Veno-venous extracorporeal lung assist with concurrent distal aortic perfusion: repair of ruptured aorta in a patient with dense ARDS.

Extracorporeal lung assist (ECLA) allowed surgical repair of a ruptured descending thoracic aorta to be performed in a patient with profound respiratory failure. Dense acute respiratory distress syndrome (ARDS) developed during his 15-day hospitalization at a regional trauma center. After transfer to a Level I facility, an additional injury was diagnosed: traumatic rupture of the aorta, contained within a pseudoaneurysm. ECLA by the veno-venous route was required immediately preoperatively and distal aortic perfusion was performed during the aortic repair. Despite deflation of the left lung, the patient was oxygenated and ventilated adequately during surgery. Cross-clamp time was 48 minutes. The patient was weaned from ECLA by the fifth postoperative day. To our knowledge, this is the first report of concurrent veno-venous pulmonary support with distal aortic perfusion.

Low blood flow extracorporeal carbon dioxide removal (ECCO2R): a review of the concept and a case report.

Despite advances in respiratory and critical care medicine, the mortality from ARDS remains unchanged. Recent research suggests current ventilatory therapy may produce additional lung injury, retarding the recovery process of the lung. Alternative supportive therapies, such as ECMO and ECCO2R, ultimately may result in less ventilator induced lung injury. Due to the invasiveness of ECMO/ECCO2R, these modalities are initiated reluctantly and commonly not until patients suffer from terminal or near-terminal respiratory failure. Low flow ECCO2R may offer advantages of less invasiveness and be suitable for early institution before ARDS becomes irreversible. We describe a patient with ARDS and severe macroscopic barotrauma supported with low flow ECCO2R resulting in significant CO2 clearance, reduction of peak, mean airway pressures and minute ventilation.

An in vitro physiologic model for cardiopulmonary simulation: a system for ECMO training.

Extracorporeal life support (ELS) systems may be run by certified perfusionists, specially trained nurses or respiratory therapy staff. Guidelines for the training, certification and retraining of ELS operators have been established by the Extracorporeal Life Support Organization. Recommendations include "... a well defined program for staff training, certification, and retraining". Some clinicians have suggested that ELS operators be certified and recertified in an animal laboratory. But such practice involves veterinary expenses, animal use issues and considerable clean-up and disposal. We describe an alternative method of training, using an in vitro physiologic model designed to simulate various pathophysiologic states. In addition, the in vitro physiologic model may be used to evaluate membrane lung characteristics. This model's ease of construction, maintenance and use for training compared with live animal techniques are discussed. Research capabilities may be more flexible than with the use of the live animal technique. The in vitro physiologic model can be a useful and convenient asset to an extracorporeal membrane oxygenation/extracorporeal carbon dioxide removal (ECMO/ECCO2R) program.

Prospective evaluation of combined high-frequency ventilation in post-traumatic patients with adult respiratory distress syndrome refractory to optimized conventional ventilatory management.

This study explores the value of combined high-frequency ventilation (CHFV) in a prospective clinical trial of 35 patients suffering from severe post-traumatic and/or septic adult respiratory distress syndrome (ARDS) who were refractory to conventional controlled mechanical ventilatory (CMV) support. The severity of ARDS was quantified by lung mechanics and gas exchange variables and the patients were classified on clinical grounds as well as on the basis of their respiratory index/pulmonary shunt relationship [RI/(Qsp/Qt)]. During the same time period as the CHFV study, data from these patients were compared to those from 88 ARDS patients who had quantitatively similar degrees of respiratory insufficiency, but who were treated only with controlled mechanical ventilation (CMV). The use of CHFV in the 35 CMV refractory patients resulted in an increase in expired tidal volume (VTE) by reducing the CMV inspired tidal volume (VTI) while increasing the volume component derived from high-frequency ventilation (HFV). This procedure appeared to reveal potentially salvageable ARDS patients who were refractory to CMV. In these patients, CHFV significantly reduced pulmonary mean airway pressure (Paw). The RI also decreased significantly and it was possible to reduce significantly the FIO2. In surviving ARDS patients treated with CHFV, an improvement in blood gases at reduced FIO2, without decreased cardiac output, was produced. The CHFV technique was used for less than or equal to 25 days and resulted in 23% survival of patients who were clinically and physiologically indistinguishable from the patients in the ARDS nonsurvivor group who were treated by CMV only. In surviving CHFV patients the decrease in Paw permitted a sustained, or increased, cardiac output with a rise in the oxygen delivery/oxygen consumption ratio, thus allowing for a higher PaO2 for any given level of pulmonary shunt.

Respiratory index/pulmonary shunt relationship: quantification of severity and prognosis in the post-traumatic adult respiratory distress syndrome.

The relationship between the respiratory index (RI = alveolar-arterial oxygen gradient [P(A-a)O2] normalized by PaO2) and the pulmonary shunt (Qsp/Qt) has been examined in 929 studies from 240 critically ill post-traumatic patients. Of these, 88 patients (443 studies) were individuals who developed post-traumatic adult respiratory distress syndrome (ARDS) and 152 were patients (486 studies) who did not develop ARDS. This study demonstrates that the RI to Qsp/Qt [RI/(Qsp/Qt)] relationship was significantly (p less than .0001) increased in patients who developed fatal ARDS compared with those who did not develop ARDS, or with those whose ARDS resolved. Because of the increased oxygen consumption (VO2) in ARDS patients in association with their severe limitations in gas exchange (RI) and increased Qsp/Qt, surviving ARDS patients had a significant increase in the cardiac index which resulted in a higher oxygen delivery to VO2 ratio. ARDS patients showed significant (p less than .0001) evidence of increased pulmonary vascular tone, correlated with the increase in the RI/(Qsp/Qt) relationship. In addition, those patients with high RI/(Qsp/Qt) also had increased right ventricular (RVSW) to left ventricular work (LVSW) ratios which were shown to be a direct function of the rise in RI. This increase in both RVSW/LVSW and RI/(Qsp/Qt) ratios was significantly (p less than .0001) correlated with an increased mortality. Thus, the RI/(Qsp/Qt) relationship, which can be obtained from arterial and mixed venous blood gases and saturations only, can be used to predict the severity of the ARDS process as well as important pulmonary vascular and right ventricular overload consequences.

Gas exchange in low-compression HFPPV is maintained at low distending pressures in the pig.

The fact that collateral ventilation normally occurs in the human lung has led to the suggestion that it might contribute to the successful clinical effects of low-compression high-frequency positive-pressure ventilation (HFPPV). As the pig has poor collateral ventilation, pulmonary vasoconstriction has to be part of the regulatory mechanisms matching ventilation-perfusion. A study was made on nine pigs anesthetized with ketamine hydrochloride intravenously to elucidate the maintenance of ventilation-perfusion balance during mechanical ventilation. Comparisons were made between the ventilatory patterns provided by a conventional ventilator (Servo-Ventilator 900C) and an improved prototype of a low-compression system for volume-controlled ventilation (system H). A ventilatory frequency of 20 breaths per min (bpm) with SV-900C (SV-20) and system H (H-20) and of 60 bpm with system H (H-60) was used. The experimental conditions were otherwise identical. Positive end-expiratory pressures (PEEP) were applied to maintain the same mean airway pressure with the three systems. The tidal volume required for normoventilation differed significantly between the three ventilatory patterns, but there were no differences in circulatory and oxygen-transport variables. By measurements of airway pressure and intrapleural liquid surface pressure, it was demonstrated that the distending pressure (at end-inspiration) was significantly lower with a low-compression system (H-20 versus SV-20), especially at a high ventilatory frequency (H-60 versus H-20). Consequently, although the mean airway pressure was set at the same level for the three different ventilatory modalities, the distending pressures required for the same alveolar ventilation and arterial oxygenation differed significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative studies of IPPV and HFPPV with PEEP in critical care patients. I: A clinical evaluation.

The effects of the ventilatory patterns of a conventional ventilator (SV-900) and a low-compression ventilator (system H) were studied in 12 patients with respiratory failure (RF). Volume-controlled ventilation at frequencies (f) of 20 breath/min (SV-20) with SV-900, and 20 (H-20) and 60 (H-60 = high-frequency positive-pressure ventilation, HFPPV) breath/min with system H was given. Inspiration constituted 25% (with an inspiratory pause of 10%) of the ventilatory cycle with SV-900 and 22% with system H. Intratracheal (ITP), intrapleural, systemic and pulmonary arterial (PAP), and central venous (CVP) pressures were measured at normoventilation. During H-60, normoventilation was provided with smaller tidal volumes and lower mean intratracheal pressures than during SV-20 and H-20. Cardiac index and oxygen transport were not affected by changes in ventilatory pattern. The respiration-synchronous variations in CVP, PAP, and pulmonary capillary wedge pressure (WP) during ventilation at 20 breath/min were abolished during HFPPV. In the most severely ill patients, long-term HFPPV was uneventful. Airway suctioning during ventilation with oxygen was an important feature of the pneumatic valve principle (system H). The results of this study indicate that volume-controlled HFPPV is as efficient and as well accepted by the patient as conventional ventilation (SV-20).

Comparative studies of IPPV and HFPPV with PEEP in critical care patients. II: Studies on intrapulmonary gas distribution.

The ventilatory patterns of a conventional ventilator for volume-controlled ventilation (SV-900) and a low-compression ventilator utilizing the pneumatic valve principle for pressure/flow-generated, volume-controlled ventilation (system H) were studied in a lung model and in 10 patients with respiratory failure. System H was used at frequencies of 20 (H-20) and 60 (H-60 = high-frequency positive-pressure ventilation [HFPPV]) breath/min, and SV-900 at a frequency of 20 (SV-20) breath/min. With system H, inspiration constituted 22% (no inspiratory pause) and with SV-900, 25% (with 10% inspiratory pause). System H delivers an instantaneous accelerating flow which rapidly decelerates during the second part of the inspiratory phase. Maximal flow rates studied were 1.3 (H-60), 0.9 (H-20), and 0.7 (SV-20) L/sec. Thus, HFPPV delivers an effective tidal volume with highest linear velocity. This increased velocity increases gas mixing by increasing turbulence in conducting airways. In the 10 patients with respiratory failure, intrapulmonary gas distribution (measured as the nitrogen washout delay) was improved from 106% during SV-20 to 74% with H-60 (p less than 0.05). H-60 also increased carbon dioxide elimination in the 2 patients with the most severe pulmonary dysfunction.