Pulmonary capillaries

Ethylene is slightly more potent as an anesthetic than nitrous oxide, and the smell of ethylene causes choking. Diffusion through the alveolar membrane is sufficiendy rapid for equilibrium to be estabUshed between the alveolar and the pulmonary capillary blood with a single exposure. Ethylene is held both ia cells and ia plasma ia simple physical solution. The Hpoid stroma of the red blood cells absorb ethylene, but it does not combine with hemoglobin. The concentration ia the blood is 1.4 mg/mL when ethylene is used by itself for anesthesia. However, ia the 1990s it is not used as an anesthetic agent. 

Crystalloid/colloid to achieve a pulmonary capillary wedge pressure (PCWP) between 15 and 18 mmHg... 

Use fluids and/or vasopressors to elevate MAP if necessary ° Maintain euvolemia (pulmonary capillary wedge pressure between 10 and 14 mmHg)... 

BP, blood pressure CO, cardiac output HR, heart rate PCWP, pulmonary capillary wedge pressure SVR, systemic vascular resistance T, increase 4, decrease 0, no or little change. 

Monitor changes in hemodynamic variables if available. Cardiac index should increase, with a goal to maintain it above 2.2 L/minute per square meter. Pulmonary capillary wedge pressure should decrease in volume overloaded patients to a goal of less than 18 mm Hg. 

Pulmonary hypertension develops late in the course of COPD, usually after the development of severe hypoxemia. It is the most common cardiovascular complication of COPD and can result in cor pulmonale, or right-sided heart failure. Hypoxemia plays the primary role in the development of pulmonary hypertension by causing vasoconstriction of the pulmonary arteries and by promoting vessel wall remodeling. Destruction of the pulmonary capillary bed by emphysema further contributes by increasing the pressure required to perfuse the pulmonary vascular bed. Cor pulmonale is associated with venous stasis and thrombosis that may result in pulmonary embolism. Another important systemic effect is the progressive loss of skeletal muscle mass, which contributes to exercise limitations and declining health status. 

The clinical scenario and the severity of the volume abnormality dictate monitoring parameters during fluid replacement therapy. These may include a subjective sense of thirst, mental status, skin turgor, orthostatic vital signs, pulse rate, weight changes, blood chemistries, fluid input and output, central venous pressure, pulmonary capillary wedge pressure, and cardiac output. Fluid replacement requires particular caution in patient populations at risk of fluid overload, such as those with renal failure, cardiac failure, hepatic failure, or the elderly. Other complications of IV fluid therapy include infiltration, infection, phlebitis, thrombophlebitis, and extravasation. 

PCWP Pulmonary capillary wedge pressure qid Four times daily (quater in die)... 

Preload The stretched condition of the heart muscle at the end of diastole just before contraction volume in the left ventricle at the end of diastole estimated by the pulmonary artery occlusion pressure (also known as the pulmonary artery wedge pressure or pulmonary capillary wedge pressure). 

Taylor AE, KA Gaar Jr. (1970). Estimation of equivalent pore radii of pulmonary capillary and alveolar membranes. Am J Physiol 218 1133-1140. 

Pulmonary surfactant decreases surface tension of alveolar fluid. Reduced surface tension leads to a decrease in the collapsing pressure of the alveoli, an increase in pulmonary compliance (less elastic recoil), and a decrease in the work required to inflate the lungs with each breath. Also, pulmonary surfactant promotes the stability of the alveoli. Because the surface tension is reduced, the tendency for small alveoli to empty into larger ones is decreased (see Figure 17.2, panel b). Finally, surfactant inhibits the transudation cf fluid out of the pulmonary capillaries into the alveoli. Excessive surface tension would tend to reduce the hydrostatic pressure in the tissue outside the capillaries. As a result, capillary filtration would be promoted. The movement of water out of the capillaries may result in interstitial edema formation and excess fluid in the alveoli. 

The diffusion of oxygen and carbon dioxide also depends on their partial pressure gradients. Oxygen diffuses from an area of high partial pressure in the alveoli to an area of low partial pressure in the pulmonary capillary blood. Conversely, carbon dioxide diffuses down its partial pressure gradient from the pulmonary capillary blood into the alveoli. 

Rate of removal of oxygen by the pulmonary capillary blood... 

Parenchymal changes affect the gas-exchanging units of the lungs (alveoli and pulmonary capillaries). Smoking-related disease most commonly results in centrilobular emphysema that primarily affects respiratory bronchioles. Panlobular emphysema is seen in AAT deficiency and extends to the alveolar ducts and sacs. 

Symptoms Symptoms include acute onset of fever, chest tightness, cough, dyspnea, nausea, and arthralgias which occur four to eight hours after inhalational exposure. Airway necrosis and pulmonary capillary leak resulting in pulmonary edema would likely occur within eighteen to twenty-four hours, followed by severe respiratory distress and death from hypoxemia in thirty-six to seventy-two hours. 

Figure 5.14 Chloride shift in a red cell (a) in a tissue capillary (b) in a pulmonary capillary...

ACE is bound to the luminal surface of vascular endothelium occurring in particularly high concentration in the pulmonary capillary bed. The product of the ACE reaction, angiotensin II, is a potent vasoconstrictor by its action on vascular smooth muscle cells allowing calcium influx and opposing the vasodilator effect of... 

C02 + H20 <-> H2CO3 <-> H+ + HC03 The reverse reaction occurs in the pulmonary capillaries. 

A higher concentration of red blood cells, total protein and leukotriene B4 has been measured in the lungs of athletes during severe exercise (i.e. high levels of pulmonary capillary pressures) compared to controls, indicating an altered integrity of the air-to-blood barrier [155]. In addition, an increased absorption rate and plasma Cmax of inhaled terbutaline during submaximal... 

West JB (2006) Vulnerability of pulmonary capillaries during severe exercise. Br J Sports Med 40 821. 

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