Variations in prevalence of hypotension, hypertension, and vasopressor use in NICUs.

OBJECTIVE: Very low birth weight infants are vulnerable to hypotension and its associated complications. Vasopressors are used to raise blood pressure (BP), but indications for use are uncertain. Our objectives were (1) to study variations in BP stability among NICUs, (2) to investigate inter-NICU differences in vasopressor use, and (3) to address the association between intraventricular hemorrhage (IVH) and abnormal BPs. STUDY DESIGN: A total of 1288 infants with birth weight <1500 g were admitted to six NICUs in Massachusetts and Rhode Island over 21 months. The lowest and highest mean BPs were collected within the first 12 hours. Also recorded were the use of vasopressors within the first 24 hours and the occurrence of IVH. Logistic regressions were used to model outcomes, controlling for gestational age and illness severity using the Score for Neonatal Acute Physiology. RESULTS: Two of the six NICUs had significantly higher percentages of infants with at least one hypotensive BP, with prevalences of 24% to 45%. Percentages of infants treated with vasopressors ranged from 4% to 39%. This range of vasopressor use could not be explained by inter-NICU differences in birth weight, illness severity, or rates of hypotension. We found a borderline association between severe IVH and hypotension (odds ratio 1.6, p=0.055), but not between severe IVH and hypertension. CONCLUSION: Wide differences exist in the prevalence of hypotension, hypertension, and vasopressor use among NICUs. We also found an association between hypotension and IVH, but not between hypertension and IVH.

Variations in blood transfusions among newborn intensive care units. SNAP II Study Group.

OBJECTIVES: Very low birth weight (< 1500 g) infants frequently require packed red blood cell transfusions, and transfusion rates vary among neonatal intensive care units (NICUs). We analyzed transfusions and compared outcomes among NICUs. STUDY DESIGN: In a 6-site prospective study, we abstracted all newborns weighing < 1500 g (total = 825) born between October 1994 and September 1995. Transfusion frequency and volume and phlebotomy number were analyzed by site and adjusted for birth weight and illness severity. We compared rates of intraventricular hemorrhage, necrotizing enterocolitis, bronchopulmonary dysplasia, growth, and length of stay between the high and low transfuser NICUs. RESULTS: Sites differed significantly in mean birth weight, illness severity, number of transfusions, pretransfusion hematocrit, blood draws, and donor number. Multivariate adjustment for these risks showed that the highest transfusing NICU transfused an additional 24 cc/kg per baby during the first 14 days and 47 cc/kg per baby after 15 days, relative to the lowest transfusing NICU. The presence of arterial catheters increased the frequency of blood transfusions. The rates of intraventricular hemorrhage, necrotizing enterocolitis, and bronchopulmonary dysplasia were not higher in the 2 lowest transfusing NICUs, nor were there differences in 28-day weight gain or length of stay. CONCLUSIONS: Major differences in transfusion practices for very low birth weight infants exist among NICUs. Because clinical outcomes were no different in lower transfuser NICUs, it is likely that transfusion and phlebotomy guidelines could result in fewer transfusions, fewer complications, and reduced cost.

Effect of varying inspiratory and expiratory times during high-frequency jet ventilation.

Although high-frequency jet ventilation may reduce barotrauma, the optimal ventilator settings at which complications are minimized have not been determined. To develop ventilator strategies applicable to the human infant, we studied six New Zealand rabbits before and after saline lung lavage. Changes in functional residual capacity (delta FRC) and airway pressure gradient (peak inspiratory pressure minus positive end-expiratory pressure) were measured while inspiratory time (TI) and expiratory time (TE) were varied. Frequencies of 120, 240, and 480 cycles per minute and inspiratory to expiratory ratios of 1:1, 1:3, 1:5, and 1:9 resulted in TI that varied from 12 to 250 msec, and TE from 62 to 450 msec. Analysis of variance demonstrated that as TI was shortened, a significantly higher airway pressure gradient was necessary to maintain a constant tidal volume. As TE was shortened, air trapping, as determined from both inadvertent positive end-expiratory pressure and delta FRC, significantly increased. Lung lavage increased the airway pressure gradient at each TI, but decreased air trapping at each TE. At no time did entrainment contribute to the delivered tidal volume. We conclude that a relatively narrow range of TI and TE may be necessary for optimal use of high-frequency jet ventilation to reduce airway pressures and minimize the risk of air trapping.

Measurement of tidal volume during high-frequency jet ventilation.

The measurement of tidal volume during high-frequency jet ventilation is difficult due to the high-frequency components of the inspiratory flow. To validate tidal volume measured with a screen pneumotachograph placed on the expiratory limb, we simultaneously determined tidal volume with a body plethysmograph in seven anesthetized normal adult New Zealand rabbits before and after saline lung lavage. Four to six comparisons of tidal volume were obtained by varying peak inspiratory pressures at each combination of frequency (120, 240, and 480/min) and inspiratory to expiratory time ratio (1:1, 1:3, 1:5, 1:9). Overall, 90% of the tidal volumes measured with the pneumotachograph were within 10% of 1 ml of the volumes determined with the plethysmograph, independent of frequency, inspiratory to expiratory time ratio, and lung compliance. There was unidirectional outward flow at the pneumotachograph during inspiration when both normal and saline lavaged lungs were being ventilated, suggesting a lack of gas entrainment. We conclude that a pneumotachograph on the expiratory limb may be used to measure tidal volume and gas entrainment in vivo during high-frequency jet ventilation. Determination of tidal volume may serve to optimize ventilator settings during high-frequency jet ventilations and facilitate an understanding of the mechanism involved in gas exchange.

Determination of the spectral emission of commercial flashbulbs by emission spectrographic techniques.

The relative energy distributions of the M-2, P-25, AG-1, and M-3 flashbulbs have been determined over the spectral range from 3400 A to 7600 A, using a National Bureau of Standards lamp as a spectral standard, and a Jarrell-Ash Ebert-mount spectrograph as a spectroradiometer. From these data and the blackbody radiation function, values for the color temperature of the flashbulbs have been calculated using a computer to derive a least-squares, best-fit value of color temperature.