[The spinal catheter in aortic surgery : Implications for anesthesia]. / Der Spinalkatheter in der Aortenchirurgie : Implikationen für die Anästhesie.

During surgical repair of aortic pathologies (e.g. dissection, aneurysms), cross-clamping of the aorta or overstenting of critical segmental arteries can lead to ischemia- and edema-related spinal cord damage with subsequent paraplegia. By regulating cerebrospinal fluid pressure, the spinal catheter is an effective method for prophylaxis and treatment of spinal cord ischemia. Due to the high complication rate of the spinal catheter a detailed risk-benefit assessment is obligatory: besides cerebrospinal fluid leakage, postpuncture headaches and local infections, feared complications, such as intracranial bleeding, meningitis and neuraxial hematomas can also occur, sometimes with a significant latent period after termination of the procedure. Adequate training of personnel in the perioperative handling of spinal catheters and meticulous adherence to drainage parameters are important components for increasing procedural safety. This is particularly true since the clinical aspects of catheter-associated complications only slightly differ from that of ischemic spinal cord injury.

LEA29Y expression in transgenic neonatal porcine islet-like cluster promotes long-lasting xenograft survival in humanized mice without immunosuppressive therapy.

Genetically engineered pigs are a promising source for islet cell transplantation in type 1 diabetes, but the strong human anti-pig immune response prevents its successful clinical application. Here we studied the efficacy of neonatal porcine islet-like cell clusters (NPICCs) overexpressing LEA29Y, a high-affinity variant of the T cell co-stimulation inhibitor CTLA-4Ig, to engraft and restore normoglycemia after transplantation into streptozotocin-diabetic NOD-SCID IL2rγ-/- (NSG) mice stably reconstituted with a human immune system. Transplantation of INSLEA29Y expressing NPICCs resulted in development of normal glucose tolerance (70.4%) and long-term maintenance of normoglycemia without administration of immunosuppressive drugs. All animals transplanted with wild-type NPICCs remained diabetic. Immunohistological examinations revealed a strong peri- and intragraft infiltration of wild-type NPICCs with human CD45+ immune cells consisting of predominantly CD4+ and CD8+ lymphocytes and some CD68+ macrophages and FoxP3+ regulatory T cells. Significantly less infiltrating lymphocytes and only few macrophages were observed in animals transplanted with INSLEA29Y transgenic NPICCs. This is the first study providing evidence that beta cell-specific LEA29Y expression is effective for NPICC engraftment in the presence of a humanized immune system and it has a long-lasting protective effect on inhibition of human anti-pig xenoimmunity. Our findings may have important implications for the development of a low-toxic protocol for porcine islet transplantation in patients with type 1 diabetes.

A haemodynamic study during OPCAB surgery using a new multi-suction cardiac positioner.

BACKGROUND: Displacement of the heart is necessary to expose the target vessel for distal anastomosis to achieve successful multivessel off-pump coronary artery bypass (OPCAB) grafting. In addition to complete revascularisation of the heart, a main challenge during the operation is to maintain haemodynamic stability during this procedure. A new heart positioner (Tentacles) was tested. METHODS: In a prospective clinical study we used the Tentacles device in 50 patients scheduled for multivessel OPCAB procedures and investigated the haemodynamic effects during displacement of the heart and while performing the anastomoses to the anterior, lateral and posterior wall. The following haemodynamic parameters were investigated: mean arterial blood pressure (MAP), cardiac index (CI) and stroke volume index (SVI). The incidence of myocardial ischaemia was monitored by transoesophageal echocardiography (TEE) and by ST-segment analysis in the electrocardiogram (ECG). RESULT: The Tentacles device permitted rapid, secure and excellent exposure of the lateral and posterior wall of the heart. During exposure of the anterior wall there was a small decrease in MAP (77 ± 10 vs.71 ± 9 mmHg, P = 0.02) in combination with an increase in the CI (3.0 ± 0.7 l vs. 3.1 ± 0.8 l/min/m2, P = 0.03). When the lateral and posterior walls of the heart were exposed, the SVI decreased significantly (36 ± 11 and 38 ± 8 mL/m2, P < 0.01 and P = 0.04, respectively) compared to baseline (44 ± 11 mL/m2) while CI and MAP remained stable. The amount of norepinephrine administered during displacement of the heart was significantly higher in all three positions (0.05 ± 0.05, 0.06 ± 0.05 and 0.04 ± 0.03 µg/kg/min, P < 0.01) compared to the physiological position (0.02 ± 0.02 µg/kg/min). Sinus rhythm was maintained throughout the operation. Neither significant changes of the ST-segment in the ECG nor incidences of wall motion abnormality in TEE were observed. Six hours postoperatively the troponin I concentration was 11.7 ± 4.3 ng/mL. CONCLUSION: The Tentacles device provided excellent access in multivessel OPCAB surgery. Haemodynamic stability was maintained in all patients; however additional catecholamine support was used when the heart was displaced. This was the case when carrying out an anastomosis on the anterior, lateral, or posterior wall.

Changes in microvascular fluid filtration capacity during 120 days of 6 degrees head-down tilt.

We used venous congestion strain gauge plethysmography (VCP) to measure the changes in fluid filtration capacity (K(f)), isovolumetric venous pressure (Pv(i)), and blood flow in six volunteers before, on the 118th day (D118) of head-down tilt (HDT), and 2 days after remobilization (Post). We hypothesized that 120 days of HDT cause significant micro- and macrovascular changes. We observed a significant increase in K(f) from 3.6 +/- 0.4 x 10(-3) to 5.7 +/- 0.9 x 10(-3) ml. min(-1). 100 ml(-1). mmHg(-1) (+51.4%; P < 0.003), which returned to pretilt values (4.0 + 0.4 x 10(-3) ml. min(-1). 100 ml(-1). mmHg(-1)) after remobilization. Similarly, Pv(i) increased from 13.4 +/- 2.1 mmHg to 28.9 +/- 2.8 mmHg (+105.8%; P < 0.001) at D118 and was not significantly different at Post (12.4 +/- 2.6 mmHg). Blood flow decreased significantly from 2.3 +/- 0.3 to 1.3 +/- 0.2 ml. min(-1). 100 ml tissue(-1) at D118 and was found elevated to 3.4 +/- 0.7 ml. min(-1). 100 ml tissue(-1) at Post. We believe that the increased K(f) is caused by a higher microvascular water permeability. Because this may result in edema formation, it could contribute to the alterations in fluid homeostasis after exposure to microgravity.

Attenuation of the near-infrared and red photoplethysmographic signal by different depth of tissues.

Photoplethysmography enables non-invasive investigation of the volume pulse in the microvasculature of patients. We previously have shown that time-discrete analysis enables identification of highly reproducible characteristics of the volume pulse in absolute values. The method would be of particular interest, if the perfusion of deeper tissue layers like the skeletal muscle can be assessed. The aim of the current study was to investigate the attenuation of the photoplethysmographic signal by different tissues and up to which depth of tissue a time-discrete analysis of the photoplethysmographic signal would be possible. For the recordings we used the time-discrete near-infra-red photoplethysmography (NIRP), a reflection photoplethysmograph measuring at wavelengths of 840 nm and 640 nm. In an in vitro circuit filled with bovine blood we generated a typical and exactly reproducible volume pulse. On a platform the NIRP sensor probe was placed above the artificial vessel and recordings of the volume pulse were obtained by varying the sensor-vessel-distance with increasing layers of water, blood-agar or bovine skeletal muscle tissue. - The amplitude of the NIR signal was attenuated to 50% by each layer of 2.01 mm of water, 1.42 mm of blood-agar and 1.05 mm of bovine skeletal muscle tissue. A time-discrete analysis could be performed up to a depth of 15 mm of water, 6 mm of blood-agar and 5 mm of bovine skeletal muscle tissue. - As the photoplethysmographic curve is strongly attenuated even by a few millimetres of water we suggest that the NIRP signal mirrors the perfusion of the superficial tissue layer and mainly originates from the subpapillary capacious plexus. - We conclude that with the equipment used in this study volume pulsations in deeper layers of tissue like skeletal musculature can not be assessed.

Changes in the arteriolar volume pulse of the finger during various degrees of tilt using near infra-red and red photoplethysmography.

1. Photoplethysmography is a widely used non invasive technique for the measurement of peripheral oxygen saturation. A more detailed analysis of the volume pulse (VP) can indicate alterations in peripheral vascular tone, due to sympathetic stimulation, stress, pain and temperature. - 2. In six healthy male volunteers we investigated changes in the VP resulting from vasoconstriction and vasodilatation induced by varies degrees of tilt. Subjects were subjected 0 degrees tilt followed by head down -8 degrees -15 degrees, -30 degrees -15 degrees, -8 degrees, 0 degrees, 15 degrees, 30 degrees , 70 degrees, 30 degrees, 15 degrees and 0 degrees. Each tilt stage was sustained for 15 minutes. Both VP - and haemodynamic changes were continuously recorded 30s before and then for 210 s after the imposition of each tilt step. We used a new computer driven soft and hardware for the analysis of the VP. 3. The VP signal was obtained with a sensor emitting 840 nm (NIR) and 640 nm (RED) light into finger tip with a sample rate of 128 Hz. All data was normalised to the initial mean value obtained at 0 degrees tilt. The signal strength parameters amplitude, and area under the curve and the first derivative of the amplitude (flux) as well as time discrete parameters, time of first maximum (Tmax), dicrote wave (Td), volume pulse decrease (Tdec) and fundamental arterial oscillation Tag = Td - Tmax were measured. 4. HR increased significantly during 30 degrees and 70 degrees tilt, but no change in the other hemodynamic parameters was observed. Amplitude, area under the curve and flux of both the Red and the NIR signal increased following head down tilt. A significant decrease of those parameters was found during foot down tilt. 5. No significant changes were found in the time discrete values, neither within each tilt step nor when compared to the initial mean value at 0 degrees tilt. 6. This study reveals that signal strength related parameters such as area under the curve, amplitude and flux reflect changes in vascular tone. Time discrete parameters however did not depict these changes and appear unsuitable for data analysis when using this specific hardware applied in the current study.

Cardiovascular monitoring of elective aortic aneurysm repair using methods of chaos analysis.

INTRODUCTION: Biological signals like arterial blood pressure (ABP) and electrocardiograms are usually displayed in a linear fashion. The often very complex structure may, however, be better described by phase space plots and time-delayed vectors, enabling an advantageous display of the dynamics contained in the signal. The potentials of such a display were investigated during elective aortic aneurysm repair, where profound haemodynamic changes frequently occur. METHOD: The peripheral volume pulse was recorded at a digit using noninvasive near infrared photoplethysmography (NIRP). All patients (n = 20, mean age 72.8 years) were invasively monitored using arterial and Swan Ganz catheters. The ABP signal was continuously recorded with a computer (sample rate 128 Hz). Two different phase space plots, [x(t), y(t + 8/128 s) and x(t), d(x(t + 8/128 s) - x(t))/dt] were calculated for the NIRP and the ABP signals and continuously displayed. The stability was subjectively assessed and the fractal dimension calculated using the 'Hausdorff dimension'. The correlation between stability, fractal dimension and frequently used parameters of patient monitoring were investigated. RESULTS: All patients included in the study had an uncomplicated operation. Cardiac index (CI) and oxygen delivery (DO2) increased, and systemic vascular resistance (SVR) decreased following declamping of the aorta. The ABP signal was generally more stable. After declamping of the aorta, 14 of 16 NIRP signals became unstable, and 9 of 14 ABP signals destabilised. The time required for stabilisation of the signal varied between the individual patients. Thirty minutes after declamping, 11 of 12 ABP signals were stable, whereas 3 out of 9 NIRP signals still revealed an unstable pattern. A fractal dimension was calculated by box counting, which revealed a linear regression over two orders of magnitude in a log-log plot (Hausdorff dimension between 1.19 and 1.71). The mean fractal dimension for NIRP was significantly higher than that of the ABP signal. On clamping and declamping of the aorta, a trend to a higher fractal dimension (p = 0.08) was observed for both signals analysed. No correlation was observed between the fractal dimension and ABP, SVR index, CI, DO2 index and oxygen consumption. DISCUSSION: The dynamic changes of the signals were emphasised when they were displayed as phase space plots calculated by time-delayed vectors. The time series of the signal revealed a fractal dimension, and the observed increase at the critical time points of the operation, where the need for cardiovascular regulation is most pronounced, support the contention that a physiological system based on non-linear behaviour may enable a rapid response to haemodynamic challenges. An on-line display of phase space plots calculated by time-delayed vectors may in future provide a valuable method of monitoring for high-risk patients.

Influence of diabetic neuropathy on skin microcirculation assessed by transcutaneous oxymetry.

Skin microcirculation was investigated in 45 patients with long term diabetes and with severe, moderate or no neuropathy, and in 15 controls. Transcutaneous oxygen pressure (tcPO2) measurements on the forefoot were performed at 37 degrees C to assess local capillary flow at rest, during leg dependency and reactive hyperaemia, and also at 44 degrees C, including the response to oxygen inhalation. TcPO2 (37 degrees C) at rest was significantly elevated with an increasing degree of neuropathy (Controls: 4.8 +/- 3.7; patients without neuropathy: 4.2 +/- 2.9; with moderate neuropathy: 6.0 +/- 2.9 (p < 0.01); with severe neuropathy: 7.2 +/- 4.2 mmHg (p < 0.001)). Leg dependency resulted in a decrease of tcPO2 in the controls, while an increase was observed in 18.6% of the measurements in patients, reflecting a disturbed vasoconstrictor response. Regardless of neuropathy, absolute tcPO2 values during reactive hyperaemia were reduced in all patient groups as well as tcPO2 (44 degrees C) and its increase during oxygen breathing. Diabetic neuropathy is likely to increase local capillary flow, while the other differences to healthy controls may be contributed to a microcirculation disorder independent of neuropathy.

Bilateral traumatic extracranial aneurysms of the internal carotid artery with delayed brain infarction.

A 24-year-old woman with a left-sided cerebral infarction presented with hemiplegia and aphasia. Five months earlier she had had a closed head injury. Angiography revealed bilateral extracranial post-traumatic aneurysms of the internal carotid artery at the atlanto-axial level. There was full recovery without operative treatment within a week.