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The flexible fiberoptic bronchoscope is used increasingly often as a multipurpose instrument in critical care medicine. In poor risk patients who need continuous mechanical ventilation, rigid open tube bronchoscopy is a problem. With the flexible fiberoptic bronchoscope, however, diagnostic and therapeutic procedures can be carried out without interruption of ongoing mechanical ventilation. This procedure offers the possibility of bronchoscopy with reduced risk in debilitated patients. However, in these critically ill patients, the cardiopulmonary system is functioning at the borderline of its ability. Therefore, even the small changes in ventilation pattern caused by flexible fiberoptic bronchoscopy (FFB) may in some cases cause dangerous cardiopulmonary distress. For example, changes of intrabronchial pressure, tidal volume, PaO2, PaCO2 and cardiac output may be caused by the procedure. Further, it is of great importance to restrict suction through the instrument to short periods to avoid dangerous alterations in the ventilation perfusion relationship. Since serious complications may occur, it is mandatory that the bronchoscopist be aware of the potential pathophysiologic effects of FFB during mechanical ventilation of critically ill patients.

In some women the inner diameter of the cricoid ring does not permit passage of a standard-size (7 mm, internal diameter [ID]) tracheal tube or a standard-size rigid endoscope through the larynx without mucosal damage. The small distance between the cricoarytenoid joints in many women and some men is the basis for of the clinical observation that women, especially, receive pressure necroses at the medial sides of the arytenoid cartilages attributable to tracheal intubation with standard tubes. The large difference in almost all sizes and shapes of the cricoid cartilage and trachea makes it impossible to standardize the rigid stents used in these organs. When transplantation to the larynx is planned, this variation of the anatomy must be considered.

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Isotope labelled microspheres were used to study the capillary blood perfusion of the rabbit tracheal mucosa. Under resting conditions the perfusion was about 0.3 ml/min - g (i.e. about 60% of the relative cerebral blood flow). Irritation of the tracheal mucosa by an endotracheal tube caused a steep rise in blood flow, tenfold or more. This was probably due to relaxation of the arterioles caused by a release of histamine-like substances. When an endotracheal tube is equipped with a small cuff (small resting diameter, low residual volume), the part of the mucosa in contact with the cuff, i.e. the mucosa covering the surface and edges of the cartilages, will be ischaemic at a cuff to tracheal wall pressure (C-T pressure) of greater than 30 millimeters of mercury. This abrupt ischaemia threshold contributes to the risk of deep mucosal damage with subsequent tracheal scarring, possibly proceeding to stenosis. Our present studies indicate that the ideal large cuff, with properties resembling those of an air cushion, will allow the major part of the arterial pressure to be propagated as far down as the capillaries. Under these conditions the cuff would permit some of the capillary blood perfusion of the tracheal mucosa covering the cartilages also at C-T pressures exceeding 30 mmHg. Although this investigation supports the concept that the ideal thin-walled large cuff interferes much less with the mucosal blood perfusion than the small cuff, we recommend that the cuff pressure be monitored and kept below 20 mmHg.