Learning Objectives
After reading this chapter, the student should be able to:
- 1.
Identify causes of emergencies as they occur before treatment, between appointments, and after obturation, differentiating urgency from a true emergency.
- 2.
Identify patients who are at greater risk for experiencing pain after endodontic procedures.
- 3.
Describe the psychological and physiologic factors that affect pain perception and pain reaction and how these are managed.
- 4.
Define the flare-up and describe its management.
- 5.
List the factors that relate to greater frequency of interappointment or postobturation flare-ups.
- 6.
Describe and outline a sequential approach to endodontic emergencies:
- a.
Determine the source of pain (pulpal or periapical)
- b.
Establish a pulpal and periapical diagnosis
- c.
Identify the etiologic factor of the pathosis
- d.
Design an emergency (short-term) treatment plan
- e.
Design a long-term treatment plan
- 7.
Outline a system of subjective and objective examinations and radiographic findings to identify the source of pain and the pulpal or periapical diagnosis.
- 8.
Describe when pretreatment emergencies might occur and how to manage these emergencies.
- 9.
Outline the steps involved in treatment of painful, irreversible pulpitis.
- 10.
Describe the steps involved in treatment of necrotic pulp with acute apical periodontitis.
- 11.
Describe treatment of acute apical abscess and include the indications and procedure for incision and drainage.
- 12.
Detail pharmacologic supportive therapy (analgesics, anxiolytics, antibiotics, and antiinflammatory agents) used in emergencies and its role in controlling pain and infection.
Introduction
Endodontic emergencies constitute approximately two-thirds of all dental emergencies, , with many patients seeking emergency care for a painful tooth. There are a very large number of hospital emergency room visits for mouth abscess/facial cellulitis. These painful and infectious emergencies pose significant challenges to patients and dental providers. Pain and/or swelling occur in patients before (pretreatment), during (interappointment), and after (postobturation) root canal treatment. Understanding the causes of such emergencies results in appropriate diagnosis and treatment protocols for resolution of signs and symptoms.
Classical studies by Stanley, Fitzgerald, and Kakehashi as well as the preponderance of endodontic literature point to a bacterial etiology as the initial causative factor for pulpal pathosis. Both primary and secondary endodontic infections are polymicrobial in nature with an average of 10 to 20 microorganisms in primary and 1 to 3 microbial species in secondary infections. Examples of endodontic pathogens include gram positive ( Enterococcus species) and gram-negative ( Porphyromonas, Prevotella, Bacteroides species) bacteria as well as members of the spirochete family ( Treponema species). Other pathogens include viruses and fungi. Bacterial byproducts from such a mixed flora therefore constitute a soup of toxins that breakdown host tissues and initiate an inflammatory response. An untimely management attenuating such a response can lead to spread of the inflammatory mediators into the periapical regions, posing greater risks, such as facial abscesses and cellulitis (see Chapter 1 ).
Bacterial toxins fall into two categories: exotoxins and endotoxins. Exotoxins are secreted and released by the microorganism to degrade host tissues such as the extracellular matrix. Many of these function via enzymatic tissue breakdown and include enzymes belonging to the family of collagenases, proteases, lipases, chondroitinases, hyaluronidases, and cysteine and serine proteinases, among others. On the other hand, endotoxins are typically cell membrane/wall components such as lipoteichoic acid (LTA) and lipopolysaccharide (LPS). Still other specialized toxins include hemolysins and flagellins. Endotoxins play a crucial role in mediating pulpal pain. Because pain is the #1 reason why patients seek dental care, an in-depth understanding of pain detection and transmission is critical for management of a painful emergency.
LPS from a known endodontic pathogen, Porphyromonas gingivalis, has been shown in recent years to activate and sensitize trigeminal sensory neurons via Toll-like receptor-4 (TLR-4) expressed on sensory neurons. , On the other hand, non-TLR mechanisms have also been demonstrated for other bacterial species such as Staphylococcus aureus and Escherichia coli . Moreover, these studies suggest that bacterium-induced pain does not depend on tissue edema or immune cell activation. Collectively, these studies demonstrate that the concentration of the bacterial load dictates hyperalgesic conditions rather than local tissue inflammation (see Chapter 1 ).
Nonbacterial etiologies can also contribute to pulpal inflammation and emergency situations. These emergency situations include pulpal inflammation caused at the time of caries removal or crown preparations performed without adequate coolant, characteristics of the cavity preparation most importantly, remaining dentin thickness over the pulp, and type of restorative material. It is well known that certain restorative materials promote marginal breakdown due to polymerization shrinkage and promote bacterial microleakage, whereas others release chemical agents such as resin monomers namely, BisGMA, urethane dimethacrylate (UDMA), and triethylene glycol dimethacrylate (TEGDMA), among others. These along with monomers present in dentin bonding agents such as hydroxyethyl methacrylate (HEMA) can be toxic to the underlying pulp if not polymerized fully. Biomaterial studies indicate that the hydrophobicity of nonpolymerized monomers displaces dentinal fluid, thereby diffusing through the tubules and into the pulp. , Collectively, factors that do not directly point to a microbial etiology must be considered in emergencies and appropriate diagnosis must be determined to deliver a suitable treatment.
Both microbial and nonmicrobial etiologies culminate in an immunologic response. Patients with emergencies often report symptoms of spontaneous pain, pain to swallow, referred pain, pain that wakes them up, and pain that lingers after a stimulus. These symptoms are often mediated by an immunologic response and by (1) inflammatory mediators and (2) fluid pressure. Management of such a painful episode cannot be efficiently achieved by pharmacologic means alone. Peripheral nerve sprouting, increased expression of tetrodotoxin resistant (TTX-R) sodium channels, as well as increased expression of transient receptor potential (TRP) channels, , all culminate in dramatic reduction of peripheral nerve thresholds of Aδ and C-fibers. Clinical studies consistently implicate preoperative pain as a strong predictor of postoperative pain. Therefore emergency protocols must make every effort to attenuate preoperative pain to minimize development of chronic odontogenic pain conditions.
Endodontic emergencies are therefore a challenge for both diagnosis and management. Knowledge and skill in several aspects of endodontics are required; failure to apply these can result in serious consequences. Incorrect diagnosis and/or treatment can shift an acute condition to a chronic pain or infection-induced life-threatening condition. The clinician must have knowledge of pain mechanisms, patient management, diagnosis, anesthesia, therapeutics, and appropriate treatment measures for both hard and soft tissues. This chapter discusses approaches to the diagnosis and treatment of various categories of emergencies. It includes a review of etiologic factors and details of a systematic approach to identifying and diagnosing the offending cause; then appropriate treatment, including pharmacotherapy, is described.
Definition
By definition, endodontic emergencies are usually associated with pain and/or swelling and require immediate diagnosis and treatment. These emergencies are caused by pathoses in the pulp or periradicular tissues. They also include severe traumatic injuries that result in luxation, avulsion, or fractures of the hard tissues. Management of emergencies related to trauma will not be included in this chapter (see Chapter 11 ).
Categories
Pretreatment Emergency
These are situations in which the patient is seen initially with severe pain and/or swelling. Problems occur with both diagnosis and treatment.
Interappointment and Postobturation Emergency
Also referred to as a “flare-up,” an interappointment and postobturation emergency problem occurs after an endodontic appointment. Although an upsetting event, this problem is easier to manage because the offending tooth has already been identified and a diagnosis has been previously established. Also, the clinician has knowledge of the prior procedure and will be better able to correct the problem.
The Challenge
It is satisfying and rewarding to successfully manage a distraught patient who has an emergency ( Fig. 9.1 ). In contrast, it is very distressing to have a patient with a flare-up after root canal treatment in a previously asymptomatic tooth. The aim is to increase occurrences in the first category and decrease those in the second.
Differentiation of Emergency and Urgency
Whether a pretreatment, interappointment, or postobturation problem, it is important to differentiate between a true emergency and the less critical urgency. A true emergency is a condition requiring an unscheduled office visit with diagnosis and treatment. The visit cannot be rescheduled because of the severity of the problem. Urgency indicates a less severe problem; a visit may be scheduled for mutual convenience of the patient and the dentist. Key questions, which may be asked by telephone, to determine severity include the following:
- 1.
Does the problem disturb your sleeping, eating, working, concentrating, or other daily activities? (A true emergency disrupts the patient’s activities or quality of life.)
- 2.
How long has this problem been bothering you? (A true emergency has rarely been severe for more than a few hours to 2 days.)
- 3.
Have you taken any pain medication? Was the medication ineffective? (Analgesics do not relieve the pain of a true emergency.)
Affirmative answers to these questions require an immediate office visit for management and constitute a true emergency. Obviously, the patient’s emotional and mental status must also be determined. To some patients, even a minor problem has major proportions and is disruptive.
Development of a System
Because a misdiagnosis will probably result in improper treatment and an exacerbation of the problem, a systematic approach is mandatory. The emotional status of the patient, pressures of time, and stress on dentist and staff should not affect such an orderly approach.
Pain Perception and Pain Reaction
Pain is a complex physiologic and psychological phenomenon. Pain perception levels are not constant; pain thresholds as well as reactions to pain change significantly in various circumstances. Psychological components of pain perception and pain reaction comprise cognitive, emotional, and symbolic factors. The pain reaction threshold is significantly altered by past experiences and by present anxiety levels and emotional status. Anxiety decreases levels of both pain perception and pain reaction.
To reduce anxiety and consequently obtain reliable information about the chief complaint and to receive cooperation during treatment, the clinician should (1) establish and maintain control of the situation, (2) gain the confidence of the patient, (3) provide attention and sympathy, and (4) treat the patient as an important individual. Providing positive written information about pain control during root canal therapy can also reduce the fear associated with an emergency endodontic procedure. By managing these pain components, pain perception and reaction thresholds are raised significantly, greatly facilitating the procedure. Psychological management of the patient is the most important factor in emergency treatment!
Adjunctive pharmacotherapy may also be required in the management of patient anxiety during emergency treatment. Reducing anxiety at this stage will not only reduce the response to potentially painful stimuli during treatment, but also will decrease the tendency for the patient to recall the endodontic procedure as unpleasant. Mild anxiety may be managed with nitrous oxide ; however, the apparatus may be a bit cumbersome when obtaining treatment radiographs. Oral benzodiazepines can be very effective in managing more significant anxiety. Triazolam has a fast onset and a relatively short half-life and, because of its lipophilic nature, can be administered sublingually for rapid absorption. Thus this anxiolytic medication is quite convenient for sedation in the dental office. One quarter of a milligram of oral triazolam has been shown to be as effective as intravenous diazepam. Of course, patients who have taken or are given an oral sedative in the dental office must have transportation provided. Importantly, the potential drug interactions with other centrally acting agents must also be considered.
System of Diagnosis
Patients in pain often provide information and responses that are exaggerated and inaccurate. They tend to be confused as well as apprehensive. Clinicians may find it easy (and tempting) to rush through the diagnosis to institute treatment for a suffering patient. After pertinent information regarding the medical and dental histories is obtained, both subjective questioning and an objective examination are performed carefully and completely (See Box 9.1 ). ,
A rule of the true emergency is that one tooth is the offender, that is, the source of pain. In the excitement of the moment, the patient might believe that the severe pain is emanating from more than a single tooth. The clinician may become convinced also, leading to overtreatment.
Medical and Dental Histories
Medical and dental histories should be reviewed first. If the patient is the dentist’s own patient, the medical history is briefly reviewed and updated. If the patient is new, a standard, complete history is obtained. An important medical complication may be easily overlooked in an emergency situation. Certainly, the need for antibiotic prophylaxis must be determined even before initiating any portion of the oral examination that might induce a bacteremia, such as periodontal probing. Either a short or a complete dental history is recorded. This process includes recollection of dental procedures, recording a chronology of symptoms, or discussing an earlier relevant comment by a dentist.
Subjective Examination
When the patient is in pain, the subjective examination comprises careful questioning and is the most important aspect of diagnosis. Questions relate to the history, location, severity, duration, character, and eliciting stimuli of pain. Questions relating to the cause or stimulus that elicits or relieves the pain help select appropriate objective tests to arrive at a final diagnosis.
Pain that is elicited by thermal stimuli and/or pain that is referred is likely to originate from the pulp. Pain that occurs on mastication or tooth contact and is well localized is probably apical.
The three important factors constituting the quality and magnitude of pain are its spontaneity, intensity, and duration. If the patient reports any of these symptoms (and assuming that the patient is not exaggerating), significant pathosis is likely to be present. Careful questioning provides important information about the source of the pain and whether it is pulpal or periradicular. In fact, a perceptive, clever clinician should be able to arrive at a tentative diagnosis by means of a thorough subjective examination; objective tests and radiographic findings are then used for confirmation. For example, a reported complaint of severe, continuous (lingering) pain when the patient drinks cold beverages and marked tenderness on mastication indicates irreversible pulpitis and symptomatic apical periodontitis. These stimuli are then repeated in an objective examination to confirm the patient’s response.
Objective Examination
An endodontic diagnosis consists of two parts: pulpal and periapical diagnoses. Therefore objective examination is a comprehensive evaluation of the health of the pulp and periapical tissues. The clinician’s first clue to identifying the offending tooth is to carefully listen to the patient’s chief complaint and reproduce it using all the available tools. Objective examination includes the following clinical tests.
Physical Condition/Extraoral Examination
It is imperative to not miss signs of an infectious spread systemically. Signs include extraoral swelling (unilateral or bilateral), facial cellulitis, lymphadenopathy, trismus, and eye shut. Such signs are commonly also involved with elevated temperature. In addition to the emotional factors that complicate the diagnosis of endodontic emergencies, physical conditions induced as a result of these situations also contribute to the problems. Pain or swelling may limit mouth opening, thereby hampering diagnostic procedures as well as treatment ( Fig. 9.2, A – D ). In addition, hypersensitivity to thermal stimuli or pressure influences diagnosis and treatment. Therefore the most severe aspect of the emergency is treated first to facilitate diagnosis.
Intraoral Examination
Included under this examination is observation for intraoral swelling or sinus tracts, as well as mirror and explorer examination to note the presence of defective restorations, discolored crowns, recurrent caries, and fractures.
Pulp Vitality Tests
Pulp vitality tests are the most commonly used objective tests for diagnosing a painful or offending tooth. Although cold, hot, and electric pulp tests (EPTs) truly test only the function of nerves rather than pulpal inflammation or vitality, they are the most convenient tests available. Among these assessments, cold testing is the most accurate test and a combination of cold with EPT increases accuracy.
Again, it is important in identifying the offending tooth to repeat tests that mimic what the patient reports subjectively. In other words, the best test is to repeat the stimulus that reportedly causes the pain. This is especially true for pulpal disease that has not extended to the periradicular tissues (e.g., irreversible pulpitis with asymptomatic apical periodontitis). It is often difficult for the patient to localize the pain to a particular tooth due to the paucity of proprioceptive neurons in the dental pulp. As in the previous example, applying cold should reproduce pain of basically the same type and magnitude as that related by the patient. If similar subjective symptoms are not reproduced, this situation may not be a true emergency; the patient may be “overreporting” (exaggerating the problem), or the pain may be referred from a source other than that perceived by the patient.
Periapical Tests
Periapical inflammation occurs as early as 1 to 3 days after pulp exposure. Conceivably, periapical symptoms such as tenderness to biting, chewing, and pain to palpation or pressure can ensue shortly after. , These symptoms often occur despite absence of periapical bone resorption on radiographic examination, and therefore clinical tests that can localize pain to the offending tooth are essential tools for diagnosis of the periapical inflammatory status. These include (1) palpation over the apex; (2) digital pressure on, or wiggling of, teeth (preferred if the patient reports severe pain on mastication); (3) light percussion with the end of the mirror handle; and (4) selective biting on an object such as a cotton swab or Tooth Slooth.
Periodontal Examination
A periodontal examination is always necessary. Probing helps in differentiating endodontic from periodontal disease. For example, a periodontal abscess can simulate an acute apical abscess ( Fig. 9.3 ); however, with a localized periodontal abscess, the pulp is usually vital (see Chapter 7 ). In contrast, an acute apical abscess is related to an unresponsive (necrotic) pulp. These abscesses occasionally communicate with the sulcus and have a deep probing defect. In addition to these tests, when the differential diagnosis is difficult, a test cavity may identify the pulp status and isolate the offending tooth. A narrow-walled, isolated probing defect may also indicate a coronal fracture that has extended beyond the level of sulcular attachment, or a vertical root fracture (see Chapter 8 ).
Radiographic Examination
Radiographic examination is a crucial tool in diagnosing the offending tooth. As stated before, patients often have difficulty localizing pulpal pain. Additionally, studies have demonstrated that approximately half the teeth with periapical pathosis are asymptomatic to periapical tests. Vitality tests certainly aid in narrowing down the source of pain to one to two teeth. When vitality tests cannot confirm the true diagnosis due to presence of crowns, multiple teeth involvement, an anxious patient, or a patient with heightened responses to clinical tests, radiographic examination can provide several key clues that point to the offender. Recurrent caries, possible pulpal exposure, internal or external resorption, unusual appearance of the lamina dura, periapical pathosis, and traceable sinus tracts are some very important identifiers that help confirm diagnosis.
Both periapical and bitewing radiographs must be exposed during initial evaluation, as clinicians must never miss an opportunity to determine restorability of a tooth in addition to identifying the cause of the emergency. Additionally, three-dimensional (3D) cone beam computed tomography (CBCT) renders diagnosis more predictable than two-dimensional (2D) imaging alone. Some of the most diagnostically challenging cases are ones with tooth fractures. A recent meta-analysis suggests that CBCT has greater accuracy in confirming tooth fractures in teeth with clinically suspected but periapical-radiography–undetected tooth fractures. CBCT imaging therefore not only elevates a clinician’s ability to accurately diagnose, but also to appropriately treat an emergency case. To this end, knowing the offending tooth’s anatomy, the 3D relationship of critical anatomic structures such as the inferior alveolar nerve (IAN), and the extent of resorptive defects, are some unique advantages of 3D imaging.
Collectively, a systematic approach to diagnosis must be followed, and a combination of subjective and objective findings are carefully collected before attempting treatment. More specifics of diagnosis are included in Chapter 4 .
Diagnostic Outcome
After carefully working through the sequence described in the previous sections, the offending tooth and the tissue (pulpal or periapical) that is the source of pain should have been identified and a pulpal and periradicular diagnosis recorded. For many reasons, all or none of these conclusions may be clear. This circumstance may not be a true emergency, or the problem may be beyond the capability of the general dentist, and the patient should be referred ( Fig. 9.4 ). However, if the diagnosis is clear, treatment planning follows.
Treatment Planning
As previously discussed, inflammation and its consequences, i.e., increased tissue pressure and release of chemical mediators in the inflamed pulp or periapical tissues, are the major causes of painful dental emergencies. Therefore reducing the irritant, reduction of pressure, or removal of the inflamed pulp or periapical tissue should be the immediate goal; this approach usually results in pain relief. Of the two, pressure release is the most effective.
Pretreatment Emergencies
These emergencies require a diagnosis and treatment sequencing. Each of these steps is important: (1) categorizing the problem, (2) taking a medical history, (3) identifying the source, (4) making the diagnosis, (5) planning the treatment, and (6) treating the patient.
Patient Management
Patient management is always the most critical factor. The frightened patient in pain must have confidence that his or her problem is being properly managed.
Profound Anesthesia
Obtaining profound anesthesia of inflamed painful tissues is a challenge. Adequate anesthesia, however, will instill confidence and cooperation and influence the patient’s desire to save the offending tooth. Maxillary anesthesia is usually obtained by infiltration, or block injections in the buccal and palatal regions. With mandibular teeth, in addition to an IAN block with lidocaine, a long buccal injection for soft tissue anesthesia as well as infiltration of articaine on the facial may be necessary. Often (particularly with mandibular molars), although all “classic” signs of profound anesthesia are present (such as lip numbness), access into the dentin or pulp is painful, presumably due to sensitized pulpal nociceptors. It is therefore prudent to retest the tooth with a cold stimulus to assess pulpal anesthesia before initiating access into the pulp space. For those patients who still respond with pain, periodontal, intrapulpal, or intraosseous injection techniques are indicated. , These supplemental injections are often administered prophylactically, particularly with painful irreversible pulpitis. Other conditions (for example, acute apical abscess) require other approaches. Chapter 8 contains details.
Management of Symptomatic Irreversible Pulpitis
Because pain is the result of inflammation, primarily in the coronal pulp, removal of the inflamed tissue will usually reduce the pain.
With or Without Symptomatic Apical Periodontitis
Teeth with caries, large restorations, cracked teeth, or trauma are some etiologies of symptomatic irreversible pulpitis . Complete cleaning and shaping of the root canals are the preferred treatments if time permits. Access to contemporary aids such as the electronic apex locator (EAL), surgical operating microscope (SOM), ultrasonic instruments, and CBCT facilitates complete instrumentation. However, during times when time – or patient-related factors prevent complete instrumentation, pulpotomy or a partial pulpectomy on the largest canals (palatal or distal root of molars) is performed. Both procedures have demonstrated greater than 90% success rate in reducing postoperative pain from moderate to severe to mild to no pain. , , On the other hand, partial pulpectomy, but not pulpotomy of severely inflamed teeth, upregulates inflammatory mediators that promote further nerve sprouting, leading to greater postoperative pain, and has been strongly discouraged. , When there is a vital, inflamed pulp, other procedures such as trephination (artificial fistulation) by creating an opening through mucosa and bone are not useful and are contraindicated. ,
An old but still popular idea is that chemical medicaments sealed in chambers help control or prevent additional pain; this idea is not true. A dry cotton pellet alone is as effective in relieving pain as a pellet moistened with camphorated monochlorophenol (CMCP), formocresol, Cresatin, eugenol, or saline. , Therefore after irrigation of the chamber or canals with sodium hypochlorite (NaOCl), a dry cotton pellet is placed, and the access is sealed temporarily. These cases can be completed in a single visit; however, results of a recent meta-analysis suggest that cases completed in one visit are more likely to have postoperative pain medication consumption. Moreover, as stated before, preoperative pain is a strong predictor of postoperative pain. Additionally, calcium hydroxide [Ca(OH) 2 ] has been shown to significantly reduce inflammatory mediators such as cytokines and neuropeptides commonly known to activate and sensitize nociceptors. , Therefore allowing further reduction in the inflammatory load with intracanal medicament placement may reduce the probability of postoperative pain associated with one-visit cases. Lastly, reducing the occlusion to eliminate contact has been shown to aid in relief of symptoms but does not prevent symptoms.
Postoperative Pharmacologic Management
Pain Management: Recent systematic reviews and meta-analysis demonstrate that 600 mg ibuprofen or 600 mg ibuprofen with N-acetyl-p-aminophenol (APAP) 1000 mg is most effective in attenuating postoperative endodontic pain. , To prevent the build-up of the arachidonic acid metabolites that contribute a large portion of the inflammatory pain stimulus, the patient should take the first dose before the loss of local anesthesia and then take the nonsteroidal antiinflammatory drug (NSAID) “by the clock,” rather than “as needed” (PRN). Administering ibuprofen to the patient while in the chair has been shown to reduce initial postoperative pain. Moreover, a newer ibuprofen formulation, ibuprofen sodium dihydrate at a 512-mg dose has been shown to have a faster onset of action than ibuprofen acid producing a greater reduction in spontaneous pain and mechanical allodynia. It is noteworthy that the U.S. Food and Drug Administration (FDA)-recommended maximum daily dose of APAP is 4 gm per day, owing to the increasing evidence of APAP-induced hepatoxicity. However, it is well known that patients often underreport their use of over-the-counter (OTC) medications, such as NyQuil, Theraflu, and so on, that contain as high as 500 to 1000 mg APAP. Therefore a lower dose of 325 to 500 mg APAP in combination with 600 mg ibuprofen will have a safer drug profile compared with 1000 mg APAP, and will avoid “therapeutic misadventures.”
For patients with severe postoperative pain, other drug classes such as opioids maybe considered. However, the clinician must be fully aware of the recent opioid crisis that prevails; opioid overdose-related deaths have increased five-fold since 1999 ( https://www.cdc.gov/drugoverdose/epidemic/index.html ). An even more striking statistic shows that prescription opioid use by adolescents between the ages of 19 to 23 has a 33% increased risk of opioid misuse at a later stage in life. Moreover, the Practitioners Engaged in Applied Research and Learning (PEARL) Network findings suggest that endodontists are second after oral surgeons in prescribing opioid-like drugs to patients. Clinicians must significantly curtail contributing to the opioid epidemic. For patients with persistent, severe pain after an endodontic procedure, opioids with less abuse potential must be considered. Tramadol, a mu-opioid agonist, at varying doses has shown to have fewer opioid-like central effects compared with morphine (RA, 2018 #924); however, it is not devoid of addiction and abuse potential and must be used judiciously for severe postoperative pain. Ultracet (325 mg APAP, 37.5 mg tramadol) is a combination drug, which is a viable option for patients with severe postoperative pain. See Fig. 9.5 for a flexible analgesic strategy.
