Cuff pressure and microvascular occlusion in the tracheal mucosa. An intravital microscopic study in the rabbit

A method is described for the intravital microscopic observations of rabbit tracheal mucosa microcirculation during compression with a thin, transparent high volume cuff. The cuff pressure (CP) required to cause complete ischemia in the mucosa over the cartilages was measured and a correlation was found to the mean arterial blood pressure (MAP). Ischemia was not observed below CP-MAP ratios of 0.40 for untreated animals or below 0.44 for animals where the MAP had been elevated by adrenalin. However, marked reduction of the microvascular blood flow was present at lower CP-MAP ratios, 0.2-0.3, which at a MAP of 75 mmHg corresponds to cuff pressures of 15-20 mmHg. It is therefore advocated that endotracheal cuff pressures are kept below these values to avoid ischemic tissue injury.

Pressure-induced ischemia. I. An experimental model for intravital microscopic studies in hamster cheek pouch

A model to study pressure-induced ischemia by intravital microscopy is presented. A hamster cheek pouch is prepared to get a single layer of epithelium, together with vessels and connective tissue. Pressure, which can be varied, is transmitted to the tissue by a pressure chamber with a rubber membrane. Microcirculatory reactions may be studied while the pressure is applied, when the pressure is released and as the tissue is regaining circulation. The local environment is controlled by irrigating the test tissue with a solution approximating the composition of interstitial fluid. Local oxygen and carbon dioxide tensions are controlled. There is a marked difference in restoration of blood flow to the tissue after 2- and 4-hour ischemia. After 2-hour ischemia the tissue regained circulation rapidly. Microbleedings developed during the postpressure observation time. After 4-hour ischemia, on the other hand, the tissue regained circulation slowly and only in one third of the microvessels. Extensive white blood cells sticking to the vessel walls were seen indicating endothelial damage. In the 4-hour experiments there were very few microbleedings compared to the 2-hour experiments.