Do maternal characteristics influence maternal-fetal medicine physicians' willingness to intervene when managing periviable deliveries?

OBJECTIVE: Determine the relative influence of patient characteristics on Maternal-Fetal Medicine (MFM) physicians' willingness to intervene when managing 23-week preterm premature rupture of membranes. STUDY DESIGN: Surveyed 750 randomly sampled US members of the Society of Maternal-Fetal Medicine. Physicians rated their willingness to offer induction, order steroids and perform cesarean across eight vignettes; then completed a questionnaire querying expectations about neonatal outcomes and demographics. RESULTS: Three hundred and twenty-five (43%) MFMs responded. Patient characteristics only influenced ⩽11% of participants' willingness ratings. Overall, provider characteristics and institutional norms were associated with willingness to perform antenatal interventions, for example, practice region was associated with willingness to offer induction (P<0.001), order steroids (P=0.008) and perform cesarean for distress (P=0.011); while institutional cesarean cutoffs were associated with willingness to order steroids and perform cesarean for labor and distress (all P<0.001). CONCLUSION: Physician-level factors and institutional norms, more so than patient characteristics, may drive periviable care and outcomes.

Response properties of the refractory auditory nerve fiber.

The refractory characteristics of auditory nerve fibers limit their ability to accurately encode temporal information. Therefore, they are relevant to the design of cochlear prostheses. It is also possible that the refractory property could be exploited by prosthetic devices to improve information transfer, as refractoriness may enhance the nerve's stochastic properties. Furthermore, refractory data are needed for the development of accurate computational models of auditory nerve fibers. We applied a two-pulse forward-masking paradigm to a feline model of the human auditory nerve to assess refractory properties of single fibers. Each fiber was driven to refractoriness by a single (masker) current pulse delivered intracochlearly. Properties of firing efficiency, latency, jitter, spike amplitude, and relative spread (a measure of dynamic range and stochasticity) were examined by exciting fibers with a second (probe) pulse and systematically varying the masker-probe interval (MPI). Responses to monophasic cathodic current pulses were analyzed. We estimated the mean absolute refractory period to be about 330 micros and the mean recovery time constant to be about 410 micros. A significant proportion of fibers (13 of 34) responded to the probe pulse with MPIs as short as 500 micros. Spike amplitude decreased with decreasing MPI, a finding relevant to the development of computational nerve-fiber models, interpretation of gross evoked potentials, and models of more central neural processing. A small mean decrement in spike jitter was noted at small MPI values. Some trends (such as spike latency-vs-MPI) varied across fibers, suggesting that sites of excitation varied across fibers. Relative spread was found to increase with decreasing MPI values, providing direct evidence that stochastic properties of fibers are altered under conditions of refractoriness.

Predicting survival in an elderly burn patient population.

The purpose of this study was to analyze the outcome of elderly burn victims and to determine an instrument to predict survival in this population. Charts of three hundred and eight burn patients > or =60 yr of age who were admitted to a university-based hospital between the years of 1977-1996 were retrospectively analyzed. The mean age of the population was 71.5+/-8.6, with a male predominance (1.8 to 1, P < 0.001). The majority of the burns were secondary to flame injuries (210, 68.6%). The median body surface area (BSAB) was 13.0% with an in-hospital mortality rate of 30.2%. We demonstrated improved survival in patients aged 60-74 yr as compared to 1965-1971 national burn survival data. A similar trend could not be shown in the very old (> 75 yr of age). Only age and BSAB were related to death by multiple stepwise forward linear regression. The Baux score, which adds age and BSAB, was predictive of outcome in 87.0% of our population. In conclusion, this study reinforces the high mortality associated with burn injuries in the elderly and the superior ability of the Baux score (age + percent burn) in predicting outcome in this population.

Auditory nerve responses to monophasic and biphasic electric stimuli.

Charge-balanced, biphasic stimulus pulses are commonly used in implantable cochlear prostheses as they can be safely delivered to living tissue. However, monophasic stimuli are more efficient (i.e. producing lower thresholds) and likely provide more spatially selective excitation of nerve fibers. We examined the neural responses to monophasic, 'pseudomonophasic', and biphasic stimuli to better understand the inherent tradeoffs of these stimuli. Using guinea pig and cat animal models, we compared the auditory nerve responses to both 40 micros monophasic and 40 micros/phase biphasic stimuli using both electrically evoked compound action potential and single-fiber recordings. We also made comparisons using a computational model of the feline auditory nerve fiber. In all cases, our stimuli were cathodic monophasic and cathodic-first biphasic pulses. As expected, monophasic stimuli provided lower thresholds relative to biphasic stimuli. They also evoked responses with relatively longer latencies. We also examined responses to charge-balanced biphasic pulses composed of two phases of differing duration (i.e. pseudomonophasic stimuli). The first phase was fixed at 40 micros, while the second phase was systematically varied from 40 to 4000 micros. With a relatively long second phase, we hypothesized that these stimuli would provide some of the beneficial features of monophasic stimuli. Both the gross-potential and single-fiber data confirmed this and indicate that the largest incremental effects of changing the second-phase duration occur for durations less than 500 micros. Consideration of single-fiber data and computer simulations suggest that these results are consistent with the neural membrane acting as a leaky integrator. The computer simulations also suggest that the integrative properties at least partially account for the difference between our monophasic-biphasic results and previously published data. Our results apply to cathodic-leading stimuli; due to differing patterns of membrane depolarization, they may not be applicable to situations using anodic-leading stimuli. Finally, we observed differences between the guinea pig and cat response patterns. Compared to cats, guinea pigs produced smaller monophasic vs. biphasic threshold differences. This interspecies disparity may be due to differences in cochlear anatomy.

Our chemical burn experience: exposing the dangers of anhydrous ammonia.

Although chemical injuries account for only a small number of one burn unit's cases, the diversity, resulting complications, and sequelae of these burns pose special problems. We reviewed a 19-year period of the chemical burn experience of our burn unit. The population of patients with these types of burns consisted of young men (mean age: 29.8 years), the majority of whom were injured on the job. Unique to our series is the largest collection of injuries (30%) resulting from the common fertilizer anhydrous ammonia. Another population of concern, accounting for 14% of the injuries in our unit, is that of patients injured at home with routine household cleaners. Nearly one half of those patients injured at home incurred injuries that required grafting. The cornerstone of chemical burn prevention and treatment involves education regarding the caustic nature of chemicals, proper handling, adequate protection, and copious irrigation of the wound at the scene. From the analysis of our retrospective review, adequate education and treatment at the scene appear to be well implemented in the industrial and farming communities. The focus of our education efforts should be directed toward the public and emphasize the safe use of household chemicals. Finally our review illuminated the potential benefit of immediate excision and grafting for decreasing the length of stay, complications, and loss of productivity.

Electrically evoked single-fiber action potentials from cat: responses to monopolar, monophasic stimulation.

We recorded action potentials from single auditory-nerve fibers of cats using monophasic current pulses delivered by a monopolar intracochlear electrode. These simple stimuli provided a means of investigating basic properties and hypotheses of electrical excitation. Standard micropipette recording techniques were used. Responses to anodic (positive) and cathodic (negative) stimulus pulses were recorded separately to evaluate stimulus polarity effects. Mean spike (action potential) latency was polarity dependent, with greater latencies for cathodic stimulation. Threshold stimulus level was also polarity dependent, with relatively lower cathodic thresholds. Both effects are consistent with trends reported in the compound action potential. Variability in single-fiber latency (i.e., jitter) was dependent upon stimulus polarity. In contrast, the slope of single-fiber input-output functions failed to show a clear polarity dependence, although such trends have been seen in the compound action potential data. We also observed a relatively greater degree of adaptation over time with anodic stimulation. Bimodal post-stimulus-time histograms were recorded in a small number (2%) of fibers, supporting the hypothesis that both the peripheral (dendritic) and central axonal processes are excitable with the same stimulus polarity, in a limited number of cases. This observation, together with analyses of interactions among measures of latency, threshold, and jitter, is consistent with the hypothesis that, with monopolar intracochlear stimulation, most fibers are stimulated at axonal (modiolar) sites and a minority of fibers nearest the electrode are stimulable at their peripheral processes.

Electrically evoked compound action potentials of guinea pig and cat: responses to monopolar, monophasic stimulation.

We recorded electrically evoked compound action potentials (EAPs) from guinea pigs and cats using monophasic current pulses delivered by a monopolar intracochlear electrode. By using simple stimuli, we sought results that could shed light on basic excitation properties of the auditory nerve. In these acute experiments, the recording electrode was placed directly on the auditory nerve. Responses to anodic and cathodic stimulus pulses were recorded separately to evaluate stimulus polarity effects. Several polarity-dependent properties were observed. Both EAP morphology and latency were polarity-dependent, with greater latencies for cathodic stimulation. Threshold stimulus level was also polarity-dependent, but in different directions in the two species: cats had lower cathodic thresholds while guinea pigs had lower anodic thresholds. We also observed that the slopes of the EAP amplitude-level functions depended upon stimulus polarity. In most cases where EAP saturation amplitude could be measured, that amplitude was similar for anodic and cathodic stimuli, suggesting that either stimulus polarity can recruit all fibers, or at least a comparable numbers of fibers. The common findings (e.g., EAP morphology and polarity-dependent latency) observed in these two species suggest results that can be extrapolated to responses obtained in humans, while the species-specific findings (e.g., dependence of threshold on polarity) may point to underlying anatomical differences that caution against overgeneralization across species. Some of our observations also bear upon hypotheses of how electrical stimuli may excite different sites on auditory nerve fibers.

The use of long-duration current pulses to assess nerve survival.

This study investigated the usefulness of long-duration current pulses in assessing the status of the auditory nerve in ears with various degrees of retrograde neural degeneration. Guinea pigs were deafened with aminoglycosides prior to acute implantation of the cochlea and collection of electrically evoked auditory brainstem responses (EABRs). Analysis of wave I evoked with long-duration current pulses suggests that this evoked response is sensitive to degeneration of the peripheral processes of the auditory nerve. Correlations with spiral ganglion cell density show that EABR measures obtained with long-duration pulses are comparable to those previously established for estimating nerve survival. Further analysis indicates that this measure may provide unique information about the degenerative state of the nerve. Threshold EABR measures using long-duration pulses are evidently more place-specific than other measures. Also, results suggest that long-duration pulses may be sensitive to two phases of the degenerative process: degradation of the peripheral processes and subsequent degeneration of neural processes central to the spiral ganglion.

Characterization of wave I of the electrically evoked auditory brainstem response in the guinea pig.

This paper examines the first component of the electrically evoked auditory brainstem response (EABR) of the guinea pig. Short (20 microseconds/phase) and long (4000 microseconds/phase) duration rectangular current pulses were applied through a bipolar intracochlear electrode in acute preparations. Short-duration pulses evoked a synchronized response relatively free of stimulus artifact; long pulses facilitated examination of the integrative capacities of nerve fibers at relatively low current levels. In deafened control subjects, wave I of the EABR consistently demonstrated two positive peaks having different latency-level and adaptation recovery functions. The early component (wave Ia) showed less decrement in latency with increasing stimulus level and recovered faster in a forward-masking paradigm. Non-monotonicities in the adaptation recovery curves were also observed, more consistently in the wave Ib data. It is proposed that wave Ia arises from stimulation of the axons proximal to the spiral ganglion while wave Ib is initiated at the peripheral dendritic processes. Implications for human cochlear implant research are discussed.

The nature of the epithelium in acquired cholesteatoma. Part 2. Cell culture.

The exact nature and role of the epithelial layer in cholesteatoma remains undetermined. The aim of this study was to investigate cholesteatoma epithelium and normal aural epithelia in common cell culture conditions. Samples of cholesteatoma, external meatal epidermis and middle ear mucosa were obtained, successfully grown in cell culture, and subcultured. No significant morphological differences were found between cholesteatoma and aural epidermis. The only differences noted were delayed onset of colony formation, and the need to subculture prior to the cultures becoming confluent in the cholesteatoma cultures. Further research is required to account for these differences in growth patterns.