Alveolar dead space as a predictor of severity of pulmonary embolism

Pediatric In-Hospital Cardiac Arrest Secondary to Acute Pulmonary Embolism

OBJECTIVES

Pulmonary embolism is a rarely reported and potentially treatable cause of cardiac arrest in children and adolescents. The objective of this case series is to describe the course of five adolescent patients with in-hospital cardiac arrest secondary to pulmonary embolism.

DESIGN

Case series.

SETTING

Single, large academic children's hospital.

PATIENTS

All patients under the age of 18 years (n = 5) who experienced an in-hospital cardiac arrest due to apparent pulmonary embolism from August 1, 2013, to July 31, 2017.

INTERVENTIONS

All five patients received systemic thrombolytic therapy (IV tissue plasminogen activator) during cardiac arrest or periarrest during ongoing resuscitation efforts.

MEASUREMENTS AND MAIN RESULTS

Five adolescent patients, 15-17 years old, were treated for pulmonary embolism-related cardiac arrests during the study period. These accounted for 6.3% of all children and 25% of adolescents (12-17 yr old) receiving at least 5 minutes of in-hospital cardiopulmonary resuscitation during the study period. All five had venous thromboembolism risk factors. Two patients had known, extensive venous thrombi at the time of cardiac arrest, and one was undergoing angiography at the time of arrest. The diagnoses of pulmonary embolism were based on clinical suspicion, bedside echocardiography (n = 4), and low end-tidal CO2 levels relative to arterial CO2 values (n = 5). IV tissue plasminogen activator was administered during cardiopulmonary resuscitation in three patients and after the return of spontaneous circulation, in the setting of severe hemodynamic instability, in the other two patients. Four of five patients were successfully resuscitated and survived to hospital discharge.

CONCLUSIONS

Pulmonary embolism was recognized as the etiology of multiple adolescent cardiac arrests in this single-center series and may be more common than previously reported. Recognition, high-quality cardiopulmonary resuscitation, and treatment with thrombolytic therapy resulted in survival in four of five patients.

Detection of Residual Pulmonary Vascular Obstruction by Ventilation-Perfusion Lung Scan Late After a First Pulmonary Embolism

The long-term impact of persistent pulmonary vascular obstruction after pulmonary embolism (PE) remains unknown. Based on ventilation-perfusion lung scan performed at discharge and 3 months after a first PE, we aimed to investigate the prognostic value on 5-year adverse events of (1) residual pulmonary vascular obstruction (RPVO) at discharge (DIS-RPVO), (2) RPVO at 3 months (3M-RPVO), and (3) relative change in RPVO between the 2 scans (RC-RPVO). We performed a prospective, multicenter cohort study from January 2007 to December 2009 including patients who survived at least 3 months after a PE. RC-RPVO was defined as (DIS-RPVO - 3M-RPVO)/DIS-RPVO. The primary end point was a combined end point at 5 years, composed of all-cause death, recurrent venous thromboembolism, chronic thromboembolic pulmonary hypertension, heart failure, and rehospitalization for cardiac causes. Receiver-operating characteristic curves were computed to define thresholds of DIS-RPVO, 3M-RPVO, and RC-RPVO predictive of the primary combined end point at 5 years. Overall, 241 patients were included (high-risk PE: 11.2%, intermediate-risk PE: 51.8%, low-risk PE: 37%). Mean DIS-RPVO was 27.9 ± 15.1%, mean 3M-RPVO was 10.3 ± 10.8%, and mean RC-RPVO was 61.7 ± 33.4%. At 5 years, 112 patients (46.5%) experienced the combined end point. Both 3M-RPVO ≥15% and RC-RPVO ≤37.5% were independently related to the occurrence of the combined end point at 5 years (p = 0.01 and p = 0.02, respectively). DIS-RPVO did not predict long-term adverse events. In conclusion, RC-RPVO ≤37.5% and 3M-RPVO ≥15% were independently related to the occurrence of adverse events 5 years after a first PE.

Circulatory collapse, right ventricular dilatation, and alveolar dead space: A triad for the rapid diagnosis of massive pulmonary embolism

A triad of circulatory collapse, right ventricular dilatation, and large alveolar dead space is proposed for the rapid diagnosis and treatment of massive pulmonary embolism. A 17year-old female on oral contraceptives collapsed at home becoming incoherent with shallow breathing. Paramedics initiated mechanical chest compression and transported the patient to our emergency department, arriving minimally responsive with undetectable blood pressure but having positive corneal reflexes and bradycardia with wide QRS. The trachea was intubated and goal-directed echocardiography revealed marked right ventricular dilatation with septal flattening. The arterial PCO₂ was 40mmHg with an end-tidal PCO₂ of 8mmHg, revealing a large alveolar dead space. Persistent hypotension, bradycardia, and fading alertness despite epinephrine and norepinephrine infusions prompted resumption of chest compression. Intravenous alteplase (10mg bolus over 10min followed by 90mg over 110min) begun 125min after collapse improved hemodynamic function within 10min allowing discontinuation of chest compression. Five and a half hours after starting alteplase, the patient was hemodynamically stable and had normal end-tidal PCO₂. A CT-angiogram showed the pulmonary arteries free of emboli but a thrombus in the right common iliac vein. The patient recovered fully and was discharged home on warfarin 8days later. Based on this and other reports, we propose a triad of circulatory collapse, right ventricular dilatation, and large alveolar dead space for the rapid diagnosis and treatment of massive pulmonary embolism, with systemic fibrinolysis as the first-line intervention.

Using the features of the time and volumetric capnogram for classification and prediction

Quantitative features derived from the time-based and volumetric capnogram such as respiratory rate, end-tidal PCO₂, dead space, carbon dioxide production, and qualitative features such as the shape of capnogram are clinical metrics recognized as important for assessing respiratory function. Researchers are increasingly exploring these and other known physiologically relevant quantitative features, as well as new features derived from the time and volumetric capnogram or transformations of these waveforms, for: (a) real-time waveform classification/anomaly detection, (b) classification of a candidate capnogram into one of several disease classes, (c) estimation of the value of an inaccessible or invasively determined physiologic parameter, (d) prediction of the presence or absence of disease condition, (e) guiding the administration of therapy, and (f) prediction of the likely future morbidity or mortality of a patient with a presenting condition. The work to date with respect to these applications will be reviewed, the underlying algorithms and performance highlighted, and opportunities for the future noted.

CO2 measurement for the early differential diagnosis of pulmonary embolism-related shock at the emergency department: A case series

Objective

An early differential diagnosis is mandatory when facing a patient with clinical shock of unclear aetiology, in order to guide proper treatment. We assessed if the expired CO₂ measurement and alveolar-arterial CO₂ calculation could improve the differential diagnosis of shock during its initial presentation, particularly in separating pulmonary embolism from other causes of shock.

Methods

We analysed the charts of 12 patients who presented with clinical shock and had end-tidal CO₂ (EtCO₂) and arterial CO₂ partial pressure (PaCO₂) measurements.

Results

In cases with pulmonary embolism-related shock (n = 3), the gradient between PaCO₂ and EtCO₂ was increased (37 vs 0.2 mmHg). There was a similar trend for a higher PaCO₂ value (60 vs 32.2 mmHg) and a lower EtCO₂ value (23 vs 32 mmHg).

Conclusion

An initial CO₂ measurement might be an easily available tool for the early diagnostic work-up of clinical shock.

Role of perioperative monitoring in diagnosis of massive intraoperative cardiopulmonary embolism

Massive thrombotic intraoperative pulmonary emboli (IOPE) is rare but carries a great degree of morbidity and mortality. This is the first study to formally assess the utility of various tools for the diagnosis of these events and the impact of each tool on mortality. Due to both the infrequent occurrence of these events and the high mortality of massive IOPE, it was cost-prohibitive to prospectively randomize patients to study commonly used diagnostic tools. Hence, a descriptive review of all reported cases in the literature was performed. This review yielded 146 cases for past 4 decades. Following a careful review of these cases, the alerting monitor for the occurrence of IOPE was recorded. Furthermore, we recorded the confirming diagnostic tool and the outcome of these patients. We compared 4 monitoring tools: (1) end-tidal carbon dioxide; (2) central catheter pressures; (3) echocardiography; and (4) standard monitoring of vital signs. Pre-event use of transesophageal echocardiography had no survival benefit. End-tidal carbon dioxide changes as an alerting tool were associated with improved survival compared to changes in vital signs (P<0.0001). Signs of right heart strain were associated with greater mortality, but direct thrombus visualization was not. Echocardiography appears to be useful for diagnosis of massive IOPE. Compared with hemodynamic collapse, end-tidal carbon dioxide decline as the presenting sign of massive IOPE may be associated with a better prognosis because it may represent earlier detection of IOPE and allow for more time to intervene.

[Utility of the dead space fraction (Vd/Vt) as a predictor of extubation success]

PURPOSE

To determine the value of Vd/Vt as a predictor of extubation failure in patients with mechanical ventilation admitted to the intensive care units.

DESIGN

A prospective, observational cohort study conducted from 1 September 2010 to 1 March 2011.

SETTING

General intensive care unit (G-ICU) of a third level university hospital.

PATIENTS OR PARTICIPANTS

The study included patients on mechanical ventilation (MV) for over 12 hours, and who in the process of weaning were subjected to low-level pressure support. Exclusion criteria were age under 18 years, ventilation via tracheotomy and patients failing to cooperate for different reasons. During the study, 392 patients were admitted to the G-ICU; of these, 214 required MV. The weaning process was started in 154 cases. Fifty-four patients were excluded from the study, and 24 were not extubated from MV. A total of 76 patients were finally extubated and analyzed.

VARIABLES OF INTEREST

Vd/Vt was calculated as the ratio (PaCO(2)-Pє CO(2))/PaCO(2), with the recorded parameters.

RESULTS

Logistic regression analysis showed a significant association between the Vd/Vt and extubation failure, with OR=1.52 (95%CI 1.11 to 2.09, p=0.008). The area under the ROC curve with respect to the prediction of extubation failure according to the Vd/Vt value was 0.94 (95%CI 0.86 to 0.98, p<0.0001).

CONCLUSIONS

Vd/Vt is a powerful predictor of extubation failure in patients on MV.

Measurement of dead space in subjects under general anesthesia using standard anesthesia equipment

BACKGROUND

Pulmonary dead space is the volume of gas that is delivered to the lungs but does not participate in gas exchange. Knowing pulmonary dead space in patients under general anesthesia is clinically useful because it can aid in detecting disease processes such as pulmonary emboli or low cardiac output states. Dead space can be simply calculated by using the Bohr equation; however, it is difficult to measure mixed exhaled carbon dioxide (PECO(2)) with a standard anesthesia machine. Previously, a study at our institution demonstrated the carbon dioxide (CO(2)) concentration in the bellows of a standard anesthesia machine is an accurate approximation of PECO(2). In this study, we used the bellows PECO(2) measurement and arterial CO(2) (PaCO(2)) to calculate pulmonary dead space. We verified the technique by adding known apparatus dead space volumes during anesthesia.

METHODS

Subjects were under general endotracheal anesthesia. A sampling line was positioned inside the ventilator bellows and connected to a capnometer. Measurements of PECO(2) and PaCO(2) from an arterial catheter were taken at baseline and after adding 100 mL and 200 mL of dead space to the endotracheal tube. Dead space was calculated using the Bohr equation (alveolar dead space/tidal volume = [PaCO(2) - PECO(2)]/PaCO(2)) at baseline and after adding 100 mL and 200 mL of apparatus dead space.

RESULTS

The dead space at baseline was 265 ± 47 mL (mean ± SD) in 10 study subjects. After adding 100 mL of dead space to the endotracheal tube, the measured dead space increased by 110 ± 46 mL. The measured dead space increased by 158 ± 39 mL after adding 200 mL.

CONCLUSIONS

Our baseline dead space measurements were in the expected range under general anesthesia. When dead space was added, we were able to calculate that an increase in dead space occurred. Our calculation was more accurate after adding a 100-mL volume than after adding 200 mL. We present a simple way to detect trends in dead space in ventilated patients using a Narkomed GS anesthesia machine (Dräger Medical, Lübeck, Germany).

Can dead space fraction predict the length of mechanical ventilation in exacerbated COPD patients?

Background

Chronic obstructive pulmonary disease (COPD) is a condition in which there is limited airflow during expiration (exhaling, or breathing out) that is not fully reversible and usually worsens over time. The disease is estimated to kill more than 100,000 Americans each year, and costs related to care of patients with COPD are significant. Physiologically, COPD represents a disruption in ventilation and in the exchange of gases in the lungs. Laboratory tests indicate elevated CO₂ levels, gradual reduction of the levels of oxygen and pH in arterial blood, and a consequent rise in the dead space fraction (DSF) of the lungs.

Objective

Patients with COPD exacerbation represent a large portion of those artificially ventilated. In an attempt to develop a prognostic tool for length of treatment, we compared the proportion of DSF to the length of mechanical ventilation (MV).

Methods

This study included 73 patients admitted to the intensive care unit (ICU) where they received MV due to exacerbation of COPD. Each patient’s arterial blood gases (ABG) were measured upon admission. PeCO₂ was tested using a Datex S/5 instrument. Subsequently, DSF was calculated using the Bohr equation. Statistical data was analyzed using SPSS software.

Results

Patients included in the study were ventilated from 6 to 160 hours (average 40 ± 47). In addition to ABG measurements, PeCO₂ (expired CO₂) levels were measured and DSF calculated for each patient. DSF values varied from 0.21 to 0.76 (average 0.119 ± 0.489). No correlation was found between DSF and length of artificial ventilation.

Conclusion

Evaluation of DSF does not provide a factor in estimating the length of treatment for patients with acute respiratory failure due to COPD exacerbation.

Prognostic stratification of acute pulmonary embolism: focus on clinical aspects, imaging, and biomarkers

Pulmonary embolism (PE) represents a common disease in emergency medicine and guidelines for diagnosis and treatment have had wide diffusion. However, PE morbidity and mortality remain high, especially when associated to hemodynamic instability or right ventricular dysfunction. Prognostic stratification to identify high risk patients needing to receive more aggressive pharmacological and closer monitoring is of utmost importance. Modern guidelines for management of acute PE are based on risk stratification using either clinical, radiological, or laboratory findings. This article reviews the modern treatment of acute PE, which is customized upon patient prognosis. Accordingly the current risk stratification tools described in the literature such as clinical scores, echocardiography, helical computer tomography, and biomarkers will be reviewed.

Persistent dyspnea complaints at long-term follow-up after an episode of acute pulmonary embolism: results of a questionnaire

BACKGROUND

There is a lack of information on long term complications of patients with pulmonary embolism (PE), including chronic complaints of dyspnea.

METHODS

Consecutive patients with a prior diagnosis of acute PE and an age and gender matched control group with no medical history of PE were presented with a questionnaire, designed to establish the presence, severity and possible causes of dyspnea in the clinical course of PE.

RESULTS

The questionnaire was taken in 48 PE-survivors 40+/-7.4 months after PE; 27 patients (56%) had complaints of dyspnea. Sixteen (35%) were categorized as NYHA class II, 6 (13%) as class III and 5 (10%) as class IV. Overall, 19 patients (70%) had new or worsened complaints after PE. The study included 61 controls. Corrected for gender, age and medical history, the control group was significantly less dyspnoeic compared to the PE survivors (p<0.001). Corrected for gender and age, patients were 4 times more often in NYHA class II (OR 3.6 95%CI 1.4-9.7) and 7-fold more often in NYHA class III or IV (OR 6.5 95%CI 1.7-24), both compared to control subjects.

CONCLUSION

A large percentage of patients with prior PE have persistent complaints of dyspnea at long term follow-up. The majority of them developed new or worsened dyspnea after the thrombo-embolic event. In comparison to a control population without a medical history of VTE, PE patients were overall significantly more dyspnoeic. An explanation for this phenomenon needs to be studied in further functional work-up of these patients.

Relationship between physiologic deadspace/tidal volume ratio and gas exchange in infants with acute bronchiolitis on invasive mechanical ventilation

OBJECTIVES

To evaluate the association between deadspace/tidal volume ratio (Vd/Vt) and gas exchange variables: Pao2, Paco2, Pao2/Fio2, arterial/alveolar oxygen tension ratio (Pao2/PAo2), alveolar-arterial oxygen tension difference/arterial oxygen tension ratio (P(A-a)o2/Pao2), carbon dioxide production (Vco2), ventilation index ([Paco2 x peak inspiratory pressure x mechanical respiratory rate]/1000), and oxygenation index ([mean airway pressure x Fio2 x 100]/Pao2), all measured at an early stage in children with obstructive acute respiratory failure.

DESIGN

Prospective, cross-sectional, observational study.

SETTING

Pediatric intensive care unit, university hospital.

PATIENTS

Twenty-nine infants with acute bronchiolitis, defined according to clinical and radiologic criteria. Children with chronic pulmonary disease, neuromuscular disease, congenital cardiopathies, or hemodynamic instability were excluded.

INTERVENTIONS

Measurements were made between 24 and 72 hrs of mechanical ventilation using volumetric capnography and arterial blood gas analysis.

MEASUREMENTS AND MAIN RESULTS

The following variables significantly correlated with Vd/Vt, calculated using Spearman's correlation coefficient (rs): Pao2 (rs = -0.63, p < .001), Pao2/Fio2 (rs = -0.56, p = .002), Pao2/PAo2 (rs = -0.46, p = .012), P(A-a)o2/Pao2 (rs = -0.46, p = .012), Paco2 (rs = 0.51, p = .005), Vco2 (rs = -0,62, p < .01), oxygenation index (rs = 0.48, p = .009), and ventilation index (rs = -0.53, p = .003). A statistically significant association was found between an increase in Vd/Vt and severity of lung injury, defined as Pao2/Fio2 <200 (p = .03, Mann-Whitney).

CONCLUSIONS

In the study population, Vd/Vt not only reflected ventilatory disorders, as is well recognized, but also was associated with disturbances of oxygenation. These results warrant further evaluation of the usefulness of serial measurement of Vd/Vt as a marker of disease severity in severe acute bronchiolitis and other causes of respiratory failure.

Acute pulmonary embolism: risk stratification in the emergency department

Pulmonary embolism is a common disease associated with a high mortality rate. Death due to pulmonary embolism occurs more commonly in undiagnosed patients before hospital admission or during the initial in-hospital stay. Thus, mortality could be reduced by prompt diagnosis, early prognostic stratification and more intensive treatment in patients with adverse prognosis. Mortality is particularly high in patients with pulmonary embolism presenting with arterial hypotension or cardiogenic shock. In patients with pulmonary embolism and normal blood pressure, a number of clinical features and objective findings have been associated with a high risk of adverse in-hospital outcome. Advanced age and concomitant cardiopulmonary disease are clinical risk factors for in-hospital mortality. The Bburden of thromboembolism, as assessed by lung scan or spiral CT, and right ventricle overload, as assessed by echocardiography and probably spiral CT, have been claimed to be risk factors for in-hospital mortality. Elevated serum levels of troponins have been shown to be associated with right ventricular overload and adverse in-hospital outcomes in patients with pulmonary embolism. Despite the currently available evidence, no definite prognostic value can be assigned to any of the individual risk factors or cluster of them. Large prospective trials should be carried out to validate individual risk factors or clusters of risk factors able to identify patients with acute pulmonary embolism at high risk for in-hospital mortality. These patients could afford the trade-off of an increased risk of side effects related to a more aggressive treatment, such as thrombolysis or surgical or interventional procedures.

Systematic errors and susceptibility to noise of four methods for calculating anatomical dead space from the CO 2 expirogram

BACKGROUND

Anatomical dead space is usually measured using the Fowler equal area method. Alternative methods include the Hatch, Cumming, and Bowes methods, in which first, second, and third order polynomials, respectively, fitted to an expired CO2 volume vs expired volume curve, intercept the x-axis at the anatomical dead space. This study assessed systematic errors and susceptibility to noise of the Fowler, Hatch, Cumming, and Bowes dead spaces calculated over 40-80% of the CO2 expirogram.

METHODS

Simulated CO2 expirograms with 220 ml anatomical dead space and varying alveolar plateau slopes were generated digitally and zero-mean Gaussian noise added. CO2 expirograms were recorded in 10 anaesthetized human subjects. Anatomical dead space was calculated by the Fowler, Hatch, Cumming, and Bowes methods.

RESULTS

The Fowler, Hatch, Cumming, and Bowes methods displayed systematic biases of -1.8%, 13.2%, 2.4%, and -1.3%, respectively, at a normalized simulated alveolar plateau slope of 1.6 litre(-1). At a noise level of 0.0066 vol/vol, the standard deviations of recovered simulated dead spaces were 70.6, 1.8, 2.4, and 3.7 ml, respectively. The Hatch, Cumming, and Bowes methods applied to human expirograms differed significantly from that of Fowler by 13, -4, and -11 ml, respectively. In the human study, the Hatch and Cumming methods yielded the lowest intra-individual dead space variability.

CONCLUSIONS

The Fowler method shows greatest susceptibility to measurement noise and the Hatch method exhibits the largest systematic error. The Cumming method, which exhibits both low bias and low noise susceptibility, is preferred for estimating anatomical dead space from CO2 expirograms.

Pulmonary embolism: an unsuspected killer

The presentation of PE is often subtle and may mimic other diseases. Many pulmonary emboli invariably preclude diagnosis by their occult nature or by leading to rapid death from cardiopulmonary arrest. In patients who do manifest symptoms from PE, accurate diagnosis is essential. Often it is difficult to distinguish the vague symptoms of PE from other diagnoses, such as acute coronary syndrome, pneumonia, COPD, CHF,aortic dissection, myocarditis or pericarditis, pneumothorax, and musculo-skeletal or gastrointestinal causes. Regardless of the presentation, the most fundamental step in making the diagnosis of PE is first to consider it. Historical clues and risk factors should raise the clinician's suspicion.PE is an unsuspected killer with a nebulous presentation and high mortality. In all likelihood, PE will remain an elusive diagnosis despite advances in technology and a wealth of research. A high index of suspicion is required, but no amount of suspicion would eliminate all missed cases. Patients with significant underlying cardiopulmonary disease seem to be the most challenging. Patients with significant comorbidity have poor reserve and are likely to have poor outcomes, especially if the diagnosis is not made and anticoagulation is not initiated early. Controversy exists over the best diagnostic approach to PE. A battery of diagnostic studies is available, with few providing definitive answers. Studies such as CT may be helpful at some institutions but offer poor predictive value at others. Other diagnostic tests are not universally available. It is hoped that further research and improvements in current diagnostic modalities will clear some of the current confusion and controversy of this ubiquitous and deadly disease.

Volumetric Capnography as a Screening Test for Pulmonary Embolism in the Emergency Department

STUDY OBJECTIVE

To compare the diagnostic performance of volumetric capnography (VCap), which is the plot of the expired CO(2) partial pressure against the expired volume during a single breath, with the PaCO(2) to end-tidal CO(2) (EtCO(2)) gradient, in the case of suspected pulmonary embolism (PE).

DESIGN

Single-center, prospective study.

SETTING

Emergency department of a teaching hospital.

PATIENTS

A total of 45 outpatients with positive enzyme-linked immunosorbent assay d-dimer levels of > 500 ng/mL. The diagnosis of PE was confirmed in 18 outpatients according to a validated procedure based on the ventilation-perfusion lung scan and/or spiral CT scanning.

INTERVENTIONS

Curves of VCap were obtained from a compact monitor connected to a computer. A sequence of four to six stable breaths allowed the calculation of the following several variables: alveolar dead space fraction; the ratio of alveolar dead space (VDalv) to airway dead space (VDaw); the VDalv to physiologic dead space (VDphys) fraction; the slope of phase 3; and the late dead space fraction (Fdlate) corresponding to the extrapolation of the capnographic curve to a volume of 15% of the predicted total lung capacity.

RESULTS

The mean (+/- SD) PaCO(2)-EtCO(2) gradient was 5.3 +/- 0.7 mm Hg in the PE-positive group and 2.8 +/- 0.7 mm Hg in the PE-negative group (p = 0.019). Four variables of the VCap exhibited a statistical difference between both groups, as follows: the VDalv/VDaw fraction(;) the slope of phase 3; the VDalv/VDphys fraction; and the Fdlate, which was 8.2 +/- 3.3% vs -7.7 +/- 2.8%, respectively (p = 0.000011). The diagnostic performance expressed as the mean area under a receiver operating characteristic curve comparison was 75.9 +/- 7.4% for the PaCO(2)-EtCO(2) gradient and 87.6 +/- 4.9% for the Fdlate (p = 0.02).

CONCLUSION

Fdlate, a variable of VCap, had a statistically better diagnostic performance in suspected PE than the PaCO(2)-EtCO(2) gradient. VCap is a promising computer-assisted bedside application of pulmonary pathophysiology. Future research should define the place of this technique in the diagnostic workup of PE, especially in the presence of positive d-dimers.

Inhibition of prostaglandin synthesis during polystyrene microsphere-induced pulmonary embolism in the rat

Our objective was to test the effect of inhibition of thromboxane synthase versus inhibition of cyclooxygenase (COX)-1/2 on pulmonary gas exchange and heart function during simulated pulmonary embolism (PE) in the rat. PE was induced in rats via intrajugular injection of polystyrene microspheres (25 micro m). Rats were randomized to one of three posttreatments: 1) placebo (saline), 2) thromboxane synthase inhibition (furegrelate sodium), or 3) COX-1/2 inhibition (ketorolac tromethamine). Control rats received no PE. Compared with controls, placebo rats had increased thromboxane B(2) (TxB(2)) in bronchoalveolar lavage fluid and increased urinary dinor TxB(2). Furegrelate and ketorolac treatments reduced TxB(2) and dinor TxB(2) to control levels or lower. Both treatments significantly decreased the alveolar dead space fraction, but neither treatment altered arterial oxygenation compared with placebo. Ketorolac increased in vivo mean arterial pressure and ex vivo left ventricular pressure (LVP) and right ventricular pressure (RVP). Furegrelate improved RVP but not LVP. Experimental PE increased lung and systemic production of TxB(2). Inhibition at the COX-1/2 enzyme was equally as effective as inhibition of thromboxane synthase at reducing alveolar dead space and improving heart function after PE.

Use of volumetric capnography to identify pulmonary dysfunction in horses with and without clinically apparent recurrent airway obstruction

OBJECTIVE

To investigate whether volumetric capnography indices could be used to differentiate between horses without recurrent airway obstruction (RAO) and horses with RAO that were in clinical remission or that had clinically apparent RAO.

ANIMALS

70 adult Swiss Warmblood horses (20 used for pleasure riding and 50 used for dressage or show jumping).

PROCEDURE

Horses were allocated to 4 groups on the basis of history, clinical signs, results of endoscopy, and cytologic findings (group 1, 21 healthy horses; group 2, 22 horses with RAO that were in remission; group 3, 16 horses with mild RAO; group 4, 11 horses with exacerbated RAO). Expiratory volume and CO2 curves were recorded by use of a computerized ultrasonic spirometer. Volumetric capnograms were plotted, and derived indices were calculated.

RESULTS

Dead-space volume (VD) was calculated by use of the Bohr equation (VD(Bohr)) and for physiologic VD (VD(phys)). Ratios for VD(Bohr) to expiratory tidal volume (VT) and VD(phys) to V(T) as well as an index of effective CO2 elimination were significantly different among groups of horses. Age and use of the horses also significantly affected volumetric capnography indices.

CONCLUSIONS AND CLINICAL RELEVANCE

Ratios of VD(Bohr) to VT and VD(phys) to VT as well as an index of effective CO2 elimination were sufficiently sensitive measures to distinguish between healthy horses and horses with RAO in remission. To optimize the ability of volumetric capnography indices to differentiate among horses in heterogeneous populations, it is important to account for effects of age and specific use of the horses.

End tidal CO(2) is reduced during hypotension and cardiac arrest in a rat model of massive pulmonary embolism

BACKGROUND

We investigated the effect of massive pulmonary embolism (MPE) on end tidal CO(2) (etCO(2)) and tested two hypotheses: (1) that etCO(2) can distinguish massive PE from hemorrhagic shock and (2) that PE with cardiac arrest reduces etCO(2) during resuscitation to a greater extent than arrhythmic cardiac arrest.

METHODS

Anesthetized, mechanically ventilated rats (N=10 per group), were subjected to either graded PE (latex microspheres), or graded hemorrhagic shock to produce a final mean arterial blood pressure, (MAP) of 40 mmHg; a third group was subjected to surgical/anesthetic control conditions. Cardiac arrest was induced by the following methods: intravenous injection of a large bolus of microspheres in the PE group, aortic puncture in the hemorrhage group, and intravenous tetrodotoxin (TTX) to produce arrhythmic cardiac arrest in the control group.

RESULTS

At a MAP of 40 mmHg, etCO(2) was significantly decreased in the PE group (18.3+/-1.9 torr) compared with both the hemorrhage (24.3+/-1.3) and the control group (35.0+/-1.3 torr; ANOVA P<0.001). The decreased etCO(2) occurred coincident with an increase in alveolar dead space fraction in the PE group. In the first minute of ventilation after cardiac arrest, the etCO(2) was significantly decreased in the PE group (6.5+/-0.9) versus both hemorrhage (16.5+/-1.1) and TTX (34.2+/-2.4 torr).

CONCLUSIONS

Massive PE with shock decreases the etCO(2) and increases the dead space fraction to a greater extent than hemorrhagic shock at the same MAP. Cardiac arrest from PE is associated with extremely low etCO(2) readings during CPR.

Validity of pulmonary function indices derived from the volumetric capnogram in horses with recurrent airway obstruction (RAO)

The objective of this study was to determine the accuracy with which pulmonary function indices derived from the volumetric capnogram can diagnose different degrees of recurrent airway obstruction (RAO) in 63 warmblood horses. The sensitivity, specificity, the area under the receiver operating curve (AUC), optimal cut-off values and predictive values of the indices were calculated. The results obtained have shown that there is no single index characterised by specificity and sensitivity to differentiate with an accuracy of >90 per cent between the different degrees of RAO compared to the clinical examination. The indices A(1)/A(2) and VD(alv)/ VT(alv) (AUC=0.55 and 0.53) appeared to have the highest relative sensitivity and specificity to differentiate between healthy horses and horses suffering from subclinical or minor RAO and the indices VD(phys)/ VT and VD(Bohr)/ VT between horses suffering from subclinical or minor RAO and horses with moderate to severe RAO (AUC=0.71 and 0.70). We do not consider it acceptable to use cut off values optimised for both maximal sensitivity and specificity, because a great number of horses would have been inappropriately classified.

Biventricular cardiac dysfunction after acute massive pulmonary embolism in the rat

Cardiac dysfunction has been documented in vivo after acute massive pulmonary embolism (AMPE). The present study tests whether intrinsic ventricular dysfunction occurs in rat hearts isolated after AMPE. AMPE was induced in spontaneously breathing ketamine-xylazine-anesthetized rats by thrombus infusion until mean arterial blood pressure (MAP) was approximately 40% of basal measurement. A hypotensive control group underwent controlled blood withdrawal to produce MAP approximately 40% of basal levels. Shams underwent identical surgical and anesthesia preparation but without pulmonary embolization. Hearts were perfused in isovolumetric mode, and simultaneous right ventricular (RV) and left ventricular (LV) pressures were measured. AMPE caused arterial hypotension with hypoxemia (PO(2) = 50 +/- 14 Torr), acidemia (pH = 7.26 +/- 0.11), and high lactate concentration (6.9 +/- 1.7 mM). Starling curves from both ventricles demonstrated that AMPE significantly reduced ex vivo systolic contractile function in the RV (P = 0.031) and LV (P = 0.008) compared with both the hypotensive control and sham hearts. AMPE did not alter coronary flow or compliance in either ventricle. Soluble tumor necrosis factor-alpha decreased in the RV (P = 0.043) and LV (P = 0.005) tissue. These data support the hypothesis that AMPE produces intrinsic biventricular dysfunction and suggest that arterial hypotension is not the principal mechanism of this dysfunction.