The purpose of oxygen administration in the NICU is to prevent free radical damage . In the present study, the median FiO2 in premature newborns was lower (24%) than in the study by van Kaam et al., who found a median FiO2 value of 28% during conventional mechanical ventilation . Furthermore, we found that newborns achieved acceptable mean SpO2 during the observation period (Figure 2). Targeting saturation to 88–93% in premature newborns and not more than 95% in full-term newborns has been a goal for several years [25, 26]. However, these targets have not yet been fully agreed upon, because the results of ongoing randomised trials testing high versus low SpO2 targets are still pending [9, 10, 27]. Our calculation of mean SpO2 may have masked episodes of hypoxemia or hyperoxia when nurses titrated FiO2. Nevertheless, it suggests that the goal for saturation targets was met to a large extent. Using SpO2 alone to guide decisions concerning oxygen administration is not evidence-based practice. Thus, nurses also have to assess skin colour, heart rate, and values from blood gases as well transcutaneous O2 measurements .
Although it has been suggested that entrenched clinical practices and cultures make it difficult to change the use of oxygen , our results showed that extremely premature newborns did not receive excessive amounts of oxygen (Tables 1 and 3). The incidence of hyperoxemia increased with GA. Because of the haemoglobin oxygen dissociation curve , sick newborns with pulmonary hypertension are at higher risk of developing high levels of hyperoxemia when they are treated with an oxygen saturation of ~95%. It is common practice in NICUs that nurses wait until an infant is stable before withdrawing arterial blood for gas analysis, and this practice will affect the results. In addition nurses’ workload is an important factor in the achievement of SpO2 goals and appropriate oxygen management in the NICU. There is evidence that compliance with saturation targets is improved with higher nurse: patient ratios . The good results for oxygen management in the NICU in the present study may in part have been due to the practice of having a 1:1 nurse:patient ratio for all infants on mechanical ventilation.
Our study revealed that low PaCO2 values occurred most commonly in extremely premature infants. Hypocarbia may cause cerebral vasoconstriction, resulting in decreased oxygen delivery to the brain [7, 10]. Moreover, in extremely preterm infants, PaCO2 in the normal range seems to yield the best electroencephalography activity . PaCO2 can be regulated by controlling the minute ventilation with TV, or the ventilator rate . It is therefore noteworthy that we found high TVs in 22% of preterm infants and 23% of newborns aged >37 weeks. Nevertheless, the median TV of 4.7 ml was lower than the 5.3 ml recorded in the study of van Kaam et al. . Mechanical ventilation using high TVs is known to cause lung damage . We did not find any significant correlation between PaCO2 and TV in the premature infants, and only a weak negative correlation in full-term infants. This suggests that the relationship between lung physiology and what happens during respirator treatment may not be simple.
Our results showed that variations in PEEP had no significant effect on MAP variability (Table 4). Changing PEEP is often an effective way to adjust oxygenation  and to regulate MAP for experienced clinicians who can accurately assess changes in measured data and calculate the impact of any adjustments . The premature newborns in our study had a PEEP mean value of 4.7 cm H2O which was similar to that observed in the study of van Kaam et al., although they suggested that PEEP values >7 cm H2O might be protective for the lungs .
It is suggested that maintaining appropriate oxygenation is hindered by insufficient communication of unit policies as well as personal bias about the best practice . Control of oxygenation and ventilation is crucial during mechanical ventilation. Therefore, further studies should identify how communication and allocation of responsibilities between nurses and physicians can reduce the incidence of hypocarbia and hyperoxemia.
One limitation of this study was that we had no record of fluctuations in oxygenation levels, nor observations of how soon after blood gas analyses adjustments were made. Regarding the analysis of the mean SaO2, it would have been helpful to include an analysis that indicated the uncertainty in the results. However, because of the volume of repeated measurements for each individual, a standard box plot could not be used. Another weakness of the study was related to the high TV values, which were presented as a general occurrence regardless of how many high values there were from each individual patient.