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Re: Echocardiographic assessment of early circulatory status in preterm infants with suspected intra
- Dr Tom Dawson, Dr Jo Fedee, Dr Gemma Holder, Dr Imogen Storey, Dr Imogen Morgan and Mrs Mary Publicover (14 March 2006)
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Preterm Left Ventricular output is not systemic blood flow.
- Nick Evans (29 March 2006)
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Dr Tom Dawson, SpR in Neonatology Birmingham Women's Hospital, Dr Jo Fedee, Dr Gemma Holder, Dr Imogen Storey, Dr Imogen Morgan and Mrs Mary Publicover
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tomcdawson{at}yahoo.co.uk Dr Tom Dawson, et al.
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Dear Editor, We have reviewed this article in our local Neonatal Journal club. We question the parameter used in this study to define the two groups, thus affecting the study conclusions. The authors state their study was "planned to evaluate early circulatory status by echocardiography in VLBW infants who were suspected of contracting intrauterine infection because of a significant increase in serum IgM at birth." This fails to satisfy the first screening question of CASP (Critical Appraisal Skills Programme), "did the study address a clearly focused issue in terms of the risk factors studied?". This article structures study and control groups using one single parameter, namely a serum IgM>20mg/dl at birth. Aspractising neonatal clinicians we have concerns about the use of this as a prognostic factor for suspected intrauterine infection. More traditional parameters for intrauterine infection are quoted in this article (clinical chorioamnionitis, septicaemia, CRP and first white cell count) and are present in both the groups studied. Any of thse parameters are established predictive indices for intrauterine infection. We are unsure why the authors selected this particular parameter of serum IgM in preference to some of the more conventional indices as listed above. The authors compare their results with those of Kempley et al. for superior mesenteric artery studies. However, Kempley selected an infected group on the basis of positive culture from admission ear swabs, gastric aspirate, and blood culture and we would doubt the validity of comparisons with this study. We would be interested to hear from any groups using IgM as the definitive measure of intrauterine infection. Yours Faithfully The BWH Neonatal Journal Club Dr Tom Dawson, SpR in Neonatology References 1) Kempley ST, Murdoch E. Splanchric haemodynamic disturbances in perinatal sepsis. Arch Dis Child Fetal Neonatal Ed. 2000; 83. F139-42. 2) WWW.phru.nhs.uk.casp |
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Nick Evans, Neonatologist Royal Prince Alfred Hospital and University of Sydney
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nevans{at}med.usyd.edu.au Nick Evans
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Dear Editor, The premise of the data interpretation in this paper is based on the rather tenacious neonatal myth that left ventricular output is a measure of systemic blood flow. This is not true in the transitional circulations because of patency of the ductus arteriosus. Preterm babies demonstrate very variable degrees of ductal constriction in the early postnatal hours and the dominant shunt direction is left to right. In those where ductal constriction fails, significant volumes of blood can move from the systemic to the pulmonary circulation even in the early hours after birth. The ductus in this situation shows a spectrum of significance that cannot be controlled for by simply representing it as open or closed, as has been done in this paper. In this haemodynamic, LVO becomes the sum of systemic blood flow and the ductal shunt, so can and often will significantly overestimate systemic blood flow. Paradoxically LVO in this situation is actually measuring pulmonary blood flow. RVO is a much better measure of systemic blood flow although this in turn can be confounded by atrial shunts. Thus in this paper the observation of higher LVO at 12 hours in the "infection" group may well reflect worse ductal constriction and resulting higher pulmonary blood flow. From these data it is not possible to draw any conclusions about the state of the systemic circulation. |
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