Increasing respiratory rate to improve CO2 clearance during mechanical ventilation is not a panacea in acute respiratory failure

BACKGROUND

Increasing respiratory rate has recently been proposed to improve CO2 clearance in patients with acute respiratory failure who are receiving mechanical ventilation. However, the efficacy of this strategy may be limited by deadspace ventilation, and it might induce adverse hemodynamic effects related to dynamic hyperinflation.

SETTING

An intensive care unit of a university hospital.

PATIENTS

We studied 14 patients with acute respiratory failure during the adjustment of ventilator settings on the first day of mechanical ventilation in volume-controlled mode.

MEASUREMENTS

After determining the positive end-expiratory pressure that suppresses any intrinsic positive end-expiratory pressure at a respiratory rate of 15 breaths/min, we compared blood gas analysis, respiratory measurements, and Doppler evaluation of right ventricular systolic function by using two different respiratory strategies with the same airway pressure limitation (plateau pressure, < or =25 cm H2O), a low-rate conventional respiratory strategy with a respiratory rate of 15 breaths/min, and a high-rate strategy with a respiratory rate of 30 breaths/min.

RESULTS

Compared with the low-rate strategy, the high-rate strategy neither significantly reduced PaCO2 (47 +/- 8 vs. 51 +/- 7 mm Hg with the low-rate strategy) nor significantly improved PaO2 (99 +/- 40 vs. 95 +/- 35 mm Hg with the low-rate strategy). It significantly increased alveolar deadspace to tidal volume ratio (21% +/- 8%, vs. 14% +/- 6% with the low-rate strategy) and produced dynamic hyperinflation, resulting in a substantial intrinsic positive end-expiratory pressure (6.4 +/- 2.7 cm H2O). Right ventricular outflow impedance was increased, resulting in a significant drop in the cardiac index (2.9 +/- 0.6 vs. 3.3 +/- 0.7 L/min/m with the low-rate strategy).

CONCLUSION

We conclude that a high respiratory rate strategy during mechanical ventilation in patients with acute respiratory failure did not improve CO2 clearance, produced dynamic hyperinflation, and impaired right ventricular ejection.

Pressure-volume curves in acute respiratory distress syndrome: clinical demonstration of the influence of expiratory flow limitation on the initial slope

The presence of an initial segment with a low compliance on the static pressure-volume (PV) curve in patients with acute respiratory distress syndrome (ARDS) indicates that some lung compartments do not initially receive insufflated gas. We tested the hypothesis that an uneven distribution of time constants, producing a "slow compartment," was in part responsible for the change in compliance between the initial and the intermediate segment of the PV curve. In 16 patients with ARDS submitted to mechanical ventilation in volume-controlled mode with a supportive respiratory rate of 15 breaths/minute, we constructed the static PV curve on the first day of respiratory support and determined the intrinsic positive end-expiratory pressure (PEEPi4) during a prolonged end-expiratory pause (4 seconds). We also measured the volume of a "slow compartment" during a prolonged expiration (> 6 seconds), and determined an external PEEP (PEEPe) suppressing PEEPi4. Among the 16 patients studied, 11 exhibited a low inflection point, associated with a "slow compartment" of 172 +/- 83 ml, responsible for a PEEPi4 of 3 +/- 2 cm H2O. Conversely, the five remaining patients had a linear PV curve, associated with a minimal "slow compartment" of 28 +/- 10 ml, responsible for a negligible PEEPi4. We observed that individual slopes of the initial segment of the PV curve were inversely and significantly correlated with the proportion of the "slow compartment" (r = -0.85). We concluded that the shape of the inspiratory PV curve in ARDS might be dependent on the presence of a "slow compartment," and demonstrated that a low external PEEP appeared sufficient to achieve a substantial mechanical improvement in clinical practice.

[Incidence of acute cor pulmonale and deep venous thrombosis in acute pulmonary embolism]

OBJECTIVE

Ultrasounds are a useful tool when looking for indirect evidence in favor of pulmonary embolism. The aim of this study was to determine the incidence of acute cor pulmonale and deep venous thrombosis revealed by ultrasonographic techniques in a population of patients presenting with pulmonary embolism.

METHODS

96 consecutive patients with a mean (+/- SD) age of 65 +/- 15 years, admitted to our hospital for pulmonary embolism were included in this study. The diagnosis of pulmonary embolism was made either by spiral computed tomography or selective pulmonary angiography. Each patient subsequently underwent both trans-thoracic echocardiography and venous ultrasonography. The diagnostic criterion used for defining acute cor pulmonale by echocardiography was the right to left ventricular end-diastolic area ratio over (or equal to) 0.6. Diagnosis of deep venous thrombosis was supported by the visualization of thrombi or vein incompressibility and/or the absence of venous flow or loss of flow variability by venous ultrasonography.

RESULTS

Using ultrasounds, an acute cor pulmonale was found in 63% of our patients while 79% were found to have deep venous thrombosis and 92% of the patients had either acute cor pulmonale or deep venous thrombosis or both. All of the patients with proximal pulmonary embolism had acute cor pulmonale and/or deep venous thrombosis. The presence of acute cor pulmonale on echocardiography was significantly higher in patients with proximal pulmonary embolism (p < 0.0001).

CONCLUSION

This study emphasizes the potential value of ultrasonographic techniques in the diagnosis of acute pulmonary embolism.

Influence of superior vena caval zone condition on cyclic changes in right ventricular outflow during respiratory support

BACKGROUND

Adequate fluid resuscitation in critically ill patients undergoing mechanical ventilation remains a difficult challenge, and diastolic and systolic right ventricular (RV) changes produced by positive airway pressure are important to consider in an individual patient with inadequate circulatory adaptation during respiratory support. We hypothesized that insufficient thoracic vena cava filling, predisposing to inspiratory collapse (zone 2 condition), may transiently affect RV outflow.

METHODS

We measured beat-to-beat superior vena caval diameter and Doppler RV outflow during a routine transesophageal echocardiographic examination in 22 patients undergoing mechanical ventilation, all of whom required hemodynamic monitoring, and we calculated a collapsibility index for the superior vena cava as maximal expiratory diameter minus minimal inspiratory diameter, divided by maximal expiratory diameter.

RESULTS

In 15 patients (group 1), the collapsibility index was low (17 +/- 7%) and was associated with a moderate inspiratory decrease in RV outflow (25 +/- 17%). However, in seven patients (group 2), we observed a high collapsibility index (71 +/- 7%), which was associated with a major inspiratory decrease in RV outflow (69 +/- 14%) combined with a reduced pulmonary artery flow period. A rapid volume expansion, only performed on group 2, markedly and significantly reduced both the collapsibility index (15 +/- 12%) and the inspiratory decrease in RV outflow (31 +/- 20%).

CONCLUSION

A major inspiratory decrease in RV outflow associated with a reduced pulmonary artery flow period in a patient undergoing mechanical ventilation reflected a high collapsibility index of the thoracic vena cava, suggesting a zone 2 condition, and may be corrected by blood volume expansion.

Gelatinase expression in pulmonary arteries during experimental pulmonary hypertension

Structural remodelling of pulmonary vessels is an important feature of pulmonary hypertension (PH), which reflects distal artery muscularization and matrix remodelling. The matrix metalloproteinases (MMPs) are involved in extracellular matrix turnover and hence, in smooth muscle cell migration and endothelial cell migration and proliferation. Among the MMPs, gelatinases (MMP-2 and MMP-9) can degrade basement membrane components and promote cell proliferation and migration. This study evaluated gelatinases in pulmonary vessels during progressive PH in two rat models: exposure to hypoxia or monocrotaline. Zymography of tissue homogenates revealed an association of progression of hypoxic PH with a time-dependent increase in gelatinase MMP-2 activity, specific to pulmonary vessels. Increased MMP-2 activity was also found 30 days postmonocrotaline. Reverse transcription polymerase chain reaction demonstrated upregulation of MMP-2 messenger ribonucleic acid. Immunolocalization showed MMP-2 throughout the pulmonary vasculature, from the trunk to the distal vessels, with strong staining of the intima, media and adventitia. MMP-2 was found in its active form and gelatinolytic activity was correlated to PH severity. Activity localization by in situ zymography corroborated with the immunolocalization findings. In conclusion, the authors demonstrated that matrix metalloproteinase-2 activity is increased in pulmonary vessels during progression of pulmonary hypertension, probably as a result of involvement in the matrix turnover associated with vascular remodelling during pulmonary hypertension.

Acute cor pulmonale in massive pulmonary embolism: incidence, echocardiographic pattern, clinical implications and recovery rate

OBJECTIVE

The indications for the use of thrombolytic agents in massive pulmonary embolism (MPE) remain controversial and it has been suggested that transthoracic echocardiographic (TTE) examination, which is able to detect an associated right ventricular dysfunction, may cast light on this question. The goal of this study was to examine the incidence of acute cor pulmonale (ACP) in MPE, diagnosed on the basis of TTE criteria, its clinical implications and its resolution rate.

DESIGN

Ten-year retrospective clinical study.

SETTING

A medical and a coronary intensive care unit, university hospital.

PATIENTS

One hundred sixty-one patients with proven MPE.

INTERVENTIONS

Acute cor pulmonale was defined as right ventricular end-diastolic area / left ventricular end-diastolic area (RVEDA/LVEDA) ratio in the long axis greater than 0.6 associated with septal dyskinesia in the short axis. ACP patients were divided into three groups according to circulatory status: 32 patients without circulatory failure constituted group 1, 32 patients with circulatory failure requiring inotropic support, but free of metabolic acidosis, constituted group 2 and 34 patients in whom circulatory failure was associated with metabolic acidosis (defined by a base deficit >5 mEq/l) constituted group 3.

RESULTS

Acute cor pulmonale was present in 61% of patients with MPE and carried a 23% mortality, but this mortality was very different in stable patients (groups 1 and 2, 64 patients, 3% mortality) and in unstable patients (group 3, 34 patients, 59% mortality). A multivariate logistic regression analysis showed that the TTE results were not predictive of the risk of death. Conversely, the same analysis showed that the presence of metabolic acidosis was a powerful predictor of death.

CONCLUSION

Because none of the TTE measurements in ACP could be used to stratify the severity of MPE, TTE was of no help in deciding on medical thrombolysis. However, depending on its severity, metabolic acidosis could justify a large cooperative study to assess the impact of thrombolytic therapy on mortality rate in this specific group.

Acute cor pulmonale in acute respiratory distress syndrome submitted to protective ventilation: incidence, clinical implications, and prognosis

CONTEXT

The incidence of acute cor pulmonale (ACP), a frequent and usually lethal complication of acute respiratory distress syndrome (ARDS) during traditional respiratory support, has never been re-evaluated since protective ventilation gained acceptance.

OBJECTIVE

We performed a longitudinal transesophageal echocardiographic (TEE) study to determine whether this incidence, and its severe implications for prognosis, might have changed in our unit as we altered respiratory strategy.

DESIGN

Prospective open clinical study.

SETTING

Medical intensive care unit of a university hospital.

PATIENTS

Seventy-five consecutive ARDS patients given respiratory support with airway pressure limitation (plateau pressure < or =30 cm H2O).

INTERVENTIONS

ACP was defined as a ratio of right ventricular end-diastolic area to left ventricular end-diastolic area in the long axis >0.6 associated with septal dyskinesia in the short axis during TEE examination.

RESULTS

Normal right ventricular function was present in 56 patients, whereas right ventricular dysfunction was observed in 19 patients after 2 days of respiratory support. ACP was associated with pulmonary artery hypertension, increased heart rate, and decreased stroke index. Significant impairment of left ventricular diastolic function was also seen. All echo-Doppler abnormalities were reversible in patients who recovered, and the mortality rate was the same in both groups (32%). However, ACP patients who recovered required a longer period of respiratory support. A multivariate analysis individualized Paco2 level as the sole factor independently associated with ACP, suggesting that ACP development in ARDS is influenced by the severity of lung damage and/or the respiratory strategy.

CONCLUSION

Evaluation of right ventricular function by TEE in a group of 75 ARDS patients submitted to protective ventilation revealed the persistence of a 25% incidence of ACP, resulting in detrimental hemodynamic consequences associated with tachycardia. However, ACP was reversible in patients who recovered and did not increase mortality.

New CT index to quantify arterial obstruction in pulmonary embolism: comparison with angiographic index and echocardiography

OBJECTIVE

This study was designed to define and evaluate a specific index to quantify arterial obstruction with helical CT in acute pulmonary embolism.

MATERIALS AND METHODS

Fifty-four patients (mean age, 56 years) with proven pulmonary emboli among 158 consecutive patients, who had undergone both CT and pulmonary angiography for clinically suspected pulmonary embolism, were eligible for the study. The CT obstruction index was defined as (n. d) (n, value of the proximal clot site, equal to the number of segmental branches arising distally; d, degree of obstruction scored as partial obstruction [value of 1] or total obstruction [value of 2]). We compared the CT obstruction index with pulmonary arterial obstruction on angiography (assessed by the Miller index), using linear regression, and correlated it with findings on echocardiography. Interobserver variability was determined for both CT and pulmonary angiography indexes.

RESULTS

The CT obstruction index (29% +/- 17%) and the Miller index (43% +/- 25%) were well correlated (r = 0.867, p < 0.0001) with an excellent concordance between investigators for both the CT index (r = 0.944, p < 0.0001) and the Miller index (r = 0.904, p < 0.0001). A CT obstruction index greater than 40% identified more than 90% of patients with right ventricular dilatation.

CONCLUSION

The degree of arterial obstruction in pulmonary embolism may be quantified by a specific CT index that appears reproducible and highly correlated to the previously described index with pulmonary angiography. Further evaluations are needed to investigate the usefulness of the CT obstruction index for stratification of patient risk and determining therapeutic options.

Positive end-expiratory pressure titration in acute respiratory distress syndrome patients: impact on right ventricular outflow impedance evaluated by pulmonary artery Doppler flow velocity measurements

OBJECTIVE

Positive end-expiratory pressure (PEEP) titration in acute respiratory distress syndrome patients remains debatable. We used two mechanical approaches, calculation of the compliance of the respiratory system and determination of the lower inflexion point of the pressure-volume curve of the respiratory system, to identify specific PEEPs (PEEPS and PEEPA) whose impact on right ventricular (RV) outflow was compared with Doppler analysis of pulmonary artery flow velocity.

DESIGN

Prospective, open, clinical study.

SETTING

Medical intensive care unit of a university hospital.

PATIENTS

Sixteen consecutive ventilator-dependent acute respiratory distress syndrome patients.

INTERVENTIONS

Two PEEPs were determined: PEEPS was the highest PEEP associated with the highest value of respiratory compliance, and PEEPA was the coordinate of the lower inflexion point of the inspiratory pressure-volume curve on the pressure axis plus 2 cm H2O.

MEASUREMENTS AND MAIN RESULTS

We observed a large difference between the two PEEPs, with PEEPA (13 + 4 cm H2O) > PEEPS (6 + 3 cm H2O). Changes in RV outflow impedance produced by tidal ventilation with zero end-expiratory pressure (ZEEP) and after application of these two PEEPs were assessed by Doppler study of pulmonary artery flow velocity obtained by a transesophageal approach, with particular reference to the end-expiratory and end-inspiratory pulmonary artery velocity-time integral, as reflecting RV stroke output, and mean acceleration as reflecting RV outflow impedance during an unchanged flow period. A significant inspiratory reduction in pulmonary artery velocity-time integral (from 11.8 + 0.3 to 10.0 + 0.3 cm) and mean acceleration (from 11.9 + 0.9 to 8.0 + 0.9 m/sec2) was observed with ZEEP, showing a reduction in RV stroke index (from 29.0 + 0.9 to 26.0 + 0.6 cm3/m2) by a sudden increase in outflow impedance during tidal ventilation. Application of PEEPA, which improved Pao2 (102 + 40 vs. 65 + 18 torr with ZEEP), worsened the inspiratory drop in RV stroke index (21.6 + 0.8 cm3/m2), resulting in a significant reduction in cardiac index compared with ZEEP (from 3.0 + 1.0 to 2.7 + 1.1). Application of PEEPS, which also significantly improved Pao2 (81 + 21 torr), was associated with a lesser impact on RV outflow impedance (inspiratory mean acceleration: 9.5 + 1 m/sec2) and cardiac index (3.2 + 1.0) than PEEPA.

CONCLUSION

RV outflow impedance evaluated by the Doppler technique appeared sensitive to PEEP titration. Application of PEEPA worsened RV systolic function impairment produced by tidal ventilation. Conversely, application of PEEPS reduced RV systolic function impairment, suggesting an association with a lower pulmonary vascular resistance.

Echocardiographic evaluation of left ventricular function in critically ill patients: dynamic loading challenge using medical antishock trousers

STUDY OBJECTIVE

We hypothesized that a dynamic left ventricular (LV) evaluation during a loading challenge might enhance diagnostic capabilities of routine transesophageal echocardiography in critically ill patients and selection of therapeutic options against circulatory failure, particularly the choice between volume expansion and vasoactive agent infusion.

DESIGN

Prospective clinical study in a group of 26 patients requiring hemodynamic support by vasoactive infusion because of low systemic arterial pressure (< 90 mm Hg by invasive monitoring) during mechanical ventilation.

SETTING

University hospital ICU.

PATIENTS

Patients required respiratory support for an episode of acute respiratory failure of various causes or for an episode of coma. They were studied by transesophageal echocardiography during mechanical ventilation in the controlled mode, before and during a loading challenge made using the legs compartment of medical antishock trousers inflated at 80 mm Hg.

MEASUREMENTS

A short-axis view of the left ventricle was obtained by a transgastric approach, and end-diastolic and end-systolic areas were measured. LV stroke area (LVSA) and LV fractional area contraction (LVFAC) were calculated.

RESULTS

Changes in LV echocardiographic measurements permitted separation of the patients into two groups. In nine patients (group 1), LVSA, used as an index of stroke output, was significantly increased during the challenge, together with a significant increase in LV end-diastolic area, suggesting preload improvement by the challenge. Conversely, in 17 patients (group 2), LVSA was significantly reduced by the challenge, together with a significant decrease in LVFAC, suggesting a negative effect of increased afterload by the challenge.

CONCLUSION

Study of the changes in LV dimensions during loading challenge in hemodynamically unstable patients was used to evaluate the balance between the adequacy of preload and the ability of the heart to pump against an increased load, and might thus guide hemodynamic support.

Left ventricular volume analysis for the detection of coronary artery disease during dobutamine stress echocardiography in patients undergoing vascular surgery

AIMS

The purpose of the study was to prospectively evaluate the effectiveness of left ventricular volume changes analysis as compared to wall motion assessment for detecting coronary artery disease during dobutamine stress echocardiography in patients undergoing elective vascular surgery.

METHODS AND RESULTS

Left ventricular volumes, measured by using the ellipsoid biplane method combining the apical four- and two-chamber echocardiographic views, and classical wall motion score were determined at rest and peak stress (dobutamine infusion 5-40 microg/kg/min+/- atropine 0.25-1mg) in 68 consecutive patients. A positive test was defined as a decrease of less than 15% in left ventricular end-diastolic or end-systolic volume at peak stress for volume analysis and as an increase in score between rest and peak stress in one or more segments for wall motion assessment. Stress test was not analysable in five patients. Coronary angiography revealed significant coronary artery disease (coronary stenosis >or=70%) in 28/63 (44%) patients: one-vessel in 15, two- or three-vessel disease in 13. Overall sensitivity and specificity for coronary artery disease detection were 56% and 97% with left ventricular volume analysis, as compared to 64% and 89% with wall motion assessment. For patients with two- or three-vessel disease, sensitivity and specificity of volume analysis reached 92%.

CONCLUSION

The present data suggest that left ventricular volume change analysis during dobutamine stress echocardiography could be a reliable method for the detection of extensive coronary artery disease for patients undergoing vascular surgery.

Pulmonary embolism detection: prospective evaluation of dual-section helical CT versus selective pulmonary arteriography in 157 patients

PURPOSE

To evaluate the accuracy of dual-section helical computed tomography (CT) in acute pulmonary embolism (PE) diagnosis.

MATERIALS AND METHODS

Of 204 consecutive patients with clinically suspected acute PE (mean age, 58 years +/- 14 [SD]), 158 were enrolled. All patients underwent dual-section helical CT (2.7-mm effective section thickness) and selective pulmonary arteriography within 12 hours of each other. Each image was analyzed independently by two observers, who determined image quality and presence of PE among arterial segments, including at the subsegmental level. The final diagnosis was made with consensus.

RESULTS

Selective pulmonary arteriography was considered optimal in 147 (93%), suboptimal in 10 (6%), and inconclusive in one (0.6%) of 158 patients. Dual-section helical CT findings were considered technically optimal in 140 (89%), suboptimal in 11 (7%), and inconclusive in six (4%). Selective pulmonary arteriography demonstrated PE in 62 patients. Four (6%) of 62 patients had isolated subsegmental PE. The sensitivity of dual-section helical CT was 90%, and the specificity was 94%. The positive and negative predictive values were 90% and 94%, respectively.

CONCLUSION

Dual-section helical CT is an improvement in helical CT that offers a high sensitivity and specificity for the depiction of PE, including at the subsegmental level. Dual-section helical CT can replace pulmonary arteriography for the direct demonstration of PE in a majority of patients.

Inhibition of matrix metalloproteinases by lung TIMP-1 gene transfer or doxycycline aggravates pulmonary hypertension in rats

Chronic hypoxic pulmonary hypertension (PH) results from persistent vasoconstriction, excess muscularization, and extracellular matrix remodeling of pulmonary arteries. The matrix metalloproteinases (MMPs) are a family of proteinases implicated in extracellular matrix turnover and hence in smooth muscle and endothelial cell migration and proliferation. Because MMP expression and activity are increased in PH, we designed the present study to investigate whether inhibition of lung MMPs in rats subjected to chronic hypoxia (CH) contributes to or protects against vascular remodeling and PH. To achieve lung MMP inhibition, rats exposed to 10% O(2) for 15 days were treated with either doxycycline (20 mg/kg per day by gavage starting 2 days before and continuing throughout the CH period) or a single dose of recombinant adenovirus (Ad) for the human tissue inhibitors of metalloproteinases-1 (hTIMP-1) gene (Ad.hTIMP-1, 10(8) plaque-forming units given intratracheally 2 days before CH initiation). Control groups either received no treatment or were treated with an adenovirus containing no gene in the expression cassette (Ad.Null). Efficacy of hTIMP-1 gene transfer was assessed both by ELISA on bronchoalveolar lavages and by hTIMP-1 immunofluorescence on lung sections. MMP inhibition in lungs was evaluated by in situ zymography and gelatinolytic activity assessment using [(3)H]gelatin. Rats treated with either doxycycline or Ad.hTIMP-1 had higher pulmonary artery pressure and right heart ventricular hypertrophy more severe than their respective controls. Worsening of PH was associated with increased muscularization and periadventitial collagen accumulation in distal arteries. In conclusion, our study provides compelling evidence that MMPs play a pivotal role in protecting against pulmonary artery remodeling.

Predictors of mortality in acute respiratory distress syndrome. Focus On the role of right heart catheterization

Right heart catheterization (RHC) has been suspected of increasing mortality. The acute respiratory distress syndrome (ARDS) is a frequent reason for RHC. We designed a retrospective cohort study of 119 consecutive ARDS patients admitted to two medical intensive care units of tertiary care hospitals in which two different approaches are used for hemodynamic monitoring: RHC on demand (Henri Mondor Hospital [HM]) and no use of RHC (Ambroise Paré Hospital [AP]). The study tried to identify risk factors for death, and to assess the influence of RHC, with adjustment for the intensity of hemodynamic support as a confounding factor, using 98 patients in whom the delay between onset of ARDS, use of vasopressors, and RHC did not exceed 48 h. Several variables, including septic shock, cause of ARDS, Simplified Acute Physiology Score (SAPS) II, use of epinephrine/norepinephrine, and presence of RHC were entered into a logistic regression model to evaluate their independent prognostic roles. Mortality was different at HM and AP (36 of 55 patients [65.5%] versus 16 of 43 patients [37.2%], p < 0.005), and 29 of the 35 RHC-monitored patients died (82.8%), as compared with 23 of 63 patients (36.5%) treated without RHC (p < 0.0001). However, administration of epinephrine/norepinephrine and a nonpulmonary cause of ARDS were each independently associated with death. It is only when administration of vasopressors was omitted from the model that RHC, septic shock, and SAPS II became independent predictors of mortality. These results suggest that: (1) the use of vasopressors, but not of RHC, represents an important prognostic factor; and (2) not taking into account the use of these drugs may be misleading when assessing the influence of RHC on outcome.

Persistent preload defect in severe sepsis despite fluid loading: A longitudinal echocardiographic study in patients with septic shock

STUDY OBJECTIVE

To investigate the rate of recovery from septic shock in patients with suspected left ventricular (LV) preload deficiency and LV systolic dysfunction.

DESIGN

A monitoring period was defined by the need for inotropic/vasopressor support, and LV function was assessed daily during this period by bedside two-dimensional echocardiography (2D-ECHO).

SETTING

University hospital ICU.

PATIENTS

During a 5-year period, 90 patients with an episode of septic shock (60% with gram-positive bacteria as the causative agent) were consecutively enrolled in the study (mean age, 55 +/- 18 years). Standard volume resuscitation combined with inotropic/vasopressor support was used to maintain systolic arterial pressure > 90 mm Hg. All patients received mechanical ventilation because of associated respiratory failure. The average duration of hemodynamic support was 4.4 +/- 1.6 days. Thirty-four patients were weaned from hemodynamic support during the monitoring period and ultimately recovered (group I). Twenty-eight patients died from refractory circulatory failure during the monitoring period, and 28 died later from ARDS or multiple organ dysfunction syndrome, leading to a 62% overall mortality rate (group II).

METHODS

Daily bedside LV volumes and ejection fraction (LVEF) were recorded using 2D-ECHO. Data obtained at the start (day 1 and day 2) and end of the monitoring period (day n) were compared.

RESULTS

LV end-diastolic volume was within the normal range of our laboratory values in all patients, but was initially smaller in group II than in group I, and remained so despite fluid loading. LVEF was significantly depressed in all patients, resulting in severe reduction in LV stroke volume (LVSV), which was initially more marked in group I. In group I patients, LVEF significantly improved during the monitoring period, resulting in an increase in LVSV.

CONCLUSION

2D-ECHO changes during hemodynamic support in 90 septic patients confirmed defective LV preload with a propensity to worsen despite fluid loading in nonsurvivors (62% in the present study). Our results are also in agreement with previous studies reporting depressed LV systolic function at the initial phase of septic shock. Since LV dysfunction was more marked in patients who recovered, we suggest that the exact significance of this finding should be reevaluated.

Cyclic changes in right ventricular output impedance during mechanical ventilation

In a context such as acute respiratory distress syndrome, where optimum tidal volume and airway pressure levels are debated, the present study was designed to differentiate the right ventricular (RV) consequences of increasing lung volume from those secondary to increasing airway pressure during tidal ventilation. The study was conducted by combined two-dimensional echocardiographic and Doppler studies in 10 patients requiring mechanical ventilation in the controlled mode because of acute respiratory failure. Continuous monitoring of airway pressure on echocardiographic and Doppler recordings provided accurate timing of each cardiac event during the respiratory cycle, with particular attention being paid to end-expiratory and end-inspiratory atrial diameters, RV dimensions, and pulmonary artery and tricuspid flow estimated by the velocity-time integral (PA(VTI) and T(VTI), respectively). At baseline, lung inflation during the inspiratory phase of mechanical ventilation produced a drop in PA(VTI) from 14.3 +/- 2.6 cm at end expiration to 11.3 +/- 2.1 cm at end inspiration. This drop occurred without reduction in right atrial diameter or in RV diastolic dimensions. It was not preceded but was followed by a decrease in T(VTI), thus confirming an increase in RV outflow impedance. Manipulation of tidal volume without changing airway pressure and manipulation of airway pressure without changing tidal volume demonstrated that tidal volume, but not airway pressure, was the main determinant factor of RV afterloading during mechanical ventilation.

Improved prognosis of acute respiratory distress syndrome 15 years on

OBJECTIVE

Evaluation of the impact of low-volume, pressure-limited ventilation on the recovery rate of acute respiratory distress syndrome (ARDS).

DESIGN

Prospective observational clinical study with historical control.

SETTING

University hospital intensive care unit (ICU).

PATIENTS

We studied two groups of, respectively, 33 and 37 ARDS patients separated by 15 years ("historical", June 1978-April 1981, and "recent", October 1993-June 1996).

METHOD

ARDS was defined as the presence of bilateral chest infiltrates and a PaO(2)/FIO(2) ratio of less than 200 mmHg under controlled ventilation regardless of PEEP level. Any cardiac participation was excluded by right heart catheterization in the "historical" group and by echo-Doppler examination in the "recent" group. The origin of ARDS was principally pulmonary (ARDS(p)) in both groups (26/33 and 29/37, respectively), and secondarily extrapulmonary (ARDS(exp)) (7/33 and 8/37, respectively). In the "historical" group, normocapnia was the major goal for respiratory support and was achieved in all patients regardless of airway pressure levels. In contrast, end-inspiratory plateau pressure in the "recent" group was limited to 30 cmH(2)O under respiratory support, regardless of PaCO(2) level. The "historical" and "recent" ARDS groups were compared with regard to therapeutic procedure and outcome.

RESULTS

Normalization of PaCO(2) (36 +/- 6 mmHg) in the "historical" group required high airway pressure (end-inspiratory plateau pressure at 39 +/- 4 cmH(2)O) and high tidal volume (13 ml/kg). Respiratory support used in the "recent" group was less aggressive, with lower airway pressure (end-inspiratory plateau pressure 25 +/- 4 cmH(2)O) and tidal volume (9 ml/kg) resulting in "permissive" hypercapnia (51 +/- 10 mmHg). Mortality rates significantly decreased from 64 % in the "historical" group to 32 % in the "recent" group (p < 0.01). This decrease concerned only ARDS(p), which was markedly predominant in both groups.

CONCLUSION

Mortality due to ARDS of pulmonary origin has declined in our unit over the last 15 years. Low-volume, pressure-limited (protective) ventilation seems the most likely reason for improved survival, despite hypercapnia.

Acute, fatal, oral chromic acid poisoning

CASE REPORT

We report a 35-year-old woman who developed severe acidosis, massive gastrointestinal hemorrhage, acute renal failure, and hepatic injury following ingestion of chromic acid (50 mL) and died 12 hours after ingestion. Postmortem liver biopsy revealed a fatty degeneration with chromium concentration 3.6 mumol/g. The kidney, with chromium concentration 2.6 mumol/g, had extensive necrosis and ischemic lesions. Erythrocyte chromium was 1903 mumol/L at 3 hours declining to 865 mumol/L at 11 hours.

[The value of transesophageal echocardiography for the diagnosis of pulmonary embolism with acute pulmonary heart disease]

Transoesophageal echocardiography is a method of visualising intracardiac thrombi and could therefore be useful for the diagnosis of pulmonary embolism, but its diagnostic value is unknown. The authors carried out a prospective study with this diagnostic tool in massive pulmonary embolism. The study protocol was to perform transthoracic echocardiography in patients with suspected acute pulmonary embolism and then to perform transoesophageal echocardiography when there were signs of acute cor pulmonale. The results of both echocardiographic investigations were compared with two reference radiological techniques: the spiral CT scan and/or pulmonary angiography. Fifty-six patients underwent transthoracic echocardiography. In the 34 patients with transthoracic echocardiographic signs of acute cor pulmonale, the positive predictive value of the investigation for pulmonary embolism was 91% and the negative predictive value was 54%. Twenty of these 34 patients underwent transoesophageal echocardiography. The sensitivity and specificity for the diagnosis of proximal embolism were 85% and 86% respectively. The limitations of the method were poor visualisation of the left pulmonary artery in which only one thrombus was detected, compared with 6 by spiral CT scan, and the absence of visualisation of lobar arteries. Consequently, the real sensitivity of transoesophageal echocardiography for visualisation of all thrombi in the pulmonary arteries in acute cor pulmonale was only 55%. In acute cor pulmonale, the diagnostic value of transoesophageal echocardiography is poor because the sensitivity for visualisation of intra-pulmonary arterial thrombi is low compared with other radiological techniques. However, in patients with proximal emboli in the right or main pulmonary artery, the diagnosis may be established in a few minutes without the need of other more invasive techniques. Nevertheless, normal transoesophageal echocardiography does not rule out the presence of proximal in the left pulmonary artery or distal emboli in the lobar arteries.

Transesophageal echocardiography for the diagnosis of pulmonary embolism with acute cor pulmonale: a comparison with radiological procedures

OBJECTIVE

The goal of the study was to assess prospectively the value of transesophageal echocardiography (TEE) for the diagnosis of massive pulmonary embolism complicated by acute cor pulmonale.

DESIGN

A prospective study conducted on 44 consecutive patients.

SETTING

A general intensive care unit (ICU) of a university hospital.

PATIENTS AND METHODS

Between May 95 and October 96, 44 consecutive patients with clinically suspected acute pulmonary embolism underwent transthoracic echocardiography (TTE), completed by TEE when acute cor pulmonale was present (30 patients). The results of the echocardiographic studies were compared with radiological investigations by helical CT or contrast angiography.

RESULTS

The high sensitivity and specificity of the presence of acute cor pulmonale on TTE for the diagnosis of pulmonary embolism was confirmed. Nineteen patients only underwent TEE. The sensitivity and the specificity of TEE in detecting a proximal pulmonary embolism were 84% and 84%, respectively. Its main limitation concerned the left pulmonary artery, in which only one thrombus was visualized by TEE whereas six were present on helical CT, and lobar pulmonary arteries which could not be visualized with TEE. Thus, the overall sensitivity of TEE for the detection of pulmonary embolism with acute cor pulmonale was only 58%.

CONCLUSION

In comparison with radiological procedures, TEE had limited accuracy for detecting pulmonary embolism with acute cor pulmonale. When the pulmonary embolism was located in the main or right pulmonary artery, TEE could clarify the diagnosis within a few minutes without further invasive diagnostic procedures. However, a negative TEE did not exclude left proximal or lobar pulmonary embolism.