Role of bedside electroencephalography in the adult intensive care unit during therapeutic neuromuscular blockade

Abstract

BACKGROUND: Size, weight and technical difficulties limit the use of ponderous strip chart electroencephalographs (EEGs) for real time evaluation of brain wave function in modern intensive care units (ICUs). Portable, computer processed, bedside EEGs provide real time brain wave appraisal for some brain functions during therapeutic neuromuscular blockade when the visual clues of the cerebral function disappear. RESULTS: Critically ill ICU patients are frequently placed in suspended animation by neuromuscular blockade to improve hemodynamics in severe organ system failure. Using the portable bedside EEG monitor, several cerebral functions were monitored continuously during sedation of selected patients in our ICU. CONCLUSIONS: The processed EEG is able to continuously monitor the end result of some therapeutics at the neuronal level when natural artifacts are suppressed or eliminated by neuromuscular blockade. Computer processed EEG monitoring may be the only objective method of assessing and controlling sedation during therapeutic musculoskeletal paralysis.

Figure 1

The ASPECT A1000^®, a typical brain wave monitor capable of real time bedside EEG.

Figure 2

(a) Cerebral electrical activity in a healthy volunteer, sitting in a quiet environment reading a magazine. Activity at normal sensitivity under 13 Hz to the left of the trend line. (b) A patient mildly sedated with lorazepam. The `monotony of sedation' pattern is illustrated. The spectral edge frequency (95% of brain wave activity occurring to the left of this line) demonstrates less variation between epochs.

Figure 3

(a) Cerebral function tracing of an ICU patient who is alert, oriented, and aware but stimulated and anxious due to the frenetic ICU environment. There is progressively increased activity in the beta (> 13 Hz) ranges. (b) The same patient sedated with a continuous infusion of 2 mg/h midazolam. Narcotics and benzodiazepines in sedative doses generally induce a gradual reduction in activity at higher alpha (8-13 Hz) and beta (> 13 Hz) frequencies and increased activity at lower frequencies, especially theta (4-8 Hz) and delta (<4 Hz). The `activity line' shifts symmetrically to the left.

Figure 4

Effect of midazolam as an intravenous sedative. This anxious patient was administered 2 mg intravenous midazolam during continuous EEG monitoring. The frequency diminished quickly in about 2 min, demonstrating the rapid clinical action of the short acting sedative. The action of propofol is similar to midazolam.

Figure 5

The effects of midazolam administration observed in a trend mode. Midazolam (4 mg) was administered in a bolus to an anxious patient at the arrow. Low frequency delta activity (thin line) shows a slow progressive increase. High frequency beta activity (thick line) decreases quickly and remains low.

Figure 6

Effect of lorazepam as an intravenous sedative. This anxious patient was administered 2 mg intravenous lorazepam during continuous EEG monitoring. The frequency diminished slowly in about 12 min, demonstrating the prolonged clinical action of the longer acting sedative.

Figure 7

Effect of fentanyl as an intravenous analgesic sedative. This anxious patient with postoperative pain was administered 100 mg intravenous fentanyl during continuous EEG monitoring. The frequency quickly diminished in about 3 min, demonstrating the rapid clinical action of the short-acting analgesic sedative.

Figure 8

Severe CNS depression produces increased amplitude in the delta band (<4 Hz) and very reduced activity in the other frequencies. (a) This patient with extremely toxic levels of ethyl alcohol was completely unresponsive on total life support, including mechanical ventilation. (b) The EEG tracing of a patient with certified brain death, established by EEG and clinical criteria. The activity line shifts to the right from electrical activity of the heart picked up by the monitor in the absence of brain electrical activity.

Figure 9

EEG assessment of cerebral responsiveness during therapeutic neuromuscular blockade, and absence of potential artifacts from face muscle activity and eye blink. (a) Brief increase in higher frequencies normally associated with increased cognitive activity indicates cerebral response to a painful somatic stimuli. (b) Cerebral response to endotracheal suctioning in a therapeutically paralyzed patient. Dramatically increased high frequency waves, possibly indicating discomfort.

Figure 10

(a) Patient with severe delirium tremens and life threatening agitation demonstrating multiple musculoskeletal artifacts on the EEG. (b) Neuromuscular blockade instituted with vecuronium and sedated with a bolus of propofol, followed by continuous infusion. (c) Patient oversedated on continuous infusion of propofol at 5 mg/kg/h. (d) Propofol infusion decreased to 2 mg/kg/h, brain wave activity increases.