Anesthesia for Abdominal Surgery - Management of Anesthesia

Standard monitors are used as described in

Standard monitors are used as described in Chapter 10.

Induction of anesthesia

Induction of anesthesia

  1. Restoration of volume deficits prior to induction should be considered (discussed in the section that follows).
  2. RSI or awake intubation is indicated for all patients considered to have full stomachs. Additional indications include conditions in which gastric emptying is delayed, intra-abdominal pressure is increased, or lower esophageal tone is compromised. Examples include trauma, bowel obstruction or ileus, hiatal hernia, gastroesophageal reflux disease, pregnancy beyond the first trimester, significant obesity, ascites, and diabetes with gastroparesis and autonomic dysfunction.

Maintenance of anesthesia

Maintenance of anesthesia

  1. Fluid replacement is guided by clinical judgment and may be aided by invasive monitoring. Traditionally, extended operative cases with significant bowel exposure and preoperative hypovolemia have necessitated fluid replacement of up to 10 to 15 mL/kg/h. Emerging evidence, though, suggests that a more restrictive approach to fluid resuscitation may be associated with faster recovery and fewer complications.
  2. A “protocol-based” strategy for fluid administration is claimed to reduce impairment of bowel motility, cardiopulmonary complications, and bowel edema. It may also improve anastomosis healing and reduce hospital length of stay (LOS). Currently, no clear consensus exists on definitions or protocols for fluid-restrictive strategies. Literature has been published measuring multiple parameters including volume of fluid, perioperative weight, and hemodynamic responsiveness. A deliberate and planned strategy for intraoperative fluid administration on a case-by-case basis would seem to be the most prudent approach.
    1. Bleeding may be estimated both by direct observation of the surgical field and suction traps and by weighing sponges. Blood loss may be concealed (eg, beneath drapes or within the patient) and labs should be checked as clinically indicated.
    2. Insensible losses may range from 0.5 to 1 mL/kg/h for larger abdominal cases.
    3. In spite of an overnight NPO period, blood volume is possibly near normal in many patients, and perceived fluid deficits may not necessitate IV fluid repletion. Clinical judgment will guide the need for resuscitation prior to starting the case.
    4. Abrupt drainage of ascitic fluid with surgical entry into the peritoneum has the potential to cause acute hypotension from a sudden decrease of intra-abdominal pressure and pooling of blood in mesenteric vessels, reducing venous return to the right heart. Postoperative re-accumulation of ascitic fluid may produce significant intravascular fluid losses.
    5. NG and other enteric drainage should be quantified and replaced appropriately.
  3. Fluid losses should be replaced with crystalloids, colloids, or blood products.
    1. Initially, fluid should be replaced by administration of an isotonic salt solution. When an isotonic crystalloid solution is used to replace blood loss, goal-directed therapy and fluid responsiveness is likely more optimal than traditional 3:1 replacement. Evidence suggests that aggressive normal saline resuscitation may cause nonanion gap metabolic acidosis.
    2. Colloids are fluids with particles large enough to exert oncotic pressure with the theory of remaining in the intravascular space longer than crystalloids. Multiple studies comparing fluid resuscitation with crystalloids to colloids have reported no benefit with colloids. Colloid solutions are more expensive than crystalloids, and routine use may not be justified. Albumin may be superior to crystalloid in certain patients including significant burns, hepatorenal disease, or acute lung injury. Hydroxyethyl starch solutions (eg, Hextend or Hespan) are non–blood-derived colloids that may also be used as methods of volume expansion but are increasingly less favorable due to deleterious effects on renal function, coagulation, and potentially all-cause mortality.
  4. Muscle relaxation is required for all but the most superficial abdominal procedures. Sufficient relaxation is critical for abdominal closure as bowel distention, edema, and organ transplantation may increase the volume of abdominal contents.
    1. Titrating relaxants to obtain a single twitch by train-of-four monitoring is generally sufficient for surgical closure and allows for reversal of muscle relaxants for extubation.
    2. Potent inhalational agents are synergistic with muscle relaxants in blocking neuromuscular conduction.
    3. Flexing the operating table may decrease tension on transverse abdominal and subcostal incisions and facilitate surgical closure without the need for profound muscular relaxation as may be requested by the surgeons.
  5. Use of nitrous oxide (N2O) may cause bowel distention as N2O diffuses into the bowel lumen. The amount of distention depends on the concentration of N2O delivered, blood flow to the bowel, and duration of N2O administration. Under normal conditions, the initial volume of bowel gas is small; doubling or tripling of this volume does not pose a significant problem. Studies have shown that N2O may be used in lower fractions and shorter (<3 hours) open and laparoscopic surgeries, without causing clinically significant bowel distention. Use of N2O is relatively contraindicated in bowel obstruction because the initial volume of bowel gas may be large.
  6. NG tubes are frequently placed in the perioperative period.
    1. Preoperative placement is indicated for decompression of the stomach, especially in trauma victims and patients with bowel obstructions. Although suction via a large-bore NG tube may reduce the volume of gastric contents, it does not completely evacuate the stomach and may facilitate aspiration by stenting open the lower esophageal sphincter. NG tubes may also compromise mask fit. Before induction, suction should be applied to NG tubes. During induction, tubes should be allowed to drain. Cricoid pressure may help to prevent passive reflux when an NG tube is present.
    2. Intraoperative placement is required to drain gastric fluid and air during abdominal surgery. NG and orogastric tubes should never be inserted with excessive force. Lubrication and head flexion facilitate insertion. Tubes can be directed into the esophagus by using a finger within the oropharynx or using Magill forceps under direct visualization with a laryngoscope.
    3. Complications of NG tube insertion include bleeding, submucosal dissection of the retropharynx, and placement in the trachea. Intracranial placement has been described in patients with basilar skull fracture. The NG tube should be secured carefully to avoid excessive pressure on the nasal septum or nares, as this may cause ischemic necrosis.
    4. As discussed in the previous section, the need for a gastric tube should be discussed with the surgeon as placement for elective procedures is not recommended in many cases.

Enhanced recovery after surgery (ERAS)

Enhanced recovery after surgery (ERAS)ERAS is a concept of multimodal evidence-based care designed to enhance postoperative recovery and optimize patients for discharge. Core tenets center on a continuum of preoperative, intraoperative, and postoperative pathway strategies.Current literature suggests that ERAS protocols may be associated with reduced hospital LOS, faster recovery, reduced overall morbidity and nonsurgical complications, and similar rates of readmission compared to traditional care. As most ERAS pathways are instituted as a “bundle” there is a paucity of evidence as to which elements of a specific bundle are more or less meaningful than others.

Notable highlights of ERAS protocols for elective colorectal surgery

Notable highlights of ERAS protocols for elective colorectal surgery are discussed in the section that follows. Specific components continue to be increasingly mapped to ERAS protocols for other surgeries.

  1. Minimization of preoperative fasting. Clear liquids and carbohydrate drinks are encouraged up to 2 hours before surgery. Modifications may be based on disease state (eg, bowel obstruction).
  2. Avoidance of routine preoperative sedative premedications due to the potential impairment of postoperative psychomotor function and ability to mobilize and begin PO intake.
  3. Avoidance of routine mechanical bowel preparation due to adverse physiologic effects related to dehydration and association with prolonged ileus and spillage of bowel contents.
  4. Avoidance of routine postoperative NG tubes to minimize patient discomfort and delay in time to oral intake. NG tubes placed intraoperatively should be removed prior to emergence.
  5. Intraoperative maintenance of normothermia.
  6. Intraoperative fluid management strategy continues to be an area of active research and debate. Goal-directed fluid management guided by administration of fluid to a physiologic objective is a cornerstone of ERAS protocols but the specific goals continues to be ill-defined. Noninvasive methods of measuring cardiac output, stroke volume, and stroke volume variation may be employed with no evidence currently suggesting any method as being superior or better than rational management by clinical judgment.
  7. Minimization of postoperative fluids to maintain normovolemia and minimize fluid overload.
  8. Use of multimodal analgesia and regional techniques to minimize opioids and, thus, facilitate early postoperative ambulation and rehabilitation.

Outline