Phase-difference and spectroscopic imaging for monitoring of human brain temperature during cooling.

Decrease of the human brain temperature was induced by intranasal cooling. The main purpose of this study was to compare the two magnetic resonance methods for monitoring brain temperature changes during cooling: phase-difference and magnetic resonance spectroscopic imaging (MRSI) with high spatial resolution. Ten healthy volunteers were measured. Selective brain cooling was performed through nasal cavities using saline-cooled balloon catheters. MRSI was based on a radiofrequency spoiled gradient echo sequence. The spectral information was encoded by incrementing the echo time of the subsequent eight image records. Reconstructed voxel size was 1×1×5 mm(3). Relative brain temperature was computed from the positions of water spectral lines. Phase maps were obtained from the first image record of the MRSI sequence. Mild hypothermia was achieved in 15-20 min. Mean brain temperature reduction varied in the interval <-3.0; -0.6>°C and <-2.7; -0.7>°C as measured by the MRSI and phase-difference methods, respectively. Very good correlation was found in all locations between the temperatures measured by both techniques except in the frontal lobe. Measurements in the transversal slices were more robust to the movement artifacts than those in the sagittal planes. Good agreement was found between the MRSI and phase-difference techniques.

Endovascular total aortic arch replacement by in situ stent graft fenestration technique.

Open surgical total aortic arch replacement is a demanding procedure which carries a substantial morbidity and mortality. A less invasive endovascular option is endovascular stent grafting using in situ fenestrations. After thoracic stent graft deployment in the arch, fenestrations are made for the major arch vessels. During this procedure, antegrade cerebral perfusion is maintained using a temporary bypass from the left femoral artery to both carotids perfusing both the anterior and posterior cerebral circulation. The endovascular technique and devices used are herein described.

Noninvasive monitoring of brain temperature during mild hypothermia.

The main purpose of this study was to verify the feasibility of brain temperature mapping with high-spatial- and reduced-spectral-resolution magnetic resonance spectroscopic imaging (MRSI). A secondary goal was to determine the temperature coefficient of water chemical shift in the brain with and without internal spectral reference. The accuracy of the proposed MRSI method was verified using a water and vegetable oil phantom. Selective decrease of the brain temperature of pigs was induced by intranasal cooling. Temperature reductions between 2 degrees C and 4 degrees C were achieved within 20 min. The relative changes in temperature during the cooling process were monitored using MRSI. The reference temperature was measured with MR-compatible fiber-optic probes. Single-voxel (1)H MRS was used for measurement of absolute brain temperature at baseline and at the end of cooling. The temperature coefficient of the water chemical shift of brain tissue measured by MRSI without internal reference was -0.0192+/-0.0019 ppm/degrees C. The temperature coefficients of the water chemical shift relative to N-acetylaspartate, choline-containing compounds and creatine were -0.0096+/-0.0009, -0.0083+/-0.0007 and -0.0091+/-0.0011 ppm/degrees C, respectively. The results of this study indicate that MRSI with high spatial and reduced spectral resolutions is a reliable tool for monitoring long-term temperature changes in the brain.

The kinetics of lipid micro-emboli during cardiac surgery studied in a porcine model.

OBJECTIVE: To study the kinetics of lipid micro-emboli during cardiac surgery. DESIGN: Eleven pigs were studied. Seven of these were put on extracorporeal circulation. A shed blood phantom consisted of blood, saline and radioactive triolein was added to the circuit. Both venous and arterial blood samples were taken at short intervals. Four animals were used to study renal kinetics without extracorporeal circulation. The same kind of shed blood phantom was infused into the ascending aorta. Samples were taken from the renal artery and vein. All samples were analyzed for radioactivity by scintillation counting. RESULTS: A median 130-fold increase in radioactivity was seen in the blood and was quickly eliminated. Systemic first-pass wedging was found to be 62%. The first-pass elimination in the kidney was 77%. No radioactivity was found in urine. CONCLUSIONS: This study shows that the turnover of lipid micro-emboli is fast, and that the majority of the emboli are trapped on their first passage through the capillary system. No evidence was found of a renal excretion of these lipid emboli.

Differential distribution of lipid microemboli after cardiac surgery.

BACKGROUND: Lipid microemboli found in shed blood during cardiac surgery have been shown to block capillaries of the brain postoperatively. In this study, the distribution of lipid microemboli in different regions of the brain and other organs was examined. A novel porcine model using radioactive lipid particles was used. METHODS: Ten animals (2 controls and 8 cases) were anesthetized and put on cardiopulmonary bypass. A shed-blood phantom was produced from arterial blood, saline, and tritium-labeled triolein. The phantom was infused into the cardiopulmonary bypass circuit. Tissue samples were taken postmortem from examined organs and prepared for scintillation counting. Levels of radioactivity were used as a measure of the uptake of lipid microemboli. RESULTS: High levels of radioactivity were found in kidney and spleen (5 to 10 times higher than in the other organs investigated). In the brain, radioactivity was found in all regions examined. The gray matter of cerebrum showed the highest level of the regions examined. CONCLUSIONS: This study shows that embolization of lipids is not a phenomenon restricted to the brain, but affected all the organs examined. The high levels found in the kidneys, and the relatively high levels in the gray matter of the cerebrum further legitimize the debate on the impact lipid microemboli has on postoperative kidney and cognitive dysfunction.

A new method of selective, rapid cooling of the brain: an experimental study.

PURPOSE: To determine whether retrograde perfusion of cooled blood into one internal jugular vein (IJV) in the pig can selectively reduce the brain temperature without affecting the core body temperature (CBT). METHODS: In 7 domestic pigs, the left IJV was catheterized on one side and a catheter placed with the tip immediately below the rete mirabile. Thermistors were placed in both brain hemispheres and the brain temperature continuously registered. Thermistors placed in the rectum registered the CBT. From a catheter in the right femoral vein blood was aspirated with the aid of a roller pump, passed through a cooling device, and infused into the catheter in the left IJV at an initial rate of 200 ml/min. RESULTS: Immediately after the start of the infusion of cooled blood (13.8 degrees C) into the IJV, the right brain temperature started to drop from its initial 37.9 degrees C and reached 32 degrees C within 5 min. By increasing the temperature of the perfusate a further drop in the brain temperature was avoided and the brain temperature could be kept around 32 degrees C during the experiment. In 4 of the animals a heating blanket was sufficient to compensate for the slight drop in CBT during the cooling period. CONCLUSIONS: We conclude that brain temperature can be reduced in the pig by retrograde perfusion of the internal jugular vein with cooled blood and that the core body temperature can be maintained with the aid of a heating blanket.

Particle separation using ultrasound can be used with human shed mediastinal blood.

BACKGROUND: Shed mediastinal blood collected by cardiotomy suction has been shown to be a large contributor to lipid microemboli ending up in different organs. The aim of this study was to test the separation efficiency on human shed blood of a new separation method developed to meet this demand. METHODS: Shed mediastinal blood collected from the pericardial cavity of 13 patients undergoing cardiac surgery with cardiopulmonary bypass was collected. The blood was processed in an eight-channel parallel PARSUS separator, and separation efficiency was determined. RESULTS: Erythrocyte recovery, in terms of a separation ratio, varied between 68% and 91%. Minor electrolyte changes took place, where levels of sodium increased and levels of potassium and calcium decreased. CONCLUSION: This study demonstrates that PARSUS technology can be used on human shed mediastinal blood with good separation efficiency. The technology is, thereby, suggested to have future clinical relevance.