No abstract

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.

Two anaesthetic procedures that did not include nitrous oxide were compared in a randomised study of 50 patients for tympanoplasty and tympanoscopy: propofol given for induction and maintenance, and thiopentone-isoflurane given for induction and maintenance, respectively. Induction in the first group was with a bolus injection of propofol and the same agent was given for the duration of anaesthesia by continuous intravenous administration. Thiopentone was given until loss of the eyelash reflex and anaesthesia maintained with isoflurane 0.4-2.0%. Analgesia was achieved in both groups by fentanyl given intravenously and by local injection of mepivacaine with ornipressin. The two patient groups were analysed for age, sex and weight as well as for side effects during the induction, maintenance and recovery periods, such as coughing, vomiting, venous pain, spontaneous movements, singultus, headaches, dysrhythmias and psychic disorders possibly due to anaesthesia. Side effects were moderate in both groups. Recovery time was statistically significantly shorter in the propofol group and the patients in this group appeared to be much more aware after recovery than those in the thiopentone-isoflurane group.

Objective: The aim of this study was to evaluate the long-term results of aortic stent placement in patients with infrarenal aortic occlusive disease. Methods: Between April 1996 and May 2014, 34 patients with symptomatic infrarenal atherosclerotic aortic stenosis or subtotal aortic occlusion underwent percutaneous angioplasty with primary aortic stent implantation. There were 21 patients with Fontaine stage of the peripheral arterial disease (PAD) II, 5 patients with stage III, and 8 patients with stage IV. One patient withdrew informed consent and was excluded from further analysis. Results: Patients (n = 34, mean age: 62 ± 12 years) were followed for a mean period of 81 months. There were 2 procedure-related access-related complications. Six patients died during follow-up from non-procedure-related causes. Eight patients had late recurrence of symptoms during follow-up. Only in 2 cases, symptomatic recurrences were due to aortic in-stent stenosis (77 and 132 months after the primary stent implantation). Additionally, these 2 patients required therapy for PAD progression distal to the aorta. Five patients required further surgical or endovascular reconstruction for PAD progression distal to the aorta. In another case, clinical treatment failure was due to the progression of atherosclerotic lesion in the perirenal, nonstented part of the abdominal aorta. The mean estimated primary patency rate was 185.6 months (95% confidence interval: 161.3-209.8). Conclusion: Endovascular stent implantation is a safe and long-term effective strategy for the treatment of infrarenal aortic occlusive disease. In our study, the recurrence of symptoms was observed mainly due to atherosclerosis progression by multilevel disease with associated infrainguinal occlusive lesions but not to aortic in-stent restenosis. The prognostic advantage for this relatively young cohort of patients can be the possibility to repeat a percutaneous procedure with less technical difficulties when compared to surgical revision.

There is a high incidence of intraoperative awareness during cardiac surgery. Mid-latency auditory evoked potentials (MLAEP) reflect the primary cortical processing of auditory stimuli. In the present study, we investigated MLAEP and explicit and implicit memory for information presented during cardiac anaesthesia. PATIENTS AND METHODS. Institutional approval and informed consent was obtained in 30 patients scheduled for elective cardiac surgery. Anaesthesia was induced in group I (n = 10) with flunitrazepam/fentanyl (0.01 mg/kg) and maintained with flunitrazepam/fentanyl (1.2 mg/h). The patients in group II (n = 10) received etomidate (0.25 mg/kg) and fentanyl (0.005 mg/kg) for induction and isoflurane (0.6-1.2 vol%)/fentanyl (1.2 mg/h) for maintenance of general anaesthesia. Group III (n = 10) served as a control and patients were anaesthetized as in I or II. After sternotomy an audiotape that included an implicit memory task was presented to the patients in groups I and II. The story of Robinson Crusoe was told, and it was suggested to the patients that they remember Robinson Crusoe when asked what they associated with the word Friday 3-5 days postoperatively. Auditory evoked potentials were recorded awake and during general anaesthesia before and after the audiotape presentation on vertex (positive) and mastoids on both sides (negative). Auditory clicks were presented binaurally at 70 dBnHL at a rate of 9.3 Hz. Using the electrodiagnostic system Pathfinder I (Nicolet), 1000 successive stimulus responses were averaged over a 100 ms poststimulus interval and analyzed off-line. Latencies of the peak V, Na, Pa were measured. V belongs to the brainstem-generated potentials, which demonstrates that auditory stimuli were correctly transduced. Na, Pa are generated in the primary auditory cortex of the temporal lobe and are the electrophysiological correlate of the primary cortical processing of the auditory stimuli. RESULTS. None of the patients had an explicit memory of intraoperative events. Five patients in group I, one patient in group II, and no patients in group III showed implicit memory of the intraoperative tape message. They remembered Robinson Crusoe spontaneously when they were asked their associations with Friday. In the awake state AEP peak latencies were in the normal range. During general anaesthesia in group I, the peaks Na, Pa did not increase in latency or decrease in amplitude before and after the audiotape presentation. The primary cortical complex Na/Pa could be identified as in the awake state. In contrast, in group II Na, Pa showed a marked increase in latency and a decrease in amplitude or were completely suppressed. CONCLUSIONS. During general anaesthesia auditory information can be processed and remembered postoperatively by an implicit memory function, when the electrophysiological conditions of primary cortical stimuli processing is preserved. Implicit memory can be observed more often when high-dose opioid analgesia is combined with receptor-binding agents like the benzodiazepines than u...