Cognitive function after hypocapnic hyperventilation

Effects of Memantine in a Mouse Model of Postoperative Cognitive Dysfunction

Persistent impairment in cognitive functioning postoperatively is reported by clinical and animal studies, and is labeled as postoperative cognitive dysfunction (POCD). Evidence points to an exaggerated neuroinflammatory response resulting from peripheral systemic inflammation after surgery, with subsequent cytokine-induced glutamatergic excitotoxicity and synaptic impairment. These immunological changes, among many others, are also observed in Alzheimer’s disease. Memantine is an N-methyl-D-aspartate receptor (NMDAR) antagonist commonly used to treat Alzheimer’s disease. Surprisingly, little research exists on the role of memantine in preventing POCD. The purpose of this study is to investigate the effects of memantine on a spectrum of cognitive functions postoperatively. Mice were divided into 3 groups and each received treatment for 4 weeks. Placebo groups received a placebo then underwent either a sham procedure or a laparotomy procedure. The memantine group received memantine hydrochloride then underwent a laparotomy procedure. Cognitive tests were performed on postoperative days (POD) 1 and 7. Compared to sham-operated mice, placebo groups that underwent a laparotomy procedure showed impaired memory in the Morris water maze test, higher anxiety-like behavior in the open field and the elevated plus maze tests, increased depression-like behavior in the tail suspension test, and lack of preference for social novelty in the three-chamber test. On the other hand, memantine-treated mice that underwent a laparotomy procedure showed enhanced memory on POD7, improved depression-like behavior on POD1 and POD7, enhanced preference for social novelty on POD1, and no improvement in anxiety-like behavior. These findings suggest a potential protective effect of memantine in mice postoperatively on memory, depression-like behavior, and preference for social novelty.

Pathogenesis and treatment of post-operative cognitive dysfunction

Cognitive disorders common in the post-operative period, are the post-operative delirium (POD) and the post-operative cognitive dysfunction (POCD). The Diagnostic and Statistical Manual of Mental Disorders (DSM) does not mention POCD as a separate disease entity, and thus little is known about the pathogenesis of this disorder. The aim of this study was to review, detect and highlight the most important data cited, regarding pathogenesis mechanisms and treatment of the post-operative cognitive dysfunction (POCD). The study was carried out from March 2015 to June 2015. Literature review was achieved by searching a number of bibliographic databases including PubMed, Google Scholar and SCOPUS, surveying published articles from 1955 to 2014. As far as the selection criteria, the material consists of scientific articles published mainly over the last fifteen years, while material published before 2000 was selected because it was considered to be important. This review showed that deficits are observed in one or more discrete areas of the patient's mental state, such as attention, concentration, memory, psychomotor speed and more. This condition is usually developed over a period of more than a week or month after surgery and is more common in elderly patients. Mechanisms that have been proposed to explain this phenomenon are hyperventilation, hypotension, cerebral microemboli and inflammatory mechanisms. Its differential diagnosis will be made mainly from delirium. POCD treatment will first include the exclusion of any other serious diseases that can cause organic psychosyndrome and then focus on the actual symptoms.

Hyperventilation and attention: effects of hypocapnia on performance in a stroop task

This study aimed to investigate the effect of hypocapnia on attentional performance. Hyperventilation, producing hypocapnia, is associated with physiological changes in the brain and with subjective symptoms of dizziness, concentration problems and derealization. In this study (N=42), we examined cognitive performance on a Stroop-like task, following either 3 min of hypocapnic or normocapnic overbreathing. Both overbreathing trials were run on separate days, each preceded by a baseline trial with the same task during normal breathing. More and other symptoms were reported after hypocapnia compared to normocapnia. Also, more errors were made and progressively slower reaction times (RT's) were observed during recovery from hypocapnia. These performance deficits were only found in participants characterized by apneas. The number of symptoms did not correlate with RT's or errors. The pattern of data suggested that hypoxia, as a result of apneas during recovery from hypocapnia, caused the cognitive performance deficit.

The effects of hypocapnic ventilation on mental function in elderly patients undergoing cataract surgery

Mental function was studied using the Rivermead Behavioural Memory Test and the Unprepared Simple Reaction Time test in 83 elderly patients for cataract surgery. Three groups of patients were studied: Group N (n = 40) whose lungs were ventilated to a mean PaCO2 of 4.9 kPa, Group H (n = 30) who were hyperventilated to a mean PaCO2 of 2.9 kPa, and Group L (n = 13) who received local anaesthesia for surgery. The psychometric tests were administered on the day before the operation, and 4 days and 4 weeks after the operation. Statistically significant changes in the performance of hyperventilated patients could not be demonstrated using these tests.

Influence of auditory or visual warning on visual reaction time with variations of subjects' alertness

The purpose of the study was to determine the effect of visual and auditory warning on visual reaction time with variations of subjects' alertness. An experimental group of 30 subjects was tested with an auditory or visual warning signal; foreperiods lasted 3, 2, and 4 sec. Reaction time was shorter as alertness improved and with an auditory warning signal. Comparable measures in a control group showed that visual reaction time was shorter when an auditory warning signal was used.

Effects of anaesthesia on some aspects of mental functioning of surgical patients

Plastic surgery patients undergoing either local (LA) or general (GA) anaesthesia of at least forty-five minutes' duration and a non-patient control group were used to examine the extent and duration of deterioration in mental functioning following GA and the factors influencing such deterioration. Mental functioning was assessed by a battery of six tests administered one week before anaesthesia, four days after anaesthesia and six weeks after anaesthesia. Mental performance of GA patients but not of LA patients was significantly impaired on the fourth postoperative day. Six weeks after anaesthesia GA patients were still performing significantly below controls. There was marked variation in the pattern of recovery, some GA patients failing to regain their pre-operative level of performance after six weeks. Severity of deterioration following general anaesthesia was significantly correlated with habitual caffeine consumption.

Reaction time course during weaning from respirator treatment

Ten patients who developed disturbed mental function during respirator weaning were studied. They were investigated during respirator treatment and 1 h after start of spontaneous ventilation with continuous reaction time measurements and clinical ratings. During the spontaneous ventilation the reaction times increased and the patients experienced fatigue. PaCO2 was higher and PaO2 was lower than during respirator treatment. A significant correlation was found between individual differences of reaction times and arterial blood gas levels in the two conditions, whereas no general correlation between reaction times and arterial blood gas levels could be established. The findings must be considered tentative, but the results of this study indicate the value of continuous reaction time measurements for quantitative assessment of mental status during respirator treatment.

Recovery after general anaesthesia for laparoscopy

Recovery after two methods of light general anaesthesia for gynaecological laparoscopy was studied. For this purpose, 30 patients were divided into two equal groups (A and B). The patients in group A were anaesthetized with thiopentone, fentanyl and suxamethonium infusion, while the patients in group B received inhalation anaesthesia with enflurane and suxamethonium infusion. Both groups were normoventilated with nitrous-oxide and oxygen mixture. A battery of recovery tests was applied in the recovery room. The patients who received inhalation anaesthesia with enflurane scored better in the recovery tests, and reached preoperative values after 3 h in the recovery room. Inhalation anaesthesia with enflurane was accepted well by the patients and provided good working conditions for the surgeons. It is suitable for outpatient gynaecological laparoscopy because it ensures rapid recovery.

Carbon dioxide homeostasis and recovery after general anaesthesia

The influence of different levels of carbon dioxide during general anaesthesia on postoperative recovery was studied. Sixty female patients were divided into two age groups. Thirty patients were over 60 years old and 30 patients were under 46 years old. Artificial ventilation with added carbon dioxide during general anaesthesia with thiopentone, nitrous oxide-oxygen, alcuronium and fentanyl was used. According to the arterial CO2 tension, patients were allocated to subgroups: hypercarbic, PaCO2 7.3 kPa, normocarbic, PaCO2 5.3 kPa and two different levels of hypocarbia: older patients PaCO2 3.7 kPa and younger patients PaCO2 2.9 kPa. As criteria for recovery, a battery of recovery tests and postoperative questionnaires were used. Regardless of age, patients subjected to hypercarbic ventilation scored better in the recovery tests than patients subjected to normo- or hypocarbia. Normocarbic ventilation also gave better results than hypocarbic ventilation. The level of hypocarbia used in the older patients and that used in the younger patients, though different, resulted in nearly the same deterioration of scoring in the recovery tests. This deterioration was seen in some patients up to 48 h postoperatively. No subjective differences were elicited from the questionnaires after various types of ventilation.

Some adverse physiological effects of hypocarbia and methods of maintaining normocarbia during controlled ventilation--a review

Some of the adverse physiological effects of hypocarbia are described and the methods available to maintain the PaCO2 within or near the normal range during controlled ventilation are reviewed.