SpO2, heart rate, and arterial blood pressure during successful or failed application of non-invasive ventilation after delivery – a single-centre study

METHODS

Parents of subjects gave their written informed consent. The study was approved by the Pomeranian Medical University Ethical Committee (decision No KB – 0012/45/01/2013).

A cohort retrospective study was conducted on a sample of 182 newborns (98 boys and 84 girls) hospitalised due to respiratory failure in the Pomeranian Medical University Department of Neonatology in Szczecin, Poland, between 2009 and 2014. The studied babies were treated with non-invasive ventilation from an I-F SiPAP system (CareFusion, Yorba Linda, USA) as the first form of respiratory support after delivery. The babies selected for the presented analysis included those in whom symptoms of respiratory failure were diagnosed after birth and who did not present with congenital malformations that might negatively influence the assessed parameters during I-F therapy.

The Silverman score was used to assess the severity of respiratory distress in the newborns before the decision about using I-F. The score comprises four inspiratory categories of movements (thoraco-abdominal, intercostal, xiphoid, and chin movements) and one expiratory category (grunting) [14]. Surfactant was not used in any of the analysed patients before or during I-F therapy.

In the present study using the I-F type device, the preferred method was breathing using two pressure levels (Biphasic), with a lower usually set no higher than 5 cm H₂O and higher at a level 8 cm H₂O or more. Usually the lowest FiO₂ necessary to maintain SpO₂ at 95% was used. In 114 (62.6%) cases pharmacological sedation (pethidine) was used during I-F method application. Indications for sedation were as follows: inability to calm a newborn baby during the application of the I-F method through non-pharmacological actions. When arterial hypotension was recognised basing on mean arterial pressure (mm Hg) lower than the gestational age (weeks) of the newborn and clinical signs of poor perfusion, fluid and/or inotropes were used to correct it.

Success was noted when the baby improved and weaning from I-F was possible. Failure was recognised when deterioration in the baby’s condition lead to intubation and mechanical ventilation or when pneumothorax was recognised. Indications for intubation were as follows: respiratory acidosis (pH < 7.20 and PCO₂ > 65 mm Hg), apnoea and bradycardia in spite of noninvasive ventilation, and hypoxia (PaO₂ < 50 mm Hg, SpO₂ < 87%) in spite of noninvasive ventilation with FiO₂ > 0.6 or pneumothorax.

A multifunctional Mindray iPM 12 monitor was used to monitored parameters (SpO₂, heart rate, and arterial blood pressure). During the I-F therapy, the parameters were recorded on an hourly basis from the monitor screen and registered on intensive care status charts. The minimum (min) and maximum (max) values of those parameters in individual newborns were analysed statistically for the entire analysed sample as well as for the subgroups that were divided according to the therapy outcome (success or failure), and the development of complications in the form of pneumothorax.

RESULTS

Mean duration of pregnancy in the studied cases was 34.1 ±3 weeks (range: 27–40 weeks); the mean body mass of the studied newborns was 2225 ±743 γ (range: 800–4660 g). Success was noticed in 130 cases (71.4%) and failure in 52 (28.6%). There were no significant differences between mean birth weight (2229 ±739 γ vs. 2217 ±761 γ at P > 0.9) as well as between mean gestational age (34.3 ±3.0 vs. 33.6 ±3.0 at P > 0.2) in the success and failure groups.

The mean length of I-F therapy in the group with successful I-F intervention was 65 hours. The mean length of I-F therapy in the group with failed intervention was 26 hours. Pharmacological sedation was used in 45 (34.6%) patients from the success group and in 51 (98.1) from the failure group due to anxiety of the newborns.

The measured values of the SpO₂, heart rate, and arterial blood pressure in all analysed cases are shown in Table 1. Min SpO₂ values ranged from 38% to 100% and max from 83% to 100% (Table 1). The min and max registered SpO₂ values were significantly higher (93.3 ±7.28 vs. 85.9 ±14.77 at P < 0.001; 99.95 ±0.31 vs. 98.6 ±3.30 at P < 0.0001) for the group with successful I-F therapy outcomes than for the group in which the therapy failed (Table 2). In the group with successful I-F therapy outcomes the minimum heart rate was significantly lower (122.5 ±12.37 vs. 135.9 ±14.97 at P < 0.0001) than in the group in which the I-F therapy failed. There was no significant difference for the maximum values (Table 2). A higher maximum systolic blood pressure (79.05 ±12.49 vs. 69.78 ±13.73 mm Hg; P < 0.0001), maximum diastolic blood pressure (57.03 ±9.31 vs. 50.41 ±13.82 mm Hg; P < 0.0003), and maximum mean arterial blood pressure (46.8 ±10.13 vs. 41.39 ±15.46 mm Hg; P < 0.001), as well as minimum mean arterial blood pressure (27.88 ±5.71 vs. 26.14 ±7.35 mm Hg; P < 0.02) were observed in the group in which the I-F therapy was successful (Table 3).

Pneumothorax was observed in nine (4.94%) newborns, and for that reason non-invasive I-F therapy was discontinued and intubation performed. It was found that the minimum and maximum registered SpO₂ values were significantly higher for the group without pneumothorax than for the group with pneumothorax (Table 4). A faster minimum heart rate (134.4 ±11.97 vs. 125.98 ±14.47 bpm) was observed in the group with pneumothorax, but the difference was of borderline statistical significance (P > 0.05). Lower values of maximum systolic pressure (Me – 63 vs. 76 mm Hg; P > 0.05), diastolic pressure (Me – 45 vs. 55 mm Hg; P > 0.05), and mean pressure (Me – 33 vs. 44 mm Hg; P > 0.05) were observed, but the differences were also of borderline statistical significance (P > 0.05) (Table 5).

DISCUSSION

Transcutaneously measured haemoglobin oxygen saturation, i.e. SpO₂, heart rate, systolic, diastolic, and mean blood pressure, are commonly used and are the most frequently chosen indicators of the welfare of newborns in intensive care units [12, 15].

These parameters are monitored particularly in newborns treated for various forms of respiratory support. The non-invasive ventilation, which is often used as the first choice of ventilation method, is becoming more and more popular. In the study presented here, the behaviour of the above-mentioned parameters of the condition of the newborn was analysed, depending on the result of the I-F therapy and the occurrence of pneumothorax complications.

Continuous pulse oximetry is possible by using modern oximeters capable of detecting even short-term desaturations, which allows for a quick response in improving the condition of the newborn. The minimum SpO₂ values found in this study ranged from 38% to 100%, and the maximum values ranged from 83% to 100%. This indicates a frequent tolerance of episodes of hyperoxia, which can lead to various adverse effects. In our protocol usually the lowest FiO₂ necessary to maintain SpO₂ at 95% was used. However, a maximum saturation of 100% was observed in individual patients in both groups. The lack of reaction of the doctor on duty to the observed SpO₂ of 100% was due to two reasons. The first was the delayed delivery of such information from the nursing staff. The second was the lack of a decision by some doctors to lower FiO₂ for fear of deterioration of the newborn. The analysis performed by us made it possible to discover this fact and to revise the conduct of medical staff in this matter.

In the literature on the use of non-invasive breathing support in preterm newborns, it is recommended that maximum SpO₂ values should not exceed 95% [16]. It should be emphasised that in the course of this study, significantly higher minimum SpO₂ values were observed in the successful I-F therapy group than in the failed group. In the latter group, SpO₂ values averaged 85.9%, which confirms the observations made by other authors proving that SpO₂ < 86% is a determinant of failure of non-invasive respiratory support. In the group with successful I-F therapy and with a mean gestational age of 34.3 weeks, the minimum SpO₂ value in this study was 93.3% (lower than the recommended 95% safe border value for newborns earlier than 32 weeks of gestation).

Mascoll-Robertson et al., in a study conducted in a group of 35 newborns qualified according to the author’s research protocol, covering a gestational age between 24 and 32 weeks, showed that newborns with SpO₂ values below 86% for more than 15% of the day required intubation and mechanical ventilation due to failure of the non-invasive ventilation [17]. In the group with this type of ventilation failure, they recorded SpO₂ values < 86% in 11% of the newborns, while in the group with successful therapy it was seen in only 3% (P < 0.02). In the successful treatment group, they most often recorded SpO₂ values > 95%, and these neonates even had reduced FiO₂ after disconnection from respiratory support, compared to pre-disconnection [17].

Interesting observations were published by Lim et al. in a group of premature newborns treated with the CPAP method [18]. The episodes of prolonged hyperoxia they recorded ≥ 96% covered 21% of the day, among them 7.8% of the day recorded SpO₂ values were ≥ 98%. This could be explained by an inadequate number of nurses. According to the nurses, optimal care for newborns treated using the CPAP method is one nurse per newborn. This allows for quick reduction the FiO₂ concentration to the child’s current situation. Hypoxia episodes < 80% with bradycardia were observed no more than once a day in 16% of the newborns. It is very interesting that the less experienced nurses reacted faster to episodes of hypoxia and hyperoxia, while the more experienced staff waited for spontaneous regulation of saturation by the child, or changed parameters other than FiO₂ concentration, e.g. CPAP pressure [18]. Hensey et al. showed that the use of oxygen supplementation at low gas flow reduces the incidence of desaturation episodes < 80% and < 85%, and shortens the length of treatment in premature babies [19]. This did not significantly affect the incidence of bradycardia < 100/min [19]. Sobczyk reports that increasing CPAP levels from 4 to 6 cm H₂O resulted in a marked increase in oxygen saturation of haemoglobin measured with a pulse oximeter in newborns with SpO₂ < 90% [20]. SpO₂ values recorded in the newborns depended not only on the state of respiratory efficiency and age of the newborn, but also on a number of other factors. Phillipos et al. noted that delaying umbilical cord closure contributed to a faster increase in SpO₂ levels and heart rate in preterm newborns requiring CPAP in the delivery room [21]. Newborns born at the same gestational age (up to 32 weeks of gestation) without breathing problems reached the required SpO₂ and heart rate limits earlier [21]. In their research, Brunherotti et al. assessed the dependence of respiratory rate, heart rate, and SpO₂ values depending on one of four body positions in newborns treated with CPAP method, born between at 26 and 33 weeks of gestation with an average body weight of 1352 γ [22]. They found no correlation between the respiratory rate and heart rate and the child’s upright position, while in the left- or right-side position they recorded significantly lower SpO₂ values than in the position on the child’s back or stomach [22]. The original pilot study was conducted by Sweet et al. in a group of 16 newborns who were born with at average gestational age of 29.8 weeks of pregnancy [23]. They assessed the behaviour of heart function, number of breaths, and SpO₂ during the suction procedure of newborns treated with CPAP. These authors emphasise that the suction procedure is painful and is associated with the possibility of bradycardia, fluctuations in blood pressure, hypoxaemia, and arrhythmia. However, they did not notice significant changes in the number of breaths and heart function, while SpO₂ decreased significantly after the neonatal suction procedure, and recovery to the value preceding the suction took place after about 10 minutes [23]. It is interesting to note that the more mature the newborn is, the longer the SpO₂ recovery time is necessary to reach to baseline SpO₂ values noticed before the suction procedures (P > 0.05). Each one-week increase in gestational age was associated with 1.7 minutes additional time to obtain primary values [23].

In the results presented in this study, we did not assess the monitored parameters immediately after neonatal suction, so it did not have a significant impact on the recorded values of parameters of the newborn.

Assessment of the condition of newborns treated with non-invasive respiratory support is mainly focused on improving the respiratory capacity of newborns. Very few reports describe how this form of therapy affects the cardiovascular system of treated newborns. This can be assessed by monitoring heart function and blood pressure. Maffei et al. in a review of non-invasive ventilation among the effects of CPAP on the cardiovascular system mention the possibility of hypotension [24]. It seems possible that decreased intrathoracic pressure with CPAP use will alter pulmonary, systemic, and trans-ductal blood flow and may contribute to a decrease in blood pressure [25].

The preferred method of measuring blood pressure in critically ill newborns is the direct method from access via the umbilical or radial artery [26]. Blood pressure measured directly by the arterial line allows continuous monitoring of this parameter; however, establishing and maintaining an arterial line may be difficult in premature newborns. It is also associated with an increased risk of thrombosis and infection [27]. The arterial line established through access from the umbilical artery should not be maintained for more than five days [28]. Many authors describe the use of an oscillometric non-invasive method of measuring blood pressure in premature babies using a suitable cuff on the right or left shoulder [15, 25, 29]. This method of measurement was also used in this study in all assessed newborns during non-invasive ventilation using the I-F method. Both compliance and differences in recorded blood pressure values measured by both methods in premature babies were described; the largest differences were observed in the range of diastolic pressure [30]. Less than 30 mm Hg mean arterial pressure can lead to unnecessary intravenous fluid and inotropic supply in a situation of low blood pressure [26]. Shimokaze et al. conducted a study comparing blood pressure values obtained by indirect oscillometric and direct methods in 74 newborns born from 24 to 42 weeks (mean 31.2 weeks) and with body weight on average 1453 γ [30]. They obtained values of coefficients systolic, diastolic, and mean arterial pressure of 0.87, 0.82, and 0.84, respectively (P < 0.001). These researchers also found that the mean systolic blood pressure values did not significantly differ depending on the measurement method used, while the diastolic blood pressure values assessed by the indirect method were underestimated, i.e. significantly lower than those found in the direct method (P < 0.001). Gestational age, body weight, and cardiac function did not significantly correlate with the blood pressure values of the neonates examined by them [30].

The literature reports most often the effect of mean blood pressure on treatment outcomes qualified as success or failure, with an emphasis on hypotensive episodes requiring pharmacological correction [25, 31–33]. It has been described that newborns remaining in the Intensive Care Unit due to respiratory failure often show a tendency of lower blood pressure during the first 24 hours of life [25]. It should be emphasised that there is no uniform definition of hypotension in premature newborns. Lakkundi defined the problem of hypotension in prematures with respiratory failure in the first 72 hours of life, with mean arterial pressure lower than the gestational age of the newborn [25]. Treatment of hypotension was initiated when clinical signs of poor perfusion occurred. They also described that the failure of INtubate, SURfactant, Extubate (INSURE) treatment was associated with a previous episode of low mean arterial pressure, which was observed in 16% of the 116 assessed neonates born at gestational age on average 26 weeks and with an average body weight of 940 γ [25].

Treatment of hypotension is based on the belief that low blood pressure negatively affects the final outcome of the newborn. Lakkundii et al. believe that non-invasive ventilation reduces the incidence of hypotension requiring treatment [25]. Probably lower incidence of continuous sedation/analgesia when using non-invasive ventilation, compared to invasive ventilation, reduces the incidence of low blood pressure episodes [25].

Korraa et al. during the kangaroo mother care of premature babies described a slowdown in heart function and an increase in blood pressure, which are associated with a decrease in the severity of stress in premature babies requiring oxygen therapy [15]. They examined children born on average at 32 weeks of gestation and with an average body weight of 2080 g. Sobczyk noticed no effect of CPAP on heart rate and average arterial blood pressure in a group of 40 newborns with gestational age of 32.5 weeks of pregnancy and with body weight 1979 γ [20]. Abdel-Hady et al. reported that CPAP + 5.0 cm H₂O had no effect on the left ventricular shortening end fraction, heart rate, and mean blood pressure [34]. Levett also found no significant effect of CPAP on heart rate and average blood pressure [35]. Yu and Rolfe stated that the use of CPAP in children with respiratory distress syndrome must be cautious and in combination with monitoring of respiratory and cardiovascular function because exceeding the proper airway pressure can lead to respiratory and circulatory system disorders [36].

In the observation conducted in this study, the group with pneumothorax had significantly lower minimum and maximum saturation values compared to the group without pneumothorax. Lower maximum systolic and mean pressure were also found but were not significant (P > 0.05). In most babies from the failure group (98.1%) indications for pharmacological sedation were observed. Anxiety was an undesirable phenomenon due to the possibility of pneumothorax. On the one hand, the anxiety of the newborn baby during the I-F method could indicate inadequately selected ventilation parameters for the child’s condition; on the other, it could be due to the discomfort caused by mounting the nasal prongs on the child’s face.

There are some limitations of our study. It was a single-centre retrospective observation in a group of more mature neonates. It is worth performing a prospective multicentre study in a group of very-low-birthweight neonates born before 32 weeks of gestation.

It should be emphasised that during the years 2009–2014 we did not have a rigid protocol for treating newborns using the I-F method. The data obtained on the basis of our analysis showed discrepancies in the field of FiO₂ used, interventions undertaken in the case of desaturation, and acceptable desaturation time. It allows us to prepare the precise protocol of the treatment with using non-invasive method of the respiratory support. We expect this to improve our results in the use of non-invasive ventilation.

CONCLUSIONS