Analgesia for the head injured patient
Case: A young adult attempted hanging victim with a decreased GCS was intubated and ventilated at a referring hospital. He required interhospital retrieval to a tertiary care facility. On arrival the team noted the patient was hypertensive, tachycardic and there apppeared to be patient-ventilator dysynchrony. He was sedated with midazolam only.
Challenge: How to achieve cerebral perfusion and neuro-protection.
Learning points: Clearly this patient needs to be properly sedated, but we must be mindful of the need to perfuse this potentially injured brain. It is common to aim for a cerebral perfusion pressure (CPP) of 60mmHg. If we initially assume a ICP of 20mmHg, then this patient needs a MAP 80mmHg. This patient’s cardiovascular observations will certainly tolerate an increase in sedation and his ICP and metabolic rate are not being helped by inadequate sedation. High arterial CO2 and raised intra-thoracic pressures generated by ‘fighting’ the ventilator should also to be avoided in this head injured patient.
“5.2 The ideal sedation regimen provides adequate analgesia and should be easily titratable to effect with minimal haemodynamic response”.
Adding fentanyl and increasing the midazolam infusion brought the cardiovascular parameters down to more reasonable levels and the patient’s ventilation settled, all benefiting the injured brain.
Here’s the full excerpt from the Neuroprotection Helicopter Operating Procedure:
5. Sedation and Paralysis
5.1. In order to avoid spikes in ICP it is imperative that the patient be adequately analgesed and sedated.
5.2 Movement between stretchers and changing ventilation circuitry are events which may cause patients to cough, gag or suffer arousal unless very well sedated. The ideal sedation regimen provides adequate analgesia and be easily titratable to effect with minimal haemodynamic responses.
5.2.1. Fentanyl is an effective analgesic with sedative properties and is cardiovascularly stable.
5.2.2. Midazolam has anticonvulsant properties which may be desirable.
5.2.3. Propofol is rapidly titratable, reduces cerebral metabolism and allows for neurologic assessment shortly after weaning. It may cause more cardiovascular depression.
5.2.4. Ketamine provides excellent analgesia as well as dissociative sedation. Historical concerns about its use in patients with raised ICP are unfounded, as it generally supports MAP and hence CPP.
5.3. The use of paralytic agents should be considered in all patients with raised ICP following adequate analgesia and sedation. Whilst muscle relaxants can mask clinical signs of seizure activity they are effective in preventing coughing and gagging and patient-ventilator asynchrony which can aggravate raised ICP.
4.4 Blood Pressure Manipulation
4.4.1 General Recommendations
Cerebral autoregulation in the injured brain may be impaired and a target CPP of 50- 70mmHg is recommended. However, unless an external ventricular drain (EVD) with pressure monitoring is present it is not possible to determine CPP. Blood pressure targets must therefore be empirically chosen and should be discussed with the receiving neurosurgical team.
Reference: Sedation for critically ill adults with severe traumatic brain injury: A systematic review of randomized controlled trials.