Ketamine Effects on Energy Metabolism, Functional Connectivity and Working Memory in Healthy Humans.

Working memory (WM) is a crucial resource for temporary memory storage and the guiding of ongoing behavior. N-methyl-D-aspartate glutamate receptors (NMDARs) are thought to support the neural underpinnings of WM. Ketamine is an NMDAR antagonist that has cognitive and behavioral effects at subanesthetic doses. To shed light on subanesthetic ketamine effects on brain function, we employed a multimodal imaging design, combining gas-free calibrated functional magnetic resonance imaging (fMRI) measurement of oxidative metabolism (CMRO 2 ), resting-state cortical functional connectivity assessed with fMRI, and WM-related fMRI. Healthy subjects participated in two scan sessions in a randomized, double-blind, placebo-controlled design. Ketamine increased CMRO 2 and cerebral blood flow (CBF) in prefrontal cortex (PFC) and other cortical regions. However, resting-state cortical functional connectivity was not affected. Ketamine did not alter CBF-CMRO 2 coupling brain-wide. Higher levels of basal CMRO 2 were associated with lower task-related PFC activation and WM accuracy impairment under both saline and ketamine conditions. These observations suggest that CMRO 2 and resting-state functional connectivity index distinct dimensions of neural activity. Ketamine’s impairment of WM-related neural activity and performance appears to be related to its ability to produce cortical metabolic activation. This work illustrates the utility of direct measurement of CMRO 2 via calibrated fMRI in studies of drugs that potentially affect neurovascular and neurometabolic coupling.

The use of propofol to prevent fetal deceleration during electroconvulsive therapy treatment.

Electroconvulsive therapy has been demonstrated to be relatively safe during pregnancy for both the mother and the fetus. One risk to the fetus is cardiac deceleration during the grand mal seizure. We present a case of a young woman in her second trimester of pregnancy with bipolar depression. She had a prolonged seizure on her second electroconvulsive therapy treatment, which led to transient fetal bradycardia that self-corrected as preparations were underway for an emergency cesarean delivery. A change of her anesthetic agent from methohexital to propofol attenuated the seizure duration resulting in the elimination of further events of fetal cardiac deceleration and a successful outcome for both mother and fetus.

Sedation during regional anesthesia: inhalation versus intravenous.

PURPOSE OF REVIEW: Sedation of patients either with or without regional anesthesia is discussed to ascertain sedation requirements in the two groups. The differences between 'monitored anesthesia care' and conscious sedation are defined. Several current and promising methods with which we can evaluate a patient's degree or level of sedation are assessed. Also noted are safety concerns regarding monitoring solutions for patients undergoing monitored anesthesia care. Well established techniques, including some which are decidedly 'low tech', are examined. Several routes of intravenous administration are discussed along with patient variables. Sevoflurane sedation is mentioned with regards to administration, advantages and drawbacks. RECENT FINDINGS: Several modalities have been studied for evaluation of a patient's level of sedation, some of which have little applicability in the operating room. Processed electroencephalographic monitoring has tremendous promise but is currently not reliable enough to assess sedation level. Sevoflurane has a role in sedation, providing the limitations are understood. One drawback of sevoflurane is its greater degree of disinhibition when compared with intravenous agents, necessitating conversion to general anesthesia. SUMMARY: Evaluating the degree of patient sedation is a need that technology has yet to meet. Several techniques have been tried in intensive care units but have little utility in the operating room. Utilization of processed electroencephalogram waveforms has the greatest potential but is of limited value at the present time. Sevoflurane is demonstrated to have a limited role in sedation but may prove useful in specific circumstances.