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Background: The use of a flexible or rigid fiberoptic bronchoscope belongs to the standard repertoire in anesthesiology. Besides a lack of training these procedures may be considerably compromised by endoscopic lens fogging. Several antifogging approaches are commercially available but to date no controlled studies regarding the efficacy of these devices in bronchoscopes exists. The aim of the present study was to compare the efficacy of different commercially available anti-fogging techniques for rigid and flexible bronchoscopes., Materials and Methods: The study was performed at the department of anesthesia in a university children's hospital. An artificial airway model was created to simulate in vivo conditions with respect to airflow, temperature and atmospheric moisture. A test picture was inserted into the artificial airway for assuring a standardized view through the bronchoscopes. Antifogging efficacy of two liquid antifog solutions (Ultrastop and Anti-Fog), two antifog wipes (Lina Clear and Reso Clear) and an induction endoscope preheater system (used after one and two induction preheating phases) was assessed by video taping of the bronchoscope view of the test picture. In addition the administration of continuous oxygen airflow of 2 l min⁻¹ through the suction channel of the flexible bronchoscope was tested as an alternative method to prevent lens fogging. All final pictures were rated by 10 staff anesthesiologists who were blinded to the antifog devices used. To assess the clinical relevance of the results, ratings were classified into a 5 grade rating scale (ranging from no visualization of any structure to excellent endoscopic view allowing safe endotracheal intubation). In addition, the failure rate of each anti-fog technique was calculated., Results: A total of 300 endoscopic test pictures were taken and assessed. Using the flexible bronchoscope, the use of anti-fog solution (failure rate 3 %) and Lina Clear wipes (failure rate 4%) showed the best results. In the rigid bronchoscope group Ultrastop solution (failure rate 5 %) and Lina Clear wipes (failure rate 3.5 %) showed superior results. The two-time use of the endoscope preheater system was effective using flexible (failure rate 6 %) and rigid bronchoscopes (failure rate 10 %). The application of a continuous oxygen flow of 2 l/min failed to provide a clear endoscopic view (failure rate 93.5 %)., Conclusions: All commercially available antifog liquids and wipes showed slightly different reduction of lens fogging. However, other factors such as frequency of usage, the type of endoscope, hygiene properties as well as cost-effectiveness might have a substantial impact on the comparison of all tested anti-fog devices. The use of an endoscope preheater system might be a conceivable alternative method to reduce lens fogging despite the higher initial cost. However, the multiple use of the preheater system cannot be recommended at present as additional handling procedures to ensure an appropriate but safe temperature of the endoscopic tip should be provided by the manufacturer. Application of a continuous oxygen flow was shown not to be effective in preventing lens fogging using a flexible fiberoptic bronchoscope.

Background: Laser surgery in endoscopy has greatly enhanced the surgical armamentarium for treating various laryngeal and hypopharyngeal disorders, but harbours a risk of tissue ignition and inflammation of surgical and anaesthetic instrumentation. However, even if non-inflammable material is used, there is still a residual fire hazard from endogenous tissue that may develop an ignitable aerosol (so-called laser smog) as an effect of laser irradiation. The aim of this study was to investigate how tissue carbonisation and vaporisation contributes to the risk of airway fire., Methods: For the simulation of gas accumulation in the hypopharynx and larynx following the European standard ISO-11990, a cylindrical steel chamber with an open and a closed end has been used to simulate the operative setting. Pork meat chunks with a tissue composition similar to the larynx and hypopharynx such as fat, muscle, cartilage and bone were introduced into this chamber. Ventilation was achieved through jet ventilation with disposable, non-inflammable laser jet catheters. The tissue was then repeatedly exposed to a laser beam in super-pulse mode (pulse rate 250 Hz) with various intensities and exposure lengths at an impact angle of 75 degrees. The laser intensity was varied from 2 to 15 W. The type, duration, intensity and incidence of tissue ignition were recorded and analysed., Results: The degree of tissue ignition correlated with laser intensity. Low laser intensity caused spark formation whereas high intensity resulted in sustained tissue fire. The type of tissue had an impact on ignition intensity thereby showing lower ignition thresholds and higher ignition susceptibility in fat-containing tissue compared to muscle. The most important factor for occurrence of tissue ignition was the chamber oxygen concentration which displayed an inverse correlation with the time until tissue ignition. Oxygen concentrations of 35% led to tissue ignition in 42 s, 40% oxygen in 20 s. Oxygen concentrations higher than 60% resulted in immediate tissue ignition., Conclusions: Despite the use of non-inflammable materials in endoscopic laser surgery of the upper airway and hypopharynx, the risk of tissue ignition remains due to the inflammable laser smog which is easily ignited in an oxygen-rich environment. Hence to minimise this risk, we recommend using oxygen concentrations lower than 40%, low laser intensities (<6 W) and limiting continuous laser activation to periods shorter than 10 s.

Background: Laser surgery within the airway is often performed with the patient under general anaesthesia and with infraglottic jet ventilation via a specially designed catheter which should not be inflammable. We investigated the laser-resistance of a recently introduced jet ventilation catheter (LaserJet) made of polytetrafluoroethylene., Methods: For the simulation of gas accumulation in the hypopharynx a cylindric steel chamber with an open and a closed end was used to simulate the operative setting according to the European standard ISO-11990. In a series of 12 tests the disposable laser jet catheter was attached to the proximal end of the oxygen supply tubing, and the distal end was introduced 10 cm into the steel chamber. The catheter was repeatedly exposed to the beam of a CO(2)-laser device with energies varying from 2-15 W and with an impact angle of 75 degrees. The changes in the catheter were assessed with and without an oxygen flow of 6 l/min. Time of exposure varied from 1 to 10 s. Size and nature of the changes in the catheter were documented., Results: We found damage to the catheter that occurred in the following order: simple (front wall) and double perforation (front and back wall), smoke emission as evidence for pyrolysis, discolouration, deformation and rupture. The extent of damage to the catheter shaft under direct laser beam exposition was dependent on the laser intensity. When there was no oxygen flow, a beam of 2 W needed 40 s to perforate the catheter shaft, while with an oxygen flow of 6 l/min, a laser intensity of 4 W needed 20 s to cause perforation. Rupture of the catheter occurred in less than 10 s with a laser intensity of 8 W or more., Conclusions: We could demonstrate that the LaserJet catheter is not inflammable and also does not sustain fire. However, it is not laser-resistant as to maintaining its texture and shape while under direct exposure to a continuous laser beam, as applied under clinical conditions. Polytetrafluoroethylene deforms and melts at temperatures above 327 degrees C which is usually exceeded by the CO(2)-laser.

This historical survey in two parts analyses the history of inhalative oxygen therapy and its interactions with the history of anaesthesiology. For this purpose, we will start with illustrating "the long way of oxygen" from its first isolation by Carl Wilhelm Scheele (1772) and Joseph Priestley (1774) to its breakthrough for therapeutic application in the 20th century. We will show that the two main factors delaying the successful implementation of a truly rational oxygen therapy were of technical nature: The complicated and costly production of the gas and insufficient means to apply it continuously and with reliable and sufficient dosages to the patients. Both problems could not be satisfactorily solved until 1902. From this year on, however, the "Linde Process" allowed cheap mass-production of oxygen. Simultaneously, various inventions of modern pressure gas technology allowed to solve the application problems. Here, a special significance is to be awarded to pressure reducing valves. These were first introduced into medical technology by Draeger Inc. (Lübeck/Germany) on a significant scale, proving particularly successful in anaesthesia and rescue-devices (e. g. in the "Roth-Draeger Anaesthesia Apparatus" [1902]). Critically discussing earlier research on the history of oxygen therapy, we therefore propose a historical reassessment, accepting the year 1902 as the internationally decisive "turning point" towards the development of modern oxygen therapy.