Sleep hypoventilation due to increased nocturnal oxygen flow in hypercapnic COPD patients

Background and objective: Several COPD treatment guidelines recommend increasing oxygen flow during sleep to avoid nocturnal desaturation. However, such an increase could have deleterious clinical and gas exchange effects. The objective of this study was to evaluate short‐term gas exchange alterations produced by increasing the nocturnal oxygen flow rate. Methods: Thirty‐eight COPD patients with chronic hypercapnic respiratory failure were evaluated. In a cross‐over study, patients were randomly assigned to receive the daytime oxygen flow rate on one night and an additional litre on the alternate night. Nocturnal pulse oximetry and arterial blood gases at awakening were measured, in each patient, on two consecutive days. Results: The administration of 1 L more oxygen during the night resulted in improved parameters of nocturnal oxygenation (oxygen pulse oximetry saturation—SpO₂; percentage of sleep time spent at SpO₂ < 90%—CT90; PaO₂ at awakening). Nevertheless, such an increase in oxygen flow during the night was also associated with greater hypercapnia and acidosis (p < 0.05) the next morning. Conclusions: The increase of oxygen flow in severe COPD patients with established daytime hypercapnia improved nocturnal oxygenation but it also led to greater hypercapnia and respiratory acidosis at awakening in a considerable proportion of these patients.     

Pulsioximetría en el diagnóstico de insuficiencia cardiaca aguda

Introduction and objectives

Oxygen saturation by pulse oximetry is commonly used for monitoring critical patients, but its utility as a diagnostic marker of acute heart failure has not been assessed. This study analyzed the diagnostic role of oxygen saturation by pulse oximetry in a series of patients with acute myocardial infarction.

Methods

In a prospective observational cohort study of 220 consecutive patients with acute myocardial infarction, data collection included baseline oxygen saturation by pulse oximetry (without oxygen), physiologic measurements, Killip class and data from portable chest radiography, recorded at the same hour on each of the first three days after admission. Patients were followed up for one year.

Results

There were 612 assessments. Baseline oxygen saturation by pulse oximetry decreased progressively in relation to the presence and the severity of acute heart failure assessed by Killip classes 1 to 3 (mean: 95, 92 and 85, respectively; P<.001) or by Radiology Score 0 to 4 (95, 94, 92, 89 and 83, respectively; P<.001), with a correlation coefficient of 0.66 and 0.63, respectively. Receiver operating characteristic curves disclosed the cut-off of oxygen saturation by pulse oximetry<93 to have the greatest area, with a sensitivity of 65%, specificity 90%, and overall test accuracy 83%. Patients grouped according to lowest oxygen saturation by pulse oximetry showed significantly different rates of one-year mortality or rehospitalization for heart failure.

Conclusions

Baseline oxygen saturation by pulse oximetry is useful in establishing the diagnosis and severity of heart failure in acute settings such as myocardial infarction and may have prognostic implications.The diagnosis may be suspected when baseline oxygen saturation by pulse oximetry is <93.Full English text available from:www.revespcardiol.org     

Pulse Oximetry in the Diagnosis of Acute Heart Failure

INTRODUCTION AND OBJECTIVES: Oxygen saturation by pulse oximetry is commonly used for monitoring critical patients, but its utility as a diagnostic marker of acute heart failure has not been assessed. This study analyzed the diagnostic role of oxygen saturation by pulse oximetry in a series of patients with acute myocardial infarction. METHODS: In a prospective observational cohort study of 220 consecutive patients with acute myocardial infarction, data collection included baseline oxygen saturation by pulse oximetry (without oxygen), physiologic measurements, Killip class and data from portable chest radiography, recorded at the same hour on each of the first three days after admission. Patients were followed up for one year. RESULTS: There were 612 assessments. Baseline oxygen saturation by pulse oximetry decreased progressively in relation to the presence and the severity of acute heart failure assessed by Killip classes 1 to 3 (mean: 95, 92 and 85, respectively; P<.001) or by Radiology Score 0 to 4 (95, 94, 92, 89 and 83, respectively; P<.001), with a correlation coefficient of 0.66 and 0.63, respectively. Receiver operating characteristic curves disclosed the cut-off of oxygen saturation by pulse oximetry<93 to have the greatest area, with a sensitivity of 65%, specificity 90%, and overall test accuracy 83%. Patients grouped according to lowest oxygen saturation by pulse oximetry showed significantly different rates of one-year mortality or rehospitalization for heart failure. CONCLUSIONS: Baseline oxygen saturation by pulse oximetry is useful in establishing the diagnosis and severity of heart failure in acute settings such as myocardial infarction and may have prognostic implications.The diagnosis may be suspected when baseline oxygen saturation by pulse oximetry is <93. Full English text available from:www.revespcardiol.org.     

Intermittent short-term negative pressure ventilation and increased oxygenation in COPD patients with severe hypercapnic respiratory failure

With the aim of testing a method that allows increasing concentrations of oxygen to be administered to patients with severe hypoxemia and hypercapnia while avoiding the risk of increasing respiratory acidosis, we studied 17 male patients with advanced chronic obstructive pulmonary disease (COPD) and severe hypercapnic respiratory failure. During 6 h and on one day only, all patients were given intermittent negative pressure ventilation (INPV) together with oxygenation starting at a concentration of 24 percent and increasing to 30 percent. Using this procedure, it was possible to raise arterial PaO2 to safe levels (from 47.2 +/- 3 mm Hg to 61.5 +/- 6 mm Hg, p less than 0.001) without increasing hypercapnia, and a significant drop in PaCO2 levels (from 74.4 +/- 9 mm Hg to 65.6 +/- 12 mm Hg, p less than 0.005) was even observed. One hour after INPV ended, the mean values of PaO2, PaCO2, oxygen saturation, and pH were also significantly better than prestudy values. We conclude that INPV and oxygen therapy with increasing oxygen flow could constitute an alternative option to intubation and mechanical ventilation in cases of severe hypercapnic respiratory failure due to advanced COPD.     

Continuous emergency department monitoring of arterial saturation in adult patients with respiratory distress

Continuous measurement of arterial oxygen saturation (SaO2) using pulse oximetry has become a common monitoring and management technique in critically ill hospitalized patients. To determine the impact of SaO2 monitoring on emergency patient management, we conducted a prospective uncontrolled clinical trial on 40 adult patients presenting to the emergency department with acute respiratory illness, such as emphysema, asthma, or pulmonary edema. Recorded data included hemograms, arterial blood gases, subsequent therapy, and response to treatment. Additionally, the "early warning" capability of SaO2 monitoring was analyzed by recording the severity and outcome of hypoxemic events during treatment. Mean duration of usage for the 40 oximeters in the ED was 1.8 hours; all probes functioned reliably over a wide range of systolic pressures (80 to 206 mm Hg), heart rates (40 to 180 beats per minute), and hematocrits (20% to 58%). There was good correlation between simultaneous pulse oximeter values and both directly measured SaO2 (r = 0.95) and saturations derived from measured arterial PaO2 (r = 0.94). The device detected several otherwise unrecognized drops in arterial saturation that were confirmed by laboratory analysis. Other clinical situations in which the pulse oximeter was found useful in the ED are reviewed. We conclude that continuous measurement of SaO2 can improve the monitoring of ED patients, increase the precision of therapy, detect hypoxemia during intubation, suctioning, and other treatments, and detect clinically unsuspected changes in arterial oxygenation.     

经纤支镜治疗急性误吸性呼吸衰竭

目的：误吸引起的急性呼吸衰竭(ARDS)通过纤维支气管镜治疗使用气管内置管供氧技术，观察此方法的临床应用价值。方法：对12例误吸性ARDS患应用纤维支气管镜检查(FOB)进行气管内误吸物吸取，并应用经纤支镜气管内置管供氧技术监测术前、术中、术后24小时动脉血氧指标、临床症状及影像学变化。结果：应用此方法能提高思考对FOB的耐受性，使气道内异物和分泌物清除更彻底，机体低氧血症明显缓解。结论：在误吸性ARDS治疗中应用气管内置管供氧技术能对气道内异物和分泌物清除更彻底，显改善机体低氧血症，本方法操作简便，在急诊内科有一定临床推广价值。     

Enhancement of exercise performance in COPD patients by hyperoxia: a call for research

This essay summarizes 16 reports, published since 1956, that describe the effects of hyperoxia on exercise endurance in persons with COPD who have severe airflow obstruction (ie, FEV(1) < 1.0 L or < 39% of predicted) and mild hypoxemia at rest (ie, PaO(2) > 62 mm Hg or arterial oxygen saturation [SaO(2)] measured by pulse oximetry of > 91%). The term hyperoxia is used because, in a proportion of study participants, oxygen administration increased exercise endurance in a dose-dependent fashion, up to a fraction of inspired oxygen of 0.5 or a flow of 100% O(2) of 6 L/min. The process appears to be dependent on an increase in PaO(2) rather than on the restoration of SaO(2) to normal levels. The results of pulmonary function tests were not predictive of response. Increased exercise performance was associated with a decrease in dyspnea, respiratory frequency, and minute ventilation. The slowing of respiratory frequency and the decrease in pulmonary air trapping likely accounted for the decrease in dyspnea. Slowing of the respiratory rate, which occurred at the expense of the retention of CO(2), is most likely due to a hyperoxia-induced decrease in chemoreceptor ventilatory drive from the aortic and carotid bodies. Research is called for to determine the following: (1) the prevalence of COPD patients who have severe airflow limitation accompanied by mild hypoxemia; (2) the proportion of these patients who show improvements in exercise performance during a test of hyperoxic exercise; and (3) whether enhanced exercise performance during a brief test translates into a meaningful increase in the ability to perform the activities of daily living.     

Descriptive analysis of emergency department oxygen use in acute exacerbation of chronic obstructive pulmonary disease

Background: Inconsistencies in oxygen therapy recommendations in acute exacerbation of chronic obstructive pulmonary disease (COPD) may result in variability in emergency department (ED) oxygen management of patients with COPD. The aim of this study was to describe oxygen management in the first 4 h of ED care for patients with exacerbation of COPD. Methods: A retrospective medical record audit was conducted at four public and one private ED in Melbourne, Australia. Participants were 273 adult ED patients with COPD presenting with a primary complaint of shortness of breath from July 2006 to July 2007. Outcome measures were physiological data, including oxygen saturation (SpO₂), oxygen delivery devices and flow rates on ED arrival, 1 and 4 h. Results: Oxygen was used in 82.0% of patients. Patients who required oxygen had higher incidence of ambulance transport (P < 0.001), triage category 2 (P= 0.006), home oxygen use (P < 0.001), and increased work of breathing on ED arrival (P < 0.001), and higher median respiratory rate (P < 0.001) and heart rate (P= 0.001). SpO₂ > 90% occurred in the majority of patients (87.5%; 96.4%; 95.6%); however, a considerable number of patients with SpO₂ < 90% were not given oxygen (61.8%; 30%; 45.5%). Conclusions: A number of patients with documented hypoxaemia were not given oxygen and there may be variables other than oxygen saturation that may influence oxygen use. Future research should focus on increasing the evidence‐based supporting oxygen use and better understanding of clinicians' oxygen decision‐making in patients with COPD.     

Pulse oximetry in sickle cell disease

The place of pulse oximetry in monitoring arterial oxygen saturation in sickle cell disease has been evaluated. In four admissions of patients with sickle cell anaemia with varying degrees of arterial haemoglobin oxygen desaturation, pulse oximetry was compared with a simultaneous assessment of oxygen saturation by arterial blood gas measurement and oxygen dissociation curve (ODC) analysis. Close agreement was found between the oxygen saturation measured by pulse oximetry and that calculated from the measured arterial partial pressure of oxygen (PaO2) with reference to the patient's own ODC. Calculation of oxygen saturation by the blood gas analyser assuming a normal ODC was erroneous. Pulse oximetry is an accurate and effective non-invasive method for monitoring the arterial oxygen saturation in sickle cell disease.     

Pulse Oximeter Oxygen Saturation in Prediction of Arterial Oxygen Saturation in Liver Transplant Candidates

Background:

Liver transplant is the only definitive treatment for many patients with end stage liver disease. Presence and severity of preoperative pulmonary disease directly affect the rate of postoperative complications of the liver transplantation. Arterial blood gas (ABG) measurement, performed in many transplant centers, is considered as a traditional method to diagnose hypoxemia. Because ABG measurement is invasive and painful, pulse oximetry, a bedside, noninvasive and inexpensive technique, has been recommended as an alternative source for the ABG measurement.

Objectives:

The aim of this study was to evaluate the efficacy of pulse oximetry as a screening tool in hypoxemia detection in liver transplant candidates and to compare the results with ABGs.

Patients and Methods:

Three hundred and ninety transplant candidates (237 males and 153 females) participated in this study. Arterial blood gas oxyhemoglobin saturation (SaO₂) was recorded and compared with pulse oximetry oxyhemoglobin saturation (SpO₂) results for each participants. The area under the curve (AUC) of receiver operating characteristic (ROC) curves was calculated by means of nonparametric methods to evaluate the efficacy of pulse oximetry to detect hypoxemia.

Results:

Roc-derived SpO₂ threshold of ≤ 94% can predict hypoxemia (PaO₂ < 60 mmHg) with a sensitivity of 100% and a specificity of 95%. Furthermore, there are associations between the ROC-derived SpO₂ threshold of ≤ 97% and detection of hypoxemia (PaO₂ < 70 mmHg) with a sensitivity of 100% and a specificity of 46%. The accuracy of pulse oximetry was not affected by the severity of liver disease in detection of hypoxemia.

Conclusions:

Provided that SpO₂ is equal to or greater than 94%, attained from pulse oximetry can be used as a reliable and accurate substitute for the ABG measurements to evaluate hypoxemia in patients with end stage liver disease.     

A comparison of pulse oximetry and respiratory rate in patient screening

Objective: To examine how well respiratory rate correlates with arterial oxygen saturation status as measured by pulse oximetry, and determine whether respiratory rate measurements detect oxygen desaturation reliably.Methods: Respiratory rate (RR) and oxygen saturation (SaO₂) were measured prospectively on 12 096 consecutive adult emergency department triage patients at a university medical center. Respiratory rate was measured by counting ausculated breath sounds for 1 min. Pulse oximetry was used to measure SaO₂. Measurements were analysed by age (with one group for 18–19 year olds, groups for every 10 yr from age 20 to age 60, and groups for every 5 yr for subsequent ages). Pearson correlation coefficients were calculated for each age group as well as the weighted average coefficient. Cases having oxygen saturation below 90% were examined to determine how frequently they exhibited increased RR (increased RRs were defined as any rate in the upper five percentile by age.Results: Correlation coefficients ranged from 0·379 to −0·465 with a weighted mean of −0·160. Coefficients for ages 18 through 70 years (representing 10 740 patients) all had magnitude <0·252. Overall, only 33% of subjects with oxygen saturation below 90% exhibited increased RR.Conclusions: Respiratory rate measurements correlate poorly with oxygen saturation measurements and do not screen reliably for desaturation. Patients with low SaO₂ do not usually exhibit increased RR. Similarly, increased RR is unlikely to reflect desaturation.     

Conscious sedation in the emergency department: the value of capnography and pulse oximetry.

STUDY OBJECTIVE: The purpose of this observational study was to describe the use of nasal capnography and pulse oximetry in monitoring heavily sedated emergency department patients. DESIGN: Prospective, nonblinded, nonrandomized, noncontrolled clinical trial. SETTING: The study was conducted in a tertiary-care hospital with 36,000 annual ED visits. TYPE OF PARTICIPANTS: Twenty-seven patients requiring sedation with benzodiazepines and/or narcotics for painful procedures. INTERVENTIONS: The ventilatory status of each patient was monitored with a capnometer by nasal cannula as well as a pulse oximeter before, during, and after administration of the sedative agents. MEASUREMENTS: Vital signs, nasal end-tidal CO2 (PETCO2) measurements, and oxygen saturation were measured at baseline, during the procedure, and for a two-hour observation period after the procedure. MAIN RESULTS: The average PETCO2 increased from 35.9 to 42.1 mm Hg during the procedure while the oxygen saturation dropped from an average of 98% to 94.3%. One patient developed clinically significant apnea after the procedure that was picked up by the apnea alarm, and eight additional patients developed clinically silent hypoxemia and increased PETCO2 during the procedure. CONCLUSION: The use of pulse oximetry is recommended for the detection of unrecognized hypoxemia during conscious sedation. Capnography by nasal cannula appears to be a useful modality in monitoring during conscious sedation, but further research and clinical experience are required before routine use can be recommended.     

How accurate are pulse oximeters in patients with acute exacerbations of chronic obstructive airways disease?

The aim of this study was to determine the extent of correlation and agreement between arterial oxygen saturation and oxygen saturation as recorded by transcutaneous pulse oximetry, with a view to identifying whether pulse oximetry can be used as an alternative to arterial values in the clinical management of patients with acute exacerbations of chronic obstructive airways disease (COAD) in the emergency department. It also aims to determine whether there is a cut-off level of oxygen saturation by pulse oximetry that can screen for significant systemic hypoxia in this group. This prospective study of patients with acute exacerbations of COAD who were deemed by their treating doctor to require an arterial blood gas analysis to determine their ventilatory status, compared arterial oxygen saturation with simultaneously recorded oxygen saturation measured by transcutaneous pulse oximetry. Data were analysed using Pearson correlation, bias plot (Bland-Altman) methods for agreement and the receiver operator characteristic (ROC) curve method for determination of a screening cut-off. Sixty-four sample-pairs were analysed for this study. Nine (14%) had significant hypoxia (arterial PO2 less than 60 mmHg). The correlation coefficient was 0.91. The bias (Bland-Altman) plot shows a constant bias of -0.758% and only fair agreement, with 95% limits for agreement of -8.2 to + 6.7%. With respect to the ROC curve analysis, the 'best' cut-off for detection of hypoxia was at oxygen saturation by pulse oximetry of 92% (sensitivity 100%, specificity 86%). In conclusion, there is not sufficient agreement for oxygen saturation measured by pulse oximetry to replace analysis of an arterial blood gas sample in the clinical evaluation of oxygenation in emergency patients with COAD. However, oxygen saturation by pulse oximetry may be an effective screening test for systemic hypoxia, with the screening cut-off of 92% having sensitivity for the detection of systemic hypoxia of 100% with specificity of 86%.     

Pulse oximetry monitoring outside the intensive care unit: progress or problem?

OBJECTIVE: To evaluate the use of continuous pulse oximetry monitoring in general care units. DESIGN: Hemoglobin oxygen saturation data collected prospectively by use of pulse oximetry with concurrent review of the medical record. SETTING: General medical-surgical nursing units in a large, tertiary care university hospital. PATIENTS: Forty patients on two nursing units monitored with continuous, bedside pulse oximetry at the request of their primary physicians. MEASUREMENTS: All patients had continuous pulse oximetry monitoring. A research associate visited the bedside two or three times daily and recorded saturation compared with time data from the previous 8.75 hours. Patients were studied for 36 hours or until pulse oximetry monitoring was discontinued. Episodes of desaturation were counted. Patient charts were reviewed for documentation of desaturation in either nursing or physician notes. Orders adjusting oxygen therapy or other respiratory therapy within 12 hours of any desaturation episode were also recorded. MAIN RESULTS: Thirty of the 40 patients (75%) had at least one episode of desaturation to less than 90%; 23 (58%) had at least one episode to less than 85%. Desaturation episodes were documented in nursing notes for only 33% of those patients who desaturated to less than 90% and in physician notes in only 7% of cases. Changes in respiratory therapy were ordered in 20% of patients who desaturated to less than 90% and in only 26% who desaturated to less than 85%. CONCLUSIONS: Despite their repeated occurrence, episodes of hypoxemia were rarely documented in either nursing or physician notes. Further, even in patients who had episodic desaturation, pulse oximetry monitoring had little effect on changes in physician-directed respiratory care.     

Target oxygen saturation range: 92–96% Versus 94–98%

This scientific letter considers the rationale for the target oxygen saturation measured by pulse oximetry (SpO₂) range of 92–96% for oxygen therapy in adult patients without COPD or other conditions associated with chronic respiratory failure, recommended by the Thoracic Society of Australia and New Zealand, in contrast to the 94–98% target range recommended by the British Thoracic Society. We conclude from the available evidence that the SpO₂ target of 92–96% may be preferable to 94–98%.     

Accuracy and response time of a portable pulse oximeter. The Pulsox-7 with a finger probe.

We studied the performance of a portable pulse oximeter in 123 consecutive adult patients by spot-checking with a finger probe and by spectrophotometry of oxygen saturation on a simultaneous arterial blood sample. 88 patients were overtly hypoxemic (HbO2 less than 90%) and 26 showed severe hypoxemia (HbO2 36-70%). The differences between the two methods showed a skewed distribution with a positive tail due to the over-estimation of lower saturation values by the pulse oximeter. Overall, the 95% confidence interval for the median difference ranged from -0.6 to +0.5%. The limits of agreement (distribution-free 95% confidence interval for the sample) were -5.8 to +11.6%. Pulse oximetry can be recommended as a first assessment of the respiratory balance only if a cut-off value of HbO2 equal to 90% in nonsmoking, air-breathing subjects is acceptable. The finger probe implies a response delay of approximately 30 s, making the instrument rather insensitive to short hypoxemic transients. With a predictive value around 90%, the pulse oximeter may be a useful portable screening tool.     

An evaluation of pulse oximetry in prehospital care.

STUDY OBJECTIVES: We performed this study to evaluate the accuracy of pulse oximetry oxygen saturation (SpO2) against direct measurements of arterial oxygen saturation (SaO2) in the field. DESIGN: Prospective, cross-sectional, paired measurements of SpO2 against SaO2. SETTING: This evaluation was done in the prehospital setting. INTERVENTIONS: A pulse oximeter with digital probe was used to measure SpO2 in 30 patients. Arterial blood gases were drawn in the field while the pulse oximeter was in use, and oxygen saturation (HbO2) was measured by CO-oximetry. MAIN RESULTS: There was no significant difference between SpO2 (94.6 +/- 5.4%) and HbO2 (94.9 +/- 5.1%) (P = .495, beta less than .2). There was a strong correlation between SpO2 and HbO2 (r = .898). The bias between SpO2 and HbO2 was -0.3, with a precision of 2.4. When SpO2 was 88% or more, HbO2 was 90% or more in every case. Mean carboxyhemoglobin was 1.3 +/- 0.9%, and mean methemoglobin was 0.9 +/- 0.3%. There was no significant difference between the pulse oximeter heart rate and the ECG heart rate (P = .223, beta less than .2). CONCLUSION: We conclude that pulse oximetry is sufficiently accurate to be useful in the field when SpO2 is more than 88%. It is potentially useful in patients with clinical signs of acute hypoxemia and in patients receiving interventions that may produce acute hypoxemia. Further work is needed to evaluate the accuracy of pulse oximetry in the settings of elevated carboxyhemoglobin, methemoglobin, and very low saturations.     

Assessment of clinical laboratory techniques in the measurement of oxygen saturation in whole blood.

The accuracy and advantages of determining percentage of hemoglobin oxygen saturation of whole blood by advanced instruments of oximetry, gas chromatography, and the computation of oxygen saturation from pO2 and pH data are compared with the Van Slyke-Neill manometric method. It was found that oximetry is extremely fast, less expensive, and more accurate than in the past, the apparatus requires little training to operate and has diminutive service maintenance. The gas chromatograph proved to be highly accurate and could serve as a standard calibration check method in place of the more time-consuming Van Slyke-Neill apparatus for oximetry and pO2 and pH electrode instrumentation. Computation of O2 saturation from pO2 and pH data also proved to be accurate, confirming that this method is more useful during cardiac surgery because it can provide additional acid-base information. In the low oxygen saturation range (less than 60%), all three methods proved to be of similar sensitivity.