Considerable attention has been paid to the determination of lung microvascular permeability in critically ill patients. Despite this, demonstrating the presence of increased capillary permeability remains a challenge. Several methods have been introduced to measure pulmonary capillary permeability in abnormal states. Most methods rely on the use of radioactive isotopes as tracers. Indicator-dilution methods introduce specifically labelled components, typically 3H2O, 14C-urea, 125I-albumin and 51Cr labeled red blood cells, into the circulation. Buy Asthma Inhalers Online
The time course of these tracers in the blood is then followed in a single pass, requiring rapid and precisely timed arterial blood sampling. Based on partitioning models for the variously labelled components, the permeable surface area for urea and the ex-travascular volume of lung water (EVLW) can be determined. It is difficult, however, to establish clinically the soundness of these determinations. This is especially true for the critical care population, where vascular tone and tissue permeability characteristics vary considerably. In addition, measuring EVLW by indicator-dilution methods is a costly and tedious bedside procedure. It has a reliability of less than 70% for the best case . External pulmonary gamma counting has the advantage of providing a more direct measure of tracer infiltration into the lung . The technique is, however, cumbersome and thus ill-suited to routine patient monitoring in a critical care environment.