33 Acute Respiratory Distress Syndrome Flashcards
1
Q
ARDS
- The pathophysiology involves…
- Complications of patient management
- The injury of the lung parenchyma is associated with…
- The pathophysiologic process leads to…
- The pathophysiologic process appears to have…
A
- The pathophysiology involves…
- An inflammatory process within the lung parenchyma leading to alveolar capillary injury
- Complications of patient management
- Include ventilator management and infection
- Can extend the alveolar capillary injury
- The injury of the lung parenchyma is associated with…
- Permeability lung edema
- Loss of normal surfactant in the airspace of the lung
- Capillary thrombi formation
- The pathophysiologic process leads to…
- Marked hypoxemia secondary to shunt physiology
- Loss of lung compliance with restrictive physiology
- The development of pulmonary hypertension
- The pathophysiologic process appears to have…
- A common clinical and pathologic progression regardless of the inciting predisposing condition
2
Q
ARDS time course
- ARDS has a recognized time course characterized by…
- The patient transitions across these pathophysiologic states over…
A
- ARDS has a recognized time course characterized by two distinct clinical phases
- The exudative phase
- The proliferative phase
- The patient transitions across these pathophysiologic states over a typical 2-week hospitalization, although the actual timing is highly variable from patient to patient
3
Q
ARDS time course:
Exudative phase
- General
- Characterized by…
- This stage typically lasts…
- This period clinically is characterized by…
- Pathologically this stage corresponds to the term…
A
- The early phase of ARDS
- Characterized by…
- Epithelial injury consisting of cellular swelling
- Denudation of type I epithelial cells
- Hyaline membrane formation
- Fibrin deposition
- Interstitial neutrophilic infiltrates
- This stage typically lasts over a 3-7 day period, but the duration is actually highly variable
- This period clinically is characterized by…
- Diffuse bilateral alveolar pulmonary infiltrates
- Marked oxygenation difficulty due to the associated intrapulmonary shunt
- Pathologically this stage corresponds to the term diffuse alveolar damage (DAD) which is characteristic of ARDS
4
Q
ARDS time course:
Proliferative phase
- General
- Characterized by…
- Characteristic changes include…
- Time interval
- This period clinically is characterized by…
A
- The second or “proliferative” phase
- Characterized by organization of the alveolar and interstitial infiltrates
- Characteristic changes include…
- Fibroblast proliferation
- Type II cell hyperplasia with lymphocyte infiltration
- At a variable time interval following the exudative stage, the patient enters this fibrotic phase characterized by extensive collagen deposition
- This period clinically is characterized by…
- Diffuse interstitial pulmonary infiltrates
- Ventilator dependence secondary to high ventilatory impedance
- Elevated deadspace ventilation
5
Q
Pathophysiology of ARDS
- Shunt physiology
- Pulmonary edema is recognized to occur in two forms
- Hydrostatic pulmonary edema
- ARDS
A
-
Shunt physiology
- The hypoxemia of ARDS occurs from shunt physiology resulting from the alveolar edema due to abnormal fluid movement at the alveolar-capillary membrane
- Pulmonary edema is recognized to occur in two forms
- Hydrostatic pulmonary edema
- Results from an imbalance of the forces normally responsible for fluid flux at the alveolar capillary membrane, specifically an elevation in left ventricular end-diastolic pressure and secondary elevation of pulmonary microvascular hydrostatic pressure
- ARDS
- A form of non-cardiogenic pulmonary edema or permeability edema that occurs in the absence of elevated pulmonary microvascular hydrostatic pressures
- Hydrostatic pulmonary edema
6
Q
Pathophysiology of ARDS:
The inflammation and repair process in the injured alveolus
A
- Both neutrophils and macrophages
- Participate in an active inflammatory process in the alveolar space
- Lead to loss of alveolar Type 1 cell function and disruption of surfactant
- Redundant inflammatory signaling pathways
- Recognized from both epithelial and endothelial injury
- Have complicated the development of effective drug therapy specific for patients with ARDS
7
Q
Signs and symptoms
- The clinical signs and symptoms in the patient with acute respiratory failure and ARDS include…
- Physical findings are nonspecific
- The clinical presentation
- The parenchymal lung disease results in…
- Early findings of progressive mechanical respiratory failure include…
- More progressive signs of abnormal respiratory muscle activation that follow these early signs
A
- The clinical signs and symptoms in the patient with acute respiratory failure and ARDS include…
- Dyspnea with acute hypoxemia
- Possibly hypercapnia
- Physical findings are nonspecific
- Tachycardia
- Tachypnea
- Elevation of the blood pressure
- The clinical presentation
- Will vary depending on the underlying condition producing the syndrome
- The parenchymal lung disease results in…
- An augmentation of the mechanical workload of the respiratory muscles
- Early findings of progressive mechanical respiratory failure include…
- Tachycardia
- Tachypnea
- A reduction in the resting tidal volume
- More progressive signs of abnormal respiratory muscle activation that follow these early signs
- Accessory muscle use
- Asynchronous respiratory muscle activity
- Frank abdominal paradox
8
Q
Distinguishing between hydrostatic (CHF) and permeability (ARDS) edema
- Careful history and detailed physical examination with attention to…
- Non-invasive techniques such as echocardiography can demonstrate evidence for…
- Radiographic findings reported to favor a cardiac etiology for respiratory failure include…
- Despite the careful use of history, physical exam, and radiographic studies, clinicians often struggle to distinguish…
- In a small fraction of patients,…
A
- Careful history and detailed physical examination with attention to…
- The presence of abnormal cardiac auscultatory findings including extra heart sounds and murmurs
- Review of body weight and fluid balance changes as well as electrocardiographic findings can support a cardiac etiology
- Non-invasive techniques such as echocardiography can demonstrate evidence for…
- Cardiac dysfunction including wall motion abnormalities or ventricular dilatation
- Radiographic findings reported to favor a cardiac etiology for respiratory failure include…
- Cephalization of venous blood flow in an erect patient
- A homogeneous, principally basal and perihilar edema distribution
- A normal or enlarged vascular pedicle
- Despite the careful use of history, physical exam, and radiographic studies, clinicians often struggle to distinguish…
- Ccardiogenic from non-cardiogenic pulmonary edema in certain critically ill patients
- In a small fraction of patients,…
- A right heart catheterization is required as a diagnostic tool to distinguish these two forms of pulmonary edema
9
Q
AECC definition:
Four recognized clinical features
A
- An acute onset of respiratory symptoms
- Bilateral airspace pulmonary infiltrates (reflecting alveolar edema) on a frontal chest radiograph
- The absence of clinical evidence for elevated pulmonary microvascular hydrostatic pressures (non-cardiogenic edema) by clinical criteria or a measured pulmonary artery occlusion pressure (PAOP ) < 18 mm Hg
- The presence of significant hypoxemia as measured by a reduction in the arterial blood gas relative to the inspired oxygen concentration or the PaO2/FiO2 (P/F) ratio
10
Q
AECC definition
- Variable severity of the syndrome leads to classification of ARDS patients into two overlapping groups
- ARDS
- The AECC definition of ARDS
- Patients that meet all the AECC criteria for ARDS, yet lack a specific predisposing condition, demonstrate…
A
- Variable severity of the syndrome leads to classification of ARDS patients into two overlapping groups
- Acute lung injury (ALI)
- A milder form of the syndrome with a P/F ratio < 300
- ARDS
- The more severe form of the disorder with a P/F ratio < 200.
- Acute lung injury (ALI)
- ARDS
- The prototype lung disease characterized by non-cardiogenic, alveolar (air-space) edema
- The AECC definition of ARDS
- Is not specific and can describe a broad range of clinical conditions
- Each component of the definition is recognized to lack precision, which creates a heterogeneous patient population particularly from the perspective of clinical research studies
- Patients that meet all the AECC criteria for ARDS, yet lack a specific predisposing condition, demonstrate…
- The pathologic equivalent of ARDS called diffuse alveolar damage at lung biopsy in only ~ 50% of the cases
- These data illustrate the non-specific nature of the clinical parameters used to identify the ARDS syndrome
11
Q
Limitations to the AECC definition
- The AECC definition does not specify…
- Investigators have demonstrated that variable PEEP and FiO2 settings, in the same patient, can produce…
- The distinction between ALI and ARDS
- The AECC radiographic criteria for ARDS
A
- The AECC definition does not specify…
- The inspired oxygen concentration (FiO2)
- The positive end-expiratory pressure (PEEP) level required to obtain the PaO2/FiO2 ratio
- Investigators have demonstrated that variable PEEP and FiO2 settings, in the same patient, can produce…
- Different PaO2/FiO2 ratios
- This could change a patient’s disease classification from normal to ALI to ARDS
- The distinction between ALI and ARDS
- Becomes dependent on the ventilator settings rather than the patient characteristics
- The distinction by gas exchange criteria does not appear to define an increased severity of disease or mortality risk
- The AECC radiographic criteria for ARDS
- Describe bilateral pulmonary infiltrates
- Although very simple in description, radiologists do not always agree if a patient has bilateral pulmonary infiltrates
- Further, bilateral pulmonary infiltrates can be homogeneously distributed (= in distribution) or heterogeneously distributed
- This distribution may actually reflect different phenotypes of the ARDS syndrome
12
Q
Limitations to the AECC definition
- The AECC definition also characterizes ARDS…
- PAOP in the patients that were thought to have ARDS and received a pulmonary artery catheter
- To address the existing limitations in the AECC ARDS definition, ARDS investigators have modified the definition to a revised of parameters called…
A
- The AECC definition also characterizes ARDS…
- By the absence of hydrostatic edema
- Based either upon clinical criteria or alternatively by measurement of the pulmonary capillary occlusion pressure (PAOP) as < 18 mm Hg
- PAOP in the patients that were thought to have ARDS and received a pulmonary artery catheter
- 18% of patients had a PAOP > 18 mm Hg
- To address the existing limitations in the AECC ARDS definition, ARDS investigators have modified the definition to a revised of parameters called…
- The Berlin criteria for ARDS
13
Q
Berlin definition
- Timing
- Chest imaging
- Origin of edema
- Oxygenation
- Mild
- Moderate
- Severe
- Although the Berlin criteria reflect an improvement in the description of the specific parameters of ARDS, they still represent…
A
- Timing
- Onset within one week of a known clinical insult or worsening respiratory symptoms
- Chest imaging
- Bilateral opacities not fully explained by effusions, lobar/lung collapse, or nodules
- Origin of edema
- Respiratory failure not fully explained by cardiac failure or fluid overload. Need an objective assessment (eg. echocardiography) to exclude hydrostatic edema if a risk factor is not present
- Oxygenation
- Mild
- 200 < P/F ratio < 300 with PEEP or CPAP > 5 cm H20
- Moderate
- 100 < P/F ratio < 200 with PEEP > 5 cm H20
- Severe
- P/F ratio < 100 with PEEP > 5 cm H20
- Mild
- Although the Berlin criteria reflect an improvement in the description of the specific parameters of ARDS, they still represent…
- Non-specific findings
- Their specificity for identifying the pathologic finding of diffuse alveolar damage remains to be determined
14
Q
Risk factors and predisposing conditions
- Predisposing conditions
- Include…
- Develpoment of ARDS
- Modifying factors
- Include…
- Development of ARDS
A
- Predisposing conditions
- Include…
- Sepsis
- Pneumonia
- Aspiration pneumonia
- Trauma
- Emergency surgery
- Only ~4% of patients with a given predisposing condition develop the ARDS syndrome
- Include…
- Modifying factors
- Other factors, both genetic and clinical
- Hypoalbuminemia
- Treatment with chemotherapy
- Alcohol use (one of the strongest modifying risk factors)
- Must be present to increase the patient’s risk of developing ARDS
- Other factors, both genetic and clinical
15
Q
ARDS outcome
- Physiologic and biochemical variables examined in the ARDS patient population to predict patient outcome
- Better severity adjusted outcome
- Worse severity adjusted outcome
- ARDS is a disorder of…
- The transpulmonary gradient (TPG)
- The development of an elevated TPG in patients with ARDS is associated with…
A
- Physiologic and biochemical variables examined in the ARDS patient population to predict patient outcome
- Traditionally recognized as a disease of severe hypoxemia
- However, the severity of the hypoxemia is not predictive of outcome in the early phases of ARDS
- In contrast, a marker of ventilation efficiency, the physiologic deadspace, is an accurate predictive marker
- Traditionally recognized as a disease of severe hypoxemia
- Better severity adjusted outcome
- Trauma as the inciting agent as compared to patients with sepsis as the predisposing condition
- Worse severity adjusted outcome
- African-American and Hispanic patients
- ARDS is a disorder of…
- The alveolus with edema and hyaline membrane formation
- A pulmonary vascular disease
- The transpulmonary gradient (TPG)
- A measure of the pulmonary vascular resistance
- The development of an elevated TPG in patients with ARDS is associated with…
- A significant increase in mortality
- Illustrates the importance of ARDS as both an epithelial (alveolus) and endothelial (pulmonary vascular) disorder