A STANDARD PROTOCOL FOR BLOOD-PRESSURE MEASUREMENT IN THE NEWBORN

Objectives. Improvements in neonatal care have resulted in increasing survival of extremely premature infants whose hospital course often ru ns into weeks or months. Some interventions during the acute care of t hese neonates, such as umbilical catheterization and use of steroids, not infrequently result in elevation of blood pressure (BP). It is, th erefore, essential that these infants be monitored accurately for poss ible hypertension during their convalescence. Unfortunately, normative data on BF in this population are scant and comparison of data from v arious studies is hampered by methodologic differences in design. Stud ies in adults address the necessity for a restful state, adopting a co mfortable position, and attempts to reduce the startle response to ini tial cuff inflation. Studies in the newborn using the oscillometric te chnique have not addressed these concerns. A standard BP measurement p rotocol was studied to determine the effect of ensuring a restful stat e, startle response to cuff inflation, and infant position on BP in cl inically stable low birth weight infants after the first week of life. Study Design. The Dianamap oscillometer was used to measure BP in inf ants with a birth weight <2500 g between 7 and 42 days postnatal age. Each infant was studied only once when they were clinically stable. BP was measured in two positions, prone and supine, in random order. Inf ants were studied at least 11/2 hours after their last feeding or medi cal intervention. An appropriate sized cuff was applied to the right u pper arm and the infant was positioned according to randomization. The infant was then left undisturbed for at least 15 minutes or until the infant was sleeping or in a quiet awake state. Three successive BP re cordings were taken at 2-minute intervals. The infant's position was C hen reversed and another 15 minutes of quiet time was allowed. Thereaf ter, a second set of three successive BP recordings were obtained. The most recent routine nursing BP measurement was also recorded. Data we re analyzed using analysis of variance and are presented as means and standard errors of the mean. Results. Sixty-four infants were studied. Birth weights ranged from 901 to 2423 g and gestational ages from 26 to 37 weeks. Overall, mean BP was significantly lower in the prone tha n supine positions (45.7 +/- 0.7 vs 47.8 +/- 0.8 mm Hg, P < .002). In either position, the first measurement was significantly higher than t he third (average difference was 3 mm Hg, P < .003). In general, the r elationships among position and order of measurement were similar for systolic and diastolic BP. Mean BPs obtained by routine nurse measurem ents were significantly higher than those in either position using our standard protocol (54.4 vs 47.0 or 49.1 mm Hg, P < .003). Moreover, t he routine nurse measurements varied more widely than did those obtain ed using the standard protocol. The standard deviation for the routine mean BP measurements by nurses was 11.4 compared with 6.8 and 8.2 for the first measurements in the prone and supine positions, respectivel y, with the standard protocol. The mean BP measurements made in the su pine position (the highest measurements obtained) using the standard p rotocol were also significantly lower than published values: 57 of 64 measurements were less than the average mean BP for age described by T an (J Pediatr. 1988; 112: 266-270). Conclusion. The statistically sign ificant difference between the prone and supine position and among suc cessive measurements in each position are not clinically relevant. The clinically significant differences between measurements obtained with this standard protocol and routine nursing measurements or published data are the result of ensuring a restful state after cuff application . We believe that measurements thus obtained are more representative o f true resting BPs in these infants. We propose that a single measurem ent obtained after a restful state has been assured after cuff applica tion would be practical for routine newborn care and be more represent ative of basal BP than that obtained immediately after cuff applicatio n. Normative data in convalescing low birth weight infants should be g enerated using a protocol that emphasizes a rest period after cuff app lication.