Introduction
Neonatal brachial plexus palsy (NBPP) is uncommon with an incidence of 0.05-0.3% but it can cause permanent functional problems in up to 20-30% of affected individuals (1). Even though many risk factors have been widely investigated, no antepartum or intrapartum risk factors have been reported to be reliable except for shoulder dystocia. Consequently, NBPP is still regarded as a non-predictable situation (2).
Although NBPP is easily recognizable in infants with loss of Moro reflex or movements in the affected extremity, different diagnostic modalities such as electromyography, magnetic resonance imaging, and ultrasonography are needed to investigate its localization, severity, and prognosis. However, these diagnostic tools need highly qualified personnel, expensive equipment, and even anesthetic interventions ranging from sedation to general anesthesia, which may cause complications (3).
Perfusion index (PI) is a non-invasive marker of pulse strength provided by new generation pulse-oximeters. It is calculated as the ratio of pulsatile and non-pulsatile blood flow and is related to cardiac output and tissue vascular resistance (4). Previously, it has been suggested that lower values of PI values are associated with neonatal pathologies caused by hypoperfusion (5) and correlate with disease severity (6).
Given its efficacy, the use of PI has been investigated in different conditions such as the screening for congenital heart diseases (7), patent ductus arteriosus (8), and tissue perfusion after red blood cell transfusions (9), and it has been reported to be an effective parameter.
Recent studies in adults have reported that PI, measured on the extremities after central and peripheral nerve blocks, increased due to vasodilation as a result of the cessation of alpha-adrenergic stimuli during regional anesthesia (10).
PI is an easy, fast, and user-independent measurement. We hypothesized that PI values may be higher on the affected extremity due to the cessation of a-adrenergic stimuli as a result of nerve injury in NBPP.
Materials and Methods
This prospective observatory study was conducted in a tertiary Maternity and Children’s Training and Research Hospital between January 2016 and July 2017. Local Ethics Committee approval was received from University of Health Sciences Turkey, İstanbul Zeynep Kamil Women and Children Diseases Training and Research Hospital (approval no: 136, date: 24.06.2016) and written informed consent was obtained from all patients. Babies with defective Moro reflex in one limb or “waiter’s tip” posture diagnosed with NBPP were included in the study. Those babies who had a limited range of movement (thought to be affected in utero or by other musculoskeletal problems), cardiovascular or respiratory impairment, birth asphyxia (pH <7.1 or base excess >12), sepsis, or congenital anomalies including congenital heart diseases were excluded from this study.
Those babies diagnosed with NBPP were evaluated via chest X-ray for clavicle fracture. On the 24th hour of postnatal life, the baby’s oxygen saturation, heart rate, arterial pressures, and PI were recorded on both their right and left upper extremities.
Their demographic data such as gestational age, birth weight, maternal age and type of delivery, and usage of auxiliary birth instruments were recorded.
The values of the affected limb were compared with other extremity values. To test our main hypothesis that PI is higher in the arm with palsy, we used pairwise Student’s t-test to identify if there was a difference between the affected and unaffected arms of the same patient. To explore further, if the fracture had a different impact rather than just brachial plexus injury, we calculated the PI difference ratios between the affected and unaffected sides. Following this, we compared these ratios between the patient groups with and without clavicle fracture again via Welch’s two sample t-test. A two-sided p-value smaller than 0.05 was accepted as significant.
Results
Fifteen patients were diagnosed as NBPP during the study period and four of them were excluded from the study due to a diagnosis of birth asphyxia. The median gestational age was 40 weeks (Q1: 38 - Q3: 40 weeks) and the median birth weight was 4,050 grams (Q1: 3,810 - Q3: 4,360 grams) (Table I). In seven babies, NBPP was on the left side and in four patients, NBPP was on the right extremitie. In eight patients, there was a loss of Moro reflex and in three of the patients, Moro reflexes were weak. All babies had higher PI levels on the extremity with NBPP, independent of being right (preductal) or left (postductal). The clinical features and PI measurements of the patients are given in Table II. The PI measured on the side with palsy [mean ± standard deviation (SD): 2.47±0.74] was significantly higher than for the unaffected arm (1.83±0.66); [t(10)=5.25, p=0.0003]. The ratio of PI differences was not statistically different between the group with brachial plexus only (mean ± SD: 25.68±13.42) and the group with clavicle fracture (mean ± SD: 22.94±14.16); [t(8)=0.31, p=0.76].
Discussion
In this study, we hypothesized that the nerve injury in NBPP may cause vasodilatation in the affected arm of the neonate and this can be shown with PI measured by a pulse-oximeter. We found statistically significant increased PI values in the affected extremities of the neonates.
In previous studies, PI was widely investigated for detecting nerve blockage. Vasodilatation occurs in the nerve-blocked part of the body as a result of the cessation of a-adrenergic stimuli (10). As there is no parasympathetic innervation of arteries/arterioles, blockage of the related nerve results in a loss of sympathetic tone below the level of the blockage and so vasodilatation occurs. With respect to this mechanism, it was investigated whether PI can be used to determine nerve blockage in regional anesthesia and if it is useful in different anesthesia modalities, such as infraclavicular and supraclavicular brachial plexus (11-13).
PI has been shown to be an effective tool for evaluating perfusion (4). Studies about PI have shown that PI values are correlated with superior vena cava flow, which reflects the cerebral blood flow (14) and also with left ventricle output (15). Lower values of PI give information about hypoperfusion, so it can be used in screening for congenital heart diseases (5), detecting patent ductus arteriosus (8), or grading the severity of illness in neonates (6,8). It is also reported that red blood cell transfusions provide increased PI (9) and surfactant treatment improves PI values (16).
PI can be affected by patent ductus arteriosus and studies have shown that in the first three days of life, PI values are lower in the left hand (postductal) than in the right hand (preductal) of the neonate (17). In our study, even though postductal PI levels (the left extremity) were expected to be lower than preductal PI levels (the right extremity) at the 24th hour of life, it was observed that even if NBPP is on the left extremity of the neonate, PI levels are higher than in the unaffected extremity.
On the other hand, as aforementioned, PI has been used in evaluating the severity of neonatal illness (6) and has been correlated with cardiac output (15). However, in the light of our findings, in cases of NBPP, monitoring the neonate from the affected extremity may show higher levels of PI on pulse-oximeter. This situation may lead to issues with fluid replacement or inotrope therapies so it may be logical to consider measurements taken from the unaffected arm for treatment plans.
NBPP is still a problem in neonatal medicine, causing functional problems in one-fourth of affected neonates. Even though NBPP can be easily diagnosed via physical examination after birth, further studies need to be done to clarify the condition. The gold standard for the evaluation of the NBPP is electro-diagnostic studies. These studies have been shown to be superior to imaging studies regarding localization and severity. However, when it comes to the issue of determining prognosis or predicting the need for microsurgery, no single imaging study has been shown to be sufficient (1,2,5,18). In addition to diagnostic studies, the presence of Horner syndrome or lower scores on the “Active Movement Scale” are predictors for early microsurgical intervention (19). Due to all this ongoing controversy, a combination of more parameters is helpful in the evaluation of NBPP. To evaluate the correlation of prognosis and increase in PI levels compared to the unaffected extremity, it was planned to follow-up the neonates in our study for three years. However, only three of the babies were brought to follow-up and it was not possible to calculate the correlation of increase in PI with prognosis. Pleasingly, all three of these patients had no disability in three years of follow-up. In future studies, we think that evaluating PI after the third day of life may eliminate the effect of ductus arteriosus in the left arm.
Study Limitations
One limitation of our study is that our sample size was small. Although the number of patients was small, we found significantly higher levels of PI in the affected limbs of the patients. Future studies are needed to evaluate the duration of PI alteration and, its correlation with other diagnostic studies, and its usefulness in long-term follow-up.
Conclusion
In conclusion, PI levels are higher in the affected extremities of newborns with NBPP compared to the unaffected side but this finding needs to be studied to determine whether it has a correlation with prognosis and whether it can be used as a predictor for early microsurgical intervention. In the future, this finding may be combined with other diagnostic modalities if further studies are carried out.
Ethics
Ethics Committee Approval: Local Ethics Committee approval was received from University of Health Sciences Turkey, İstanbul Zeynep Kamil Women and Children Diseases Training and Research Hospital (approval no: 136, date: 24.06.2016).
Informed Consent: Written informed consent was obtained from all patients.
Peer-review: Extrenally and internally peer-reviewed.
Authorship Contributions
Design: E.D., S.T., Data Collection or Processing: E.D., Analysis or Interpretation: S.T., G.K., Literature Search: E.D., A.U.Z., G.K., Writing: A.U.Z.
Conflict of Interest: The authors declare that they have no conflict of interest.
Financial Disclosure: The authors declared that this study received no financial support.
