VENTILATOR MANAGEMENT:
Are You Kidding Me?
Susan Marie Baro, DO, FACOS
Associate Trauma and Surgical Critical Care
Associate Director Surgical Critical Care
Physician Director Blood Conservation Program
OBJECTIVES
• Review basic modes of ventilation
• Understand and treat ARDS and ALI
(Acute Lung Injury)
• Review recommendations for ventilator
settings
TRAUMA AND THE VENTILATOR
• Patients with severe trauma are at a high
risk for developing respiratory failure
• Acute Lung Injury
• Acute Respiratory Distress Syndrome
• Goals of treatment should be to identify
those most likely to develop severe
respiratory insufficiency and to institute
therapy as soon as possible
ATELECTASIS
• Positive pressure and low oxygen
concentrations
– minimize or reverse the formation of atelectasis during
mechanical ventilation and general anesthesia
• Within 5 minutes of induction with general
anesthesia
– increased densities appear in the dependent regions of
both lungs
ATELECTASIS
• Develops with both IV and Inhalation
anesthesia
• Develops with both spontaneous and
paralyzed mechanical vent
• CXR/CT may not show extent
– Collapsed lung comprises 4 times more lung
tissue than aerated regions
– Small amount of compressed lung tissue can
account for a significant increase in shunt
fraction
ATELECTASIS
• 3 Mechanisms of Atelectasis Formation
– Compression and absorption
• Major cause with anesthesia
– Loss of Surfactant
– High Inspired Oxygen Concentration
• Can be avoided or minimized with vital capacity
maneuvers or positive end expiratory pressure (PEEP)
• FiO2 1.00 pre-induction and prior to extubation both
contribute to atelectasis
– Likely explains the hypoxia seen in the PACU
– 0.8 and 0.3 both studied and found to have decreased
atelectasis
IN TRAUMA
• During acute trauma resuscitation patients
are generally given 100% oxygen to
augment O2 delivery to potentially
ischemic tissues
• Pre-oxygenation with 100% and early
hyper-oxygenation post intubation
routinely practiced
THE VENTILATOR (cont.)
• Ideally Mechanical Ventilation should:
– Potentiate alveolar recruitment
– Optimize intrapulmonary gas distribution
– Narrow time-constant discrepancies
• Thereby distribute pressure and volume to
dependent and nondependent regions
proportionally
VENTS IN THE OR
• If the vent setting in the ICU exceed the
capabilities of the OR Vent
– Patient should be transported to the OR on
the ICU vent
– Patient should remain on the ICU vent
throughout the procedure
– All efforts should be made to avoid derecruitment
VENTILATOR MODES
• Mode
– The pattern in which breaths are delivered
• Characterized by a group of variables set
in different combinations and fashions
• Variables:
– Respiratory Rate, Tidal Volume or Pressure,
Inspiratory Flow, Inspiratory Time/Pause, I:E
Ratio, PEEP, Inspiratory Trigger
VENTILATOR MODES
• Trigger
– Initiates the breath
– Time, flow, pressure
• Limit
– Governs the gas delivery
– Pressure, flow volume
• Cycle
– Terminates the breath
– Flow, time, volume, pressure
MORE COMMON
VENTILATOR MODES
• Controlled Mandatory
• BiLevel Positive Airway
•
•
•
•
Ventilation (CMV)
Intermittent Mandatory
Ventilation (IMV)
Pressure/Volume Control
Vent (PCV)
Assist Control (AC)
– Pressure or Volume
•
•
•
Pressure (BiPAP)
Airway Pressure Release
Vent (APRV)
Synchronized Intermittent
Mandatory Vent (SIMV)
Pressure Support Vent
(PSV)
Continuous Positive
Airway Pressure (CPAP)
LESS COMMON
VENTILATOR MODES
• Mandatory Minute Vent
•
•
•
(MMV)
Adaptive Support Vent
(ASV)
Proportional Assist Mode
(PAV)
Volume Assured Pressure
Support (VAPS)
• Pressure Regulated
•
•
•
Volume Control
(PRVC)
Volume Vent Plus
(VVP+)
Inverse Ration Vent
(IRV)
Neurally Adjusted
Ventilatory Assist (NAVA)
MODES
• Mandatory
– CMV
– IMV
• Spontaneous/Triggered
– CPAP
– PSV
• Hybrid
– AC
– SIMV
– BiPAP
• APRV
CONTROLLED MANDATORY
VENTILATION (CMV)
• Preset TV at a time triggered RR
• Vent controls the TV and RR
• May require sedation (possibly paralysis)
for patient comfort
• Can be pressure controlled or volume
controlled
INTERMITTENT MANDATORY
VENTILATION (IMV)
• Patient initiates own breath
– Different from CMV
• Periodic volume/pressure targeted breaths
•
•
occur at set interval (time triggered)
Between breaths, patient breathes
spontaneously at any desired baseline
pressure/volume without getting a
mandatory breath
Vent always gives breath even if patient
exhaling - Get stacking of breaths
CPAP
• Triggered/Spontaneous Mode
• Helpful to improve oxygenation in patient
with refractory hypoxemia and low FRC
(functional residual capacity)
• Adjusted to provide the best oxygenation
with the lowest possible pressure and the
lowest FiO2
• PEEP without the preset vent rate or
volume
PSV
• Patient triggered, pressure limited flow
cycle
• Inspiration initiated by negative
pressure/flow change (patient)
• Expiration initiated by decreased flow
(patient)
• Purely spontaneous
ASSIST CONTROL (AC)
• Mandatory breath either patient triggered
(spontaneous respiration) or time
triggered (preset RR)
• Spontaneous effort
– With respiratory assist
• Assist Mode
– Patient initiates all breathes but the vent cycles at
initiation to give preset TV
– Patient controls rate but always gets a full breath
SYNCHRONIZED INTERMITTENT
MADATORY VENTILATION(SIMV)
• Vent delivers controlled breath (mandatory) at
•
•
•
or near time of patients spontaneous breath
(time triggered)
Mandatory breath is synchronized with patients
spontaneous breathing effort to avoid breath
stacking
Patient triggered
If patient fails to initiate breath within a
predetermined interval, vent will provide a
mandatory breath at the end of the time period
BiPAP
• 2 levels of pressure set
– Hi and Low levels are set
• At either pressure level patient can breath
spontaneously
• May be supported with Pressure Support
• Initial settings
– IPAP ~ 8 cm H2O
– EPAP ~ 4 cm H2O
APRV - BiVENT
• A bi-level form of ventilation with sudden
short releases in pressure to rapidly
reduce FRC and allow for ventilation
• Provides 2 levels of CPAP and allows
spontaneous breathing at both levels
when spontaneous effort is preserved
• Set Phigh and Plow
• Both pressure levels are time triggered
and time cycled
APRV - BiVENT
• Inverse I:E Ratio
• Set Thigh and Tlow
• Allows spontaneous breathing patient to
breath at a high CPAP level but drops
briefly ( ~1 sec) periodically to allow low
CPAP level for extra CO2 elimination
(airway pressure release)
APRV - BiVENT
• Mandatory breaths occur when the
pressure limit rises from the lower CPAP
level to the higher CPAP level
• Allows Inverse Ratio Vent (IRV) with or
without spontaneous breathing
• Improves patient-ventilator synchrony if
spontaneous breathing is present
• Improves mean airway pressure
APRV - BiVENT
• Improves oxygenation by stabilizing
collapsed alveoli
• Allows patient to breath spontaneously
while continuing lung recruitment
• Lowers PIP
APRV - BiVENT
• Disadvantages
– Variable Tidal Volume
– Could be harmful to patients with high
expiratory resistance (COPD, Asthma)
– Some form of Auto PEEP usually present
– Caution with hemodynamically unstable
pateints
– Can get asynchrony if spontaneous breaths
out of synch with release time
PEEP PHYSIOLOGY
• Re-inflates collapsed alveoli and maintains
alveolar inflation during exhalation
• PEEP leads to decreased alveolar
distending pressures
– Increases FRC by alveolar recruitment
– Improves ventilation
– Increases ventilation and perfusion
– Improves oxygenation
– Decreased work of breathing
PEEP DISADVANTAGES
• High intra-thoracic pressures can cause
decreased venous return
• May produce pulmonary barotrauma
• May worsen air trapping in obstructive
pulmonary diseases
• Increases intracranial pressure
• Can cause alterations in renal function and
water metabolism
RUN OF THE MILL VENT SETTING
• Tidal Volume ~ 8 ml/kg PBW/IBW
– Decrease Tidal Volume to 6 ml/kg in ARDS
• Respiratory Rate 12 – 16 breaths per minute
• PEEP 5 – 10 cm H2O
• Peak flow rate that creates an Inspiratory to
Expiratory (I:E) ratio of 1:2 to 1:3
• Lowest Fraction of Inspired Oxygen (FiO2)
sufficient enough to meet oxygenation goals
PREDICTED BODY WEIGHT (PBW)
or IDEAL BODY WEIGHT (IBW)
• Males: IBW inKg
50 kg + 2.3 kg for each inch over 5 feet
• Females: IBW in Kg
45.5 kg + 2.3 kg for each inch over 5 feet
ACUTE RESPIRATORY FAILURE
Acute Respiratory
Distress Syndrome
(ARDS)
Acute Lung Injury
(ALI)
•
•
•
•
Acute onset
B/L Infiltrates on CXR
PaO2/FiO2 ratio < 300
Non cardiogenic
pulmonary edema
•
•
•
•
Acute onset
B/L Infiltrates on CXR
PaO2/FiO2 ratio < 200
Non cardiogenic
pulmonary edema
VENTILATOR ASSOCIATED
LUNG INJURY
• Iatrogenic
• High volume, low PEEP vent settings
– Induce parenchymal damage through overdistension or “stretch” of the aerated lung
– Cause repeated opening and closing or
“shear” of the collapsed de-recruited lung
– Results in disruption of the normal alveolar
integrity and can perpetuate the inflammatory
response
ALI/ARDS Multicenter Trial
• Randomized to
– “Traditional” TV Vent
• 12 ml/kg and
• end inspiratory Plateau Pressure of < 50 cm H2O
– “Low Volume” TV Vent
• 6 ml/kg with
• end inspiratory plateau pressure of < 30 cm H2O
• Study stopped after 861 patients
secondary to significantly decreased
mortality in the study arm group
– 39.8 vs 31% (p=0.007)
RECOMMENDATIONS FOR
VENT SETTINGS
• Low Tidal Volumes: 6 – 8 ml/kg
• Limit Peak/Plateau Pressure: < 35 cm H2O
• Set PEEP above the lower inflection point on
the pressure – volume curve
• Adjust I:E Ratio and Respiratory Rate as
needed to achieve the above
• Wean FiO2 to obtain PaO2 80 – 100 mm Hg
– or an oxygen saturation of 93- 97%
• Early conversion to pressure limited mode
RISK FACTORS FOR ARDS
•
•
•
•
•
•
•
•
•
Shock
Pulmonary Contusions
Fractures
Multiple Tranfusions
Pneumonia
ISS > 16
Trauma Score < 13
Surgery to Head
DIC
Early Findings
• +/- Admission lactate,
•
•
•
•
•
•
pH, base deficit, and
serum bicarbonate
Gastric Aspiration
Near Drowning
Smoke Inhalation
Fat Emoblism
Sepsis
Blunt Injury
ARDS IN TRAUMA
• Trauma is 2o only to sepsis in regard to
risk factors for ARDS
– 12-39%
• Of the 14 main risk factors identified as
highly associated with subsequent ARDS
– 8 may be seen early in the trauma patient
with 3 more seen in days to weeks
ARDS
• Early ARDS (< 48 hours)
– Characterized by hemorrhagic shock and
capillary leak
• Late ARDS ( > 48 hours)
– Follows pneumonia and is more closely
associated with MSOF
ARDS (cont.)
• Initial Stages
– Increased capillary permeability results in lung edema
– Positive pressure must exceed the sum of interstitial
pressures and superimposed hydrostatic pressure to
re-open lung units
• Following the Initial Phase
– Alveolar edema becomes organized and is replaced by
fibrinous material
• Recruitment maneuvers to open collapsed alveoli become
less effective as the response to pressure increases
• Favors over-distension
• Therefore – Lung recruitment needs to be instituted early!
ARDS and RECRUITMENT
• Greatest frequency of opening lung units
– Occurs at ~ 25 cm H2O
• Maximal frequency of estimated
transpulmonary opening pressure
– Between 20 – 25 cm H2O
• Different regions of the lung are recruited at
differing pressures
– Ranges from 10 – 45 cm H2O
• Majority of de-recruitment
– Occurs at PEEP values spanning 0 – 15 cm H2O
ARDS PROGRESSION
• Over-distension creates dead space
• Progressive over-distension initiates
capillary compression
• Blood flow is then redistributed to less
ventilated regions
• Subsequently aggravating hypoxemia
ARDS PROGRESSION (cont.)
• Recruitment require sufficient airway
pressures to exceed the critical opening
pressure of the airways
• Also requires time in addition to critical
opening pressure
• As pressure is reached and maintained,
time allows redistribution of delivered gas
volume
ARDSp vs ARDSexp
• Pulmonary (Primary or Direct Insult) ARDS
– ARDSp
• ExtraPulmonary (Secondary or Indirect)
ARDS
– ARDSexp
ARDS
•
•
•
•
ARDSp
Consolidation
Alveolar filling of fibrin,
edema, blood cells, and
collagen
Stiffer lungs
May not improve with
PEEP
•
•
•
•
ARDSexp
Atelectasis of alveolar
architecture
Accompanied by
microvascular congestion
Stiffer thoraco-abdominal
cage and a more
compliant lung
Likely improves with PEEP
ARDS and SPONTANEOUS
BREATHING
• Crucial to improve V/Q
• Significant difference between the
distribution of gas flow (V) in mechanical
vent (CMV) vs spontaneous breathing
• Mechanical Vent
– TV delivered to nondependent poorly perfused lung
• Spontaneous Breathing
– preferentially directed to dependent lung regions
where blood flow (Q) is higher
ARDS and SPONTANEOUS
BREATHING
• Allows diaphragm to move to help
maintain its muscle mass
• Under-ventilated lung units can lead to
increased shunt
• Spontaneous breathing does not lead to
an increase in oxygen consumption (VO2)
ARDS and SPONTANEOUS
BREATHING
• Traditionally spontaneous breathing in
ALI/ARDS was discouraged
• Controlled vent with neuromuscular
blockade and/or heavy sedation all causes
disproportionate under-ventilation of
dependent lung regions
NONINVASIVE POSITIVE
PRESSURE VENTILATION (NIPPV)
• Increasingly popular
• Improves PaO2/FiO2 ration
• Increased TV
• Decreased RR
• Mean pressure support level of 12 cm H2O
with PEEP 4.5 cm via face mask
• May be alternative to ET intubation
– No facial fx’s, mental status to cooperate, ability to protect
airway, low aspiration risk
ARDS RECOMMENDATIONS
• PEEP
– Should be applied early
– Start at 10 cm H2O
• If massive fluid resuscitation, pulmonary
contusion, direct pulmonary injuries,
morbidly obese
– may require higher starting settings
• If hypotensive with PEEP
– suggestive of under-resuscitation
ARDS RECOMMENDATIONS
• If at risk for ALI/ARDS
– Start “Open Lung” techniques prior to
deterioration of blood gases or CXR findings
– APRV early for recruitment
• Give enough PEEP to preserve a PaO2/FiO2
ratio at the highest possible value
ARDS RECOMMENDATIONS
• Plateau Pressure
– Should be limited to < 35 cm H2O
– Plateau pressure is an acceptable correlate to
transpulmonary pressure (hard to measure)
• Ventilator associated lung injury occurs
> 35 cm H2O
• Utilize Decreased TV, Decreased RR, and
Increased Inspiration time
• Change to pressure modes of vent and/or
Inverse-Ratio Ventilation
ARDS RECOMMENDATIONS
• Tidal Volume: 6 – 8 ml/kg
– Over-distension causes lung injury
– Occurs at the upper end of the pressure-volume
curve above the upper inflection point
• Volutrauma
– Occurs secondary to high TV or to high PEEP without
limiting volume setting
• If increased PEEP (for oxygenation)
– PIP/Plateau pressure needs to be limited by
decreased TV or change to pressure limited mode
ARDS RECOMMENDATIONS
• Recruitment maneuvers
– Work because opening (or distending) pressures
needed to open collapsed alveoli are higher than the
pressures required to keep recruited alveoli open
– Pressure can be decreased after the maneuver
• Continuous sustained pressure of 30 – 45
cm H2O for 30 seconds, as tolerated
• After a recruitment maneuver, PEEP should
be increased from its previous level in order
to maintain alveolar patency
ARDS RECOMMENDATIONS
• Avoid oxygen toxicity
• Give enough to maintain normal arterial
oxygenation
• If in high concentrations – check ABG’s
frequently and adjust accordingly to
decrease as soon as possible
ARDS RECOMMENDATIONS
• During manual ventilation
• Deliver breath so it is just possible to see
the chest rise and fall
• Monitor peripheral O2 Saturations and End
Tidal CO2
• Aim for SpO2 93- 97%
• Aim for ETCO2 35 – 40 mm Hg
ARDS RECOMMENDATIONS
• Permissive Hpercapnia
• Likely will do OK if keep pH > 7.2
• If PaO2/FiO2 ratio marginal, accepting a
higher PaCO2 in exchange for maintaining
an adequate mean airway pressure and
limiting peak/plateau pressure is
reasonable
• Caution with TBI
ARDS RECOMMENDATIONS
• Optimize positioning
– Frequent turning
– Suctioning
– Chest physiotherapy
• Mobilize early
• Intermittent Prone Positioning
– Still controversial in some literature
– Likely not done soon enough
– Usually reserved for patients who do not respond to
vent management strategies