Seizure identification in the ICU using quantitative EEG displays

OBJECTIVE

To evaluate the diagnostic accuracy of 2 quantitative EEG display tools, color density spectral array (CDSA) and amplitude-integrated EEG (aEEG), for seizure identification in the intensive care unit (ICU).

METHODS

A set of 27 continuous EEG recordings performed in pediatric ICU patients was transformed into 8-channel CDSA and aEEG displays. Three neurophysiologists underwent 2 hours of training to identify seizures using these techniques. They were then individually presented with a series of CDSA and aEEG displays, blinded to the raw EEG, and asked to mark any events suspected to be seizures. Their performance was compared to seizures identified on the underlying conventional EEG.

RESULTS

The 27 EEG recordings contained 553 discrete seizures over 487 hours. The median sensitivity for seizure identification across all recordings was 83.3% using CDSA and 81.5% using aEEG. However, among individual recordings, the sensitivity ranged from 0% to 100%. Factors reducing the sensitivity included low-amplitude, short, and focal seizures. False-positive rates were generally very low, with misidentified seizures occurring once every 17-20 hours.

CONCLUSIONS

Both CDSA and aEEG demonstrate acceptable sensitivity and false-positive rates for seizure identification among critically ill children. Accuracy of these tools would likely improve during clinical use, when findings can be correlated in real-time with the underlying raw EEG. In the hands of neurophysiologists, CDSA and aEEG displays represent useful screening tools for seizures during continuous EEG monitoring in the ICU. The suitability of these tools for bedside use by ICU nurses and physicians requires further study.

Giant cavernous carotid aneurysms: clinical presentation in fifty-seven cases

OBJECTIVES

To review the presenting symptoms and ophthalmic findings of 57 patients with cavernous carotid aneurysms of giant size (> or = 2.5-cm diameter).

MATERIALS AND METHODS

Hospital charts of 57 patients with giant cavernous carotid aneurysms who presented to University Hospital in London, Ontario, Canada between 1961 and 1993 were reviewed. All patients were proven by cerebral angiography to have unruptured giant cavernous carotid aneurysms.

RESULTS

Forty-six patients (81%) were women (mean age, 54 years). The most common presenting symptoms were diplopia (89%), retroorbital pain (61%), headache (19%), diminished or blurred vision (14%), and photophobia (4%). The most common clinical sign was partial or complete ophthalmoplegia (93%). Trigeminal nerve involvement was found in 37% of patients. Other clinical signs included ptosis, decreased visual acuity, proptosis, and visual field defects.

CONCLUSIONS

This study characterizes a large group of patients with giant cavernous carotid aneurysms seen over a 30-year period at a single institution. As in previous studies, diplopia and retroorbital pain were the most common symptoms. The high incidence of ophthalmoplegia observed in this study may be explained by a greater compressive and/or ischemic effect of giant aneurysms compared with their smaller counterparts.

Anomalous fluorescence enhancement of Cy3 and cy3.5 versus anomalous fluorescence loss of Cy5 and Cy7 upon covalent linking to IgG and noncovalent binding to avidin

This study provides a critical examination of protein labeling with Cy3, Cy5, and other Cy dyes. Two alternate situations were tested. (i) Antibodies were covalently labeled with Cy dye succinimidyl ester at various fluorophore/protein ratios and the fluorescence of the labeled antibodies was compared to that of free Cy dye. (ii) Fluorescent biotin derivatives were synthesized by derivatizing ethylenediamine with one biotin and one Cy3 (or Cy5) residue. The fluorescence properties of these biotin-Cy dye conjugates were examined at all ligand/(strept)avidin ratios (0 </= n </= 4). The results showed an astounding discrepancy between Cy3 and Cy5: Cy3-labeled antibodies fluoresced very well, even at high Cy3/protein ratios, and the same applied to (strept)avidin with up to four bound biotin-Cy3 conjugates. In contrast, antibodies with six covalently bound Cy5 labels (obtained with the recommended procedure) were almost nonfluorescent, only at 2-3 Cy5 labels/IgG some moderate fluorescence was obtained. By analogy, the biotin-Cy3 conjugate fluoresced intensely, even at high ligand/avidin ratio, in contrast to the weakly fluorescing biotin-Cy5 conjugate. Three mechanisms are responsible for the discrepancy between Cy3 and Cy5. (i) Attachment of Cy3 to a protein's surface causes an anomalous enhancement in fluorescence (by 2-3-fold) while no enhancement occurs with Cy5. (ii) Mutual quenching of IgG-bound Cy dyes by resonance energy transfer is much more pronounced for Cy5 labels than for Cy3. (iii) In IgG with six bound Cy5 labels, about one-third of the labels adopt a nonfluorescent state which is characterized by a large UV-vis absorption maximum at 600 nm instead of at 650 nm. Cy3.5 was found to mimick the properties of Cy3, while Cy7, and to some extent also Cy5.5, were similar to Cy5. In conclusion the Cy dye series is divided into two groups: Antibodies with multiple Cy3 or Cy3.5 labels yield bright fluorescence while extensive quenching occurs in antibodies labeled with Cy5 and Cy7.

Mitochondrial neurogastrointestinal encephalomyopathy: an autosomal recessive disorder due to thymidine phosphorylase mutations

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive disorder defined clinically by severe gastrointestinal dysmotility; cachexia; ptosis, ophthalmoparesis, or both; peripheral neuropathy; leukoencephalopathy; and mitochondrial abnormalities. The disease is caused by mutations in the thymidine phosphorylase (TP) gene. TP protein catalyzes phosphorolysis of thymidine to thymine and deoxyribose 1-phosphate. We identified 21 probands (35 patients) who fulfilled our clinical criteria for MNGIE. MNGIE has clinically homogeneous features but varies in age at onset and rate of progression. Gastrointestinal dysmotility is the most prominent manifestation, with recurrent diarrhea, borborygmi, and intestinal pseudo-obstruction. Patients usually die in early adulthood (mean, 37.6 years; range, 26-58 years). Cerebral leukodystrophy is characteristic. Mitochondrial DNA (mtDNA) has depletion, multiple deletions, or both. We have identified 16 TP mutations. Homozygous or compound heterozygous mutations were present in all patients tested. Leukocyte TP activity was reduced drastically in all patients tested, 0.009 +/- 0.021 micromol/hr/mg (mean +/- SD; n = 16), compared with controls, 0.67 +/- 0.21 micromol/hr/mg (n = 19). MNGIE is a recognizable clinical syndrome caused by mutations in thymidine phosphorylase. Severe reduction of TP activity in leukocytes is diagnostic. Altered mitochondrial nucleoside and nucleotide pools may impair mtDNA replication, repair, or both.

Preparation of thiol-reactive Cy5 derivatives from commercial Cy5 succinimidyl ester

The present study offers reliable protocols for the preparation of new thiol-reactive Cy5 derivatives which are urgently needed for single molecule fluorescence microscopy. In a systematic approach, two alternate strategies were found for the extension of commercial amine-reactive Cy5 with thiol-reactive end groups. In the two-step method, Cy5 succinimidyl ester was first reacted with ethylenediamine under conditions which gave approximately 99% asymmetric "Cy5-amine" and only approximately 1% symmetric product with two Cy5 residues. Subsequently, "Cy5-amine" was derivatized with commercial heterobifunctional cross-linkers to introduce thiol-reactive end groups (maleimide or pyridyldithio). Alternatively, commercial Cy5 succinimidyl ester was reacted with a primary amine (MTSEA, methanethiosulfonylethylamine, or PDEA, pyridyldithioethylamine) or a secondary amine (PEM, piperazinylethylmaleimide) to give the corresponding thiol-reactive derivatives in a single step. Results were good for MTSEA, moderate for PEM, and poor for PDEA. An additional drawback of the one-step method was the need for rigorous removal of unreacted Cy5 succinimidyl ester, which would label lysine residues on probe molecules. It is concluded that, except for the Cy5-MTSEA conjugate, the two-step method is much more general, reliable, and easier to follow by the typical biophysicist, biologist, etc., for whose benefit, these procedures are being published. All thiol-reactive Cy5 derivatives showed similar absorption and fluorescence properties as Cy5 succinimidyl ester, and fluorescence was fully retained after binding to thiols on proteins. The kinetics of protein labeling was also examined in order to get an idea of proper labeling conditions.