The use of pulse oximetry to monitor oxygen saturation has increased significantly in the past decade. Although oxygenation has always been an important parameter to measure, a simple, reliable, noninvasive method was not available until recently. The development of reliable pulse oximeters that can continuously monitor arterial oxygen saturation has been described as the most significant technological advance in oxygenation monitoring.1 Pulse oximeters were initially used in operating rooms, but now are found in critical care units, postanesthesia care units, and general units when the patient's oxygenation is questioned.2
Because many of the patients being monitored in these areas are over 65 years of age, it becomes important to know the normal oxygen saturation level in this age group. Although it is known that the aging process causes some physiological changes in the lung, the effect of these changes on oxygen saturation is not clearly documented. Previous research has determined that the normal partial pressure of oxygen (PO2) is lower in the elderly.3 Although it seems logical that oxygen saturation would also be lower, this has not been documented in the literature. An additional area of concern is the effect of altitude on the oxygen saturation of the elderly. It is known that oxygen saturation is decreased at moderate altitude, with normal being 92% to 100% versus 95% to 100% at sea level; however, the degree of change in the elderly is not known. Knudson suggests that the normal arterial oxygen saturation may drop into the range that is usually interpreted as mild hypoxemia in elderly persons at high altitude.3 Because of the frequent occurrence of cardiac or respiratory disease in the elderly, the potential for serious reductions in arterial and tissue oxygenation in this population must be considered.
Oximetry produces an optical measurement of the oxygen saturation in the blood. This measurement is based on the two forms of hemoglobin, deoxygenated hemoglobin and oxygenated hemoglobin normally present in the blood. The character of the light absorbance is different in these two forms of hemoglobin. The pulse oximeter measures oxygen saturation by detecting changes in infrared light absorbance. This is measured via a sensor that contains two light-emitting diodes and one photodiode. This sensor is clipped painlessly to a finger or an ear lobe, or it can be taped to the skin of the nose or temple. The amount of oxygenated hemoglobin present in the finger or othei part of the body determines the amount of light absorbed. Deoxygenated hemoglobin absorbs more red light than does oxygenated hemoglobin, but changes in hemoglobin oxygen saturation affect infrared light absorbance less than they affect red light absorbance. As a result, changes in the absorbance of red light and the absorbance of infrared light produce a ratio of oxygenated hemoglobin to deoxygenated hemoglobin, which is calculated by the oximeter and displayed as an oxygen saturation percentage.4
The accuracy of pulse oximeters in measuring arterial oxygen saturation in comparison with arterial blood gases has been established through previous studies. Hess and associates found the arterial oxygen saturation from the pulse oximeter to have a 0.96 correlation with the arterial oxygen saturation obtained from blood gases when the oxygen saturation was between 77% and 100%. 4 This difference in oxygen saturation was not considered to be clinically significant. In seven research studies using a similar oximeter, the correlations of oximeter saturation with arterial blood gases ranged from 0.91 to 0.99 An
Respiratory Changes with Aging
A variety of changes occur in the respiratory system with advancing age. These changes include decreased respiratory muscle strength, decreased compliance of the chest wall, and enlargement of the alveolar ducts leading to decreased pulmonary diffusing capacity.12 In addition lung weight is reduced by about 21%.13 Researchers have found that partial pressure of oxygen in arterial blood (PaO2) is reduced in healthy persons older than 60. 14 Sorbini and associates found that at sea level the arterial oxygen tension (PaO2)decreased in a linear fashion from a normal of 94 in a group with a median age of 23 to 74.3 in a group with a median age of 71. The arterial carbon dioxide tension remained within the normal range at all ages.14 Changes in carbon dioxide level are considered to reflect pulmonary disease while a reduction in oxygenation is considered to be a normal part of the aging process. 13
Changes with Aging
Like the respiratory system, cardiovascular changes also occur with aging. Many of the cardiovascular that occur are more likely due the presence of disease than the aging process.13 Due to the fact that approximately half of the persons over have some evidence of heart disit is difficult to differentiate normal changes from those due to disease.15 One of the changes commonly found in the elderly is an increase in the incidence of systolic and systolicdiastolic hypertension. The change is primarily due to the effects of arteriosclerosis.12 Maximum heart rate also with age due to changes in conduction system and decreased baroreceptor sensitivity.12*13 Some studies are inconclusive regarding the of aging on cardiac output.16·17 changes in the cardiovascular system can result in decreased organ perfusion.13
Effects of Altitude on Oxygenation
The amount of oxygen available for use by the tissues depends on a number of factors, including the functioning of the respiratory and circulatory systems and external factors, such as the available inspired oxygen. As the altitude increases above sea level, the barometric pressure decreases. Although the air is always 21% oxygen, the actual amount of oxygen inhaled is reduced at higher altitudes, resulting in varying degrees of hypoxia. The majority of the undesirable physiological and clinical changes occur at levels above 3,000 m (9,843 ft), but some individuals are affected at altitudes above 2,000 m (6,562 ft).18 The effects of altitude are more significant in those with chronic pulmonary or cardiac disease. ,9
This study sought answers to four research questions:
1 . What are the oxygen saturation levels of the well elderly?
2. Are the oxygen saturation levels of the well elderly who live at moderate altitude and those who live at low altitude within normal limits for their place of residence?
3. Is there a significant difference in the oxygen saturation levels of the well elderly who live at moderate altitude and those who live at low altitude?
4. Is there a significant difference in the oxygen saturation levels within these two groups according to gender?
Elderly is defined as those individuals 65 years of age or older.
Oxygen saturation is the oxygen content of the blood divided by its oxygen capacity. It is expressed in volume percent. The normal range for individuals under 65 years of age living at sea level is 95% to 100%. For those living at moderate altitude, it is 92% to 100%.
Moderate altitude is an area ranging from 2,000 m (6,562 ft) to 3,000 m (9,843 ft). In this study, moderate altitude was defined as 7,200 ft.
Low altitude is an area measuring less than 915 m (3,000 ft). In this study, low altitude was defined as 541 ft.
Data for this exploratory study were collected from a convenience sample of 91 noninstitutionalized subjects. They ranged in age from 65 to 91 years, with a mean age of 77.5 years. Twenty-eight of the subjects were men and 63 were women. Fifty of the participants (15 men and 35 women) were obtained from the senior center of a Western community at an altitude of 7,200 ft, and were designated as the moderate altitude group. The remaining 41 subjects (13 men and 28 women) were obtained from the senior center of a Southwestern city, located at 541 feet above sea level, and were known as the low altitude group. The mean age of the moderate altitude group was 76.2 years; that of the low altitude group was 74.8 years.
Pulse oximeters obtain data regarding oxygen saturation levels.
AU potential subjects were screened for a history of pulmonary disease prior to being asked to participate in the study. Those with chronic respiratory illnesses, such as bronchitis, asthma, emphysema, and lung cancer were excluded from the study, as were those with recent or current acute respiratory problems, ie, pneumonia, colds, and allergies.
The data regarding oxygen saturation levels were obtained using the same Nellcor N- 100 pulse oximeter at both study sites. The oximeter was calibrated in accordance with the manufacturer's directions. After placing the oximeter on either index finger, one measurement was taken per subject.
All data were analyzed using descriptive statistics, chi-square, and analysis of variance. The .05 level was set as the acceptable level of significance for this study.
OXYGEN SATURATION OF SUBJECTS LIVING AT MODERATE ALTITUDE*
OXYGEN SATURATION OF SUBJECTS LIVING AT LOW ALTITUDE*
The findings of this study suggest that the normal oxygen saturation levels of the well elderly are lower than those of younger people, regardless of place of residence (research question l).As seen in the Figure, 75%, or 69 of the 91 subjects, had an oxygen saturation of 95% or less. Only one subject had a saturation level of 100%, whereas a level of 99% was obtained for two of the participants. The remaining 19 subjects had saturation levels ranging from 96% to 98%.
When the data were examined to determine if the oxygen saturation levels of subjects living at moderate altitude and those living at low altitude were within normal limits for their place of residence, it was found that both groups were at the lower limits of normal for their respective altitudes (research question 2). That is, 44%, or 22 of the 50 participants, living at an altitude of 7,200 ft had oxygen saturation levels ranging from 92% to 94%, whereas 18% (9 subjects) had a saturation level of 91% (Table 1). Twelve subjects had levels between 87% and 90%, and 7 received readings ranging from 95% to 98%. None had oxygen saturation levels of 99% or 100%.
The findings were similar for the 4 1 participants in the low altitude group (Table 2). Thirteen subjects, 32%, had oxygen saturation levels of 95% to 96%, whereas 20%, or 8 subjects, experienced a level of 94%. Eight subjects had readings of 88% to 93%, and 10, or 24%, had readings of 97% to 98%. In contrast to those in the moderate altitude group, 2 subjects in the low altitude group had saturation levels of 99% and one had a level of 100%.
Further analysis regarding the oxygen saturation levels of those living at moderate altitude and those residing at low altitude revealed a significant difference between the two groups (research question 3). Analysis of variance showed that the mean oxygen saturation level of the moderate altitude group was 92% and that of the low altitude group was 95% (F= 31. 23, P=.000\). There were no significant differences in the saturation levels within these two groups according to gender (research question 4).
The following are identified as limitations of the study:
* A convenience sample was used without allowing for random selection.
* Health status for inclusion in the study was based on self- report. Therefore, it is possible that people with undiagnosed respiratory disease may have been included in the study.
* The use of a single oximeter reading may not have allowed for individual variations in oxygenation.
There are several implications of findings for nurses who work with the well elderly at various altiudes. Nurses must recognize that nornal oxygen saturation levels are differ;nt for those over 65 years of age who reside at moderate altitude and those ivho live at low altitude. Saturations are significantly lower in the aged who live at a moderate altitude. Such information should enable nurses to better evaluate the oxygenation status of their clients in relation to their place of residence rather than assuming that it is the same for all aged individuals. This may be particularly important when the elderly who live at a low altitude travel to a moderate altitude. Until their bodies adapt to the changes in altitude, their saturation levels may appear to be abnormally low in comparison to those who usually live at that altitude.
Older individuals who reside at low altitude and travel to areas of moderate altitude should be cautioned to modify their activities for several days after arrival. Because of the lower partial pressure of oxygen at higher altitudes, the risk of cardiac or pulmonary problems, (ie angina and pulmonary edema), may be increased. Individuals should carefully monitor their own responses to exercise in the higher altitude and decrease their activities if they develop symptoms of dyspnea. Nurses who practice at moderate altitudes need to inquire about the clients' usual place of residence if they present to a health-care facility with complaints of respiratory or cardiac difficulties, such as chest pain and shortness of breath.
Nurses must be aware that the usual oxygen saturation levels of the well elderly are at the lower limits of normal for their place of residence. Normal saturation at moderate altitude is 92% to 100%; the subjects in this study tended to have levels ranging from 91% to 93%. The normal oxygen saturation level for those at low altitude is 95% to 100%; participants in this study tended to have saturations ranging from 93% to 95%. Lower saturation levels may adversely affect various physiological functions, such as tissue oxygenation and wound healing, cardiopulmonary activity, peripheral vascular integrity, and cerebrovascular functioning. It is important to carefully assess older clients for signs and symptoms indicating alterations in any of these areas and plan appropriate interventions.
OXYGEN SATURATION OF THE WELL ELDERLY LIVING AT MODERATE AND LOW ALTITUDE*
It is important to evaluate changes in oxygen saturation levels against an individual's normal level. In both groups, a wide range of oxygen saturation levels existed. In the low altitude subjects, the saturation ranged from 88% to 100%, and in the moderate altitude subjects it ranged from 87% to 97%. Changes in oxygen saturation, like changes in blood pressure, need to be evaluated against the person's own level. Because pulse oximeters are used frequently during and after surgery, it is important to know an individual's oxygen saturation level before the procedure to evaluate changes afterwards.
Finally, because adequate oxygenation is so essentia] to physical and psychological functioning, additional nursing research studies are needed in this area. Future studies might investigate the effect of various altitudes on oxygen saturation levels in the well elderly over 85 years of age. The influence of high altitude, over 10,000 ft, on saturations could be compared with that of moderate and low altitudes in the well elderly in 10-year age increments. Another important area of study is the oxygen saturation of well elderly who travel from low altitude areas to areas of moderate altitude. It is important that nurses who provide care to the elderly take the lead in this research because they understand the unique needs of this population.
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OXYGEN SATURATION OF SUBJECTS LIVING AT MODERATE ALTITUDE*
OXYGEN SATURATION OF SUBJECTS LIVING AT LOW ALTITUDE*