Petter Aadahl

Regional Anesthesia for Endovascular Treatment of Abdominal Aortic Aneurysms

Purpose: To investigate the feasibility of regional anesthesia for endovascular repair of abdominal aortic aneurysms (AAAs). Methods: Since February 1995, 21 patients (17 men and 4 women; median age 67 years, range 49 to 80) have been treated with endovascular technique for true infrarenal AAA using Mialhe Stentor bifurcated grafts. A single dose of spinal anesthesia combined with epidural anesthesia was used in all procedures. Electrocardiography and arterial blood pressure were monitored. Results: No cases of emboli, hematoma, or graft migration were seen, and there were no reoperations or conversions to open operation. Arterial blood pressure was stable at a satisfactory level from induction of anesthesia throughout the procedure, and there was no period of clinically significant hypotension during any implantation. One patient died on the second postoperative day from cardiac and renal insufficiency. Three endoleaks were observed during the procedure; one healed spontaneously within 5 weeks, and the other two were repaired by endovascular techniques after 1 and 4 months, respectively. During follow-up, one patient died at 6 months from pancreatic carcinoma. Conclusions: The application of regional anesthesia is feasible for endovascular treatment of AAA. The arterial blood pressure remained stable throughout the procedure, and all patients, with two exceptions, were mobilized on the first day and placed on a regular diet. Based on these early results, it appears that regional anesthesia is feasible, effective, and safe for endovascular AAA repair.

Continuous measurement of blood glucose: validation of a new intravascular sensor.

Background: Tight blood glucose control is used extensively in perioperative and critically ill patients. Several studies, however, have shown contradictory effects on patient outcomes. A major problem of these studies has been inadequate control of the prime variable, blood glucose. This paper describes the validation of a new intravascular continuous blood glucose sensor. Methods: The glucose sensor was placed in the superior caval vein of seven anesthetized pigs. Sensor readings were compared with arterial blood gas readings. Fluctuations in blood glucose were created using intravenous glucose and insulin. A total of 807 paired sensor and blood gas readings were obtained. Results: The sensor was tested with a range of blood glucose values (0.63–15.75 mM [mean bias, 0.0131 mM]). Analysis using Bland–Altman plots yielded 95% limits of agreement at −0.908 and 0.934 mM. There were 121 paired measurements with a mean value below 2.2 mM, yielding 95% limits of agreement at −0.553 and 0.466 mM. Conclusions: The performance of the sensor was in agreement with blood gas measurements in a wide range of glucose values. For the clinician, it is noteworthy that performance was equally good in the hypoglycemic area.

Rectal lactate levels in endoluminal microdialysate during routine coronary surgery

The aim of this prospective study was to determine the feasibility of intestinal endoluminal microdialysis as a new method for clinical monitoring of the adequacy of splanchnic perfusion in the large bowel. A microdialysis catheter for continuous lactate, glycerol, glucose and pyruvate measurements attached to a tonometric catheter was placed into the lumen of the recto‐sigmoid junction prior to surgery in 13 patients undergoing elective cardiac surgery with cardiopulmonary bypass (CPB). Lactate was also measured in blood and muscle. CPB was associated with a 10‐fold increase in luminal lactate from 0.16 (0.01) to 1.67 (0.38) mmol.l−1 (p < 0.001). Muscular lactate increased from baseline levels 1.20 (0.21) to 1.77 (0.36) mmol.l−1 during CPB (p = 0.01), but the muscular lactate–pyruvate ratio remained unchanged. Arterial lactate increased only slightly from 0.9 (0.05) to 1.1 (0.06) mmol.l−1 (p = 0.027) during CPB. Increased lactate concentrations in the large bowel during CPB are suggestive of local lactate production consistent with impaired oxygen delivery. Intestinal endoluminal microdialysis is a potential clinically applicable method for monitoring intestinal metabolism. Combined with tonometry, microdialysis provides the opportunity to monitor both circulation and metabolism in the rectal mucosa.

CEREBRAL HAEMODYNAMICS DURING THORACIC- AND THORACOABDOMINAL AORTIC ANEURYSM REPAIR

OBJECTIVE To investigate cerebral haemodynamics during operations for thoracic and thoracoabdominal aortic aneurysms. DESIGN Prospective clinical study. MATERIAL 10 patients operated on consecutively with resection for thoracic (5) or thoracoabdominal aortic (5) aneurysms. METHODS Blood flow velocity of the middle cerebral artery was measured through a temporal approach using a TC Doppler with a 2 MHz probe. Recordings were made during induction of anaesthesia and performed continuously before, during and after cross-clamping of the aorta. RESULTS Following 10 min. of aortic cross-clamping blood flow velocity of the middle cerebral artery increased from 44 to 55 cm/s (p < 0.01). A further increase to 69 cm/s (p < 0.01) was observed 5 min after declamping. The pulsatility index averaged 0.74 increasing to 1.21 (p < 0.05) at clamping and 0.87 (p < 0.05) after declamping. CONCLUSION There was an increased blood flow velocity of the middle cerebral artery during cross-clamping of the descending thoracic aorta in patients operated on for thoracic and thoracoabdominal aortic aneurysms. This increase in cerebral blood flow and blood volume could explain the acute increase in cerebrospinal fluid pressure observed during cross-clamping of the thoracic aorta.

Three-dimensional endovascular navigation with electromagnetic tracking: ex vivo and in vivo accuracy.

Purpose To evaluate the accuracy of a 3-dimensional (3D) navigation system using electromagnetically tracked tools to explore its potential in patients. Methods The 3D navigation accuracy was quantified on a phantom and in a porcine model using the same setup and vascular interventional suite. A box-shaped phantom with 16 markers was scanned in 5 different positions using computed tomography (CT). The 3D navigation system registered each CT volume in the magnetic field. A tracked needle was pointed at the physical markers, and the spatial distances between the tracked needle positions and the markers were calculated. Contrast-enhanced CT images were acquired from 6 swine. The 3D navigation system registered each CT volume in the magnetic field. An electromagnetically tracked guidewire and catheter were visualized in the 3D image and navigated to 4 specified targets. At each target, the spatial distance between the tracked guidewire tip position and the actual position, verified by a CT control, was calculated. Results The mean accuracy on the phantom was 1.28±0.53 mm, and 90% of the measured distances were ≤1.90 mm. The mean accuracy in swine was 4.18±1.76 mm, and 90% of the measured distances were ≤5.73 mm. Conclusion This 3D navigation system demonstrates good ex vivo accuracy and is sufficiently accurate in vivo to explore its potential for improved endovascular navigation.

Side-branched AAA stent graft insertion using navigation technology: a phantom study.

Objective: To evaluate the feasibility of a side-branched stent graft inserted in an artificial abdominal aortic aneurysm (AAA), using navigation technology, and to compare procedure duration and dose of radiation with control trials. Methods: A custom-made stent graft was inserted into an artificial AAA using navigation technology in combination with fluoroscopy. The navigation technology was based on three-dimensional visualization of computed tomography data and electromagnetic tracking of microposition sensors. The stent graft had integrated position sensors in side branch and introducer and was guided into proper position with the aid of three-dimensional images. Control trials were performed with fluoroscopy alone. Results: It was feasible to insert a side-branched stent graft using three-dimensional navigation technology. The navigation-guided trials had a significantly lower X-ray load (p < 0.001), but showed no difference in the duration of the procedures (p = 0.34) as compared with controls. Conclusions: Inserting a side-branched stent graft in an artificial AAA using navigation technology is feasible. Side-branched stent grafts and navigation systems may become useful in the endovascular treatment of complicated aortic aneurysms.

Continuous monitoring of the bronchial epithelial lining fluid by microdialysis.

BackgroundContents of the epithelial lining fluid (ELF) of the bronchi are of central interest in lung diseases, acute lung injury and pharmacology. The most commonly used technique broncheoalveolar lavage is invasive and may cause lung injury. Microdialysis (MD) is a method for continuous sampling of extracellular molecules in the immediate surroundings of the catheter. Urea is used as an endogenous marker of dilution in samples collected from the ELF. The aim of this study was to evaluate bronchial MD as a continuous monitor of the ELF.MethodsMicrodialysis catheters were introduced into the right main stem bronchus and into the right subclavian artery of five anesthetized and normoventilated pigs. The flowrate was 2 μl/min and the sampling interval was 60 minutes. Lactate and fluorescein-isothiocyanate-dextran 4 kDa (FD-4) infusions were performed to obtain two levels of steady-state concentrations in blood. Accuracy was defined as [bronchial-MD] divided by [arterial-MD] in percent. Data presented as mean ± 95 percent confidence interval.ResultsThe accuracy of bronchial MD was calculated with and without correction by the arteriobronchial urea gradient. The arteriobronchial lactate gradient was 1.2 ± 0.1 and FD-4 gradient was 4.0 ± 1.2. Accuracy of bronchial MD with a continuous lactate infusion was mean 25.5% (range 5.7–59.6%) with a coefficient of variation (CV) of 62.6%. With correction by the arteriobronchial urea gradient accuracy was mean 79.0% (57.3–108.1%) with a CV of 17.0%.ConclusionUrea as a marker of catheter functioning enhances bronchial MD and makes it useful for monitoring substantial changes in the composition of the ELF.

Three-Dimensional Electromagnetic Navigation vs. Fluoroscopy for Endovascular Aneurysm Repair: A Prospective Feasibility Study in Patients:

Purpose To evaluate the in vivo feasibility of a 3-dimensional (3D) electromagnetic (EM) navigation system with electromagnetically-tracked catheters in endovascular aneurysm repair (EVAR). Methods The pilot study included 17 patients undergoing EVAR with a bifurcated stent-graft. Ten patients were assigned to the control group, in which a standard EVAR procedure was used. The remaining 7 patients (intervention group) underwent an EVAR procedure during which a cone-beam computed tomography image was acquired after implantation of the main stent-graft. The 3D image was presented on the navigation screen. From the contralateral side, the tip of an electromagnetically-tracked catheter was visualized in the 3D image and positioned in front of the contralateral cuff in the main stent-graft. A guidewire was inserted through the catheter and blindly placed into the stent-graft. The placement of the guidewire was verified by fluoroscopy before the catheter was pushed over the guidewire. If the guidewire was incorrectly placed outside the stent-graft, the procedure was repeated. Successful placement of the guidewire had to be achieved within a 15-minute time limit. Results With in 15 minutes, the guidewire was placed correctly inside the stent-graft in 6 of 7 patients in the intervention group and in 8 of 10 patients in the control group. In the intervention group, fewer attempts were needed to insert the guidewire correctly. Conclusion A 3D EM navigation system, used in conjunction with fluoroscopy and angiography, has the potential to provide more spatial information and reduce the use of radiation and contrast during endovascular interventions. This pilot study showed that 3D EM navigation is feasible in patients undergoing EVAR. However, a larger study must be performed to determine if 3D EM navigation is better than the existing practice for these patients.

Microcirculation of the spinal cord during proximal aortic cross clamping

The relationship between the cerebrospinal fluid pressure (CSFP) and the microcirculation of the spinal cord was studied during cross-clamping (XC) of the thoracic aorta in pigs. CSFP was recorded via an intrathecal catheter. The microcirculation was measured by the laser Doppler technique using a needle probe inserted percutaneously into the spinal cord. A left thoracotomy was performed, and the thoracic aorta was cross-clamped for 30 minutes distal to the left subclavian artery. Prior to XC a pulsatile flux recording from the spinal cord (SCF) was observed. Following cross-clamping of the aorta SCF was dramatically reduced ( P P SCF increased 51% following removal of 1 ml of cerebrospinal fluid ( P Occlusion of the azygos vein increased CSFP 1.3 mmHg ( P P In conclusion, SCF was significantly influenced by changes in CSFP during XC of the thoracic aorta. The findings support the theory that removal of spinal fluid during XC of the thoracic aorta may increase the perfusion pressure to the spinal cord, thereby improving its blood supply.

Pharmacology of Intravenous Insulin Administration: Implications for Future Closed-Loop Glycemic Control by the Intravenous/Intravenous Route

BACKGROUND Our group is attempting to construct an artificial pancreas based on intravenous glucose monitoring and intravenous insulin delivery. To do so, the pharmacology of intravenous insulin administration must be studied. We used a pig model to determine the inherent lag time in the insulin/blood glucose system. The goal was to suggest a method that reduces the blood glucose level in a rapid and yet predictable manner. METHODS Six pigs received continuous intravenous insulin infusions at 0.04, 0.08, or 0.4 IU/kg/h for 60 min. Two pigs received short-term intravenous infusions at 0.4 IU/kg/h for 2 min, repeated five times at 60-min intervals. Four animals received five intravenous insulin bolus injections at 60-min intervals, two at 0.01 IU/kg and two 0.02 IU/kg, with a final dose of 0.04 IU/kg. The blood glucose level was measured every 1-5 min. RESULTS A high rate of intravenous insulin infusion led to rapid declines in blood glucose levels. The same rapid decline was achieved when the infusion was halted after 2 min. Using the latter method and with intravenous insulin boluses, blood glucose levels started to rise again after approximately 15-20 min. Insulin boluses led to a first detectable decrease in blood glucose level after 2-6 min and to a maximum rate of decrease shortly thereafter. CONCLUSIONS We found that intravenous bolus injections of insulin lowered blood glucose levels rapidly and predictably. Repetitive small intravenous insulin boluses together with an accurate and fast-responding intravascular continuous glucose monitor should be studied as a method of closed-loop glycemic control.