BarbComa AKA Barbiturate Coma - Important Details

Indications

• Potentially survivable head injury.
• No surgically treatable lesion accounting for intracranial hypertension (except when used for preparation for surgery).
• Other conventional therapies for controlling ICP have failed (posture, hyperventilation, osmotic and tubular diuretics, corticosteroids).
• ICP > 20 to 25 mmHg for more than 20 min, or >40 mmHg at any time.
• Unilateral cerebral hemispheric edema with significant (>.7 mm) shift of midline structures shown on CT.
• A low Glasgow Coma score.

Benefits

• Decrease in cerebral metabolic rate (CMRO2), caused by decrease in synaptic transmission, presumably by affecting GABA transmission.
• Decrease in cerebral blood volume and ICP, due to increase in cerebrovascular resistance, due vasoconstriction - Both CMRO2 and CBF are decreased in a dose dependent fashion: About 50% decrease at a dose sufficient to produce isoelectric EEG.
• Promote or induce hypothermia.
• Increase in IC glucose, glucagon, and phosphocreatine energy store.
• Decrease in nitrogen excretion following acute head injury.
• Shunt blood from regions of normal perfusion to those of reduced CBF due to vasoconstriction.
• Anticonvulsant prophylaxis.
• Stabilization of lysosomal membranes.
• Decrease in excitatory neurotransmitters and IC calcium.
• Free radical scavenging ( thiopental only).

Risks

• Direct myocardial depressant.
• Increase in venous capacitance, due to central and peripheral sympatholytic action.
• Impaired gastrointestinal motility Increased hepatic microsomal activity.
• Direct CNS depressant, resulting in unreliable neurological examination.
• Possible allergic reaction Impaired lymphocyte immune response and function.

Goals

• Maintenance ICP < 20 mmHG.
• Therapeutic EEG response: burst suppression or cortical electrical silence (with preservation of SSEP and BAEF).

Dosing Regimens

Pentobarbital

• Loading:30-40 mg/Kg over 4 hours (~2500mg/70Kg)
• Maintenance: 1.8-3.3mg/Kg/hr (~175mg/70Kg)

• Maintenance: .3-3mg/Kg/hr
• Loading: 3-6mg/Kg over 30min

Thiopental

• Loading: 3mg/Kg bolus, followed by 10-20mg/Kg over 1 hr
• Maintenance: 3-5 mg/Kg/hr
• Therapeutic serum level: 6-8.5 mg/dl
• Weaning: dosage is halved q 12 hr.

Monitoring

Cardiovascular

• A-line: arterial BP, blood gases
• PA catheter: CO, CI, SV, SVR, PVR, right heart filling pres., PCWP
• Bladder catheter: urine output

Cerebrovascular And Neurophysiological

• ICP: maintain < 25 mmHg, preferably less
• CPP: maintain > 70 mmHg
• EEG: burst suppression, or cortical electrical silence optional
• Brain temperature
• Jugular bulb O2 monitor/ oxymeter catheter
• Somatosensory or brainstem auditory evoked potentials (SSEP, BAEF)

Other Monitoring

• Core body temperature: NP, TM, E: 32 to 35 degrees C is acceptable
• Serum barbiturate levels
• nasogastric catheter: pH and output
• intake and output

Therapeutic End Points

• ICP < 20 mmHg for at least 48 hours, at a minimum
• Resolution of intracranial mass effects or midline shift, preferably
• ICP must remain controlled with conventional therapies

• Diagnosed brain death
• Uncontrollable ICP despite adequate serum levels, EEG burst-
• Suppression, or electrical silence
• Intolerable side effects; (Hypotention not responsive to cardiac inotropes, peripheral vaso-pressors, or intravenous fluid therapy (cardiac isotopes: dopamine, dobutamine, epinephrine) (peripheral vasopressors: ephedrine, phenylephrine); (IV fluids: packed RBCs, albumine, hetastarch, LR); Progressive pulmonary dysfunction; Sepsis.)