PubMed Health⌕ Search

Biomedical subjects

M Niklas

Publications and source records attributed to M Niklas.

11 recordsLinked to original sources
PubMed2004

Effects of Pringle manoeuvre and ischaemic preconditioning on haemodynamic stability in patients undergoing elective hepatectomy: a randomized trial.

BACKGROUND: The Pringle manoeuvre and ischaemic preconditioning are applied to prevent blood loss and ischaemia-reperfusion injury, respectively, during liver surgery. In this prospective clinical trial we report on the intraoperative haemodynamic effects of the Pringle manoeuvre alone or in combination with ischaemic preconditioning. METHODS: Patients (n=68) were assigned randomly to three groups: (i) resection with the Pringle manoeuvre; (ii) with ischaemic preconditioning before the Pringle manoeuvre for resection; (iii) without pedicle clamping. RESULTS: Following the Pringle manoeuvre the mean arterial pressure increased transiently, but significantly decreased after unclamping as a result of peripheral vasodilation. Ischaemic preconditioning improved cardiovascular stability by lowering the need for catecholamines after liver reperfusion without affecting the blood sparing benefits of the Pringle manoeuvre. In addition, ischaemic preconditioning protected against reperfusion-induced tissue injury. CONCLUSIONS: Ischaemic preconditioning provides both better intraoperative haemodynamic stability and anti-ischaemic effects thereby allowing us to take full advantage of blood loss reduction by the Pringle manoeuvre.

Adult↗
PubMed2000

Description and validation of a novel liquid metal-free device for venous congestion plethysmography.

We present a newly developed electromechanical sensor with automated calibration for strain-gauge plethysmography (filtrass) and compare it to a conventional mercury-in-Silastic strain-gauge plethysmograph (MSG). Fluid filtration capacity (K(f)) and isovolumetric venous pressure (Piv) of the limb were assessed noninvasively with both devices in 29 healthy volunteers. We found significantly higher K(f) and Piv values with MSG [4.6 +/- 2.0 x 10(-3) ml. min(-1). mmHg(-1). 100 ml tissue(-1) (K(f) units; K(f)U) and 21.2 +/- 8.1 mmHg for Pvi], than with filtrass, giving values of 3.1 +/- 0.8 K(f)U and 15.1 +/- 7.1 mmHg. Because K(f) and Piv are profoundly influenced by the calibration, we investigated the quality of the calibration signal and its impact on the obtained values. We could show that the reproducibility of repeated calibrations was higher with filtrass (58% lower mean +/- SD). The data were grouped according to the quality of calibration, and we found no significant difference in K(f) and Piv between filtrass (3.0 +/- 0.7 K(f)U and 15.9 +/- 6.9 mmHg, respectively) and MSG with good calibration signal (3.3 +/- 0. 8 K(f)U and 18.6 +/- 7.1 mmHg, respectively; no significant difference). However, we obtained significantly higher MSG values (5. 6 +/- 2.0 K(f)U and 23.1 +/- 8.4 mmHg, respectively; P < 0.001) in the group with a bad calibration signal. We suggest that the filtrass sensor, which performs an automatic, standardized calibration procedure and shows a linear signal response to stretch, gives highly reproducible and reliable results and thus is more suitable for routine application.

Adult↗
PubMed1998

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.

Agar↗
PubMed1997

[Early detection of TUR(transurethral resection) syndrome--ethanol measurement in ventilated patients].

A major complication of transurethral resection of the prostate (TURP) is the excessive absorption of irrigation solution resulting in hypervolemia and dilutional hyponatremia. Marking the irrigation fluid with ethanol is a method for the early detection of fluid absorption. Currently this method is being used in spontaneously breathing patients undergoing regional anaesthesia. The goal of this study was to determine whether this method is also reliable for patients undergoing general anaesthesia. Fifty-nine patients underwent TURP in either spinal anaesthesia (SPA), or general anaesthesia with semi-open (ITNO) and semi-closed (ITNC) systems. Plasma alcohol concentrations ([Eth]p), exhaled ethanol ([Eth]e), plasma sodium concentration ([Na+]), and central venous pressure (CVP) were measured. The irrigation fluid contained ethanol in an concentration of approx. 1%. We assumed that significant fluid absorption took place when [Eth]p exceeded 0.1/1000. Measurements were performed immediately prior to and during surgery at 10-minute intervals. [Eth]p correlated directly with [Eth]e for both forms of anaesthesia. [Eth]p and [Na+] correlated inversely both for SPA and ITNC. Changes in [Eth]p did not parallel changes in CVP. Clinically relevant episodes of fluid absorption were accompanied by the detection of exhaled ethanol in all groups. We conclude that measuring exhaled ethanol is a minimal invasive monitoring technique that allows the detection of significant fluid absorption in both spontaneously breathing as well as ventilated patients with sufficient sensitivity. The ethanol levels are not predictive of the sodium concentration both in SPA and general anaesthesia. Thus, additional determinations of [Na+] is recommended whenever [Eth]e exceeds 0.2/1000.

Anesthesia, General↗
PubMed1997

Hyperosmotic-hyperoncotic solutions during abdominal aortic aneurysm (AAA) resection.

A largely positive perioperative fluid balance during both elective and emergency abdominal aortic aneurysm repair (AAA) may put patients at risk of developing left ventricular failure and may thus contribute to morbidity. In the present paper we report on a prospective study using hyperosmotic-hyperonocotic solutions (HHS) infused during clamping of the aorta, for the prevention of declamping shock, and the associated reduction in perioperative fluid requirements. The major aim of this paper was to determine the efficacy of an HHS infusion when given over 20 minutes and to detect possible adverse effects of HHS. For perioperative fluid replacement 12 patients received crystalloid solutions with HHS [250 ml of 7.2% NaCl combined with either 6% Dextran (n = 3), 6% Hydroxyethylstarch (HES, n = 4) or 10% HES (n = 5)]. In 16 controls, crystalloids with 1000 ml of HES 10% were infused. Patients were invasively monitored and hemodynamic parameters frequently assessed during the operation, which were statistically analyzed in relation to the start of the fluid loading during clamping of the aorta. One patient showed an anaphylactoid reaction to HES, otherwise no side effects of HHS were observed during infusion (no hypotension, no pathological EKG changes). Plasma sodium and chloride concentration as well as osmolality rose resulting in an osmotic gradient and a desired intravascular volume expansion. Prior to declamping pulmonary capillary wedge pressure had increased to the desired value of > 13 mmHg and < 18 mmHg. Oxygen delivery was significantly elevated upon HHS and remained so post declamping, whereas no change was observed in controls. During clamping systemic vascular resistance was significantly decreased, but was unchanged in controls. The perioperative fluid balance of patients receiving HHS was 2471.0 +/- 948.6 ml, which was significantly less than + 3386.7 +/- 1247.9 ml of controls (P < 0.01). We suggest that HHS opens new perspectives in perioperative fluid management of both elective and emergency AAA repair, since hemodynamic parameters are improved and the overall fluid balance is less positive, thus decreasing the likelihood of edema formation. Moreover, the previously described positive microcirculatory effects of HHS may be particular beneficial in some high-risk patients.

Aged↗
PubMed1996

Time discrete, near infrared photoplethysmography (NIRP) for non-invasive investigation of the volume pulse in man.

UNLABELLED: In pulse oximetry the principles of photoplethysmography are used for determination of heart rate and in some devices to also display the volume pulse. It has been suggested, that a more detailed analysis of the signal may allow quantitative analysis of peripheral hemodynamic events. We describe a new computer assisted time discrete analysis of the volume pulse, studying its reliability and the method s fundamental assumption of a linear relationship between changes in amplitude and changes in time sequences of the volume pulse. METHOD: In a finger clip two diodes emit near infrared (840 nm, NIR) and red light (640nm, RED) into the finger tip, where it is remitted mainly by the erythrocytes. 70 sec of recorded signal is filtered and the resulting volume pulse analysed off-line using a computer. On each volume pulse the time of the first (Tmax), the second maximum (time of dicrote, Td) and the duration of the volume pulse (Tp) are measured and the mean values displayed. In addition, the fundamental arterial oscillation Tag = Td - Tmax and all the above values in relation to Tp are calculated. Using NIRP, 54 healthy young volunteers (19 female, mean age 27.0 +/- 3.4 years) were studied and the individual mean values calculated from 960 measurements. The reliability during 10 repetitive measurements was investigated in 26 of the 54 volunteers. In 12 subjects 5 repetitive measurements were obtained from each finger and compared with each other. In 11 subjects the linear relationship between amplitude and time sequence was tested on > 30 000 single volume pulses. The finger clip photoelectrode was levelled with the right atrium in all measurements, skin close to the clip and room temperature were recorded. RESULTS: From the mean individual values the following time discrete values were calculated for the NIR signal (n = 41): Tp = 882.3 +/- 142.6 ms, Tmax = 214.8 +/- 28.3 ms, Td = 452.7 +/- 32.4 ms, Tdec = 667.4 +/- 133.6 ms, Tag = 237.9 +/- 36.3 ms, Tmax/Tdec = 0.34 +/- 0. 07, Td/Tdec = 0.7 +/- 0.11. For each parameter the individual standard deviation during 10 repetitive measurements (26 subjects) ranged between 2.2 and 6.1%. The time sequences found were not significantly different between the individual fingers. A linear relationship between changes in time sequence and changes in amplitude was found in all tested subjects (mean r = 0.96). CONCLUSION: These results show, that the values obtained with time discrete NIRP are highly reproducible and show an individual SD of less than 6.5% under steady state conditions. The linear relationship between time sequence and amplitude found in the present study has to be confirmed in further studies on patients with pathologies of the macro- and microcirculation.

Adult↗
PubMedDate not supplied

Prevalence of cyclic changes in limb volume (volumotion) of male patients with knee injury and the effects of ischemia/reperfusion due to tourniquet.

During surgery of limbs tourniquet up to a maximum of 2 h is frequently applied which may cause ischemia/reperfusion injury (IRI). During this condition the presence of vasomotion may have consequences for the perfusion and nutritive state of the tissues. We used a noninvasive plethysmographic method to investigate periodic changes in limb circumference (volumotion) in healthy male patients (n = 24) undergoing surgery for knee injury. To facilitate surgery a tourniquet was applied to the thigh, which caused an IRI of the leg. Results are given as mean of all values +/- SEM. Immediately after tourniquet release (duration 57.75 +/- 5.19 min) blood lactate levels in the femoral vein increased significantly from 1.40 +/- 0.08 to 2.59 +/- 0.20 mmol/l (p < 0.001) and pH fell from 7.39 +/- 0.01 to 7.32 +/- 0.01 (p < 0.001). Preoperatively 10 out of 24 patients (42%) showed signs of volumotion on the injured leg with a periodicity ranging from 0.8 to 6.9 cycles/min, whereas none showed volumotion in the control leg (p < 0.001). In the second measurement, taken after surgery and reperfusion while peripheral sympathetic nerves were blocked, 7 out of 18 patients (39%) showed volumotion on the injured leg and 0 on the control leg (p < 0.004). 6 h after IRI, volumotion was observed in 11 out of 17 patients (65%) on the injured leg and in 1 patient (6%) on the control leg (p < 0.001). The mean volume change in the patients with volumotion on the injured leg was 0.057 +/- 0.007 ml/100 ml tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

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.

Aged↗