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Biomedical subjects

Ralf Kuhlen

Publications and source records attributed to Ralf Kuhlen.

27 records · Page 2Linked to original sources
PubMed2003

Extracorporeal gas exchange with the DeltaStream rotary blood pump in experimental lung injury.

In most severe cases of the acute respiratory distress syndrome, veno-venous extracorporeal membrane oxygenation (ECMO) can be used to facilitate gas exchange. However, the clinical use is limited due to the size and the concomitant risk of severe adverse events of conventionally-used centrifugal blood pumps with high extracorporeal blood volumes. The DeltaStream blood pump is a small-sized rotary blood pump that may reduce extracorporeal blood volume, foreign surfaces, contact activation of the coagulation system, and blood trauma. The aim of the present study was to test the safety and efficacy of the DeltaStream pump for ECMO in animals with normal lung function and experimental acute lung injury (ALI). Therefore, veno-venous ECMO was performed for 6 hours in mechanically ventilated pigs with normal lung function (n=6) and with ALI induced by repeated lung lavage (n=6) with a blood flow of 30% of the cardiac output. Gas flow with a FiO2 of 1.0 was set to equal blood flow. With a mean activated clotting time of 121 +/- 22 s, no circulatory impairment or thrombus formation was revealed during ECMO. Furthermore, free plasma Hb did not increase. In controls, hemodynamics and gas exchange remained unchanged. In animals with ALI, hemodynamics remained stable and gas transfer across the extracorporeal oxygenators was optimal, but only in 2 animals was a marked increase in PaO2 observed. CO2 removal was efficacious in all animals. We concluded that the DeltaStream blood pump may be used for veno-venous ECMO without major blood damage or hemodynamic impairment.

Animals↗
PubMed2003

Modulating the pulmonary circulation: an update.

PURPOSE OF REVIEW: Disorders of the pulmonary circulation might develop as a primary disease process of the pulmonary vascular bed or, more often, as the acute or chronic consequence of pulmonary or cardiac pathologies. For the anaesthesiologist and intensivist it is particularly interesting to gain insight into the regulation of the pulmonary circulation since pulmonary hypertension and concomitant right heart failure contribute to high perioperative mortality rates in patients at risk, especially after cardiac surgery. Therefore, modulation of the pulmonary circulation may be a life-saving therapy in patients suffering from acute or chronic pulmonary circulatory disorders. Furthermore, routinely performed intra-operative interventions such as the use of volatile anaesthetics or cardiopulmonary bypass systems may have relevant side effects on the pulmonary circulation. RECENT FINDINGS: This review focuses on new insights into the modulation of pulmonary circulation during general anaesthesia with volatile anaesthetics and anaesthesiological management during cardiopulmonary surgery. Recent publications in the field of cardiopulmonary bypass surgery, one-lung ventilation and heart and lung transplantation are discussed. Furthermore, the role of conventional and experimental therapeutic strategies to modulate pulmonary circulation in intensive care medicine is reviewed. SUMMARY: Despite the performance of a large number of clinical and experimental studies, the pathophysiology of pulmonary circulatory disorders is not completely understood. Therefore, any new therapy has to be carefully evaluated as a therapeutic option. Several formerly experimental therapeutic interventions such as inhaled vasodilators, however, appear to have found their way into clinical practice for selected indications.

Journal Article↗
PubMed2003

Anaesthetic considerations in patients with chronic pulmonary disease.

PURPOSE OF REVIEW: Chronic pulmonary diseases are getting more important in daily anaesthetic practice, because prevalence is increasing and improved anaesthetic techniques have led to the abandonment of previous contraindications to anaesthesia. It is therefore essential for the anaesthetist to be up to date with current clinical concepts and their impact on the conduction of anaesthesia as well as new insights into how to anaesthetise these patients safely. RECENT FINDINGS: If patients are treated adequately, open and minimally invasive operations can be safely performed under regional and general anaesthesia. The management of acute exacerbations remains challenging, and first-line medical treatment should be supported by non-invasive ventilation. In controlled mechanical ventilation, parameters should be set to avoid dynamic hyperinflation. SUMMARY: Assessing the functional status of patients admitted for surgery remains a difficult task, and in patients identified as being at risk by clinical examination additional spirometry and blood gas measurements may be helpful. If there are flow limitations and signs of respiratory failure, the anaesthetist should be highly alarmed and monitor the patient closely and invasively, yet there is no reason to deny any patient a substantially beneficial operation.

Journal Article↗
PubMed2002

High-frequency oscillatory ventilation in experimental lung injury: effects on gas exchange.

OBJECTIVE: To compare ventilation-perfusion (V(A)/Q) distributions during improvement of oxygenation caused by high-frequency oscillatory ventilation (HFOV) and pressure-controlled mechanical ventilation with high PEEP levels (CMV) in experimental acute lung injury (ALI). DESIGN: Prospective, controlled animal study. SETTING: Animal research facility of a university hospital. INTERVENTIONS: Twelve pigs with oleic acid-induced ALI were randomised to HFOV ( n=6) or to CMV ( n=6) with a PEEP of 15 mbar for 1 h. The mean airway pressure was adjusted in both groups to achieve comparable improvements in arterial oxygen partial pressure (PaO(2)) and to avoid clinically relevant impairments of cardiac output, as assured by adequate mixed venous oxygen saturation and lactate levels. V(A)/Q distributions were determined by the multiple inert gas elimination technique (MIGET). MEASUREMENTS AND RESULTS: Arterial oxygen partial pressure improved during CMV with a mean airway pressure of 20 mbar ( p<0.05) whereas HFOV revealed comparable improvements with a mean airway pressure of 40 mbar ( p<0.05). Shunt decreased and blood flow to normal V(A)/Q areas increased due to CMV and HFOV ( p<0.05). The perfusion of low V(A)/Q areas remained unchanged. Statistical analysis did not reveal differences of PaO(2), shunt or blood flow to low V(A)/Q areas between the groups. CONCLUSIONS: In this model of acute lung injury CMV and HFOV improved gas exchange due to similar changes in V(A)/Q distribution. However, mean airway pressure had to be adjusted twofold higher during HFOV then during CMV to achieve comparable improvements in gas exchange.

Animals↗
PubMed2002

Pressure support compared with controlled mechanical ventilation in experimental lung injury.

UNLABELLED: It has been suggested that, in acute lung injury (ALI), spontaneous breathing activity may increase oxygenation because of an improvement of ventilation-perfusion distribution. Pressure support ventilation (PSV) is one of the assisted spontaneous breathing modes often used in critical care medicine. We sought to determine the prolonged effects of PSV on gas exchange in experimental ALI. We hypothesized that PSV may increase oxygenation because of an improvement in ventilation-perfusion distribution. Thus, ALI was induced in 20 pigs by using repetitive lung lavage. Thereafter, the animals were randomized to receive either PSV with a pressure level set to achieve a tidal volume >4 mL/kg and a respiratory rate <40 min(-1) (n = 10) or controlled mechanical ventilation (CMV) with a tidal volume of 10 mL/kg and a respiratory rate of 20 min(-1) (n = 10). Positive end-expiratory pressure was set at 10 cm H(2)O in both groups. Blood gas analyses and determination of ventilation-perfusion (.V(A)/.Q) distribution were performed at the onset of ALI and after 2, 4, 8, and 12 h. The main result was an improvement of oxygenation because of a decrease of pulmonary shunt and an increase of areas with normal .V(A)/.Q ratios during PSV (P < 0.005). However, during CMV, a more pronounced reduction of shunt was observed compared with PSV (P < 0.005). We conclude that, in this model of ALI, PSV improves gas exchange because of a reduction of .V(A)/.Q inequality. However, improvements in .V(A)/.Q distribution may be more effective with CMV than with PSV. IMPLICATIONS: Assisted spontaneous breathing may have beneficial effects on gas exchange in acute lung injury. We tested this hypothesis for pressure support ventilation in an animal model of acute lung injury. Our results demonstrate that pressure support does not necessarily provide better gas exchange than controlled mechanical ventilation.

Air Pressure↗
PubMed2002

The role of spontaneous breathing during mechanical ventilation.

The tremendous progress in microprocessor-driven ventilator technology over the last years has facilitated the introduction of a broad variety of different ventilatory modes into the clinical practice of mechanical ventilation. Many of these newer modalities are designed for partial ventilatory support, which might reflect the complexity of the issue of patient ventilator interactions when spontaneous breathing activity is present compared to controlled mechanical ventilation. There are reasons to believe that allowing some degree of spontaneous breathing activity during mechanical ventilation is useful not only to gradually withdraw ventilatory assistance in the process of weaning but also to avoid some of the adverse effects of mechanical ventilation in the early phase of acute respiratory failure when classically controlled modes of ventilation are used. It is the aim of this article to review the effects of preserved spontaneous breathing activity during mechanical ventilation with different ventilatory modalities in acute respiratory failure patients.

Hemodynamics↗
PubMedDate not supplied

Analysis of respiratory pressure-volume curves in intensive care medicine using inductive machine learning.

We present a case study of machine learning and data mining in intensive care medicine. In the study, we compared different methods of measuring pressure-volume curves in artificially ventilated patients suffering from the adult respiratory distress syndrome (ARDS). Our aim was to show that inductive machine learning can be used to gain insights into differences and similarities among these methods. We defined two tasks: the first one was to recognize the measurement method producing a given pressure-volume curve. This was defined as the task of classifying pressure-volume curves (the classes being the measurement methods). The second was to model the curves themselves, that is, to predict the volume given the pressure, the measurement method and the patient data. Clearly, this can be defined as a regression task. For these two tasks, we applied C5.0 and CUBIST, two inductive machine learning tools, respectively. Apart from medical findings regarding the characteristics of the measurement methods, we found some evidence showing the value of an abstract representation for classifying curves: normalization and high-level descriptors from curve fitting played a crucial role in obtaining reasonably accurate models. Another useful feature of algorithms for inductive machine learning is the possibility of incorporating background knowledge. In our study, the incorporation of patient data helped to improve regression results dramatically, which might open the door for the individual respiratory treatment of patients in the future.

Adult↗