Oxygen Saturation in Preterm Infants: Hitting the Target

Laura A. Stokowski, RN, MS


February 06, 2014

In This Article


Babies whose oxygen saturation levels fluctuate widely and repeatedly are often called "swingers" by NICU nurses. Typically, these babies are on CPAP, a mode of respiratory support that is particularly prone to unstable SpO2 levels because it is relatively easy for positive pressure to escape into the surrounding air rather than reach the baby's lungs. Rapid oxygen desaturation can be precipitated by crying, squirming, and even small positional changes that dislodge the prongs or mask, not to mention the apnea and periodic breathing that are characteristic of these infants.

When the baby's SpO2 level drops, some nurses, after assessing the infant for an obvious and correctable cause, will opt for the "wait it out" approach, but this inevitably means a prolonged episode in the hypoxic range before the infant recovers. Other nurses respond with a miniscule change in FiO2, but it is frustratingly easy to overshoot and cause the SpO2 to swing up into the hyperoxia range. The entire shift is an endless exercise in silencing alarms and dialing the FiO2 up and down, while you wonder, for the umpteenth time, whether automated oxygen control for the neonate will ever be perfected.[2]

By studying a sample of preterm infants on CPAP, Lim and colleagues remind us how labile these infants can be, and hold up a mirror for us to reflect on how we manage (or fail to manage) supplemental oxygen delivery in the NICU. The 31% of the time that infants spent in the target range is lower than the average time found in previous research,[3] but it is obviously good news that only 9% of the total SpO2 recording time was spent in the hypoxic range. I would have expected this number to be higher. However, it must be evaluated in context with the alarm limits used in this study, which were perhaps a little lower than those in many NICUs, and certainly lower than what are now recommended.

The 59% of time in the hyperoxia range is less unexpected, but concerning nonetheless. Personal observation in the NICU tells me that nurses get much less excited by "high sats" than "low sats," which is unfortunate, because the nature of oxygen saturation monitoring is such that at higher levels, a small change in oxygen saturation can result in a very big, and dangerous, increase in the arterial blood oxygen level (remember the oxyhemoglobin/saturation dissociation curve?), elevating the risk for toxicity in infants on supplemental oxygen.

Saturation Targets: What's Just Right?

Oxygen saturation targets for preterm infants have been the subject of research, debate, and controversy ever since the use of pulse oximetry became standard in the NICU. It is a complicated, "pick your poison" sort of issue, and the question about what is really best for the babies, if answered at all, is always couched in uncertainty and qualified by the "need for further research." It is doubtful that the kind of randomized trial that would be definitive will ever be attempted.

We now have the results of a systematic review and meta-analysis[4] of the major studies of outcomes of what have come to be known as "low" vs "high" oxygen saturation targets for extremely preterm infants, the most vulnerable population with respect to oxygen levels. With data from almost 5000 infants born at < 28 weeks' gestational age, the risk for mortality and necrotizing enterocolitis were significantly increased in low (85%-89%) vs high (91%-95%) targeted groups. Severe retinopathy of prematurity was significantly reduced in the low vs high targeted groups. No between-group differences were found for bronchopulmonary dysplasia, brain injury, or patient ductus arteriosus. The conclusion was that in extremely preterm infants, SpO2 should be targeted at 90%-95% until the infant reaches 36 weeks' postmenstrual age.

The bad news, for nurses who have this responsibility, is that this is a tight and difficult target to maintain. Targets are not precisely the same thing as alarm limits, although both must be carefully coordinated. If the alarm limits are too wide, the benefit of having a target at all is lost. Setting them too narrowly is also fraught with problems: mainly, a dramatic increase in the number of alarms. If these alarms are just repeatedly silenced, they can lead to "alarm fatigue" -- the desensitization that results from hearing too many marginally significant or inactionable alarms. Excessive alarms can create many other problems, as well. They provoke anxiety in parents, contribute to noise levels, distract nurses during critical tasks, and undermine patient safety.

One option is to set the alarm limits precisely at the SpO2 target levels of 90% (low) and 95% (high). This might be manageable for the most stable infants. However, with such narrow alarm limits, the SpO2 variability that often goes hand-in-hand with CPAP could tether the nurse to the bedside for the entire shift. Even with an upper alarm limit of 92%, the infants in the current study who were receiving oxygen spent a median of 21% of the time with SpO2 levels ≥ 96%, demonstrating how difficult it is to maintain targets over the long haul. What would have happened if the upper alarm limit had been set at 96%?

It is probably more common to set the limits 1% or 2% lower and higher than the targeted range. The widening of the alarm limits will most certainly reduce the number of alarms, but it may also inadvertently reduce the amount of time that the infant spends in the targeted range. The fact that nurses in this study adjusted the baby's FiO2 only a little more than once an hour suggests that they were more tolerant of high saturation levels and tended to pursue other interventions, rather than increasing the FiO2, in response to low saturation levels.

Finally, this study supports the need for adequate nurse-to-patient ratios as a key element in alarm management in neonates. Sink and colleagues[5] found that nurses caring for fewer babies on high-frequency ventilation were better able to achieve oxygen saturation targets and that with enough nurses, babies on nasal cannulae experience less hyperoxemia. Nurses with more patients to care for will find it more difficult to keep patients within narrow SpO2 targets, and it is unrealistic to expect otherwise. The finding that less experienced nurses were more successful in SpO2 targeting may reflect a greater attentiveness to monitor alarms by newer nurses, or a tendency on the part of more experienced nurses to wait longer time for self-recovery or to attempt other interventions before adjusting the FiO2.

On behalf of the authors, lead author Kathleen Lim said, "Our study demonstrates that SpO2 targeting is challenging in preterm infants receiving CPAP support, and we are seeing similar challenges even as SpO2 target ranges are revised. Clinical managers should be aware of the influence of NICU operational factors (eg, staff-to-patient ratio) on oxygen targeting, and researchers should examine approaches aimed at improving the effectiveness of SpO2 targeting, including automated oxygen control."



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