Chapter 44. Ambulatory, Nonoperating Room, & Office-Based Anesthesia

• Out of the operating room anesthesia requires the anesthesia provider to work in remote locations in a hospital, where ease of access to the patient and anesthesia equipment is compromised; furthermore, the staff at these locations may be unfamiliar with the requirements for safe anesthetic delivery.
• In their guidelines and statements, the American Society of Anesthesiologists reminds anesthesia staff that it is important that both the physical and operational infrastructure is in place at any location to ensure the safe conduct of anesthesia.
• The underlying reason for ambulatory anesthesia and surgery is that it is less expensive and more convenient for the patient than inpatient admission.
• Regional and local anesthetic techniques are becoming increasingly popular in managing ambulatory orthopedic surgery.
• In general, ambulatory surgeries should be of a complexity and duration such that one could reasonably assume that the patient will make an expeditious recovery.
• Factors considered in selecting patients for ambulatory procedures include: systemic illnesses and their current management, airway management problems, sleep apnea, morbid obesity, previous adverse anesthesia outcomes (eg, malignant hyperthermia), allergies, and the patient’s social network (eg, availability of someone to be responsive to the patient for 24 h).

Outpatient/ambulatory anesthesia is the subspecialty of anesthesiology that deals with the preoperative, intraoperative, and postoperative anesthetic care of patients undergoing elective, same-day surgical procedures. Patients undergoing ambulatory surgery rarely require admission to a hospital and are fit enough to be discharged from the surgical facility after the procedure.

Nonoperating room anesthesia (or out of the operating room anesthesia) refers to both inpatients and ambulatory surgery patients who undergo anesthesia in settings outside of a traditional operating room. These patients can vary greatly, ranging from claustrophobic individuals in need of anesthesia for magnetic resonance imaging (MRI) procedures to critically ill septic patients undergoing endoscopic retrograde cholangiopancreatography in the gastrointestinal suite.

Office-based anesthesia refers to the delivery of anesthesia in a practitioner’s office that has a procedural suite incorporated into its design. Office-based anesthesia is frequently administered to patients undergoing cosmetic surgery, and anesthesia for dental procedures is also routinely performed in an office-based setting.

Although treatment may be similar for inpatients, ambulatory surgery center patients, out of the operating room patients, and office-based anesthesia patients, there are nonetheless various guidelines and statements from the American Society of Anesthesiologists (ASA) that pertain to these different locations. All of these recommendations should be reviewed at the ASA website (www.asahq.org/For-Healthcare-Professionals/Standards-Guidelines-and-Statements.aspx), as they are subject to change and modification.

Most patients are no longer admitted prior to the day of elective surgery. The trend for same-day admittance has been facilitated by advancements in surgical technique and technology (eg, laparoscopy), resulting in less invasive surgery, advancements in anesthesia care (eg, shorter acting medications) and improved postoperative pain and nausea management.

The use of short-acting anesthetic agents (eg, propofol, desflurane, and rocuronium) has likewise contributed to making ambulatory surgery easier; however, such cases were performed successfully using thiopental, isoflurane, and succinylcholine when the newer agents were not available. Although inhalational agents (eg, sevoflurane and desflurane) lead to prompt emergence, they also contribute to postoperative nausea and vomiting (PONV). Propofol, which may have antiemetic effects as a part of total intravenous anesthesia (TIVA), can potentially reduce PONV; however, TIVA may require more time for patients to meet discharge criteria.

With an aging and increasingly obese population, patients with significant comorbidities present for ambulatory surgery. Although age per se is not a factor in determining candidacy for ambulatory procedures, each patient must be considered in the context of his or her comorbidities, the type of surgery to be performed, and the expected response to anesthesia.

Patients with known or likely difficult airways should probably not be candidates for office-based procedures; however, they may be appropriately cared for in a well equipped and fully staffed ambulatory surgery center. Important considerations for such patients include the availability of difficult airway equipment, such as an intubating LMA or videolaryngoscope, the availability of additional experienced anesthesia providers, and surgeons/anesthesiologists capable of performing emergency tracheostomy/cricothyroidotomy. If there are concerns regarding the ability to manage the airway in an ambulatory surgery setting, or if a surgical airway is thought to be a possibility, the patient may be better served in a hospital setting where immediate consultation and assistance is available.

Similarly, patients with unstable comorbid conditions, such as decompensated congestive heart failure or uncontrolled hypertension, may benefit more from having their procedure performed in a hospital than a free-standing facility. Indeed, many patients undergo ambulatory procedures in a hospital, as opposed to a free-standing surgery center or office. Such patients have the benefit of both the availability of a hospital’s resources and the convenience of being an ambulatory patient. Should their condition warrant additional care, hospital admittance is possible; however, such flexibility comes with the costs associated with hospital care.

The anesthesiologist must know which preexisting medical conditions predict a specific intraoperative and/or postoperative adverse event (AE) for the patient in question. Likewise, procedures suitable for ambulatory surgery should have a minimal risk of perioperative hemorrhage, airway compromise, and no particular requirement for specialized postoperative care. Based on risk identification, the anesthesiologist should be able to mitigate unforeseen AEs and provide optimal care for patients in this type of setting. Although current evidence-based medicine can provide recommendations for some high-risk ambulatory issues, evidence is lacking for most such situations.

Obesity and Obstructive Sleep Apnea

Obesity is associated with many concomitant disease states, such as hypertension, diabetes, hyperlidipemia, and obstructive sleep apnea (OSA). The physiologic derangements that accompany these conditions include changes in oxygen demand, carbon dioxide production, alveolar ventilation, and cardiac output. Patients with obesity and OSA are at increased risk of postoperative respiratory complications, such as prolonged airway obstruction and apnea. Scores for predicting the probability of these complications can aid in the preoperative assessment and referral to a hospital setting (Tables 44-1 and 44-2). Although a sleep study is the standard way to diagnose sleep apnea, many patients with OSA have never been identified as having OSA. Consequently, an anesthesiologist may be the first physician to detect the presence or risk of sleep apnea. The ASA has provided suggestions on the types of procedures and anesthetics that can safely be used in ambulatory patients with OSA (Table 44-3). In addition to the usual discharge criteria, the ASA also recommends the following in patients with OSA:

• Return of room air oxygen saturation to baseline level
• No hypoxemic episodes or periods of airway obstruction when left alone
• Monitoring for 3 hours longer prior to discharge than patients without OSA
• Monitoring for 7 hours following an episode of airway obstruction or hypoxemia while breathing room air in an unstimulating environment

According to the ASA Task Force on Obesity and OSA, these OSA patients can be managed safely as outpatients; however, they have an increased risk of postoperative complications requiring increased monitoring, availability of radiologic/laboratory services, and availability of continuous positive airway pressure and mechanical ventilation, thus making an office-based setting potentially inadequate for managing complications that may arise. Nonetheless, under certain conditions, anesthesia and surgery can be performed in an ambulatory surgery center or hospital outpatient facility.

Cardiac Conditions

Increasingly, patients present to ambulatory surgery with a variety of cardiac conditions treated both pharmacologically and mechanically (eg, cardiac resynchronization therapy, implantable cardioverter-defibrillators [ICDs], stents). It is therefore likely that anesthesia staff working in ambulatory settings will encounter increasing numbers of such patients, who, despite a cardiac history, have stable cardiac conditions. Patients previously treated with stents are likely to be on antiplatelet regimens. As always, these agents should not be discontinued unless a discussion has occurred between the patient, cardiologist, and surgeon regarding both the necessity of surgery and the discontinuation of antiplatelet therapy. Likewise, β-blockers should be continued perioperatively. Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers may contribute to transient hypotension with anesthesia induction, but their continuation or discontinuation perioperatively seems to have minimal effects, as patients so treated likely will need to have intraoperative hypotension corrected in either case. The ASA guidelines recommend that patients presenting with a pacemaker or ICD should not leave a monitored setting until the device is interrogated, if electrocautery was employed; however, this ASA recommendation is controversial, as some argue that if bipolar cautery is used at a distance of greater than 15 cm from the device, immediate interrogation of the device is not necessary prior to discharge from a monitored setting. Likewise, if an ICD is present, and there is anticipated electromagnetic interference the device’s antitachycardia features should be inhibited perioperatively (see Figures 44-1 and 44-2).

Glucose Control

In a consensus statement on perioperative glucose control, the Society for Ambulatory Anesthesia found insufficient evidence to make strong recommendations about glucose management in ambulatory patients, and thus management suggestions parallel those of the inpatient population; however, the panel recommends a target intraoperative blood glucose concentration of <180 mg/dL.

Malignant Hyperthermia

Patients with a history of malignant hyperthermia can be safely given nontriggering anesthetics and discharged as ambulatory patients. Prophylactic dantrolene should not be administered.

Intraoperative management in the ambulatory patient undergoing surgery is aimed at providing rapid emergence, good analgesia, and minimal PONV while creating acceptable operating conditions. Often these goals compete with one another. Although inhalational anesthesia with sevoflurane may speed emergence, compared with total intravenous anesthesia (TIVA), the likelihood of PONV may be greater, if an additional prophylactic drug is not administered. Numerous studies conducted by regional anesthesiologists have shown how regional anesthesia can speed discharge time, compared with general anesthetics, in the ambulatory population—in part, by potentially reducing the incidence of PONV. Nitrous oxide increases the likelihood of PONV, but this effect can be overcome by adding a prophylactic agent. Likewise, multimodal perioperative analgesia can be approached using a variety of drugs, including local anesthetics, acetaminophen, and nonsteroidal anti-inflammatory agents (NSAIDs) to reduce the use of opioids, which contribute to PONV risk.

Thromboembolism remains a risk after ambulatory and office-based surgery, as with inpatient surgery. Pneumatic compression devices and pharmacologic thromboprophylaxis should be used in patients at increased risk. During monitored anesthesia care, supplemental oxygen can contribute to operating room fires by creating an oxygen-rich environment that facilitates ignition by cautery devices. During head and neck surgery, anesthesia providers must be especially vigilant not to create an environment where fire becomes more likely. When oxygen is administered via a nasal cannula or face mask, the minimal amount of supplemental oxygen should be delivered, if any, and tenting of the drapes around the patient’s head should be prevented.

Managing a patient’s emergence, postoperative pain, and PONV is critical to expediting discharge. A plan to handle complications, such as postoperative pain and PONV, should be in place preoperatively to standardize and streamline management as much as possible.

The entire anesthetic experience of the ambulatory surgery patient should be focused on minimizing complications, especially postoperative pain and PONV. Multimodal approaches to both complications are advised; see Chapter 17 for a discussion of PONV management. Use of a combination of agents (eg, ondansetron, dexamethasone, and droperidol) has shown greater efficacy than monotherapy (eg, ondansetron alone) in patients at high risk of PONV. Likewise, analgesia regimens that minimize opioid use reduce PONV.

Pain management is centered on the combined use of regional techniques, opioids, and NSAIDSs (multimodal analgesia). Gabapentinoids (gabapentin, pregabalin) may have beneficial effects as part of a multimodal pain regimen. Likewise, oral, rectal, or intravenous acetaminophen or NSAIDs can be useful in the ambulatory setting. Cyclooxygenase-2 selective inhibitors have been used as part of multimodal pain management approaches, but their potential for prothrombotic effects has restricted their use.

Scoring systems have been devised to facilitate timely and safe PACU discharge and assess home readiness after ambulatory surgery. The Aldrete scoring system, which includes activity, respiration, circulation, consciousness, and oxygen saturation, helps guide recovery from the PACU in the ambulatory surgery unit. Scoring systems and guidelines that standardize patient discharge from the ambulatory surgery center to home are also available (see Tables 44-4, 44-5, 44-6, and 44-7).

Criteria for discharge generally require that the patient:

• Is alert and oriented to time and place
• Has stable vital signs
• Has pain controlled by oral analgesics or peripheral nerve block
• Has nausea or emesis controlled
• Is able to walk without dizziness
• Has no unexpected bleeding from the operative site
• Is able to take oral fluids and void
• Has discharge instructions and prescriptions from the surgeon and anesthesiologist
• Accepts readiness for discharge
• Has a responsible adult escort present

Increasingly, patients are not being required to drink or void before discharge from ASCs. Such patients require plans and instructions for follow-up care to provide for possible rehydration and bladder catheterization, if required.

Various complications can occur that necessitate emergent transfer to a nearby hospital. Some surgical complications cannot be repaired in the ambulatory operating suite. Inadequately controlled pain and postoperative nausea and vomiting are the two most frequent causes of unplanned hospital admission from ASCs, with other causes less frequent. Accreditation agencies mandate that office based operating rooms have emergency equipment, drugs, and protocols for patient transfers. In addition to advanced cardiac life support medications, dantrolene and intravenous lipid emulsion should be available to treat malignant hyperthermia and local anesthetic-induced cardiotoxicity. Additionally, surgeons operating in an office-based practice must have admitting privileges at a nearby hospital or arrangements with an accepting physician to provide for patient transfer, if necessary in addition to a hospital transfer protocol in place. The American Association for Accreditation of Ambulatory Surgery Facilities reviewed 1,141,418 outpatient procedures from 2001 to 2006 in the facilities it accredits and noted 23 deaths. Pulmonary embolism following abdominoplasty was the leading cause of death in an office-based surgery facility (Figures 44-3 and 44-4).

Off-site anesthesia (nonoperating room anesthesia) encompasses all sedation/anesthesia provided by anesthesiology services outside of the operating room environment. Over the past few decades, requests for these services in remote locations have been steadily increasing, and in many large hospitals today more anesthetics are routinely administered for procedures off-site than in the operating room suite. According to some estimates, nonoperating room anesthesia accounts for 12.4% of all anesthetic care in the United States. As a result, some clinical facilities have determined that is it safer and more cost-effective to assign anesthesia team(s) for scheduled blocks of times to provide care for such procedures, and some institutions are constructing procedural suites where bronchoscopy, gastrointestinal endoscopy, cardiac, and interventional radiology procedures can be performed in a centralized area for increased safety and efficiency. It is important to remember that the same basic standards for anesthesia care need to be met, regardless of the location. Furthermore, the challenges of unfamiliar environments that are far removed from the surgical suite, including anesthesia-naïve personnel, require advance planning for the off-site anesthesiologist.

Unlike patients undergoing office-based or ambulatory surgery center procedures, out of the operating room patients are frequently among the sickest of inpatients. Anesthesia staff are often called to work in the gastrointestinal suite, cardiac catheterization laboratory, electrophysiology laboratory, radiology suite, radiation oncology suite, and, occasionally, the critical care unit. Often these locations were constructed without anticipation that anesthesia would be provided there. Consequently, anesthesia work space is routinely constrained, and access to the patient is limited. Moreover, the procedure physicians and ancillary staff in these areas often fail to understand what is required to safely deliver anesthesia (hence the frequent request to “give them a squirt” of propofol) and do not know how to assist the anesthesia provider when difficulty arises. As noted in the ASA guidelines, the expectations for out of the operating room anesthesia are the same as in any practice location (Table 44-8).

Basic principles for nonoperating room anesthesia can be broadly classified into three categories: patient factors, environmental issues, and procedure-related aspects. Patient factors include comorbidity, airway assessment, fasting status, and monitoring. Environmental issues include anesthesia equipment, emergency equipment, and magnetic and radiation hazards. Procedure-related aspects include duration, level of discomfort, patient position, and surgical support.

The ASA Closed Claims Database has demonstrated that claims related to out of the operating room anesthesia care have a greater severity of injury than closed claims related to operating room anesthesia care. Monitored anesthesia care was the primary technique in more than half of the claims reviewed. Many of these closed claims arose from injuries related to inadequate oxygenation/ventilation during procedures in the gastrointestinal suite. Suggested requirements for the safe delivery of out of the operating room anesthesia are presented in Tables 44-9, 44-10, 44-11, and 44-12.

Increasingly, nonanesthesia providers in the gastrointestinal lab and the emergency department provide sedation with a variety of agents, including propofol and ketamine. In fact, some reports indicate that nonanesthesia providers provide administer sedation and analgesia for almost 40% of the procedures performed in the United States. The ASA guidelines and the Joint Commission have described the continuum of depth of sedation, ranging from minimal sedation to general anesthesia (Table 44-13). Recently, the Centers for Medicare and Medicaid Services has mandated that all sedation in a hospital be under the direction of a physician—generally, the anesthesia service chief. Consequently, anesthesiologists must not only from time to time provide anesthesia in a nonoperating room setting, but must also develop policies and quality assurance review mechanisms for nonanesthesia providers to safely provide sedation. Such policies should be focused on assuring that the “sedationist” has the necessary skills to provide for patient rescue, should mild or moderate sedation become deep sedation or general anesthesia.

Risks associated with sedation/analgesia are highlighted in Table 44-14. Sedation providers should know how to reverse benzodiazepines and opioids and provide bag/mask airway support and to be facile in the use of airway adjuvants. A mechanism to ensure the timely arrival of anesthesia personnel capable of airway rescue must likewise be incorporated into such policies.

Anesthesia services are requested at various locations throughout the hospital facility; some of these are delineated in Table 44-15. As noted throughout this chapter, routine anesthetic standards apply wherever the patient is anesthetized. Out of the operating room patients often present with a wide range of illnesses, unlike the elective patients generally found in an ambulatory setting. Furthermore, disposition postprocedure (whether discharge or admission), needs appropriate coordination by the anesthesiologist for postanesthesia care and/or safe transport from the remote unit.

Patients presenting to the gastrointestinal endoscopy suite include healthy individuals for routine diagnostic screenings, as well as patients with fulminant cholangitis and sepsis or coexisting difficult airways. As always, the patient’s condition, as well as the specific diagnostic/therapeutic procedure, determines both the anesthetic techniques (propofol deep sedation or general anesthesia vs. general anesthesia with LMA or endotracheal tube) and the monitoring required.

General anesthesia is usually required in patients undergoing endoscopic procedures for airway and pulmonary pathology; an added complexity may include the presence of a shared airway, and, in many patients, marginal pulmonary status.

Patients undergoing cardiac catheterization are routinely sedated by cardiologists without involvement of an anesthesiologist. Occasionally, a patient with significant comorbidities, (eg, morbid obesity) requires the presence of a qualified anesthesia provider. General anesthesia is often required for placement of aortic stents, which are increasingly being performed by cardiologists in the cardiac catheterization laboratory. Anesthesia staff should be prepared with arterial pressure monitoring and the necessary vascular access to facilitate resuscitation, should emergent open aneurysm repair be required.

Patients requiring electrophysiology procedures for catheter-mediated arrhythmia ablation often need general anesthesia. Such patients frequently have both systolic and diastolic heart failure, leading to potential hemodynamic difficulties perioperatively. Sudden hypotension can herald the development of pericardial tamponade secondary to catheter perforation of the heart. Other patients require sedation for the placement of ICDs. Once placed, the device will be tested by inducing ventricular fibrillation. During testing, deeper levels of sedation are required, as the defibrillation shock can be frightening and very uncomfortable. Likewise, anesthesia staff are called upon to provide anesthesia for cardioversion of patients in atrial fibrillation. These patients usually have associated cardiac diseases and require brief intravenous anesthetics to facilitate cardioversion. Oftentimes, a transesophageal echocardiogram must be performed prior to cardioversion to rule out clot in the left atrial appendage. In such cases, anesthesia staff may also provide sedation for this procedure. Determination as to whether a patient needs sedation or general anesthesia with or without intubation is dependent upon routine patient assessment.

Children and some adults (ie, those that are claustrophobic, developmentally disabled, or have conditions that prevent them to be still or to lie flat) require anesthesia or sedation for MRI and computed tomography (CT). Additionally, painful CT-guided biopsies may require anesthesia management. Anesthetic technique is dependent upon patient comorbidities.

MRI creates numerous problems for anesthesia staff. First, all ferromagnetic materials must be excluded from the area of the magnet. Most institutions have policies and training protocols to prevent catastrophes (eg, oxygen tanks flying into the scanner). Second, all anesthetic equipment must be compatible with the magnet in use. Third, patients must be free of implants that could interact with the magnet, such as pacemakers, vascular clips, ICDs, and infusion pumps. As with all out of the operating room anesthesia, the exact choice of technique is dependent upon the patient’s comorbidities. Both deep sedation and general anesthesia approaches with intubation or supraglottic airways can be used, depending on practitioner preference and patient requirements.

Patients usually require general anesthesia and tight blood pressure control to facilitate coiling and embolization of cerebral aneurysms or arteriovenous malformations. Patients taken to the radiology suite for relief of portal hypertension via creation of a transjugular intrahepatic portosystemic shunt (TIPS) are frequently hypovolemic, despite profound ascites, and at risk of esophageal variceal bleeding and aspiration. General anesthesia with intubation is preferred for management of the TIPS procedure.

Anesthesia for electroconvulsive therapy is often provided in a separate suite in the Psychiatry Unit or a monitored area in the hospital (eg, PACU). Patient comorbidity, drug interactions with various psychotropic medications, multiple anesthetic procedures, and effects of anesthetic agents on the quality of electroconvulsive therapy also need to be taken into account.

Anesthesia staff are at times called to provide anesthesia in the intensive care unit (ICU) for bedside tracheostomy or emergent chest and abdominal exploration in patients considered too critically ill to tolerate transport to the operating room. In most of these cases, the anesthesia staff generally employ ICU ventilator and monitors. Intravenous agents are typically used along with muscle relaxants. When performing anesthesia for bedside tracheostomy, it is important that the endotracheal tube not be withdrawn from the trachea until end tidal CO2 is measured from the newly placed tracheostomy tube.

Pediatric patients deserve special mention; the (Table 44-16). Anesthesia considerations for nonoperating room anesthesia are summarized in Table 44-17.

Acute Hypoxia after TIPS Procedure in the Radiology Suite

A 58-year-old Caucasian female with decompensated cryptogenic cirrhosis and refractory ascites, currently on the liver transplant list, is scheduled for an urgent TIPS procedure.

What does a TIPS procedure entail? What are its indications and contraindications?

TIPS (transjugular intrahepatic portosystemic shunt) involves the passage of a catheter, usually inserted through the internal jugular vein and directed into the liver, which creates a low-resistance conduit between a portal vein and a hepatic vein by deployment of an intrahepatic expandable stent. Hemodynamically, this allows immediate decompression of portal hypertension by partial or complete diversion of portal flow from hepatic sinusoids into the inferior vena cava and the systemic circulation.

Indications for the TIPS procedure include: variceal bleeding not controlled by endoscopic or medical therapy, intractable ascites, hepatic hydrothorax, Budd-Chiari syndrome, hepatorenal syndrome and hepatopulmonary syndrome, and bridge to liver transplantation. Some contraindications of TIPS are: primary prevention of variceal hemorrhage, congestive heart failure, severe pulmonary hypertension and tricuspid regurgitation, severe hepatic failure, hepatocellular carcinoma, active intrahepatic or systemic infection, and severe coagulopathy or thrombocytopenia.

What are the anesthetic strategies for TIPS? What are some preoperative and intraoperative concerns in these patients?

TIPS can be performed under moderate sedation, monitored anesthesia care, or general anesthesia. Given the usual need for long immobilization, potential risk of aspiration, and significant comorbidity, general anesthesia is often the recommended anesthetic plan.

Preoperative considerations include: risk of aspiration, gastrointestinal bleeding, decreased functional residual capacity from ascites, pleural effusions, coagulopathy, thrombocytopenia, and hepatic encephalopathy. Special intraoperative considerations should include careful hemodynamic monitoring (usually via arterial catheter), frequent performance of blood gases for electrolyte abnormalities and coagulation parameters, and testing to determine blood glucose and urine output levels. Altered pharmacokinetics of anesthetic agents should also be kept in mind.

Following informed consent and plan for general anesthesia, the patient is induced with etomidate, fentanyl, and succinylcholine, using rapid sequence induction; atraumatic intubation is accomplished uneventfully. Prior to placement of the TIPS, the radiologist evacuates approximately 8 L of ascitic fluid.

What are your concerns about this paracentesis? How would you balance these hemodynamic fluid shifts?

Large volume paracentesis is believed to be a relatively safe and effective procedure; however, it can lead to paracentesis-induced circulatory dysfunction (PICD), a frequently occurring silent complication. PICD is characterized by a marked activation of the renin-angiotensin axis, as well as accentuation of an already established arteriolar vasodilatation that may be combated with salt-free albumin as the plasma expander of choice, especially if at least 8 L are evacuated.

The TIPS procedure lasts about 2 hours; the patient is reversed appropriately with neostigmine and glycopyrrolate. She emerges smoothly and is transferred to the PACU on oxygen via a face mask at 6 L/min. Within 15 min of admission to the PACU, the patient complains of mild chest pain and shortness of breath. Bilateral wheezing is noted, followed by crackles at the bases.

What are some complications of TIPS procedure? How would you attempt to manage this patient?

Complications following TIPS are not insignificant; 3-month mortality has been reported to be approximately 32% to 45%. Complications can be broadly categorized as being associated with the anesthesia, patient comorbidity, and procedure. Patient- and anesthesia-related factors are similar to the ones described in the previous section. With regard to procedure-related factors, special note should be made of cardiopulmonary consequences resulting from a sudden increase in pulmonary artery pressures and systemic pressures, leading to pulmonary congestion.