Central venous catheters may be a potential source of massive air emboli during vascular procedures involving extracorporeal circulation: an experimental study.

Central venous catheters are mandatory during every major procedure involving extracorporeal circulation. Air emboli potentially could enter the circulation through this device when negative pressure is applied in the venous cannula. The following experimental study was initiated by a fatal massive air embolus during a vascular procedure involving cardiopulmonary bypass. An experimental setup was established, simulating a real scenario. The experiment was performed with a 40% glycerol/water mixture which exhibits properties and fluid dynamics close to blood. A heart-lung machine provided circulation of the fluid. The flow was adjusted according to the gravitational status. A triple-lumen central venous catheter with one line open to air was lowered into the liquid. The disconnected lumen of the central venous catheter was manipulated so it approached and was located in close proximity to the venous cannula. An air flow of up to 300 ml/min could be obtained from the central venous catheter with a flow in the cardiopulmonary bypass circuit of 2.3 L/min. A linear relationship was observed between flow in the circuit and air flow. Consecutive measurements proved consistent with acceptable results, proving that a disconnected central venous catheter might, under certain circumstances, be a source of massive air emboli during cardiopulmonary bypass.

In vivo characterization of ischemic small intestine using bioimpedance measurements.

The standard clinical method for the assessment of viability in ischemic small intestine is still visual inspection and palpation. This method is non-specific and unreliable, and requires a high level of clinical experience. Consequently, viable tissue might be removed, or irreversibly damaged tissue might be left in the body, which may both slow down patient recovery. Impedance spectroscopy has been used to measure changes in electrical parameters during ischemia in various tissues. The physical changes in the tissue at the cellular and structural levels after the onset of ischemia lead to time-variant changes in the electrical properties. We aimed to investigate the use of bioimpedance measurement to assess if the tissue is ischemic, and to assess the ischemic time duration. Measurements were performed on pigs (n = 7) using a novel two-electrode setup, with a Solartron 1260/1294 impedance gain-phase analyser. After induction of anaesthesia, an ischemic model with warm, full mesenteric arterial and venous occlusion on 30 cm of the jejunum was implemented. Electrodes were placed on the serosal surface of the ischemic jejunum, applying a constant voltage, and measuring the resulting electrical admittance. As a control, measurements were done on a fully perfused part of the jejunum in the same porcine model. The changes in tan δ (dielectric parameter), measured within a 6 h period of warm, full mesenteric occlusion ischemia in seven pigs, correlates with the onset and duration of ischemia. Tan δ measured in the ischemic part of the jejunum differed significantly from the control tissue, allowing us to determine if the tissue was ischemic or not (P < 0.0001, F = (1,75.13) 188.19). We also found that we could use tan δ to predict ischemic duration. This opens up the possibility of real-time monitoring and assessment of the presence and duration of small intestinal ischemia.

Comparison of four different FIM configurations--a simulation study.

Focused impedance measurements (FIM) are used in several fields, and address the problem of measuring the volume impedance of an object within a volume conductor. Several electrode configurations are possible, and these have different properties. Sensitivity fields of four configurations have been investigated. We present one new development of an existing FIM configuration, and we made finite element models of the configurations to analyse and compare them both graphically and numerically. The models developed have a variable-sized mesh that allows us to build complex models that fit easily in computer memory. We found that one configuration in particular, FIM4, was superior to the others in most aspects. We also analysed the effects of very high sensitivities in and under the electrodes. We found that even if the sensitivity is very high under the electrodes, the effects of inhomogeneities were not as high as one might expect.

A novel method for indirectly monitoring arterial pO(2) during cardiopulmonary bypass.

Arterial blood oxygen tension (P(a)O(2)) is a vital variable that has to be monitored during cardiopulmonary bypass (CPB). The aim of this study was to develop an alternative method for continuously P(a)O(2) monitoring during CPB, based on measurements of exhaust-gas from an oxygenator. A total of 15 adult patients undergoing CPB (n = 81 samples) were included in a study in order to develop an appropriate algorithm for P(a)O(2) estimation based on exhaust gas monitoring of the oxygen tension (P(ex)O(2)). The acquired data was used as a basis for developing a statistical prediction algorithm designed for continuously estimating the P(a)O(2)-level based on exhaust gas data in combination with data from the surrounding medical equipment. A new instrument was developed in order to implement this P(a)O(2) prediction algorithm and was tested on five patients (n = 39 samples). When the first sample was used for calibrating the instrument, the mean (SD) error was 8.7% (7.3%) with a 95% CI of 6.1-11.3%. Our results indicate that a pO(2)-exhaust monitoring device with adequate precision is obtainable, but further studies are required.

Integrated neuronavigation system with intraoperative image updating.

OBJECTIVE: Recently, MRI has entered the field of image-guided surgery as a new intraoperative imaging modality. In spite of its obvious benefits, this type of iMRI scanner has some drawbacks that have limited its utilization. The goal of the work presented here was to overcome some of these disadvantages. METHODS: A system that allows intraoperative images to be acquired during surgery and have the ability to conduct surgery outside the constraints of the narrow gap of the open magnet was implemented. Ability to conduct tasks inside the scanner with real-time image guidance was also maintained. The system allowed navigation with neuronavigation tools both inside the gap of an open magnet and outside the magnet, utilizing two different optical camera-sets and a dynamic reference frame. Automatic patient registration was implemented. RESULTS: The average difference between tracking position measured outside and inside the magnet was 0.8 +/- 0.1 mm. CONCLUSION: In the work presented in this note we have introduced a dynamic reference frame to compensate for transport of the patient to a location outside the scanner employing a second camera set. The integrated system showed adequate accuracy.