4 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
7 Ventilator-Induced Lung Injury Atelectotrauma Vs Volutrauma Atelectrauma:Repetitive alveolar collapse and reopening of the under-recruited alveoliVolutrauma:Over-distension of normally aerated alveoli due to excessive volume deliveryDreyfuss: J Appl Physiol 19927
8 Spectrum of Regional Opening Pressures (Supine Position) InflatedSuperimposedPressureConsolidationSmall AirwayCollapse10-20 cmH2OAlveolar Collapse(Reabsorption)20-60 cmH2O=Lung Units at Risk for TidalOpening & Closure(from Gattinoni)
9 How Much Collapse Is Dangerous Depends on the Plateau 2060100Pressure [cmH2O]40Total Lung Capacity [%]R = 22%R = 81%R = 93%R = 0%R = 59%Some potentially recruitable units open only at high pressureMore ExtensiveCollapse ButLower PPLATLess ExtensiveGreater PPLATR = 100%From Pelosi et al AJRCCM 2001
10 Effect of lung expansion on pulmonary vasculature 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.
11 VALI vs VILI Ventilator-associated lung injury (VALI) Acute lung injury that resembles ARDS in patients receiving MVVALI may be associated with pre-existing lung pathologyVALI is associated only with MVVentilator induced lung injury (VILI)Acute lung injury directly induced by MV in animal models
12 Histopathology of VILI Belperio et al, J Clin Invest Dec 2002; 110(11):
13 Mechanisms of Airspace Injury Airway Trauma“Stretch”“Shear”
17 The PEEP Effect NEJM 2006;354:1839-1841 taken at the end of inspiration.A=0, B=15, C=15 x3, D= 15*5 F=0*1, G = 0*3, H =0*5NEJM 2006;354:
18 Avoiding Atelectotrauma :How much PEEP is enough Avoiding Atelectotrauma :How much PEEP is enough? ARDSnet protocol: PEEP - FiO2 CombinationsGOAL: PaO mm Hg or SpO %Use these FiO2/PEEP combinations to achieve oxygenation goal.FIO220.127.116.11.18.104.22.168.0PEEP58101214161820-24New Eng J Med. 2000;342(18)
27 Baro-trauma Etiology :Directly related to airway pressures/PEEP Incidence4% - 15%Highest in ARDSIncidence now decreased secondary to lung protective ventilation
28 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.
29 Barotrauma-Complications PneumothoraxInterstitial emphysemaPneumomediastinum-leads to PTX in 42% of patients in one studyPneumopericardiumSubcutaneous emphysemaPneumoperitoneum
34 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.
35 Oxygen Toxicity Absorptive atelectasis Accentuation of hypercapnia Chronic respiratory failure: PCO2 with PO2Damage to airwaysBronchopulmonary dysplasiaDiffuse alveolar damage
37 Infectious complications of Mechanical ventilation
38 Maxillary Sinus and Middle Ear Effusion Maxillary effusion20% in patients intubated for > 7 days.47% when the gastric tube is placed nasally95%Secondarily infected maxillary effusion (45-71% of effusions)Middle ear effusion (29%) with 22% of them become infectedHearing impairment that may contribute to the confusion and delirium in elderly population
39 VAP: Definitions VAP – ventilator associated pneumonia >48 hours on ventCombination of:CXR changesSputum changesFever, ↑ WBCpositive sputum cultureOccurs secondary to micro-aspiration of upper airway secretions
41 Risk Factors for VAP No 1 risk factor is endotracheal intubation Factors that enhance colonization of the oropharynx &/or stomach:Poor oral hygieneConditions favoring aspiration into the respiratory tract or reflux from GI tract:Supine positionNGT placementRe-Intubation and self-extubationSurgery of head/neck/thorax/upper abdomenGERDComa/ depressed Glascow coma scale
42 Significance of VAPMortality 20-70%(Leading cause of mortality from nosocomial infections in hospitals)Increases mechanical ventilation daysIncreases ICU stay by 4.3 daysIncreases hospital LOS by 4-9 daysIncreases cost -Excess costs of approximately 11,000 -$40,000/patient
43 VAP prevention :VAP Bundle Elevation of the head of the bed 30-45oUse 15-30o for neonates and small infants, otherwise 30-45oDaily sedation vacations (minimize duration of intubationDaily assessment of readiness to extubatePeptic ulcer disease (PUD) prophylaxisOral care protocol (chorhexidine)DVT prophylaxis option
44 HOB 30-45o decrease risk of aspiration 45o head-up tilt is the goal in all patients unless contraindicatedNo benefit of semi-recumbency ~30o over standard care ~10oSupine position is harmful
45 HOB Elevation Leads to Significant reduction in VAP Studies have also shown a dramatic decrease in VAP when a simple HOB elevation is done.These data are from a study by Drakulovic et al in 86 intubated and mechically ventilated patients in a medical and respiratory ICU.Subjects were randomly assigned to either 0 degrees or 45 degree HOB elevation.VAP was detected in 2 of 39 patients (5%) in the HOB elevation to 45 degree group and 11 of 47 patients (23%) of the 0 degree HOB elevation.The risk reduction was 78% for patients placed in the HOB elevation to 45 degrees.Dravulovic et al. Lancet 1999;354:
47 HandwashingStrict handwashing before and after handling patient or patient’s equipment or supplies
48 Does the VAP bundle work in real life NHSN 50th Percentile 4.1
49 Complications of Mechanical Ventilation Complications related to IntubationMechanical complications related to presence of ETTVentilator induced lung injuryComplications related to OxygenInfectious complications of mechanical ventilation
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