**4.4 GPDs with triphasic morphology (GDPs TM)**

## *4.4.1 EEG characteristics*

GPDs TM (**Figure 10**) [7] are known as moderate to high voltage EEG discharges (100-300uv), with a frequency varying from 1 to 2 Hz; they are usually characterized by the presence of 3 phases: Negative–positive –negative in polarity with a predominant positive phase; often, there is a frontal predominance, and sometimes an anterior –posterior or posterior –anterior phase lag.

### *4.4.2 Etiology*

GPDs with triphasic morphology are reported in metabolic disturbances, hypertensive encephalopathy, subcortical white-matter disease, infections, strokes, hypoglycemia hypernatremia/hyponatremia, postictal states, lithium and baclofen toxicity.

#### *4.4.3 GPDs with triphasic morphlogy and seizures*

GDPs TM association with seizures has been discussed by several authors especially concerning nonconvulsive status epilepticus (NCSE) where the

### *Periodic EEG Patterns in the Intensive Care Unit (ICU): Definition, Recognition and Clinical… DOI: http://dx.doi.org/10.5772/intechopen.95503*

improvement of both EEG and patient level of consciousness with BDZs is consistent with NCSE; Jirsh et al. define a possible NCSE in a patient, a state where BDZs abolish GPDs TM without clinical improvement [34] (**Figures 10** and **11**); patients with GDPs and TM are likely to develop seizures as those without (25% vs. 26%) [35]; furthermore anterior to posterior "phase lag" does not occur with GDPs TWs related NCSE.
