Blood Pressure in Neonates: What is the Target?
Myron Yaster MD, Justin L. Lockman MD, MSEd, and Francis Veyckemans MD
Before we start today’s PAAD, a brief anesthesia history lesson that you might find interesting. When I started my career in the late 1970s, we measured blood pressure in children and adults with a manually inflated BP cuff and auscultation of Korotkoff sounds over the brachial artery. (In adults, the alternative we used at the University of Pennsylvania was an oscillotonometer. Amazingly, I still have mine!). In the operating room, most people accomplished taking a blood pressure by placing a slim rubber stethoscope head over the brachial artery under the BP cuff. Plastic tubing connected the stethoscope to our molded earpiece via a 3-way stopcock. When we wished to take a BP measurement, we switched the stopcock from the precordial stethoscope to the BP cuff stethoscope and inflated the cuff. Unfortunately, this did not work very well in newborns and infants, who were too small for the available BP stethoscopes and in whom Korotkoff sounds were usually unobtainable. Instead, we taped a Doppler ultrasound probe over the brachial or radial artery, inflated a BP cuff and listened for the return of Doppler tones that indicated the systolic BP. Then we wrote the value on our hand-written anesthetic record. This worked most of the time, but the Doppler probe was easily dislodged by small movements, and the setup could be very temperamental.
This changed dramatically with the development of automated non-invasive blood pressure (NIBP) monitors, which also were originally based on oscillotonometry, and were initially studied and validated by Dr. Robert Friesen.1 How he did this was discussed in the November 1, 2021 PAAD, “Remembering the classics: Noninvasive blood pressure monitoring in neonates and infants”.
Unbelievably to me, in 2023, we still don’t have standard values for normal newborn blood pressures that we can reliably use perioperatively. Today’s PAAD is a game changer with a free on line calculator that all of us can and should use. Myron Yaster MD
Original article
van Zadelhoff AC, Poppe JA, Willemsen S, Mauff K, van Weteringen W, Goos TG, Reiss IKM, Vermeulen MJ, de Graaff JC. Age-dependent changes in arterial blood pressure in neonates during the first week of life: reference values and development of a model. Br J Anaesth. 2023 May;130(5):585-594. doi: 10.1016/j.bja.2023.01.024. Epub 2023 Feb 28. PMID: 36858885
What could be more essential than measuring arterial blood pressure perioperatively? Both hypo- and hypertension require immediate intervention during anesthesia. [For more on how best to treat hypotension in children, check out tomorrow’s PAAD on ephedrine dosing – it may surprise you!] But what are “normal” mean, systolic, and diastolic pressures measured non-invasively in the first week of life in full term, premature and extremely low birth weight infants? Most anesthesiologists use the patient’s gestational age as a rule of thumb to estimate expected minimum mean arterial pressure during the first 48 hours after birth, based on a consensus statement of neonatologists2.
Surprisingly, until today’s study by van Zadelhoff et al.3 there were few evidence-based reference values to really guide us during the following days or weeks. This moderate scale (n=607), retrospective cohort study was performed from the Electronic Health Records in a NICU at the Erasmus MC-Sophia Children’s Hospital, Rotterdam, The Netherlands. Key patient demographic information included gestational age, date and time of birth, sex, and weight. Maternal and delivery information were included as well. “Noninvasive arterial pressure measurements were made in low acuity patients at least once every 2 h in the first 24 h after birth and once every 24 h after the first 24 h. Noninvasive arterial pressure was measured with an oscillometric method using Dräger Infinity® M540 monitors”.2 Infants less than 26 weeks gestation were routinely monitored with intra-arterial monitors. Importantly, high-risk patients (ventilated, intracerebral hemorrhage, etc.) and patients with shock requiring inotropes were excluded.
What did they find? “Mean and diastolic arterial pressure rapidly increased within the first day in the lowest gestational age (24–32 weeks) group; the curves flatten thereafter. This observation was most pronounced in patients with the lowest gestational age. The rapid increase in diastolic arterial pressure within the first hours after birth occurred in all gestational age groups. The systolic arterial pressure showed a more gradual increase within the first 48 h[ours] after birth in gestational age groups 24 until 33 weeks with a near linear increase in the older gestational age groups.” Thus, our “rule of thumb” guide is correct in the first day or 2 of life and then fails. The authors built a model that is open sourced and available to all of us to use for the reference values for individual neonates as percentile curves of normal blood pressure for the first 7 days after birth for patients from 24 to 41 weeks of gestation. This model/calculator incorporates both gestational and chronologic age and can be found as a calculator at http://bloodpressure-neonate.com/
When using the calculator, you input the patient’s gestational age and postnatal/chronological age. The calculator provides the median (P50) for mean, systolic, and diastolic blood pressures with -2SD (P2.3), -1SD (P16), +1SD (P84) and +2SD (P97.7). This could be used to determine a neonate’s pre-induction blood pressure baseline value according to its gestational and postnatal age, and could help in diagnosing hypotension under anesthesia. However, it should be kept in mind that the result is population-based and that interindividual variations will still exist (as illustrated in this paper). Moreover, there are no magic numbers: the tolerable drop in systolic or mean blood pressure under anesthesia is lower if the neonate presents with pulmonary hypertension, a congenital heart disease or intracranial hypertension, patients excluded in this study. There is also still much to be discovered about the autoregulation curves (cerebral and otherwise) of neonates,and we don’t yet know if even maintaining the blood pressures at the mean will be protective – after all, many of these smallest infants will go on to develop cognitive deficiencies even without anesthesia, and we don’t yet know which ones (or why).
Nonetheless, this calculator is absolutely revolutionary and fantastic. Because it is open sourced, it could eventually [after further validation of this model with a prospective, multicenter, and ideally multinational study] be put into electronic medical records, the PediCrisis app, or on your cell phone. Alternatively, the web site address could, after this validation, be printed onto the “cheat sheet” educational trifolds that many institutions provide to their trainees.
There are many limitations to this study and therefore the calculator. Only healthy NICU patients were studied and obviously none of the patients were anesthetized. Future studies championed by SPA’s Quality and Safety Committee and the Informatics group working with the authors could address these issues and even expand the observations beyond the first weeks of life. After all, we already make these routine measurements in all of our practices, and mining them should be “a low-lying fruit.”
As the authors conclude: “Reference values for noninvasive blood pressure for various age groups presented here will be useful in guiding clinical decision-making for preterm and term born neonates in the first week of life in intensive care units and by inference during anaesthesia.”2
Download the calculator today, and let us know what you think!
http://bloodpressure-neonate.com/
References
1. Friesen RH, Lichtor JL. Indirect measurement of blood pressure in neonates and infants utilizing an automatic noninvasive oscillometric monitor. AnesthAnalg. 1981 1981;60(10):742-745. Not in File.
2. (Levene MI. Development of audit measures and guidelines for good practice in the management of neonatal respiratory distress syndrome. Report of a Joint Working Group of the British Association of Perinatal Medicine and the Research Unit of the Royal College of Physicians. Arch Dis Child 1992; 67: 1221-7)
3. van Zadelhoff AC, Poppe JA, Willemsen S, et al. Age-dependent changes in arterial blood pressure in neonates during the first week of life: reference values and development of a model. British journal of anaesthesia. May 2023;130(5):585-594. doi:10.1016/j.bja.2023.01.024