Transcript Ventilator Management

Ventilator Management
Michael Schmitz, DO, MS
Emergency Medicine/Internal Medicine
October 10, 2007
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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Nomenclature
A/C 600/14/50%/+5
Volume Cycled Ventilation
• A/C Ventilation
• SIMV
Pressure Cycled Ventilation
• Pressure Support
(PSV)
• Airway Pressure
Release (APRV)
Flow Rate / I:E Ratio
• Flow Rate: a measure of the rate of delivery of
oxygen through the system to the patient.
(usually 60 liters per minute)
• I:E Ratio: a measure of total inspiratory time to
expiratory time. (1:3) is ideal
– Inspiratory time = Tidal Volume / Inspiratory flow
– An increase in flow rate will shorten inspiratory time and
decrease I:E
– Insufficient flow rates contribute to patient dyspnea
– Insufficient expiratory time increases mean airway
pressure, the likelihood of barotrauma and auto-PEEP.
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
Flow Pattern
• Constant (square)
• Decelerating (ramp)
-possibly better in
COPD
• Sinusoidal
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
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
ACV without PEEP
ACV with PEEP
• Extrinsic PEEP
(ePEEP): applied
through a mechanical
ventilator
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
Positive End-Expiratory Pressure
Supraphysiologic PEEP: (> 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
Positive End-Expiratory Pressure
Auto-PEEP
• Intrinsic PEEP (iPEEP, aka occult, ventassociated) occurs because of incomplete
ventilation: Initiating a new breath prior to
complete exhalation causes air-trapping
Auto-PEEP
• Causes: high minute
volume ventilation,
expiratory flow
limitation or increased
expiratory resistance
• Hypoxemia,
hypotension and
barotrauma can occur
as a result
Auto-PEEP
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
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
Consequences of MV
• Barotrauma causes
damage to adjacent
alveoli via stretching and
shearing forces.
• High peak airway
pressures are directly
correlated with
barotrauma
Consequences of MV
• Complications of
alveolar rupture can be
devastating:
– Pulmonary interstitial
emphysema
– Pneumomediastinum
– SQ Emphysema
– Pneumothorax
– Pneumoperitoneum
Ventilator Synchrony
• Setting the ventilator to cycle with the patient’s 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
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.
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)
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Patient failed conservative management
Severe, persistent acidosis
Continued arterial hypoxemia despite initial therapy
Patient fatigue
Altered mental status
Additional major illness (pulmonary embolism, AMI)
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
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
Respiratory Distress in MV
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 / πr 4)
Obstructive Lung Diseases
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Asthma
Chronic bronchitis
Emphysema
Congenital bullous
lung disease
Pathophys COPD
Pathophys Emphysema
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
Vent Guidelines
VENT Guidelines
Higher flow rates are highly beneficial
Vent Guidelines
Vent Guidelines
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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
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
Pathophys Asthma
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
Vent Settings Asthma
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
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
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
References
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“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
• Harrison’s Principles of Internal Medicine 16th
Edition
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”