complications of mechanical ventilation. ventilator-induced lung injury (vili) overdistention...
TRANSCRIPT
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Complications of Mechanical Ventilation
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Ventilator-Induced lung injury (VILI)
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The Problem of Heterogeneity in ARDS
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The Problem of Heterogeneity Especially in ARDS
• Some lung units may be overstretched while others remain collapsed at the same airway pressure.
• Finding the right balance of TV and PEEP to keep the lung open without generating high pressures is the goal.
• This presents major difficulty for the clinician, who must apply only a single pressure to ventilate patients
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Ventilator-induced Lung Injury (VILI)
OverOverDistensionDistension
CollapseCollapse
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Pinsp = 40 mbar
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Ventilator-Induced Lung Injury Atelectotrauma Vs Volutrauma
Atelectrauma: Repetitive alveolar collapse and reopening of the under-recruited alveoli
Volutrauma:Over-distension of normally aerated alveoli due to excessive volume delivery
Dreyfuss: J Appl Physiol 1992
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Spectrum of Regional Opening Pressures (Supine Position)
Superimposed Pressure Inflated 0
Alveolar Collapse(Reabsorption) 20-60 cmH2O
Small AirwayCollapse
10-20 cmH2O
Consolidation
(from Gattinoni))
Lung Units at Risk for Tidal Opening & Closure
=
OpeningPressure
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Effect of lung expansion on pulmonary vasculature. Capillaries that are embedded in the alveolar walls undergo compression even as interstitial vessels dilate. The net result is usually an increase in pulmonary vascular resistance, unless recruitment of collapsed units occurs.
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VALI vs VILI
• Ventilator-associated lung injury (VALI)– Acute lung injury that resembles ARDS in
patients receiving MV– VALI may be associated with pre-existing
lung pathology– VALI is associated only with MV
• Ventilator induced lung injury (VILI)– Acute lung injury directly induced by MV in
animal models
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Histopathology of VILI
Belperio et al, J Clin Invest Dec 2002; 110(11):1703-1716
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Mechanisms of Airspace Injury
“Stretch”
“Shear”
Airway Trauma
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ARDS
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ARDS after PEEPpreventing atelectotrauma
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Atelectetrauma
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The PEEP Effect
NEJM 2006;354:1839-1841
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Avoiding Atelectotrauma :How much PEEP is enough? ARDSnet protocol:
PEEP - FiO2 Combinations
FIO20.3
0.4
0.4
0.5
0.5
0.6
0.7
0.7
0.7
0.8
0.9
0.9
0.9
1.0PEEP
5 5 8 8 10 10 10 12 14 14 14 16 1820-24
GOAL: PaO2 55-80 mm Hg or SpO2 88-95%
Use these FiO2/PEEP combinations to achieve oxygenation goal.
New Eng J Med. 2000;342(18)1301-1308New Eng J Med. 2000;342(18)1301-1308New Eng J Med. 2000;342(18)1301-1308New Eng J Med. 2000;342(18)1301-1308
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Zone of↑ Risk
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Biotrauma
Biophysical biochemical Injury due to MVHigh volume & Low PEEP
Cytokines, complement, prostanoids, leukotrienes, O2
- Proteases
Organ dysfucntion
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Lung-Protective VentilationARDS Network, 2000: Multicenter randomized,861Pts
Lung-protective ventilation Conventional ventilation
Tidal Volume (ml/kg) 6 12
Pplateau <30 <50
PEEP Protocol Protocol
Actual PEEP 8.1 9.1
Result (p<0.001) 31.0% 39.8%
Principle for FiO2 and PEEP AdjustmentFiO2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
PEEP 5 5-8 8-10 10 10-14 14 14-18 18-24
NEJM 2000; 342: 1301-1308
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Lung-Protective VentilationLow VT Low Plateau pressure
• Result:– 22% reduction in mortality (31% vs 39.8%)– Increase ventilator-free days
NEJM 2000; 342: 1301-1308
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Volume
Pressure
Zone ofOverdistention
“Safe”Window
Zone ofDerecruitment
and Atelectasis
Injury
Injury
Optimized Lung Volume “Safe Window”
• Overdistension – Edema fluid accumulation– Surfactant degradation– High oxygen exposure– Mechanical disruption
• Derecruitment, Atelectasis– Repeated closure / re-expansion– Stimulation inflammatory
response– Inhibition surfactant– Local hypoxemia– Compensatory overexpansion
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Dependent to Non-dependent Progression of Injury
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Effect of 45 cmH2O PIP
Control 5 min 20 min Control 5 min 20 min
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Baro-trauma
• Etiology :Directly related to airway pressures/PEEP
• Incidence– 4% - 15%– Highest in ARDS– Incidence now decreased secondary to lung
protective ventilation
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Barotrauma-Pathophysiology
• Some alveoli become more distended than others. Alveolar pressure increases and forms a pressure gradient between the alveoli and adjacent perivascular sheath.
• Air dissects into the perivascular sheath leading to perivascular interstitial emphysema (PIE) and further moves into areas of least resistance including subcutaneous tissue and tissue planes.
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Barotrauma-Complications
• Pneumothorax• Interstitial emphysema• Pneumomediastinum-
leads to PTX in 42% of patients in one study
• Pneumopericardium• Subcutaneous
emphysema• Pneumoperitoneum
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Gas Extravasation
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Barotrauma
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Oxygen Toxicity : FIO2 > 60 % for > 24h
• Absorptive atelectasis
– O2/N2 = 21/79
>>>>>> 50/50 Carbon dioxide
Water vapour
Oxygen
Nitrogen
2A2A2A2A NPOHPC OPOPp re s s u reA lv e o la r
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Hyperoxia toxicity: mechanism
• Free radicals: lipid peroxidations, especially in the cell membranes, inhibit nucleic acids and protein synthesis, and inactivate cellular enzymes.
• Explosive free radical production leading to swamping of the anti-oxidant enzyme systems and as a result free radicals escape inactivation.
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Oxygen Toxicity
• Absorptive atelectasis– O2/N2 = 21/79 >>>> 50/50
• Accentuation of hypercapnia– Chronic respiratory failure:
PCO2 with PO2
• Damage to airways– Bronchopulmonary
dysplasia
• Diffuse alveolar damage
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Infectious complications of Mechanical ventilation
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Maxillary Sinus and Middle Ear Effusion
• Maxillary effusion – 20% in patients intubated for > 7 days.
– 47% when the gastric tube is placed nasally
– 95%
• Secondarily infected maxillary effusion (45-71% of effusions)
• Middle ear effusion (29%) with 22% of them become infected
• Hearing impairment that may contribute to the confusion and delirium in elderly population
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VAP: Definitions
• VAP – ventilator associated pneumonia– >48 hours on vent– Combination of:
• CXR changes• Sputum changes• Fever, ↑ WBC• positive sputum culture
• Occurs secondary to micro-aspiration of upper airway secretions
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Organism Entry for VAP
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Risk Factors for VAP
• No 1 risk factor is endotracheal intubation • Factors that enhance colonization of the oropharynx &/or
stomach:– Poor oral hygiene
• Conditions favoring aspiration into the respiratory tract or reflux from GI tract:– Supine position– NGT placement– Re-Intubation and self-extubation– Surgery of head/neck/thorax/upper abdomen– GERD– Coma/ depressed Glascow coma scale
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Significance of VAP
• Mortality 20-70%(Leading cause of mortality from nosocomial infections in hospitals)
• Increases mechanical ventilation days• Increases ICU stay by 4.3 days• Increases hospital LOS by 4-9 days• Increases cost -Excess costs of
approximately 11,000 -$40,000/patient
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VAP prevention :VAP Bundle
• Elevation of the head of the bed 30-45o
• Use 15-30o for neonates and small infants, otherwise 30-45o
• Daily sedation vacations (minimize duration of intubation
• Daily assessment of readiness to extubate• Peptic ulcer disease (PUD) prophylaxis • Oral care protocol (chorhexidine)• DVT prophylaxis option
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HOB 30-45o decrease risk of aspiration
• 45o head-up tilt is the goal in all patients unless contraindicated
• No benefit of semi-recumbency ~30o over standard care ~10o
• Supine position is harmful
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HOB Elevation Leads to Significant reduction in VAP
Dravulovic et al. Lancet 1999;354:1851-1858
0
5
10
15
20
25%
VA
P
Supine HOB Elevation
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Handwashing
• Strict handwashing before and after handling patient or patient’s equipment or supplies
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Does the VAP bundle work in real life
CCU VAP Bundle Compliance Vs Infection Rate
0
5
10
15
20
25
30
35
40
Oct
-06
No
v-06
Dec
-06
Jan
-07
Feb
-07
Mar
-07
Ap
r-07
May
-07
Jun
-07
Jul-
07
Au
g-0
7
Sep
-07
Oct
-07
No
v-07
Dec
-07
Jan
-08
Feb
-08
0%
20%
40%
60%
80%
100%
VAP Infection Rate VAP Bundle Compliance%
Linear (VAP Infection Rate) Linear (VAP Bundle Compliance%)
NHSN 50th Percentile 4.1
NHSN 50th Percentile 4.1
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Complications of Mechanical Ventilation