Informative and target level-controlled
Measuring sedation depth
The regular evaluation of the desired degree of sedation facilitates the dosing of sedatives, the sedation depth being interventions, dependent primarily on the disease of the patient and his current state as well as the necessary diagnostic and therapeutic interventions.
The goal is a calm patient, easily woken up, who is cooperative, oriented and free from sensitivity to pain, anxiety and stress.
Deeper degrees of sedation are mostly not necessary and should be avoided whenever possible. In principle the diagnostic and therapeutic measures and thus also the degree of sedation should be oriented towards the physiological day-night rhythm.
According to the concordant opinion the written sedation concept should be checked regularly and in short intervals and adapted to the needs of the patient with regard to its effectiveness in order to avoid overdoses or underdosing. A proven way is the use of scoring systems because they permit the description of the degree of sedation by means of defined categories.
Thereby misunderstandings between members of the treatment team can be largely excluded. The desired sedation score is determined by the doctor as target value for day and night. The actual quality of the sedation should be documented by the nursing staff as actual value at least twice per shift. After appropriate training the nursing staff can independently carry out an individual adjustment of the drug doses predefined limits. It could be shown that a protocol-supported sedation regime shortens the duration of the ventilation and of the stay in intensive care - independently from the set score.
Ideally the score system should provide information with which the degree of sedation of the patient can be captured in a simple, valid and reproducible way, and if possible independently from the substances used for the pain therapy.
Over the last few years the RASS Score (Richmond Agitation Sedation Scale) has established itself worldwide, it allows a differentiated evaluation of the state of consciousness.
|4||Combative||Combative, violent, immediate danger to staff|
|3||Very agitated||Pulls or removes tubes or catheters; aggressive|
|2||Agitated||Frequent non-purposeful movement, fights ventilator|
|1||Restless||Anxious, apprehensive, movements not aggressive or lively|
|0||Alert and calm|
|– 1||Drowsy||Not fully alert, but has sustained awakening to voice (eye opening & contact > 10 sec)|
|– 2||Light sedation||Briefly awakens to voice (eyes open & contact < 10 sec)|
|– 3||Moderate sedation||Movement or eye opening to voice (but no eye contact)|
|– 4||Deep sedation||No response to speech, but movement or opening of eyes by physical stimulus|
|– 5||Unarousable sedation||No response to voice or physical stimulation|
For relaxed patients the informative value the scores determined by subjective criteria is insufficient. Blood pressure and heart rate are no sufficiently specific or sensible markers that can safely capture a sedation that is too low in these critically ill and ventilated patients. Likewise, the monitoring of deep degrees of sedation, for example in patients with brain injuries, is possible only with restrictions by means of sedation scores. In recent times therefore increasingly monitoring procedures are being tested that are based on brain waves. Thereby the raw EEG signals are processed mostly electronically until bedside online statements on the cerebral function state of the patient are obtained. The bispectral index (BIS) for example uses a dimensionless scale from 0 (isoelectric EEG) up to 100 (complete alertness) for the characterization of the state of consciousness.
Although the BIS index is a useful procedure for the objective capture of the depth of anaesthesia, the fields of application in intensive care treatment are still limited. For instance, the BIS index between patients which on the basis of subjective criteria showed the same degrees of sedation can vary significantly. Particularly under light sedation conventional scores seem to be reproducible to a higher extent. Problematic are also interferences of EEG signal by muscle artefacts in not elated, light sedated patients are unavoidable and often do not allow an interpretation of the degree of sedation.
Accordingly, the BIS index is validated only for the determination of the depth of anaesthesia using different anaesthetics such as Propofol or Midazolam, but not for the measurement of the sedation depth in intensive care patients.
The evaluation of the state of consciousness by the BIS index can therefore – as a complement to conventional procedures – until now be recommended for deep sedated patients or relaxed patients in which a sufficient sedation depth must be assured to avoid awareness phenomena.