William N. Bernhard

Physical Characteristics of and Rates of Nitrous Oxide Diffusion into Tracheal Tube Cuffs

Physical characteristics and time-related volume changes in air-inflated tracheal tube cuffs exposed to nitrous oxide were measured in an environmental chamber. Cuff wall diameter, thickness, residual volume, and length were also measured. Gas volumes in most air-inflated tracheal tube cuffs increased 1.7 to 7 ml within 30 min of exposure to pure nitrous oxide. Diffusion rates into most cuffs varied inversely with cuff thickness and directly with the partial pressure of nitrous oxide. There were significant differences in diffusion rates among cuffs of the same composition with different densities or porosities as well as among cuffs of different compositions. Cuff diameters ranged from 13.8 to 32 mm; thicknesses from .033 to .55 mm; residual volumes from .22 to 19.4 ml; lengths from 23.1 to 49.1 mm. Intracuff volume and pressure increase related to gas diffusion into air-inflated cuffs should be periodically adjusted or pressure automatically controlled during nitrous oxide anesthesia. Large-diameter, thin-walled cuffs are recommended.

Cuffed tracheal tubes--physical and behavioral characteristics.

This study compares physical and behavorial characteristics of currently used cuffed tracheal tubes. Variability in physical and behavioral characteristics between size 8 tracheal tubes and cuffs exists: radius of tube curvature varies from 12.1 to 15.8 cm, bevel angle 39 to 56°, bevel direction 73 to 107°, distance from proximal end of bevel to cuff 15.4 to 24.4 mm, internal tube diameter 7.5 to 8.8 mm, wall thickness 1.14 to 2.37 mm, force to collapse 1020 to 3103 g, angle to kink 52 to 96°, and indentation hardness 65.4 to 83.1. Cuff lengths vary from 29.7 to 45.3 mm, thickness 0.03 to 0.54 mm, diameter 14.5 to 32 mm, and cuff resting volume 0.15 to 19.9 ml. We recommend use of a soft, thermolabile, kink- and collapse-resistant tracheal tube fitted with a soft, thin-walled, tough, compliant, moderately long cuff, with a moderately large resting volume and diameter larger than tracheal diameter. Argyle, National Catheter, Ohio, Portex, Rusch “safety,” and Shiley tracheal tubes resist collapse and kinking. Argyle, Lanz, National Catheter “hi-lo,” National Catheter “intermediate hi-lo,” Ohio, and Portex “profile” cuffs are thin and have diameters larger than the average male tracheal diameter.

Impact of cardiopulmonary resuscitation training on resuscitation.

Restoration of adequate spontaneous circulation after “arrest” and cardiopulmonary resuscitation (CPR) of 546 patients before and 460 patients after initiation of a CPR training course in a 500-bed city hospital is reported. Between January 1972 and June 1976, adequate circulation after CPR was present in 38.6% of patients before and 50.4% after training ICU nurses and house physicians in modern resuscitation techniques. Factors crucial to resumption of adequate circulation are: (1) CPR training of all hospital personnel so that effective CPR can be started immediately after recognition of an arrest situation, (2) production of a palpable pulse with closed chest cardiac massage, and (3) prompt effective therapy so that the time interval between arrest and resumption of adequate spontaneous circulation is short.

Intermittent exposure to 40 percent oxygen prolongs rat survival in 100 percent oxygen.

Prior intermittent exposure to 40 percent O2 protected rats against fatal O2 toxicity. Protection was not absolute, however, for the death of most rats in 100 percent O3 was not prevented but delayed considerably. Furthermore, those rats which did survive exposure to 100 percent O2 for long periods by virtue of prior adaptation to increased O2 concentrations had pathologic changes in the lungs typical of chronic O2 toxicity. The very early demise of some rats indicated that 1 of 12 animals is hypersensitive to high concentrations of inspired O2.