CHAPTER 22 Sedation for Percutaneous Procedures

INTRODUCTION

‘Sedation and analgesia’ describe a state in which patients can tolerate unpleasant procedures while maintaining cardiac and respiratory function and still maintain the ability to respond purposefully to both verbal commands and tactile stimulation. The Task Force on sedation and analgesia decided that the term ‘sedation and analgesia’ (sedation/analgesia) more accurately defines this therapeutic goal than does the commonly used but imprecise term ‘conscious sedation.’ This level of sedation does not include a level in which the only intact reflex is withdrawal from a painful stimulus.¹ Although sedation has been described as ‘light sleep’² and textbooks note that ‘the terms sleep, hypnosis, and unconsciousness are used interchangeably in anesthesia literature to refer to the state of drug-induced sleep,’³ pharmacological sedation is not the same as physiological sleep.

During interventional procedures the goal is to provide enough sedation to keep the patient comfortable, relaxed, and communicative. Even though this preferred light sedation is relatively safe, rescue medications and equipment to support respiration and circulation should be readily available.

LEVELS OF SEDATION

See Table 22.1.

Table 22.1 Definition of General Anesthesia and Levels of Sedation/Analgesia ¹

Minimal sedation (anxiolysis) is a drug-induced state during which patients respond normally to verbal commands. Although cognitive function and coordination may be impaired, ventilatory and cardiovascular functions are unaffected.

Moderate sedation/analgesia (i.e. ‘conscious sedation’) is a drug-induced depression of consciousness during which patients respond purposefully* to verbal commands, either alone or accompanied by light tactile stimulation. No interventions are required to maintain a patent airway, and spontaneous ventilation is adequate. Cardiovascular function is usually maintained.

Deep sedation/analgesia is a drug-induced depression of consciousness during which patients cannot be easily aroused but respond purposefully* following repeated verbal or painful stimulation. The ability to independently maintain ventilatory function may be impaired, necessitating assisted airway support. Cardiovascular function is usually maintained.

General anesthesia is a drug-induced loss of consciousness during which patients are not arousable, even by painful stimulation. The ability to independently maintain ventilatory function is often impaired. Patients often require assistance in maintaining a patent airway, and positive-pressure ventilation may be required because of depressed respiration or drug-induced neuromuscular depression. Cardiovascular function may be impaired. Because sedation is a continuum, it is not always possible to predict how an individual patient will respond. Hence, practitioners intending to produce a given level of sedation should be able to rescue patients whose level of sedation becomes deeper than initially intended. Individuals administering moderate sedation/analgesia (i.e. ‘conscious sedation’) should be able to rescue patients who enter a state of deep sedation/analgesia, while those administering deep sedation/analgesia should be able to rescue patients who enter a state of general anesthesia.

Deep sedation and general anesthesia are not usually recommended for most of pain management procedures, as an awake, cooperative patient is needed to prevent complications related to nerve injury, allergic reactions, or medication toxicity (Table 22.2).

Table 22.2 Ramsay Level of Sedation Scale ²

Clinical Score	Level of Sedation Achieved
6	Asleep, no response
5	Asleep, sluggish response to light glabellar tap or loud auditory stimulus
4	Asleep, but with brisk response to light glabellar tap or loud auditory stimulus
3	Sleepy, but responds to commands
2	Patient cooperative, oriented and tranquil
1	Patient anxious, agitated or restless

GENERAL PREPARATION

The risks, benefits, and alternatives of sedation should be explained to the patient in lay terms. The main goals in administering sedatives and analgesic medications are to facilitate the completion of a potentially difficult procedure and to provide a safe and comfortable environment for the patient. The most feared risk of sedation is respiratory depression, which can result in catastrophic consequences if not recognized and treated promptly. The patient may also decline sedation, at which point alternatives can be considered including local anesthesia, relaxation techniques and, for pediatric patients, general anesthesia. After thorough explanation is provided and all questions are answered, informed consent is obtained before any sedation is administered.

Preprocedural assessment

All patients who are scheduled to receive sedation should be thoroughly evaluated prior to the procedure. Relevant issues that should be addressed include past medical history, past surgical history to include any anesthetic complications, drug allergies, and current medications to include anticoagulants, smoking, alcohol use and recreational drug history, and NPO status. The risk stratification classification of the American Society of Anesthesiologists (ASA) provides an excellent preprocedure assessment tool for this purpose (Table 22.3).

Table 22.3 American Society of Anesthesiologist Physical Class Risk Stratification

Class I	Normal healthy patient
Class II	Mild systemic disease
Class III	Severe systemic disease
Class IV	Life-threatening illness
Class V	Moribund patient

Table 22.4 provides a summary of the American Society of Anesthesiologists preprocedure fasting guidelines. The recommendations apply to healthy patients who are undergoing elective procedures. They are not intended for women in labor. Following the guidelines does not guarantee complete gastric emptying has occurred.

Table 22.4 Summary of American Society of Anesthesiologists Preprocedure Fasting Guidelines for Healthy Patients Who Are Undergoing Elective Procedures

Ingested Material	Minimum Fasting Period
Clear liquids	2 h
Nonhuman milk	6 h
Light meal	6 h

The fasting periods noted in Table 22.4 apply to all ages.

Examples of clear liquids include water, fruit juices without pulp, carbonated beverages, clear tea, and black coffee.

Since nonhuman milk is similar to solids in gastric emptying time, the amount ingested must be considered when determining an appropriate fasting period.

A light meal typically consists of toast and clear liquids. Meals that include fried or fatty foods or meat may prolong gastric emptying time. Both the amount and types of foods ingested must be considered when determining an appropriate fasting period.

Airway assessment procedures for sedation and analgesia

The airway should be evaluated prior to giving sedative medications. Oversedation will cause respiratory depression and may require respiratory support. Oversedation can also cause aspiration, obstruction, bronchospasm, and laryngospasm requiring tracheal intubation and ventilatory support. Intubation may be especially difficult in patients with atypical airway anatomy. Airway abnormalities may also increase the likelihood of airway obstruction following the administration of sedatives and analgesics. Warning signs of a difficult airway are listed in Table 22.5. Recommendations for frequency of monitoring and documentation during sedation/analgesia are listed in Table 22.6.

Table 22.5 Warning Signs of a Difficult Airway

Previous problems with sedation

Stridor, snoring, or sleep apnea

Advanced rheumatoid arthritis

Chromosomal abnormality (e.g. trisomy 21)

Significant obesity (especially involving the neck and facial structures)

Short neck and limited neck extension

Decreased hyoid-mental distance (<3 cm in an adult)

Neck or anterior mediastinal mass

Cervical spine disease or trauma

Tracheal deviation

Dysmorphic facial features (e.g. Pierre–Robin syndrome)

Small opening (< 3 cm in an adult)

Edentulous

Protruding incisors

Loose or capped teeth

Dental appliances

High, arched palate

Macroglossia

Tonsillar hypertrophy

Nonvisible uvula

Micrognathia

Retrognathia

Trismus and significant malocclusion

Table 22.6 Recommendations for Frequency of Monitoring and Documentation During Sedation/Analgesia ¹

Monitoring	Conscious Sedation	Deep Sedation
Heart rate	Continuous	Continuous
Oxygen saturation	Continuous	Continuous
Respiratory rate	Minimum of every 15 min	Minimum of every 5 min
Noninvasive blood pressure	Minimum of every 15 min	Minimum of every 5 min
Level of consciousness	Minimum of every 5 min	Minimum of every 5 min