Mechanical ventilation
Transcript of Mechanical ventilation
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Date:09/03/2014
DR Nirmal TapariaMD Medicine
Physician & IntensivistAshwini Hospital
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MECHANICAL VENTILATION
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Presentation
Different settings to consider
Monitoring of the patient
Different type of patientCOPD, AsthmaARDS
Trouble shooting
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Indications for intubationIndications for intubation
•Criteria•Clinical deterioration• Tachypnea: RR >35• Hypoxia: pO2<60mm Hg • Hypercarbia: pCO2 >
55mm Hg•Minute ventilation<10 L/min• Tidal volume <5-10 ml/kg• Negative inspiratory force
< 25cm H2O (how strong the pt can suck in)
•Initial vent settings•FiO2 = 50%
•PEEP = 5cm H2O
•RR = 12 – 15 breaths/min
•VT = 10 – 12 ml/kg
• COPD = 10 ml/kg (prevent overinflation)
• ARDS = 8 ml/kg (prevent volutrauma)
• Permissive hypercapnea
•Pressure Support = 10cm H2O
How the values trend should significantly impact clinical decisions
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Principles (1): VentilationPrinciples (1): VentilationThe goal of ventilation is to facilitate CO2 release and maintain normal PaCO2
•Minute ventilation (VE)•Total amount of gas
exhaled/min.
•VE = (RR) x (TV)
•VE comprised of 2 factors• VA = alveolar ventilation
• VD = dead space ventilation
•VD/VT = 0.33
•VE regulated by brain stem, responding to pH and PaCO2
•Ventilation in context of ICU
• Increased CO2 production
• fever, sepsis, injury, overfeeding
• Increased VD
• atelectasis, lung injury, ARDS, pulmonary embolism
•Adjustments: RR and TV
V/Q Matching. Zone 1 demonstrates dead-space ventilation (ventilation without perfusion). Zone 2 demonstrates normal perfusion. Zone 3 demonstrates shunting (perfusion without ventilation).
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Principles (2): OxygenationPrinciples (2): OxygenationThe primary goal of oxygenation is to maximize O2 delivery to blood (PaO2)
•Alveolar-arterial O2 gradient (PAO2 – PaO2)
•Equilibrium between oxygen in blood and oxygen in alveoli
•A-a gradient measures efficiency of oxygenation
•PaO2 partially depends on ventilation but more on V/Q matching
•Oxygenation in context of ICU
•V/Q mismatching• Patient position (supine)• Airway pressure, pulmonary
parenchymal disease, small-airway disease
•Adjustments: FiO2 and PEEP
V/Q Matching. Zone 1 demonstrates dead-space ventilation (ventilation without perfusion). Zone 2 demonstrates normal perfusion. Zone 3 demonstrates shunting (perfusion without ventilation).
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Ventilator settings
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Ventilator settings
1. Ventilator mode
2. Respiratory rate
3. Tidal volume or pressure settings
4. Inspiratory flow
5. I:E ratio
6. PEEP
7. FiO2
8. Inspiratory trigger
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CMV
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A/CV
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Assist/Control ModeAssist/Control Mode
•Control Mode•Pt receives a set number of
breaths and cannot breathe between ventilator breaths
•Similar to Pressure Control
•Assist Mode•Pt initiates all breaths, but
ventilator cycles in at initiation to give a preset tidal volume
•Pt controls rate but always receives a full machine breath
•Assist/Control Mode•Assist mode unless pt’s
respiratory rate falls below preset value
•Ventilator then switches to control mode
•Rapidly breathing pts can overventilate and induce severe respiratory alkalosis and hyperinflation (auto-PEEP)
Ventilator delivers a fixed volume
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SIMV
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IMV and SIMV IMV and SIMV
Volume-cycled modes typically augmented with Pressure Support
•IMV• Pt receives a set number of
ventilator breaths• Different from Control: pt can
initiate own (spontaneous) breaths
• Different from Assist: spontaneous breaths are not supported by machine with fixed TV
• Ventilator always delivers breath, even if pt exhaling
•SIMV• Most commonly used mode• Spontaneous breaths and
mandatory breaths• If pt has respiratory drive, the
mandatory breaths are synchronized with the pt’s inspiratory effort
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PSV(pressure support ventilation)
Spontaneous inspiratory efforts trigger the ventilator to provide a variable flow of gas in order to attain a preset airway pressure.
Can be used in adjunct with SIMV.
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Pressure ventilation vs. volume Pressure ventilation vs. volume ventilationventilationPressure-cycled modes deliver a fixed pressure at variable volume (neonates)
Volume-cycled modes deliver a fixed volume at variable pressure (adults)
•Pressure-cycled modes•Pressure Support Ventilation
(PSV)•Pressure Control Ventilation
(PCV)•CPAP•BiPAP
•Volume-cycled modes•Control•Assist•Assist/Control• Intermittent Mandatory
Ventilation (IMV)•Synchronous Intermittent
Mandatory Ventilation (SIMV)
Volume-cycled modes have the inherent risk of volutrauma.
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Respiratory Rate
1. What is the pt actual rate demand?
2. New rate=old rate x co2 ÷ TV
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Tidal Volume or Pressure setting
Maximum volume/pressure to achieve good ventilation and oxygenation without producing alveolar overdistention
Max cc/kg? = 10 cc/kg
Some clinical exceptions
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Inspiratory flow
Varies with the Vt, I:E and RR
Normally about 60 l/min
Can be majored to 100- 120 l/min
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I:E Ratio
1:2
Prolonged at 1:3, 1:4, …
Inverse ratio
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FIO2
The usual goal is to use the minimum Fio2 required to have a PaO2 > 60mmhg or a sat >90%
Start at 100%
Oxygen toxicity normally with Fio2 >40%
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Inspiratory Trigger
Normally set automatically
2 modes:
Airway pressureFlow triggering
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Positive End-expiratory Pressure (PEEP)
What is PEEP?
What is the goal of PEEP?
Improve oxygenation
Diminish the work of breathing
Different potential effects
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PEEP
What are the secondary effects of PEEP? Barotrauma Diminish cardiac output
Regional hypoperfusion NaCl retention Augmentation of I.C.P.? Paradoxal hypoxemia
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PEEP
Contraindication:No absolute CI
BarotraumaAirway traumaHemodynamic instability I.C.P.?Bronchospasm?
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PEEP
What PEEP do you want?
Usually, 5-10 cmH2O
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Monitoring of the patient
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Look at your patient
Question your pt
Examine your pt
Monitor your pt
Look at the synchronicity of your pt breathing
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Pressures
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Compliance pressure (Pplat)
Represent the static end inspiratory recoil pressure of the respiratory system, lung and chest wall respectively
Measures the static compliance or elastance
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PplatMeasured by occluding the ventilator 3-5 sec at the end of inspiration
Should not exceed 30 cmH2O
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Peak Pressure (Ppeak)
Ppeak = Pplat + Pres
Where Pres reflects the resistive element of the respiratory system (ET tube and airway)
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PpeakPressure measured at the end of inspiration
Should not exceed 50cmH2O?
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Auto-PEEP or Intrinsic PEEP
What is Auto-PEEP?
Normally, at end expiration, the lung volume is equal to the FRC
When PEEPi occurs, the lung volume at end expiration is greater then the FRC
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Auto-PEEP or Intrinsic PEEP
Why does hyperinflation occur?
Airflow limitation because of dynamic collapse
No time to expire all the lung volume (high RR or Vt)
Expiratory muscle activityLesions that increase expiratory resistance
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Auto-PEEP or Intrinsic PEEP
Auto-PEEP is measured in a relaxed pt with an end-expiratory hold maneuver on a mechanical ventilator immediately before the onset of the next breath
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Auto-PEEP or Intrinsic PEEP
Adverse effects:
Predisposes to barotrauma Predisposes hemodynamic compromises Diminishes the efficiency of the force
generated by respiratory muscles Augments the work of breathing Augments the effort to trigger the ventilator
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Different types of patient
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COPD and Asthma
Goals:
Diminish dynamic hyperinflationDiminish work of breathingControlled hypoventilation
(permissive hypercapnia)
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Diminish DHI
Why?
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Diminish DHI
How?Diminish minute ventilation
Low Vt (6-8 cc/kg)Low RR (8-10 b/min)Maximize expiratory time
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Diminish work of breathing
How: Add PEEP (about 85% of PEEPi)
Applicable in COPD and Asthma.
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Controlled hypercapnia
Why?
Limit high airway pressures and thus diminish the risk of complications
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Controlled hypercapnia
How?
Control the ventilation to keep adequate pressures up to a PH > 7.20 and/or a PaCO2 of 80 mmHg
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Controlled hypercapnia
CI:Head pathologiesSevere HTNSevere metabolic acidosisHypovolemiaSevere refractory hypoxiaSevere pulmonary HTNCoronary disease
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A.R.D.S.
Ventilation with lower tidal volume as compared with traditional volumes for acute lung injury and the ARDS
The Acute Respiratory Distress Syndrome Network
N Engl J Med 2000;342:1301-08
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Methods
March 96 – March 9910 university centersInclusion:Diminish PaO2Bilateral infiltrateWedge < 18
ExclusionRandomized
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Methods
A/C 28d or weaning2 groups: 1. Traditional Vt (12cc/kg) 2. Low Vt (6cc/kg)
End point: 1. Death 2. Days of spontaneous breathing 3. Days without organ failure or barotrauma
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ResultsThe trails were stopped after 861 pt because of lower mortality in low Vt group
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Vent settings to improve Vent settings to improve <oxygenation><oxygenation>
•FIO2
•Simplest maneuver to quickly increase PaO2
•Long-term toxicity at >60%• Free radical damage
•Inadequate oxygenation despite 100% FiO2 usually due to pulmonary shunting•Collapse – Atelectasis•Pus-filled alveoli – Pneumonia•Water/Protein – ARDS•Water – CHF•Blood - Hemorrhage
PEEP and FiO2 are adjusted in tandem
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Vent settings to improve Vent settings to improve <ventilation><ventilation>
•Respiratory rate•Max RR at 35 breaths/min •Efficiency of ventilation
decreases with increasing RR• Decreased time for alveolar
emptying
•TV
•Goal of 10 ml/kg•Risk of volutrauma
•Other means to decrease PaCO2
•Reduce muscular activity/seizures
•Minimizing exogenous carb load•Controlling hypermetabolic
states
•Permissive hypercapnea•Preferable to dangerously high
RR and TV, as long as pH > 7.15
RR and TV are adjusted to maintain VE and PaCO2
•I:E ratio (IRV)• Increasing inspiration time
will increase TV, but may lead to auto-PEEP
•PIP•Elevated PIP suggests need
for switch from volume-cycled to pressure-cycled mode
•Maintained at <45cm H2O to minimize barotrauma
•Plateau pressures•Pressure measured at the
end of inspiratory phase•Maintained at <30-35cm
H2O to minimize barotrauma
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Vent settings to improve Vent settings to improve <oxygenation><oxygenation>
•PEEP • Increases FRC
• Prevents progressive atelectasis and intrapulmonary shunting
• Prevents repetitive opening/closing (injury)
•Recruits collapsed alveoli and improves V/Q matching• Resolves intrapulmonary shunting• Improves compliance
•Enables maintenance of adequate PaO2 at a safe FiO2 level
•Disadvantages• Increases intrathoracic pressure (may
require pulmonary a. catheter)• May lead to ARDS• Rupture: PTX, pulmonary edema
PEEP and FiO2 are adjusted in tandem
Oxygen delivery (DO2), not PaO2, should be used to assess optimal PEEP.
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Trouble Shooting
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Trouble Shooting
Doctor, doctor, his pressures are going up!!!
What is your next step?
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Trouble Shooting
1. Call the I.T., he will take care of it!
2. Where is the staff?
3. I dont know this pt, and run!
4. Ask which pressure is going up
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Trouble Shooting
Ppeak is up
Look at your Pplat
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Trouble Shooting
If your Pplat is high, you are faced with a COMPLIANCE problem
If your Pplat is N, you are faced with a RESISTIVE problem
DD?
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Trouble Shooting
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Trouble Shooting
Doctor, doctor, my patient is very agitated!
What is your next step?
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Trouble Shooting
1. Give an ativan to the nurse!
2. Give haldol 10mg to the patient!
3. Take 5mg of morphine for yourself!
4. Look at your pt!
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Trouble Shooting
At the time of intubation, fighting is largely due to anxiety
But what do you do if pt is stable and then becomes agitated?
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Trouble Shooting
1. Remove pt from ventilator
2. Initiate manual ventilation
3. Perform P/E and assess monitoring indices
4. Check patency of airway
5. If death is imminent, consider and treat most likely causes
6. Once pt is stabilized, undertake more detailed assessement and management
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Trouble Shooting
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ConclusionType of patient Tidal Volume RR PEEP FIO2 Ins. Flow I:E Note Note
Normal 10 cc/kg 10 to 12 0 to 5 100%. 60 l/min 1:2.
ARDS 6 cc/kg 10 to 12 5 to 15 100%. 60 l/min 1:2.
COPD 6 cc/kg 10 to 12 5 to 10 100%. 100 to 120 1:3 to 1:4 PH>7.2PCO2 <80 mmhgTrigger to consider
Trauma 10 cc/kg 10 to 12 0. 100%. 60 l/min 1:2.
Pediatric 8-10 cc/kg Varies age 3 to 5 100%. 60 l/min 1:2. Trigger to consider
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Ventilator management algorithimVentilator management algorithimInitial intubation• FiO2 = 50%
• PEEP = 5
• RR = 12 – 15• VT = 8 – 10 ml/kg
SaO2 < 90% SaO2 > 90%
SaO2 > 90%• Adjust RR to maintain PaCO2
= 40• Reduce FiO2 < 50% as
tolerated• Reduce PEEP < 8 as tolerated• Assess criteria for SBT daily
SaO2 < 90%• Increase FiO2 (keep
SaO2>90%)• Increase PEEP to max 20• Identify possible acute lung
injury• Identify respiratory failure
causes
Acute lung injury
No injury
Fail SBT
Acute lung injury• Low TV (lung-protective)
settings• Reduce TV to 6 ml/kg• Increase RR up to 35 to
keep pH > 7.2, PaCO2 < 50
• Adjust PEEP to keep FiO2 < 60%SaO2 < 90% SaO2 > 90%
SaO2 < 90%• Dx/Tx associated conditions
(PTX, hemothorax, hydrothorax)
• Consider adjunct measures (prone positioning, HFOV, IRV)
SaO2 > 90%• Continue lung-
protective ventilation until:
•PaO2/FiO2 > 300•Criteria met for
SBT
Persistently fail SBT• Consider tracheostomy• Resume daily SBTs with
CPAP or tracheostomy collar
Pass SBT
Airway stableExtubate
Intubated > 2 wks
• Consider PSV wean (gradual reduction of pressure support)
• Consider gradual increases in SBT duration until endurance improves
Prolonged ventilator dependence
Pass SBT
Pass SBT
Airway stable
Modified from Sena et al, ACS Surgery: Principles and Practice (2005).
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Spontaneous Breathing TrialsSpontaneous Breathing Trials
•Settings•PEEP = 5, PS = 0 – 5, FiO2 <
40%•Breathe independently for 30
– 120 min•ABG obtained at end of SBT
•Failed SBT Criteria•RR > 35 for >5 min
•SaO2 <90% for >30 sec
•HR > 140•Systolic BP > 180 or < 90mm
Hg•Sustained increased work of
breathing•Cardiac dysrhythmia•pH < 7.32
SBTs do not guarantee that airway is stable or pt can self-clear secretions
Causes of Failed SBTs TreatmentsTreatments
Anxiety/Agitation Benzodiazepines or haldol
Infection Diagnosis and tx
Electrolyte abnormalities (K+, PO4-)
Correction
Pulmonary edema, cardiac ischemia
Diuretics and nitrates
Deconditioning, malnutrition Aggressive nutrition
Neuromuscular disease Bronchopulmonary hygiene, early consideration of trach
Increased intra-abdominal pressure
Semirecumbent positioning, NGT
Hypothyroidism Thyroid replacement
Excessive auto-PEEP (COPD, asthma)
Bronchodilator therapy
Sena et al, ACS Surgery: Principles and Practice (2005).
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Indications for extubationIndications for extubation
•Clinical parameters•Resolution/Stabilization of
disease process•Hemodynamically stable• Intact cough/gag reflex•Spontaneous respirations•Acceptable vent settings
•FiO2< 50%, PEEP < 8, PaO2 > 75, pH > 7.25
•General approaches•SIMV Weaning•Pressure Support
Ventilation (PSV) Weaning•Spontaneous breathing
trials• Demonstrated to be superior
No weaning parameter completely accurate when used alone
Numerical Parameters
Normal Range
Weaning Threshold
P/F > 400 > 200
Tidal volume 5 - 7 ml/kg 5 ml/kg
Respiratory rate 14 - 18 breaths/min
< 40 breaths/min
Vital capacity 65 - 75 ml/kg 10 ml/kg
Minute volume 5 - 7 L/min < 10 L/min
Greater Predictive Value
Normal Range
Weaning Threshold
NIF (Negative Inspiratory Force)
> - 90 cm H2O > - 25 cm H2O
RSBI (Rapid Shallow Breathing Index) (RR/TV)
< 50 < 100
Marino P, The ICU Book (2/e). 1998.
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