Use of the alveolar-arterial oxygen gradient in the diagnosis of pulmonary embolism

PrEdictive value of coMbined pre-test proBability and blOod gas anaLysis In pulmonary emboliSM-the EMBOLISM study

In patients with suspected pulmonary embolism (PE), the number of unnecessary computed tomography pulmonary angiography (CTPA) scans remains high, especially in patients with low pre-test probability (PTP). So far, no study showed any additional benefit of capillary blood gas analysis (BGA) in diagnostic algorithms for PE. In this retrospective analysis of patients with suspected PE and subsequent CTPA, clinical data, D-dimer levels and BGA parameters (including standardized PaO2) were analyzed. Logistic regression analyses were performed to identify independent predictors for PE and reduce unnecessary CTPA examinations in patients with low PTP according to Wells score. Of 1538 patients, PE was diagnosed in 433 patients (28.2%). The original Wells score (odds ratio: 1.381 [95% CI 1.300-1.467], p < 0.001) and standardized PaO2 (odds ratio: 0.987 [95% CI 0.978-0.996], p = 0.005) were independent predictors for PE. After cohort adjustment for low PTP a D-dimer cut-off < 1.5 mg/L (278 patients (18.1%) with 18 PE (6.5%)) was identified in which a standardized PaO2 > 65 mmHg reduced the number of unnecessary CTPA by 31.9% with a 100% sensitivity. This approach was further validated in additional 53 patients with low PTP. In this validation group CTPA examinations were reduced by 32.7%. No patient with PE was missed. With our novel algorithm combining BGA testing with low PTP according to Wells score, we were able to increase the D-Dimer threshold to 1.5 mg/L and reduce CTPA examinations by approximately 32%.

Evaluation of two different etorphine doses combined with azaperone in blesbok (Damaliscus pygargus phillipsi) immobilisation

Chemical immobilisation is essential for veterinarians to perform medical procedures in wild African ungulates. Potent opioids combined with neuroleptic drugs are most often used for this purpose. The present study aimed at comparing the quality of immobilisation and effects on physiological variables between a high (high etorphine-azaperone [HE]: 0.09 mg kg-1) and low etorphine dose (low etorphine-azaperone [LE]: 0.05 mg kg-1), both combined with azaperone (0.35 mg kg-1), in 12 adult female boma-acclimatised blesbok. It was hypothesised that a reduction in etorphine's dose in combination with azaperone would result in less cardiorespiratory impairment but likely worsen the quality of immobilisation. Both treatments resulted in rapid induction and recovery times. Overall inter-treatment differences occurred in pulse rate (HE and LE: 52 ± 15 and 44 ± 11 beats minute-1, p 0.0001), respiratory rate (HE and LE: 15 ± 4 and 17 ± 4 breaths minute-1, p 0.006), partial pressure of exhaled carbon dioxide (HE and LE: 62.0 ± 5.0 and 60.0 ± 5.6 millimetre of mercury [mmHg], p 0.028) and arterial carbon dioxide (HE and LE: 58.0 ± 4.5 and 55.0 ± 3.9 mmHg, p 0.002). Both HE and LE led to bradycardia, hypertension and marked hypoxia to a similar extent. Furthermore, quality of induction, immobilisation and recovery were similar in both treatments. The role of azaperone in the development of cardiorespiratory compromise and gas exchange impairment that occurred when these combinations were used is still unclear. Further studies are recommended to elucidate drug- and dose-specific physiological effects in immobilised antelope.

Pulmonary vascular improvement in severe COVID-19 patients treated with tocilizumab

As of October 2020 management of Coronavirus disease 2019 (COVID-19) is based on supportive care and off-label or compassionate-use therapies. On March 2020 tocilizumab - an anti-IL-6 receptor monoclonal antibody - was suggested as immunomodulatory treatment in severe COVID-19 because hyperinflammatory syndrome occurs in many patients similarly to the cytokine release syndrome that develops after CAR-T cell therapy. In our retrospective observational study, 20 severe COVID-19 patients requiring intensive care were treated with tocilizumab in addition to standard-of-care therapy (SOC) and compared with 13 COVID-19 patients receiving only SOC. Clinical respiratory status, inflammatory markers and vascular radiologic score improved after one week from tocilizumab administration. On the contrary, these parameters were stable or worsened in patients receiving only SOC. Despite major study limitations, improvement of alveolar-arterial oxygen gradient as well as vascular radiologic score after one week may account for improved pulmonary vascular perfusion and could explain the more rapid recovery of COVID-19 patients receiving tocilizumab compared to controls.

Pulmonary Embolism in Intensive Care Unit

Management of pulmonary embolism (PE) has become more complex due to the expanded role of catheter-based therapies, surgical thrombectomies, and cardiac assist technologies, such as right ventricular assist devices and extracorporeal support. Due to the heterogeneity of PE, a multidisciplinary team approach is necessary. The manifestation of PE response teams are in response to this complex need and similar to the proliferation of stroke, trauma, and rapid response teams. Intensive care units are an ideal location for formulating a comprehensive treatment plan that necessitates an interaction between multiple specialties. This article addresses the unique needs of critically ill patients with PE.

Arterial blood gas analysis utility in predicting lung injury in blunt chest trauma

BACKGROUND

thoracic trauma is one of the leading causes of death in all age groups and accounts for 25-50 % of all traumatic injuries. With the term lung injury in blunt chest trauma, we identified a spectrum of conditions: lung contusion, pneumothorax and haemothorax. The aim of this study was to evaluate the utility of arterial blood gas analysis parameters in predicting lung injury in blunt chest trauma.

METHODS

we included 51 patients presenting to the Emergency Department of "C.T.O." Hospital in Naples [Italy] for blunt chest trauma. The patients were assigned to the Lung Injury Group or to the Non-Lung Injury Group basing on CT scan findings. For each patient, we calculated the alveolar-arterial oxygen gradient [AaDO₂], the AaDO₂ augmentation, the arterial partial pressure of oxygen deficit [PaO₂ Deficit] and the ratio between arterial partial pressure of oxygen and fraction of inspired oxygen [P/F]. Areas under the curve [AUC] and receiver operating characteristic [ROC] curve were used to compare the performance of each different test in relation to the detection of lung injury in blunt chest trauma.

RESULTS

patients with lung injury had lower oxygen saturation, arterial partial pressure of oxygen, P/F and higher PaO₂ Deficit, AaDO₂, AaDO₂ augmentation than patients without lung injury. PaO₂ Deficit, AaDO₂ and AaDO₂ augmentation showed a good accuracy to predict lung injury in blunt chest trauma.

CONCLUSION

our study demonstrates that the combination of different arterial blood gas analysis variables may be a fast approach for identifying patients with lung injury in the setting of blunt chest trauma in the Emergency Department.

Is Bedside End-Tidal CO2 Measurement a Screening Tool to Exclude Pulmonary Embolism in Emergency Department?

Background

Pulmonary embolism (PE) is among the most difficult conditions to diagnose in emergency department. The majority of patients thought to have PE are tested positive for D-dimer and subsequently tested with advanced diagnostic modalities. Novel noninvasive tests capable of excluding PE may obviate the need for advanced imaging tests. We studied the role of combined clinical probability assessment and end-tidal carbon dioxide (ETCO₂) measurement for diagnosis of possible PE in emergency department.

Methods

We included 100 consecutive subjects suspected to have PE and a positive D-dimer test to study clinical probability of PE and ETCO₂ levels. ETCO₂ > 34 mm Hg was found to be the best cut-off point for diagnosing PE. PE was ultimately eliminated or diagnosed by spiral computed tomography (CT).

Results

Diagnostic performances of tests were as follows: ETCO₂ and D-dimer had a sensitivity of 100% and a negative predictive value (NPV) of 100% at the cut-off levels of 34 mm Hg and 500 ng/mL, respectively; Wells score had a sensitivity of 80% and NPV of 69.7% at a score of 4.

Conclusions

ETCO₂ alone cannot reliably exclude PE. Combining it with clinical probability, however, reliably and correctly eliminates or diagnoses PE and prevents further testing to be done.

Hypoxia as an independent predictor of adverse outcomes in pulmonary embolism

Background

The purpose of this study was to investigate the correlation between the computed tomography pulmonary artery obstruction index and parameters of functional lung impairment in acute pulmonary embolism, and establish the value of these parameters in prognosticating right ventricular dysfunction and 30-day mortality.

Methods

This study included 322 consecutive patients (mean age 45.6 ± 13.2 years, 46.9% male) with acute pulmonary embolism, free of other cardiopulmonary disease, who underwent computed tomography pulmonary angiography. Correlations of arterial CO2, O2, and alveolar-arterial oxygen gradient with the computed tomography pulmonary artery obstruction index, measured using the Qanadli score, were analyzed. Logistic regression was used to identify independent predictors of right ventricular dysfunction and 30-day mortality.

Results

Of the 322 patients, 196 (60.9%) had right ventricular dysfunction, and 58 (18.0%) died within 30 days. The pulmonary artery obstruction index had a significant correlation with partial pressures of arterial O2 ( r = −0.887, p < 0.001) and CO2 ( r = −0.618, p = 0.019) and alveolar-arterial oxygen gradient ( r = +0.874, p < 0.001). Arterial O2 pressure had a good predictive accuracy and discriminative power for both right ventricular dysfunction (sensitivity 80.6%, specificity 85.1%, area under the curve 0.91) and 30-day mortality (sensitivity 77.8%, specificity 82.0%, area under the curve 0.89).

Conclusions

In patients with acute pulmonary embolism, free of other cardiopulmonary disease, parameters of functional impairment have a strong correlation with computed tomography pulmonary artery obstruction index. Hypoxia is an independent predictor of both right ventricular dysfunction and 30-day mortality in these patients.

Assessment of the alveolar-arterial oxygen gradient as a screening test for pulmonary embolism in pregnancy

OBJECTIVE

The objective of the study was to determine whether the alveolar-arterial (A-a) oxygen gradient is an adequate screening test for pulmonary embolism (PE) in pregnancy and postpartum.

STUDY DESIGN

A chart review was performed at Tampa General Hospital. Patients who had a workup for a PE consisting of a computed tomography pulmonary angiogram and an arterial blood gas from 2002 to 2009 were included in the analysis. Sensitivity, specificity, and negative and positive predictive values were calculated. Additionally, common clinical signs and symptoms were assessed for their ability to accurately predict PE.

RESULTS

Of 102 patients, there were 13 PEs (2 antepartum and 11 postpartum). The best sensitivity, specificity, and negative and positive predictive values for A-a gradients were 76.9%, 20.2%, 80.0%, and 11.5%, respectively.

CONCLUSION

The A-a gradient is a poor screening test for PE in pregnancy and postpartum. Suspicion of PE should prompt early imaging studies to rapidly make the diagnosis and begin treatment.

Integrated strategies for the diagnosis of venous thromboembolism

Diagnosis of deep vein thrombosis (DVT) and pulmonary embolism (PE) is an important medical problem because of the high fatality rate from PE and the large number of cases not diagnosed before causing death. Over the last decade, there has been considerable research into the diagnostic process. It is widely accepted that venous ultrasound imaging is an accurate test for the diagnosis of DVT and is the imaging test of choice. For PE, computer tomographic pulmonary angiography (CTPA) is replacing ventilation perfusion lung scanning. Technology for CTPA is rapidly evolving and multi-row detector scans have quite reasonable sensitivity and specificity. Despite the accuracy of imaging tests, the post-test probability of disease is highly dependent on pretest probability. Clinical evaluation tools have developed that enable us to accurately categorize patients' risk prior to diagnostic imaging. One advantage of this characterization is an ability to exclude the diagnosis of DVT or PE if clinical probability is sufficiently low and when the D-dimer is negative. There are now a number of D-dimer assays that have well-defined specificities and sensitivities, which enable use in conjunction with clinical probability. A careful combination of clinical assessment, D-dimer and imaging enables safe PE rule out protocols without imaging, an ability to suspect false positive imaging results, and more accurate determination of true positive imaging. These integration strategies result in safer, more convenient and cost-effective care for patients.

Usefulness of arterial blood gas analysis and D-dimer measurement in the assessment of pulmonary embolism after orthopedic surgery

BACKGROUND

Deep venous thrombosis (DVT) and pulmonary embolism (PE) after spinal or lower extremity surgery are well recognized as common complications. Since 1995 we have investigated the incidence of PE after orthopedic surgery using ventilation-perfusion (V/Q) lung scans, and the prevalence of PE was about 10%. With a view to detecting early-stage PE by simple examinations, we evaluated the use of both the blood gas analysis and the D-dimer measurement after spinal or lower extremity surgery.

METHODS

Altogether, 85 patients who underwent spinal or lower extremity surgery were eligible for the study. Pneumatic sequential leg compression devices (PSLCDs) were utilized continuously both intra- and postoperatively. Arterial blood gas analysis and D-dimer measurement were performed pre- and postoperatively on days 3 and 7. We set lung scan criteria as follows: postoperative decrease in Pa(O2) (deltaPa(O2) by > or = 10 torr (group G), postoperative D-dimer of > or = 1 microg/ml (group D), or both. Patients with the criteria went on to undergo lung scans, and PE was diagnosed by the existence of any mismatch between ventilation-perfusion (V/Q) lung scans.

RESULTS

A total of 44 (51.8%) patients met the lung scan criteria and underwent perfusion lung scans, 10 (11.7%) of whom were diagnosed as PE. In groups G and D, about 30% showed PE. Moreover, six (85.7%) of the seven patients with both criteria showed a significant increase (83.7%) in the prevalence of PE.

CONCLUSIONS

Patients with the above criteria showed a high prevalence of PE. Moreover, 10 (11.7%) of the 85 patients were diagnosed as having PE, which corresponded to the prevalence in our former studies where lung scans were performed in all patients. The blood gas analysis and the D-dimer measurement may be utilized as the first screening examinations.

Acute pulmonary embolism: correlation of CT pulmonary artery obstruction index with blood gas values

OBJECTIVE

The purpose of our study was to investigate the relation between the pulmonary artery obstruction index assessed with helical CT and impairment in blood gases in patients with acute pulmonary embolism.

SUBJECTS AND METHODS

Helical CT pulmonary angiography was performed in 78 patients who were suspected of having acute pulmonary embolism and selected as being free of underlying cardiopulmonary disease. Findings consistent with acute pulmonary embolism were observed in 34 patients. The severity was assessed by the pulmonary artery obstruction index, defined as Sigma (n x d), where n is the number of segmental arteries occluded and d is the degree of obstruction. Spearman's rank correlation coefficients were used to assess the correlation between the index of arterial obstruction and arterial partial pressure of oxygen (Pao(2)); alveolar-arterial difference in partial pressure of oxygen (Pao(2)-Pao(2)); arterial partial pressure of carbon dioxide (Paco(2)); and arterial oxygen saturation (Sao(2)). The statistical difference of the arterial blood gas values between the two groups of patients (those with and those without pulmonary embolism) was evaluated using the Mann-Whitney U test. Blood gases were comparatively evaluated below and above different index values (from 40% to 70%) and different Paco(2) values (25, 30, and 35 mm Hg) as possible indexes of embolism severity using the same test. The level of significance was set at 95% (p = 0.05).

RESULTS

The values of Pao(2), Sao(2), and Paco(2) were significantly lower (p = 0.024, p = 0.0062, and p = 0.000075, respectively) and the values of Pao(2)-Pao(2) were significantly higher (p = 0.0169) in the pulmonary embolism group than in the no-pulmonary-embolism group. A significant correlation was observed between the obstruction index and Pao(2) (r = -0.33, p = 0.05), Paco(2) (r = -0.34, p = 0.05), Pao(2)-Pao(2) (r = 0.39, p = 0.02), and Sao(2) (r = -0.35, p = 0.04). Using cutoff values for the pulmonary artery obstruction index of 40%, 50%, 60%, and 70%, we observed that Paco(2) and Pao(2)-Pao(2) differed significantly between above and below the 40% (p = 0.018 and p = 0.03), 50% (p = 0.0087 and p = 0.029), and 60% (p = 0.005 and p = 0.003) cutoffs. Pao(2) differed significantly for the cutoff values of 60% (p = 0.03) and 70% (p = 0.004). The same was observed for Sao(2) at 60% (p = 0.05) and 70% (p = 0.03). Comparisons for Paco(2) showed that a value of 30 mm Hg significantly separates levels of the pulmonary artery obstruction index (p = 0.002), with 78% sensitivity and 82% specificity indicating a pulmonary artery obstruction index greater than 50%.

CONCLUSION

In patients with acute pulmonary embolism but no other underlying cardiopulmonary disease, the severity of the pulmonary arterial tree obstruction assessed using the CT obstruction index is significantly correlated to the blood gas values. The strongest correlation was observed between the index and the Pao(2)-Pao(2). Furthermore, a Paco(2) value of 30 mm Hg or less is highly suggestive of an obstruction index of more than 50% of the arterial bed.

Diagnosis and treatment of venous thromboembolism in pregnancy

Suspected or confirmed venous thromboembolism (VTE) (deep-vein thrombosis and pulmonary embolism) in non-pregnant patients are common clinical problems with ample clinical research upon which diagnostic and treatment recommendations are based. Unfortunately, the level of complexity is increased in the diagnostic and therapeutic management of pregnancy-associated VTE by evolving physiological changes in expectant mothers, the effects of diagnostic and therapeutic management on the unborn child and the lack of validation of these management strategies in pregnancy. This chapter considers the epidemiology, pathogenesis, diagnosis and treatment of pregnancy-associated VTE. It highlights the poverty of research upon which to base clinical recommendations for this common problem yet offers practical but conservative approaches to patients with suspected and confirmed pregnancy-associated VTE.

Diagnosis of pulmonary embolism: when is imaging needed?

Recent advances in the management of patients with suspected pulmonary embolism have improved diagnostic accuracy and made management algorithms safer and more accessible. Ongoing clinical trials are evaluating whether these diagnostic processes can be made even simpler and less expensive. It is now possible to identify low-risk patients with suspected pulmonary embolism in whom imaging procedures can be avoided altogether.

CT of pulmonary thromboembolic disease

A good quality CT pulmonary angiogram has a high accuracy rate for the evaluation of pulmonary embolism. Investigators have reported that the subsegmental emboli can be missed; however, visualization of smaller arterial branches, and therefore, detection of small emboli may improve with the availability of multidetector scanners. Some of the advantages of using CT for pulmonary embolism compared with lung scintigraphy include: (1) direct visualization of emboli on CT, (2) evaluation of lung parenchyma and mediastinum, which may provide an alternate diagnosis, and (3) capability to acquire CT venogram without additional contrast with "one-stop examination" for evaluation of thromboembolic disease.

Diagnosis of pulmonary embolism

Pulmonary embolism (PE) is a common, lethal yet treatable disease. The clinical diagnosis of PE remains to be a problem due to the nonspecific presenting signs, symptoms, electrocardiographic findings, arterial blood gas abnormalities and chest X-ray changes. Despite these nonspecific clinical findings, clinicians are adept at assigning pretest probability using overall clinical assessment. Clinical models have been developed to improve the accuracy of pretest probability assessment. D-dimers are becoming a widely available clinical tool useful in the diagnostic management of suspected PE. The limitations of the imaging modalities for PE [ventilation-perfusion (V/Q) scanning, spiral computerised tomography, pulmonary angiography and venous leg imaging] necessitate the use of these tests in series and in combination with clinical pretest probability assessment and D-dimer in diagnostic management algorithms. These algorithms permit safe diagnostic management of patients with suspected PE while limiting invasiveness, inaccessibility and expense.

Diagnostic value of arterial blood gas measurement in suspected pulmonary embolism

Pulmonary embolism (PE) is a common and lethal yet treatable condition. Several authors have reported on the diagnostic value of combinations of arterial blood gas (ABG) and other clinical data (i. e., prediction rules), and have claimed that these combinations can be safely used to exclude PE. The purpose of this investigation was to evaluate the diagnostic value of ABG measurement and to attempt to validate the ABG prediction rules published by these various authors for the assessment of patients with suspected PE. Two hundred ninety-three consecutive patients referred for imaging to investigate suspected PE were approached to participate in the investigation. ABG and other clinical data were obtained from consenting and eligible patients before an outcome classification (PE versus non-PE) was performed. None of the ABG data or prediction rules had sufficient negative predictive value, specificity, or likelihood ratios to be useful in the management of patients with suspected PE. We conclude that ABG data alone or in combination with other clinical data are not useful in the assessment of suspected PE.

New diagnostic tests for pulmonary embolism

In 1990, the multicenter Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED), sponsored by the National Institutes of Health, compared the diagnostic value of the radioisotopic ventilation-perfusion lung scan (V/Q scan) with that of pulmonary angiography for the diagnosis of pulmonary embolism (PE). Despite the endurance of the radioisotopic V/Q scan as the most widely used test for evaluation of pulmonary embolism (PE), a better screening tool is clearly needed for use in the emergency department. During the past decade, several new modalities have emerged for evaluation of patients with suspected PE. We evaluate the diagnostic utility of the D-dimer test and the alveolar dead space determination as potential screening tests and of spiral computed tomography, magnetic resonance imaging, transthoracic echocardiography, and transesophageal echocardiography as potential confirmatory tests for PE. For comparison, recent data on the diagnostic utility of the alveolar-arterial oxygen gradient and the V/Q scan are included. The potential application of these new tests to a hypothetical ED population is described.

Diagnostic value of gas exchange tests in patients with clinical suspicion of pulmonary embolism

OBJECTIVE: To assess the value of parameters derived from arterial blood gas tests in the diagnosis of pulmonary embolism. METHOD: We measured alveolar-arterial partial pressure of oxygen [P(A-a)O2] gradient, PaO2 and arterial partial pressure of carbon diaxide (PaCO2) in 773 consecutive patients with suspected pulmonary embolism who were enrolled in the Prospective Investigative Study of Acute Pulmonary Embolism. DIAGNOSIS: The study design required pulmonary angiography in all patients with abnormal perfusion scans. RESULTS: Of 773 scans, 270 were classified as normal/near-normal and 503 as abnormal. Pulmonary embolism was diagnosed by pulmonary angiography in 312 of 503 patients with abnormal scans. Of 312 patients with pulmonary embolism, 12, 14 and 35% had normal P(A-a)O2, PaO2 and PaCO2, respectively. Of 191 patients with abnormal scans and negative angiograms, 11, 13 and 55% had normal P(A-a)O2, PaO2 and PaCO2, respectively. The proportions of patients with normal/near-normal scans who had normal P(A-a)O2, PaO2 and PaCO2 were 20, 25 and 37%, respectively. No differences were observed in the mean values of arterial blood gas data between patients with pulmonary embolism and those who had abnormal scans and negative angiograms. Among the 773 patients with suspected pulmonary embolism, 364 (47%) had prior cardiopulmonary disease. Pulmonary embolism was diagnosed in 151 (41%) of 364 patients with prior cardiopulmonary disease, and in 161 (39%) of 409 patients without prior cardiopulmonary disease. Among patients with pulmonary embolism, there was no difference in arterial blood gas data between patients with and those without prior CPD. CONCLUSION: These data indicate that arterial blood gas tests are of limited value in the diagnostic work-up of pulmonary embolism if they are not interpreted in conjunction with clinical and other laboratory tests.

Use of the alveolar-arterial oxygen gradient in the assessment of acute pulmonary embolism

To evaluate the utility of the alveolar-arterial (A-a) oxygen gradient in the diagnosis of acute pulmonary embolism (PE), a retrospective analysis was done of consecutive emergency department patients who underwent pulmonary angiography for the presumed diagnosis of acute PE. Patients were categorized into two groups depending on the presence or absence of prior cardiopulmonary disease. Arterial blood gas samples were chosen for analysis only if obtained when the PE first was suspected clinically (before lung scans or angiograms) and the patient was breathing room air. A total of 152 patients met all study criteria; 59 patients (39%) had angiographically documented emboli. In comparison with the study patients in whom PE was excluded, there was no significant difference in mean PaO2 (64 v 67 mm Hg) or A-a gradient (39 v 36 mm Hg). Various combinations of the A-a gradient and blood gas levels failed to exclude PE in more than 35% of patients with no prior cardiovascular disease and in 25% of patients with prior cardiovascular disease. The A-a gradient did show a linear correlation with the severity of the PE, as assessed by the PaO2 (r = -0.87) and pulmonary artery mean pressure (r = 0.63). These results indicate that the A-a oxygen gradient, in combination with blood gas levels, may contribute to the formulation of a clinical assessment. However, these laboratory parameters are of insufficient discriminant value to permit exclusion of the diagnosis of PE.

Guidelines for the use of imaging techniques for the investigation of venous thromboembolic disease

The diagnosis of venous thromboembolic disease remains a difficult challenge. Chest radiography, ventilation/perfusion lung scanning, noninvasive leg testing, and pulmonary angiography were evaluated with regard to sensitivity, specificity, positive and negative predictive values. The need for treatment, observation, or serial testing with respect to risks and benefits of treatment and likelihood of serious outcomes was evaluated. The evidence for conclusions was based on the methodology and values of the Canadian Task Force on the Periodic Health Examination. The Diagnostic Imaging Advisory Group of the Canadian Association of Emergency Physicians developed eight recommendations.

Alveolar-arterial oxygen gradient in acute pulmonary embolism in pregnancy

OBJECTIVE

Our goal was to determine the prevalence of normal alveolar-arterial gradients in pregnant patients with documented pulmonary embolism.

STUDY DESIGN

A retrospective chart review was performed on all pregnant women with pulmonary embolism at two large obstetric centers between 1990 and 1995. Alveolar-arterial gradients were calculated from room air arterial blood gas values and compared with values from patients who had been established as normal.

RESULTS

Ten of 17 patients with pulmonary embolism identified had alveolar-arterial gradients that were normal.

CONCLUSIONS

In our study 58% of pregnant women with documented pulmonary embolism had a normal alveolar-arterial gradient. This markedly differs from the published data in nonpregnant patients, in which the incidence of normal alveolar-arterial gradients in pulmonary embolism has ranged from 1.9% to 20%. This suggests that the alveolar-arterial gradient should not be used to determine the likelihood of pulmonary embolism in pregnant women because this could lead to the withholding of appropriate treatment for this life-threatening condition.

Syncope as an emergency department presentation of pulmonary embolism

Pulmonary embolism presenting as an isolated syncopal spell can be a difficult clinical correlation to make. We present three cases of pulmonary embolism-induced syncope and review the pathophysiology and diagnostic considerations in this setting. Pulmonary embolism should be considered in the differential diagnosis of every syncopal event that presents to the emergency department, even in the face of cardiac dysrhythmias and normal pulse oximetry values.

Clinical aspects of pulmonary embolism

Pulmonary embolism is a common disease in the United States, affecting as many as 500,000 persons annually. Unfortunately, this disorder is commonly undiagnosed, resulting in significant excess morbidity and mortality. The clinical symptoms and signs caused by pulmonary embolism are nonspecific and may be confused with a variety of other cardiopulmonary disorders having similar presentations. However, accurate diagnostic tests are available for diagnosing pulmonary embolism, even in the face of coexistent cardiopulmonary disorders. This article describes the clinical characteristics of pulmonary venous thromboembolism, reviewing its typical symptoms and signs, its routine laboratory tests, and chest radiographic abnormalities.

The clinical features of acute pulmonary embolism in ambulatory patients

OBJECTIVE

To identify clinical findings and predisposing conditions associated with acute pulmonary embolism (PE) in ambulatory patients being evaluated for PE.

METHODS

A prospective observational study was conducted. A standardized multicomponent data collection form was administered to ambulatory subjects being evaluated for PE. The diagnosis of PE was confirmed or excluded using a combination of scintillation lung scanning, lower-extremity venous Doppler ultrasonography, and selective use of pulmonary angiography.

RESULTS

Data collection was completed for 170 subjects, with 26 (15%) cases of PE. Subjects with PE were significantly older (56 vs 41 years, 99% CI for difference of 15 years [6 to 25 years]), were more likely to report unexplained dyspnea (92% vs 69%, 99% CI for difference of 23% [7% to 40%]), and waited longer after symptom onset to seek medical evaluation (73 vs 36 hours, 99% CI for difference of 37 hours [11 to 63 hours]). No difference was found for multiple variables commonly associated with PE. Assignment to risk categories was of limited diagnostic utility. For example, low-risk assignment yielded 85% sensitivity, 20% specificity; high-risk assignment: 31% sensitivity, 85% specificity, with diagnostic accuracy below 80% in both categories.

CONCLUSIONS

Among outpatients selected for evaluation for PE, further risk stratification demonstrated poor diagnostic utility. Clinical features alone cannot be used to differentiate presence or absence of PE in at-risk ambulatory patients.

Use of the alveolar dead space fraction (Vd/Vt) and plasma D-dimers to exclude acute pulmonary embolism in ambulatory patients

OBJECTIVE

To evaluate the utility of a modified calculation of the alveolar dead space fraction (Vd/Vt), combined with plasma D-dimers, to aid in the exclusion of acute pulmonary embolism (PE).

METHODS

A prospective comparison of screening modalities was performed in a metropolitan teaching ED. Ambulatory patients evaluated for PE underwent simultaneous end-tidal CO2 and arterial blood gas determinations, as well as venous latex-agglutination D-dimer quantification. The modified Bohr equation was used to calculate Vd/Vt as an index of alveolar dead space. Acute PE was diagnosed or excluded using appropriate combinations of clinical suspicion, ventilation-perfusion lung scanning, lower-extremity venous Doppler ultrasonography, pulmonary angiography, and comprehensive follow-up.

RESULTS

Of 170 subjects studied, PE was confirmed (PE+) in 26 (15%) and excluded (PE-) in 144 (85%). In the PE+ group, Vd/Vt was 0.31 +/- 0.13 (mean +/- SD), and in the PE- group, Vd/Vt was 0.06 +/- 0.10 (p < 0.05, t-test). Regarding false-negative rates, Vd/Vt was normal (i.e., < 0.2) in 3/26 PE+ patients and D-dimer concentrations were normal (< 0.5 microgram/L) in 4/26 patients in the PE+ group. The combination of a normal Vd/Vt and D-dimer concentration was 100% sensitive (95% CI = 88-100%) in excluding PE. False-positive testing (either test positive) occurred in 49/144 subjects (specificity 65%, 95% CI = 52-73%). The age-adjusted alveolar-arterial O2 gradient was 33 +/- 38 torr in the PE+ group vs 13 +/- 37 torr in the PE- group (p = 0.11).

CONCLUSIONS

In ambulatory patients, the finding of Vd/Vt < 0.2 and D-dimers < 0.5 microgram/L lowers the probability of acute PE.

Alveolar-arterial oxygen gradient in the assessment of acute pulmonary embolism

PURPOSE

The purpose of this investigation is to evaluate the utility of the alveolar-arterial (A-a) oxygen gradient in the diagnosis of acute pulmonary embolism (PE) among patients who participated in the Prospective Investigation of Pulmonary Embolism Diagnosis (PIO-PED).

METHODS

Pulmonary embolism was diagnosed (n = 280) or excluded (n = 499) by angiography in all patients. Patients were then categorized as (1) the entire cohort, (2) no prior cardiopulmonary disease and no prior PE, and (3) no prior PE or deep venous thrombosis. Normal values of the A-a gradient were defined in three ways: (1) values < or = 20 mm Hg; (2) values < or = age/4 + 4; and (3) values based on age from the literature.

RESULTS

When a normal A-a gradient was defined as < or = 20 mmHg, 11 to 14% of patients with PE in the three categories of patients had a normal A-a gradient. When the equation age/4 + 4 was used, 8% to 10% of patients with PE in the three categories of patients had a normal A-a gradient. With age-related values from the literature, 20 to 23% of patients with PE in the three categories of patients had a normal A-a gradient. The A-a gradient was normal in comparable percentages of patients who did not have PE.

CONCLUSION

Normal values of the A-a gradient did not exclude the diagnosis of acute PE.