ECMO: an alternative support for acute respiratory failure caused by tuberculosis?

Late diagnosis of tuberculosis (TB) may result in the development of severe acute respiratory failure. High mortality rates with conventional ventilation have been reported. Extracorporeal membrane oxygenation (ECMO) may represent an effective alternative treatment. We report a case of complicated pulmonary TB in a man who successfully underwent 3 months of ECMO.

Caesarean delivery of a patient with truncus arteriosus.

Truncus arteriosus Type IV is a rare congenital cardiac malformation characterized by agenesis of the pulmonary arteries. Pulmonary perfusion is ensured by bronchial arteries. One common arterial trunk arises from both ventricles and systemic pulmonary and coronary arteries originate from this common vessel. Survival is rare without surgical correction. We report a case of uncorrected truncus arteriosus Type IV in a 28-year-old primigravid woman who underwent caesarean section.

Extracorporeal circulation in sheep with normal bleeding time using a surface heparinized circuit.

Bleeding due to systemic heparinization represents the major side effect of extracorporeal respiratory support. In the present animal study, a surface heparinized system (Carmeda Biological Active Surface) was applied to assess the feasibility of prolonged perfusion at low circulating heparin levels. Eight sheep divided into two groups: group A (5 animals) and group B (3 animals) underwent venovenous bypass using a heparin coated surface circuit. The following protocol was used: a) 24 hours at high heparin dose (30 to 100 U/kg/hr with an ACT [activated coagulation time] three to four times normal); b) 24 hours at low heparin dose (3 to 8 U/kg/hr with an ACT within the normal range); c) 24 hours at high heparin dose. Group B animals also received fresh frozen sheep plasma (14 ml/kg/day). During Period b, the clotting times were within baseline range. The bleeding time showed a dramatic decrease after change from a to b (27.9 +/- 3 minutes vs. 10.2 +/- 5.6 minutes). There was a negative relationship between antithrombin III (AT III) and thrombin coagulase time (TC); the latter is considered to be an aspecific indicator of circulating fibrin(ogen) degradation products. Maintaining AT III over 70%, TC changes were only minor. The use of the bioactive heparin surface allowed the performance of a 24 hour bypass, with normal coagulation times, at low circulating heparin levels.

Relationships between lung computed tomographic density, gas exchange, and PEEP in acute respiratory failure.

Twenty-two patients with acute respiratory failure underwent lung computed tomography (CT) and physiological measurements at 5, 10, and 15 cm H2O positive end-expiratory pressure (PEEP) to investigate the relationship between morphology and function. Lung densities were primarily concentrated in the dependent regions. From the frequency distribution of CT numbers (difference in x-ray attenuation between water and lung) and lung gas volume measurements the authors obtained a quantitative estimate of normally inflated, poorly inflated, and non-inflated lung tissue weight. This estimated average lung weight was increased twofold above normal and excess lung weight correlated with the mean pulmonary artery pressure (P less than 0.01). Venous admixture correlated with the non-inflated tissue mass (P less than 0.01). Increasing PEEP caused progressive clearing of radiographic densities and increased the mass of normally inflated tissue (anatomic recruitment), while reducing venous admixture. The cardiac index decreased after increasing PEEP while oxygen delivery was unchanged. The authors conclude that CT scan lung density and oxygen exchange efficiency are correlated; the main effect of augmenting PEEP is to recruit perfused alveolar units that were previously collapsed.

The prone position in ARDS patients. A clinical study.

The gas exchange and hemodynamics were evaluated before, during, and after a two-hour period of prone position in 13 moderate-severe ARDS patients. Lung computerized tomography was obtained in both the supine and prone positions in two of these patients. Average arterial oxygenation improved after prone positioning (p less than 0.01). A PaO2 improvement of at least 10 mm Hg after 30 minutes of prone position was used as a criterion to discriminate between responders and nonresponders to the postural change. Eight patients met the "responders" group criterion, and in the five nonresponder patients, the PaO2 did not change significantly throughout the study. Computerized tomograms in the prone position showed disappearance of posterobasal densities and appearance of new densities in the anterior regions, in both patients studied. One of these was a responder, the other a nonresponder. A brief test period in prone position is indicated in ARDS patients to identify those who may benefit from this postural treatment. The definite mechanism of the arterial oxygenation improvement observed remains to be clarified.

Cardiopulmonary response to extracorporeal venous CO2 removal in awake spontaneously breathing dogs.

The ventilatory response to a reduction in mixed venous PCO2 has been reported to be a decrease in breathing even to the point of apnea with no change in arterial CO2 partial pressure (PaCO2), whereas a recent report in exercising dogs found a small but significant drop in PaCO2 (F. M. Bennett et al. J. Appl. Physiol. 56: 1335-1337, 1984). The purpose of the present study was to attempt to reconcile this discrepancy by carefully investigating the cardiopulmonary response to venous CO2 removal over the entire range from eupnea to the apneic threshold in awake, spontaneously breathing normoxic dogs. Six dogs with chronic tracheostomies were prepared with bilateral femoral arteriovenous shunts under general anesthesia. Following recovery, an extracorporeal venovenous bypass circuit, consisting of a roller pump and a silicone-membrane gas exchanger, was attached to the femoral venous cannulas. Cardiopulmonary responses were measured during removal of CO2 from the venous blood and during inhalation of low levels of CO2. Arterial PO2 was kept constant by adjusting inspired O2. The response to venous CO2 unloading was a reduction in PaCO2 and minute ventilation (VE). The slope of the response, delta VE/delta PaCO2, was the same as that observed during CO2 inhalation. This response continued linearly to the point of apnea without significant changes in cardiovascular function.(ABSTRACT TRUNCATED AT 250 WORDS)

Low-frequency positive-pressure ventilation with extracorporeal CO2 removal in severe acute respiratory failure.

Forty-three patients were entered in an uncontrolled study designed to evaluate extracorporeal membrane lung support in severe acute respiratory failure of parenchymal origin. Most of the metabolic carbon dioxide production was cleared through a low-flow venovenous bypass. To avoid lung injury from conventional mechanical ventilation, the lungs were kept "at rest" (three to five breaths per minute) at a low peak airway pressure of 35 to 45 cm H2O (3.4 to 4.4 kPa). The entry criteria were based on gas exchange under standard ventilatory conditions (expected mortality rate, greater than 90%). Lung function improved in thirty-one patients (72.8%), and 21 patients (48.8%) eventually survived. The mean time on bypass for the survivors was 5.4 +/- 3.5 days. Improvement in lung function, when present, always occurred within 48 hours. Blood loss averaged 1800 +/- 850 mL/d. No major technical accidents occurred in more than 8000 hours of perfusion. Extracorporeal carbon dioxide removal with low-frequency ventilation proved a safe technique, and we suggest it as a valuable tool and an alternative to treating severe acute respiratory failure by conventional means.

Adult respiratory distress syndrome profiles by computed tomography.

Ten patients with full-blown ARDS, on mechanical ventilation with PEEP underwent lung CT. Seven normal subjects were also studied. Three tomographic levels (apex, hilum, and base) were selected. The most consistent morphologic finding in ARDS was the presence of densities in the dependent regions of the lung. Assuming that the three levels were a representative sample of the whole lung, the lung weight was computed from the mean CT number and lung gas volume. Analysis of the CT number frequency distribution revealed three definite patterns of distribution: type 1, bimodal, with one mode in the normal CT number range; type 2, unimodal narrow distribution, with the mode in the CT range of water; and type 3, unimodal broad distribution in the abnormal CT number range.

Morphological response to positive end expiratory pressure in acute respiratory failure. Computerized tomography study.

Ten patients with acute respiratory failure (ARF), (4 pneumonia, 4 sepsis, 2 polytrauma), underwent computerized tomography (CT) of the lungs, (apex, hilum, base), at 5, 10, 15 cm H2O positive end expiratory pressure (PEEP). The ARF lungs, on CT scan, appeared as a patchwork of normal and dense areas with generally well defined boundaries. Most of the densities were found in the dependent regions. The areas of density were correlated with PaO2 (r = 0.51). The PEEP increase resulted in a significant expansion of total cross-sectional lung surface area. The dense areas decreased significantly at the hilum and base when increasing PEEP while the changes at the apex were not significant. The changes of density with PEEP were highly correlated with the changes in oxygenation (r = 0.91). In the individual patient, however, the modifications of gas exchange can not be entirely predicted from morphological changes, possibly due to a diversion of pulmonary blood flow.

Constant mean airway pressure with different patterns of positive pressure breathing during the adult respiratory distress syndrome.

Twenty-one ARDS patients were divided into two groups of severity according to FIO2 and PEEP required to maintain an adequate gas exchange. The 10 most severe patients (group A) underwent continuous positive pressure ventilation (CPPV) (I/E 3:1) with the mean airway pressure maintained at 21 +/- 6.2 cmH2O. The PEEP values were 12.6 +/- 4.3 cmH2O during CPPV and 6.5 +/- 3.7 cmH2O during IRV (p less than 0.01). Eleven less severe ARDS patients (group B) underwent CPPV and positive pressure spontaneous breathing (CPAP) at constant mean airway pressure of 14.3 +/- 3.8 cmH2O. The PEEP was 7 +/- 2.5 cmH2O during CPPV and 14.9 +/- 4.3 cmH2O during CPAP (p less than 0.001). In five patients of each group, the SF6 shunt was measured as representative of true shunt. The results showed that gas exchange, including true shunt, and haemodynamics did not change between CPPV and IRV and between CPPV and CPAP tests. Taken with previous work on mean airway pressure, our results further support the concept that the main determinant of oxygenation and haemodynamics is the mean airway pressure, irrespective of the PEEP level and of the mode of ventilation.

Mean airway pressure vs. positive end-expiratory pressure during mechanical ventilation.

To investigate the effects of both positive end-expiratory pressure (PEEP) and mean airway pressure (Paw) on gas exchange, we used lung lavage to induce severe respiratory insufficiency in six lambs. The animals were then mechanically ventilated at constant tidal volume, respiratory rate, and inspired O2 fraction. PEEP levels were varied -5, +5 and +10 cm H2O around the pressure (Pflex) corresponding to a major change in slope of the inspiratory limb of the respiratory volume-pressure curve. In each animal the effects of the three PEEP levels were studied at two Paw levels, differing by 5 cm H2O. Increasing Paw significantly improved PaO2 and reduced venous admixture. A 5-cm H2O PEEP increase from +5 to +10 did not affect oxygenation; however, oxygenation was significantly better when PEEP was greater than Pflex. Both PaCO2 and anatomic dead space were higher at higher PEEP, and decreased with increasing Paw. Hence, Paw was a major determinant of oxygenation, although a PEEP greater than Pflex appeared necessary to optimize oxygenation at a constant Paw.

The role of total static lung compliance in the management of severe ARDS unresponsive to conventional treatment.

A group of 36 patients with severe adult respiratory distress syndrome (ARDS) meeting previously established blood gas criteria (mortality rate 90%) became candidates for possible extracorporeal respiratory support [low frequency positive pressure ventilation with extracorporeal CO2 removal (LFPPV-ECCO2R)]. Before connecting the patients to bypass we first switched the patients from conventional mechanical ventilation with positive end expiratory pressure (PEEP) to pressure controlled inverted ratio ventilation (PC-IRV), and then when feasible, to spontaneous breathing with continuous positive airways pressure (CPAP). Forty eight hours after the patients had entered the treatment protocol, only 19 out of the 36 patients in fact required LFPPV-ECCO2R, while 5 were still on PC-IRV, and 12 were on CPAP. The overall mortality rate of the entire population was 23%. The only predictive value of success or failure of a particular treatment mode was total static lung compliance (TSLC). No patients with a TSLC lower than 25 ml (cm H2O)-1 tolerated either PC-IRV or CPAP, while all patients with a TSLC higher than 30 ml (cm H2O)-1 were successfully treated with CPAP. Borderline patients (TSLC between 25 and 30 ml (cm H2O)-1) had to be treated with PC-IRV for more than 48 h, or were then placed on LFPPV-ECCO2R if Paco2 rose prohibitively. We conclude that TSLC is a most useful measurement in deciding on the best management of patients with severe ARDS, unresponsive to conventional treatment.