Sedation monitoring

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.

Rationale for the monitoring of sedation in ICU

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:

• A large number of ICU patients require sedation for a variety of reasons (that 85% of ICU patients will require sedation is a conservative estimate)
• Continuous sedation, eg. by infusion of anaesthetic agent, or intermittent use of longer acting agents, is usually prescribed as a range of doses, titrated to achieve a specific sedative effect
• To be able to describe and measure the specific sedative effect is therefore essential, as it would then act as the target for sedation, and guide adjustments for dosing
• The fine individualised control of sedation dosing would prevent undersedation and oversedation, both of which have undesirable consequences (anxiety, hypertension, tachycardia, psychological trauma, versus depressed respiratory drive, decreased cooperation with care, and adverse haemodynamic effects of the sedating agent)

Methods of 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:

• Qualitative clinical observation
  • Where you eyeball the patient, or assess their responsiveness, and determine whether their level of arousal is appropriate for the conditions and your goals for them, and then determine whether the level of sedation is appropriate for this level of arousal
• Quantitative scales
  • Designed in an effort to introduce validity and reliability/reproducibility  into the subjective process of clinical assessment
  • Approximately 30-40 of these exist
  • None are universally accepted
  • Common ones include:
    • the Ramsay Scale (1974), developed to monitor
    • the modified Glasgow Coma Scale (1987), developed originally to monitor the then-novel agent propofol
    • the Sedation Agitation Scale (1994), developed to monitor a continuous infusion of haloperidol
    • the Richmond Agitation and Sedation Scale (2003), developed specifically to monitor ICU sedation with a variety of agents
    • the Adaptation to the Intensive Care Environment (ATICE) scale (2003) designed specifically for intubated patients
    • the COMFORT scale (1992) designed specifically for paediatric patients
• Objective measurements of sedation
  • Vital signs
    • Heart rate and heart rate variability
    • Blood pressure
    • Respiratory rate
  • Responsiveness/arousal
    • Lower oesophageal sphincter contractility measurement
  • Neurophysiology
    • Frontalis muscle electromyogram
    • Sensory evoked potentials
    • EEG and affiliated methods (eg. BIS)
• Pharmacokinetic models
  • Though strictly speaking not an instrument of monitoring sedation, something like a TIVA model can be used to administer a sedating agent with a known dose-reponse relationship (like propofol) in a controlled manner, targeting a specific effect site concentration. 

Arguments for the routine monitoring of sedation

• ICU therapies are titrated to clinical effect using measurable endpoints (eg. noradrenaline and blood pressure), and so sedation should be regarded in the same way
• Without adequate assessment of the level of sedation, the titratable sedating agents cannot be targeted to achieve a specific outcome
• Monitoring is usually cheap (using available staff, for example) and often already integrated into routine bedside assessments
• The cost of monitoring equipment is offset by the cost saved by the theoretical improvement in the efficiency of the use of sedating agents (i.e. using less of the agent) and the shorter ICU length of stay which should result from better sedation control
• The use of a reliable scale could form a part of a sedation algorithm to standardise care
• The 2021 KSCCM guidelines and the 2018 SCCM guidelines recommend the routine use of sedation assessment scales

Arguments against routine monitoring of sedation

• Some of the measurement techniques are either uncomfortable (eg. itchy head electrodes) or intrusive (eg. where the patient's level of responsiveness is tested by verbal or physical stimuli, disturbing them from sleep)
• The use of validated scales does not appear to improve ICU length of stay
• There are hidden costs in training staff to use monitoring equipment and quantitative scales
• Reliance on sedation monitoring equipment may result in an underappreciation of clinical signs which could be more valid and reliable
• Reliance on monitoring scales to drive sedation algorithms is only as safe as the staff are well-trained in the use of those scales

The Richmond Agitation and Sedation Scale

"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:

• Quantify the depth of sedation or the level of arousal/agitation as a value
• Offer a reproducible bedside method of measuring this value using precise criteria
• Simplify the selection an prescription of sedation targets
• Optimise the dosing of sedation by providing a measurable endpoint 
• Allow the comparison of sedation/agitation measurements for research

"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:

Rass Score	Description
+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:

• RASS has good reliability and validity across a range of critically ill populations (Ely et al, 2003)
• The inter-rater reliability is very good (Almgren et al, 2010)
• It is easy to administer and is not culturally specific (which means it translates easily across cultural and language boundaries)
• Unlike many other scales the RASS has good "resolution" at the mild-moderate range of sedation (corresponding to RASS scores of +1 to -4), allowing the fine titration of sedation
• The scale has been studied extensively and compared to numerous other scales, making it a de facto "gold standard" in the field
• It is referenced in analgesia and sedation guidelines (such as the 2021 KSCCM guidelines and the 2018 SCCM guidelines)
• The familiarity with this scale means less time spent on orienting and training new staff (as compared to adopting a less widely known scale)

Disadvantages of the RASS would probably be better worded as "limitations":

• It will not work on patients who are deaf (and will not hear the assessor's "loud speaking voice")
• It will not work on blind patients (as they will not make eye contact)
• Some people with autism spectrum disorders actively avoid eye contact
• It is difficult to assess in patients with severe sensory loss, eg. those with high spinal injury
• It can't be used to assess the level of sedation in patients who are paralysed or under the effect of neuromuscular junction blockers
• The scoring of the level of agitation (above +1) relies on the observation of specific behaviours, which can be transient and subjective, i.e. a patient is +1 until they are suddenly a +4 and throwing a chair at you. 
• Repeated observations will yield a progressively higher score