Over the next few days several PAADs will be devoted to hypotension. I’m reposting this PAAD published a few months ago to set the stage.
On the first day on the pediatric anesthesia resident rotation, there is invariably the panicked call for help by the new anesthesia resident who with a loaded syringe of phenylephrine in hand is ready to treat, or already treating hypotension, that is, BPs less than 100 mm Hg. After a brief moment, you ask/tell the resident in the “voice of command” to “put down the syringe” and point out that blood pressures are normally lower in children and IV fluids (volume) and turning down the volatile anesthetic agents are the first line of therapy, not vasoactive agents like phenylephrine. But, the resident asks: “How low is low and how and when do you decide to treat?” In 2022, it’s pretty simple…you instruct the resident to download the Society for Pediatric Anesthesia’s Pedi Crisis app and go to the HYPOTENSION tab to discover normal for age BP values and a decision tree on how and when to treat. Simple enough? Well not exactly. In Very Low Birth Weight (VLBW) newborns (<1500 grams), the norms for BP even in 2022 are not so clear. Further, in the operating room, we are not only dealing with emergent, critically ill neonate, who usually arrive to the OR fluid depleted and in extremis, we are compounding the issue of hypotension and hypoperfusion by our anesthetic drugs, blood and evaporative fluid loss, and a cold environment. Today’s PAAD reviews a recent article that provides some insight from the NICU.
And Happy Halloween to all! Myron Yaster MD
Original article
Jay P Goldsmith, Erin Keels and Committee On Fetus And Newborn And The National Association Of Neonatal Nurses. Recognition and Management of Cardiovascular Insufficiency in the Very Low Birth Weight Newborn. Pediatrics. 2022 Mar 1;149(3):e2021056051. PMID: 35224636
Caring for very low birth weight (VLBW) infants is a technical challenge for all of us. Often these infants are quite ill, require urgent or emergent surgery under emotionally difficult conditions. The basic internist medical consultant recommendation: “avoid hypoxia, hypotension, and hypothermia can be a significant challenge. I (MY) have always hated this medical consultant recommendation…not that it’s wrong but have always wondered who these consultants recommend hypoxia and hypotension for? But I digress…In infants, and particularly VBLW infants, we would add a fourth “h” – hyperoxia; but we will leave that for another issue of PAAD.
Recently the AAP published a clinical report which provides an excellent update on “Recognition and Management of Cardiovascular Insufficiency in the Very Low Birth Weight Newborn” The paper is an update on a 2011 practice guideline from NANN on managing hypotension in VLBW infants.
Key points:
1. The consequences of hypoperfusion can be devastating. Short of death of the infant, end organ damage, including renal failure, lung injury, intraventricular hemorrhage (IVH), and long-term neurodevelopmental impact.
2. We use BP as a gauge of systemic hypoperfusion and in the VLBW, measuring BP accurately is a challenge (see below). It is not the only gauge of hypoperfusion though. Capillary refill times, urine output, NIRS and other signs of end organ perfusion are equally or more important.
3. There is no consensus that a specific blood pressure (BP) threshold in VLBW infants predicts hypoperfusion and end organ damage.
4. Frequently used numeric thresholds, such as a BP measurement that is below a mean arterial pressure (MAP) of 30 mmHg, or a MAP value that is less than the infant’s gestational age in weeks, are arbitrary and not
supported by high-level evidence. Currently the Pedi Crisis app does not have these values and may be an issue for upcoming versions of the app.
5. Published arbitrary values that reflect population “norms” will vary by gestational age, postnatal age, and weight and do not necessarily correlate with inherent physiologic responses or cardiovascular insufficiency.
6. What is hypotension in VLBW?
a. The most common definitions of hypoperfusion in the neonate, during the transition, are (1) a BP measurement that falls below a MAP of 30 mmHg, or (2) a MAP that is less than the gestational age (in weeks) of the infant.
b. The Management of Hypotension in the Preterm Extremely Low Gestational Age Newborn (HIP) Trial defined hypotension as a MAP “1 mmHg below a MAP value equivalent to gestational age that persisted over a 15-minute period.”
c. Because 90% or more of extremely preterm infants born between 23 and 26 weeks’ gestation will maintain a MAP of 30 mmHg or greater after 3 postnatal days,46 many investigators, including the HIP Trial group, used this definition to specify hypotension in the first 72 hours of life.
7. How do you measure blood pressure accurately in the VLBW?
a. The standard measurement of MAP is through the use of an arterial catheter, either peripherally inserted through the radial artery or centrally inserted through the umbilical artery. This method provides direct measurement but is subject to numerous problems.
b. The accuracy of noninvasive cuff BP readings can be confounded by the size and fit of the cuff on the infant’s limb, the infant’s position (prone or supine), and the infant’s state of arousal.
8. Evolving techniques to assess organ blood flow and low system blood flow.
Perhaps a combination of perfusion index (difference between the infrared signal of pulsatile and non-pulsatile flow), functional echocardiography, amplitude-integrated electroencephalography (aEEG), and near-infrared spectroscopy (NIRS) may provide a method for noninvasive, continuous monitoring of the hemodynamics and perfusion in neonates during transition, but more research is needed. And, some of these techniques are quite difficult to do in the current operating room environment. However, NIRS is now a near universal feature of most cardiac anesthetics. Should we incorporate it in ALL newborn anesthetics?
9. The authors go on to discuss the effectiveness of various pharmacologic interventions which are available to support blood pressure, cardiac output and systemic perfusion.
Recommendations from the Clinical Update
The diagnosis of cardiac insufficiency in the VLBW infant should not be based on a threshold BP value alone. The measurement of BP in this population is not simple and may be erroneous.
a. Assessment of BP should be based on multiple parameters including gestational age, weight, and postnatal age using standardized tables.
b. The treatment of cardiac insufficiency is not without hazard, and the decision to treat should consider the potential complications of such treatment.
c. Delayed cord clamping, decreased blood sampling, appropriate ventilatory management (ie, avoiding excessive mean airway pressure and hypocarbia), and other attempts to avoid hypovolemia, anemia, and decreased cardiac output may have an important role.
So, what should we do tomorrow if we have a VLBW infant for an urgent procedure under anesthesia? Stay tuned!