Relationship Between Non-Invasive Blood Pressure ( NIBP ) , on First Day of Life with Birth Weight

Address for correspondence: Dr. Baljeet Maini Associate Professor, Department of Paediatrics MMIMSR, Mullana Ambala, India E-mail: mainibaljeet@gmail.com Tel: +91 8059931611 1Garima Chawla, Post doctoral fellow in Paediatric endocrinology (SGRH New Delhi), 2Baljeet Maini, Associate Professor, Department of Paediatrics, Maharishi Markandeshwar Institute of Science and Research (MMIMSR), Mullana, Ambala, India. 3Anand Kumar Bhardwaj, Professor, Department of Paediatrics, Maharishi Markandeshwar Institute of Science and Research (MMIMSR), Mullana, Ambala, India Abstract


Introduction
I mprovements in neonatal care have resulted in increasing survival of sick newborns 1 .In newborn, circulatory system undergoes greatest change in physiology.These diff erences in circulatory system also refl ect in arterial blood pressure of neonate.The newborn is incapable of maintaining adequate cerebral blood fl ow by arteriolar vasodilata on when perfusion pressure falls and is prone to cerebral ischemia with only modest fall in blood pressure 2 .The signs and symptoms in neonates with abnormal blood pressure may be absent or non specifi c, thereby making blood pressure monitoring in neonates mandatory 3 .
Invasive procedures like intra arterial catheters provides accurate and reproducible blood pressure measurements But this method is associated with many hazardous complica ons 4 .Recent advancements include development of noninvasive methods like oscillometric method and doppler ultrasound probe.Of these oscillometric method is most o en adopted in neonatal intensive care units because of its extensive advantages 5 .
There is no available informa on, in currently available literature, on blood pressure values in Indian newborns.Establishment of normal values of blood pressure in newborn is thus necessary so that pathological altera ons can be detected especially in sick neonates.We therefore conceptualized this study in our centre to add to literature and hoping, for be er clinical care of Indian neonates, in future.

Material and Methods
This observa onal cohort study was conducted in ter ary level Neonatal Unit of Maharishi Markandeshwar Ins tute of Medical Science and Research, (MMIMSR) Hospital, Ambala, India.Purposive method of sampling was used to recruit the babies with the aim of including as much as number of eligible babies in the study dura on i.e. between November 2010 and July 2012.Parents were informed about the study and a wri en consent was taken.Prior approval of the Ins tu on Ethics Commi ee was taken for conduc ng the study.
Exclusion criteria: Following babies were excluded from the study group: • Extremely low birth weight (<1000 gram birth weight), owing to unit protocol of administering iv fl uids soon a er birth.
• Newborn babies admi ed in nursery for any other sickness • Babies with congenital malforma ons requiring immediate interven on

• Newborns on following drugs
Cor costeroids

Theophylline
Vasopressor drugs • Maternal history of diabetes, substance abuse The study cohort was subjected to non-invasive blood pressure (NIBP) measurement by oscillometric method between 6 to 24 hours of birth.Cuff bladders of diff erent sizes were chosen in a way so as to have a width covering 2/3rd of upper arm and encompassing the en re arm.Before recording the blood pressure it was ensured that the baby was in calm and quiet posi on.Babies were le undisturbed for at least 15 minutes a er applying the cuff or un l the baby slept or was in a quiet awake state, in absence of struggling, crying and movement.No seda on was given to any baby.The blood pressure was recorded in the right arm using mul para monitor (Excello Eco, BPL health care, Pallakad, India) by oscillometric method.Three readings of blood pressure were taken at two minute interval with the child lying in supine posi on and in a res ul state.Values were discarded if there was considerable movement of the infant.Averages of the three systolic, mean and diastolic readings were used for analysis.
Sta s cal analysis: Data was analysed over an SPSS version 15.5 for WINDOWS-7.Pearson Chi Square test was used to obtain 'p' value for correla on between BP and birth weight; and BP and period of gesta on at the me of birth.('p' value of <0.05 being signifi cant).

Results
One hundred and sixty four newborns were included in the study.There were 87(53.1%)males and 77(46.9%)female babies.Seventeen (10.4%) were early preterm, 46 (28%) late preterm and 101 (61.6%) term newborns.Out of 164 newborns, 96 (58.5%) were >2500 grams; 59 (36%) were low birth weight and 9(5.5%) were very low birth weight.None of the subjects included were <1000grams.The newborns included in our study had gesta onal age of 33-41 weeks with mean gesta on age of 37 + 2 weeks and a mean birth weight of 2505 + 585 grams.Figure 1 shows systolic, diastolic and mean blood pressures measured by oscillometric method in newborns included in our study against their birth weights.It is evident from fi gure 1 that there is a progressive rise in systolic, diastolic and mean arterial blood pressure values with an increase in birth weight.Further, we derived normogram of 10th, 50th, 75th and 95th percen les for systolic, diastolic and mean BPs for birth weight from available data (Figures 2,3 &4).For babies less than 1500grams, the values of systolic, diastolic and mean BP were found to be 53.7   The rise in systolic blood pressure with rising birth weight was highly signifi cant (χ2 = 296.255,df = 4, p = 0.00).Similar were the results for diastolic and mean BPs, (χ2 = 249.009,df = 4, p = 0.00) and (χ2 = 265.476,df = 4, p = 0.00) respec vely (Tables 1,2,3).

Discussion
This study provides norma ve non invasive Blood Pressure (NIBP) data -systolic, diastolic and mean BP values for 164 healthy newborns on day 1 of life, with gesta on age 33-41 weeks ( mean 37 + 2 weeks) & birth weight 1011 -3820 grams (mean 2505+585) in newborns aged 6 -24 hours, using oscillometric method.All infants were clinically and hemodynamically stable on day 1 of life.
The sample size is comparable to that of various published studies on BP in term and preterm newborns.Closest to our study in terms of sample size was study by Alison L. Kent et.al. 6 .
Hegyi et al provided a large dataset on BP in 1105 premature infants with birth weight ranging from 501 -2000 grams ; however the study group consisted of heterogenous group of newborns including those on ven lator and /or on inotropic support 7 .
Oscillometric method was used in our study for BP assessment which is the now commonly employed method in clinical prac ce.Though, Invasive blood pressure monitoring is the gold standard, but besides clinical risks, it has other problems too.The pressure reading is aff ected by the mechanical proper es of the intra-arterial catheter, the transducer system and presence of air bubbles 8,9 .These cause excessive damping leading to low systolic and high diastolic readings with minimal eff ects on mean BP.Therefore, while measuring BP by an arterial line, mean BP is assessed; but the normograms that are available for newborns are of systolic BP and hypotension and hypertension are also defi ned on basis of systolic BP 10 .Invasive methods thus fall into disadvantage.Moreover, catheterisa on cannot be jus fi ed to obtain norma ve data in healthy newborns.Alison L.Kent et.al. 6 and Nwankuo et.al. 11 also used oscillometric method to determine norma ve BP values in babies.
The method used in our study emphasized the presence of res ul state while taking the BP& readings were taken a er 6 hrs of life 10 .Alison L. Kent et al recorded BP on day 1 of life between 12 and 24 hours of life to allow for resolu on of fetal circula on.Similar to our study, values were discarded if there was considerable movement of the infant and averages of three systolic, mean and diastolic were used for the analyses 6 .
In our study the average values of systolic, diastolic and mean BPs were (67.9 + 7), (39.4 + 5.7) and (51.4 + 5.9) mm Hg respec vely.In the study by Nwankwo MU et.al. 11 , the average systolic BP (in mm Hg) was (65.2 + 1), diastolic BP (36.1 + 0.8) and mean BP was ( 47 + 0.8).The median BP values were reported by Alison L Kent et al in term babies as 65 mm Hg, 45 mm Hg and 48  mm Hg for systolic, diastolic and mean blood pressure respec vely 6 .
In our study, a posi ve correla on was observed between BP & birth weight.Tin et al also found that systolic blood pressure from 4 -24 hours of life was higher in babies with a higher birth weight 12 .
was observed the mean values of systolic, diastolic and mean blood pressure were higher for newborns with higher birth weight.These results were comparable to studies in the past by Alison L Kent et.al. 6,13 .Their study revealed that there was signifi cant diff erence between the 28 -29 week and 30 -31 week group in terms of systolic BP and diastolic BP, with the younger gesta on age group tending to have lower average BPs.
However, the results of our study were in contrast to that of Hegyi et al which concluded that birth weight and gesta on age correlated with blood pressure limits only in infants with low Apgar score.In their study, in healthy infants, limits of systolic and diastolic blood pressure were independent of birth weight and gesta onal age 7 .Table 4 gives Sample size and method of BP es ma on used in other studies and present study.
Limita ons of the study: Small sample size and blood pressure values being single point values i.e. at fi rst day of life only.Very small number of babies in very low birth weight category puts a diffi culty for extension of study results to larger popula on.
Strength of the study: Despite its limita ons, our study has biggest strength of being a pioneer study of its type in Indian literature.In India, where we face lot of neonatal morbidity and mortality, there is a need for improving our management protocols for sick neonates.While technology is improving day by day, we s ll need to improvise our knowledge of those parameters, which can be of paramount importance, but s ll not established.Oscillometric method of BP es ma on is a safe, and most importantly cost eff ec ve such parameter.This study throws some light on the s ll dark issue of non-availability of BP values in Indian neonates.

Conclusion
Blood pressure on day 1 of life appears to be directly related to birth weight.The eff ect is seen in all (i.e.systolic, diastolic and mean) blood pressure values.This may be related to adap ve changes in cardiovascular system with increasing body size.
Recommenda ons: we recommend that more studies (of large sample sizes) should be carried out so that database of NIBP in Indian newborns can be created for both normal and low birth weight babies.Further, the studies should be carried out for the en re newborn period so that age wise normograms can be created.

Fig 2 :Fig 1 :
Fig 2: Cen les for Systolic Blood Pressure on Day 1 of Life for Birth Weight >1000 grams

Fig 4 :
Fig 4: Cen les for Mean Blood Pressure on Day 1 of Life for Birth Weight >1000 grams

Fig 3 :
Fig 3: Cen les for Diastolic Blood Pressure on Day 1 of life for Birth Weight >1000 grams Birth weight (grams)

Table 1 :
Systolic BP (SBP) and Birth weight

Table 2 :
Diastolic blood pressure and Birth weight

Table 3 :
Mean BP (MBP) and Birth Weight

Table 4 :
Various studies on Blood Pressure es ma on of Neonates