Practice variation among Dutch paediatricians in palivizumab prescription rates: the importance of parental counselling approach.

AIM: To investigate differences in palivizumab prescription rates between Dutch paediatricians, and the role of parent counselling in this practice variation. METHODS: A retrospective chart review of premature infants <32 weeks of gestation, aged less than six months at the start of the winter season, born between January 2012 and July 2014, in three secondary hospital-based paediatric practices in the Netherlands. RESULTS: We included 208 patients, 133 (64%) of whom received palivizumab. Prescription rates varied considerably between the three hospitals: 8% (6/64), 89% (32/36) and 99% (97/98). A noticeable difference in the way parents were counselled about palivizumab was the use of the number needed to treat (NNT). In the hospital with the lowest prescription rate (8%), an NNT of 20 to prevent one hospitalisation was explicitly discussed with parents. Bronchiolitis-related hospital admissions occurred in 11.3% of patients receiving palivizumab compared to 20.0% in nonimmunised infants (p = 0.086). CONCLUSION: Considerable practice variation exists among Dutch paediatricians regarding palivizumab prescription rates. The counselling method seems to play an important role. Presenting palivizumab prophylaxis as a preference-sensitive decision, combined with the explicit use and explanation of an NNT, leads many parents to refrain from respiratory syncytial virus immunisation.

Renal responses to prolonged (48 h) hypoxemia without acidemia in the late-gestation ovine fetus.

The effect of sustained moderate hypoxia on renal blood flow and renal function was studied in the ovine fetus (123-129 days). The experiments consisted of 48 h of isocapnic hypoxia, not resulting in acidemia, but sufficient to produce redistribution of blood flow in favor of the brain at the expense of the carcass. Hypoxemia was induced by maternal nitrogen inhalation. Fetal arterial O(2) saturation and arterial O(2) pressure (Pa(O(2))) decreased from, respectively, 50.6 +/- 3.0% and 17.2 +/- 0.9 mmHg during control to 36.4 +/- 2.7% and 13.4 +/- 0.7 mmHg on the first and to 32.2 +/- 2. 2% and 12.4 +/- 0.7 mmHg on the second day of hypoxemia. Fetal renal blood flow and urine production rate were continuously measured using ultrasonic flow transducers. Fetal renal blood flow increased during hypoxemia from 11.8 +/- 1.6 to 15.6 +/- 1.8 ml/min and remained elevated throughout the 48-h hypoxemia period (P < 0.01). Renal blood flow was inversely correlated with fetal Pa(O(2)) (r is -0.69, P < 0.0001). Fetal urine production rate, glomerular filtration rate, filtration factor, osmotic clearance, and free water clearance did not significantly change from control values during hypoxemia or recovery. We conclude that hypoxemia without acidemia results in an immediate and considerable increase in fetal renal blood flow, which remains elevated for the entire hypoxemic period.

Effect of location of the sensor on reflectance pulse oximetry.

OBJECTIVE: The influence of the location of the sensor on reflectance pulse oximetry during fetal monitoring in labour was investigated using the newborn infant as a model. METHODS: Seven healthy infants were studied between 19 and 48 hours after term delivery. Recordings of reflectance pulse oximetry were obtained from eight different sites on the infant's head. The relative changes in red to infrared light (R/IR) were determined. In pulse oximetry R/IR values are converted to arterial oxygen values by means of an empirically derived calibration curve. RESULTS: Significantly lower R/IR values were found at the forehead compared with the fontanelle, the parietal and occipital position, and the temporal area. Conversion to oxygen saturation values revealed a difference of up to 13.4% in oxygen saturation between the forehead and the occipital area. CONCLUSION: Assuming that the arterial blood oxygen saturation did not change substantially, our findings indicate that in reflectance pulse oximetry there is no unique relation between R/IR and arterial oxygen saturation. The differences in reflectance pulse oximetry at the various sites are explained by differences in optical properties (scattering and absorption) of the tissue underneath the sensor. These will affect the red and infrared light reaching the detectors in a different way, and consequently R/IR changes. Because during intrapartum monitoring exact positioning of the sensor on the fetal head is usually impossible, the accuracy of fetal reflectance pulse oximetry is impaired.

Reflectance pulse oximetry at the forehead of newborns: the influence of varying pressure on the probe.

OBJECTIVE: Transmission pulse oximetry (TPO) is not a practical method of intrapartum fetal monitoring of arterial oxygen saturation. Reflectance pulse oximetry (RPO) requires a sensor applied to the skin of the fetal head and may be a useful technique. During labor, various degrees of pressure will be exerted on the RPO sensor. Previous studies have shown that moderate pressure on the sensor can improve the RPO signal. At increasing pressure, however, blood flow underneath the sensor will be occluded. This study examines the influence of pressure applied to the RPO sensor on the signal from the forehead of healthy newborns as a model for the fetal situation. METHODS: After institutional approval, 12 healthy newborns were studied. The RPO probe was placed at the forehead. Pressure on the probe was increased stepwise from 0 to 80 mmHg, and the effect on the ratio between the relative changes of the red and infrared light intensities (R/IR, inversely related to oxygen saturation) and pulse sizes was evaluated. Additionally, the effect of firm pressure (> 150 mmHg) on the probe was evaluated. RESULTS: R/IR values remained virtually unchanged when pressure onto the probe was increased from 0 to 80 mmHg, although the standard deviation slightly decreased. The pulse size increased as pressure on the probe increased. During firm pressure on the probe (> 150 mmHg), plethysmographic signals remained detectable, but R/IR values markedly increased. CONCLUSIONS: In newborns, mild to moderate pressure on the probe has little influence on the RPO signal at the forehead. Even during firm pressure, RPO can be used to obtain pulsatile signals, that presumably derive from tissue underneath the skull, such as the cerebral circulation.

Reflectance pulse oximetry at the forehead improves by pressure on the probe.

In this study, we investigated the possibility of improving reflectance (back-scatter) pulse oximetry measurements by pressure applied to the probe. Optimal signal detection, with the probe applied to an easily accessible location, is important to prevent erroneous oxygen saturation readouts. At the foreheads of 10 healthy adult volunteers, the effects of pressure applied onto the reflectance pulse oximeter probe were studied. Distances between the LEDs (660 nm and 940 nm) and the three photodiodes in the sensor were 4 mm, 7 mm, and 10 mm. For each detector, recordings were evaluated regarding red-to-infrared (R/IR) ratios and pulse sizes in relation to the stepwise increased pressure applied to the probe. R/IR variability decreased with applied pressures between 60 and 120 mm Hg. These findings are partly attributed to a corresponding increase in red and infrared pulse sizes at the detectors, which results in an improved signal-to-noise ratio. It is thought that pressure onto the oximeter sensor forces venous blood out of the tissues underneath the sensor. Consequently, the disturbing influence of pulsating and non-pulsating venous blood is reduced. Moreover, the increased difference in vessel diameter between diastole and systole and the corresponding difference in light absorption and an increase in flow velocities, causes an increase in pulse size with increasing pressure on the probe. Pressure applied to the probe may be useful in increasing the accuracy of reflectance pulse oximetry.

Laser Doppler blood flowmetry using two wavelengths: Monte Carlo simulations and measurements.

A new laser Doppler blood flowmeter for measuring skin perfusion is presented. The flowmeter consists of a probe that uses two different wavelengths and is able to measure at different depths. It may be used to distinguish the superficial microcirculation of the skin providing nutritional flow and the flow in deeper situated blood vessels (thermoregulatory flow). Measurements and Monte Carlo simulations of the Doppler signals for human skin are shown.

Fiber-coupled self-mixing diode-laser Doppler velocimeter: technical aspects and flow velocity profile disturbances in water and blood flows.

The effects of disturbances of the flow pattern in front of the fiber facet of a fiber-coupled self-mixing diode-laser Doppler velocimeter system are investigated. This was done by comparing measurements and calculations of the Doppler frequency spectrum with the expected values. The calculated Doppler spectrum was obtained from the calculation of light scattered (with or without Doppler shift) by the moving particles in front of the fiber facet. The velocity profile of the particles was calculated with a finite-element method. Measurements were done with water (with polystyrene spheres) and whole blood as the samples. Good agreement between measurements and calculations were obtained. The velocimeter was modeled as a five-mirror setup. The reflectivity of the fiber facet closest to the laser turns out to have the most influence on the sensitivity and stability of the laser. Direct reflection of unwanted light back into the laser cavity was avoided by placing a glass plate in front of the fiber. Design consi ations are presented.

A semiconductor laser used for direct measurement of the blood perfusion of tissue.

An instrument consisting merely of a semiconductor laser in its own housing was used to measure the blood perfusion in tissue. Use is made of the feedback of Doppler-scattered light to the photodiode in the laser housing. A recording perfusion of a finger under occlusion of blood flow in the arm is shown.

Condensed Monte Carlo simulations for the description of light transport.

A novel method, condensed Monte Carlo simulation, is presented that applies the results of a single Monte Carlo simulation for a given albedo micro(s)/(micro(alpha) & micro(s)) to obtaining results for other albedos; micro(s) and micro(alpha), are the scattering and absorption coefficients, respectively. The method requires only the storage of the number of interactions of each photon with the medium. The reflectance and transmittance of turbid slabs can thus be found from a limited number of condensed Monte Carlo simulations. We can use an inversion procedure to obtain the absorption and scattering coefficients from the total reflectance and total transmittance of slabs. Remitted photon densities from a semi-infinite medium as a function of the distance between the light source and the detector for all albedos can be found even from the results of a single condensed Monte Carlo simulation. The application of similarity rules may reduce further the number of Monte Carlo simulations that are needed to describe the influence of the distribution of scattering angles on the results.

Optical properties of human dermis in vitro and in vivo.

Condensed Monte Carlo simulation results have been used for calculating absorption and reduced scattering coefficients from the literature data on the measured total transmittance and total reflectance of samples of the human skin in vitro. The results of several measuring methods have been compared. We have also estimated the range for absorption coefficients and reduced scattering coefficients at 660 and 940 nm from measured intensities at the skin surface as a function of the distance from the location where the light enters the skin by using condensed Monte Carlo simulations for a homogeneous semi-infinite medium. The in vivo values for the absorption coefficients and the reduced scattering coefficients appear to be much smaller than the values from the in vitro measurements, that have been assumed until now. The discrepancies have been discussed in detail. Our in vivo results are in agreement with other in vivo measurements that are available in the literature.

Reflectance pulse oximetry in fetal lambs.

Transmission pulse oximetry is used for monitoring in many clinical settings. However, for fetal monitoring during labor and in situations with poor peripheral perfusion, transmission pulse oximetry cannot be used. Therefore, we developed a reflectance pulse oximeter, which uses the relative intensity changes of the reflected red and infrared light (red/infrared ratio) to measure the arterial oxygen saturation. The performance of the reflectance pulse oximeter was studied in acute experiments in fetal lambs. By stepwise reduction of the inspired oxygen concentration of the ewe, measurements were done at the fetal scalp at various arterial oxygen saturation levels (17-82%). Reflectance pulse oximeter readings were averaged over periods of 15 s and compared with simultaneously taken fetal arterial blood samples. A calibration curve for the relationship between red/infrared ratio and arterial oxygen saturation was obtained from 53 measurements in four fetal lambs, by linear regression analysis [red/infrared = 4.088-(0.038.SaO2), r = 0.96]. In these experiments, the pulse oximeter showed a precision of 4.7% oxygen saturation around the calibration curve, with a 95% confidence interval of +/- 9.4%.

Analytical calculations and Monte Carlo simulations of laser Doppler flowmetry using a cubic lattice model.

In addition to the static cubic lattice model for photon migration in turbid biological media by Bonner et al. [J. Opt. Soc. Am. A 4, 423-432 (1987)], a dynamic method is presented to calculate the average absolute Doppler shift as a function of the distance between the point of injection of photons into the medium and the point of detection. At every lattice point a moving particle is assumed with a constant velocity in random directions. The velocity direction fluctuates randomly in time. When a photon is scattered at a lattice point it has a finite probability to be Dopper shifted, since in reality not every scattering event occurs with a moving particle. Calculated average absolute Doppler shifts are verified with Monte Carlo simulations. We verified the applicability of the derived formulas for continuous isotropic and continuous anisotropic media. Good agreement is found between the calculated and simulated average absolute Doppler shifts. Small differences between calculated and simulated average abso ute Doppler shifts can be explained by the assumptions made in the theory. Furthermore the calculations of the average absolute Doppler shift confirm the theory of Bonner et al. that the first moment ?omega? of a spectrum S(omega) measured with a blood perfusion meter is linearly proportional to the average number m of scattering events with a moving particle in case of m < 1 and linearly proportional to the square root of m in the case of m > 1. It is confirmed that the average absolute Doppler shift depends on the average number of scattering events at the position of the detection. This effect is, apart from the size and position of the probe volume, essential for the interpretation of the signal measured with a laser Doppler perfusion meter.

Laser Doppler velocimeter based on the self-mixing effect in a fiber-coupled semiconductor laser: theory.

A laser Doppler velocimeter that consists of a semiconductor laser coupled to a fiber and that uses the self-mixing effect is presented. The velocimeter can be used for solids and fluids. A theoretical model is developed to describe the self-mixing signals as a function of the amount of feedback into the laser and the distance from the laser to the moving object. Good agreement is found between this theory and measurements.

Self-mixing laser-Doppler velocimetry of liquid flow and of blood perfusion in tissue.

The velocimetry method of self-mixing, i.e., the feedback of Doppler-scattered light into the laser cavity, is used for the measurement of liquid flow and of blood perfusion in human tissue. The method is elucidated by the registration of the blood perfusion of a finger under repeated occlusion of the veins in the upper arm and with the velocity measurement of a liquid flow containing scattering particles.