Can electrophysiological assessments of brain function be useful to the intensive care physician in daily clinical practice?

Mismatch negativity to predict subsequent awakening in deeply sedated critically ill patients

BACKGROUND

Mismatch negativity (MMN) is the neurophysiological correlate of cognitive integration of novel stimuli. Although MMN is a well-established predictor of awakening in non-sedated comatose patients, its prognostic value in deeply sedated critically ill patients remains unknown. The aim of this prospective, observational pilot study was to investigate the prognostic value of MMN for subsequent awakening in deeply sedated critically ill patients.

METHODS

MMN was recorded in 43 deeply sedated critically ill patients on Day 3 of ICU admission using a classical 'odd-ball' paradigm that delivers rare deviant sounds in a train of frequent standard sounds. Individual visual analyses and a group level analysis of recordings were performed. MMN amplitudes were then analysed according to the neurological status (awake vs not awake) at Day 28.

RESULTS

Median (inter-quartile range) Richmond Assessment Sedation Scale (RASS) at the time of recording was -5 (range, from -5 to -4.5). Visual detection of MMN revealed a poor inter-rater agreement [kappa=0.17, 95% confidence interval (0.07-0.26)]. On Day 28, 30 (70%) patients had regained consciousness while 13 (30%) had not. Quantitative group level analysis revealed a significantly greater MMN amplitude for patients who awakened compared with those who had not [mean (standard deviation) = -0.65 (1.4) vs 0.08 (0.17) μV, respectively; P=0.003).

CONCLUSIONS

MMN can be observed in deeply sedated critically ill patients and could help predict subsequent awakening. However, visual analysis alone is unreliable and should be systematically completed with individual level statistics.

Glucose metabolism in cardiovascular surgery

During the past few years, it has become evident that metabolic control is a major determinant of postoperative outcomes, not only for diabetic patients but for all patients undergoing surgery.In cardiac and vascular surgery, myocardial ischemia is a common challenge and the management of hyperglycemia should be part of the strategy aimed at optimizing cardiac protection during these types of surgery, since performed in high risk patients. Little informations are available on the relation between glucose substrate and the type of anesthesia and few studies have been performed on glucose metabolism in the perioperative risk assessment as well as on intraoperative and post surgical management of hyperglycemia in patients submitted to cardiac and vascular surgery. Evidence exists that even slight increased in glycemia are detrimental for patients (diabetic and non) elective for cardiac and vascular surgery, though the precise details of the timing of insulin therapy, the desired target serum glucose level, and the duration of therapy are so far to be completely elucidated. Anesthestiologists can therefore affect outcome by simply preserving a normal blood glucose concentration initiating in the operating room. The challenge to optimize glucose control should begin during preoperative evaluation.

No difference indicated in electroencephalographic power spectral analysis in 3- and 6-month-old infants fed soy- or milk-based formula

Increasing concern has been recently raised on the possible effects of soy-derived phyto-oestrogens on the development of cognitive functions in infants. However, limited studies have been conducted to date, and no data have been made available for determining whether infant soy formula can affect normal development of the human brain. We compared electroencephalographic (EEG) spectral power derived from high-density recordings of infants fed milk-based or soy formula (46 fed milk-based formula and 39 fed soy formula) at 3 and 6 months of age. The spectral parameters included absolute power, relative power and spectral edge frequency (SEF) at 85%, 90% and 95% levels. The frequency domain contained four bands (0.1-3, 3-6, 6-9 and 9-12 Hz). EEG signals were collected from eight brain areas in each hemisphere. The results showed that the highest spectral power was mainly distributed in the low-frequency bands and was predominant in the frontal and anterior temporal areas. None of the spectral variables significantly differed between the soy- and milk-fed infants (anova, all P > 0.2). However, significant effects were indicated on the SEFs for factors of sex, age and brain area (all P < 0.01). Hemispheric differences in the absolute and relative power were also indicated. Our results suggest that the EEG power spectral development of soy-fed infants does not differ from that of infants fed milk-based formula. In addition, EEG spectral development appears more advanced in female than in male infants at 6 months.

Early renal replacement therapy in patients with postoperative acute liver failure associated with acute renal failure: effect on postoperative outcomes

BACKGROUND

Acute liver failure after major surgical procedures is associated with a high risk of multiple organ failure, including acute renal failure. The optimal time to initiate renal replacement therapy for acute renal failure is controversial because of the poor overall clinical outcomes.

STUDY DESIGN

From July 2002 to January 2005, all patients who had no history of liver disease, but developed acute liver failure and subsequent renal failure requiring renal replacement therapy after major surgery, at a surgical intensive care unit, were retrospectively analyzed. Patients were divided into early or late dialysis groups based on an arbitrary blood urea nitrogen cut-off level of 80 mg/dL before renal replacement therapy.

RESULTS

Eighty consecutive patients (21 women), with a mean age of 57.8+/-17.0 (SD) years, comprised the study group. The late dialysis group (n=26) had a higher ICU mortality rate (p=0.02) and a lower renal function recovery rate (p=0.02) than the early dialysis group (n=54). Fifty-three (66.3%) patients died during their ICU stay. Independent risk factors for ICU mortality were renal replacement therapy modality (intermittent hemodialysis versus continuous venous-venous hemofiltration; odds ratio [OR]=4.32, 95% CI 1.26 to 14.79; p=0.02), predialysis APACHE II score> 20 (OR=6.52, 95% CI 1.61 to 26.36; p < 0.01), and late dialysis (OR=4.01, 95% CI 1.05 to 15.27; p=0.04).

CONCLUSIONS

The mortality rate in postoperative patients with acute liver failure-associated acute renal failure was very high. Earlier initiation of renal replacement therapy, based on the predialysis blood urea nitrogen level, with continuous venous-venous hemofiltration might provide a better ICU survival rate.