Training in obstetric general anaesthesia: a vanishing art?

General anaesthesia in obstetric practice has largely been replaced by the use of regional techniques. We have studied this phenomenon and the subsequent impact on training in this technique both retrospectively and with a prospective audit. There has been a decline in the use of general anaesthesia for Caesarean section such that trainee anaesthetists are getting less practical exposure to this important procedure. Audit revealed a deficit with consultant involvement in training and heightened awareness has resulted in improved supervision. Possible implications for future consultant working practices are discussed.

Epidural pain relief in labour: potencies of levobupivacaine and racemic bupivacaine.

We have compared the minimum local analgesic concentrations (MLAC) of levobupivacaine relative to racemic bupivacaine in a prospective, randomized, double-blind, sequential allocation study. Women in labour were given a 20-ml bolus of epidural levobupivacaine or bupivacaine diluted to a concentration determined by up-down sequential allocation. The initial concentration was 0.07% w/v for both drugs. Efficacy was defined using a visual analogue pain score (VAPS) at 10 mm or less within 30 min. The MLAC of levobupivacaine was 0.083% w/v (95% CI 0.065-0.101) and the MLAC of bupivacaine 0.081% w/v (95% CI 0.055-0.108). In molar terms, the MLAC of levobupivacaine was 2.87 mmol litre-1 (95% CI 2.25-3.49) and the MLAC of bupivacaine 2.49 mmol litre-1 (95% CI 1.69-3.32). With regard to the commercial preparations, the potency ratio levobupivacaine: bupivacaine was 0.98 (95% CI 0.67-1.41), and this is unlikely to be of clinical relevance. In molar terms, the ratio was 0.87 (95% CI 0.60-1.25). With regard to toxicity, the evidence should be evaluated in the light of a possible 13% potency difference in molar concentration in favour of racemic bupivacaine.

Preterm labor and congenital candidiasis. A case report.

Intrauterine infection with Candida is a rare complication of pregnancy. We report a case of preterm labor associated with Candida chorioamnionitis and the subsequent delivery of an infant with congenital Candida infection. We also discuss possible factors responsible for the increased invasiveness of this usually benign condition and management considerations once the diagnosis is made.

The Canadian Association of Emergency Physicians (CAEP/ACMU).

The Canadian Association of Emergency Physicians is a diverse group of 500 practitioners providing emergency care to the ill and injured. The specialty section of the organization represents Royal College certificants and is 120 strong. The Association, with headquarters in Ottawa, has a major interest in the continuing education of its members, policy development and the improvement of emergency health care in the country.

Recent developments in care of the newborn.

New developments in newborn care include body fluid precautions, especially the use of gloves and the use of mechanical suction instead of oral suction. Artificial surfactant is still investigational, but results to date are favorable. A recent report may lead to modification of practices for management of infants with possible meconium aspiration.

Mucocutaneous and invasive candidiasis among very low birth weight (less than 1,500 grams) infants in intensive care nurseries: a prospective study.

To determine whether mucocutaneous candidiasis presages the development of invasive candidiasis and to assess factors influencing the development of mucocutaneous candidiasis and invasive candidiasis among infants requiring neonatal intensive care, all infants admitted to our neonatal intensive care unit during a 47-month period were prospectively examined twice weekly for mucocutaneous candidiasis. Because 16 of 18 (89%) infants in whom invasive candidiasis (defined by positive cultures of blood, CSF, deep tissue or greater than or equal to 2 supra-pubic urine aspirates) developed had birth weights less than 1,500 g, further analysis was focused toward the very low birth weight group. Of 358 very low birth weight infants hospitalized for less than three days and serially studied until discharge from the neonatal intensive care unit, mucocutaneous candidiasis developed in 28 (7.8%), invasive candidiasis developed in 16 (4.5%), and in 323 there was no evidence of mucocutaneous candidiasis or invasive candidiasis. Although many risk factors were shown by univariate analysis to be significantly more common among those with invasive candidiasis and mucocutaneous candidiasis, adjustment for the covariant effects of duration of hospitalization and gestational age revealed that only prolonged duration of antibiotic therapy and duration of endotracheal intubation were significantly associated with invasive candidiasis. Invasive candidiasis developed later in nine of 28 (32%) infants with mucocutaneous candidiasis despite nystatin therapy of mucocutaneous candidiasis in all nine (median duration of therapy before invasive candidiasis, nine days). Very low birth weight infants in whom mucocutaneous candidiasis develops are at significantly greater risk of invasive candidiasis developing later than those in whom mucocutaneous candidiasis did not develop (9/28 v 7/330, P less than .001).

Life span of intravenous cannulas in a neonatal intensive care unit.

Peripheral intravenous cannula use in a neonatal intensive care unit was surveyed prospectively to ascertain the rate of complications and the factors influencing the life span of an intravenous cannula. During a three-month period in which 199 intravenous cannulas were inserted in 69 patients, only two significant infiltrations (1%) were observed in more than 5000 hours of intravenous therapy. None of the factors studied, including weight, age, type and rate of fluid administration, and type of medication (except pancuronium bromide), had any discernible effect on the functional life span of intravenous cannulas. Pancuronium was associated with a significant prolongation of cannula life span--from 30 to 50 hours. We conclude that in this setting, the rate of clinically significant complications from intravenous cannula therapy is low.

Lateral positioning of the stable ventilated very-low-birth-weight infant. Effect on transcutaneous oxygen and carbon dioxide.

Eighteen stable very-low-birth-weight (VLBW) mechanically ventilated infants with chronic lung disease were studied to examine the effects of right and left lateral positioning in contrast to supine positioning on transcutaneous (tc) oxygen (tcPO2) and carbon dioxide measurements (tcPCO2). The neonates were studied at a median postnatal age of 31 days (range, 17 to 57 days) and had median birth weights and gestational ages of 975 g (range, 570 to 1360 g) and 27.5 weeks (range, 24 to 30 weeks), respectively. Median fraction of inspiratory oxygen was 0.32 (range, 0.23 to 0.40). The sequence of study positions was randomly determined. Sleep state as well as tcPO2 and tcPCO2 were recorded every 30 s for five minutes. A significant difference in mean tcPO2 or tcPCO2 was not detected for any of the positions. Lateral positioning may facilitate the development of midline behavior in VLBW infants. Care givers are often reluctant to position infants in side lying, however, because of concerns that ventilation or oxygenation might be compromised. We conclude that placing the stable VLBW mechanically ventilated infant in a side-lying position has no deleterious effects on oxygenation and ventilation, as measured by tcPO2 and tcPCO2, and therefore should be encouraged.

Stratified volume holographic optical elements.

A computational algorithm for analyzing diffraction properties of optical devices, the optical beam propagation method, has suggested a new class of devices by which Bragg regime (thick grating) response can be obtained from a spaced sequence of thin grating layers. Such stratified volume holographic optical elements (SVHOE's) can emulate distributed volume gratings in terms of diffraction efficiency and angular selectivity and in addition possess periodic diffraction properties that might serve, for example, as interconnections for optical cellular logic arrays. SVHOE's also offer a unique capability for altering the device diffraction response on a layer-by-layer basis, allowing for control of both the diffraction peak width and the angular separation of adjacent peaks.

Temporal response of the acoustooptic modulator in the high scattering efficiency regime.

An efficient and rigorous algorithm is proposed for analyzing the temporal response of the Bragg acoustooptic modulator in the high scattering efficiency regime. Computer studies of this model successfully predict pulse profile asymmetries that have been observed experimentally and cannot be predicted by the usual Green's function (small signal) models of the acoustooptic coupling. The technique of predistorting the electronic video signal by passing it through a nonlinear electronic network to linearize the modulator response is effective only for slowly varying video signals. Residual nonlinearities appear for rapidly varying video signals.

Scophony light valve.

The optical modulator in a flying spot scanner converts the electronic video signal into a corresponding temporal modulation of a light beam. An alternative configuration, which directly exploits the spatial modulation of an acoustooptic cell, is the Scophony scanner, first developed by the Scophony Laboratories of London during the 1930s. The Scophony scanner responds like a coherent imaging system, whereas the flying spot scanner performs like an incoherent imaging system, when the light source is spatially coherent. The Scophony response is intimately linked to the concepts of FM blur and the deflector as video spectrum bandpass filter.

Temporal response of the acoustooptic modulator: physical optics model in the low scattering efficiency limit.

The Green's function model of the acoustooptic modulator proposed by E. I. Gordon et al. is reformulated in Fourier transform space to simplify the mathematics and to underscore the physics. Numerical studies of response to sinusoidal video signals and to square pulse trains indicate that the modulator can be approximated by a linear invariant model with a suitably scaled Gaussian impulse response. An angular scattering window analogy is proposed to explain the characteristics of the modulator.

Temporal response of the acoustooptic modulator: geometrical optics model in the low scattering efficiency limit.

A phenomenological model of the acoustooptic modulator is proposed. The temporal response of the deflected light power is a quadratic invariant function of the video signal amplitude. The two-dimensional response kernel is defined by an overlap integral of the incident light and sound field profiles, similar to a convolution operator. When the incident light is focused to reduce risetime, the light throughput efficiency and the deflected light profile degrade because the modulator is a linear filter with limited angular passband operating on the propagation angle spectrum of the incident light.