ICU patients are subjected to inhuman stresses and their physiology is exploited in awful invasive ways which cause distress, and which we have an imperative to relieve. And on a more pragmatic note, we often need them to keep still and to not fidget with the lifesaving devices attached to them, whereas they want to move around, self-reposition, remove the painful tubes, and breathe in a pattern that interferes with your genius-level ventilation strategy. For these humanitarian and entirely convenience-based reasons, ICU patients require sedation. They seem to agree: when asked about their experience in the ICU, critically ill patients emerging from delirium following their ICU discharge reported wanting more sedation during their stay.
Unfortunately sedation is also not without its side effects, some of which directly antagonise the goals of the intensivist (better blood pressure, faster liberation from the ventilator, and so forth). There must therefore be some kind of compromise here, a mutually acceptable level of sedation that relieves patient distress and permits intrusive care while maintaining the kind of waking physiological normality that is necessary for the critical illness to resolve faster. To identify and target this level of sedation is the main reason we have sedation monitoring instruments.
This topic has one up only once in the CICM Second Part exams, where in Question 21 from the first paper of 2023 the examiners asked for the "purpose, components, advantages, and disadvantages" of the Richmond Agitation Sedation Scale. The RASS is definitely the most commonly used scale, but other scales do exist, and other methods of monitoring sedation besides that, which means this could again arise in future papers. To prepare for that possibility, this chapter applies the "purpose, components, advantages, and disadvantages" structure to a series of available sedation measurement techniques, and tries to do a "critically evaluate" of sedation monitoring as a concept.
In the grim Gothic age of the ICU, when there was only darkness and beeping, the patients were generally quite heavily sedated. There were several legitimate reasons for this, not the least of which being the extremely unpleasant actions of the mechanical ventilators of that era (many of which did not have patient-triggered modes). The other reasons were mainly related to the historical origin of intensive care practice, as an extension of anaesthetic care protruding out of the operating theatre to take over large portions of the recovery ward with ventilated patients. General anaesthesia and sometimes also neuromuscular junction blockade continued for these patients, and usually the drugs being used were ones which have a tendency to accumulate, which delayed extubation and generally frustrated the process of deescalating ICU support.
So, with such long-acting drugs, and with the persistence of highly noxious intrusive therapies, sedation monitoring would not have been especially effective. All the patients need sedation all of the time, and the appropriate depth is "deep", and the drugs are so slow to wear off that there is no point titrating anything - just prescribe a dose and hope for the best. It is therefore unsurprising that the literature of the 1960s and 1970s is fairly scant with methods of sedation monitoring, and wherever they appeared, they were mainly concerned with being able to objectively detect occult pain in the deeply paralysed and sedated patient (eg. this paper by Campbell, 1970).
It is therefore not especially surprising that the need to monitor the depth of sedation appears to have mainly been guided by the development of shorter-acting agents (eg. propofol) which allowed the depth of sedation to be more finely titrated, and in fact, it appears that the earliest quantitative sedation scales were first developed to monitor a sedation experiment using some novel short-acting sedative agent. For example, the Ramsay scale, one of the first ones developed (in 1974), was mainly meant to help assess the efficacy of alphaxalone-alphadolone, a short-acting steroidal anaesthetic agent which has subsequently been dismissed from human use.
Anyway: to summarise the modern rationale for sedation monitoring:
There is no gold standard for sedation measurement, and measurement instruments are usually compared to each other in terms of validity, applicability, responsivity, inter- and intra-rater reliability, and cost. The assessment measurement and documentation is made complex by the fact that subjectively experienced variables such as "comfort" and "stress" are difficult to define and express in a reproducible way that would be consistent among patients. Moreover the more sedated the patient is, the less effective the subjective self-reporting of comfort becomes. Lastly, the effects of sedation overlap with natural sleep and the CNS-depressant effects of disease.
Using a structure suggested in Rinaldi et al (2006), methods of measuring sedation can be loosely separated into the following broad categories:
"Purpose, components, advantages, and disadvantages" was the structure asked of the candidates by the writers of Question 21 from the first paper of 2023, and this is what was borrowed for the sections below.
How do you score a RASS? The instructions, according to Sessler et al (2002), are as follows:
1. Observe patient. Is the patient alert and calm? (score 0)
a. Does patient have behavior that is consistent with restlessness or agitation? (score +1 to +4 using level criteria)
2. If patient is not alert, in a loud speaking voice state patient's name and direct patient to open eyes and look at speaker. Repeat once if necessary. Can prompt patient to continue looking at speaker.
a. Patient has eye opening and eye contact, which is sustained for more than 10 seconds (score −1).
b. Patient has eye opening and eye contact, but this is not sustained for 10 seconds (score −2).
c. Patient has any movement in response to voice, excluding eye contact (score −3).
3. If patient does not respond to voice, physically stimulate patient by shaking shoulder and then rubbing sternum if there is no response to shaking shoulder.
a. Patient has any movement to physical stimulation (score −4). b. Patient has no response to voice or physical stimulation (score −5).
The purpose of the RASS, according to Sessler & Keane (2000) who designed it (when it was still called the MASS), was "to optimally titrate medications and to evaluate events surrounding delirium and agitated behavior", as well as to address the limitations of previous existing systems, which the authors believed were "insufficient assessment of agitation, insufficient levels of sedation for effective medication titration, inexact criteria, and/or lack of validation". For the purpose of answering CICM SAQs, this is probably a bit vague. Perhaps the purpose of the RASS could just be a generic purpose of all sedation measuring scales, which is to:
"Components" of the RASS are probably the ten gradations of the scale, as RASS does not have "domains" per se (whereas the GCS has eye response, motor response and verbal response components). Those scores are:
|+4||Combative, violent, danger to staff|
|+3||Pulls or removes tube(s) or catheters; aggressive|
|+2||Frequent nonpurposeful movement, fights ventilator|
|+1||Anxious, apprehensive, but not aggressive|
|0||Alert and calm|
|-1||Awakens to voice (eye opening/contact) > 10 seconds|
|-2||Light sedation; briefly awakens to voice (eye opening/contant) < 10 seconds|
|-3||Moderate sedation; movement or eye opening. No eye contact|
|-4||Deep sedation; no response to voice, but movement or eye opening to physical stimulation|
|-5||Unarousable; no response to voice or physical stimulation|
Advantages of the RASS are hard to describe, because it is not clear whether these are advantages of RASS versus not measuring sedation at all, or advantages of the RASS as compared to all the other sedation monitoring methods. The latter seems like a more sophisticated answer, and would probably appear more attractive to the examiners:
Disadvantages of the RASS would probably be better worded as "limitations":