Postoperative reading speed does not indicate implicit memory in elderly cardiac patients after propofol and remifentanyl anaesthesia

Implicit Memory and Anesthesia: A Systematic Review and Meta-Analysis

General anesthesia should induce unconsciousness and provide amnesia. Amnesia refers to the absence of explicit and implicit memories. Unlike explicit memory, implicit memory is not consciously recalled, and it can affect behavior/performance at a later time. The impact of general anesthesia in preventing implicit memory formation is not well-established. We performed a systematic review with meta-analysis of studies reporting implicit memory occurrence in adult patients after deep sedation (Observer's Assessment of Alertness/Sedation of 0-1 with spontaneous breathing) or general anesthesia. We also evaluated the impact of different anesthetic/analgesic regimens and the time point of auditory task delivery on implicit memory formation. The meta-analysis included the estimation of odds ratios (ORs) and 95% confidence intervals (CIs). We included a total of 61 studies with 3906 patients and 119 different cohorts. For 43 cohorts (36.1%), implicit memory events were reported. The American Society of Anesthesiologists (ASA) physical status III-IV was associated with a higher likelihood of implicit memory formation (OR:3.48; 95%CI:1.18-10.25, p < 0.05) than ASA physical status I-II. Further, there was a lower likelihood of implicit memory formation for deep sedation cases, compared to general anesthesia (OR:0.10; 95%CI:0.01-0.76, p < 0.05) and for patients receiving premedication with benzodiazepines compared to not premedicated patients before general anesthesia (OR:0.35; 95%CI:0.13-0.93, p = 0.05).

Transcanal Cochlear Implantation Under Monitored Anesthesia Care

OBJECTIVE

Given the associated risk of general anesthesia in elderly patients with cardiovascular disease, the authors set out to determine the feasibility of transcanal cochlear implantation under local anesthesia with monitored anesthesia care.

METHODS

A 70-year-old man with a history of coronary artery bypass grafting, diabetes mellitus, and an American Society of Anesthesiologists Class III cardiac status underwent cochlear implantation under local with monitored anesthesia care.

RESULT

With the described technique and regimen of intravenous remifentanil and dexmedetomidine, the patient tolerated the 60-minute procedure without tachycardia, hyper- or hypotension, or cardiac ischemia.

CONCLUSION

Cochlear implantation using the pericanal electrode technique performed under local anesthesia with monitored anesthesia care is possible in patients at risk for undergoing general anesthesia for cochlear implantation.

[Cognitive dysfunction after abdominal surgery in elderly patients]

Elderly patients often suffer from postoperative cognitive deficits (POCD) after serious surgical operations. The reasons for this are not well understood. We investigated the influence of the invasiveness of the operation and the duration of the operation as well as the patient's preoperative physical status on measures of cognitive dysfunction. In a prospective study 59 elderly patients (mean age 69.2 years) were subjected to a neuropsychological test battery and a questionnaire following an abdominal surgical operation. The postoperative recovery with a focus on memory function was assessed using the Wechsler Memory Scale (WMS) seven days after the operation. Self-reported cognitive deficits were studied using the a questionnaire of experienced attention deficits (FEDA) three months after the operation. Postoperative psychological and self-reported test results varied as a function of the invasiveness and the duration of the operation. After more invasive operations patients reported a stronger deficit in activities of daily living and a reduction in drive than after less invasive operations. In addition, the duration of anesthesia influenced the experienced deficits. The self-reported deficits were more strongly influenced by the features of the operation than the psychological test data. The physical status of the patients according to the American Society of Anesthesiologists (ASA) along with the duration of anesthesia as covariate was identified as a good predictor for the cognitive recovery post operation.

[Ureteroscopy under intravenous analgesia with remifentanil]

In a prospective study, from September 2000 to September 2001, all ureteroscopies ( n=140) were performed under local and intravenous patient controlled analgesia using continuous infusion of remifentanil (Ultiva). The dosage of 0.15 micro g/kg/min was adapted to changing intraoperative pain (range 0.08-0.30 micro g/kg/min). Preoperative sedation with midazolam 2 mg was given 5 min prior to ureteroscopy. The efficacy of monitored anesthesia care ("Big MAC") was quantified by the patient using a visual analogue pain scale. A total of 97.1% (136/140) of the procedures were performed and finished under remifentanil. Only four male patients underwent conversion to general anesthesia due to insufficient analgesia. All but one patient would choose remifentanil again for first line anesthesia. Significant differences in pain scale values were noticed for male/female patients and ureteroscopies above/below the iliac vessel crossing. Side effects were rare being mainly hypoxic events (pO(2)<90% in 5.1%). Indication, intraoperative procedure, average surgery time (24 min), complications and primary success rate (96.6/90/63.3% stone free for distal/mid/proximal ureter, respectively) did not differ from the control group under general anesthesia. Ureteroscopies with remifentanil are safe, universally applicable because of refifentanil's organ independent esterase metabolism and as effective as general anesthesia. There is no need for PACU stay for patients due to the ultra-short drug half-life, and therefore remifentanil is cost effective and perfect in an outpatient setting.

Absence of explicit and implicit memory in unconscious patients using a TCI of propofol

BACKGROUND

Episodes of implicit memory have been described during propofol anaesthesia. It remains unclear whether implicit memory is caused by short periods of awareness or occurs in an unconscious subject.

METHODS

Sixty patients were randomized in an experimental group (EG), a control group (CG) and a reference group (RG). Loss of consciousness (LOC) was obtained by progressive stepwise increases of propofol using a target-controlled infusion device (Diprifusor, Alaris Medical Systems, San Diego, CA). A tape containing 20 words was played to the patients in the CG before the start of anaesthesia and to the patients in the EG at a constant calculated concentration of propofol associated with LOC. The tape was not played to the patients in the RG. Three memory tests were performed postoperatively.

RESULTS

Explicit and implicit memories were evidenced in the CG but not in the EG.

CONCLUSION

In our group of young ASA I/II patients, in the absence of any noxious stimulus, no implicit or explicit memory was found when the calculated concentration of propofol using a Diprifusor was maintained at the level associated with LOC.

Implicit memory varies as a function of hypnotic electroencephalogram stage in surgical patients

Previous studies have observed a correlation of implicit memory with certain electroencephalogram (EEG) measures during anesthesia. Here, we tested the relationship between hypnotic depth determined by computer system (Narcotrend(TM)) and implicit memory in anesthetized patients, assessed by a postoperative reading speed test. Thirty-two patients undergoing laparoscopic herniotomy and 30 age-matched volunteer controls were included the study. All patients received IV midazolam 2-3 mg followed by an induction dose of propofol and remifentanil. The anesthesia was maintained with propofol and remifentanil infusions and cisatracurium. Each patient was exposed to 2 of 4 stories, repeated 6 times. The first story was presented during light to moderate hypnotic EEG stages, and the second story was presented during deep hypnosis. Presentation of stories was balanced between patients and hypnotic stages. The controls listened to the two stories without receiving anesthesia. The reading speed for the previously presented stories and two new stories was measured approximately 7 h later with a computer program. No signs of inadequate anesthesia were observed, and no explicit memories of intraoperative events were revealed by a structured interview. No change of reading speed was observed for words presented during deep hypnotic stages. In contrast, an increased reading speed of 20 ms per word was found for content words (i.e., nouns, verbs, and adjectives), but not for function words (conjunctions, prepositions, and so on), presented during light to moderate hypnotic stages. Increased reading speed for semantically rich content words indicates that anesthetized patients are able to process acoustic information during light and moderate, but not deep, hypnosis.

IMPLICATIONS

In this study, implicit memory was observed during general anesthesia at light to moderate, but not deep, hypnotic stages. Hypnotic stages were determined by a commercial electroencephalogram device, and implicit memory was measured by using a postoperative reading speed task. During lighter phases of anesthesia, patients should be protected against acoustic information that could negatively influence their postoperative outcome.