Much has been written on the topic of cord clamping. There is delayed cord clamping of course but institutions differ on the recommended duration. Thirty seconds, one minute or two or even sometimes three have been advocated for but in the end do we really know what is right? Then there is also the possibility of cord milking which has gained variable traction over the years. A recent review was published here.
Take the Guessing Out of the Picture?
Up until the time of birth there is very little pulmonary blood flow. Typically, about 10% of the cardiac output passes through the lungs and the remained either moves up the ascending aorta or bypasses the lungs via the ductus arteriosus. After birth as the lung expands, pulmonary vascular resistance rapidly decreases allowing cardiac output to take on the familiar pattern which we all live with. Blood returning from the systemic venous circulation no longer bypasses the lung but instead flows through pulmonary capillaries picking up oxygen along the way. One can imagine then that if a baby is born and the cord is clamped right away, blood returning from the systemic circulation continues to bypass the lung which could lead to hypoxemia and reflexive bradycardia. This has been described previously by Blank et al in their paper Haemodynamic effects of umbilical cord milking in premature sheep during the neonatal transition.
A group of researchers from the Netherlands published a very interesting paper Physiological-based cord clamping in preterm infants using a new purpose-built resuscitation table: a feasibility study this month. The study centres around a resuscitation table called the Concord that is brought to the mother for resuscitation after birth. The intervention here was applied to infants 26 to 35 weeks gestational age.
The cord was clamped after each of the following was achieved for an infant indicating successful transition with opening of the lung and establishment of an FRC.
1. Establishment of adequate breathing (average tidal volume ≥4 mL/kg) on CPAP. They used a mask capable of measuring expired tidal volumes.
2. HR above 100 bpm
3. SpO2 above 25th percentile using FiO2 <0.4
In this way, the cord was only clamped once the baby appeared to have physiologically made the transition from dependence on umbilical cord blood flow to ventilation perfusion matching in the lung. Although 82 mothers consented only 37 preterm infants were included in the end. Exclusion criteria were signs of placental abruption or placenta praevia, signs of severe fetal distress determined by the clinician and the necessity for an emergency caesarean section ordered to be executed within 15 min. This really was a proof of concept study but the results are definitely worth looking at.
How Did These Babies Do?
There are many interesting findings from this study. The mean time of cord clamping was 4 minutes and 23 seconds (IQR 3:00 – 5:11). Heart rate was 113 (81–143) and 144 (129–155) bpm at 1 min and 5 min
after birth. Only one patient developed bradycardia to <60 BPM but this was during a mask readjustement. The main issue noted as far as adverse events was hypothermia with a mean temperature of 36.0 degrees at NICU admission. Almost 50% of infants had a temperature below 36 degrees. Although the authors clearly indicate that they took measures to prevent heat loss it would appear that this could be improved upon!
What stands out most to me is the lengthy duration of cord clamping. This study which used a physiologic basis to determine when to clamp a cord has demonstrated that even at 1 minute of waiting that is likely only 1/4 of the time needed to wait for lung expansion to occur to any significant degree. I can’t help but wonder how many of the patients we see between 26-35 weeks who have a low heart rate after delivery might have a higher heart rate if they were given far more time than we currently provide for cord clamping.
I can also see why cord milking may be less effective. Yes, you will increase circulating blood volume which may help with hemodynamic stability but perhaps the key here is lung expansion. You can transfuse all the blood you want but if it has nowhere to go just how effective is it?
As we do more work in this area I have to believe that as a Neonatal community we need to prepare ourselves for the coming of the longer delay for cord clamping. Do we need to really have the “Concord” in every delivery or perhaps it is time to truly look at durations of 3-4 minutes before the team clamps the cord.