Pulse oximeter, the fifth vital sign: a safety belt or a prison of the mind?

Arterial Oxygen Saturation: A Vital Sign?

ABSTRACT

The physical examination is a key part of a continuum that extends from the history of the present illness to the therapeutic outcome. An understanding of the pathophysiological mechanism behind a physical sign is essential for arriving at the correct diagnosis. Early detection of deteriorating physical/vital signs and their appropriate interpretation is thus the key to achieve correct and timely management. By definition, vital signs are "the signs of life that may be monitored or measured, namely pulse rate, respiratory rate, body temperature, and blood pressure." Vital signs are the simplest, cheapest and probably the most inexpensive information gathered bedside in outpatient or hospitalized patients. The pulse oximeter was introduced in the 1980s. It is an accurate and non-invasive method for the measurement of arterial hemoglobin oxygen saturation (SaO2). Pulse oximetry-based arterial oxygen saturation can be effectively used bedside in in-hospital and ambulatory patients with diagnosed or suspected lung disease. The present pandemic of COVID-19 should be considered as a wake-up call. Articles related to arterial oxygen saturation and its importance as a vital sign in patient care were searched online especially in PubMed. Available studies were studied in full length and data was extracted. Discussion: A. Clinical Utility of Oxygen Saturation Monitoring: There are many studies reporting the clinical applicability and usefulness of pulse oximetry in the early detection of hypoxemic events during intraoperative and postoperative periods. B. Role of clinical expertise accompanied by knowledge of physiology: A diagnostic sign is useful only if it is interpreted accurately and applied appropriately while evaluating a patient. The World Health Organisation also appreciates these facts and published "The WHO Pulse Oximetry Training Manual." Understanding the physiology behind and overcoming limitations of the diagnostic sign by clinical expertise is important. While using pulse oximetry, a clinician needs to keep in mind the sigmoidal nature of the oxygen-Hb dissociation curve. Considering these benefits of SaO2 measurement, there have been several references in the past to consider oxygen saturation as the fifth vital sign. In the present pandemic oxygen saturation i.e., SpO2 (arterial oxygen saturation) measured by pulse oxymeter, has been the single most important warning and prognostic sign be it for households, offices, street vendors, hospitals or governments. Measurement of trends of SaO2 added with respiratory rate will provide clinicians with a holistic overview of respiratory functions and multidimensional conditions associated with hypoxemia.

A Comprehensive Assessment of The Eight Vital Signs

The term “vital sign” has been assigned to various phenomena with the presumptive intent to emphasize their importance in health care resulting in the emergence of eight vital signs with multiple designations and overlapping terms. This review developed a case definition for vital signs and identified and described the fifth through eighth vital signs. PubMed/Medline, Google and biographical databases were searched using the individual Medical Subject Headings (MeSH) terms, vital sign and fifth, vital sign and sixth, vital sign and seventh, and vital sign eighth. The search was limited to human clinical studies written in English literature from 1957 up until November 30, 2021. Excluded were articles containing the term vital sign if used alone without the qualifier fifth, sixth, seventh, or eighth or about temperature, blood pressure, pulse, and respiratory rate. One hundred ninety-six articles (122 for the fifth vital sign, 71 for the sixth vital sign, two for the seventh vital sign, and one for the eighth vital sign) constituted the final dataset. The vital signs consisted of 35 terms, classified into 17 categories compromising 186 unique papers for each primary authored article with redundant numbered vital signs for glucose, weight, body mass index, and medication compliance. Eleven terms have been named the fifth vital sign, 25 the sixth vital sign, three the seventh, and one as the eighth vital sign. There are four time-honored vital signs based on the case definition, and they represent an objective bedside measurement obtained noninvasively that is essential for life. Based on this case definition, pulse oximetry qualifies as the fifth while end-tidal CO2 and cardiac output as the sixth. Thus, these terms have been misappropriated 31 times. Although important to emphasize in patient care, the remainder are not vital signs and should not be construed in this manner.

The influence of reducing fever on blood oxygen saturation in children

Laboratory-based studies on the oxyhemoglobin dissociation curve (ODC) suggest that high blood temperature decreases the affinity of hemoglobin for oxygen. The aim of the study was to evaluate the influence of pyrexia on oxygen saturation (SpO2) in children presenting to the emergency department. Normoxemic children with body temperature at or above 38.5 °C were included. Patients with a dynamic respiratory disease were excluded. SpO2 was measured before and after antipyretic treatment. The changes in body temperature and SpO2 were assessed and compared to the changes predicted from the ODC. Thirty-four children completed the study. Mean temperature at presentation was 39.17 ± 0.549 °C and mean SpO2 was 96.15 ± 2.21%. The mean decrease in temperature after antipyretic treatment was 1.71 ± 0.67 °C and mean increase in SpO2 was 0.95 ± 1.76%. Among children in whom pyrexia decreased by 1.5 °C or more, the mean increase in SpO2 was 1.45 ± 1.57%. The measured increase in SpO2 was close to the increase anticipated from the ODC.

CONCLUSION

Pyrexia was associated with decreased SpO2 in normoxemic children. The influence of pyrexia in children with low-normal oxygen saturation is expected to be much higher because of the non-linear shape of the ODC. Physicians treating patients with fever should be aware of this effect, especially in patients with borderline hypoxia. What is Known: • High blood temperature decreases the affinity of oxygen to hemoglobin. • It is not known whether fever would decrease SpO 2 . What is New: • Fever is associated with decreased SpO 2 .

The role of pulse oximetry in chiropractic practice: a rationale for its use

OBJECTIVE

Pulse oximetry is used regularly to assess oxygen saturation levels. The objective of this commentary is to discuss a rationale for using pulse oximetry in chiropractic practice.

DISCUSSION

Pulse oximetry may offer doctors of chiropractic a way to monitor patients' oxygen saturation levels. Quantification of saturation values with heart rate may give clinical aid to the management of chiropractic patients. Markedly reduced saturation levels may necessitate medical referral, whereas mildly reduced levels could lead to changes in chiropractic management.

CONCLUSIONS

Pulse oximetry has the potential to be an integral part of chiropractic practice.