Print version ISSN 0102-3586
J. Pneumologia vol.29 no.6 São Paulo Nov./Dec. 2003
Mara Harumi MiyakeI; Solange DicciniII; Ana Rita de Cássia BettencourtII
specialized in Intensive Care and Surgical Nursing Grant holder at the chair
of Foundations of Nursing and Medical-Surgical Nursing - Nursing Deparment of
the Unifesp Universidade Federal do Esrado de São Paulo.
IINurse with a PhD in Pulmonary Sciences associated Professor in the Discipline of Foundations of Nursing and Medical-Surgical Nursing of the Nursing Department of Unifesp
Pulse oximetry is a noninvasive method to measure the saturation of peripheral
oxyhaemoglobin (SpO2). Its usually used in emergency, intensive
care and operating room units. Pulse oximeter readings have limited accuracy
in the presence of methemoglobin, carboxyhemoglobin, anaemia, peripheral vasoconstriction,
nail polish, fluorescent light, and motion.
OBJECTIVES: To evaluate the interferences of the color of nail polishes and time on SpO2 in healthy individuals.
METHODS: Sixty-one healthy female volunteers, ages ranging from 18 to 32 years. The nail polish colors used to evaluate SpO2 were: base coat on the little finger, light pink on the ring finger, sparkling light pink on the medium finger and red on the thumb. The index finger was used as control and thus, did not receive nail polish. The time for each color was evaluated every minute until 5 minutes were completed.
RESULTS: When the SpO2 measurement was compared with the control, the base coat (p = 0.56), light pink (p = 0.56) and sparkling light pink (p = 0.37) colors didnt present statistically significant differences. Only the red presented a significant variation (p < 0,001), however it was within normal parameters. SpO2 didnt vary significantly with time.
CONCLUSION: Despite the difference found with the red color, all the SpO2 values achieved were inside the normal range for a healthy individual. Pulse oximeter readings are not significantly affected by the color of nail polish in relation to time.
Key words: Nail polish. Oxygen saturation. Pulse oximetry.
Acronyms and abbreviations
used in this paper
FiO2 Fraction of inspired oxygen
PaO2 Partial oxygen pressure
StO2 Oxygen saturation
T0 Time zero
T1 Time 1 ( one minute)
T2 Time 2 (two minutes)
T3 Time 3 (three minutes)
T4 Time four (four minutes)
T5 Time five (five minutes)
Pulse oximetry is a noninvasive method used to measure heart rate and arterial oxygen saturation (SpO2).(1,2) Pulse oximetry techniques have been developed through more than 100 years of technological and experimental advances. (3)
Pulse oximetry is widely used for patients that require continuous monitoring of oxygen saturation. It is primarily used in hospital wards, emergency rooms, intensive care units, operating rooms, pulmonary outpatient clinics and home care. It is a noninvasive, safe, affordable tool that provides immediate data and does not require specialized personnel.(3)
Various principles are involved in pulse oximetry. Since oxyhemoglobin (HbO2) and deoxyhemoglobin (Hb) absorb different amounts of light in the red and infrared spectrums, spectrum photometry permits the analysis of SpO2 levels. In addition, pulse oximetry employs plethysmography, in which changes in volume and light absorption of arterial blood in the tissues are measured during pulsation. The pulse oximeter determines SpO2 from reflected light in the red (660-nm) and infrared (940-nm) spectrums along the arteriolar bed and measures the changes in light absorption during the pulsation cycle. The pulse oximetry sensor has red and infrared light-emitting diodes (LEDs) on one side and a photoreceptor on the other.(4)
Light transmission through the skin, veins and capillaries is constant. During arterial pulsation, the oxygenated blood enters the tissue, changing its characteristics of light reflection and absorption. Oxygen saturated hemoglobin absorbs more infrared light, while unsaturated hemoglobin absorbs more red light. The difference between the two components of light absorbed pulsing (arterial) and not pulsing (venous) is continuously analyzed by a microprocessor that indicates hemoglobin saturation in arterial blood, thereby eliminating the effects of nonpulsing absorbents such as tissues, bones and venous blood.(1,3,4)
Partial oxygen pressure in the arterial blood (PaO2) undergoes a linear decrease with age, due to the greater difference between blood flow and ventilation. Values of (PaO2) for individuals at 20, 25, 30, 40 and over 50 are about 100 mmHg, 98 mmHg, 96 mmHg, 91 mmHg and 87 mmHg, respectively.(5)
Normal values of SpO2 at room temperature at a fraction of inspired oxygen (FiO2) of approximately 21% range between 96% and 100%, corresponding to a PaO2 of 90 to 100 mmHg. An SpO2 of 91% to 92% is observed when the PaO2 is approximately 60 mmHg, with a standard deviation of ± 3%.(5)
Several factors can limit the accuracy of pulse oximetry. When the SpO2 drops below 70%, pulse oximetry ceases to give precise readings. In addition, pulse oximetry is only sensitive to HbO2 and Hb. Therefore, when carboxyhemoglobin (COHb), which has a greater affinity with carbon monoxide or methemoglobin (MetHb), which causes iron ions to oxidize into the ferric form and hinders the hemoglobin to oxygen bond, are present, pulse oximetry typically overestimates the SpO2. Furthermore, substances such as intravenous dyes (methylene blue, indocyanine green, indocarmine red) and certain colors of nail polish can cause inaccurate readings. Skin pigmentation, poor blood flow to tissues (cause by a state of shock, etc.), deviation of the hemoglobin saturation curve (presence of venous pulsation in the digits), increased serum levels of lipids and bilirubin (which artificially alter levels of serum COHb and MetHb) can also affect the pulse oximetry sensor. Moreover, inaccurate readings can result from the influence of ambient light (fluorescent lamps and fiberoptic instruments), movement, incompatibility with display equipment and lack of equipment calibration.(2,3,5)
According to Wahr et al.,(5) nail polish of various brands and colors can affect pulse oximetry readings in both the red and the infrared spectrum. This interference can result in SpO2 values that are 3% to 5% lower than the actual values. In the current literature, little reference is made to nail polish and pulse oximetry. Only a few prospective clinical studies of this subject have been conducted.(6,7)
In clinical practice, removal of nail polish is not always carried out. This is due to emergency situations, an urgent need to transfer the patient to the operating room or, in cases of outpatient surgery, when the patient is often admitted shortly before the operation. There are only a few articles based upon scientific evidence that might prove or disprove the theory that nail polish interferes with pulse oximetry readings, and most of these are national studies.(7-8) That is why this study, aiming to evaluate the interference of nail polish color and of time on SpO2 in healthy individuals, was carried out.
A total of 61 healthy volunteers with ages ranging from 18 to 35 years (mean, 22±4) were studied. All were students of the graduate nursing program at the Federal University of São Paulo (UNIFESP), were studied. Exclusion criteria included: history of pathological, cardiac, pulmonary, hematological conditions, metabolic disturbances in substances such as lipids and bilirubin3,5 and previous use of nail polish. All volunteers were informed about the objectives of the work and gave written informed consent, after which, a form for data collection was adopted. The Ethics Committee of the institution approved the study.
The survey was carried out from November to December of 2000 IN the laboratory of the Nursing Department of UNIFESP. The data collection form comprised fields for entering volunteer registration number and initials, age and SpO2 readings for each color of nail polish used in the study.
Prior to initiating data collection, 10 volunteers were submitted to a pre-test, in which SpO2 was checked in all fingers of the left hand, without nail polish. No differences in SpO2 were detected among these volunteers.
At the nursing laboratory, each volunteer was seated for 10 minutes while the nail polish was applied and allowed to dry on the fingernails of the left hand. The colors chosen were those most commonly used. Various colors of Colorama® brand nail polish were applied as follows, natural color on the little finger, light pink on the ring finger, light pink with glitter on the middle finger and red on the thumb. The index finger was considered the control and, therefore, no nail polish was applied. The first coat of nail polish was applied starting from the left little finger and proceeding to the right thumb, and the second was applied in an identical fashion. Under a professional hair dryer at maximum cool airflow, positioned at a distance of 10 cm, the nail polish was completely dry in 7 min.
For pulse oximetry, a portable oximeter (model DX-2405; Dixtal Biomédica Ind. Com. Ltda., São Paulo) with a clip-type sensor was used. Data referring to the SpO2 for each color were recorded in a sequence identical to that of the nail polish application.
In the second round of data collection, the time variable for each color of nail polish was studied. The initial SpO2 reading was considered time 0 (TO), the reading at 1 min was considered time 1 (T1) and so on up to 5 min (T5), for a total of 6 readings. Time was controlled using an Ari-timer Unicef 0601 digital chronometer.
For statistical analysis of the SpO2 reading for each type of nail polish color, the Wilcoxon test was used. The Friedman test was used for analysis of SpO2 variation over time.
Analysis of the effect of the presence of nail polish
Table 1 shows the comparative analyses of SpO2 for each nail polish in relation to the control.
In the comparison between the nails coated with the natural color and the control condition no statistically significant difference was found regarding mean SpO2 (p = 0.56). In 49 (80.3%) of the 61 subjects, SpO2 values were comparable. In 5 (8.2%) of the subjects, readings on the nail with the natural color were higher by 1%, and in 7 (11.5%) they were lower by 1%.
In the comparison between nails with light pink nail polish and controls, no statistically significant difference was found in mean SpO2 (p = 0.56). In 49 (80.3%) of the 61 subjects, SpO2 values were comparable. In 7 (11.5%) of the subjects, the readings on the nail with light pink nail polish were higher by 1%, and in 5 (8.2%) they were lower by 1%.
In the comparison between nails with light pink glitter nail polish and controls, no significantly statistical difference was found regarding the mean SpO2 (p = 0.37). In 50 (82%) of the 61 subjects, SpO2 values were comparable. In 4 (6.6%) of the subjects, the readings on the nail coated with light pink glitter nail polish were higher by 1%, and in 7 (11.5%) they were lower by 1%.
In the comparison between nails with red nail polish and controls, a statistically significant difference in mean SpO2 was found (p<0.0001). The mean SpO2 measured on nails with red nail polish was significantly lower than that measured on the control nails. In 28 (45.9%) of the 61 subjects, SpO2 values were comparable. In 1 (1.6%) of the subjects, the readings on the nail coated with red nail polish were higher by 1%, and in 28 (45.9%) they were lower by 1%. In 3 (4.9%) of the subjects, readings on the finger with red nail polish were lower by 2%, and in 1 (1.6%) they were lower by 3%.
Notwithstanding the differences found with the use of red nail polish, all SpO2 readings were within the 96% to 99% range of acceptability.
Analysis of the time variable
Analysis related to time of exposure to each condition revealed that there were no differences in SpO2 among the 6 readings (T0, T1, T2, T3, T4 and T5) taken during the following 5 minutes. As seen in Table 2, all 6 readings were identical for any given condition in all 61 volunteers. For nails painted with natural, light pink and light pink glitter nail polish, as well as for control nails, SpO2 was at 98%. For nails painted with red nail polish, SpO2 was at 97% (Table 2).
Pulse oximetry is recommended for patients at risk for hypoxemia, because it is an accurate method that is easy to use and provides early detection of decreased oxygen saturation.(10)
Changes in the SpO2 values must be carefully evaluated. Various factors may interfere with the reliability of the pulse oximetry sensor. The most significant factors are technical limitations: excess ambient light,(11) positioning and location of the sensor (finger, toe or earlobe),(12) and movement of the patient.(13,14) Physiological limitations include skin pigmentation,(15) onychomycosis,(16) shape of the oxygen dissociation curve,(3,5) presence of carboxyhemoglobin or methemoglobin,(17,18) dyes such as methylene blue,(19) poor peripheral blood flow(20) and nail polish.(7)
There have been only a few studies investigating the effect of nail polish on SpO2 readings.(7,9) Kataria and Lampkin(8) evaluated 15 volunteers and reported that the presence of nail polish did not interfere, although the color of nail polish used was not reported.
In a study carried out by Coté et al.,(7) 14 volunteers were analyzed with regard to interference of nail polish with pulse oximetry readings. Black, dark brown, blue and green nail polish produced a significant drop in SpO2 readings, whereas colors such as red and wine produced no such changes. The authors used American brands of nail polish brands. However, they did not specify the ages of their subjects or possible pathologic conditions. Neither did they state the time of stabilization for the performance of the measurement of oxygen saturation or conditions of exercise or rest under which the individuals were evaluated. In contrast, Brand et al.(9) analyzed 12 healthy, nonsmoking volunteers and reported that the blue, green and lemon green colors caused no statistically significant differences in pulse oximetry readings.
In our study, we used the natural, light pink, light pink and glitter and red colors. Only the red color presented significant interference in SpO2 readings. However, values remained within the range of acceptability (from 96% to 99%).
Analyzing the previously mentioned studies, we perceived that the nail polish colors used, such as black, blue and green do not correspond to those used in Brazilian society, in which there is a trend toward using shades of pink, beige, red or wine. One of the limitations of our study is that it is impossible to test all nail polish colors available on the local market.
Another noteworthy constraint is that our results cannot be extrapolated to unhealthy individuals such as those suffering from cardiovascular, hematological or pulmonary disorders.
Nail polish was found to interfere with SpO2 readings in some studies, but not in all. This may lead us to believe that the use of nail polish may not actually interference with pulse oximetry at all and underscores the need for further studies on the subject.
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Submitted for publication on June/11/03 Accepted after review on Oct./15/03