Published on January 26, 2024, 3:08 pm
A breakthrough technique is helping anesthesiologists to track changes in states of consciousness more effectively. The conscious mind has long been a subject of contemplation and exploration, yet many aspects still remain elusive, including how to measure and assess consciousness itself. This poses a challenge for anesthesiologists who aim to disconnect patients from the outside world and their inner thoughts during surgery.
General anesthesia has revolutionized medical procedures, enabling advancements such as microscopic vascular repairs and solid organ transplants. However, it also presents the opportunity to study consciousness in ways that were not previously possible. Anesthetics allow researchers to induce profound and reversible changes in conscious states, providing insights into brain responses during these transitions.
One of the hurdles faced by anesthesiologists is accurately measuring the transition from one state to another without interrupting the process. Many existing approaches inadvertently disrupt what they are trying to study—the very act of assessing the system affects the system. When studying human consciousness, determining whether someone is conscious can arouse them, complicating the assessment.
To address this challenge, a simple approach called the “breathe-squeeze method” has been developed. This technique offers a way to study changes in conscious states without interrupting those shifts. Researchers have used electroencephalography (EEG) to analyze electrical activity in the brains of individuals receiving anesthetics for decades. They can observe specific patterns, known as anesthetic signatures, which indicate altered brain functioning.
Studies using EEG have revealed that most anesthetics slow down brain rhythms and increase their size, leading to impaired communication between different regions of the brain. For example, propofol—a commonly used drug for general anesthesia—disrupts the typical coordination between brain regions involved in processing sensory information.
Consciousness is not a binary state; instead, it exists on a continuum with various levels and types of brain functioning. Connected consciousness refers to being aware of one’s environment through senses and behavior, while disconnected consciousness occurs when one is disconnected from their surroundings, such as during dreaming or deep sleep. Unconsciousness, as experienced in a coma, can be thought of as a state of oblivion without subjective experiences or memory.
Understanding the transitions between these different states is crucial for gauging the appropriate levels of general anesthesia and advancing knowledge in anesthesiology, consciousness research, sleep studies, and coma research. To map the transition out of connected consciousness more accurately, researchers have recently adopted a new approach that measures a person’s ability to generate volitional behaviors without external prompting.
Traditionally, researchers utilized verbal commands to assess sedation onset by observing behavioral responses. However, this method had limitations—the cues were not standardized across studies and could potentially arouse participants during the transition. By contrast, the breathe-squeeze method offers enhanced sensitivity and precision in measuring the onset of sedation without disrupting the transition.
The breathe-squeeze exercise involves participants squeezing a handheld dynamometer whenever they breathe in. Researchers track these squeezes using a dynamometer and an electromyography sensor to measure muscle response. During sedation experiments with dexmedetomidine—a commonly used anesthesia drug—participants gradually stopped squeezing as brain concentrations of dexmedetomidine increased. Interestingly, after discontinuing the sedative infusion, participants spontaneously resumed squeezing synchronously with their breaths after 20 to 30 minutes.
Comparisons between verbal command-based assessments and the breathe-squeeze method showed that participants ceased performing the task at lower dexmedetomidine concentrations using the latter technique. This highlights how external cues can affect conscious states differently—they can either be internally generated (like reminding oneself to squeeze) or externally prompted (in response to verbal commands). These findings refine our understanding of the continuum of consciousness.
In addition to its scientific value, it was discovered that many participants found the breathe-squeeze task helpful for calming their minds and bodies. Consequently, this method has been implemented in clinical practice when inducing general anesthesia for major surgeries, as it provides patients with a more serene experience.
The researchers are now analyzing EEG data along with structural magnetic resonance imaging (MRI) data from the volunteers to gain further insights into the transition from connected to disconnected consciousness. These findings can contribute to improving clinical care for patients undergoing surgery under anesthesia, as well as aiding those individuals experiencing sleep disorders or comas. The research also raises thought-provoking philosophical questions about the nature of consciousness itself and what it truly means to be conscious.
This study exemplifies the significant progress being made in understanding and measuring states of consciousness using innovative techniques. By bridging the gap between scientific exploration and clinical applications, researchers hope to provide safer and more tailored anesthesia experiences while uncovering the mysteries of consciousness.