
• Requires close patient monitoring
• Try to prevent ineffective triggering
• Adjust oxygen flow rate in proportion to tidal
  volume
• may increase peak airway pressure
• Adequate sedation is critical
• Any increased sense of effort (fatigue vs. forced
  exhalation) on the part of the patient
  contributes to sensation of dyspnea

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Case Presentation

• 65 year-old man BIBEMS c/o increasing dyspnea
  over 3 days associated with temperature of 100.3
  and increase in thickened, green sputum. He has a
  history of emphysema, is on home oxygen and has
  been using his inhalers without relief.

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The Decision To Intubate

• Initiation of mechanical ventilation in COPD
  patients is associated with high patient
  mortality and poor potential for weaning
• Indications (E.B.M. vs. clinical gestalt)
• Patient failed conservative management
• Severe, persistent acidosis
• Continued arterial hypoxemia despite initial
  therapy
• Patient fatigue
• Altered mental status
• Additional major illness (pulmonary embolism, AMI)

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• The usual vent settings are applied
• Some time passes.

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WARNING LOW EXHALED VOLUME
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Respiratory Distress in MV

• Ventilator Malfunction or Circuit Leak
• Ventilator Inadequate ventilator settings
• Inadequate Tidal volume, FiO2, Flow rate,
  Positive end expiratory pressure (PEEP) or
  over/undersensitivity
• Airway (increased Ppeak-Pplat)
• ENDOTRACHEAL TUBE MIGRATION, patient biting tube,
  balloon cuff leak, deflation or rupture
• Bronchospasm, increased airway resistance imposed
  by heat and moisture exchanger, obstruction by
  secretions, blood or foreign object

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Respiratory Distress in MV

• Lungs (Ppeak-Pplat unchanged or decreased)
  pneumonia, atelectasis, pulmonary edema,
  aspiration of gastric contents, pneumothorax,
  pleural effusion, pulmonary embolus,
  ENDOTRACHEAL TUBE MIGRATION!
• Extrapulmonary Abdominal distension, delerium,
  anxiety, pain, stroke, seizure

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Respiratory Distress in MV
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What to Do?

• Protocol

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Goals for COPD patients

• Adequate patient monitoring
• Optimize ventilator settings to minimize
  excessive work of breathing
• Assure Synchrony
• Detect auto-PEEP and prevent barotrauma
• Prevent further respiratory muscle atrophy
• Intubate using the widest diameter ET tube
  possible (R 8nl / pr 4)

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Obstructive Lung Diseases

• Asthma
• Chronic bronchitis
• Emphysema
• Congenital bullous
• lung disease

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Pathophys COPD
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Pathophys Emphysema
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Vent Guidelines

• Emphasis on assisted modes of ventilation
  (patient initiated), institution preference for
  A/C vs. IMV with PSV (to overcome ET tube)
• SIMV probably causes excess work, b/c of high
  resistance circuit but debatable requires close
  patient monitoring

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Vent Guidelines
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VENT Guidelines

• Higher flow rates are highly beneficial

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Vent Guidelines
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Vent Guidelines

• Tidal Volume 5-7 ml/kg
• Set Rate 4 less than spontaneous rate
• FiO2 adjust to PaO2 of at least 60 mmHg
• Triggering -1 to -2 cm H2O
• Prevent Auto-PEEP with sufficient PEEP
• Flow rate Increase to provide increased
  expiratory time (70-90 lpm)
• Continue inhaled medications requires sufficient
  tidal volume and inspiratory time

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Pathophys Asthma

• Airway narrowing caused by smooth muscle
  contraction, wall thickening and increased
  secretions combine to reduce air flow rates
• Primarily a disease of the AIRWAYS with decreased
  elastic recoil of the lungs during attack
• ABG for PaCO2 to identify respiratory failure

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Pathophys Asthma
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Vent Settings Asthma

• Respiratory rate 10 to 14 breaths/min
• (allows more time for exhalation)
• Tidal volume less than 8 mL/kg
• Minute ventilation less than 115 mL/kg
• Inspiratory flow of 80 to 100 L/min
• Extrinsic postive end-expiratory pressure less
  than 80 percent of the intrinsic PEEP
• Continue inhaled medications and steroids

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Vent Settings Asthma
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Vent Settings Asthma

• Intubate with largest diameter tube possible!
  (8.0 mm and up)
• First priority is to minimize auto-PEEP and keep
  plateau pressures low!
• Lower respiratory rate and tidal volume may be
  necessary causing PaCO2 to increase (permissive
  hypercapnia)
• Sedation, then paralysis to force synchrony
• Heliox

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Osteopathic Considerations

• Findings reflect anatomical changes related to
  increased lung volumes and impaired ventilation
• Thoracic Vertebral Dysfunction
• Rib Dysfunction (stuck in exhalation)
• Diaphram Dysfunction (stuck down)
• Law of LaPlace T Pr
• Lymphatic obstruction lymphatic drainage
  impaired by positive pressure

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Summary

• The need to initiate mechanical ventilation in
  patients with obstructive lung disease in the
  emergency department is associated with a higher
  inpatient mortality
• Patients with obstructive lung disease require
  close monitoring of all physiologic parameters to
  prevent complications associated with positive
  pressure ventilation
• Assessing a distressed ventilator dependent
  patient requires an organized approach
• In general low tidal volumes, higher flow rates
  and application of a conservative amount of PEEP
  are appropriate initial settings for patients
  with obstructive lung disease

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References

• The ICU Book Marino PL, 2nd Edition
• Respiratory Physiology West JB, 5th Edition
• Pulmonary Pathophysiology Grippi MA
• Textbook of Medical Physiology Guyton and Hall
  9th Edition
• Chest Radiology Companion Stern EJ, White CS
• Harrisons Principles of Internal Medicine 16th
  Edition

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References

• www.utdol.com
• principles of mechanical ventilation,
  alternate modes of mechanical ventilation,
  positive end expiratory pressure,
  pathophysiologic consequences of positive
  pressure ventilation, mechanical ventilation in
  acute respiratory failure complicating COPD,
  mechanical ventilation in adults w/ status
  asthmaticus

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