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Baby in the NICU

Getting to the heart of cardiac output

Baby in the NICU

To keep infants in the neonatal intensive care unit (NICU) as healthy as possible, it’s important to keep close tabs on their vital signs. During their NICU stay, most babies have continuous monitoring of their blood pressure, respiratory rate and blood oxygen saturation. And although continuous monitoring of heart rate is also typically standard, other information about heart function – such as cardiac output, a measure of how well the heart is pumping blood – remains a challenge to obtain in these vulnerable babies.

Clinical markers like blood pressure, heart rate and urine output are available, but they are indirect measures of cardiac output, how much blood the heart pumps per minute. Less invasive techniques, such as Doppler ultrasound, can be imprecise. Respiratory mass spectrometry or catherization would provide more precision by directly calcuating cardiac output but carry risks or are not feasible for neonates.

Clinicians at Children’s National Health System hypothesized that COstatus monitors could offer a way to directly measure cardiac output among neonates. The COstatus monitor – a minimally invasive way to measure hemodynamics – captures cardiac output, total end diastolic volume, active circulation volume and central blood volume.

The research team tested the approach by leveraging ultrasound dilution: Injecting saline, which has an ultrasound velocity of 1533m/second, slows the ultrasound velocity of blood from its normal rate of 1580m/second and produces a dilution curve.

“It is feasible to directly measure neonatal cardiac output by ultrasound dilution via the COstatus monitor in the first two weeks of life with no adverse events,” says Khodayar Rais-Bahrami, M.D., a Children’s neonatologist and senior author for the research presented during the Pediatric Academic Societies 2018 annual meeting. “When we took consecutive measurements, we saw very little variance in the parameters.”

The COstatus monitor uses an extracorporeal loop that is connected to arterial and venous catheters. The 12 neonates included in the study already had umbilical venous catheters as well as either a peripheral arterial line or umbilical arterial catheter. The infants ranged in weight from 0.72 to 3.74 kg and were born at 24 to 41.3 gestational weeks.

The infants’ cardiac output was measured 54 times from 1 to 13 days of life. Up to two measurement sessions occurred daily for a maximum of four days. The mean cardiac output was 0.43 L/minute with a mean cardiac index of 197mL/kg/minute.

Future research will describe normal cardiac output ranges for neonates as well as how these measurements evolve during the first week of life.

In addition to Dr. Rais-Bahrami, study co-authors include Simranjeet S. Sran, M.D., and Mariam Said, M.D., a Children’s neonatologist.

newborn in incubator

Tracking oxygen saturation with vital signs to identify vulnerable preemies

 

Khodayar-Rais-Bahrami

What’s known

Critically ill infants in neonatal intensive care units (NICU) require constant monitoring of their vital signs. Invasive methods, such as using umbilical arterial catheters to check blood pressure, are the gold standard but pose significant health risks. Low-risk noninvasive monitoring, such as continuous cardiorespiratory monitors, can measure heart rate, respiratory rate and blood oxygenation. A noninvasive technique called near-infrared spectroscopy (NIRS) can gauge how well tissues, including the brain, are oxygenated. While NIRS long has been used to monitor oxygenation in conditions in which blood flow is altered, such as bleeding in the brain, how NIRS values relate to other vital sign measures in NICU babies was unknown.

What’s new

A research team led by Khodayar Rais-Bahrami, M.D., a neonatologist at Children’s National Health System, investigated this question in 27 babies admitted to Children’s NICU. The researchers separated these subjects into two groups: Low birth weight (LBW, less than 1.5 kg or 3.3 pounds) and moderate birth weight (MBW, more than 1.5 kg). Then, they looked for correlations between information extracted from NIRS, such as tissue oxygenation (specific tissue oxygen saturation, StO2) and the balance between oxygen supply and consumption (fractional tissue oxygen extraction, FTOE), and various vital signs. They found that StO2 increased with blood pressure for LBW babies but decreased with blood pressure for MBW babies. Brain and body FTOE in LBW babies decreased with blood pressure. In babies with abnormal brain scans, brain StO2 increased with blood pressure and brain FTOE decreased with blood pressure. Together, the researchers suggest, these measures could give a more complete picture of critically ill babies’ health.

Questions for future research

Q: Can NIRS data be used as a surrogate for other forms of monitoring?

Q: How could NIRS data help health care professionals intervene to improve the health of critically ill infants in the NICU?

Source: Significant correlation between regional tissue oxygen saturation and vital signs of critically ill infants.” B. Massa-Buck, V. Amendola, R. McCloskey and K. Rais-Bahrami. Published by Frontiers in Pediatrics Dec. 21, 2017.