Anesthesia and perioperative management of colorectal surgical patients – A clinical review (Part 1)

Colon blood flow and oxygenation

Perioperative factors affecting CBF are not well studied in humans. Preoperative medical conditions which may predispose colonic tissue to hypoxia include smoking, atherosclerosis, cardiac failure, and sickle cell anemia. During the perioperative period, CBF is affected by blood gas composition,[1] volume status,[2] intra-abdominal pressure,[3] intraluminal pressure,[4] type and volume of fluid therapy,[5] anesthetic agents and anesthetic techniques,[6,7] and critical conditions such as hemorrhage[8] and sepsis.[9] It would be difficult to predict changes in CBF when many of these factors coexist during surgery or the postoperative period.

Regional anesthetic techniques increase CBF by causing sympatholysis. This has been shown with both spinal[7] and epidural techniques. In a canine model, high spinal anesthesia increased CBF by 22% and decreased vascular resistance by 44%, while the oxygen consumption of the colon was reduced significantly.[7] In human patients, epidural block with local anesthetic has a favorable effect on colonic blood flow and oxygenation.[10]

Preoperative assessment

Significant number of patients aged over 75 years present with rectal cancer Kingston et al. found that the general fitness of a patient is a better predictor for outcome after surgery for CR cancer than chronological age.[11]

Anemia, electrolyte imbalance, nutritional deficiency (e.g., hypoalbuminemia), and weight loss should be identified and corrected. In elective cases for noncancer surgery, a detailed evaluation and treatment of medical problems are possible. However, in patients requiring cancer or urgent surgery (e.g., for obstruction or perforation), time may be limited. During emergency surgery, the main goals are to identify deteriorating vital physiological end organ functions and their causes, e.g., sepsis and hypovolemia. History, clinical examination, a review of monitored parameters, and laboratory investigations (e.g., arterial blood gas analysis and serum electrolytes) are vital to judge the severity of problems (e.g., fluid deficit). Cardiac and respiratory diseases are commonly present among the patients undergoing major CR surgery. One third of the patients may have significant cardiac or pulmonary problems during the preoperative period.[12] Cardiopulmonary exercise testing (CPET) has been suggested as an integrated objective measurement of functional reserve and is useful in predicting complications and outcome. The results of CPET have a high predictive value for patients at risk of developing cardiopulmonary complications in the postoperative period.[13] In a study by Snowden, the anaerobic threshold (AT) was lower in the group with more than one complication (11.9 vs. 9.1 ml/ kg/ min; P=0.001).[14] Wilson et al. studied the predictive value of AT and ventilatory equivalent for carbon dioxide (VE/VCO₂) using CPET for patients undergoing high-risk surgery. They demonstrated a VE/VCO₂ > 34 and an AT ≤ 10.9 ml/kg/min were significant predictors of all-cause hospital and 90 days mortality. They also found that CPET was more useful in predicting the risk of death in patients with no history of ischemic heart disease or risk factors for it.[15]

Preoperative preparation

To improve recovery after CR surgery, traditional clinical measures such as mechanical bowel preparation (MBP) and routine insertion of nasogastric tubes have been challenged. It does not prevent any abdominal infectious complications but may increase cardiac complications.[20] It is also associated with a poor patient experience. One recent meta-analysis[21] and guideline[22] suggest that the routine use of MBP should be omitted in elective CR surgery. Routine insertion of nasogastric tubes is not recommended as their use is associated with a delayed return of bowel function and an increase in pulmonary complications.[23]

Stress and immune responses

Preoperative nutritional support,[34] presence or absence of peritonitis, intraoperative use of anesthetic agents and anesthetic technique employed,[35] perioperative use of adjuvants such as beta-blockers[36] or alpha-agonists,[37] postoperative analgesia, and patient pathway[38] (e.g., conventional or enhanced recovery program) may modify the stress response. Surgical factors which influence the stress response during CR surgery are duration of open surgery,[39] urgency of surgery,[40] open vs. laparoscopy techniques,[41] and amount of blood loss and blood transfusion.[42] An exaggerated stress response has been associated with postoperative bowel dysfunction, fatigue, delayed wound healing, infectious complications such as wound infection, anastomotic leak and cardiopulmonary complications. It may delay recovery, increase susceptibility for metastasis in cancer patients,[43] and have long-term side effects such as the formation of adhesions.[44] The recovery of a suppressed immune function is faster in laparoscopic surgery and this may influence recurrence in cancer surgical patients.[45]

Intraoperative anesthetic management

The goals of perioperative anesthetic management for CR surgical patients are minimizing stress and immune responses, maintaining systemic and colonic blood flow and oxygenation, meticulous fluid and electrolyte therapy, multimodal analgesia, and prevention of postoperative gut dysfunction [Figure 1].

The perioperative use of ß-blockers and α2-agonists may be useful, particularly for high-risk patients. However, their routine use is not recommended until large studies showing clinical benefits in this specific surgical population are available. Antiemetics should be considered to prevent PONV. Other factors can also influence the incidence of PONV. In comparison to 30% oxygen, supplemental oxygen at 80% has been found to reduce the incidence of PONV two- to five-fold after CR surgery, possibly due to decreased serotonin levels in plasma.[57]

Maintaining perioperative normothermia reduces postoperative cardiac and coagulation complications and should be standard care during colon surgery. Hypothermia causes several undesirable systemic changes, including an exaggerated stress response[58] and suppression of the immune function[59] in patients undergoing CR surgery. Active thermoregulation should be carried out both during open and laparoscopic CR surgery, as the reduced bowel exposure during the latter does not compensate for the marked effects of anesthesia on temperature regulation.[60] During laparoscopic surgery, systemic physiological changes due to pneumoperitoneum may cause cardiorespiratory problems. Patients should be carefully positioned and their positioning carefully maintained to prevent Trendelenburg position-related complications. Brachial plexus injury[61] and lower limb compartment syndromes[62,63] have been reported with laparoscopic large bowel surgery.

General anesthetic agents and technique

At present, there is no evidence to recommend specific anesthetic or analgesic agents for CR surgical patients. However, short acting agents are useful if patients are for fast track CR surgery. During prolonged laparoscopic-assisted surgery, sevoflurane-based anesthesia was associated with earlier eye opening and tracheal extubation in comparison to propofol-based anesthesia. In the latter group, the incidence of postoperative colon dysfunction (POCD) on day 2 and day 3 was higher.[64] For open surgery, Jenesen et al.[65] studied three different anesthetic techniques (isoflurane/nitrous oxide, propofol/air, or propofol/nitrous oxide), with fentanyl and vecuronium. There were no significant differences in overall recovery, bowel function (passage of flatus and oral intake), postoperative hospital stay, and complications. Volatile agents differ in their effects on CBF and oxygenation. Muller et al.[66] studied the effects of desflurane and isoflurane on intestinal tissue oxygen pressure during open CR surgery. On completion of the anastomosis, mean tissue oxygen pressure was higher in the isoflurane group than in the desflurane group. This may be due to preservation of reactive hyperemia by isoflurane. No difference between groups could be observed with regards to splanchnic hemodynamics and global oxygenation. Intraoperative use of xenon decreased superior mesenteric artery blood flow, but had no detrimental effect on colon oxygenation.[67] During CR surgery, diffusion of nitrous oxide (N₂O) into the bowel lumen may cause distention and might therefore affect surgical handling and bowel recovery. Scheilein et al.[68] found an earlier return of bowel function with air in comparison to N₂O during isoflurane anesthesia. In contrast, Krough et al.[69] found no differences between air and N₂O in terms of postoperative bowel function and recovery. The use of N₂O is not associated with a recurrence of CR cancer.[70] Use of neostigmine has been suggested to be hazardous during the use of bowel surgery. Doses as little as 0.5 mg were associated with violent bowel contractions with intraluminal pressures increasing markedly up to 70 mm of Hg.[71] In addition, it decreased CBF up to 50% in some animals, which was attributed to a decrease in cardiac output and/or contractility. Fortunately, effects are less severe if an anticholinergic is used simultaneously.[71]

Use of regional analgesia and anesthesia

Epidural analgesia is recommended for open CR surgery.[72] In the case of laparoscopic surgery, an epidural may be beneficial if the patient has significant preoperative respiratory disease. It may be beneficial to insert an epidural catheter if conversion to open surgery is likely. Sole regional anesthesia, e.g., combined spinal-epidural technique, is possible for low anterior resections of the rectum.[73] The use of intraoperative thoracic epidural anesthesia and analgesia has been associated with an increase in colonic blood flow[10,74] and better gastrointestinal recovery. Pain control with epidural analgesia does not, however, affect the incidence of CR cancer recurrence.[75] Spinal with light general anesthesia has also been found to be beneficial.[76,77] Recently, Kumar et al. reported continuous spinal anesthesia using microcatheter for high-risk patients.[78] A wide variety of CR surgical procedures were performed with anesthetic block height T6-T7. After establishing spinal anesthesia with heavy 0.5% bupivacaine and fentanyl, 0.5% isobaric bupivacaine was used to extend spinal anesthesia. However, the microcatheter was removed at the end of surgery.

Optimization of hemodynamics

Several studies have demonstrated that, for patients undergoing CR surgery, goal-directed hemodynamic management reduces postoperative gastrointestinal complications.[79] Fluids alone or fluids and inotropes are used to achieve defined end points. Flow-, pressure-, or volume-based goals have been used.[79] Interestingly, intraoperative[80] or postoperative[81] changes in central venous oxygen saturation (ScvO₂) have been found to predict complications. Intraoperative maintenance of ScvO₂ > 73% may prevent complications.[80] The perioperative use of dopexamine to improve the splanchnic circulation is controversial. Davies et al. studied high-risk patients (anaerobic threshold T of <11 ml/kg/min or an AT of 11–14 ml/kg/min with a history of ischemic heart disease). Low-dose dopexamine (0.5 mcg/ kg/min) was administered with goal-directed fluid therapy. It was associated with earlier enteral diet tolerance, but there were no differences in complications or length of stay.[82] Stroke volume guided fluid and low-dose dopexamine therapy may improve global oxygen delivery, microvascular flow, and tissue oxygenation.

SP conceptualized the article. SP designed overall structure, figures and tables for part 1 and part 2. SP searched and collected literature for all sections. SP responded to reviewers’ comments and was responsible for revisions and correspondence.

SP wrote CBF and stress response sections. SP and UP wrote preoperative assessment and intraoperative management. SB and SP wrote preoperative preparation and postoperative care. JB and SP organized references and contributed for revision. Authors contributed for revision of their sections and for final revision.