AUTOPILOT-BT: a system for knowledge and model based mechanical ventilation

A closed-loop system (AUTOPILOT-BT) for the control of mechanical ventilation was designed to: 1) autonomously achieve goals specified by the clinician, 2) optimize the ventilator settings with respect to the underlying disease and 3) automatically adapt to the individual properties and specific disease status of the patient. The current realization focuses on arterial oxygen saturation (SpO(2)), end-tidal CO(2) pressure (P(et)CO(2)), and positive end-expiratory pressure (PEEP) maximizing respiratory system compliance (C(rs)). The "AUTOPILOT-BT" incorporates two different knowledge sources: a fuzzy logic control reflecting expert knowledge and a mathematical model based system that provides individualized patient specific information. A first evaluation test with respect to desired end-tidal-CO(2)-level was accomplished using an experimental setup to simulate three different metabolic CO(2) production rates by means of a physical lung simulator. The outcome of ventilator settings made by the "AUTOPILOT-BT" system was compared to those produced by clinicians. The model based control system proved to be superior to the clinicians as well as to a pure fuzzy logic based control with respect to precision and required settling time into the optimal ventilation state.

Worldwide variation of dialysis-associated peritonitis in children

Peritonitis is the most common cause of dialysis failure in children on chronic peritoneal dialysis. We performed a prospective study of 501 peritonitis episodes in 44 pediatric dialysis centers located in 14 countries that examined peritonitis etiology, efficiency of opinion-based management guidelines, and final outcomes. Culture-negative incidence varied significantly from 11% in North America to 67% in Mexico. Argentina and North America had the highest rate of Gram-negative episodes. Pseudomonas-based peritonitis was eightfold more common in the United States than in Europe, and correlated with the frequency of exit site cleansing and topical mupirocin administration. Significant regional variation in antibiotic susceptibility was noted for the first generation cephalosporins and aminoglycosides. Initial response rates to standardized empiric antibiotic treatment did not differ between regions; however, final outcomes were significantly less favorable in Eastern Europe. The wide regional variation in culture-negative peritonitis, and the distribution and antibiotic susceptibilities of causative bacteria needs to be taken into consideration when the guidelines for empiric therapy of pediatric dialysis-associated peritonitis are revised.

Frühwarnsystem zur Flüssigkeitsüberwachung der Lunge bei terminaler Herzinsuffizienz

HISTORY AND ADMISSION FINDINGS

A 38-year-old man was admitted for increasing dyspnea, nausea and emesis during the preceding year. Clinically he was in heart failure NYHA stage III. He had not been on any regular medication and had no other medical complaints. Physical examination revealed a pulse of 100/min., hypotension (100/60 mmHg) and jugular vein distension. Bilateral pulmonary rales were noted on auscultation. A slight edema of both lower legs was noted.

INVESTIGATIONS

A 12-lead electrocardiogram showed complete left bundle branch block with a QRS duration of 160 ms. Chest x-ray revealed cardiomegaly with pulmonary vascular congestion. Transthoracic echocardiography demonstrated reduced left ventricular function with an ejection fraction of 10-15%. Left heart catheterization excluded coronary heart disease and confirmed the decreased left ventricular function.

TREATMENT AND COURSE

Medical treatment for heart failure secondary to dilated cardiomyopathy was initiated without significant improvement in clinical status. Cardiac resynchronization therapy (CRT) was therefore performed with implantation of a biventricular pacer with defibrillator (CRT-D) and a fluid status monitoring system (OptiVol). Subsequently the patient was able to increase his physical activity to NYHA class II and was followed in our outpatient clinic. Since initial treatment the patient has been seen twice for clinical signs of pulmonary edema. Both times the fluid monitoring system of the CRT-D gave an alarm signal early enough to allow cardiac re-compensation by expanding the current medication. Both times hospital admission was avoided.

CONCLUSIONS

Cardiac resynchronization therapy has been established as an adjunct to optimal pharmacological therapy in eligible patients with severe heart failure. A fluid status monitoring system integrated into the device measures intrathoracic impedance, allowing patients to be alerted before the onset of symptoms of fluid overload. Thus, treatment can be adjusted and hospitalization is avoidable.

Moisturizing and mechanical characteristics of a new counter-flow type heated humidifier

BACKGROUND

During mechanical ventilation effective conditioning of inspired air is important. In this respect, conventional humidifiers do not perform optimally. By design, a counter-flow-type humidifier should improve humidification and heating, but may increase resistance.

METHODS

We investigated mechanical impedance and work of breathing (using pressure-flow characteristics and additional pressure-time product) of a new counter-flow-type humidifier, a conventional heated humidifier, and a passive heat and moisture exchanger (HME) in physical models of the respiratory system. We investigated moisturizing performance (amount of vaporized water at different air flows and ventilatory frequencies) of the two heated humidifiers. Ease of breathing through both heated humidifiers was investigated in 12 healthy volunteers blinded to the type of humidifier.

RESULTS

Moisturizing performance of the conventional heated humidifier was flow-independent (approximately 32.5 mg vaporized water per breath at inspiratory flow rates of 30-120 litre min (- 1); P > 0.05) but decreased (10%; P < 0.0001) with increasing ventilatory rates (12-20 min (- 1)). In contrast, moisturizing performance of the counter-flow-type humidifier (approximately 33.5 mg vaporized water per breath) was both flow- and rate-independent (P = 0.75). In addition, the counter-flow humidifier caused less physical work (approximately 25%) and resistance (approximately 50%) (both P < 0.05) than the other two devices. The passive HME displayed the least favourable mechanical characteristics. Ten of 12 volunteers felt breathing through the counter-flow humidifier easier than through the heated humidifier (P < 0.05).

CONCLUSION

Compared with a conventional humidifier, the new counter-flow-type humidifier displayed improved air conditioning and mechanical characteristics. Its lower resistance, particularly at low airflows, should be of clinical benefit during spontaneous breathing and triggered assisted ventilation.