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 Table of Contents  
ORIGINAL ARTICLE
Year : 2019  |  Volume : 39  |  Issue : 4  |  Page : 172-176

Do anthropometrical indices correlate with pulse oximetry among children attending a private hospital in Enugu?


1 Department of Paediatrics, College of Medicine, University of Nigeria Teaching Hospital, University of Nigeria, Enugu State, Nigeria
2 Department of Community Medicine, Enugu State University Teaching Hospital, Enugu State, Nigeria

Date of Submission17-Dec-2018
Date of Decision18-Dec-2018
Date of Acceptance30-Dec-2018
Date of Web Publication13-Aug-2019

Correspondence Address:
Dr. Josephat M Chinawa
Department of Paediatrics, College of Medicine, University of Nigeria Teaching Hospital, University of Nigeria, PMB 01129, Enugu State
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jmedsci.jmedsci_199_18

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  Abstract 

Background: Pulse oximetry remains the most common investigation in pediatric cardiology as it acts as a window to unravel most abnormalities in cardiac functions and structure. Objectives: The objective of this study was to determine what is actually the normative pulse oximetry reading among children and to determine if anthropometry has any effect on pulse oximetry. Methodology: A cross-sectional prospective study in which pulse oximetry readings were ascertained among healthy children attending a private clinic in Enugu over a 3-year period. Data Analysis: Data were analyzed using Stata 10 software (STATA 10, College Station, Texas, USA: Stata [Corp]) Means and 95% confidence intervals were calculated for all the individuals. The level of statistical significance was considered P < 0.05. Results: A total of 349 individuals were recruited consecutively. The median value of oxygen saturation (SpO2) was 98% (93%–99%). Females had a significantly higher SpO2 than the males (Wilcoxon-Mann–Whitney test, Z = 2.064, P = 0.04). There was a positive correlation between the SpO2 and age, weight, and height of the patients. Of these anthropometry, height is the most correlated with SpO2. On the other hand, there was a negative correlation between SpO2 and heart rate of the subjects (rho = −0.1845, P = 0.0005). There was no correlation between SpO2 and patient's body mass index (BMI). Conclusion: The normal oximetry reading among children in this study is 98% with a positive correlation with age, weight, and height and a negative correlation with heart rate but no correlation with patient's BMI.

Keywords: Pulse oximetry, anthropometry, children


How to cite this article:
Chinawa JM, Chukwu BF, Chinawa AT. Do anthropometrical indices correlate with pulse oximetry among children attending a private hospital in Enugu?. J Med Sci 2019;39:172-6

How to cite this URL:
Chinawa JM, Chukwu BF, Chinawa AT. Do anthropometrical indices correlate with pulse oximetry among children attending a private hospital in Enugu?. J Med Sci [serial online] 2019 [cited 2019 Aug 22];39:172-6. Available from: http://www.jmedscindmc.com/text.asp?2019/39/4/172/252648


  Introduction Top


Oxygen saturation (SpO2) is usually detected with arterial blood gas. Nonetheless, it can also be measured by pulse oximetry.[1] Pulse oximetry is normally used for checking SpO2 and is very useful in rural communities or developing countries.[2] Normal pulse oximetry readings range from 95% to 100% at the sea level.[2] SpO2 can be defined as the fraction of SpO2 hemoglobin to that of total hemoglobin in the blood.[3] Pulse oximetry is used in determining the percentage of oxygen bound to hemoglobin in the blood.[3],[4],[5],[6],[7],[8],[9],[10],[11] The pulse oximeter consists of a small device which sticks to the body such as a finger, earlobe, or foot and shows its readings through wireless. The device uses light-emitting diodes in conjunction with a light-sensitive sensor to measure the absorption of red and infrared light in the extremity.[12] The use of pulse oximetry reduces the need for arterial blood gas analysis. While arterial blood gas remains the gold-standard for assessing ventilation and oxygenation, in those patients in whom blood gas analysis is indicated, arterialized capillary samples also have a valuable role in patient care.[12]

In Nigeria, the measurement of SpO2 by means of pulse oximetry is routinely done both for children with hypoxia-related illness such as cyanotic congenital cardiac defects and pneumonias. However, much is not known on the actual normative values and cutoff points of SpO2 in normal children as we rely on that given by western world. Again it is not clear if this pulse oximetry is affected by height, weight, or body mass index (BMI) or if there is any gender difference in the values obtained by the oximetry.

There is indeed paucity of data in the country on normative values of SpO2 on Nigerian child. Whether SpO2 really depends on anthropometry like peak expiratory flow rate still remains conjectural.

This work is thus aimed at determining normative values of SpO2 by means of pulse oximetry among Nigerian children and to find out if height or BMI has any link with pulse oximetry.


  Methodology Top


Study area

The study was carried out at a private children's hospital in Enugu, Southeast, Nigeria. It is a center that manages common pediatric illnesses mainly on an outpatient basis.

Study population

There are about 10,000 children registered at the private hospital with an average of nine new patients a month. The clinic runs every day and is manned by 1 consultant, a resident pediatrician, and a medical officer.

The individuals studied included 349 children aged from 6 months to 18 years who only attended outpatient clinic and who are on follow-up or who had no illness but accompany their siblings to the hospital with their parents. Patients excluded include those with congenital cardiac anomalies, pneumonia, or hypoxemia while those included are those who had no known illness and who gave consent.

Children who fulfilled the inclusion criteria were consecutively recruited into the study.

Ethical clearance for the study was obtained from the Research and Ethical Committee of the University of Nigeria Teaching Hospital.

Measurement of oxygen saturation

Here, the index finger of the subject is used. The correct measurement is detected if the oximeter displayed the subject's heart rate and SpO2 and if the heart rate is compatible with age.[3],[4],[5] We use normative values for heart rate and age to check for this. The oximeter pulse rate displayed on the screen was compared with the simultaneous measurement of the radial pulse obtained by palpation on the other hand to be sure that signals were coincident.[3],[4],[5] If the sensor was not able to track the pulse during the measurement period due to excessive patient motion, no saturation reading was obtained, and a check sensor signal was displayed.[6]

The technique of pulse oximetry is by the use of spectrophotometric emission.[13],[14] The ratio of absorbance at these wavelengths is calculated and calibrated against direct measurements of arterial SpO2.[13],[14] The waveform, which as seen on pulse oximeter help the clinician to eliminate all artefacts [Figure 1]. SpO2 was measured on two occasions, and the best is taken and documented. All readings were taken when the child is calm and awake. Weight and height were measured by standard measurements.
Figure 1: Scatter plot of oxygen saturation (%) against age of subjects in kg

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Data analysis

Data were analyzed using Stata 10 software (STATA 10, College Station, Texas, USA: StataCorp).

Means and 95% confidence intervals were calculated for all the individuals. The level of statistical significance is considered as P < 0.05.


  Results Top


A total of 349 individuals were recruited consecutively, comprising 50.14% males and 49.86% females. The data distribution was nonparametric. The median age was calculated as 3 years (range: 6 months–18 years). Individual's age and sex are as shown in [Table 1] while the anthropometric parameters and heart rate are summarized in [Table 2]. The median value of SpO2 was 98% (range: 93%–99%).
Table 1: Age and sex of individuals

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Table 2: Anthropometric parameters and heart rate of individuals

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Females had a significantly higher SpO2 than the males (Wilcoxon-Mann–Whitney test, Z = 2.064, P = 0.04). It was also significantly lower in children who are 5 years or less than those above 5 years of age (Mann–Whitney t-test, Z = −3.368, P = 0.001). Correlation between SpO2 and the dependent variables is depicted in [Table 2]. There was a weak positive correlation between the SpO2 and age, weight, and height of the patients. On the other hand, there was a weak negative correlation between SpO2 and heart rate of the individuals (rho = −0.1845, P = 0.0005). [Table 3] There was no correlation between SpO2 and patient's BMI. [Figure 1], [Figure 2], [Figure 3] are scatter plots showing the graphical correlation between the SpO2 and dependent variables.
Table 3: Correlation between oxygen saturation and dependent variables

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Figure 2: Scatter plot showing a positive correlation between oxygen percentage saturation and weight of patient with 95% confidence interval

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Figure 3: The scatter plot shows a negative correlation between the percentage oxygen saturation and subjects' heart rate at 95% confidence intervals

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  Discussion Top


This study revealed that the normal pulse oximetry reading among children in Enugu is 98%. This is indeed quite similar to that of Mau et al.[15] who obtained a reading of 97% among Caucasians. Mau et al.[15] noted in his study that though normal SpO2 can occur with airway pulmonary or cardiovascular systems and respiratory infection, nevertheless, saturation <97% is associated with a higher risk of anomalies of cardiovascular systems and respiratory infection. This study, therefore, goes a long way to at least, in part, show a level wherein if it falls <2 standard deviations can be used as an acceptable point for hypoxemia and possibly give oxygen therapy if the need arises. One important thing to note here is that most studies where SpO2 values were taken are mainly among the mixed population of children and adult, this study is thus unique in that it deals more on children.

Furthermore, Schult and Canelo-Aybar [16] noted that SpO2 in healthy children aged 5–16 years Residing in Huayllay, Peru at 4340 m was noted to be 85.7%, 14.2% lower than those at sea level. This suggests a decreasing trend of SaO2 when altitude increased. We noted no correlation between SpO2 and BMI in this present study. Although a study has shown that increased BMI is associated with increased SpO2.[17] They attributed this to the fact that young children have increased lean body mass when they are overweight since they become stronger to move their weight, the converse is true in adults. In a study by Jerrold et al.[18], it was noted that above a BMI of about 30, there was an inverse relationship between BMI and SpO2 in fingertip blood. This inverse relation in SpO2 with higher BMI is even made worse when walking. These varying results of BMI and SpO2 indicate that caution should be taken when using BMI as a predictor for SpO2 in children.[18] When we looked at the weight of our subjects and height in isolation, we noted that weight has a positive correlation with SpO2. This same finding is also true for the height of our individuals. Height, however, remains the most dependent anthropometric variable with SpO2 in terms of correlation.

We noticed a significant increase of SpO2 with age. This is also corroborated in a study, where mean value for the SpO2 of hemoglobin observed in children aged <1 month (92.6%) was statistically different from that in children between 13 and 18 months of age (93.7%).[19]

However, the proportion of fetal hemoglobin seen in younger infants may explain this. Again, the deviation to the left of the fetal hemoglobin saturation curve usually produces higher SpO2 readings for fetal hemoglobin when compared to adult hemoglobin.[19],[20] Moreover, there exists a natural selection to increase the frequency of alleles enhancing oxygen transfer, and this is strongest early in life and decreases in strength with age. This could explain the increase of SpO2 at early childhood as seen in our study.[21]

We noted significant higher pulse oximetry readings among females when compared to their male counterparts. The significantly higher value could result from their smaller muscle mass, lower capillary density, and lower oxidative potential. Schult and Canelo-Aybar [16] in his study in Bolivia noted that although there were no sex differences for SpO2, the difference seems to develop in adulthood. Our findings are also different from that of Reuland et al.[22] who noted no differences in gender values of SpO2 among children aged 5–16 years.

There exists a converse relationship between pulse rate and SpO2 in our study. This rise of pulse rate and fall in SpO2 can be explained by the fact that a reduced cardiac output would cause an increased rate of oxygen consumption and decrease in stroke volume and increase heart rate.[23]

Limitation

Pulse oximetry offers a noninvasive way of checking SpO2 level. However, there are limitations with this measurement that could lead to erroneous results. Black, brown, or blue fingernail polish could falsely have decreased SpO2 levels.


  Conclusion Top


The normal oximetry reading among normal Igbo children is 98% with a positive correlation with age, weight, and height and a negative correlation with heart rate but no correlation with patient's BMI. Height, however, remains the most correlated anthropometric variable with SpO2.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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Severinghaus JW. Simple, accurate equations for human blood O2 dissociation computations. J Appl Physiol 1979;46:599-602.  Back to cited text no. 8
    
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Severinghaus JW. Blood gas calculator. J Appl Physiol 1966;21:1108-16.  Back to cited text no. 10
    
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Zavorsky GS, Cao J, Mayo NE, Gabbay R, Murias JM. Arterial versus capillary blood gases: A meta-analysis. Respir Physiol Neurobiol 2007;155:268-79.  Back to cited text no. 11
    
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Lozano JM, Duque OR, Buitrago T, Behaine S. Pulse oximetry reference values at high altitude. Arch Dis Child 1992;67:299-301.  Back to cited text no. 12
    
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Mau MK, Yamasato KS, Yamamoto LG. Normal oxygen saturation values in pediatric patients. Hawaii Med J 2005;64:42, 44-5.  Back to cited text no. 15
    
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Schult S, Canelo-Aybar C. Oxygen saturation in healthy children aged 5 to 16 years residing in Huayllay, Peru at 4340 m. High Alt Med Biol 2011;12:89-92.  Back to cited text no. 16
    
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Hakala K, Mustajoki P, Aittomäki J, Sovijärvi AR. Effect of weight loss and body position on pulmonary function and gas exchange abnormalities in morbid obesity. Int J Obes Relat Metab Disord 1995;19:343-6.  Back to cited text no. 17
    
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Jerrold P, Michael L, Iman AK, Stacy F, Andrew M. The Effect of BMI on oxygen saturation at rest and during mild walking. J Appl Med Sci 2015;2:2241-328.  Back to cited text no. 18
    
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Hay WW Jr. The uses, benefits, and limitations of pulse oximetry in neonatal medicine: Consensus on key issues. J Perinatol 1987;7:347-9.  Back to cited text no. 19
    
20.
Harris AP, Sendak MJ, Donham RT, Thomas M, Duncan D. Absorption characteristics of human fetal hemoglobin at wavelengths used in pulse oximetry. J Clin Monit 1988;4:175-7.  Back to cited text no. 20
    
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Cynthia MB. Oxygen saturation increases during childhood and decreases during adulthood among high altitude native Tibetans residing at 3800–4200 m. High Alt Med Biol 2000;1:25-32.  Back to cited text no. 21
    
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Reuland DS, Steinhoff MC, Gilman RH, Bara M, Olivares EG, Jabra A, et al. Prevalence and prediction of hypoxemia in children with respiratory infections in the Peruvian Andes. J Pediatr 1991;119:900-6.  Back to cited text no. 22
    
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Reybrouck T, Fagard R. Gender differences in the oxygen transport system during maximal exercise in hypertensive subjects. Chest 1999;115:788-92.  Back to cited text no. 23
    


    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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