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(Mis) Using pulse oximetry: a review of pulse oximetry use in acute care medical wards
(Mis) Using pulse oximetry: a review of pulse oximetry use in acute care medical wards Stephen B. Simon and Robyn A. Clark
Background: Nurses routinely use pulse oximetry (SpO2 ) monitoring equipment in acute care. Interpretation of the reading involves physical assessment and awareness of parameters including temperature, haemoglobin, and peripheral perfusion. However, there is little information on whether these clinical signs are routinely measured or used in pulse oximetry interpretation by nurses. Aim: The aim of this study was to review current practice of SpO2 measurement and the associated documentation of the physiological data that is required for accurate interpretation of the readings. The study reviewed the documentation practices relevant to SpO2 in five medical wards of a tertiary level metropolitan hospital. Method: A prospective casenote audit was conducted on random days over a three-month period. The audit tool had been validated in a previous study. Results: One hundred and seventy seven episodes of oxygen saturation monitoring were reviewed. Our study revealed a lack of parameters to validate the SpO2 readings. Only 10% of the casenotes reviewed had sufficient physiological data to meaningfully interpret the SpO2 reading and only 38% had an arterial blood gas as a comparator. Nursing notes rarely documented clinical interpretation of the results. Conclusion: The audits suggest that medical and nursing staff are not interpreting the pulse oximetry results in context and that the majority of the results were normal with no clinical indication for performing this observation. This reduces the usefulness of such readings and questions the appropriateness of performing ‘‘routine’’ SpO2 in this context. Crown Copyright c 2003 Published by Elsevier Science Ltd. All rights reserved.
Keywords: pulse oximetry monitoring, clinical observations, medical wards Stephen B. Simon RN, BN, MN (Research), Nurse Manager Projects, Internal Medical Service, Royal Adelaide Hospital, North Terrace, Adelaide 5000, Australia Robyn A. Clark RN. RM., ICU Cert., BN, MEd., FRCNA, Clinical Lecturer, Department of Clinical Nursing, The Adelaide University, Royal Adelaide Hospital, Frome Road, Adelaide 5005, Australia Correspondence to: Stephen B. Simon Tel.: +61-08-8222-5836; fax: +61-8222-5588; E-mail: [email protected]
INTRODUCTION The use of oximetry has been increasing across this studyÕs acute medical wards for the past ten years. A survey of patient care plans in 2001 demonstrated that at any given time, 50% of patients had SpO2 monitoring.
BACKGROUND Traditional vital signs have consisted of temperature, pulse respiratory rate, and blood pressure. In
Clinical Effectiveness in Nursing (2002) 6, 106–110 Crown Copyright doi:10.1016/S1361-9004(02)00088-2
C
recent times it has been suggested that these four parameters could be supplemented with other measurements such as nutritional status, smoking status, spirometry, and pulse oximetry (Evans et al. 1999). A systematic review completed by Jensen et al (1998) on the effectiveness of SpO2 found that pulse oximeters were accurate within 2% (2SD) or 5% (2SD) of in vitro oximetry in the range of 70% to 100% SpO2 . In comparing ear and finger, probes, readings from finger probes were more accurate. Pulse oximeters may fail to record accurately the true SpO2 during severe or rapid desat-
2003 Published by Elsevier Science Ltd. All rights reserved.
(Mis) Using pulse oximetry: a review of pulse oximetry use in acute care medical wards 107
uration, hypotension, dyshaemoglobin, and low perfusion states (Jensen et al. 1998; Sidhu 1997). Pulse oximetry is perhaps the most commonly recommended addition to the traditional vital signs. It has been suggested that in the newborn skin colour alone is an inadequate indicator of oxygenation and that pulse oximetry will provide important information for clinicians (Katzman 1995). It may also be useful in situations such as pulmonary outpatient departments, for patients receiving oxygen therapy and those with moderate to severe pulmonary disease who may have borderline hypoxaemia (Neff 1988). Although limited studies are available to support this (Levin et al. 2001; Buckley et al. 1997) pulse oximetry has been recommended for patient with haemodynamic monitoring, perioperative patients and patients in emergency departments. Holburn and Allen (1989) have reported that the use of pulse oximetry significantly changed medical treatment for the acutely ill in the emergency department and reduced the need for arterial blood gas analysis by 37%. In the systematic review of vital signs research published by the Joanna Briggs Institute for Nursing and Midwifery 1999 no studies were identified that evaluated pulse oximetry in the general wards. A pulse oximeter monitor measures the oxygen saturation in the mixed capillary blood of the peripheral circulation. Normal sites for measurement include fingers, toes, earlobe, and bridge of the nose. The value presented by the monitor represents the ratio of oxyhaemoglobin to all haemoglobin capable of transporting O2 . It is based on the distinct light absorption capacities of oxyhaemoglobin compared to deoxyhaemoglobin. In essence, it measures the ‘‘redness’’ of the blood (Wesmiller & Hoffman 1989). The pulse oximeter, however, only measures the percentage of saturated haemoglobin. It does not measure the amount of oxygen available for tissues, rather it gives an indication of what may be available. The amount of oxygen in the blood is dependent on the amount of dissolved oxygen, the amount of haemoglobin, and the affinity of haemoglobin for O2 (Ganong 1996). Other factors that affect the affinity of haemoglobin for oxygen and the amount of oxygen available for body tissues are blood pH and temperature (Goodfellow 1997). For example, two patients may present with a Pulse oximeter reading of 85%. However they may have two very different PaO2 levels as demonstrated in the following two case vignetteÕs. Case One: This patient presented with a Staphylococcal aureus septicaemia from an infected wound. They had a normal haemoglobin of 150 g/ L, a blood gas analysis that showed a PaCO2 of 46.7 mmHg, HCO3 of 15, pH 7.13. Their oral body temperature was 39 C. This patient had a PaO2 of 72 mmHg and 2.16 ml of dissolved oxygen.
Case Two: This patient presented with a slow bleeding gastric ulcer for which they were self medicating with large doses of antacid. Their haemoglobin was low, at 91 g/L, and a blood gas analysis showed a PaCO2 of 47 mmHg, HCO3 37.7, and pH 7.53. Their body temperature was 36 C. However, in contrast to Case One, this patient only had a PaO2 of 43 mmHg, and 1.29 ml of dissolved oxygen per litre, a hypoxic picture. These patients, who had the same pulse oximetry reading of 85%, would require different approaches to treatment of their hypoxia. If these patients did not have a blood gas that highlighted these differences would clinicians have enough information to implement appropriate oxygen therapy? Clinical evaluation is enhanced therefore, when these parameters are known, and the saturation reading becomes more significant. Another factor to consider when monitoring pulse oximetry is the relationship between saturation and arterial blood oxygen measurement. This is not linear. In fact the curve has a safe zone and a very steep slope where the difference between PaCO2 and SpO2 widens rapidly. (Ganong 1996; Dickson 1995). The saturation reading can also be affected by probe location, ambient light, other patient physiology such as: abnormal haemoglobin, carbon monoxide levels of smokers, skin pigment, hyperbilirubinaemia, nail polish, or careless procedure such as using the same arm for blood pressure whilst taking a reading. Finally, although compared to blood gas analysis pulse oximetry is an inexpensive safe and non-invasive process for the patient (Miller 1998), the high usage of the technology leads to considerable wear and tear, which can make the maintenance and replacement of consumables such as the finger probes an expensive exercise. It is also expensive in terms of staff time, as in the medical areas of this study, there is only one machine per ward. In the process of ‘‘routinisation’’ of this observation, time is wasted waiting for this resource ‘‘to do the obs’’.
AIMS AND OBJECTIVES OF THE STUDY Aim The aim of this study was to review current practice of SpO2 measurement and documentation by nurses in the setting of five acute medical wards.
Objectives The objectives were to: •
determine who initiated pulse oximetry readings for the individual patient e.g., nurse or medical officer; and what if any were the clinical indications;
108 Clinical Effectiveness in Nursing
•
•
•
•
determine if pulse oximetry was performed in the context of known baseline parameters, e.g,. haemoglobin, blood gas, temperature, oxygen therapy, or peripheral perfusion measurement; determine the extent of interpretation of SpO2 results by nurses as documented in patient case notes; to examine the ‘‘routinisation’’ of this observation and the possible use of pulse oximetry monitoring when not clinically indicated; make recommendations for further research.
METHOD A prospective casenote review was employed using a data collection tool, which had been tested during an initial pilot study. A convenience sample was used by reviewing all casenotes of the inpatients on the five pre-selected wards to find who had had SpO2 readings. Data was collected over a 3-month period on random days to gain adequate numbers, and ensure patient data was not repeated. The inclusion criteria was all patients having pulse oximetry readings in the pre-selected ward on the day of audit. Patients who did not have documented oxygen saturation results were excluded from the audit. To meet the aims of the study the research team reviewed documentation of the following issues associated with the monitoring of SpO2 : most recent SpO2 reading; lowest SpO2 reading; presence of a medical order for oximetry and/or oxygen therapy; current haemoglobin; comparison of admission haemoglobin, and current haemoglobin; presence of an arterial blood gas; the days elapsed since the latest blood gas and current SpO2 reading; the SpO2 reading at the time of the arterial gas; the patient temperature and respiratory rate at the time of the blood gas; documentation of peripheral perfusion; documented interpretation of the SpO2 ; and, the need for oximetry in the nursing care plan. The data was entered onto a spreadsheet, and analysis utilised descriptive statistics, frequencies, means and standard deviations.
RESULTS One hundred and seventy seven patients casenotes were reviewed in the period of the study in 5 acute medical wards. The mean of the most recent SpO2 was 95.6% (SD 3.57, range 60–96%). The mean of the lowest recorded SpO2 was 94.5% (SD 3.99, range 60–99%). Fifty nine patients had a documented blood gas taken on average 8.9 days prior to the most recent SpO2 . The mean of the arterial blood gas for these 59 patients was pH 7.42, PaO2 83.7 mmHg, PaCO2
42.4 mmHg, HCO3 28.19 ml/eq and a matching saturation of 95.8%. Temperature at the time of the blood gas had a mean of 37.17 C, whereas the mean temperature with the most current SpO2 was 36.46 C. The mean respiratory rate at the time of the blood gas was 23.5 breaths per minute. The mean respiratory rate at the time of the latest SpO2 was 19.95 breaths per minute. Ninety two percent of all patients had a documented haemoglobin (Hb) level. Medical orders requesting oximetry monitoring was present in 41.8% of patients. Oxygen therapy orders were present in 20% of patients having oximetry readings, however, 22% had oxygen therapy current. Assessment of peripheral perfusion was documented on only one patient. 44.2% of patients had a nursing care plan entry for oximetry readings. However, in the written nursing care report 66.7% of entries had either no reference to the SpO2 , or made no interpretation of the results.
DISCUSSION Of the 177 casenotes reviewed, there were 254 recorded oximeter readings. These were divided into two separate groupings: the most recently recorded SpO2 , and the lowest recorded SpO2 . In the most recent SpO2 group, the highest reading was 96%, and the lowest reading was 60%. In the lowest recorded SpO2 group, the highest reading was 99%, and the lowest was 60%. Of these 254 results, 95 (37%) were above 97% and 64 were below 95% (25%). Based on the physiology presented in this article, the 95 patients with SpO2 readings of 97–99% had a normal SpO2 and did not require further investigation. It may also be argued that 25%, that is, those with SpO2Õs below 95%, needed other parameters such as haemoglobin levels, pH, and body temperature to assist in interpreting the result. The remaining 34% with results between 95– 97% may also have required other clinical information to make meaningful clinical interpretation of these results (York & Moddemann 1989). The low number of blood gases appears to indicate that the pulse oximeter was being used as the sole indicator of arterial blood oxygen levels, instead of being used as designed, which is as an instrument to measure oxygen saturation of haemoglobin (Tittle & Flynn 1997). As illustrated, the blood gas analysis had an abnormal, though not markedly so, picture. The data illustrated 31 of the 59 readings having abnormal pH with the most acidic reading being 7.16, and the highest alkalosis 7.53. Temperature also changed between readings. Therefore, the oxyhaemoglobin curve would have moved, at times considerably between admission and the 8th day (the
(Mis) Using pulse oximetry: a review of pulse oximetry use in acute care medical wards 109
average gap between blood gas and latest saturation reading). Saturation on admission and 8 days later would therefore, be representing different arterial oxygen concentration values. No evidence was found that indicated this fact was being considered in the decision making process. The haemoglobin levels found in this study illustrates an important observation when thinking of using the pulse oximeter. It can be noted that half the population had haemoglobin levels below normal. Few had haemoglobinÕs in the higher 140– 150 g/L range. It may be advocated that with this picture, the observer of patient clinical signs should always be aware of the personÕs haemoglobin levels. Haemoglobin is not only important in oxygen transport, but knowledge of haemoglobin levels can be an important clinical marker of exercise tolerance, healing speed, and in part, nutritional adequacy. As saturation measures the amount of oxygen attached to each haemoglobin, not the amount of haemoglobin present, the saturation reading will not tell the observer whether the total amount of oxygen present is low. A patient with 50 g of haemoglobin per litre can still have a 100% saturation reading. However, the blood can only carry one third the total of a person with a haemoglobin of 150 g/L, which is 100% saturated. A haemoglobin of 50 g/L, therefore, supplies the cells with one third the usual supply. The heart that extracts up to 85% of the supplied oxygen to it will be at clinical risk if action is not taken, if the heart work rate to increases, such as in infective states. In this situation oxygen therapy may be useful until transfusion can take place. Notably there was a drop of 14 g/L from admission to the studyÕs most recent SpO2 reading (average from 24 patients who had readings that could be compared), not a large fall, but still a part of the larger clinical picture. Knowing both haemoglobin and saturation will assist in a more complete picture of clinical relevance. Finally, it was found that nurses initiated more than half the readings themselves, that appeared to be a ‘‘routinisation’’ of the ‘‘patient obs’’. Is it arguable that the saturation was being done outside of context in these cases because, though a nurse can determine frequency and the action of doing a saturation reading, they are unable to order blood tests needed for further information.
SUMMARY The aim of this study was to: 1. Determine if pulse oximetry was performed in the context of know baseline parameters, e.g., haemoglobin, blood gas, temperature, or oxygen therapy. The audit demonstrated that only 10% of patients reviewed had all of the baseline parameters required to make
2.
3.
4.
5.
meaningful interpretation of the SpO2 results or conversely 90% did not. Determine the extent of interpretation of SpO2 results by nurses through the examination of documentation. The audit demonstrated that in 66.8% of the casenotes reviewed, where SpO2 results that had been documented, there was neither mention of this procedure in the nursing care plan nor interpretation in the nursing notes apart from the re-entry of the results. Determine whether the pulse oximeter use was as a result of a medical order. The audit demonstrated that 58% of the pulse oximetry monitoring review was nurse initiated. To examine the possible routinisation of the observation and the possible use of pulse oximetry monitoring when not clinically indicated. This aim was not possible to judge as 90% of patients did not have sufficient baseline parameters to determine if there was an underlining respiratory problem. However, as the observation was generally a spot observation, with 78% of patients not receiving oxygen therapy, and the majority having saturation readings greater than 95% (York & Moddemann 1989), from this data it can be hypothesised that pulse oximetry was used in the majority of cases where it was not clinically indicated. And finally the main aim of this audit was to establish a framework and make recommendations on which to conduct further research. These recommendations are presented below.
RECOMMENDATIONS 1. An interpretive study to review the current practices of ‘‘routine obs’’ in the acute care setting. 2. A study to determine the current nursing and medical knowledge of pulse oximetry monitoring. 3. An interventional study to determine the cost benefit of using pulse oximetry only when clinically indicated in the general ward areas.
CONCLUSION The data illustrated that the use of pulse oximetry was performed with very little documentation of interpretation of the results. It showed that the majority of readings are done as stand alone observations. There appeared to be a large number of SpO2 observed that had no clinical application, and therefore it could be deducted that the time used to perform these observations could have been more significantly focused. The data did not demonstrate evidence that the oximeter was being used as a trend measure for titrating oxygen therapy. Finally,
110 Clinical Effectiveness in Nursing
oximetry readings in this study were useful in what appeared to be 10% of all patients on which it was used. The audits suggest that medical and nursing staff are not interpreting the pulse oximetry results in context and that the majority of the results were normal with no clinical indication for performing this observation. This reduces the usefulness of such readings and questions the appropriateness of performing ‘‘routine’’ SpO2 in this context. A more rationale approach to using the pulse oximeter in medical wards is recommended. REFERENCES Buckley TA, Short TG, Rowbottom YM, Oh TE 1997 Critical incident reporting in the intensive care unit. Anaesthesia 52(5): 403–409 Dickson SL 1995, October Understanding the oxyhaemoglobin dissociation curve. Critical Care Nurse: 54–58 Evans D, Hodgkinson B, Berry J, 1999. Vital signs: A systematic review, The Joanna Briggs Institute for Evidence Based Nursing and Midwifery, Adelaide, South Australia Ganong WF 1996 Review of medical physiology. Appleton and Lange. Prentice-Hall, Connecticut Goodfellow LM 1997 Application of pulse oximetry and the oxyhemoglobin dissociation curve in respiratory management. Critical Care Nursing Quarterly 20(2): 22–27
Holburn CJ, Allen MJ 1989 Pulse oximetry in the accident and emergency department. Archives of Emergency Medicine 6(2): 137–142 Jensen A, Onyskiw JE, Prasad NGN 1998, Nov/Dec Meta-analysis of oxygen saturation monitoring by pulse oximetry in adults. Heart and Lung 27(6): 387–408 Katzman GH 1995 The newborn SpO2 : a routine vital sign whose time has come? Pediatrics 95(1): 161–162 Levin KP, Hanusa BH, Rotondi A, Singer DE, Coley CM, Marrie TJ, Kapoor, Wishwa N, Fine MJ 2001 Arterial Blood Gas and Pulse Oximetry in Initial Management of Patients with Community-acquired Pneumonia. Journal of General Internal Medicine 16(9): 590–598 Logan KP, Hanusa BH, Rotondi A, Singer DE, Coley CM, Marrie TJ, Kappor WN, Fine MJ 2001 Arterial blood gas and pulse oximetry in initial management of patients with community-acquired pneumonia. Journal of General Internal Medicine 16(9): 590–598 Miller P 1998 Using pulse oximetry to make clinical nursing decisions. Orthopaedic Nursing 11(4): 39–42 Neff TA 1988 Routine oximetry. A fifth vital sign. Chest 94(2): 227 Sidhu A 1997 Limitations in predicting pO2 from sO2 measured by pulse oximetry. Neonatal Intensive Care 10(3): 16–18 Tittle M, Flynn MB 1997 Correlation of pulse oximetry and co-oximetry. Dimensions of Critical Care Nursing 16(2): 88–95 Wesmiller SW, Hoffman LA 1989 Interpreting your patientÕs oxygenation status. Orthopaedic Nursing 8(6): 56–60 York L, Moddemann G 1989 Arterial blood gases. AORN Journal 49(5): 1308–1329
Background: Nurses routinely use pulse oximetry (SpO2 ) monitoring equipment in acute care. Interpretation of the reading involves physical assessment and awareness of parameters including temperature, haemoglobin, and peripheral perfusion. However, there is little information on whether these clinical signs are routinely measured or used in pulse oximetry interpretation by nurses. Aim: The aim of this study was to review current practice of SpO2 measurement and the associated documentation of the physiological data that is required for accurate interpretation of the readings. The study reviewed the documentation practices relevant to SpO2 in five medical wards of a tertiary level metropolitan hospital. Method: A prospective casenote audit was conducted on random days over a three-month period. The audit tool had been validated in a previous study. Results: One hundred and seventy seven episodes of oxygen saturation monitoring were reviewed. Our study revealed a lack of parameters to validate the SpO2 readings. Only 10% of the casenotes reviewed had sufficient physiological data to meaningfully interpret the SpO2 reading and only 38% had an arterial blood gas as a comparator. Nursing notes rarely documented clinical interpretation of the results. Conclusion: The audits suggest that medical and nursing staff are not interpreting the pulse oximetry results in context and that the majority of the results were normal with no clinical indication for performing this observation. This reduces the usefulness of such readings and questions the appropriateness of performing ‘‘routine’’ SpO2 in this context. Crown Copyright c 2003 Published by Elsevier Science Ltd. All rights reserved.
Keywords: pulse oximetry monitoring, clinical observations, medical wards Stephen B. Simon RN, BN, MN (Research), Nurse Manager Projects, Internal Medical Service, Royal Adelaide Hospital, North Terrace, Adelaide 5000, Australia Robyn A. Clark RN. RM., ICU Cert., BN, MEd., FRCNA, Clinical Lecturer, Department of Clinical Nursing, The Adelaide University, Royal Adelaide Hospital, Frome Road, Adelaide 5005, Australia Correspondence to: Stephen B. Simon Tel.: +61-08-8222-5836; fax: +61-8222-5588; E-mail: [email protected]
INTRODUCTION The use of oximetry has been increasing across this studyÕs acute medical wards for the past ten years. A survey of patient care plans in 2001 demonstrated that at any given time, 50% of patients had SpO2 monitoring.
BACKGROUND Traditional vital signs have consisted of temperature, pulse respiratory rate, and blood pressure. In
Clinical Effectiveness in Nursing (2002) 6, 106–110 Crown Copyright doi:10.1016/S1361-9004(02)00088-2
C
recent times it has been suggested that these four parameters could be supplemented with other measurements such as nutritional status, smoking status, spirometry, and pulse oximetry (Evans et al. 1999). A systematic review completed by Jensen et al (1998) on the effectiveness of SpO2 found that pulse oximeters were accurate within 2% (2SD) or 5% (2SD) of in vitro oximetry in the range of 70% to 100% SpO2 . In comparing ear and finger, probes, readings from finger probes were more accurate. Pulse oximeters may fail to record accurately the true SpO2 during severe or rapid desat-
2003 Published by Elsevier Science Ltd. All rights reserved.
(Mis) Using pulse oximetry: a review of pulse oximetry use in acute care medical wards 107
uration, hypotension, dyshaemoglobin, and low perfusion states (Jensen et al. 1998; Sidhu 1997). Pulse oximetry is perhaps the most commonly recommended addition to the traditional vital signs. It has been suggested that in the newborn skin colour alone is an inadequate indicator of oxygenation and that pulse oximetry will provide important information for clinicians (Katzman 1995). It may also be useful in situations such as pulmonary outpatient departments, for patients receiving oxygen therapy and those with moderate to severe pulmonary disease who may have borderline hypoxaemia (Neff 1988). Although limited studies are available to support this (Levin et al. 2001; Buckley et al. 1997) pulse oximetry has been recommended for patient with haemodynamic monitoring, perioperative patients and patients in emergency departments. Holburn and Allen (1989) have reported that the use of pulse oximetry significantly changed medical treatment for the acutely ill in the emergency department and reduced the need for arterial blood gas analysis by 37%. In the systematic review of vital signs research published by the Joanna Briggs Institute for Nursing and Midwifery 1999 no studies were identified that evaluated pulse oximetry in the general wards. A pulse oximeter monitor measures the oxygen saturation in the mixed capillary blood of the peripheral circulation. Normal sites for measurement include fingers, toes, earlobe, and bridge of the nose. The value presented by the monitor represents the ratio of oxyhaemoglobin to all haemoglobin capable of transporting O2 . It is based on the distinct light absorption capacities of oxyhaemoglobin compared to deoxyhaemoglobin. In essence, it measures the ‘‘redness’’ of the blood (Wesmiller & Hoffman 1989). The pulse oximeter, however, only measures the percentage of saturated haemoglobin. It does not measure the amount of oxygen available for tissues, rather it gives an indication of what may be available. The amount of oxygen in the blood is dependent on the amount of dissolved oxygen, the amount of haemoglobin, and the affinity of haemoglobin for O2 (Ganong 1996). Other factors that affect the affinity of haemoglobin for oxygen and the amount of oxygen available for body tissues are blood pH and temperature (Goodfellow 1997). For example, two patients may present with a Pulse oximeter reading of 85%. However they may have two very different PaO2 levels as demonstrated in the following two case vignetteÕs. Case One: This patient presented with a Staphylococcal aureus septicaemia from an infected wound. They had a normal haemoglobin of 150 g/ L, a blood gas analysis that showed a PaCO2 of 46.7 mmHg, HCO3 of 15, pH 7.13. Their oral body temperature was 39 C. This patient had a PaO2 of 72 mmHg and 2.16 ml of dissolved oxygen.
Case Two: This patient presented with a slow bleeding gastric ulcer for which they were self medicating with large doses of antacid. Their haemoglobin was low, at 91 g/L, and a blood gas analysis showed a PaCO2 of 47 mmHg, HCO3 37.7, and pH 7.53. Their body temperature was 36 C. However, in contrast to Case One, this patient only had a PaO2 of 43 mmHg, and 1.29 ml of dissolved oxygen per litre, a hypoxic picture. These patients, who had the same pulse oximetry reading of 85%, would require different approaches to treatment of their hypoxia. If these patients did not have a blood gas that highlighted these differences would clinicians have enough information to implement appropriate oxygen therapy? Clinical evaluation is enhanced therefore, when these parameters are known, and the saturation reading becomes more significant. Another factor to consider when monitoring pulse oximetry is the relationship between saturation and arterial blood oxygen measurement. This is not linear. In fact the curve has a safe zone and a very steep slope where the difference between PaCO2 and SpO2 widens rapidly. (Ganong 1996; Dickson 1995). The saturation reading can also be affected by probe location, ambient light, other patient physiology such as: abnormal haemoglobin, carbon monoxide levels of smokers, skin pigment, hyperbilirubinaemia, nail polish, or careless procedure such as using the same arm for blood pressure whilst taking a reading. Finally, although compared to blood gas analysis pulse oximetry is an inexpensive safe and non-invasive process for the patient (Miller 1998), the high usage of the technology leads to considerable wear and tear, which can make the maintenance and replacement of consumables such as the finger probes an expensive exercise. It is also expensive in terms of staff time, as in the medical areas of this study, there is only one machine per ward. In the process of ‘‘routinisation’’ of this observation, time is wasted waiting for this resource ‘‘to do the obs’’.
AIMS AND OBJECTIVES OF THE STUDY Aim The aim of this study was to review current practice of SpO2 measurement and documentation by nurses in the setting of five acute medical wards.
Objectives The objectives were to: •
determine who initiated pulse oximetry readings for the individual patient e.g., nurse or medical officer; and what if any were the clinical indications;
108 Clinical Effectiveness in Nursing
•
•
•
•
determine if pulse oximetry was performed in the context of known baseline parameters, e.g,. haemoglobin, blood gas, temperature, oxygen therapy, or peripheral perfusion measurement; determine the extent of interpretation of SpO2 results by nurses as documented in patient case notes; to examine the ‘‘routinisation’’ of this observation and the possible use of pulse oximetry monitoring when not clinically indicated; make recommendations for further research.
METHOD A prospective casenote review was employed using a data collection tool, which had been tested during an initial pilot study. A convenience sample was used by reviewing all casenotes of the inpatients on the five pre-selected wards to find who had had SpO2 readings. Data was collected over a 3-month period on random days to gain adequate numbers, and ensure patient data was not repeated. The inclusion criteria was all patients having pulse oximetry readings in the pre-selected ward on the day of audit. Patients who did not have documented oxygen saturation results were excluded from the audit. To meet the aims of the study the research team reviewed documentation of the following issues associated with the monitoring of SpO2 : most recent SpO2 reading; lowest SpO2 reading; presence of a medical order for oximetry and/or oxygen therapy; current haemoglobin; comparison of admission haemoglobin, and current haemoglobin; presence of an arterial blood gas; the days elapsed since the latest blood gas and current SpO2 reading; the SpO2 reading at the time of the arterial gas; the patient temperature and respiratory rate at the time of the blood gas; documentation of peripheral perfusion; documented interpretation of the SpO2 ; and, the need for oximetry in the nursing care plan. The data was entered onto a spreadsheet, and analysis utilised descriptive statistics, frequencies, means and standard deviations.
RESULTS One hundred and seventy seven patients casenotes were reviewed in the period of the study in 5 acute medical wards. The mean of the most recent SpO2 was 95.6% (SD 3.57, range 60–96%). The mean of the lowest recorded SpO2 was 94.5% (SD 3.99, range 60–99%). Fifty nine patients had a documented blood gas taken on average 8.9 days prior to the most recent SpO2 . The mean of the arterial blood gas for these 59 patients was pH 7.42, PaO2 83.7 mmHg, PaCO2
42.4 mmHg, HCO3 28.19 ml/eq and a matching saturation of 95.8%. Temperature at the time of the blood gas had a mean of 37.17 C, whereas the mean temperature with the most current SpO2 was 36.46 C. The mean respiratory rate at the time of the blood gas was 23.5 breaths per minute. The mean respiratory rate at the time of the latest SpO2 was 19.95 breaths per minute. Ninety two percent of all patients had a documented haemoglobin (Hb) level. Medical orders requesting oximetry monitoring was present in 41.8% of patients. Oxygen therapy orders were present in 20% of patients having oximetry readings, however, 22% had oxygen therapy current. Assessment of peripheral perfusion was documented on only one patient. 44.2% of patients had a nursing care plan entry for oximetry readings. However, in the written nursing care report 66.7% of entries had either no reference to the SpO2 , or made no interpretation of the results.
DISCUSSION Of the 177 casenotes reviewed, there were 254 recorded oximeter readings. These were divided into two separate groupings: the most recently recorded SpO2 , and the lowest recorded SpO2 . In the most recent SpO2 group, the highest reading was 96%, and the lowest reading was 60%. In the lowest recorded SpO2 group, the highest reading was 99%, and the lowest was 60%. Of these 254 results, 95 (37%) were above 97% and 64 were below 95% (25%). Based on the physiology presented in this article, the 95 patients with SpO2 readings of 97–99% had a normal SpO2 and did not require further investigation. It may also be argued that 25%, that is, those with SpO2Õs below 95%, needed other parameters such as haemoglobin levels, pH, and body temperature to assist in interpreting the result. The remaining 34% with results between 95– 97% may also have required other clinical information to make meaningful clinical interpretation of these results (York & Moddemann 1989). The low number of blood gases appears to indicate that the pulse oximeter was being used as the sole indicator of arterial blood oxygen levels, instead of being used as designed, which is as an instrument to measure oxygen saturation of haemoglobin (Tittle & Flynn 1997). As illustrated, the blood gas analysis had an abnormal, though not markedly so, picture. The data illustrated 31 of the 59 readings having abnormal pH with the most acidic reading being 7.16, and the highest alkalosis 7.53. Temperature also changed between readings. Therefore, the oxyhaemoglobin curve would have moved, at times considerably between admission and the 8th day (the
(Mis) Using pulse oximetry: a review of pulse oximetry use in acute care medical wards 109
average gap between blood gas and latest saturation reading). Saturation on admission and 8 days later would therefore, be representing different arterial oxygen concentration values. No evidence was found that indicated this fact was being considered in the decision making process. The haemoglobin levels found in this study illustrates an important observation when thinking of using the pulse oximeter. It can be noted that half the population had haemoglobin levels below normal. Few had haemoglobinÕs in the higher 140– 150 g/L range. It may be advocated that with this picture, the observer of patient clinical signs should always be aware of the personÕs haemoglobin levels. Haemoglobin is not only important in oxygen transport, but knowledge of haemoglobin levels can be an important clinical marker of exercise tolerance, healing speed, and in part, nutritional adequacy. As saturation measures the amount of oxygen attached to each haemoglobin, not the amount of haemoglobin present, the saturation reading will not tell the observer whether the total amount of oxygen present is low. A patient with 50 g of haemoglobin per litre can still have a 100% saturation reading. However, the blood can only carry one third the total of a person with a haemoglobin of 150 g/L, which is 100% saturated. A haemoglobin of 50 g/L, therefore, supplies the cells with one third the usual supply. The heart that extracts up to 85% of the supplied oxygen to it will be at clinical risk if action is not taken, if the heart work rate to increases, such as in infective states. In this situation oxygen therapy may be useful until transfusion can take place. Notably there was a drop of 14 g/L from admission to the studyÕs most recent SpO2 reading (average from 24 patients who had readings that could be compared), not a large fall, but still a part of the larger clinical picture. Knowing both haemoglobin and saturation will assist in a more complete picture of clinical relevance. Finally, it was found that nurses initiated more than half the readings themselves, that appeared to be a ‘‘routinisation’’ of the ‘‘patient obs’’. Is it arguable that the saturation was being done outside of context in these cases because, though a nurse can determine frequency and the action of doing a saturation reading, they are unable to order blood tests needed for further information.
SUMMARY The aim of this study was to: 1. Determine if pulse oximetry was performed in the context of know baseline parameters, e.g., haemoglobin, blood gas, temperature, or oxygen therapy. The audit demonstrated that only 10% of patients reviewed had all of the baseline parameters required to make
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meaningful interpretation of the SpO2 results or conversely 90% did not. Determine the extent of interpretation of SpO2 results by nurses through the examination of documentation. The audit demonstrated that in 66.8% of the casenotes reviewed, where SpO2 results that had been documented, there was neither mention of this procedure in the nursing care plan nor interpretation in the nursing notes apart from the re-entry of the results. Determine whether the pulse oximeter use was as a result of a medical order. The audit demonstrated that 58% of the pulse oximetry monitoring review was nurse initiated. To examine the possible routinisation of the observation and the possible use of pulse oximetry monitoring when not clinically indicated. This aim was not possible to judge as 90% of patients did not have sufficient baseline parameters to determine if there was an underlining respiratory problem. However, as the observation was generally a spot observation, with 78% of patients not receiving oxygen therapy, and the majority having saturation readings greater than 95% (York & Moddemann 1989), from this data it can be hypothesised that pulse oximetry was used in the majority of cases where it was not clinically indicated. And finally the main aim of this audit was to establish a framework and make recommendations on which to conduct further research. These recommendations are presented below.
RECOMMENDATIONS 1. An interpretive study to review the current practices of ‘‘routine obs’’ in the acute care setting. 2. A study to determine the current nursing and medical knowledge of pulse oximetry monitoring. 3. An interventional study to determine the cost benefit of using pulse oximetry only when clinically indicated in the general ward areas.
CONCLUSION The data illustrated that the use of pulse oximetry was performed with very little documentation of interpretation of the results. It showed that the majority of readings are done as stand alone observations. There appeared to be a large number of SpO2 observed that had no clinical application, and therefore it could be deducted that the time used to perform these observations could have been more significantly focused. The data did not demonstrate evidence that the oximeter was being used as a trend measure for titrating oxygen therapy. Finally,
110 Clinical Effectiveness in Nursing
oximetry readings in this study were useful in what appeared to be 10% of all patients on which it was used. The audits suggest that medical and nursing staff are not interpreting the pulse oximetry results in context and that the majority of the results were normal with no clinical indication for performing this observation. This reduces the usefulness of such readings and questions the appropriateness of performing ‘‘routine’’ SpO2 in this context. A more rationale approach to using the pulse oximeter in medical wards is recommended. REFERENCES Buckley TA, Short TG, Rowbottom YM, Oh TE 1997 Critical incident reporting in the intensive care unit. Anaesthesia 52(5): 403–409 Dickson SL 1995, October Understanding the oxyhaemoglobin dissociation curve. Critical Care Nurse: 54–58 Evans D, Hodgkinson B, Berry J, 1999. Vital signs: A systematic review, The Joanna Briggs Institute for Evidence Based Nursing and Midwifery, Adelaide, South Australia Ganong WF 1996 Review of medical physiology. Appleton and Lange. Prentice-Hall, Connecticut Goodfellow LM 1997 Application of pulse oximetry and the oxyhemoglobin dissociation curve in respiratory management. Critical Care Nursing Quarterly 20(2): 22–27
Holburn CJ, Allen MJ 1989 Pulse oximetry in the accident and emergency department. Archives of Emergency Medicine 6(2): 137–142 Jensen A, Onyskiw JE, Prasad NGN 1998, Nov/Dec Meta-analysis of oxygen saturation monitoring by pulse oximetry in adults. Heart and Lung 27(6): 387–408 Katzman GH 1995 The newborn SpO2 : a routine vital sign whose time has come? Pediatrics 95(1): 161–162 Levin KP, Hanusa BH, Rotondi A, Singer DE, Coley CM, Marrie TJ, Kapoor, Wishwa N, Fine MJ 2001 Arterial Blood Gas and Pulse Oximetry in Initial Management of Patients with Community-acquired Pneumonia. Journal of General Internal Medicine 16(9): 590–598 Logan KP, Hanusa BH, Rotondi A, Singer DE, Coley CM, Marrie TJ, Kappor WN, Fine MJ 2001 Arterial blood gas and pulse oximetry in initial management of patients with community-acquired pneumonia. Journal of General Internal Medicine 16(9): 590–598 Miller P 1998 Using pulse oximetry to make clinical nursing decisions. Orthopaedic Nursing 11(4): 39–42 Neff TA 1988 Routine oximetry. A fifth vital sign. Chest 94(2): 227 Sidhu A 1997 Limitations in predicting pO2 from sO2 measured by pulse oximetry. Neonatal Intensive Care 10(3): 16–18 Tittle M, Flynn MB 1997 Correlation of pulse oximetry and co-oximetry. Dimensions of Critical Care Nursing 16(2): 88–95 Wesmiller SW, Hoffman LA 1989 Interpreting your patientÕs oxygenation status. Orthopaedic Nursing 8(6): 56–60 York L, Moddemann G 1989 Arterial blood gases. AORN Journal 49(5): 1308–1329