When the patient is waking up from the painful stimulus, the Awakening Index mirrors the strength of the bursts in the sympathetic nerves. The area under the skin conductance peak increases accordingly. The color code turns blue. The patient may need both more analgesia and hypnotics.
The graph shows the Awakening Index during sedation in anaesthesia and intensive care without analgesia, small dose of analgesia and huge dose of analgesia recorded when the same tetanic stimulus was given during hypnotic sleep. An immediate warning is observed, with a two second delay, when the patient has too little analgesia and wakes up from anaesthesia. Then the patient is in need of both analgesia and hypnotics.
(Reference: Storm H, Støen R, Klepstad P, Skorpen F, Qvigstad E and Ræder J. Nociceptive stimuli responses at different levels of general anaesthesia and genetic variability. Acta Anaesthesiol Scand 2013; 57: 89–99)
The Skin Sympathetic Nerves (assessed by micro-neurography) are the only sympathetic nerves in the body which have acetylcholine acting on muscarinic receptors. Their activity, assessed by how forceful they fire, is directly mirrored in real time in the Awakening Index by calculating the area under the skin conductance recording.
During anaesthesia, why can blood pressure and heart rate decrease while the Skin Conductance Algesimeter Index and the Awakening Index are 0.00? And why can blood pressure and heart rate increase while the Skin Conductance Algesimeter Index remains at 0.00?
The Skin Conductance Algesimeter indices (Pain or Nociceptive Index and Awakening Index) are 0.00 when the patient has enough or too much analgesia. The Skin Conductance Algesimeter should therefore be used as an individual nociceptive warning when the patient has too little analgesia or hypnotics. The Nociceptive Index shows peaks per second (how often the skin sympathetic nerves are firing), and the need for more analgesia. The Awakening Index shows the area under the curve, microsiemens x sec, (how forcefully the skin sympathetic nerves are firing). If the Awakening Index increases above 0.00 into the blue coloured area, the patient is about to wake up from the stimulus and needs both more analgesia and hypnotics. Moreover, unlike blood pressure and heart rate, when the patient is overly sedated, the blood pressure and heart rate continue to decrease whereas the skin conductance indices stay at 0.00. Accordingly, if the level of sedation decreases or if the surgeon influences a forceful stimulus both blood pressure and heart rate will increase and the PainMonitor indices will be 0.00, until more analgesia and/or hypnotics are needed. When the skin conductance peaks per sec increases above 0.00 more analgesia is needed, and when the area under the curve increases above 2.0 the patient needs more hypnotics.
The existing device:
It is possible to choose the Awakening Index and the Pain (nociceptive) Index when using the Awakening Index:
The Med-Storm software can be installed on the PhilipsMX patient monitor with iPC, the Philips Intellevue, the Mindray patient monitor with iView and the bridge-solution (in process), and works on the Draeger Explorer (USB ports as it is basically a flat panel PC), and some Nihon Koden patient monitors.
A standalone monitor is available:
If the area under the skin conductance recording increases, the Awakening Index turns blue, and the patient is about to wake up from anaesthesia and needs both analgesia and hypnotics. This emphasize that these indices, Awakening Index and Nociceptive (Pain) Index, have a unique possibility to tailor the need of analgesia and hypnotics during awakening from sedation for patients individually. Clinicians report less use of opioids and less respiratory and blood circulatory side effects when they tailor the need of analgesia and hypnotics after the Skin Conductance Algesimeter indices.