Table 1 Mechanism of action, cerebral physiologic effects and main advantages/disadvantages of sedatives/analgesics in patients with acute brain injury
From: Optimizing sedation in patients with acute brain injury
Mechanism of action | CNS effects | Advantages | Disadvantages | |
|---|---|---|---|---|
Propofol | GABA-R agonist | ↓ ICP | Rapid onset and short duration of action | No amnesia, especially at low doses |
↓ CMRO2, ↓ CBF, preserved CO2 reactivity and cerebral autoregulation | Clearance independent of renal or hepatic function | No analgesic effect | ||
↓ Cerebral electrical activity, can be used to induce EEG burst suppression (at high dose) | No significant drug interactions | Tolerance and tachyphylaxis | ||
↓ MAP, ↓ CPP (particularly in hypovolemic patients) | ||||
↑ Triglycerides, ↑ caloric intake | ||||
Propofol infusion syndrome (↓ HR, ↓ pH, ↑ lactate, ↑ CPK, myocardial failure) | ||||
Midazolam | GABA-R agonist | ↓ CMRO2, ↓ CBF | Amnesia | Tolerance and tachyphylaxis |
Slight ↓ ICP | Rapid onset of effect in acutely agitated patient | Hepatic metabolism to active metabolite | ||
Preserved CO2 reactivity and cerebral autoregulation | Less haemodynamic instability than propofol (may prevent CPP reductions) | May accumulate in renal dysfunction | ||
Anti-epileptic effect | May prolong the duration of MV | |||
May increase ICU delirium | ||||
Barbiturates | GABA-R agonist | ↓↓ CBF that is proportional to the ↓↓ CMRO2 (up to 60 %) during burst suppression | By ↓↓ CBF and CBV, barbiturates have a strong effect on ↓↓ ICP | Hypotension, ↓↓ MAP/CPP |
↓↓ ICP | Indications for barbiturates are limited to the treatment of refractory ICP and refractory status epilepticus, titrated to the lowest effective dose; EEG may help with the titration of barbiturate therapy | Immune suppression, increased risk of infections (pneumonia) | ||
Adrenal dysfunction | ||||
Morphine | μ-receptor agonist | ↑ ICP and ↓ MAP/CPP transiently following bolus | Low cost | Low predictability to control ICP |
Histamine release | ||||
Accumulation with hepatic/renal impairment | ||||
Fentanyl, sufentanil | μ-receptor agonists | ↑ ICP and ↓ MAP/CPP transiently following bolus | More potent opioid than morphine (sufentanil is 1000× more potent than morphine) | Accumulation with hepatic impairment |
Control ICP during endotracheal suctioning | May prolong the duration of MV | |||
Remifentanil | μ-receptor agonist | No changes in ICP or CBF during drug infusion | 500× more potent than morphine | Hyperalgesia at the cessation of drug infusion |
Rapid onset and short duration of action to permit neurological assessment | Limited effect to control ICP during painful procedures | |||
Clearance independent of renal or hepatic function | Tachyphylaxis | |||
Higher cost than other opiates | ||||
Dexmedetomidine | α2-agonist | ICP ↓ or unchanged | Sedative, analgesic and anxiolytic | Very limited clinical experience in patients with ABI |
CPP ↑ or unchanged | Short acting, no accumulation, patient may be frequently assessed neurologically | In non-neurointensive care population: | ||
SjvO2 unchanged | Minimal respiratory depression | ● hypotension, bradycardia | ||
PbtO2 unchanged | May reduce incidence/severity of delirium | ● arrhythmias including atrial fibrillation | ||
● hyperglycaemia | ||||
May require high doses; deep sedation may not be possible | ||||
High cost | ||||
Ketamine | NMDA-R antagonist | ICP ↓ or unchanged | Short acting, fast onset | Hallucinations/emergence phenomena |
CPP ↑ or unchanged | Induces sedation, analgesia and anaesthesia | |||
No change in SjvO2 or cerebral blood flow velocities | Does not depress respiration | |||
Haemodynamic stability, preserves MAP | ||||
May be used as an adjunct for refractory seizures | ||||
No withdrawal symptoms | ||||
Inhaled anaesthetics | Not fully established: may act at several sites (reduction in junctional conductance; activation of Ca2+-dependent ATP-ase; binding to the GABA-R, the large conductance Ca2+-activated K+ channel, and the glutamate receptor) | ↓ Cerebral electrical activity, ↓ CMRO2 | ↑ CBF in patients with cerebral ischaemia (0.8 % isoflurane) | ↑ ICP due to ↑ CBV |
Dose-dependent effects on CBF: ↓ CBF at low concentrations, ↑ CBF at high concentrations | Rapid elimination | Myocardial depression | ||
Malignant hyperthermia | ||||
Not widely available, requires specific systems and expertise | ||||
Data very preliminary |