CCN
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Critical Care Nurse. 2002;22: 69-74
Copyright © 2002 by the American Association of Critical-Care Nurses.
This Article
Right arrow Full Text (PDF)
Right arrow Respond to This Article
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Grap, M. J.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Grap, M. J.

Protocols for Practice
Applying Research at the Bedside

Pulse Oximetry*

Mary Jo Grap, PhD, RN, CCRN

Mary Jo Grap is currently an associate professor in the School of Nursing, Virginia Commonwealth University, Richmond, Va.

* This article was first published in CRITICAL CARE NURSE February 1998. An update follows. Back

This column is designed to provide the latest research findings in patient care in a format that is easy to understand and integrate into clinical practice. The information is drawn from individual protocols in the various Protocols for Practice series available from AACN, which cover research-based practice protocols in detail.

Pulse oximetry is a noninvasive technology used to estimate oxyhemoglobin saturation. As many as 87% of nurses report that they regularly use this technology to assess the status of patients; however, a recent report of hospital staff’s knowledge of pulse oximetry showed that only 36% of the nursing staff felt they had adequate training in the use of pulse oximetry. In addition, only 68.5% of all hospital staff tested (nursing and medical staff) correctly stated what pulse oximeters measure. Answers to questions regarding the principles of pulse oximetry, potential errors, normal ranges, or the physiology of oxygen hemoglobin dissociation varied but generally reflected limited understanding.1 The questions and answers presented here may enhance your understanding of this commonly used technology.

Q: What does pulse oximetry measure?

Pulse oximetry is used for continuous noninvasive measurement of arterial oxygen saturation. Most of the oxygen transported by the blood is bound to hemoglobin, and the degree of binding—the saturation—is determined by the percentage of hemoglobin that is loaded with oxygen.2 The pulse oximeter detects and calculates the absorption of light by functional hemoglobins to produce a measurement, SpO2, that is an estimate of arterial oxygen saturation (SaO2). Functional hemoglobins are those active in the transport of oxygen: oxygenated and deoxygenated (reduced) hemoglobin. Absorption of light by oxygenated hemoglobin differs from the absorption by deoxygenated hemoglobin. The pulse oximeter probe contains two light-emitting diodes on one side, which emit two wavelengths of monochromatic light—red and infrared—and a photo detector on the other side (Figure 1Go). The two diodes are cycling on and off 400 or 480 times per second, with only one on at a time.3 This enables a single detector to be used to sample first one wavelength and then the other.



View larger version (15K):
[in this window]
[in a new window]
  		Figure 1 Placement of the photodetector and light-emitting diodes of a pulse oximetry sensor

 
Both wavelengths of light are also absorbed by venous blood and tissues. The hemoglobin absorption of light is analyzed over a full pulse beat to make the saturation measurement independent of these factors. The total absorption of light has a constant component from the tissue and from steadily flowing venous blood, and a changing component as a result of arterial pulsation. The constant component is subtracted from the total, so that the net absorption of each wavelength can be attributed to arterial blood only.3 A calculation based on previously determined calibration curves is used to relate this transcutaneous light absorption to directly measured SaO2. Pulse oximeters are calibrated empirically by using observations taken from healthy volunteers.4 To estimate SpO2 with a wide range of pulse amplitudes, the pulse oximeter automatically increases its amplifications as the pulse signal decreases. The saturation values that are displayed are not instantaneous but are averages taken over 3 to 10 seconds to help reduce the effect of pressure wave variations due to motion of the subject.5

Therefore, pulse oximetry measures only the percentage of hemoglobin that is carrying oxygen. It provides no specific information about the patient’s overall level of hemoglobin, adequacy of ventilation, or how well the oxygenated hemoglobin is being delivered to the tissues.

Q: How accurate is pulse oximetry?

Numerous studies have addressed the accuracy of pulse oximeters, primarily over the range of 70% to 100% saturation. Excellent correlation has been found between pulse oximetry and the "goldstandard" in vitro CO-oximetry measurements.6–8 These have been found to be accurate for SpO2 from 70% to 100% and within ± 2%. For SpO2 above 70%, approximately 68% of the data will fall within ±2% of the actual saturation, and 95% of the data will fall within ±4% of the actual saturation. For example, in a patient with a pulse oximeter reading of 92%, 95% of the time the true SaO2 value, as measured by arterial blood gases, would be between 88% and 96%. For saturations below 70%, manufacturers generally state that accuracy is "unspecified." Pulse - rate monitoring with pulse oximetry ranges from 20 to 30, to 250 beats per minute, with manufacturers accuracy statements indicating a range from ±1 to 2 beats per minute for the scale stated.9,10

Q: When should pulse oximetry be used?

Because desaturation is detected earlier by pulse oximetry than by clinical observation,7,11,12 the use of pulse oximetry is recommended for any patient at risk for hypoxemia (Table 1Go7–53).


View this table:
[in this window]
[in a new window]
  		Table 1 Circumstances in which pulse oximetry is recommended

 
Because the algorithms used for deriving SpO2 from light absorption are based on healthy volunteers, single pulse oximetry measurements for patients with low arterial saturation (less than 70%) may result in inaccuracies; however, even in these patients it is a valuable tool for showing trends.19,54–56 In addition, pulse oximetry may be less useful in the presence of dyshemoglobins2,57–61 such as carboxyhemoglobin, which is seen in smokers, patients suffering from carbon monoxide inhalation, and patients undergoing dapsone therapy; and methemaglobin, seen in patients undergoing nitrate, nitroprusside, or lidocaine therapy. It may also be less useful in patients with severe anemia, because the hemoglobin level may be too low to ensure proper functioning of the oximeter.62–64

Q: What is the best location for the pulse oximeter probe?

Choose a site with the best pulsatile vascular bed: the finger (Figure 2Go), toe, ear lobe, and bridge of the nose have been used. In infants, flexible probes work through the palm, foot, penis, or arm. The cheek or wing of the nostril have also been used. However, overall performance of finger probes is generally found to be better than performance of probes at other sites.8 However, because the ear-lobe is the least vasoactive site and is least susceptible to signal loss, it may show faster response and greater accuracy during periods of vasoconstriction and hypotension. Nose and forehead probes perform poorly when SpO2 is low. Manufacturers generally recommend use of the foot for infants56,65–70 (Figure 3Go).



View larger version (19K):
[in this window]
[in a new window]
  		Figure 2 Finger placement of a pulse oximetry sensor

 


View larger version (11K):
[in this window]
[in a new window]
  		Figure 3 Sensor placement on the foot of an infant

 
When placing probes on fingers or toes, remove nail polish, especially blue, black, green, brown/ red, or synthetic nails; or place the probe sideways on the finger. Synthetic nails and some colors of nail polish may result in errors of 3% to 6%. In addition, SpO2 values may be lower in dependent extremities than in nondependent sites. Blood flow to the extremity where the sensor is placed should not be impeded in any way. The sensor should be placed on the extremity opposite arterial lines and noninvasive blood pressure monitoring devices so that pulsatile flow is not interrupted.2,22,71–73

Q: What are normal parameters and what should also be assessed with pulse oximetry?

Optimal SpO2 is greater than 95%; SpO2 less than 90% reflects desaturation. However, SpO2 is not an adequate monitor of ventilation. In situations of ventilation or acid-base abnormalities (resulting in shifts of the oxyhemoglobin dissociation curve), arterial blood gases must also be monitored. Remember that measurements during hypoperfusion and vasoconstriction may not be accurate. Nursing care decisions should be based on SpO2 trends rather than on isolated values. If SpO2 measurements and other oxygenation assessment data conflict, obtain arterial blood gases to verify oxygenation status. Include pulse oximetry measurement as only one part of a total oxygenation and ventilation assessment. Also remember that SpO2 indicates the amount of hemoglobin that is saturated with oxygen. It does not provide any information about the amount of hemoglobin present, the adequacy of ventilation, or cardiac output. These must also be assessed on a regular basis.

In summary, pulse oximetry is an extremely valuable, noninvasive technology and with a complete understanding of its uses and limitations, this technology can assist nurses in providing comprehensive care to their patients.

This article is based on the protocol "Pulse Oximetry" by Mary Jo Grap, from the Noninvasive Monitoring series of AACN’s Protocols for Practice. It can be obtained from AACN, 101 Columbia, Aliso Viejo, CA 92656–1491, (800) 899-AACN.

Acknowledgments

"Pulse Oximetry" by Mary Jo Grap, one of AACN’s Protocols for Practice, was sponsored by Nellcor Puritan Bennett.

References

  1. Kruger PS, Longden PJ. A study of a hospital staff’s knowledge of pulse oximetry. Anaesth Intensive Care. 1997;25:38–41.[Medline]
  2. Ralston AC, Webb RK, Runciman WB. Potential errors in pulse oximetry. I. Pulse oximeter evaluation. Anaesthesia. 1991;46:202–206.[Medline]
  3. Severinghaus JW, Honda Y. History of blood gas analysis. VII. Pulse oximetry. J Clin Monit. 1987;3:135–138.[Medline]
  4. Szaflarski NL, Cohen NH. Use of pulse oximetry in critically ill adults. Heart Lung. 1989;18:444–453.[Medline]
  5. Severinghaus JW. History and recent developments in pulse oximetry. Scand J Clin Lab Invest Suppl. 1993;214:105–111.[Medline]
  6. Technology Subcommittee of the Working Group on Critical Care. Non-invasive blood gas monitoring: a review for use in the adult critical care unit. Can Med Assoc J. 1992;146:703–721.[Abstract]
  7. Severinghaus JW, Kelleher JF. Recent developments in pulse oximetry. Anesthesiology. 1992;76:1018–1038.[Medline]
  8. Tittle M, Flynn MB. Correlation of pulse oximetry and co-oximetry. Dimens Crit Care Nurs. 1997;16:88–95.[Medline]
  9. Kelleher JF. Pulse oximetry. J Clin Monit. 1989;5:37–62.[Medline]
  10. Tremper KK, Barker SJ. Pulse oximetry. Anesthesiology. 1989;70:98–108.[Medline]
  11. Eichhorn JH. Pulse oximetry as a standard of practice in anesthesia. Anesthesiology. 1993;78:423–426.[Medline]
  12. Cote CJ. Pulse oximetry during conscious sedation. JAMA. 1994;271:429–430.
  13. Cote CJ, Rolf N, Liu LM, et al. A single-blind study of combined pulse oximetry and capnography in children. Anesthesiology. 1991;74:980–987.[Medline]
  14. Fiechter FK. Results of a quality assurance study on the use of pulse oximetry in the postanesthesia care unit. J Post Anesth Nurs. 1991;6:342–346.[Medline]
  15. Moller JT, Johannessen NW, Berg H, Espersen K, Larsen LE. Hypoxaemia during anaesthesia—an observer study. Br J Anaesth. 1991;66:437–444.[Abstract/Free Full Text]
  16. Miyasaka K, Katayama M, Kusakawa I, Ohata J, Kawano T, Honma Y. Use of pulse oximetry in neonatal anesthesia. J Perinatol. 1987;7:343–345.[Medline]
  17. Friesen RH. Pulse oximetry during pulmonary artery surgery. Anesth Analg. 1985;64:376.[Free Full Text]
  18. Jennis MS, Peabody JL. Pulse oximetry: an alternative method for the assessment of oxygenation in newborn infants. Pediatrics. 1987;79:524–528.[Abstract/Free Full Text]
  19. Mihm FG, Halperin BD. Noninvasive detection of profound arterial desaturations using a pulse oximetry device. Anesthesiology. 1985;62:85–87.[Medline]
  20. Moore FA, Haenel JB, Moore EE, Abernathy CM. Hypoxic events in the surgical intensive care unit. Am J Surg. 1990;160:647–651.[Medline]
  21. Fanconi S, Doherty P, Edmonds JF, Barker GA, Bohn DJ. Pulse oximetry in pediatric intensive care: comparison with measured saturations and transcutaneous oxygen tension. J Pediatr. 1985;107:362–366.[Medline]
  22. Peabody JL, Jennis MS, Emery JR. Pulse oximetry—an alternative to transcutaneous PO2 in sick newborns. Adv Exp Med Biol. 1987;220:145–150.[Medline]
  23. Hay WW, Jr, Brockway JM, Eyzaguirre M. Neonatal pulse oximetry: accuracy and reliability. Pediatrics. 1989;83:717–722.[Abstract/Free Full Text]
  24. Schnapf BM. Oxygen desaturation during fiberoptic bronchoscopy in pediatric patients. Chest. 1991;99:591–594.[Abstract/Free Full Text]
  25. O’Connor KW, Jones S. Oxygen desaturation is common and clinically under-appreciated during elective endoscopic procedures. Gastrointest Endosc. 1990;36:S2–4.[Medline]
  26. Bell GD, McCloy RF, Charlton JE, et al. Recommendations for standards of sedation and patient monitoring during gastrointestinal endoscopy. Gut. 1991;32:823–827.[Abstract/Free Full Text]
  27. Al-Hadeedi S, Leaper DJ. Falls in hemoglobin saturation during ERCP and upper gastrointestinal endoscopy. World J Surg. 1991;15:88–94.[Medline]
  28. Bendig DW. Pulse oximetry and upper intestinal endoscopy in infants and children. J Pediatr Gastroenterol Nutr. 1991;12:39–43.[Medline]
  29. Hensley FA, Jr, Dodson DL, Martin DE, Stauffer RA, Larach DR. Oxygen saturation during preinduction placement of monitoring catheters in the cardiac surgical patient. Anesthesiology. 1987;66:834–836.[Medline]
  30. Dodson SR, Hensley FA, Jr, Martin DE, Larach DR, Morris DL. Continuous oxygen saturation monitoring during cardiac catheterization in adults. Chest. 1988;94:28–31.[Abstract/Free Full Text]
  31. Holburn CJ, Allen MJ. Pulse oximetry in the accident and emergency department. Arch Emerg Med. 1989;6:137–142.[Medline]
  32. Jones J, Heiselman D, Cannon L, Gradisek R. Continuous emergency department monitoring of arterial saturation in adult patients with respiratory distress. Ann Emerg Med. 1988;17:463–468.[Medline]
  33. Lambert MA, Crinnion J. The role of pulse oximetry in the accident and emergency department. Arch Emerg Med. 1989;6:211–215.[Medline]
  34. Maneker AJ, Petrack EM, Krug SE. Contribution of routine pulse oximetry to evaluation and management of patients with respiratory illness in a pediatric emergency department. Ann Emerg Med. 1995;25:36–40.[Medline]
  35. Galdun JP, Paris PM, Stewart RD. Pulse oximetry in the emergency department. Am J Emerg Med. 1989;7:422–425.[Medline]
  36. Kulick RM. Pulse oximetry. Pediatr Emerg Care. 1987;3:127–130.[Medline]
  37. McGuire TJ, Pointer JE. Evaluation of a pulse oximeter in the prehospital setting. Ann Emerg Med. 1988;17:1058–1062.[Medline]
  38. Phillips GD, Runciman WB, Ilsley AH. Monitoring in emergency medicine. Resuscitation. 1989;18(suppl):S21–35.
  39. Rotello LC, Warren J, Jastremski MS, Milewski A. A nurse-directed protocol using pulse oximetry to wean mechanically ventilated patients from toxic oxygen concentrations. Chest. 1992;102:1833–1835.[Abstract/Free Full Text]
  40. Withington DE, Ramsay JG, Saoud AT, Bilodeau J. Weaning from ventilation after cardiopulmonary bypass: evaluation of a non-invasive technique. Can J Anaesth. 1991;38:15–19.[Medline]
  41. Niehoff J, DelGuercio C, LaMorte W, et al. Efficacy of pulse oximetry and capnometry in postoperative ventilatory weaning. Crit Care Med. 1988;16:701–705.[Medline]
  42. Rasanen J, Downs JB, Malec DJ, DeHaven B, Garner WL. Real-time continuous estimation of gas exchange by dual oximetry. Intensive Care Med. 1988;14:118–122.[Medline]
  43. King T, Simon RH. Pulse oximetry for tapering supplemental oxygen in hospitalized patients. Evaluation of a protocol. Chest. 1987;92:713–716.[Abstract/Free Full Text]
  44. Prakash O. Oximetry in the weaning of the ventilator patient. In: Payne JP, Severinghaus JW, eds. Pulse Oximetry. New York, NY: Springer-Verlag; 1986:119–124.
  45. Fanconi S. Pulse oximetry and transcutaneous oxygen tension for detection of hypoxemia in critically ill infants and children. Adv Exp Med Biol. 1987;220:159–164.[Medline]
  46. Evans A, Winslow EH. Oxygen saturation and hemodynamic response in critically ill, mechanically ventilated adults during intrahospital transport. Am J Crit Care. 1995;4:106–111.
  47. Guidelines Committee, American College of Critical Care Medicine, Society of Critical Care Medicine and the Transfer Guidelines Task Force. Guidelines for the transfer of critically ill patients. Am J Crit Care. 1993;2:189–195.
  48. Hanna D. Guidelines for pulse oximetry use in pediatrics. J Pediatr Nurs. 1995;10:124–126.[Medline]
  49. Runcie CJ, Reeve W. Pulse oximetry during transport of the critically ill. J Clin Monit. 1991;7:348–349.
  50. Tyler IL, Tantisira B, Winter PM, Motoyama EK. Continuous monitoring of arterial oxygen saturation with pulse oximetry during transfer to the recovery room. Anesth Analg. 1985;64:1108–1112.[Abstract/Free Full Text]
  51. Agency for Health Care Policy and Research. Acute pain management: operative or medical procedures and trauma, Part 1. Clin Pharm. 1992;11:309–331.[Medline]
  52. Hedges JR, Cionni DJ, Amsterdam JT, Embry S. Oxygen desaturation in adults following inhaled metaproterenol therapy. J Emerg Med. 1987;5:77–81.[Medline]
  53. American Academy of Pediatrics Committee on Drugs. Guidelines for monitoring and management of pediatric patients during and after sedation for diagnostic and therapeutic procedures. Pediatrics. 1992;89:1110–1115.[Abstract/Free Full Text]
  54. Severinghaus JW, Naifeh KH, Koh SO. Errors in 14 pulse oximeters during profound hypoxia. J Clin Monit. 1989;5:72–81.[Medline]
  55. Severinghaus JW, Naifeh KH. Accuracy of response of six pulse oximeters to profound hypoxia. Anesthesiology. 1987;67:551–558.[Medline]
  56. Kagle DM, Alexander CM, Berko RS, Giuffre M, Gross JB. Evaluation of the Ohmeda 3700 pulse oximeter: steady-state and transient response characteristics. Anesthesiology. 1987;66:376–380.[Medline]
  57. Anderson ST, Hajduczek J, Barker SJ. Benzocaine-induced methemoglobinemia in an adult: accuracy of pulse oximetry with methemoglobinemia. Anesth Analg. 1988;67:1099–1101.[Medline]
  58. Barker SJ, Tremper KK, Hyatt J. Effects of methemoglobinemia on pulse oximetry and mixed venous oximetry. Anesthesiology. 1989;70:112–117.[Medline]
  59. Eisenkraft JB. Pulse oximeter desaturation due to methemoglobinemia. Anesthesiology. 1988;68:279–282.[Medline]
  60. Varon AJ. Methemoglobinemia and pulse oximetry. Crit Care Med. 1992;20:1363–1364.
  61. Vegfors M, Lennmarken C. Carboxyhaemoglobinaemia and pulse oximetry. Br J Anaesth. 1991;66:625–626.[Abstract/Free Full Text]
  62. Lee S, Tremper KK, Barker SJ. Effects of anemia on pulse oximetry and continuous mixed venous hemoglobin saturation monitoring in dogs. Anesthesiology. 1991;75:118–122.[Medline]
  63. Severinghaus JW, Koh SO. Effect of anemia on pulse oximeter accuracy at low saturation. J Clin Monit. 1990;6:85–88.[Medline]
  64. Ralston AC, Webb RK, Runciman WB. Potential errors in pulse oximetry. III: effects of interferences, dyes, dyshaemoglobins, and other pigments. Anaesthesia. 1991;46:291–295.[Medline]
  65. Palve H, Vuori A. Pulse oximetry during low cardiac output and hypothermia states immediately after open heart surgery. Crit Care Med. 1989;17:66–69.[Medline]
  66. Rutherford KA. Principles and application of oximetry. Crit Care Nurs Clin North Am. 1989;1:649–657.[Medline]
  67. Robertson RE, Kaplan RF. Another site for the pulse oximeter probe. Anesthesiology. 1991;74:198.
  68. Rosenberg J, Pedersen MH. Nasal pulse oximetry overestimates oxygen saturation. Anaesthesia. 1990;45:1070–1071.[Medline]
  69. Broome IJ, Reilly CS. Explanation for the overestimation of oxygen saturation seen using nasal pulse oximetry. Anaesthesia. 1991;46:424.
  70. Lema GE. Oral pulse oximetry in small children. Anesth Analg. 1991;72:414.
  71. New W Jr. Pulse oximetry. J Clin Monit. 1985;1:126–129.[Medline]
  72. Cote CJ, Goldstein EA, Fuchsman WH, Hoaglin DC. The effect of nail polish on pulse oximetry. Anesth Analg. 1988;67:683–686.[Abstract/Free Full Text]
  73. Rubin AS. Nail polish color can affect pulse oximeter saturation. Anesthesiology. 1988;68:825.[Medline]




This Article
Right arrow Full Text (PDF)
Right arrow Respond to This Article
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Grap, M. J.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Grap, M. J.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS