Hemodynamic and respiratory factors that influence the opening of patent foramen ovale in mechanically ventilated patients.

BACKGROUND: Patent foramen ovale (PFO) is an anatomic variant that may lead to several pathological conditions, notably right to left shunt, paradoxical embolism, hypoxemia, and cerebral fat embolism. Mechanical positive pressure ventilation may increase the prevalence of PFO opening in Intensive Care Unit (ICU) patients; however, the respiratory and hemodynamic determinants of PFO opening have been poorly investigated. Contrast-enhanced transesophageal echocardiogram (ce-TEE) is considered the gold standard for PFO detection. We prospectively performed a multicenter study using ce-TEE in order to determine the respiratory and hemodynamic factors that may lead to PFO opening. METHODS: One hundred and eight consecutive ICU adult patients under mechanical ventilation from three tertiary care hospitals, were included in the study. A standard multiplane ce-TEE was performed, and the dimensions and function of the right and left ventricle were studied. In each patient, the right ventricle (RV) end-diastolic area, RV end-systolic area, left ventricle (LV) end-diastolic area, and LV ejection fraction were measured using the modified Simpson's rule and the four-chamber view. At least three bubble tests were performed to detect PFO opening. Ventilatory parameters such as tidal volume, plateau pressure, static lung compliance, and positive end-expiratory pressure were recorded during the bubble test. RESULTS: Data for 81 men and 27 women were analyzed. PFO was detected in 27 % of the study population. Statistical significance was found between the presence of PFO and plateau pressure (odds ratio 3.421, 95 % CI: 1.2-9.4, p =0.017). Additionally, the presence of right ventricular dilatation (RV>LV) was strongly associated with PFO opening (odds ratio 3.163, 95 % CI: 1.2-8.075, p =0.018). CONCLUSIONS: In this group of mechanically ventilated, critically ill adult patients, right ventricular dilatation and plateau pressure above 26 mmHg were significantly associated with foramen ovale opening. Hippokratia 2016, 20(3): 209-213.

Resting energy expenditure in brain death.

OBJECTIVE: To evaluate resting energy expenditure (REE) in brain dead patients and to investigate the hypothesis that the reduction in REE results from a decrease in cerebral blood flow. DESIGN: Prospective, open labeled, control study. SETTING: General intensive care unit of a tertiary referral teaching hospital. PATIENTS: 30 critically ill patients with isolated head injury divided in two groups: group 1 patients (n = 10) with a Glasgow Coma Scale (GCS) score of 4 to 8 and group 2 patients (n = 20), in whom the final outcome was brain death (GCS = 3). Group 2 patients were divided into two subgroups: Group 2 a (n = 11) were admitted as brain dead (GCS = 3) and group 2 b (n = 9) were admitted with a GCS > 3 and progressed to brain death. INTERVENTIONS: Clinical and instrumental, using transcranial Doppler sonography (TCD), diagnosis of brain death. Cerebral blood flow studies of the middle cerebral artery bilaterally by bidimensional TCD and measurement of REE using indirect calorimetry. MEASUREMENTS AND RESULTS: Measurements of REE and TCD studies were performed simultaneously on admission and after hemodynamic and neurologic stabilization. In cases with progressive neurologic deterioration, serial measurements were performed REE values were expressed as percentage of basal metabolic rate (%BMR), which were estimated according to each patient's gender, age, height, and weight. Group 1 patients, had normal TCD patterns throughout their hospitalization and their REE value was 21 +/- 11 % higher than BMR. Group 2 patients demonstrated TCD patterns compatible with brain death and their REE value was 24.5 +/- 11 % lower than BMR (p < 0.01). Group 2 a patients, who were admitted as brain dead and remained brain dead, had REE values 30 +/- 11 % lower than BMR (p < 0.01). Group 2 b patients, who were not brain dead on admission but progressed to brain death, in serial measurements revealed a significant relationship between REE and TCD findings (R = -0.77, p < 0.0001). In this subgroup of patients, with multiple regression analysis a significant relationship was found only between REE and the TCD pattern, but not with body temperature. CONCLUSIONS: In brain dead patients, REE decreases to values lower than BMR. This can be attributed to the cessation of cerebral blood flow and consequently cerebral metabolism and not to hypothermia.

Tidal volume reduction for prevention of ventilator-induced lung injury in acute respiratory distress syndrome. The Multicenter Trail Group on Tidal Volume reduction in ARDS.

Because animal studies have demonstrated that mechanical ventilation at high volume and pressure can be deleterious to the lungs, limitation of airway pressure, allowing hypercapnia if necessary, is already used for ventilation of acute respiratory distress syndrome (ARDS). Whether a systematic and more drastic reduction is necessary is debatable. A multicenter randomized study was undertaken to compare a strategy aimed at limiting the end-inspiratory plateau pressure to 25 cm H2O, using tidal volume (VT) below 10 ml/kg of body weight, versus a more conventional ventilatory approach (with regard to current practice) using VT at 10 ml/kg or above and close to normal PaCO2. Both arms used a similar level of positive end-expiratory pressure. A total of 116 patients with ARDS and no organ failure other than the lung were enrolled over 32 mo in 25 centers. The two groups were similar at inclusion. Patients in the two arms were ventilated with different VT (7.1 +/- 1.3 versus 10.3 +/- 1.7 ml/kg at Day 1, p < 0.001) and plateau pressures (25.7 +/- 5. 0 versus 31.7 +/- 6.6 cm H2O at Day 1, p < 0.001), resulting in different PaCO2 (59.5 +/- 15.0 versus 41.3 +/- 7.6 mm Hg, p < 0.001) and pH (7.28 +/- 0.09 versus 7.4 +/- 0.09, p < 0.001), but a similar level of oxygenation. The new approach did not reduce mortality at Day 60 (46.6% versus 37.9% in control subjects, p = 0.38), the duration of mechanical ventilation (23.1 +/- 20.2 versus 21.4 +/- 16. 3 d, p = 0.85), the incidence of pneumothorax (14% versus 12%, p = 0. 78), or the secondary occurrence of multiple organ failure (41% versus 41%, p = 1). We conclude that no benefit could be observed with reduced VT titrated to reach plateau pressures around 25 cm H2O compared with a more conventional approach in which normocapnia was achieved with plateau pressures already below 35 cm H2O.

Outcome in severely head injured patients with and without multiple trauma.

BACKGROUND: This work attempts to analyse the potential role of multiple injury in the outcome of non-shock severely head injured patients with a Glasgow Coma Scale (GCS) of 8 or less. METHODS: 386 non-shock adult patients of < 65 years (mean age 33.74 +/- 14.7), treated with the same therapeutic protocol, were studied retrospectively. Multiple traumatised patients classified into Injury Severity Scale (ISS) of < or = 9 and > 9. The ISS classification was also tested in two subgroups of patients with GCS 3-5 and GCS 6-8. RESULTS: The overall mortality of the 386 patients was 22.79%. Those suffering from extracranial injuries (n = 146, 37.82%) and those without (n = 240), presented similar mortality (21.23% vs 23.75% respectively). The multiple traumatised victims presented mean ISS 9.3 +/- 8.17. Those with ISS > 9 had greater mortality than those with ISS < or = 9, but the difference was not statistically significant (p > 0.05). The influence of ISS was not also significant in the mortality, either patients were of GCS 3-5 or GCS 6-8. CONCLUSIONS: Multiple trauma in non-shock patients, as it is expressed by ISS does not have any influence on mortality. Mortality is depending on the severity of the intracranial pathology. Perhaps head injury and extracranial injuries have synergistic effect on morbidity.

Influence of continuous haemofiltration-related hypothermia on haemodynamic variables and gas exchange in septic patients.

OBJECTIVE: To investigate the influence of continuous haemofiltration (CHF) on haemodynamics, gas exchange and core temperature in critically ill septic patients with acute renal failure. PATIENTS AND METHODS: In 20 patients (17 male, 3 female) ultrafiltration rate, core temperature, gas exchange and haemodynamic variables were measured at regular intervals during the first 48 h of haemofiltration. Baseline data were compared to those obtained 30 min after initiating CHF and also to those during hypothermia (if observed). MAIN RESULTS: Haemodynamic variables remained remarkably constant throughout the study period. In patients with a relatively low ultrafiltration rate (855 +/- 278 ml/h) temperature did not change, while in patients with a high ultrafiltration rate (1468 +/- 293 ml/h) core temperature significantly decreased from 37.6 +/- 0.9 degrees C to 34.8 +/- 0.8 degrees C (p < 0.001). There was a statistically significant correlation between temperature decrease and ultrafiltration rate (r = -0.68, Y = 1.8-0.003 X, p < 0.01). Hypothermic patients also showed a mean decrease in VO2 from 141 +/- 22 ml/min/m2 to 112 +/- 22 ml/min/m2 (p < 0.01) with a concomitant increase in PaO2 from 103 +/- 37 mmHg to 140 +/- 42 mmHg (p < 0.001) and in PvO2 from 35 +/- 4 mmHg to 41 +/- 5 mmHg (p < 0.001). CONCLUSIONS: 1) Continuous haemofiltration does not cause significant alternations in haemodynamic variables. 2) Hypothermia frequently occurs in patients undergoing continuous haemofiltration with high ultrafiltration rates. These hypothermic patients show a reduction in VO2 leading to an increase in PvO2 and PaO2. This mild hypothermia in these circumstances has no evident deleterious effects.

The influence of position on ventilation-perfusion distribution after abdominal surgery.

The effects of a change in position on gas exchange and ventilation perfusion (VA/Q) distribution were studied in 12 patients, after abdominal surgery. VA/Q distribution was determined from retention and excretion curves of six inert gases of different solubilities, in supine and sitting patients, during spontaneous breathing. Changing position from supine to sitting resulted in an increase in minute ventilation and a decrease in PaCO2 without any change in PaO2. With regard to VA/Q distribution, an estimated shunt of 5.2% +/- 3.4 was documented in all the patients in the supine position, and was associated with a large percentage of low VA/Q regions (20.0% +/- 13.0) in six of them. Patients with associated estimated shunt and low VA/Q regions were those with the greatest amount of venous admixture (respectively: 27.3% +/- 7.2, and 14.9% +/- 3.0, for patients without low VA/Q regions, P less than 0.01). When patients were placed in the sitting position, the estimated shunt was not reduced, but the percentage of low VA/Q regions decreased when it was documented. Despite the improvement of VA/Q distribution in the sitting position, the lack of significant change in PaO2 may be explained by the simultaneous decrease in PVO2 caused by a decrease in cardiac output.

Intrapulmonary shunt is not increased by 100% oxygen ventilation in acute respiratory failure.

Increase of shunt has been demonstrated during short periods of pure oxygen breathing, mostly in patients with mild acute respiratory failure (ARF). Twenty patients with a large range of venous admixture (12 to 63%) were studied when FIO2 was increased from maintenance to one. Intrapulmonary shunt was measured with both the conventional oxygen method [QS/QT (O2)] and the multiple inert gas elimination technique [QS/QT (IG)]. Mean venous admixture decreased from 29 to 24% when FIO2 was increased and QS/QT (IG) remained unaltered. The pattern of blood flow distribution remained similar in both conditions, even in the eleven patients with ARF secondary to bacterial pneumonia and who had a low V/Q mode, highly liable to collapse with 100% oxygen. As no increase in shunt was documented in these patients, reluctance to measure shunt during 100% oxygen breathing should be re-evaluated.

Mechanical ventilation with 100% oxygen does not increase intrapulmonary shunt in patients with severe bacterial pneumonia.

Pure oxygen ventilation has been shown to increase the right to left shunt QS/QT in both normal and diseased lungs. Nitrogen absorption atelectasis, an explanation of the phenomenon, is likely to occur in lung units with low ventilation/perfusion ratio. In 11 patients with severe unilateral or bilateral bacterial pneumonia, we assessed the effects of increasing FlO2 from maintenance level (m = 0.44 +/- 0.11) to 1.0. Venous admixture (QVA/QT) was calculated using the O2 method, and the distribution of the VA/Q ratios were assessed with the 6 inert gas (IG) technique providing the distribution between the true shunt (QS/QT IG) and the low VA/Q units. Although a large part of perfusion was distributed preferentially to low VA/Q units, ranging from 2 to 43% of cardiac output, thus placing large zones of lung parenchyma at risk of absorption atelectasis, QVA/QT decreased from 31 +/- 13% to 25 +/- 10% and IG shunt did not increase after 30 min of O2 ventilation. In addition, QS/QT IG remained unaltered despite PVO2 increased from 32 to 43 mmHg, suggesting a poor level of hypoxic vasoconstriction in human bacterial pneumonia.

Total respiratory pressure-volume curves in the adult respiratory distress syndrome.

To assess the value of measuring compliance in the adult respiratory distress syndrome, sequential pressure-volume curves were obtained in 19 patients with this syndrome. Analysis of the pressure-volume curves allowed separation of the patients into the following four groups: (1) group 1 (n = 6), normal compliance measured during deflation, little hysteresis, and no inflection in the ascending limb of the pressure-volume tracing; (2) group 2 (n = 8), normal compliance during deflation, increased hysteresis, and presence of an inflection; (3) group 3 (n = 10), decreased compliance during deflation, marked hysteresis, and presence of an inflection; and (4) group 4 (n = 10), reduced compliance during deflation, no increased hysteresis, and no inflection. These patterns were correlated with the stage of the adult respiratory distress syndrome and to the pattern of the chest x-ray film. Group 2 corresponds to the initial stage of the syndrome and to pure alveolar opacities on the chest x-ray film. Group 3 is seen later in the course of the syndrome and corresponds to mixed alveolar and interstitial opacities. Group 4 corresponds to patients with end-stage adult respiratory distress syndrome (two weeks) and a predominant interstitial pattern on the chest x-ray film. Group 1 corresponds to a nearly normal chest x-ray film and to recovery.

[Acute respiratory distress syndrome in the adult. Distribution of the ventilation-perfusion ratio]. / Syndrome de détresse respiratoire aiguë de l'adulte. Distribution des rapports ventilation/perfusion.

Hypoxemia in the acute respiratory distress syndrome may be due to a variety of causes: trùe pulmonary shunt, decreased ventilation/perfusion ratios, impaired diffusion and/or fall of mixed venous oxygen. In order to sort out these different tension mechanisms, 18 patients with acute respiratory distress syndrome were explored by the inert gas method. In 6 of them hypoxemia was due to a true shunt (35 +/- 10%). The remaining 12 patients also had a true shunt (26.5 +/- 9.5%), but 4.5% of the cardiac output was distributed to areas with a ventilation/perfusion ratio between 0.1 and 0.005. Thus, in these 18 patients with acute respiratory distress, hypoxemia could be explained essentially by a true shunt.

Redistribution of pulmonary blood flow induced by positive end-expiratory pressure and dopamine infusion in acute respiratory failure.

The mechanism by which mechanical ventilation (MV) with positive end-expiratory pressure (PEEP) improves hypoxemia in patients with acute respiratory failure (ARF) is unclear, and may be attributed in part to a decrease in cardiac output inducing by itself a reduction of the shunt. Using the multiple inert gas elimination technique we evaluated the effects of PEEP on ventilation-perfusion (VA/Q) distribution in 8 patients while cardiac output was maintained at control value by means of a dopamine infusion. In each patient, evaluation was performed during MV without PEEP (control) then with PEEP (17 +/- 2 cm H2O) and dopamine. After application of PEEP, PaO2, PvO2, and oxygen transport (TO2) increased significantly, whereas venous admixture decreased from 37.5 +/- 5 to 17 +/- 2% (p less than 0.01). Comparison of VA/Q distribution during PEEP and zero end-expiratory pressure documented a redistribution of pulmonary blood flow; the shunt decreased markedly from 30 +/- 4 to 13 +/- 2% (p less than 0.001), whereas the fraction of cardiac output distributed to "normal" VA/Q ratio units (0.1 to 10) increased from 62 to 78.5% (p less than 0.001). Dead space increased slightly with PEEP, from 44 to 49% (p less than 0.01) of total ventilation. The pattern of ventilation distribution was essentially unaltered; specifically, no additional high VA/Q mode was observed during PEEP. It is concluded that cardiac output maintenance with dopamine infusion during PEEP does not suppress the beneficial effects of PEEP on gas exchange, but induces a redistribution of pulmonary blood toward the main VA/Q ratio.

[Increase in functional residual capacity induced by positive end-expiratory pressure. Prediction using the thoracopulmonary pressure curve]. / Augmentation de la capacité résiduelle fonctionnelle induite par la ventilation en pression positive expiratoire. Prédiction par la courbe pression-volume thoracopulmonaire.

Prediction of FRC using a respiratory P-V curve (2 1 syringe method) has been tested in eight patients with normal lungs and in 12 ARDS patients. FRC was measured using nitrogen dilution technique with a closed circuit. Correlation between measured and predicted FRC was excellent, especially when the expiratory limb of the P-V curve was used (r = 0.92, in patients with pulmonary edema, and r = 0,97 when patients were evaluated after a few weeks). PEEP induced increase in FRC was larger between 10 and 20 cmH2O than between 0 and 10 cmH2O. As expected, Qs/Qt decrease was correlated with the FRC augmentation.