Introduction:Previous studies have proven the success of the EsophagealTracheal Combitube (ETC) as a primary airway, but not as a rescue airway.Objective:The object of this study was to observe success and complication rates of paramedic placement of an ETC as a rescue airway, and to compare success rates with endotracheal tube (ETT) intubation. The primary outcome indicator was placement with successful ventilation. Complication rates, esophageal placement, and return of spontaneous circulation (ROSC) were secondary measures.Methods:A retrospective review of the records of patients who had ETC attempts by Emergency Medical Services (EMS) was conducted for a period of three years. Complications were defined a priori. The ETC is used primarily as rescue airway for a failed attempt at an endotracheal tube (ETT) intubation. A control group for ETT placements was drawn from the EMS quality assurance (QA) database for the same period.Results:Esophageal-Tracheal Combitube insertion was attempted on 162 patients, of which, 113 (70%) were successful, 46 (28%) failed, and the outcome of three (2%) was not recorded. Inability to place the ETC occurred in 29 (18%) patients, and accounted for 48% (22/46) of failures. The use of the ETC caused dental trauma in one patient, and one placement of the ETC was related to the onset of subcutaneous emphysema. Blood in the ETC from active upper gatrointestinal bleeding occurred in nine patients (6%), and four tubes (3%) became dislodged en route to the hospital. The a priori complication rate was 44/162 (27%). Inability to determine placement of the ETC due to emesis from both ports occurred in 21 cases. Combining these problems with the a priori complications, the overall rate was 40% (65/162). EsophagealTracheal Combitube location was noted in a subset of 90 charts, of which, 76 (84%) were esophageal, and 14 (16%) were tracheal. Thirteen of 126 (10%) patients in cardiac arrest had return of spontaneous circulation (ROSC) in the field after placement of the ETC. An ETT was attempted in 128 control patients, of which, 107 (84%) were successful, 21 (16%) failed (odds ratio (OR) for ETT vs. ETC = 2.1; 95% CI = 1.12–3.86).Conclusion:Despite a low ROSC rate, the complication and success rates of ETC are acceptable for a rescue airway device. Tracheal placement of the Combitube is uncommon, but requires fail-safe discrimination. Similar to previous reports, the success ratio for ETT was greater than for the ETC.

Objective: To describe the clinical presentation of patients with cyclic antidepressant (CA) and use of sodium bicarbonate (NaHCO 3 ) in the treatment of this overdose in the prehospital setting. Methods: A three year retrospective observational review of records was performed using the San Diego County Quality Assurance Network database for prehospital providers. All adult patients who were treated with NaHCO 3 by paramedics for a CA overdose were included. Demographic data, presenting cardiovascular and neurological symptoms, paramedic treatments, and any changes in status were reviewed. Results: Twenty one patients were treated by paramedics with NaHCO 3 for CA overdose. Seventeen patients (80%) presented with mental status changes, including 11 presenting with a GCS<8. Seven of the 21 (33%) presented with a cardiac arrhythmia expected to possibly respond to NaHCO 3 treatment. Seven of the 21 (33%) were hypotensive, and five (24%) patients had reported seizure activity. Only 2 of the 21 patients (10%) treated with NaHCO 3 had recorded improvements after administration of the drug, while the other 19 remained stable without any deterioration. Sixteen of 21 patients (76%) were given NaHCO 3 for indications on standing order, while five patients were treated outside the standing order indications by base physician order with none of the five patients having any change in status ater treatment. Conclusions: After prehospital NaHCO 3 use in patients with CA overdose, there were no complications reported, two patients improved in status and the others remained unchanged. Base hospital physician orders of NaHCO 3 for indications beyond the standing orders were not associated with changes in patient status.

Theory is compared with experiment. The applicability of the theory to a sample which is magnetically sufficiently simple is demonstrated by comparing certain qualitative predictions of the theory with experiment. In particular it is shown that the ascending branches of all minor loops coincide if they are all started at the same point. The ascending branch of a minor loop coincides with the ascending virgin curve if they both start at the same point and if the gain of the flux and mmf channels of the minor loop are reduced by a factor of 2. The virgin curve is the locus of apexes of centered minor loops. The relation between height and width of minor loops is shown to agree quantitatively with theory. The shape of a branch of a single minor loop is also found to agree. The first three terms of the Fourier analysis of mmf for sinusoidal flux variation are found to be in good agreement with theory except for the third harmonic which at least has the correct order-of-magnitude. Theory and experiment are shown to be in good agreement in the Rayleigh region. However, the applicability of the present theory is not confined to the Rayleigh region, but applies right up to saturation for a specimen meeting the criteria of simplicity. The predicted relation between the Rayleigh constants and the coercive force is shown to hold. Finally the distribution function is calculated from a minor loop and shown to be an exponential with reasonable accuracy.

Tape-wound cores of grain-oriented 50%–50% NiFe were studied in this investigation. The internal field generated by the sample was measured by means of anhysteretic magnetization curves. It was found that, in some cases, the internal field was regenerative, i.e., of the same polarity as the average magnetization. In some cases both a regenerative field and a degenerative demagnetizing field could be separately observed. The demagnetizing field is not a linear function of flux. If the internal field is regenerative, the anhysteretic susceptibility is negative. In order to measure negative anhysteretic susceptibility it is necessary to control the flux of the sample and measure the required magnetomotive force rather than vice versa. Otherwise one measures a spurious infinite susceptibility. A regenerative internal field explains the tendency of minor loops, for some cores, to drift away from the center of the major loop and into plus or minus saturation (``minor loop drift''). This is shown to be a case of positive feedback in which the loop gain exceeds unity and the system is unstable. The regenerative internal field is shown to be the result of magnetostatic interaction between pole-bearing domain walls. The internal field is not a single-valued function of flux, but depends on the detailed magnetization pattern of the sample. The characteristic field of the interaction is of the order of several A/m. The characteristic length is of the order of 10 m.

The theory of the spring model of hysteresis is compared with experiment for a number of magnetic materials. The properties of the spring model as they relate to minor hysteresis loops are summarized. Loops from tape-wound cores of various materials are compared with these predictions to see if the cores obey the model. It is found that some cores, square orthonol and square Permalloy 80, fit the model quite well. Other cores, round orthonol, supermalloy, and magnesil, deviate considerably from the predictions of the model. It is believed that these cores can be made to obey the model by taking into account an internal self-generated field which acts on the domain walls in addition to the applied field.