Intraoperative Awareness Controversies and Non-Controversies
Intraoperative Awareness Controversies and Non-Controversies
It is self-evident that the avoidance of neuromuscular blocking agents does not in itself prevent intraoperative awareness if insufficient concentrations of hypnotic agents are administered. In 1846, Abbott received ether for a tumour removal and was aware, although not in pain, during the procedure. Gray popularized the use of neuromuscular blocking agents as essential components of general anaesthesia in Liverpool in the late 1940s. The underlying principle of the new technique was 'minimal narcotization with adequate curarization.' The motivations were to minimize the cardiovascular depressant effects of high concentrations of ether, cyclopropane, kemithal, or thiopental and to facilitate more rapid emergence of patients from the vulnerable state of general anaesthesia after surgery. Despite the advent of modern general anaesthetic agents over the last four decades, with less cardiovascular depression and rapid elimination, the practice of pharmacological paralysis with limited hypnotic administration continued to be popular and still has proponents in modern practice. In the seminal observational study by Sandin and colleagues, the incidence of unintended awareness among patients who received general anaesthesia without neuromuscular blocking agents was 0.1%, compared with 0.18% when patients were pharmacologically paralysed. A mundane explanation for the reduction in awareness in non-pharmacologically paralysed patients is that patient movement can potentially alert anaesthetists to the possibility of inadequate general anaesthesia. However, it is also possible that the need for or use of neuromuscular blocking agents covaries with other important risk factors for intraoperative awareness. Interestingly, only patients who had been pharmacologically paralysed reported anxiety and psychological symptoms in relationship to their awareness experience. In a comprehensive literature review, Ghoneim and colleagues endorsed the finding that pharmacological paralysis was an important risk factor for distressing awareness experiences. This important insight has again been corroborated in the recently published NAP5 study, where the overwhelming majority of awareness reports were from patients who had received neuromuscular blocking drugs and also where the anaesthetic concentration was reduced towards the end of surgery before antagonizing neuromuscular blockade. The avoidance or minimization of pharmacological paralysis might be the most effective currently available method to prevent traumatic intraoperative awareness.
Non-controversial: The Incidence of Intraoperative Awareness and Distressing Awareness Is Higher When Neuromuscular Blocking Agents Are Administered
It is self-evident that the avoidance of neuromuscular blocking agents does not in itself prevent intraoperative awareness if insufficient concentrations of hypnotic agents are administered. In 1846, Abbott received ether for a tumour removal and was aware, although not in pain, during the procedure. Gray popularized the use of neuromuscular blocking agents as essential components of general anaesthesia in Liverpool in the late 1940s. The underlying principle of the new technique was 'minimal narcotization with adequate curarization.' The motivations were to minimize the cardiovascular depressant effects of high concentrations of ether, cyclopropane, kemithal, or thiopental and to facilitate more rapid emergence of patients from the vulnerable state of general anaesthesia after surgery. Despite the advent of modern general anaesthetic agents over the last four decades, with less cardiovascular depression and rapid elimination, the practice of pharmacological paralysis with limited hypnotic administration continued to be popular and still has proponents in modern practice. In the seminal observational study by Sandin and colleagues, the incidence of unintended awareness among patients who received general anaesthesia without neuromuscular blocking agents was 0.1%, compared with 0.18% when patients were pharmacologically paralysed. A mundane explanation for the reduction in awareness in non-pharmacologically paralysed patients is that patient movement can potentially alert anaesthetists to the possibility of inadequate general anaesthesia. However, it is also possible that the need for or use of neuromuscular blocking agents covaries with other important risk factors for intraoperative awareness. Interestingly, only patients who had been pharmacologically paralysed reported anxiety and psychological symptoms in relationship to their awareness experience. In a comprehensive literature review, Ghoneim and colleagues endorsed the finding that pharmacological paralysis was an important risk factor for distressing awareness experiences. This important insight has again been corroborated in the recently published NAP5 study, where the overwhelming majority of awareness reports were from patients who had received neuromuscular blocking drugs and also where the anaesthetic concentration was reduced towards the end of surgery before antagonizing neuromuscular blockade. The avoidance or minimization of pharmacological paralysis might be the most effective currently available method to prevent traumatic intraoperative awareness.
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