Pleural Disease Flashcards
Pleura anatomy cartoon
Stomata
Openings between mesothelial cells on the parietal, but not visceral, pleural surface. Each stoma leads to lymphatic channels, allowing a passageway for liquid from the pleural space to the lymphatic system.
The blood supply of the pleura comes from. . .
. . . the bronchial arteries.
Pleural fluid formation and resorption
Formation of fluid is ongoing primarily from the parietal pleural surface, and fluid is resorbed through the stomata into the lymphatic channels of the parietal pleura
Pleural volume vs daily formation/resorption equilibrium
In the average healthy adult, the pleural volume is ~10 mL.
However, the daily formation and resorption of pleural fluid is 15-20 mL. Thus, the pleura is constantly cycling fluid at the rate of 1.5-2x its fluid load per day.
Pleural fluid exchange diagram
Starling Equation
How fluid travels at the parietal vs visceral pleura
At the parietal pleura, fluid is driven by hydrostatic pressure from the pleural capillaries into the pleural space.
At the visceral pleura, fluid is driven by hydrostatic pressure from the visceral pleural capillaries somewhat into the pleural space, but primarily into pulmonary venous circulation.
Remember: At the parietal pleura, systemic arterial blood (~80-120 mmHg) drains into the systemic venous circulation (~40-50 mmHg). At the visceral pleura, systemic arterial blood drains into the pulmonary venous circulation (~8-10 mmHg).
Thus, most of the fluid in the pleura comes from the parietal pleura, because it has a greater driving pressure forcing fluid into the pleural space (about 9 cm H2O).
Respiratory pleural pump
The movement of respiration is thought to help drive pleural fluid through stomata into lymphatic ducts, which are then sealed off with one-way valves.
The essential problem of pleural effusion
A tilted equilibrium: The rate of pleural fluid accumulation exceeds the homeostatic rate of pleural fluid resorption.
This may be the result of changes in relative permeability (K and σ) or changes in the relative pressures (P and π).
Most common diseases that cause pleural effusion through a change in K and σ
- Inflammation
- Neoplasty
In both of these cases, the increased permeability is termed an exudate due to its high protein content
Most common diseases that cause pleural effusion through a change in P and π
- Hypertension
- Congestive heart failure
- Hypoproteinemia (may be secondary to cirrhosis)
In these cases, the fluid is protein-poor, and is thus termed a transudate.
Pleural effusion secondary to lymphatic disease
Blockage of lymphatic ducts that drain the pleura can result in a fluid backup, increasing lymphatic pressure and thus leaving fluid stuck in the pleura.
As a rule of thumb, exudation implies ___ where as transudation implies ___.
As a rule of thumb, exudation implies primary pathology of the pleura where as transudation implies secondary pathology of the pleura to some other disease process.
Why is pulmonary hypertension such a big contributer to pleural effusions?
Because it makes the visceral pleura start to participate in pleural fluid accumulation!
Normally the visceral pleura contributes very little fluid to the pleura due to its drainage into low-pressure pulmonary circulation. However, if pulmonary pressure increases, excess fluid will readily drain into the relatively low pressure pleural space.
Parapneumonic effusion
A pleural effusion caused by a pneumonia that extends to the pleural space. Histamine, prostaglandins, cytokines, and other mediators spill over and cause leakiness in the vessels leading to the pleura as well as the lung parenchyma, resulting in an effusion.
Empyema thoracis
Pus in the pleural space
Pleural effusion second to pancreatitis
Pancreatitis can lead to ascites in the abdomen. This fluid can then travel through the lymphatics draining the diaphragm and end up in the pleura, through a circuitous and unintuitive route.
Nevertheless, this is not uncommonly observed. So be aware, if your patient has pancreatitis leading to acsites, they may be at risk of pleural effusion.
Pleuritic chest pain
Sharp pain aggravated by respiration and sometimes hard to localize
On physical exam, pleural fluid is ___ to percussion, pulmonary fluid is ___ to percussion, and pneumothorax is ___ to percussion.
On physical exam, pleural fluid is dull to percussion, pulmonary fluid is dull to percussion, and pneumothorax is hyperresonant to percussion.
Major finding of inflammatory pleural effusion on physical exam
Pleural rub on auscultation
Loculations
Fibrous bands of tissue that may form in long-standing pleural effusions.
These bands of tissue may straddle the pleural fluid in, making it appear as though it is not quite following gravity downward the way one may expect. Ultrasonography is extremely helpful in these cases.
If loculation has occurred, these fibrous bands must be removed for adequate drainage of the fluid.
___ allows determination of the cellular and chemical characteristics of pleural effusion fluid
Thoracentesis allows determination of the cellular and chemical characteristics of pleural effusion fluid.
Pleurodesis
In some cases with recurrent large effusions causing dyspnea, the fluid is initially drained with a tube passed into the pleural space, and an irritating agent (e.g., talc or a tetracycline derivative) is instilled via the tube into the pleural space to induce inflammation and cause the visceral and parietal pleural surfaces to become adherent (fibrosis).
Common causes of pneumothorax
- Trauma
- Iatrogenesis
- Tear of a cyst/bleb/bulla bordering the visceral pleura
Most common cause of pneumothorax in AIDS patients
Pneumocystis jiroveci
Presumably because of necrosis or cyst formation adjacent to the visceral pleura
Tension pneumothorax is a not uncommon complication of ____.
Tension pneumothorax is a not uncommon complication of mechanical ventilation.
Tension pneumothorax
Pneumothorax with pressure greater than 1 atm
This tension within the pleural space is believed to occur as a result of a “one-way valve” mechanism by which air is free to enter the pleural space during inspiration, but the site of entry is closed during expiration
Sufficiently high pressures will shift mediastinal contents to the other side.
In tension pneumothorax, venous return to the heart will ___.
In tension pneumothorax, venous return to the heart will decrease.
For most cases of pneumothorax, after the site of entry into the pleural space is closed, the air is ___.
For most cases of pneumothorax, after the site of entry into the pleural space is closed, the air is spontaneously resorbed
However, it can be removed faster through medical intervention if necessary (ex, catheterization)
If ___ is administered to the patient with a pneumothorax, the process of resorption can be hastened
If pure O2 is administered to the patient with a pneumothorax, the process of resorption can be hastened
In arterial blood, most of the nitrogen is replaced by O2. As a result, Pn2 in the capillary blood surrounding the pneumothorax becomes quite low, and the gradient for resorption of nitrogen from the pleural space has been increased considerably
Pneumothorax is ___thorax
Pneumothorax is Nitrothorax
It’s! All! Nitrogen!
Hydropneumothorax
When fluid and air are both in the pleural space.
Fluid no longer appears as a meniscus tracking up along the lateral chest wall. Rather, the fluid falls to the most dependent part of the pleural space and appears as a liquid density with a perfectly horizontal upper border
___ because of a tension pneumothorax is an emergency, and a needle, catheter, or tube must be inserted immediately to relieve the pressure.
Hemodynamic compromise because of a tension pneumothorax is an emergency, and a needle, catheter, or tube must be inserted immediately to relieve the pressure.
How do chest wall volume, lung volume, and airway resistance change in pneumothorax?
Chest wall volume up
Lung volume down
Airway resistance up
Normal total protein and LDH for pleural fluid
45% of systemic concentrations or less
Nephrotic syndrome
Characterized by high levels of protein excretion in the urine. As a result, patients with nephrotic syndrome often have hypoalbuminemia and edema, possibly including pleural effusion transudate.
Pancreatitis produces a pleural ___.
Pancreatitis produces a pleural exudate.
When should you tap a pleural effusion?
Effusions should generally be tapped early in the clinical course, especially if etiology is uncertain
Causes of Pleural Effusion - Transudates
Causes of Pleural Effusion - Exudates
Light’s Criteria
A pleural exudate is present if any of the following criteria are met:
- Pleural fluid / serum protein >0.5
- Pleural fluid / serum LDH >0.6
- Pleural fluid LDH >2/3 upper limit of normal serum value
