Major Abdominal Surgery





Introduction


Major abdominal surgery encompasses a broad range of operations with a wide variety of procedures that fall under this category. The perioperative management after a low-risk procedure such as a herniorrhaphy is going to be different from the management following a high-risk procedure such as a pancreaticoduodenectomy. The majority of patients undergoing major abdominal surgery often present with cancer and other medical comorbidities and are put at an elevated risk of a large number of medical and surgical perioperative complications. There are a significant number of factors that make up the risk profile of patients undergoing major abdominal surgery ( Fig. 33.1 ). This elevated risk results from the problem of a significant surgical stress response in older patients with minimal functional or physiologic reserve.




Fig. 33.1


Overview of the risk profile of patients undergoing major abdominal surgery.


An evidence-based practice that has been gaining momentum in recent years is Enhanced Recovery After Surgery (ERAS). ERAS are evidence-based protocols that seek to standardize perioperative management and have been shown to improve outcomes such as rates of surgical site infections, decrease length of stay, and lower health-care costs. ERAS protocols consist of process measures that aim to decrease the physiologic stress response to surgery and maintain postoperative physiologic function.


In this chapter, we will explore several areas of perioperative management uniquely associated with major abdominal surgery. We will address prevention of pulmonary complications, fluid management strategies, nutrition, and surgical site infections (SSIs). The prevention and treatment of delirium, deep venous thrombosis, and urinary tract infections (UTI) are important in the management of patients following major abdominal surgery and are covered in depth in the other chapters in this textbook.


Pulmonary Management


Patients undergoing major abdominal surgery in particular have an elevated risk of developing pulmonary complications. These include hypoxemia during induction of anesthesia and atelectasis after extubation. Patients undergoing surgery in the upper abdomen and bariatric surgery represent the higher risk cohorts for perioperative pulmonary complications. The closer the operative procedure is to the diaphragm the more likely respiratory compromise is, because postoperative pain will inhibit deep breaths and increase splinting.


Reducing Postoperative Pulmonary Complications


Induction of general anesthesia involves the administration of sedative hypnotic drugs and neuromuscular blockers to secure the airway through translaryngeal placement of a cuffed plastic (endotracheal) tube. The major early complications of this process include aspiration of gastric contents, hypoxemia, and failure to obtain an adequate airway. Preoxygenation is widely used to reduce the risk of hypoxemia as a result of airway complications ( Fig. 33.2 ). The principle behind preoxygenation is replacing the nitrogen content of the lungs with oxygen to increase apneic time (i.e., the time between administration of drugs that halt respiration and the restoration of ventilation). However, at the other end of the spectrum, the overuse of oxygen leading to hyperoxia can also cause damage because of oxygen free radicals and increased atelectasis. Oxygen should be titrated to produce normal saturations and arterial oxygen levels, avoiding hyperoxia with prolonged periods of high inspired oxygen.




Fig. 33.2


Preoxygenation for prevention of atelectasis. CPAP , Continuous positive airway pressure; FRC , functional residual capacity; PEEP , positive end-expiratory pressure.


Other potential problems that occur with induction of anesthesia include decreased functional residual capacity (FRC) and atelectasis. Both neuromuscular blockade and anesthesia induced by sedative hypnotic agents cause significant reduction (16%–20% in the supine position) in FRC. Atelectasis is caused by high inspired oxygen tension (absorption atelectasis) and also results from compression of pulmonary tissue by the heart, particularly the left lower lobe and the juxtadiaphragmatic region (compression atelectasis). The combination of loss of FRC and compressive and absorptive atelectasis commonly results in postintubation hypoxemia and increased airway pressures.


Prolonging apneic oxygenation (the time from onset of apnea until hypoxemia develops) and preventing atelectasis on induction of anesthesia can help prevent some of these problems. Evidence suggests that patient positioning may have a significant impact on the apneic duration in high-risk profile patients, such as pregnant women and the morbidly obese. Intubating patients with the head elevated or in reverse Trendelenburg position is recommended in the majority of patients. Postoperative patient positioning also plays a role in reducing pulmonary complications. The transport of critically ill patients in the semirecumbent position is associated with a lower incidence of nosocomial pneumonia, and maintaining head of bed elevation in mechanically ventilated patients has been demonstrated to increase end expiratory lung volume and reduce respiratory complications. In non-critically ill patients, patient positioning with maintaining head of bed elevation has been demonstrated to reduce postoperative pulmonary complications, especially pneumonia, after major abdominal surgery.


Lung protective ventilation strategy during surgery with low tidal volumes (4 to 5 mL/kg), positive end-expiratory pressure (PEEP) (6 to 8 cm H 2 O) and lung recruitment are associated with improved outcomes. There is considerable evidence that mechanical ventilation with high tidal volumes that cause alveolar stretching can initiate ventilator-associated lung injury. Although lung protective strategies have been routinely accepted in the postoperative phase of care, their usage intraoperatively remains suboptimal.


Other postoperative interventions including head of bed following major abdominal surgery have been demonstrated to reduce pulmonary complications such as pneumonia. These include early mobilization, utilizing regional anesthesia, incentive spirometry, oral hygiene, and smoking cessation. These interventions have been shown to function best as a pulmonary bundle, and all contribute individually toward improving postoperative pulmonary outcomes and should be utilized in postoperative major abdominal surgery patients. Many of these components also align with ERAS recommendations. Early mobilization includes mandatory ambulation in the early postoperative period with “enforced” time out of bed ambulating or in a chair. Prolonged bed rest or immobilization postoperatively is associated with decreased ventilation, atelectasis, and increased rates of pneumonia, and early mobilization has been shown to decrease rates of chest complications. The use of regional anesthesia such as epidural use also has significant benefits to postoperative pulmonary function. Epidural use both reduces opioid use, which has been demonstrated to reduce rates of pneumonia and pulmonary complications, and improves postoperative oxygenation and lung function.


Pulmonary Management After Bariatric Surgery and in the Morbidly Obese


A unique population frequently seen in major abdominal surgery is the morbidly obese, especially those undergoing bariatric procedures. Morbidly obese patients have significantly more atelectasis than nonobese patients, and atelectasis in the obese persists for a longer duration when compared to normal weight patients ( Fig. 33.3 ). Postoperative patient positioning with the head of bed elevated helps to prevent this atelectasis in obese patients and early mobilization leads to lung recruitment and should be encouraged. Obese patients have also been associated with a higher risk for aspiration caused by increased gastric and esophageal pressures, as well as increased work of breathing because of reduced FRC and expiratory reserve volume (ERV). Morbid obesity is also associated with dramatic reductions in total respiratory system compliance, which leads to significantly increased perioperative risk in terms of primary and secondary respiratory failure. Positive pressure ventilation should be utilized in any obese patients at induction and following intubation and especially with warning signs for insufficient ventilation, such as desaturation, tachypnea, tachycardia, or hypercarbia ( Fig. 33.2 ).




Fig. 33.3


Percentages of pulmonary atelectasis in morbidly obese compared with nonobese patients, shown at three stages: before anesthesia induction, after extubation, and 24 hours later.

(Redrawn from Eichenberger A, Proietti S, Wicky S, et al. Morbid obesity and postoperative pulmonary atelectasis: An underestimated problem. Anesth Analg 2002;95:1788–1792.)


Because of these unique physiologic issues, medications used for anesthesia, such as sedative drugs, and postoperative analgesia for pain control promote obstruction of the upper airways and may lead to postoperative hypoxemia. Recommendations for postoperative analgesia management following abdominal surgery in the obese and bariatric surgery include multimodal pain management strategies and utilizing regional and local anesthesia techniques such as epidurals and local wound infiltration (bariatric). Reducing the consumption of narcotics by utilizing nonopioid alternatives such as non-steroidal anti-inflammatory drugs (NSAIDs) helps reduce the risk of postoperative hypoxemia. If patient-controlled analgesia is being utilized, bolus dose rather than continuous infusion is recommended, especially in patients with obstructive sleep apnea (OSA). Additionally, the use of local wound infiltration with laparoscopic surgery has successfully assisted with minimizing opioids and improving patient comfort. In particular, longer acting agents such as ropivacaine or levobupivicaine have been demonstrated to be more effective than short-acting agents such as lidocaine. In those undergoing open surgery, thoracic epidural analgesia has been associated with improved lung function and faster recovery of spirometric values in obese patients.


OSA occurs in up to 70% of morbidly obese patients undergoing bariatric surgery. Obese patients should be screened for OSA using the STOP-BANG questionnaire preoperatively. Immediately following surgery, patients with OSA should be monitored with continuous pulse oximetry and respiratory rate monitoring. The treatment for OSA is noninvasive positive pressure (NIPP) support, with continuous positive airway pressure (CPAP), with or without inspiratory pressure support (biphasic positive airway pressure [BiPAP]), and there should be high vigilance postoperatively for the need to use CPAP or BiPAP in these patients in addition to routine oxygen supplementation ( Fig. 33.4 ). NIPP use is indicated for hypoxia when oxygen saturation reaches below 90% in the postoperative period. All patients with a diagnosis of OSA should receive CPAP or BiPAP in the recovery room (this is titrated to response) and at night while they sleep. Patients treated with home CPAP therapy at baseline should continue their CPAP postoperatively and may even need slightly higher CPAP values because of the respiratory effects of perioperative medications. Oxygen therapy should be used cautiously because its use has been associated with a higher risk of apnea and hypopnea in patients with OSA postoperatively. The risk of postoperative respiratory failure and airway obstruction in patients with OSA (in particular, those with an apnea–hypopnea index > 30) cannot be overemphasized.




Fig. 33.4


Risks and management strategies for patients with obstructive sleep apnea/hypopnea syndrome or morbid obesity undergoing major surgery. CPAP , Continuous positive airway pressure; NIPPV , noninvasive positive-pressure ventilation; PACU , postanesthesia care unit; PEEP , positive end-expiratory pressure.


Fluid Management


Perioperative fluid management is a complex process involving the patient’s preexisting disease, preoperative volume status, physiologic reserve, degree of perioperative stress, and perioperative fluid losses. Fluid management during all phases of care are frequently influenced by external variables with abdominal surgery. For example, preoperatively, the use of mechanical bowel preparations or functional barriers to hydration such as esophageal cancer can influence fluid status. Intraoperatively, operative case duration varies greatly and can lead to insensible losses, or varying degrees of intraoperative blood loss, which can impact hemodynamic status. Postoperatively, the patient’s ability to tolerate fluids influences fluid resuscitation. Fluid management following major abdominal surgery can be a challenge and requires unique adaptation for each patient. Because Chapter 16 in this textbook addresses perioperative fluid management, we will focus on specific factors that impact fluid management in patients undergoing major abdominal surgery.


Perioperative care is characterized by dramatic changes in fluid and electrolyte content and distribution in the various fluid spaces in the body. These changes are predictable and follow a characteristic pattern of a biphasic ebb-and-flow. Initially, after an injury or a surgical incision, there is significant peripheral vasoconstriction, a shunting of blood from the periphery to the midline to preserve vital organs, and a drop in body temperature. The second phase, the hypermetabolic (or flow) phase, occurs within hours and is characterized by a dramatic increase in cardiac output, driven by catecholamines, vasodilation, increased capillary permeability, and an increase in temperature. A period of fluid sequestration occurs because of the extravasation of fluid that follows widespread capillary leak; urinary output falls and tissue edema may become evident. Eventually, a state of equilibrium arrives, usually day 2 postoperatively, when active sequestration stops. This is followed by a phase of diuresis during which the patient mobilizes fluid and recovers. The clinician must be aware of the stages of the stress response when deciding whether to administer fluid and electrolytes. Additionally, extensive fluid shifts are to be expected in the perioperative period, and it may be worthwhile to obtain a preoperative weight to have a baseline goal for the patient’s postoperative diuresis.


Patients undergoing abdominal surgery are usually entering surgery dehydrated secondary to preoperative fasting, the use of mechanical bowel preparations, or their primary disease (e.g., esophageal cancer). This leads to varying preoperative hydration deficits amongst different patients. Various anesthesia society guidelines are now supporting the use of clear liquids fluids up to 2 hours and solid food up to 6 hours before induction of anesthesia, which has been demonstrated to reduce insulin resistance and patient discomfort and has less impact on intravascular volume, especially for patients who received a mechanical bowel preparation. This has led to reduced intraoperative requirements; however, after undergoing mechanical bowel preparations significant fluid and electrolyte derangements can still occur. Although general guidelines can be followed ( Fig. 33.5 ), preoperative fluid administration should be individualized to replace preoperative intravascular deficits rather than following a formula.




Fig. 33.5


Replacing dehydration losses by prehydration. BSS , Balanced salt solution; GI , gastrointestinal; NS , normal saline.


Intraoperatively, the goal is to maintain a near zero fluid balance without significant weight gain of 2.5 kg or more. Excessive crystalloid has been shown to increase the risk of pulmonary complications and lead to prolonged ileus in patients undergoing abdominal surgery. Postoperatively, following most major abdominal surgery, early oral intake including fluids and solids is encouraged. Provided that patients tolerate oral intake and are encouraged to drink adequate amounts of water (approximately 25–35 mL/kg of water per day), the early discontinuation of routine intravenous (IV) fluids has been recommended for most major abdominal surgeries. Following the discontinuation of IV fluids, urine output and other clinical markers of hydration should be monitored to assess for any need to restart fluids.


Postoperative Nausea and Vomiting and Ileus


Postoperative nausea and vomiting (PONV) affects 25% to 35% of surgical patients and has an even higher incidence in patients undergoing major abdominal surgery with an incidence as high as 70% following colorectal surgery. Its etiology is often attributed to the combined use of inhalational anesthesia medication, nitrous oxide, and opioid medications for postoperative pain control. Patients with a history of PONV or motion sickness have a higher likelihood of developing postoperative PONV. In an effort to reduce the incidence of PONV, anesthesiologists are now more frequently utilizing antiemetic prophylaxis and reducing the use of inhalational anesthetics in exchange for medications like propofol. Additional evidence has shown that minimizing preoperative fasting, utilizing preoperative carbohydrate loading, and maintaining adequate hydration in patients postoperatively have assisted with decreasing PONV.


An inevitable consequence following major abdominal surgery and a leading cause of PONV is the development of a postoperative ileus. Postoperative ileus involves transiently delayed recovery of gastrointestinal function following surgery and has been attributed to reduced intestinal smooth muscle contractility caused by the inflammatory response and edema from bowel manipulation and stress from surgery. Ileus has been associated with higher rates of complications and prolonged hospital length of stay, and risk factors for ileus include increasing age, poor preoperative nutritional status, opioid use, long operative duration, emergency surgery, and excessive fluid use. Patients’ responses to ileus vary greatly, with some patients remaining asymptomatic and able to tolerate oral intake while others experience significant gastrointestinal symptoms with an inability to tolerate oral intake for several days.


Several strategies have been demonstrated to accelerate the return of bowel function to reduce the duration of postoperative ileus, and these are commonly found components of ERAS pathways. Opioids have been shown to reduce gut motility and to exacerbate postoperative ileus, and thus opioid sparing pain management strategies have been associated with reducing the duration of postoperative ileus. Multimodal pain management utilizing NSAIDs and regional anesthesia such as epidurals and nerve blocks has been shown to decrease the time of return of gastrointestinal function and improve pain control. Goal-directed fluid management, with avoidance of over-resuscitation has also been shown to reduce edema and to decrease ileus with faster return of flatus. Early mobilization has also been shown to improve gastrointestinal function and to reduce ileus.


Historically, nasogastric intubation use has been prophylactically placed during abdominal surgery and kept in place postoperatively until passage of flatus. However, there has been strong evidence to demonstrate that routine use of nasogastric tube (NGT) decompression following abdominal surgery should be avoided and that the NGT should be removed before reversal of anesthesia. There has been no demonstrated benefit to routine prophylactic use of NGT in multiple different patient populations undergoing various types of major abdominal surgery, even including following gastroduodenal and pancreatic surgery. Avoiding NGT use has been associated with earlier return of bowel function and reduced rates of fever, atelectasis, and pneumonia. However, delayed gastric emptying can still occur and there is a higher incidence of emesis without routine NGT use, therefore significant emesis should be treated with insertion of a NGT to avoid fatal aspiration. Despite this complication, the benefit of routine NGT use does not outweigh the risks and routine prophylactic NGT use is not recommended.


Nutrition


During the stress response, the demand for substrate to fuel tissue repair and leukocyte activity results in increased energy expenditure (evident as an increase in oxygen consumption and CO 2 production), increased substrate turnover with protein catabolism, and enhanced glycogenolysis and gluconeogenesis to provide energy for the process. Perioperative malnutrition is reported to impair wound healing and anastomotic strength and believed to increase infectious risk. The four basic goals of perioperative nutritional therapy include provision of metabolic substrate, retardation of the loss of lean body mass and physiologic reserve, improvement in wound healing and immune function, and prevention of fluid and electrolyte disturbances.


Prior to major abdominal surgery, it is important for patients to be screened for nutritional status and those found to be at risk should be given nutritional support. Many patients undergoing major abdominal surgery, especially for cancer, are at a high risk of having significant unplanned weight loss prior to surgery and are often malnourished. The addition of oral supplements may help malnourished patients achieve nutritional goals both prior to surgery and during their recovery postoperatively when they are back at home. Ideally in the significantly malnourished, beginning nutritional supplementation 7–10 days preoperatively has the greatest effect and has been shown to reduce the risk of anastomotic leaks and infectious complications. With the obesity epidemic, overweight or obese patients are often actually malnourished and are hiding underlying muscle wasting, and this patient population should not be overlooked with preoperative nutrition screening. Bariatric surgery patients in particular require a nutritional evaluation, specifically checking selective micronutrient measurements (bariatric surgery ERAS), and those undergoing gastric bypass and malabsorptive procedures, such as biliopancreatic diversion, require an even more extensive nutritional evaluation.


The standard practice of fasting from midnight is no longer recommended prior to surgery for patients undergoing major abdominal surgery. While this was previously thought to ensure an empty stomach and reduced risk of pulmonary aspiration, two meta-analyses, including a Cochrane review, demonstrated no reduction in gastric contents or change to pH of gastric fluid between patients fasting since midnight compared with those allowed to take in clear fluids until 2 hours before surgery, and no increase in complication rates. Imaging studies have actually demonstrated complete gastric emptying from clear liquids within 90 minutes of intake. Fasting from midnight has been shown to increase patient discomfort, insulin resistance, and reduce patients’ intravascular volume, especially in those undergoing mechanical bowel preparation. Several anesthesia societies are now recommending clear fluids to be allowed until 2 hours before surgery and solid food until 6 hours before surgery. In addition to allowing clear fluids, the ingestion of a carbohydrate loaded clear fluid 2 to 3 hours before surgery is thought to help maintain a metabolically fed state in patients through surgery. There has been evidence to suggest that preoperative intake of a carbohydrate treatment reduces preoperative thirst, hunger, anxiety, and plays a role in reducing postoperative insulin resistance. Additionally, two meta-analyses have found that preoperative carbohydrate loading in patients undergoing major abdominal surgery was associated with reduced length of stay.


Following surgery, enteric feeding is effective when therapy can be successfully initiated and maintained and is preferable to the IV approach. Patients fed enterally have been shown to have fewer complications such as reduced infectious complications, improved nutritional markers, and shorter length of stay. Historically, following abdominal surgery patients were not fed until patients passed flatus. However, new evidence does not support this practice. Early feeding postoperatively has been associated with reduced length of stay and reduced complications and does not demonstrate any increase in rates of complications such as emesis, NGT reinsertion, SSIs, anastomotic dehiscence, or mortality. However, caution should be used in patients with delayed gastric emptying who have documented gastroparesis or are taking prokinetic agents. Additionally, patients scheduled for gastrointestinal operations, patients with a previous Whipple procedure, patients with achalasia, and patients with neurological disease with dysphagia have a higher risk of delayed gastric emptying.


Postoperative patients following most major abdominal surgery should be able to drink immediately following recovery from anesthesia and advance to a regular diet as tolerated, which allows for spontaneous enteral consumption of calories. Studies on “immunonutrition” diets with special dietary components aimed at enhancing immune function, such as glutamine, omega-3 fatty acids, arginine, and nucleotides, have had mixed results thus far and require further study.


Surgical Site Infections


SSIs are the second most common cause of nosocomial infection. Up to 20% of patients undergoing major abdominal surgery will develop an SSI. The Centers for Disease Control and Prevention (CDC) estimate that approximately 500,000 SSIs occur annually in the United States. Patients who develop SSIs have longer and costlier hospitalizations than patients who do not develop such infections. They are twice as likely to die, 60% more likely to spend time in an ICU, and more than five times more likely to be readmitted to hospital. This translates to significant increases in health-care costs. Programs that reduce the incidence of SSIs such as SSI prevention bundles or the use of ERAS can substantially decrease morbidity and mortality and reduce the economic burden for patients and hospitals. SSIs are covered in Chapter 28 , but we will focus on the aspects of SSI specific to major abdominal surgery.


Many patients undergoing major abdominal surgery will undergo procedures that entail entry into a hollow viscus under controlled conditions and thus should receive antimicrobial prophylaxis. The CDC has developed guidelines for prevention of SSIs, and Table 33.1 shows the four classes of surgical wounds: class I (clean), class II (clean-contaminated), class III (contaminated), and class IV (dirty-infected). Antibiotic prophylaxis is indicated for most clean–contaminated and contaminated (or potentially contaminated) operations ( Fig. 33.6 ). Patients undergoing class IV (dirty–infected) operations should not receive antimicrobial prophylaxis. They should receive therapeutic antimicrobials directed at anticipated organisms based on the anatomic location and clinical situation surrounding the injury. In such scenarios, therapeutic agents are started at the time of injury or suspected infection, often before the patient presents to the operating room.


Jun 9, 2021 | Posted by in ANESTHESIA | Comments Off on Major Abdominal Surgery
Premium Wordpress Themes by UFO Themes