4.1 Q: What is the best CSI range for general surgery?
A: Usually the best range lies between 40 and 60, but there are always individual variations, as certain anaesthetic techniques may require a deeper level of consciousness.
4.2 Q: Does the CSM need to be calibrated?
A: The CSM does not need any calibration at start-up. The monitor carries out an automatic initialisation procedure when pressing the POWER ON button.
4.3 Q: Must the patient be awake when applying CSM?
A: No, the patient can also be asleep when applying the CSM.
4.4 Q: How is it possible not to have a baseline adjustment?
A: The CSM system uses EEG parameters that are common to all patients with a normal, unaltered EEG signal.
4.5 Q: Can this monitor be used in gas anaesthesia or is it only a TIVA monitor?
A: The CSM works just as well with all common gases such as enflurane, halothane, isoflurane, desflurane, sevoflurane as with the intravenous hypnotic agents.
4.6 Q: What does the EMG indicator in the CSM show?
A: The EMG indicator shows the total power of electrical activity in the frequency range 75-85Hz.
4.7 Q: Is the EMG activity included in the algorithm that calculates the index?
A: No, the EMG is not included in the CSI calculation.
4.8 Q: Is the EMG signal detected by the CSM influenced by the action of neuromuscular blocking agents?
A: The EMG bar in the CSM cannot substitute a Train of Four (TOF) measurement. The reason for this is that the facial muscles are much more resistant to muscle relaxants than for example hypothenar (wrist) muscles. On the other hand, if the EMG in the CSM is 0 then the patient is most likely to be without muscular response.
4.9 Q: Why does the EMG bar sometimes shows activity during diathermia?
A: The EMG bar shows the muscular electrical activity in non-paralysed patients, and no or low activity in patients who have received neuromuscular blocking agents. The use of diathermy might cause some interference in the frequency range where the EMG is measured (75-85Hz). This interference does not affect the CSI calculation, which is performed below 42 Hz.
4.10 Q: What is the behaviour of the CSM during hypothermia?
A: We have not undertaken any specific study on the effect of hypothermia on the CSI. Nevertheless, we know that in these patients brain activity is very low (you could expect to see high levels of burst suppression, for example). In the A-line we have seen that the AAI typically decreases to the 5 to 10 range. As the CSM algorithm at these levels has behaviour similar to the AAI system, we could expect to see low CSI values (see also section 7.3).
4.11 Q: Can the CSM be used in mobile settings (i.e. ambulances)?
A: Yes. The size of the CSM makes it suitable for use in mobile settings.
4.12 Q: Why use the CSM when other patient parameters (blood pressure, heart rate, capnogrphy, etc.) are available?
A: Many recent studies indicate that hemodynamic variables alone are not sufficient estimators of depth of anaesthesia. The information gained from the monitors (heart rate, blood pressure, capnography, etc.) is often insufficient to tell the true hypnotic state of the patient. Moreover, in many cases the information given by the level of consciousness monitors precedes hemodynamic responses by several minutes.
4.13 Q: What is the level of anaesthesia per CSI unit number?
A: The CSI scale shows a good correlation with anaesthetic drugs dosage (effect-site concentration of propofol or end-tidal sevoflurane, for example).
Nevertheless, it is not possible or advisable to state a specific equivalent drug concentration value for the CSI unit simply because the same drug concentration does not have the same effect on all patients. It depends on features like age, body mass, blood volume considerations, etc.
Furthermore, patients undergoing surgery also receive analgesics, muscular relaxants and other drugs, and all of these can influence the anaesthetic depth.
4.14 Q: What does a drop in CSI from 35 to 30 mean?
A: Both values are well below the “surgical anaesthesia” level of the CSI scale, indicating that the depth of anaesthesia is becoming deeper. At this level, many things could cause such a small decrease in CSI. Of course, it will also depend on the duration of the decrease itself. A surgical stimulus might have been stopped, or an analgesic drug dose increased. All aspects of the procedure should be taken into consideration.
4.15 Q: CSI is variable, not constant, why?
A: The CSI is intentionally variable in order to catch responses to stimuli. Check all possible stimuli being given to the patient which may increase their anaesthetic depth.
4.16 Q: CSM responds quickly, but does not give a warning of impending arousal
A: The CSM does not automatically give an “arousal warning” or any other prediction of the clinical state of the patient. This type of prediction is difficult, as we have to take into consideration that the CSI can respond to factors such as stimuli during surgery that could cause a momentary increase in the patient’s level of arousal (and consequently an increase in the index value). The monitor allows the user to set an alarm limit to signal when the CSI reaches a pre-determined value.
4.17 Q: What is the difference between Awareness, Consciousness and Depth of Anaesthesia?
A: The term “awareness” is generally used to describe the experiences of some patients having total recall of events during their anaesthesia. For example, they might be able to repeat sentences or comments that the surgeon made during the operation.
The term “Level of consciousness” has been used extensively. It basically means a continuous scale ranging from awake to asleep.
The term “depth of anaesthesia” is less precise because anaesthesia consists of 3 components, hypnotics, analgesics and muscle relaxants. The CSM monitors the effect of the hypnotic component and indirectly the effect of the two others.
Having said this, please do bear in mind that different authors and healthcare professionals do use the terms differently and randomly switches between the three terms.
4.18 Q: How many different levels of consciousness are there?
A: Level of consciousness is probably a continuous scale ranging from awake to deeply anaesthetised where the level of consciousness is very low. A low level of consciousness could also be expressed by the fact that the patient has no recall and neither implicit nor explicit memory of events from the operation period.
4.19 Q: The patient moves his legs several times during the operation. CSI-value lays around 41 and 42. EMG-value goes up to approximately 60 and does not fall until the gas pressure is increased.
A: CSI is an expression of the patient’s hypnotic level. The movements might take place independently of the level of consciousness, if the movements are in a nature of reflexes controlled by the autonomous nervuous system (ANS). In this case it might be ok to administer more analgesics or muscle relaxant if the patient’s movements disturb the work of the surgeon.
Had the information from the CSM not been available, it would have been hard to tell whether the movements were due to the patient not being fast asleep, but now CSM proves that this is the case. The movements stop when the gas percentage goes up, which is due to most volatile gasses having an analgesic effect as well.
4.20 Q: The patient has a racking cough when an oesophagus probe is inserted. The CSI-value lays on approximately 42.
A: This situation is similar to the one described in the previous question. Coughing is a reflex controlled by ANS.
4.21 Q: The patient wakes up in recovery room when the CSI-value is 56.
A: During recovery there might be several artefacts, movement of the patient, wires, electrodes, high EMG activity resulting in the updating speed of the CSM to increase with considerably more than the usual 10 to 20 sec. This situation might therefore occur. On the other hand, if the patient wakes up during the operation without moving, CSM will rise fast, and it is in a situation like this that the CSM is of real help.
4.22 Q: Can artefacts influence the CSI?
A: Danmeter A/S has put a lot of effort into eliminating influence from artefacts on the CSI. These artefacts could be diathermy, EMG and other signals that will contaminate the EEG. If the EEG is contaminated and this is not detected by the artefact restrictions in the CSM, the clinician must identify situations where the EEG (CSI) does not accurately correlate to the clinical signs.
4.23 Q: When is the EMG typically high?
A: The EMG activity is typically high in the awaken state and in the emergence from anaesthesia.
4.24 Q: Can the CSM be used on patients with known neurological disorders?
A: Because of very limited clinical experience on such patients the CSI should be interpreted with caution, especially in the presence of any neurological conditions or drugs which may affect the integrity of the EEG signal.
4.25 Q: Can the CSM be used on patients with pacemaker?
A: The CSM can be used on patients with pacemakers. Occasionally, some interferences could be detected as periods with elevated CSI values or with no index on screen.
4.26 Q: Why do sometimes the CSI changes slightly when Extra Corporeal Circulation (ECC) is started?
A: The use of ECC changes the blood volume of the patient; hence the plasma concentration of the anaesthetic agent is changed. In consequence the effect site concentration is altered; and therefore the CSI will change accordingly.
4.27 Q: Can the CSM be used when the agents are Ketamine or Nitrous Oxide (N2O)?
A: As opposed to most commonly used volatile and intravenous hypnotic agents, Ketamine is a “dissociative" drug. It activates some areas of the brain while inhibiting others. The result is an altered EEG signal. For this reason the CSM (as well as all EEG-based monitors for depth of anaesthesia) cannot provide reliable information on these patients. Nitrous Oxide is primarily used as an analgesic drug. The CSM responds to hypnotic agents. You will find NO changes in EEG (CSI) using N2O alone (normal doses), but you will find changes in the CSI in combination with a narcotic, as N2O potentiates its effect.
4.28 Q: What does the Signal Quality Index (SQI) show?
A: SQI% measures the quality of the acquired EEG signal. The calculation is based on a number of artefacts during the last minute. This quantity is displayed numerically as a percentage (0-100%, 100% equals best signal quality) in Display Mode A. If SQI is decreased because of extensive use of diathermy, it will increase again as soon as the diathermy is stopped.
4.29 Q: What could cause the Signal Quality Index (SQI) to decrease?
A: If the impedance of the white or black sensors exceeds 1kΩ, the SQI will fall gradually. Poor impedance conditions may cause the SQI to fall to 50%. See question 3.14 on sensor impedance. Always check all sensors and cable connections.
Some mechanical devices (e.g. patient warmers) could generate high frequency activity, especially when in close proximity to the CSM sensors. If possible move disturbing device away from CSI sensors. Check grounding on disturbing device. Reduce the influence from disturbing device running the CSM on batteries.
4.30 Q: What is displayed when artefacts are present?
A: SQI will decrease as long as the artefacts are present. Other parameters are replaced by - -.
4.31 Q: What is displayed when sensor alarm is present?
A: The sensor alarm makes the red error light turn on and all parameters are replaced by -?-.