How to read a medline finger pulse oximeter

Correspondence: Hajime Yamazaki, Department of Anesthesiology, Surgical Science, Tokai University School of Medicine, 143 Shimokasuya, Isehara, Kanagawa, 259-1143, Japan, Tel +81 463 93 1121, Fax +81 463 91 9260, Email pj.ca.iakot-u.cci.si@emijah-y

Copyright © 2012 Yamazaki et al, publisher and licensee Dove Medical Press Ltd

This is an Open Access article which permits unrestricted noncommercial use, provided the original work is properly cited.

Abstract

Background

Stellate ganglion block (SGB) is a widely used procedure for treatment of pain in the head and upper body, but the clinical signs used to verify the effectiveness of SGB can be ambiguous or variable in some patients. We observed the chronological changes in perfusion index (PI) from pulse oximetry to determine if these changes correlated with the clinical signs associated with an effective SGB. We hypothesized that PI could provide an easy method to assess the effectiveness of SGB.

Method

We compared the chronologies in PI on the treated and untreated sides of 21 patients in whom treatment by SGB was found to be effective. The SGB was performed by administering 6 mL of 1% mepivacaine. The effectiveness of the SGB was confirmed on the basis of clinical signs. Additionally, in two patients we tested whether increased PI on the treatment side correlated with increased microcirculation as measured by laser-Doppler blood flowmetry.

Results

On the side treated by SGB, PI increased 61.4% in the earlobe and 60.5% from baseline values in the upper limbs, at 5 minutes after initiation of the procedure. Differences in PI before and after treatment were significant at both sites. No time-course increases in PI were found on the untreated side at either site. Following SGB, increases in PI correlated with increases in blood flow as measured by laser-Doppler flowmetry.

Conclusion

PI increased in the earlobe and upper limbs on the treated side of 21 patients who received an effective SGB but not on the untreated side. The positive correlations between changes in PI and both presence of clinical signs and changes in blood flow in the skin microcirculation indicate a sympatholytic effect, suggesting that the PI could be useful in determination of the efficacy of SGB.

Keywords: stellate ganglion block, pulse oximetry, peripheral perfusion, perfusion index, skin microcirculation

Introduction

A stellate ganglion block (SGB) is defined as a nerve block which simultaneously blocks the cervical sympathetic trunks, the vertebral ganglia, the preganglionic and postganglionic fibers of the lower cervical sympathetic ganglia, and the upper thoracic sympathetic ganglia. SGB is mainly used for treatment of painful disorders of the head and neck, upper limbs, and upper chest. The presence of clinical signs such as Horner’s sign, hypohidrosis and vasodilatation in the upper limbs are used to verify that SGB is effective in the clinical settings. However, these signs can be ambiguous in some patients. Perfusion index (PI), which is automatically calculated by pulse oximetry, provides an indication of peripheral perfusion at the sensor site. We examined the relationship between the presence of clinical signs and changes in PI after SGB to determine if PI could be used to verify the efficacy of SGB. Additionally, we verified that increased PI correlates with increased skin microcirculation (sympatholytic effect) by studying changes in PI and changes in blood flow as measured by laser-Doppler flowmetry following effective SGB.

Methods

Following our institutional ethics committee approval and obtaining written informed consent, a retrospective survey of patients scheduled for SGB between June and November 2006 was conducted. Exclusion criteria included patients receiving treatment for circulatory disturbances in the upper limbs, diabetes mellitus, or hypertension. For procedure, the ambient temperature was 24°C to 25°C and patients were put in a supine position. The pulse oximetry sensors (LNCS adult adhesive sensors connected to Masimo SET® Radical™ pulse oximeters; Masimo Corp, Irvine, CA) were affixed, bilaterally, to the patients’ earlobes, and the tips of their thumbs. The pulse oximeters were connected to personal computers with data collection software ( Physiolog™; Masimo Corp) for the continuous recording of PI. The baseline PI value was recorded after 15 minutes of bed rest, before the SGB procedure. Blood pressure and pulse rate were measured from the upper arm on the opposite side of the SGB. The SGB was performed by using 6 mL of 1% mepivacaine (Carbocaine®; Hospira Inc, Lake Forest, IL) according to the paravertebral approach, using the anterior tubercle of the 6th cervical transverse process as a marker. The efficacy of the SGB was determined on the basis of clinical signs by confirming the presence or absence of Horner’s sign, flushing and hypohidrosis on the face, and vasodilatation and hypohidrosis in the upper limbs on the treated side, compared to the side opposite the SGB (untreated side). To evaluate the correlation between PI and blood flow after SGB, pulse oximeter sensors and laser-Doppler blood flow meter sensors (CSF-2000®; Cyber Firm Inc, Tokyo, Japan) were attached, side by side, on the earlobes on the side treated by SGB of two patients. The SGB was performed according to the procedure described above. PI and laser-Doppler blood flowmetry measurements were recorded on the same time axis using data collection software specific for each measurement (Physiolog™ for PI and Trend BASIC™; Cyber Firm Inc, Tokyo, Japan, for the blood flow meter). The mean ± standard deviation for each measurement was calculated. The change in PI was calculated as ([post PI–pre PI]/pre PI) × 100 and expressed as a percentage. Statistical analyses were performed using the one-way analysis of variance, a Bonferroni/Dunn posthoc test, and Spearman’s rank correlation coefficient. The criterion for significant difference was P < 0.05.

Results

SGB was performed on 30 patients within the study period. The efficacy of SGB was determined on the basis of the observation of Horner’s sign, flushing and hypohidrosis on the face, and vasodilatation and hypohidrosis in the upper limbs; and the results showed that SGB was effective in 21 patients (70%). The remaining nine patients showed the presence of Horner’s sign but clinical signs in the upper limbs were absent (Table 1). In all patients, there was no significant difference in blood pressure or pulse rate before and after the SGB.

Table 1

Patient diagnosis requiring treatment with SGB

N = 21DiagnosisCervical spondylosis13 (61.9%)Cervical disc hernia1 (4.8%)Herpes zoster5 (23.8%)Facial palsy1 (4.8%)Sudden deafness1 (4.8%)Age (years)54.4 (34–71)Gender (male:female)11:10Block side (R:L)9:12

Open in a separate window

Note: Data shown are number (percentage) or mean (range).

Abbreviation: SGB, stellate ganglion block.

PI changes in the earlobe following SGB

In patients for whom SGB was effective, baseline values of PI in the earlobes ranged from 0.13 to 1.25 on both sides of the patient. On the side of the SGB, PI rose continuously during the 30-minute observation period. At 5 minutes, PI increased by 61.4% from baseline (P = 0.042). No changes from baseline were observed on the untreated side (Figure 1).

Open in a separate window

Figure 1

Chronological changes in PI in the upper limbs of a patient. The arrow indicates the time that SGB was performed. PI values on the side of the SGB increased chronologically, whereas those of the opposite side did not significantly following SGB. PI showed high frequency variations on both sides, but a time-course increase in PI was found only on the side of the SGB.

What are the 2 readings on a pulse oximeter by finger?

What is normal SpO2 and BPM?