Although widely utilized in a variety of clinical venues and delivered by nurses and physicians with a broad range of clinical training and experience, core principles guiding safe sedation practice are not well established. Sedation practices (ie, drug choice and dose, patient preparation, procedure room equipment for safe sedation delivery, patient monitoring standards, practitioner training requirements, sedation goals) are often left to the discretion of the individual sedation practitioner and are not well regulated. The chapter will discuss core concepts of anesthetic pharmacology that apply to sedation practice (Table 27–1) that sedation practitioners should consider prior to administering sedatives and analgesics.
|The sedation continuum|
|The difference between moderate and deep sedation|
|The importance of recognizing deeper-than-intended sedation|
|The time to peak effect of common analgesics and sedatives used in sedation practice|
|The influence of sedative–analgesic interactions on responsiveness, respiratory depression, and analgesia|
THE SEDATION CONTINUUM
No discussion of safe sedation techniques can begin without first asking “What is sedation?” In general, sedation is a drug-induced, depressed level of consciousness that allows a patient to safely tolerate a procedure or noxious stimuli, while maintaining innate cardiopulmonary functions. Defining sedation more specifically is a difficult task. Terms such as procedural sedation, conscious sedation, deep sedation, sedation and analgesia, monitored anesthetic care, moderate sedation, anxiolysis, and minimal sedation are often used interchangeably in the literature and in daily discussions between caregivers and medical specialists. This lack of standardized language and definitions concerning the practice of sedation has served to confuse communication as well inhibit the development of consistent sedation guidelines, standards, and techniques.1,2
Currently, the majority of position papers, practice guidelines, and medical literature use the definition and taxonomy put forth by the American Society of Anesthesiologist (ASA), called the sedation continuum.3 This sedation continuum presents stages of central nervous system depression that eventually culminate in general anesthesia. Four sedation states are defined: minimal sedation, moderate sedation, deep sedation, and general anesthesia. Each of these states is differentiated by responsiveness to stimulation, ability to maintain a natural airway, adequacy of spontaneous airway, and impairment of cardiovascular functions. For purposes of clarity, the ASA sedation continuum will be used throughout this chapter (Table 27–2).3
|Deep Sedation/Analgesia||General Anesthesia|
|Responsiveness||Normal response to verbal stimulation||Purposeful response to verbal and tactile stimulation||Purposeful response following repeated painful stimulation||Unarousable, even with painful stimulus|
|Airway||Unaffected||No intervention required||Intervention may be required||Intervention often required|
|Spontaneous ventilation||Unaffected||Adequate||May be inadequate||Usually inadequate|
|Cardiovascular function||Unaffected||Usually maintained||Usually maintained||May be impaired|
An important consideration of the sedation continuum is the correlation of central nervous system depression and ability to maintain vital cardiopulmonary functions. As central nervous system depression increases, a patient’s ability to maintain vital cardiopulmonary function decreases. Loss of responsiveness to verbal and tactile stimulation is an important transition increasing the likelihood of adverse cardiopulmonary events. Once the patient is unresponsive, mitigation of these risks is a function of the provider’s skill in managing a patient under general anesthesia (Figure 27–1).
Sedation is a drug-induced state of central nervous system depression that produces dose-related adverse cardiopulmonary effects along a continuum. As the dose increases, the patient moves along the continuum toward deeper sedation states, and the likelihood of intervention to counter adverse cardiopulmonary events increases.
Although the sedation continuum provides a conceptual and intellectual framework with which to understand sedation, its definitions and distinctions are artificial and imperfect. The continuum is a progression of central nervous system depression, which cannot always be rigidly categorized into distinct clinical states. A patient’s physiologic features may overlap more than one sedation state, and the speed with which a patient moves through these states is unpredictable. Furthermore, a patient may clinically skip states all together.
An important premise of the sedation continuum is that the loss of responsiveness to verbal and tactile stimulation is an important transition that correlates with the increasing likelihood of adverse cardiopulmonary events. The ability of a patient to respond purposefully to verbal commands is an important distinction between moderate and deep sedation. A patient who responds can self-rescue. This marks the increasing likelihood that a patient will lose the innate ability to maintain his or her cardiopulmonary function without provider rescue. Typically, if a patient remains responsive to voice and tactile stimulation (moderate sedation), with airway obstruction or hypoventilation, the situation can generally be resolved by stimulation and asking the patient to take a deep breath. If a patient is unresponsive, then the burden of rescue falls to the provider. Provider rescue may involve one or more simultaneous activities (Table 27–3).
|Call for help.|
|Stop administration of sedatives and analgesics.|
|Consider reversal agents if appropriate.|
|Return patient to intended sedation state.|
|Consider cancelling procedure if difficult to complete at intended sedation state.|
Preserving responsiveness is a critical safety feature in moderate sedation as it enables a patient to respond, with prompting, should airway obstruction or hypoventilation occur. If a patient becomes unresponsive, a feature of deep sedation and general anesthesia, then rescue is entirely dependent on the skills of the sedation practitioner.
PHARMACODYNAMIC MODELING FOR SEDATION
In this chapter, previously published pharmacodynamic models4, 5, 6, 7, 8, 9, 10, and 11 are used to illustrate the profiles of anesthetic drugs used in sedation practice and illustrate key concepts vital to the practice of safe sedation. As with all models, their predictions are inherently wrong and are unlikely to consistently predict an individual patient’s response. However, they are useful to visualize anesthetic behavior as it pertains to sedation. Model assumptions and limitations, presented in Table 27–4, should be considered when interpreting models predictions.