High risk of cognitive and functional decline after postoperative delirium. A three-year prospective study

BACKGROUND/AIMS

The aim of the study was to investigate the association of postoperative delirium with the outcomes of cognitive impairment, functional disability and death.

METHODS

Hip surgery patients aged 60 years or over (n = 200) underwent preoperative and daily postoperative assessment of their cognitive status during hospital stay. Outcome variables were determined at an average of 8 and 38 months after discharge from hospital.

RESULTS

Fourty-one patients developed postoperative delirium. Delirium was a strong independent predictor of cognitive impairment and the occurrence of severe dependency in activities of daily living. The associations were more marked for the long- than for the short-term outcome. Thirty-eight months after discharge from hospital, 53.8% of the surviving patients with postoperative delirium suffered from cognitive impairment, as compared to only 4.4% of the nondelirious participants. Logistic regression analysis adjusted for age, sex, medical comorbidity and preoperative cognitive performance revealed highly significant associations between delirium and cognitive impairment (OR = 41.2; 95% CI = 4.3-396.2), subjective memory decline (OR = 6.2; 95% CI = 1.5-25.8) and incident need for long-term care (OR = 5.6; 95% CI = 1.6-19.7).

CONCLUSION

The present study confirms a poor prognosis after delirium in elderly patients. The findings suggest that delirium does not simply persist for a certain time but also predicts a future cognitive decline with an increased risk of dementia.

Anesthetics drug pharmacodynamics

Anesthesia cannot be defined in an unambiguous manner. The essential components of general anesthesia are absence of consciousness and pain. This translates into two particular qualities: (1) sedation and hypnosis, i.e., mental blockade and (2) analgesia/antinociception, i.e., sensory blockade. Anesthetic actions on these two subcomponents are difficult to separate. On the one hand, very few anesthetics act exclusively on one of these components. On the other hand, these components are closely related to each other. Unconsciousness prevents (conscious) perception of pain, and nociception may serve as an arousal stimulus and change the level of sedation and hypnosis. The art of anesthesia lies in adequate dosing of drugs to reach both mental and sensory blockade. Drug administration can be based on pharmacokinetic considerations. Pharmacokinetic models allow an estimation of what happens to the administered drug in the body. Models with an effect site compartment may facilitate a tailored administration of anesthetic drugs. Finally, the quantification of pharmacodynamic effects allows a precise titration of drugs. Clinical assessment of mental blockade is often dichotomous, and therefore not very helpful to guide drug administration. Several scoring systems exist, but once consciousness is lost they become less reliable, in particular because reaction to stimuli is assessed, which mixes assessment of mental blockade with assessment of sensory blockade. Clinical assessment of analgesia requires a conscious patient, so antinociception is difficult to measure. Several methods of objective quantification on the basis of electrical brain activity are discussed including EEG and evoked potentials. Despite numerous indexes of the hypnotic component of anesthesia, there is no parameter that unambiguously quantifies the level of mental or sensory blockade.

The Narcotrend monitor and the electroencephalogram in propofol-induced sedation

BACKGROUND

The Narcotrend (NCT) is a one-channel electroencephalogram (EEG) monitor of the level of sedation. It is based on a visual EEG scoring system, which was developed by Loomis and modified by Kugler, to yield a visual expert classification (VEC) scheme for differentiation of six levels of sedation (A-F), which are subdivided into 16 substages. We designed the present study to test whether results of the automated classification of one-channel NCT input reflect those from VEC of five-channel EEG.

METHODS

Twelve healthy male volunteers received propofol using two different infusion regimens in a randomized, crossover design with concomitant NCT monitoring and VEC. Scoring results of NCT were compared with those of VEC.

RESULTS

During the infusion period, score differences of more than three substages were observed in 14 of 24 (= 58%) propofol administrations (4%-7% of total data). Often, the NCT indicated lighter sedation than VEC, which revealed more delta activity from nonfrontal leads. During recovery, NCT reported deeper sedation than VEC in 6 of 24 (= 25%) propofol administrations. Discordant trends (periods of at least five subsequent epochs with monotonic, but opposite trends for both NCT and VEC) were noted in 9 of 24 propofol administrations (37%). Furthermore, NCT had several periods when no staging information was displayed, varying from a few seconds to 10 min.

CONCLUSIONS

As the algorithm of NCT is proprietary and not accessible to the public, reasons for the observed differences between NCT and VEC cannot be analyzed and explanations must remain speculative.

Sevoflurane Affects Neurogenesis After Forebrain Ischemia in Rats

BACKGROUND

The effect of sevoflurane on the neuroregenerative potential after neuronal injury is unclear. We investigated the effect of low and high concentrations of sevoflurane on endogenous neurogenesis after cerebral ischemia.

METHODS

Anesthetized and ventilated rats were randomized to four different treatment groups. Groups 1 and 2: 1.4% sevoflurane; Groups 3 and 4: 2.8% sevoflurane. In Groups 1 and 3, no cerebral ischemia was induced (sham-operated). In Groups 2 and 4, 10 min of forebrain ischemia was induced by bilateral carotid artery occlusion plus hemorrhagic hypotension. Physiological variables were maintained constant. Bromodeoxyuridine was given as a marker of neurogenesis. After 28 days brains were perfused. Histopathological damage of the hippocampus was evaluated in hematoxylin and eosin (HE) stained sections using the HE-index (0 = no damage; 1 = 1%-10% damage; 2 = 11%-50% damage; 3 = 51%-100% damage). Immunohistochemistry was used to detect bromodeoxyuridine-positive neurons. Eight untreated rats were investigated as naive controls (Group 5).

RESULTS

In neither sham-operated group was histopathological damage or change in neurogenesis observed compared to naive controls. In rats anesthetized with 1.4% sevoflurane, cerebral ischemia caused mild neuronal damage (HE-index of 0.64 +/- 0.84) and increased neurogenesis by 60% when compared with respective sham-operated animals; with 2.8% sevoflurane, the HE-index was 1.22 +/- 1.14, and the number of newly generated neurons increased by 230% when compared with respective sham-operated animals.

CONCLUSION

The present data suggest that high concentrations of sevoflurane stimulate neurogenesis in the dentate gyrus after cerebral ischemia.

Teletherapeutic drug administration by long distance closed-loop control of propofol †

BACKGROUND

The objective of this pilot study was to investigate the feasibility of an EEG-controlled closed-loop administration of propofol over a long distance of about 200 km.

METHODS

We performed a teletherapeutic propofol infusion during total intravenous anaesthesia with propofol in 11 patients undergoing general surgery. The teletherapeutic system consisted of a computer at the patient site in Munich and a computer at the control site in Erlangen, which were connected via the internet through a virtual private network. The patient's EEG signal was sent to the control site computer, where the median frequency (MEF) of the EEG power spectrum was calculated. The propofol infusion, determined by a model-based adaptive feedback algorithm to maintain a MEF of 1.5 to 2 Hz, was sent to the patient site computer connected to the infusion pump. The quality of the control was assessed by the performance error defined as the percentage deviation of the measured MEF from the set point and the necessity of interventions by the anaesthetist at the patient site.

RESULTS

During closed-loop administration of propofol [83 (52) min] the median performance error of the system was - 4.6 (4.4)% and the median absolute performance error was 18.8 (5.7)%. From a total number of 10 905 transmitted EEG epochs, there were five epochs with transmission errors, without further consequences for drug control. In one patient, teletherapy was stopped because the internet connection was interrupted.

CONCLUSIONS

Teletherapeutic drug administration could be realized over a longer distance. Further studies have to investigate the practicability and safety of teletherapeutic drug control in anaesthesia.

Corresponding minimum alveolar concentrations of isoflurane and isoflurane/nitrous oxide have divergent effects on thalamic nociceptive signalling

BACKGROUND

Suppression of nociceptive signalling in the thalamus is considered to contribute significantly to the anaesthetic state. Assuming additivity of anaesthetic mixtures, our study assessed the effects of corresponding minimum alveolar concentrations (MACs) of isoflurane and isoflurane/nitrous oxide on thalamic nociceptive signalling.

METHODS

Nociceptive response activity (elicited by controlled radiant heat stimuli applied to cutaneous receptive fields) of single thalamic neurons was compared in rats anaesthetized at approximately 1.1 and approximately 1.4 MAC isoflurane with that at approximately 1.1 and approximately 1.4 MAC isoflurane/nitrous oxide.

RESULTS

Under baseline anaesthesia ( approximately 0.9 MAC isoflurane), noxious stimulation elicited excitatory responses in all neurons (n = 19). These responses were uniformly suppressed at approximately 1.1 and approximately 1.4 MAC isoflurane. In contrast, at approximately 1.1 and approximately 1.4 MAC isoflurane/nitrous oxide, excitatory responses no different to baseline were still present in 64 and 37% of the neurons, respectively.

CONCLUSIONS

These data demonstrate a pronounced nitrous oxide-induced response variability. It appears that, with respect to thalamic transfer of nociceptive information, the interaction of isoflurane and nitrous oxide may not be compatible with the concept of additivity and that the antinociceptive potency of nitrous oxide is considerably less than previously reported.

Nitrous oxide (N2O) pre- and postsynaptically attenuates NMDA receptor-mediated neurotransmission in the amygdala

The gaseous anaesthetic N(2)O displays analgesic, anxiolytic, and amnesic properties and has addictive psychedelic effects. N(2)O can further act as a neuroprotective agent, but may also become neurotoxic under certain conditions. Here, we employed whole-cell patch-clamp techniques in acute brain slices, and electrical afferent and infrared-guided laser stimulation to examine how N(2)O (65%) can affect NMDA receptor (NMDAR)-mediated synaptic transmission to principal neurons (PNs) of the adult murine basolateral amygdala (BLA). The BLA plays a critical role in anaesthetic-induced amnesia, the formation of aversive memories, as well as in fear and addictive behaviour. We evoked NMDAR-mediated excitatory postsynaptic currents (NMDAR-EPSCs) in PNs of the BLA (BLA-PNs). We found these currents to be markedly decreased by N(2)O via pre- and postsynaptic actions: Without changing their kinetics and open probability, N(2)O impeded the voltage-dependent channel opening of NMDARs in BLA-PNs and diminished their unitary conductance as estimated by non-stationary fluctuation analysis. In addition, our data speak in favour of a N(2)O-produced reduction in the probability of glutamate release at the synapses generating the NMDAR-EPSCs. It is conceivable that these effects not only contribute to anaesthesia and anxiolysis, but also have bearings on learning and memory as well as excitotoxicity in the amygdala.

Application of Generalized Dynamic Neural Networks to Biomedical Data

This paper reviews the application of continuous recurrent neural networks with time-varying weights to pattern recognition tasks in medicine. A general learning algorithm based on Pontryagin's maximum principle is recapitulated, and possibilities of improving the generalization capabilities of these networks are given. The effectiveness of the methods is demonstrated by three different real-world examples taken from the fields of anesthesiology, orthopedics, and radiology.

The influence of injection rate on the hypnotic effect of propofol during anesthesia: a randomized trial

OBJECTIVE

Previous studies suggested that slow injection of propofol may increase the hypnotic effect during induction of anesthesia. The aim of the present study was therefore to investigate whether injection rate of propofol has an influence on its maximum effect.

DESIGN

Randomized, single-blind trial.

SETTING

This study has been carried out in the operating rooms of a university hospital. An anesthesiologist and a resident performed the study with the aid of changing nursing staff.

PARTICIPANTS

We investigated 99 unpremedicated patients aged 18 to 60 years with American Society of Anesthesiologists (ASA) physical status 1-3.

INTERVENTIONS

Anesthesia was induced by intravenous injection of propofol (2 mg/kg). Propofol was manually injected in group 1 over a period of 5 s; in group 2 (120-s injection interval), and in group 3 (240-s injection interval), propofol was administered by an injection pump. After loss of consciousness, mask ventilation was performed with 100% oxygen. Bispectral index (BIS) was used to measure the hypnotic effect of propofol. After the decrease of BIS to the minimum value (i.e., maximum hypnotic effect) and the following increase of BIS to 60, the study period was finished and anesthesia was performed according to clinical criteria.

OUTCOME MEASURES

We analyzed whether injection speed has an influence on the maximum hypnotic effect of a given dose of propofol (2 mg/kg).

RESULTS

BIS(min) marks the maximum electroencephalogram (EEG) effect of the propofol bolus as measured by the BIS. The lowest mean BIS(min) was measured in group 1 (28.7 +/- 10.3). In group 2, BIS(min) was 33.0 (+/-13.9), and in group 3, BIS(min) was 36.4 (+/-11.0). There were no significant differences between group 2 and groups 1 or 3, but there were significant differences between groups 1 and 3. In group 1, BIS(min) was reached after 102.91 s (+/-44.20), in group 2 after 172.33 s (+/-29.76), and in group 3 after 274.21 s (+/-45.40). These differences were statistically significant for all comparisons. In summary, the lowest value for BIS(min) was achieved in the group with the fastest rate of propofol injection (group1, 5 s). The highest BIS(min) was obtained in the group with the slowest rate of injection (group 3, 240 s). The hemodynamic parameters were not significantly different among groups.

CONCLUSIONS

The hypnotic peak effect of propofol is lower with extremely slow injection (240 s versus 5 s). For clinically usual injection rates (5 s and 120 s), there was no significant difference in propofol peak effect.

Contributions of GABAergic and glutamatergic mechanisms to isoflurane-induced suppression of thalamic somatosensory information transfer

Indications for a pivotal role of the thalamocortical network in producing the state of anesthesia have come from in vivo animal studies as well as imaging studies in humans. We studied possible synaptic mechanisms of anesthesia-induced suppression of touch perception in the rat's thalamus. Thalamocortical relay neurons (TCNs) receive ascending and descending glutamatergic excitatory inputs via NMDA and non-NMDA receptors (AMPAR) and are subjected to GABA(A)ergic inhibitory input which shapes the sensory information conveyed to the cortex. The involvement of these synaptic receptors in the suppressive effects of the prototypic volatile anesthetic isoflurane was assessed by local iontophoretic administration of receptor agonists/antagonists during extracellular recordings of TCNs of the ventral posteromedial nucleus responding to whisker vibration in rats anesthetized with isoflurane concentrations of approximately 0.9 vol.% (baseline) and approximately 1.9 vol.% (ISO high). ISO high induced a profound suppression of response activity reflected by a conversion of the sustained vibratory responses to ON responses. Administration of NMDA, AMPA, or GABA(A)R antagonists caused a reversal to sustained responses in 88, 94 and 88% of the neurons, respectively, with a recovery to baseline levels of response activity. The data show that the block of thalamocortical transfer of tactile information under ISO high may result from an enhancement of GABA(A)ergic inhibition and/or a reduction of glutamatergic excitation. Furthermore, they show that the ascending vibratory signals still reach the thalamic neurons under the high isoflurane concentration, indicating that this input is resistant to isoflurane while the attenuation of excitation may be brought about at the corticothalamic glutamatergic facilitatory input.

Concurrent recording of AEP, SSEP and EEG parameters during anaesthesia: a factor analysis

BACKGROUND

Spontaneous EEG, mid-latency auditory evoked potentials (AEP) and somatosensory evoked potentials (SSEP) have been used to monitor anaesthesia. This poses the question as to whether or not EEG, AEP and SSEP vary in parallel with varying conditions during surgical anaesthesia.

METHODS

A total of 81 variables (31 EEG, 22 SSEP, 28 AEP) were simultaneously recorded in 48 surgical patients during anaesthesia. A total of 307 cases of the 81 variables in stable anaesthetic states were recorded. A factor analysis was performed for this data set.

RESULTS

Sixteen variables were excluded because of multicollinearity. We extracted 13 factors with eigenvalues >1, representing 78.3% of the total variance, from the remaining 65 x 307 matrix. The first three factors represented 12%, 11% and 10% of the total variance. Factor 1 had only significant loadings from EEG variables, factor 2 only significant loadings from AEP variables and factor 3 only significant loadings from SSEP variables.

CONCLUSION

EEG, AEP and SSEP measure different aspects of neural processing during anaesthesia. This gives rise to the hypothesis that simultaneous monitoring of these quantities may give additional information compared with the monitoring of each quantity alone.

Sevoflurane Impairs Cerebral Blood Flow Autoregulation in Rats: Reversal by Nonselective Nitric Oxide Synthase Inhibition

In this study, we investigated the effects of 1.0 and 2.0 minimum alveolar anesthetic concentration (MAC) sevoflurane on cerebral blood flow (CBF) autoregulation before and after nonselective inhibition of nitric oxide (NO) synthase in rats. Rats were randomly assigned as follows: Group 1 (n = 8): 1.0 MAC sevoflurane; Groups 2 and 3 (n = 8 per group): 2.0 MAC sevoflurane. Assessment of autoregulation within a mean arterial blood pressure range of 140-60 mm Hg was performed by graded hemorrhage before and after administration of l-arginine methyl ester (l-NAME, 30 mg/kg IV, Groups 1 and 2) or during hypocapnia (Group 3). In 10 additional animals, brain tissue NO(2)(-) concentrations were measured at 1.0 and 2.0 MAC sevoflurane. CBF autoregulation was maintained with 1.0 MAC sevoflurane (Group 1) regardless of NO synthase status indicating that CBF autoregulation might not be related to NO availability. Sevoflurane dose-dependently increased brain tissue NO(2)(-) and impaired CBF autoregulation. Administration of l-NAME (Group 2) but not hypocapnia (Group 3) restored CBF autoregulation. This suggests that sevoflurane impairs the autoregulatory capacity secondary to an increase of the perivascular NO availability and questions the importance of basal cerebrovascular tone in terms of vasodilatory capacity during hypotensive challenges.

IMPLICATIONS

The present study suggests that the volatile anesthetic sevoflurane dose-dependently impairs cerebrovascular autoregulation by mechanisms secondary to increase of perivascular nitric oxide availability.

Long-term effects of hypothermia on neuronal cell death and the concentration of apoptotic proteins after incomplete cerebral ischemia and reperfusion in rats

BACKGROUND

The present study investigates the long-term effects of postischemic hypothermia on neuronal cell damage and concentration changes of apoptotic proteins after cerebral ischemia.

METHODS

Sixty-four Sprague-Dawley rats were anesthetized, intubated and ventilated with 2.0 Vol% isoflurane and 70% N2O/O2. After preparation the animals were randomly assigned to the following groups: group 1 (n = 32, fentanyl-N2O/normothermia 37.5 degrees C), and group 2 (n = 32, fentanyl-N2O/hypothermia 34.0 degrees C. Ischemia (45 min) was induced by common carotid artery occlusion plus hemorrhagic hypotension (MAP = 40 mmHg). Arterial blood gases and pH were maintained constant. After 1, 3, 7, or 28 days (each n = 8) the brains were removed, frozen and cut. Neuronal damage was assessed by analyzing Bax, Bcl-2, p53, and Mdm-2 proteins, activated caspases-3-positive and eosinophilic cells. A third group (n = 8) of untreated animals served as naive controls.

RESULTS

In hypothermic animals, Bax concentration was decreased by 50-70% over time compared to normothermia. On days 1 and 3, Bcl-2 was increased by 50% with hypothermia. The amount of activated caspase-3-positive cells in the ischemic hemisphere was 0.5% in the hypothermic and 1-2% in the normothermic animals. Of the hippocampal cells, 10-25% were eosinophilic in both groups over time.

CONCLUSION

The present data show that hypothermia prevents an ischemia-induced increase of the pro-apoptotic protein Bax for as long as 28 days and increases the concentration of the antiapoptotic protein Bcl-2 up to 3 days compared to normothermic animals. Therefore, after cerebral ischemia, hypothermia has the sustained neuroprotective potential to shift apoptosis-related proteins towards neuronal cell survival.