Sudan Journal of Medical Sciences Volume 16, Issue no. 4, doi:10.11131/2017/sjms.v16i4.9948 Production and Hosting by Knowledge E Research Article Comparison of Pocket Pulse Oximeter and Standard Pulse Oximeter With ABG Analysis in Critically Ill Patients Jeswanth Reddy N.1, Kiran H. S.2*, B. J. Subhash Chandra2, Basavana Gowdappa H.2 1Department of General Medicine, Melmaruvathur Adhiparasakthi Institute of Medical Sciences & Research, Melmaruvathur, Kancheepuram district, Tamil Nadu, India 2Department of General Medicine, JSS Medical College and Hospital, JSSAHER, Mysore, Karnataka, India ORCID: Kiran H. S.: https://orcid.org/0000-0002-6070-6529 Abstract Background: Pulse oximetry (SpO2) is a standard monitoring device in patients presenting to EMDs and intensive care units (ICUs). Pocket pulse oximeters (PPOs) are used widely in wards, EMDs, and small hospitals/clinics. These inexpensive PPOs also guide therapeutic interventions. Few studies have evaluated the accuracy of SpO2 in patients presenting to critical care areas vis-à-vis devices like PPO and standard pulse oximeter (SPO). This study becomes extremely relevant in view of the ongoing crisis of the COVID-19 pandemic wherein SpO2 monitoring is very important in hospitals, quarantine centers, small clinics, or even at home. Methods: Patients presenting to critical areas who underwent arterial blood gases (ABG) analysis on the recommendation of the treating physician between November 2016 and October 2018 were included in this study. Along with the ABG analysis, a simultaneous assessment of SpO2 was done with a single PPO and SPO and all values were noted. Statistical analysis was done using the SPSS v.21.0 for Windows. Results: The study included 300 patients. We compared the O2 saturations of ABG, SPO, and PPO with respect to sex, different age groups, and at different levels of ABG pCO2, HCO3, and pH in all patients. All parameters were compared using the Pearson’s correlation test; the results showed that ABG O2 saturations were closer to the SPO than the PPO but the differences were not statistically significant as the Pearson’s correlation values for all parameters were >0.8. We also compared the parameters by Bland Altman Plot and all observations were outside 95% CI (confidence interval), which means that there was a good agreement between O2 saturations by all three methods, that is, ABG, SPO, and PPO; however, ABG O2 saturations were closer to SPO than PPO but this difference was not statistically significant. Hence, we conclude that the PPO is a useful tool for reliable monitoring of O2 saturations. Conclusion: This study highlights that inexpensive and noninvasive PPO can be used as a standard monitoring device with reliability in critically ill patients presenting to EMDs, ICUs, and small hospitals/clinics, quarantine centers, and even at home. Keywords: pulse oximeter, standard pulse oximeter, pocket pulse oximeter, arterial blood gas analysis, oxygen saturation How to cite this article: Jeswanth Reddy N., Kiran H. S., B. J. Subhash Chandra, Basavana Gowdappa H. (2021) “Comparison of Pocket Pulse Oximeter and Standard Pulse Oximeter With ABG Analysis in Critically Ill Patients,” Sudan Journal of Medical Sciences, vol. 16, Issue no. 4, pages 509–518. DOI 10.18502/sjms.v16i4.9948 Page 509 Corresponding Author: Kiran H. S.; email: drhskiran@gmail.com Received 12 October 2021 Accepted 01 December 2021 Published 31 December 2021 Production and Hosting by Knowledge E Jeswanth Reddy N. et al.. This article is distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use and redistribution provided that the original author and source are credited. Editor-in-Chief: Prof. Mohammad A. M. Ibnouf http://www.knowledgee.com mailto:drhskiran@gmail.com https://creativecommons.org/licenses/by/4.0/ https://creativecommons.org/licenses/by/4.0/ Sudan Journal of Medical Sciences Jeswanth Reddy N. et al. 1. Introduction Pulse oximeter is a device for noninvasive measurement of SpO2 (oxygen saturation) in blood [1].Sending specific wavelengths of light through nail bed based on differ- ential absorption of the wavelengths of the light by deoxygenated and oxygenated hemoglobin, the pulse oximeter calculates and shows an SpO2 value [1]. Nowadays, pulse oximeter SpO2 is considered as a “fifth vital sign” (in addition to temperature, blood pressure, pulse, and respiratory rate) in clinical assessment [2].Ever since its inception in 1970s, it is being used in various clinical settings [3].Pocket pulse oximeters (PPOs) are increasingly being used in wards, critical care areas, peripheral clinics, etc. Their small size, handy nature, and affordable cost have established their role in modern clinical care just like thermometers in the management of patients with fever [3]. However, these commercially available pocket devices have not been ade- quately evaluated [2]. Hence, we wanted to find out the reliability of pocket pulse oximeter (PPO) vis-à-vis standard pulse oximeter (SPO – which comes with a fin- ger probe connected to a standard monitor), and ABG (arterial blood gases) anal- ysis. Although this study was done in pre-COVID era, it becomes extremely rele- vant in view of the ongoing crisis of COVID-19 pandemic wherein SpO2 monitoring is very important in hospitals, quarantine centers, small clinics, or even at home [4, 5]. 2. Materials and Methods This observational prospective and comparative study was undertaken at a medical college teaching hospital. The study included 300 patients admitted to critical care areas between November 2016 and October 2018. Consecutive patients presented to critical areas who underwent ABG analysis as per the decision of the treating physician were included by convenience sampling. Patients with shock in whom pulse oximetry does not record the saturation (SpO2) and patients with anemia and abnormal hemoglobin were excluded. Along with the ABG analysis, a simultaneous assessment of SpO2 was done with a single PPO and SPO, and all values were noted. SpO2 obtained by PPO, SPO were compared with each other and with var- ious parameters of ABG analysis. To ensure the accuracy of the measurement, the values were recorded only after the PPO sensor showed a steady pulse and/or pulse waveform. doi:10.11131/2017/sjms.v16i4.9948 Page 510 Sudan Journal of Medical Sciences Jeswanth Reddy N. et al. Table 1: Descriptive statistics comparing SPO vs ABG O2 saturation. N Minimum Maximum Mean Std. Deviation Difference between ABG and SPO SPO2% 300 –10.00 5.9 –0.2262 1.65147 Table 2: Descriptive statistics comparing PPO vs ABG O2 saturation. N Minimum Maximum Mean Std. Deviation Difference between ABG and PPO SPO2% 300 –13 6.9 0.46 1.727 3. Results Out of the 300 patients included in the study, 69% were male and 31% female. Pearson’s correlation showed that ABG O2 saturation was closer to SPO than PPO in both males and females; however, these differences were within the acceptable limits. Hence, there was no statistically significant difference between males and females for monitoring O2 saturation by PPO. Furthermore, 5% of the patients were <20 years old, 27% between 20 and 40, 34% between 40 and 60, 29% between 60 and 80, and 5% >80. Across all age groups, ABG O2 saturations were closer to SPO than PPO but this difference was not significant as the Pearson’s correlation values were >0.8, which is considered to have excellent correlation. Hence, age does not have any statistically significant influence on PPO saturation monitoring. According to the Pearson’s correlation, there was an excellent correlation between the saturation recorded by PPO and SPO with ABG O2 saturation. SPO values were closer to ABG O2 saturation than PPO but this difference was not significant. Linear regression showed standardized coefficient error of 0.868 and 0.878 with PPO and SPO, respectively, when compared with the saturations of ABG which is insignificant as the standardized coefficient error is <0.1 (standardized coefficient error <0.1 is insignificant). Only 10/300 (3.3%) patients were beyond 95% CI (Confidence interval) which means there is a good agreement between the two methods (ABG SaO2 and SPO). Overall, 13/300 (4.3%) observations were outside 95% CI, which means there is still a good agreement between the two methods (ABG SaO2 and PPO). Only 6/300 (2%) had >95% CI, which means there is a good agreement between the two methods. doi:10.11131/2017/sjms.v16i4.9948 Page 511 Sudan Journal of Medical Sciences Jeswanth Reddy N. et al. Figure 1: Bland Altman Plot comparing SPO vs ABG O2 saturation. Figure 2: Bland Altman Plot comparing PPO vs ABG O2 saturation. Finally, to conclude, based on the Bland Altman Plot, while ABG is in better agreement with SPO than PPO, both were within the acceptable limits. doi:10.11131/2017/sjms.v16i4.9948 Page 512 Sudan Journal of Medical Sciences Jeswanth Reddy N. et al. Figure 3: Bland Altman Plot of agreement between PPO vs SPO. Table 3: Descriptive statistics showing agreement between PPO and ABG O2 saturation. Mean Median Standard deviation Minimum Maximum Percentile 25 Percentile 75 Difference between SPO and PPO 0.69 1.00 0.73 –1 2.00 0.00 1.00 Hence, based on the Bland Altman Plot, PPO can be a reliable tool for monitoring saturation. We also compared the saturations of all three, that is, ABG, PPO, and SPO at different levels of ABG PCO2 values to determine whether PCO2 levels have any influence. Results showed that there was a better correlation between ABG and SPO O2 saturations than PPO but the difference was within the acceptable limit. So, ABG PCO2 does not influence the saturation monitoring by PPO. We also compared the saturations of all three, that is, ABG, PPO, and SPO at different levels of ABG HCO3 values to determine whether HCO3 level has any influence. Results showed that there was a better correlation between ABG and SPO than between ABG and PPO but the difference was within the acceptable limit. So, HCO3 level does not influence the saturation monitoring by PPO. In addition, neither respiratory acidosis/alkalosis nor metabolic acidosis/alkalosis affect the PPO saturation monitoring. Both in metabolic acidosis and alkalosis ABG, values of O2 saturation are closer doi:10.11131/2017/sjms.v16i4.9948 Page 513 Sudan Journal of Medical Sciences Jeswanth Reddy N. et al. to SPO than PPO but within acceptable limits. Similarly, in respiratory acidosis or alkalosis, ABG values of O2 saturation are closer to SPO than PPO but within acceptable limits. 4. Discussion PPO is nowadays a ubiquitous, disseminated technology used for monitoring O2 sat- uration in patients presenting to critical care units such as EMDs, ICUs, small hos- pitals/clinics owing to their ease of use and the ability to provide continuous and immediate oxygen saturation values [1–3]. Furthermore, PPO is a noninvasive method for monitoring oxygen saturation (SO2), so knowing its precision and accuracy is of great importance in clinical practice [1, 2]. Hence, this study was carried out to compare the O2 saturation of PPO with that of SPO and ABG O2 saturations and to examine the effect of several factors on this relationship. Our study showed that SPO O2 saturation was more closely related to ABG values than PPO across all parameters, that is, sex, different age groups, and at different levels of ABG pCO2, HCO3, and pH. Similarly, ABG O2 saturation was more closely related to SPO than PPO across all parameters. There was a better correlation between ABG and SPO than PPO, however, as per the statistical analysis, those differences were within acceptable limits and statistically insignificant. Hence, inexpensive PPO can be used as a standard monitoring device with reliability in critically ill patients. Van de Louw A et al. noted large differences between saturation measured by PPO and ABG in critically ill patients with poor reproducibility of SpO2 [6], however, our study showed that there was an excellent correlation between the saturations recorded by PPO, SPO, and ABG (as the Pearson’s correlation values >0.8 are considered to have excellent correlation; linear regression showed a standardized coefficient error of 0.868 which occurred between PPO and ABG saturation which is insignificant as the standardized coefficient error is <0.1 which is considered insignificant; Bland Altman Plot also showed an excellent correlation between the two as 13/300 (4.3%) observations were outside 95% CI, which means that there is a good agreement between the two methods). Da Costa JC et al. showed that PPO was less precise than SPO but had agreement limits that were comparable [7]. Our study also showed the same results. Moreover, Van de Louw et al. [6] compared only ABG and PPO and da Costa JC et al. [7] compared only between SPO and PPO, but in this study, we compared all three methods of monitoring doi:10.11131/2017/sjms.v16i4.9948 Page 514 Sudan Journal of Medical Sciences Jeswanth Reddy N. et al. O2 saturation, that is, ABG, SPO, and PPO, which showed a good correlation between all three methods. Wilson et al. showed that PPO overestimates ABG-determined SaO2 by a mean of 2.75% in patients with sepsis and septic shock [8]. This overestimation is exacerbated by the presence of hypoxemia. When SaO2needs to be determined with a high degree of accuracy, ABG is recommended. In our study, we have excluded patients with shock, hence the issue does not arise at all. Moreover, Seguin et al. demonstrated that neither anemia nor acidosis alters the precision of measurements, thus PPO remains a valuable tool in the care of ICU patients [9]. In this study, we excluded patients with anemia. In our study also, acidosis, either respiratory or metabolic, does not alter the precision of measurement as the Pearson’s correlation values were >0.8, which means that there exists a good correlation. In our study, we also compared O2 saturations at different levels of ABG alkalosis, that is, both respiratory and metabolic alkalosis and results showed that alkalosis also do not alter the precision of measurement as the Pearson’s correlation values obtained were >0.8. Munoz et al. reported that carbon dioxide arterial tension status can impair the agreement between arterial oxygen saturation and arterial oxygen saturation measured by pulse oximetry, particularly in patients with hypercapnia [10]. Therefore, it is likely that arterial oxygen saturation measured by oximetry may not be sufficiently accurate when assessing patients for long-term home oxygen therapy and should not substitute the gold standard arterial oxygen tension measured in arterial blood. Our study also showed that there exists differences between the saturations recorded by PPO and ABG at different levels of ABG pCO2, but these differences were within agreeable limits by Pearson’s correlation. One of the most important part of COVID-19 patient management is PPO more so because of “silent hypoxia” [3, 11, 12]. Many countries have adopted PPO at primary healthcare/home settings [3].In a recent study done to assess the correlation between PPO (SpO2) and ABG analysis (SaO2) in patients with COVID-19, who were fit to be shifted from an ICU to a ward, it was found that PPO correlated with SaO2 measurement; although suboptimal, it was within the acceptable levels for Food and Drug Authority approval [13]. doi:10.11131/2017/sjms.v16i4.9948 Page 515 Sudan Journal of Medical Sciences Jeswanth Reddy N. et al. 5. Limitations and Highlights In this study, we excluded patients with shock, anemia, and abnormal hemoglobin levels [14]. Hence, we could not estimate the correlation between ABG, PPO, and SPO in the above situations. This is the first ever study of its kind in our country since we compared, simultaneously, saturations recorded by PPO and SPO with ABG which, to the best of our knowledge, none of the other studies have done so far. 6. Conclusion This study highlights that inexpensive PPO can be used as a standard monitoring device with reliability in critically ill patients presenting to EMDs, ICUs, and small hospitals/clinics in the periphery; more so, during the current COVID-19 pandemic. Acknowledgements The authors dedicate this article to Dr Takuo Aoyagi (who passed away last year) – “the father of the pulse oximeter” – for his contributions in its development [15]. The authors are also thankful to their laboratory department for its support. Ethical Considerations Institutional Ethics Committee approval and informed consent of patients were obtained. Competing Interests None. Availability of Data and Material All relevant data and methodological details pertaining to this study are available to any interested researchers upon reasonable request to the corresponding author. doi:10.11131/2017/sjms.v16i4.9948 Page 516 Sudan Journal of Medical Sciences Jeswanth Reddy N. et al. Funding None. References [1] Torp, K. D., Modi, P., and Simon, L. V. (2021). Pulse oximetry. Treasure Island, FL: StatPearls Publishing. [2] Hafen, B. B. and Sharma, S. (2021). Oxygen saturation. Treasure Island, FL: StatPearls Publishing. [3] Singh, A., Kataria, S., Das, P., et al. (2020). A proposal to make the pulse oximetry as omnipresent as thermometry in public health care systems. Journal of Global Health, vol. 10, no. 2, p. 0203102. [4] Michard, F., Shelley, K., and L’Her, E. (2021). COVID-19: pulse oximeters in the spotlight. Journal of Clinical Monitoring and Computing, vol. 35, no. 1, pp. 11–14. [5] Quaresima, V. and Ferrari, M. (2020). 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Accuracy and reliability of pulse oximetry at different arterial carbon dioxide pressure levels. European Respiratory Journal, vol. 32, no. 4, pp. 1053–1059. [11] Wilkerson, R. G., Adler, J. D., Shah, N. G., et al. (2020). Silent hypoxia: a harbinger of clinical deterioration in patients with COVID-19. American Journal of Emergency Medicine, vol. 38, no. 10, pp. 2243.e5–2243.e6. doi:10.11131/2017/sjms.v16i4.9948 Page 517 Sudan Journal of Medical Sciences Jeswanth Reddy N. et al. [12] Brouqui, P., Amrane, S., Million, M., et al. (2021). Asymptomatic hypoxia in COVID-19 is associated with poor outcome. International Journal of Infectious Diseases, vol. 102, pp. 233–238. [13] Philip, K. E. J., Bennett, B., Fuller, S., et al. (2020). Working accuracy of pulse oximetry in COVID-19 patients stepping down from intensive care: a clinical evaluation. BMJ Open Respiratory Research, vol. 7, no. 1, p. e000778. [14] Moyle, J. (2021). Pulse oximetry gives artificially high readings in presence of carboxyhaemoglobin. BMJ, vol. 373, p. n1103. [15] Yamakage, M. (2021). Pulse oximetry: the outstanding achievements of Dr. Takuo Aoyagi. Journal of Anesthesia, vol. 35, article 605. doi:10.11131/2017/sjms.v16i4.9948 Page 518 Introduction Materials and Methods Results Discussion Limitations and Highlights Conclusion Acknowledgements Ethical Considerations Competing Interests Availability of Data and Material Funding References