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• Physiolgical transition ?
  David J Hutchon
  Published on: 5 January 2018
• Answer to: "Physiolgical transition ?"
  Jeroen J van Vonderen
  Published on: 22 March 2016

• Published on: 5 January 2018

  Physiolgical transition ?

  • David J Hutchon, Emeritus Consultant Obstetrician Darlington Memorial Hospital

  Dear Sir,

  We congratulate the authors on this study of neonatal transitional circulation performed so quickly after birth. The authors state that the ductal flow ratio reported in their study reflects pulmonary and haemodynamic transition and can be used to monitor neonatal transition in healthy infants. The implication is that their study describes a physiological transition in healthy term infants, but we question that this is the case.

  Delivery by elective caesarean section is not a physiological birth but it does permit the neonate an atraumatic birth. We are particularly concerned that the transition may have been disrupted by the timing of cord clamping which was between 30 and 60 seconds. While this is considered delayed cord clamping by some, most guidelines recommend a minimum of 60 seconds have elapsed before the circulation is interrupted by cord clamping. The WHO advises 3 minutes.(1) Not all of the babies in the series had established respiration before clamping and cord clamping before the onset of respiration has a marked effect on cardiac output.(2) It is therefore questionable that the mean and range of results published represents a normal transition in healthy infants.

  The normal fetal circulation is well described with the two ventricles pumping in parallel, the right ventricular output being significantly more than the left and the flow across two shunts, right to left in the ductus arteriousus and right to left across the foram...

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  Dear Sir,

  We congratulate the authors on this study of neonatal transitional circulation performed so quickly after birth. The authors state that the ductal flow ratio reported in their study reflects pulmonary and haemodynamic transition and can be used to monitor neonatal transition in healthy infants. The implication is that their study describes a physiological transition in healthy term infants, but we question that this is the case.

  Delivery by elective caesarean section is not a physiological birth but it does permit the neonate an atraumatic birth. We are particularly concerned that the transition may have been disrupted by the timing of cord clamping which was between 30 and 60 seconds. While this is considered delayed cord clamping by some, most guidelines recommend a minimum of 60 seconds have elapsed before the circulation is interrupted by cord clamping. The WHO advises 3 minutes.(1) Not all of the babies in the series had established respiration before clamping and cord clamping before the onset of respiration has a marked effect on cardiac output.(2) It is therefore questionable that the mean and range of results published represents a normal transition in healthy infants.

  The normal fetal circulation is well described with the two ventricles pumping in parallel, the right ventricular output being significantly more than the left and the flow across two shunts, right to left in the ductus arteriousus and right to left across the foramen ovale. The normal neonatal circulation is also well described with equal outputs by both ventricles and closed shunts. A closer look at the results suggest some anomalous flow not readily compatible with the end result of the neonatal circulation. For example at ten minutes the mean right ventricular output is 343 mls/kg/min and mean left ventricular output is 212 mls/kg/min and the DA flow is 8mls/kg/min left to right. (ratio R to L =0.9). Where does the right ventricle get the 343 output as only 212 - 8 are reaching the systemic circulation and returning to the right atrium. Also if the pulmonary blood flow is 343+8 = 351, the excess of 141 must be spilling left to right across the foramen ovale. Reverse flow in the foramen ovale is described but has not been quantified. We question that these flows are evidence that this heart is now close to transitioning to a parallel ventricular pattern with equal outputs. Reverse flow across the foramen ovale of 141 is contributing to over 40% of the right ventricular output. This blood has just been through the pulmonary circulation and is oxygenated but is now returning to the right ventricle to be pumped through the pulmonary circulaton once more. Such flow is completely inefficient. Can the authors explain this anomaly in physiogical terms or could this finding in fact be a demonstration that the early clamping at under 60 seconds sometimes before the onset of respiration has indeed disrupted the transitional circulation ?

  Reference 1. World Health Organization (WHO), US Agency for International Development (US AID), Maternal and Child Health Integrated Program (MCHIP). (2013). Delayed cord clamping of the umbilical cord to reduce infant anaemia. Updated 2013. Available from: http://www.mchip.net/node/1562 (Accessed June 12, 2014). 2. Bhatt S, Alison BJ,Wallace EM, Crossley KJ, Gill AW, Kluckow M, et al. Delaying cord clamping until ventilation onset improves cardiovascular function at birth in preterm lambs. J Physiol 2013 591(Pt 8): 2113-26.

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  Conflict of Interest:
  I am a co-inventer of the LifeStart trolley

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• Published on: 22 March 2016

  Answer to: "Physiolgical transition ?"

  • Jeroen J van Vonderen, PhD-student
  • Other Contributors:
    • Arjan B. te Pas, Stuart B. Hooper and Arno A.W. Roest

  Response to "Physiological transition ?"

  Thank you for your response to our research "Non-invasive measurements of ductus arteriosus flow directly after birth".

  We agree with Dr. Hutchon that a caesarian section can influence the respiratory transition of a newborn infant. As such, our results reflect the transition after elective caesarian section with cord clamping within 1 minute after birth, which...

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  Response to "Physiological transition ?"

  Thank you for your response to our research "Non-invasive measurements of ductus arteriosus flow directly after birth".

  We agree with Dr. Hutchon that a caesarian section can influence the respiratory transition of a newborn infant. As such, our results reflect the transition after elective caesarian section with cord clamping within 1 minute after birth, which we have indicated is a limitation of our study as stated in the Discussion section of our manuscript. However, as cord clamping was delayed between 30-60 s after birth, most newborns will have commenced breathing before the cord was clamped. While many guidelines suggest a fixed time interval of 1-3 minutes between birth and cord clamping, this is not physiological and is only relevant to individual infants because most infants will have commenced breathing within this time. We agree that infants that did not started breathing sufficiently before cord clamping could have had a less efficient transition, but our small sample size prohibits a more detailed subgroup analysis. However, as all of these infants had a normal "clinical" transition and did not require respiratory support or any other specialized medical care, we feel that the potential influence of cord clamping before the start of breathing had no significant clinical impact. With regard to the WHO advice, the observations from Bhatt et al. show that the timing of cord clamping is probably less important than the occurrence of breathing before the cord is clamped.(1) It would be interesting to compare the transition of neonates after vaginal delivery to our results. However, no data within the first 10 minutes after vaginal delivery is present as our report is the first to assess hemodynamic changes during this time frame. This study may therefore be regarded as a starting point for future research on hemodynamic changes directly after birth.

  As we have described in a previous publication, aeration of the lung and the consequent rise in preload is most likely responsible for the increase in left ventricular output (LVO).(2) The increase in preload will cause a pressure gradient to exist over the Ductus Arteriosus (DA) and foramen ovale (FO). As Dr. Hutchon suggests the resulting shunt over the FO could explain differences between LVO and right ventricular output (RVO). However, we must stress that the simple mathematical calculation of adding or subtracting mean blood flows and outputs from a group of infants, which were measured using echocardiography at different time points is not a legitimate way of making comparisons. The values stated in our manuscript are mean values and although they were all measured within a small time range, it is not possible to make these measurements simultaneously. As these parameters are very dynamic and change over time, ideally they should be measured simultaneously and comparisons should be made in individual infants rather between groups means. Furthermore, Doppler derived measurements of absolute volume are based on several assumptions and cardiac output can range from 150 ml/kg/min to 273 ml/kg/min for LVO and from 200 to 310 ml/kg/min for RVO in term neonates depending on the site of measurement, the vascular diameter and Doppler method used.(3) As such we believe that the calculation of shunting across the FO as done by Dr. Hutchon is based on too many assumptions for any valid conclusions to be drawn. We consider that our figures are neither an anomaly nor a sign of a disrupted transitional circulation, but merely reflect the suboptimal assessment of absolute volumes with echocardiography.

  This is the main reason that we did not focus on the absolute differences between LVO and RVO at the described time points. Instead we used the Doppler derived measurements to assess differences over time during the first 10 minutes after birth in LVO, RVO and blood flow shunt over the DA. Furthermore, we calculated the ratio between DA right-to-left vs. left-to-right flow based on the velocity time integral of the flow patterns. As this is a dimensionless parameter that is not influenced by assumptions or inaccuracies in the measurement of vessel diameter, it is more appropriate to use for investigations into the hemodynamic transition.

  The matter of whether left-to-right shunting across the FO is a normal physiological process is an interesting point and one that hasn't really been addressed previously, mostly because it was previously considered to be a one way valve. Nevertheless, as the two ventricles act as two independent pumps working at different outputs throughout fetal life, we consider that it is unrealistic to expect that the ventricles will immediately synchronize their outputs at birth. Instead we believe that there will be a period of adjustment during the immediate newborn period and theoretically bidirectional flows in both the FO and the DA would allow both ventricular outputs to come into balance without triggering systemic hypotension or pulmonary hypertension.

  References

  (1) Bhatt S, Alison BJ, Wallace EM, Crossley KJ, Gill AW, Kluckow M, et al. Delaying cord clamping until ventilation onset improves cardiovascular function at birth in preterm lambs. J Physiol 2013;591:2113 -26.

  (2) van Vonderen JJ, Roest AA, Siew ML, Blom NA, van Lith JM, Walther FJ, et al. Noninvasive measurements of hemodynamic transition directly after birth. Pediatr Res 2014;75:448-52.

  (3) de Waal KA. The methodology of Doppler-derived central blood flow measurements in newborn infants. Int J Pediatr 2012;2012:680162.

  Conflict of Interest:

  None declared

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  Conflict of Interest:
  None declared.

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