CHAPTER 11

Sedation for Interventional Pain Procedures

Nancy Staats

INTRODUCTION

•   Many patients with acute and chronic pain may require sedation for interventional pain procedures.

•   Patients may have extreme anxiety about the pending procedure or be in so much pain that even positioning them without some analgesia and/or sedation becomes impractical.

•   There is great variability in type of sedation required to perform minimally invasive procedures, and depends on the procedure, the surgeon, and the patient.

•   Some physicians perform most procedures without any sedation, while other physicians may want deeper level of sedation for some or many of their procedures.

•   The personnel may differ depending on the locations of the procedures performed. Sometimes, a sedation nurse (RN or other) trained in OR sedation administers the medication, and other times the sedation is administered by an anesthesiologist.

•   The choice of anesthesia may differ depending on locations: (1) office-based procedures, (2) surgicenters, and (3) hospital.

•   While both scenarios occur, it should be noted that current FDA recommendations state that propofol should only be administered by an individual trained in airway management (ie, anesthesiologist or CRNA).

•   Currently, there is no consensus on the appropriate overall strategy.

There are a wide range of procedures being performed—from epidural steroid injections to implantation of spinal cord stimulators. Different procedures may require different levels of and different sedation techniques in order to optimize the outcome and the experience for the patient. Some proponents of using an anesthesiologist for sedation point to an appropriate analgesic experience for the patient, lack of movement, and safety in the operating room. Others are less inclined to utilize an anesthesiologist, citing risk of overuse of sedative medications, sometimes even resulting in spinal cord injury with deep sedation, along with an increased cost of care. When appropriately used, sedation can make the experience safer, more effective, efficient, and more comfortable without jeopardizing patient safety. Clearly if sedation is utilized, it is important to follow safe guidelines. There remain some principles that should be followed in providing sedation when performing interventional procedures.

TYPES OF ANESTHESIA

•   General anesthesia: rarely used for pain management procedures and will not be covered in this chapter.

•   Monitored anesthesia care or moderate sedation: used most often.

•   Conscious sedation or light anesthesia: appropriate for some procedures where patient’s feedback is important, eg, cervical blocks.

•   Local anesthesia: can be used for many of the minor procedures, such as trigger points and some epidural steroid injections. The payment for anesthesia for some of the more minor procedures can be dictated by particular insurers/providers in the region; this will also not be covered in this chapter.

•   Regional anesthesia: rarely used and will not be covered in this chapter.

PREOPERATIVE ASSESSMENT

As with any patient undergoing anesthesia of any kind, patients need an appropriate preoperative assessment, including risk level. While many of the procedures performed by the interventional pain physician may be considered minor, it is important to consider preoperative risk factors. Sicker patients have increased risk, even for a minor procedure. Complete preoperative assessment guidelines are readily available elsewhere they include but are not limited to:

•   Airway assessment

•   Adverse reaction to drugs/substances

        Contrast (possible co-reaction with allergy to shellfish)

        Antibiotics

        Allergies to anesthetics, egg whites, sulfites

        Latex

•   NPO status

•   Medications, including anticoagulants

•   Cardiopulmonary function and vital signs

•   Obesity/BMI and associated issues

•   Mental status

•   Counseling regarding procedure and expectations of the patient

RELEVANT FACTORS SPECIFIC TO THE CHRONIC PAIN PATIENT

•   High level of anxiety

•   Use of opioids and anxiolytics

•   Previous painful experience with pain procedures

•   Location of the block and prone position making difficult to mask

•   Chronic use of opiates—this can delay gastric emptying and increase nausea

•   Hypertension is not unusual in patients undergoing a procedure, particularly those having pain

PREOPERATIVE ANTICOAGULANTS

Chronic or acute use of medications that interfere with coagulation—though controversy exists, in general the patient taking NSAIDs or other classes of anti-inflammatory agents, including aspirin, are at low risk. For certain larger procedures, however, a PFA (platelet function assay) may be warranted. Warfarin should be stopped 4 to 5 days before the spinal procedures, and check INR and/or PT/PTT on the day of procedure. For more details, refer to anticoagulation chapter in this book. Weigh risks of stopping the anticoagulants to risks of epidural and/or spinal hematoma. The important factor is communication between the patient, surgeon and the anesthesiologist to decide the appropriate preoperative tests in order to minimize late cancellations.

MULTIPLE ALLERGIES

Multiple allergies (it’s important to inquire about “true” allergies). True allergy to local anesthetics, and particularly the amide local anesthetics, is extremely

•   Allergy to egg products, and particularly egg whites, has been considered a relative contraindication to propofol use; however, clinically significant allergic reactions to propofol are fortunately quite rare. There seems to be a higher risk when patients have multiple allergies, in particular multiple food allergies, and history of anaphylaxis.

•   Allergy to sulfites can occur, although not as common as allergy to sulfa. Use the sulfite-free preparation of Propofol.

•   Allergy to antibiotics is often real (ask for specifics, to determine whether it is in fact a true allergy or merely a vasovagal reaction from a shot, GI symptoms, etc) and care needs to be taken, avoiding the offending class of antibiotic.

•   Allergy to contrast solutions or iodine is also common, and there can be crossover with reactions to shellfish; consider pretreatment with diphenhydramine, H₂ blocker, and steroid. Consider using gadolinium-based contrast gadopentetate dimeglumine (Magnevist).

Follow the NPO guidelines appropriately and optimally. Our policy is NPO for 8 hours for solids and 4 hours for clear liquids; sips of water or other clear liquid up to 2 hours before is permitted. However, it is anesthesiologist’s responsibility to individualize the anesthetic plan for safety and efficiency.

REALISTIC EXPECTATIONS

Sometimes, the patient states “just put me out, I don’t want to feel a thing!” One must take the time to educate the patient regarding the reasons for the procedure and why their input may be critical to its safety and success. Furthermore, having realistic expectations makes it easier for everyone, and the vast majority of patients will understand when it is explained to them. The patient provides valuable feedback, whether negative (intraneural or intravascular placement) or positive (stimulator in the correct place). Many patients are comforted knowing that they will have someone with them for the entire time, making sure they are safe, stable, and as comfortable as possible.

DIAGNOSTIC BLOCKS

When performing diagnostic procedures, it is best to avoid opioid analgesics as they can alter the response to the diagnostic test. Diagnostic medial branch facet injections, discography, and diagnostic sympathetic blocks are common examples of such diagnostic procedures. After each block, the interventional pain physician will want to understand the response to the block. For example, if a patient has excellent relief with a medial branch block under most circumstances that may lead to performance of a radio frequency (RF) ablation. For example, if a patient received fentanyl prior to the injection or during the injection, the response is unreliable and may lead to ineffective RF ablation.

INTRAOPERATIVE CARE

Similar to any patient undergoing sedation, the pain patient undergoing an interventional procedure requires continuous monitoring of oxygen saturation, blood pressure, electrocardiogram, and respiratory rate throughout (see Table 11-1). We often give an anxiolytic agent like midazolam immediately upon entering the OR, prior to final positioning. We then explain everything and sedate with propofol to achieve an appropriate level of sedation for the procedure. Opioids may be needed in patients in significant pain prior to the procedure, although they need to be avoided during any diagnostic blocks. It is very important not to over-sedate patients undergoing a cervical block near the spinal cord.

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