Blood pressure and blood volume in preterm infants.

Abstract

Neonatal respiratory distress syndrome EDITOR,-Professor Southall and colleagues' question the comments of the working group on the management of neonatal respiratory distress syndrome regarding parameters of oxygenation.2 We write in support of the provisional and practical suggestion of an arterial oxygen saturation (Sao2) range of 85-93% and suggest that much of the data quoted by Southall et al is not applicable to this clinical setting.Professor Southall and colleagues suggest an upper limit for Sao2 of 96% and quote four studies in support of this choice. In two of these papers,3 4 the majority of the patients were not preterm and were receiving treatment for other conditions, mainly congenital heart disease. These infants constitute a very different population from those suffering from respiratory distress syndrome. Our own study of 477 measurements made in clinical practice using Ohmeda Biox oximeters on a population under 33 weeks' gestation found that if the saturation value was 93% or below the arterial oxygen tension (Pao2) was never greater than 12 kPa. Our recommended lower limit for saturation was originally based on a study of 'well' preterm infants at discharge from hospital. It has now been confirmed in a study of nondistressed preterm neonates investigated during their first week of life.4 It does not seem unreasonable to aim to achieve the same range of Sao2 in 'sick' preterm infants. The argument that the latter group had recently experienced a physiological intrauterine PaQ2 of 4-5-6-0 In 31 infants the mean arterial blood pressure (MABP) was measured by invasive arterial methods. Blood volume was assessed using an indocyanin green dye dilution method described previously in this age group.2 The infants had a median gestational age of 26 weeks (range 25-31 weeks) and a median birth weight of 900 g (range 580-1380 g). Readings were all obtained in the first three days of life.The median blood volume observed in our infants was 85 ml/kg (range 46-131 ml/kg), very similar to both the 83 ml/kg of Bauer et al and to previously published data. We found a median MABP of 36 mm Hg (range 18-47). We found no significant relationship, on regression analysis, between observed blood volume and MABP, p=0-42 (figure).

Treating hypotension in the preterm infant: when and with what: a critical and systematic review

“…61 However, most infants who are hypotensive are not hypovolemic, but have normal circulating blood volumes. Cohort studies performed 13 to 30 years ago by Barr, 62 Wright 63 and Bauer 64 showed no relationship between blood volume and BP, a more recent study confirms this. 65 There are many uncontrolled evaluations of the effect of volume infusion which were not eligible for our systematic review, many of which showed little or no response to volume administration.…”

”Children are not Small Adults!“

“…Numerous investigators have failed to demonstrate an increase in blood pressure with expansion of the plasma volume in the neonatal age group – the use of dopamine appears to be much more effective in this regard (28, 31, 34–36). Unfortunately, an understanding of the physiologic basis for these abnormalities in peripheral vasoregulation during the neonatal period is far from complete.…”

Haemodynamically unstable preterm infant: an unresolved management conundrum

“…Gestational age and day of life had significant correlations for both systolic and diastolic BP (p<0.0001). Given that the correlation between BP and blood volume is poor [67], volume expansion should be used judiciously when targeting numerical hypotension. Volume expansion could be considered in the setting of hypovolaemia (antepartum haemorrhage, donor twin) and/or suggestive echocardiographic features.…”