Mechanical Ventilation: The Basics and Beyond

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Mechanical Ventilation The Basics and Beyond

• Presented By
• Diana Gedamke, BSN, RN, CCRN
• Marion College - Fond du Lac

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Mechanical Ventilation

• an opening must be attempted in the trunk of
  the trachea, into which a tube of reed or cane
  should be put you will then blow into this, so
  that the lung may rise againand the heart
  becomes strong
• Andreas Vesalius (1555)

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Mechanical Ventilation

• First described in 1555
• First used in patient care during the polio
  epidemic of 1955
• Medical students became human ventilators
• First positive pressure ventilator was used at
  Massachusetts General Hospital

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Indications for MV

• Acute Respiratory Failure (66)
• Coma (15)
• Acute Exacerbation of COPD (13)
• Neuromuscular Disorders (5)
• Esteban et al. How is mechanical ventilation
  employed in the intensive care unit? An
  international utilization review. Am J Respir
  Crit Care Med 2000161 1450 - 8.

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Indications for MV

• Acute Respiratory Failure
• ARDS
• Heart Failure
• Pneumonia
• Sepsis
• Complications of Surgery
• Trauma

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Objectives of MV

• Decrease WOB
• Reverse life-threatening hypoxemia or acute
  progressive respiratory acidosis
• Protect against ventilator-induced lung injury
• Wean and extubate as soon as possible

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Caring for the Mechanically Ventilated Patient

• Endotracheal tube
• Position
• Stability
• Cuff inflation
• Patency
• Oral cavity
• Trauma to lip and palate
• Secretions

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Caring for the Mechanically Ventilated Patient

• Patient Position
• Patient-Ventilator Synchrony
• Physical Assessment
• VS, General assessment, breath sounds
• Ventilator Mode
• Alarms
• Reason for intubation
• MV in disease states
• Does patient still need to be intubated and
  mechanically ventilated?

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Endotracheal Tube

• Nasal or oral
• Size (6 8.5 cm)
• Position
• 21 cm from the teeth in women 23 cm in men
• Confirm position by CXR (even when breath sounds
  are bilateral)
• 3 - 5 cm above carina
• Affects of head position

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Endotracheal Tube

• Position
• End Tidal CO2 to confirm ETT placement

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Normal Airway
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Endotracheal Tube Positioning
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Complications of Intubation and Mechanical
Ventilation

• Sinusitis - occurs in gt 25 of patients
  ventilated gt 5days nasal gt oral subtle findings
  (unexplained fever leukocytosis), polymicrobial
• Laryngeal damage - ulceration, granulomas, vocal
  cord paresis, laryngeal edema
• Aspiration/Ventilator-associated pneumonia -
  occurs despite cuffed tube
• Tracheal necrosis - tracheal stenosis,
  tracheomalacia
• Death ventilator malfunction/inadvertent
• disconnection/endotracheal tube
  dysfunction/VAP

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Preventing Infection

• Sterile suctioning
• assess as routine part of assessment only
  suction when patient needs it
• Elevate HOB to 45 degrees

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Positive Pressure Ventilation

• Volume-cycled ventilation
• Pressure-preset ventilation

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PB 7200
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Volume-cycled Ventilation

• Delivers a preset volume of gas with each machine
  breathairway pressures increase in response to
  the delivered breath
• Airway pressures are higher in patients with low
  compliance or high resistancehigh pressures
  indicate risk of ventilator-induced lung injury

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Spontaneous Breathing vs. Positive Pressure
Ventilation
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Volume-cycled Ventilation

• Assist Control (AC)
• Synchronized Intermittent Mandatory Ventilation
  (SIMV)

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Assist-control (AC)

• Most widely used mode of MV
• Delivers a minimum number of fixed-volume breaths
• Patients can initiate extra assisted breaths
  (will get full set volume with each effort)

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Pressure-time TracingsAssist Control Mode
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Synchronized Intermittent Mandatory Ventilation
(SIMV)

• Delivers preset number of fixed-volume breaths
• Patient can breathe spontaneously between breaths
  (rate and depth determined by patient)
• Patients often have trouble adapting to
  intermittent nature of ventilatory assistance

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Pressure-time TracingsSIMV Mode
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Pressure-preset Ventilation

• Delivers a predefined target pressure to the
  airway during inspiration
• Resulting tidal volume (VT) and inspiratory flow
  profile vary with the impedance of the
  respiratory system and the strength of the
  patients inspiratory efforts
• Includes pressure-control (PC) and Pressure
  support (PS)

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Pressure-control (PC) Ventilation

• Delivers a preset gas pressure to the airway for
  a set time and at a guaranteed minimum rate
• Patient can breathe in excess of set rate
• Tidal volume achieved depends on pressure level,
  lung mechanics, and patient effort
• Inspiratory flow rate variable

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Pressure Support (PS)

• Delivers preset airway pressure for each breath
• Variable parameters Inspiratory and expiratory
  times (respiratory rate), flow rate, and tidal
  volume (VT)

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SIMV PS

• Spontaneous breaths allowed in SIMV are assisted
  by PS

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New Modes of MV

• New modes often introduced
• Involves nothing more than a modification of the
  manner in which positive pressure is delivered to
  the airway and of the interplay b/n mechanical
  assistance and patients resp effort
• Goals enhance respiratory muscle rest, prevent
  deconditioning, improve gas exchange, prevent
  lung damage, improve synchrony, foster lung
  healing

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Ventilator Settings

• Respiratory rate
• Tidal volume
• FiO2
• InspiratoryExpiratory (IE) ratio
• Pressure limit
• Flow rate
• Sensitivity/trigger
• Flow waveform

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Inspiratory Flow (V) Waveform

• Square waveform Decelerating
  Waveform
• (constant flow)
  (decelerating flow)

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Inspiratory Flow (V) Waveform

• Square waveform volume of gas is evenly
  distributed across inspiratory time. Has highest
  peak pressure and lowest mean airway pressure.
  Ideal for those at risk for autopeeping due to
  short inspiration time

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Inspiratory Flow (V) Waveform

• Decelerating waveform Volume of gas flow is
  high at the beginning of inspiration then tapers
  off toward the end of the breath. Has lowest
  peak pressure and highest mean airway pressure.
  Increased inspiratory time useful in ARDS.

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Patient-Ventilator Synchrony

• Check for
• Symmetric chest inflation
• Regular breathing pattern
• Respiratory rate lt 30 bpm
• Synchrony between patient effort and machine
  breath
• Paradoxical breathing

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Patient-Ventilator Synchrony

• Inspiratory effort expended by patients with
  acute respiratory failure is 4 - 6 x normal
• Dont eliminate respiratory effort causes
  deconditioning and atrophy

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Patient-Ventilator Asynchrony

• Possible causes
• Anxiety or pain
• Ventilator settings may not be appropriate
  check ABG and alert individual responsible for
  ventilator orders
• Auto-PEEP
• Pneumothorax

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Ventilator Alarms and Common Causes
High Pressure Low Pressure Low Exhaled Volume
Kink in tubing Patient biting ETT Ventilator disconnected from ETT Pressures exceeding high pressure limit
Secretions Cuff leak Cuff leak
Coughing Extubation Ventilator disconnected
Bronchospasm
Foreign body
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Definitions

• PEEP positive-end-expiratory pressure applied
  during mechanical ventilation
• CPAP - continuous positive airway pressure
  applied during spontaneous breathing

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PEEP

• Improves oxygenation - increases functional
  residual capacity (FRC) above closing volume to
  prevent alveolar collapse
• permits reduction in FIO2
• Reduces work of breathing
• Increases intrathoracic pressure - decreases
  venous return to right heart - decreases CO
• Titrate to least amt. necessary to achieve O2 sat
  gt 90 or PO2 gt 60 mm Hg with FiO2 lt 0.6

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Auto-PEEP

• Auto-PEEP/intrinsic PEEP (PEEPi)/inadvertent
  PEEP/occult PEEP - positive end expiratory
  alveolar pressure occurring in the absence of set
  PEEP. Occurs when expiratory time is inadequate.

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Assessing Flow Waveform for Presence of Auto-PEEP
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Resistance and Compliance
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Definitions

• Peak Airway Pressure (Ppk)
• An increase in Ppk indicates either an increase
  in airway resistance or a decrease in compliance
  (or both).
• Plateau Pressure (Ppl) - end-inspiratory alveolar
  pressure

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Airway Pressure Analysis
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Ventilator-Induced Lung Injury

• High volumes and pressures can injure the lung,
  causing increased permeability pulmonary edema in
  the uninjured lung and enhanced edema in the
  injured lung
• Alveolar overdistention repeated collapse and
  re-opening of alveoli

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Mechanical Ventilation in Obstructive Lung Disease

• resistance to expired flow
• results in air trapping/hyperinflation
• hyperinflation may result in cardiopulmonary
  compromise
• Goal meet minimal requirements for gas exchange
  while minimizing hyperinflation
• Allow increased time for expiratory flow

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Increasing Time for Exhalation

• Decrease inspiratory time
• Increase flow rate
• Square waveform
• Decrease minute ventilation (VE)
• RR x TV

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Monitoring Patients with Obstructive Lung Disease
Requiring Mechanical Ventilation

• Monitor plateau pressure in general, Pplat lt
  30 cm H20 to decrease risk of hyperinflation and
  alveolar overdistension
• Permissive hypercapnia

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Respiratory Failure Due to Asthma

• Watch for overventilation post intubation
• High Ppk common
• May require sedation to establish synchronous
  breathing with ventilator
• Avoid paralytics
• Ventilate as stated above (Increase exhalation
  time by decreasing RR and TV, increasing
  inspiratory flow rate, and using square waveform)
• May want to use SIMV

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Respiratory Failure Due to COPD

• Ppk typically not as elevated as in asthma when
  it is, think other pathologic processes
• Many patients with COPD have chronic hypercapnia
  ventilatory support titrated to normalize pH and
  not PCO2
• Small levels of set PEEP may decrease WOB
• May try NIPPV

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Noninvasive Positive Pressure Ventilation (NIPPV)

• Cooperative patient
• Functionally intact upper airway
• Minimal amount of secretions
• Done by full face or nasal mask
• Watch for gastric distension may increase risk
  of aspiration
• May use standard ventilators
• Monitor patients closely for decompensation and
  need for intubation

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ARDS A Three Lung Unit Model
Normal
Non-recruitable
Recruitable
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Respiratory Failure Due to ARDS

• Refractory hypoxemia
• Avoid ventilator induced lung injury
• pressure-limited approach
• keep Pplat lt 30 cm H20
• small tidal volumes (6 ml/kg)
• permissive hypercapnia
• Avoid O2 toxicity apply moderate levels of PEEP

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ARDS

• May need to increase inspiratory time
• Inverse ratio ventilation (IRV)
• IE gt 11
• May require sedation/paralysis
• Use as second-line strategy if PEEP fails to
  improve oxygenation

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Mechanical Ventilation in Patients with
Neuromuscular Weakness

• Present with acute or subacute respiratory
  failure, usually with hypercapnia
• progressive neurologic dysfunction (amyotrophic
  lateral sclerosis, muscular dystrophies,
  Guillain-Barre, CNS dysfunction due to head
  injury or drug ingestion)
• usually ventilated without difficulty unless RF
  is complicated by secondary conditions
  (atelectasis or pneumonia)
• lung compliance and gas exchange remain
  relatively normal

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Does My Patient Still Need to Be Intubated and
Mechanically Ventilated?

• Evaluate daily when patient is hemodynamically
  stable and improving
• Use weaning checklist

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Discontinuation of MV

• Most (80 - 90) are able to have MV discontinued
  after reversal of physiologic process requiring
  support
• No single approach to weaning has been shown to
  be better than any other
• A particular approach, when improperly applied,
  can prolong process
• General rules work, rest, feed, allow to sleep

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Weaning Checklist

• 1. Patient status
• Reversal of physiologic derangements requiring
  ventilatory support
• Globally improving patient
• 2. Mental status
• Alert, cooperative, able to follow commands
• 3. Secretions/airway protection
• Absence of copious, thick, secretions
• Patient ability to handle secretions/protect
  airway/intact gag reflex

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Weaning Checklist

• 4. Oxygenation
• In general, need Pa02 gt 60 torr (SaO2 gt90) on
  FiO2 lt 0.4 and PEEP lt 5.0 cm H2O
• Ventilation
• Baseline PCO2 achieved with Ve lt 12 L/min
• Rapid shallow breathing index, f/VT lt 100 during
  spontaneous breathing (VT is in liters, e.g.
  25/.4 62.5 with Ve 10 L/min is predictive of
  success)

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Weaning Checklist

• If criteria 1 5 are met, decrease ventilatory
  support by, decreasing pressure support, or a
  trial of CPAP or t-piece. If tolerating after 2
  hours, extubate.
• If any of the above criteria are not met,
  continue ventilatory support and correct
  physiologic derangements (see below).
• With regard to 5 (ventilation), if f/VT gt 100,
  there is inadequate strength (assessed by NIF) or
  excessive ventilatory load (assessed by
  compliance) or both. (The patient must be strong
  enough for any given load to maintain spontaneous
  respirations.)

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Weaning Checklist

• NIF must be more negative than 25 cm H2O
• If not, increase strength (check TFTs, nutrition,
  Ca, Mg, PO4, K, avoid fatigue, avoid lung
  hyperinflation,? paralytics, ? aminoglycosides, ?
  critical illness polyneuropathy)
• Increased ventilatory load what is causing
  decreased compliance? (ARDS, pulmonary edema,
  pneumonia, atelectasis)

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Weaning Methods

• 1. Trials of spontaneous breathing alternating
  with full ventilatory support
• 2. SIMV (longer than spontaneous breathing and
  PS)
• 3. PS

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Weaning

• Monitor clinical parameters HR, RR, subjective
  distress, pulse oximetry, cardiac rhythm
• If patient deteriorates either clinically or
  physiologically, terminate weaning trial
• In general, initiate only one weaning trial in a
  24-hour period

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Extubation

• Reliable indices are not available
• LOC
• Gag
• Cough
• Secretions
• Head lift
• Do early in day
• Suction and re-intubation equipment
• Laryngeal edema, laryngeal spasm

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Re-intubation

• 10 - 20 of patients require re-intubation
• Mortality in these patients is gt 6x as high as
  mortality among patients who can tolerate
  extubation

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Case Study

• You are the ICU nurse picking up Mr. James, who
  was admitted and intubated yesterday for
  pneumonia. You enter the room and notice that he
  is tachypneic and restless. His ventilator
  settings are AC, rate 14, VT 700, FiO2 60. He
  is currently breathing at a rate of 24. His O2
  sat is 100.

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Case Study

• What lab test would you check to assess his
  ventilatory status?
• ABG
• What are possible causes of his increased
  respiratory rate?
• Secretions, anxiety, pain, vent settings may not
  be appropriate

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Case Study

• ABG results pH 7.48, PCO2 28, pO2 120
• Based on the ABG, his vent settings are changed
  to SIMV, rate 10, PS 10, VT 700, FiO2 40. How
  will these settings help Mr. James?

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Case Study

• You are the ICU nurse caring for a patient that
  was intubated for an exacerbation of COPD. When
  you enter the room, you notice that the patient
  is breathing out of synchrony with the ventilator
  and appears agitated and restless. The high
  pressure alarm is sounding. What could be the
  possible causes?

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Case Study

• Secretions, wrong vent settings (possible
  hyperinflation), anxiety

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Case Study

• You start your shift at 700 am and are picking
  up a patient that has been intubated for over a
  week for ARDS. You are told that he is doing
  well and may be able to be weaned today. When
  you complete your assessment, what will you
  specifically look at to report on rounds?

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Case Study

• Patient status
• Mental status
• Secretions/airway protection
• Oxygenation
• Ventilation

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Case Study

• Patient status
• Reversal of physiologic derangements requiring
  ventilatory support
• Globally improving patient
• 2. Mental status
• Alert, cooperative, able to follow commands
• 3. Secretions/airway protection
• Absence of copious, thick, secretions
• Patient ability to handle secretions/protect
  airway/intact gag reflex

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Case Study

• Oxygenation
• In general, need Pa02 gt 60 torr (SaO2 gt90) on
  FiO2 lt 0.4 and PEEP lt 5.0 cm H2O
• Ventilation
• Baseline PCO2 achieved with Ve lt 12 L/min
• Rapid shallow breathing index, f/VT lt 100 during
  spontaneous breathing (VT is in liters, e.g.
  25/.4 62.5 with Ve 10 L/min is predictive of
  success)

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Case Study

• Increase strength check TFTs, nutrition, Ca,
  Mg, PO4, K, avoid fatigue, avoid lung
  hyperinflation,? paralytics, ? aminoglycosides, ?
  critical illness polyneuropathy
• Decrease load ARDS, pulmonary edema, pneumonia,
  atelectasis

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Case Study

• Your patient with ARDS remains hypoxemic despite
  a high FIO2. What are other strategies to
  improve oxygenation?
• Increase PEEP, check HBG, prone positioning,
  change vent settings to increase inspiratory time

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Case Study Question

• In caring for a ventilated patient, what
  strategies should you use to decrease the risk of
  VAP?
• Closed suctioning only when needed
• Frequent oral care
• Upright patient

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Case Study Question

• Your intubated patient is requiring moderate
  amounts of PEEP to improve oxygenation. Discuss
  strategies to decrease the risk of complications
  from increased PEEP.
• Increase volume, vasopressors, positive inotropic
  therapy, may need to decrease PEEP

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Case Study

• You are caring for a patient that was intubated
  for hypoxemic respiratory failure due to ARDS.
  Initial vent settings are AC, RR 18, TV 10 cc/kg,
  PEEP 7.5 cm H2O. On these settings, her Ppk is
  45 cm H2O and Pplat is 38 cm H2O. There is no
  auto-PEEP. ABG is PO2 70 mm Hg, PCO2 46 mm Hg,
  and pH 7.32. Which of the following ventilator
  changes would you make first?

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Case Study

1. decrease FiO2
2. decrease TV
3. increase PEEP
4. decrease inspiratory flow rate
5. change to pressure control

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References

• Tobin MJ. Advances in mechanical ventilation. N
  Engl J Med, Vol. 344, No. 26, June 28, 2001.
• Hall et al. Principles of Critical Care (2nd
  ed). 1999. (MV chapter)
• Campbell RS et al. Pressure-controlled versus
  volume-controlled ventilation does it matter?
  Resp Care 2002 (474)416 - 426.