Anesthetic Management: Intraoperative Period

INTRAOPERATIVE PERIOD

Antithrombotic Prophylaxis

Antithrombotic prophylaxis reduces perioperative venous thromboembolism and related morbidity and mortality. Both pneumatic compression devices and anticoagulant medications are now commonly used. Because neuraxial anesthesia techniques are commonly employed for many patients during major abdominal, vascular, thoracic and orthope-dic surgery, appropriate timing and administration of antithrombotic agents in these cases is of critical importance in order to avoid the risk of epidural hematoma. International recommendations on the management of anticoagulated patients receiving regional anesthesia have been recently revised and published and are discussed.

Antibiotic Prophylaxis

Appropriate selection and timing of preoperative antibiotic prophylaxis reduces the risk of surgi-cal site infections. Antibiotics should be adminis-tered within 1 h before skin incision and, based on their plasma half-life, should be repeated during prolonged surgeries to ensure adequate tissue con-centrations. Antibiotic prophylaxis of surgical site infections should be discontinued within 24 h after surgery (current guidelines permit cardiothoracic patients to receive antibiotics for 48 h following surgery).

Strategies to Minimize the Surgical Stress Response

The surgical stress response is characterized by neu-roendocrine, metabolic, and inflammatory changes initiated by the surgical incision and subsequent procedures that can adversely affect organ function and perioperative outcomes, especially in elderly and physiologically compromised patients. These responses include a transient but reversible state of insulin resistance, characterized by decreasedperipheral glucose uptake and increased endogenous glucose production. The magnitude of the surgical stress response is related to theintensity of the surgical stimulus; can be amplified by other factors, including hypothermia and psy-chological stress; and can be moderated by periop-erative interventions, including deeper planes of general anesthesia, neural blockade, and reduction in the degree of surgical invasiveness. Much recent effort has focused on developing surgical and anes-thetic techniques that reduce the surgical stress response, with the goal of lowering the risk of stress-related organ dysfunction and perioperative compli-cations. An overview of several techniques that have proved effective in ERP protocols follows.

A. Minimally Invasive Surgery

Laparoscopic procedures are associated with a reduced incidence of surgical complications, espe-cially surgical site infections, compared with the same procedures performed in “open” fashion. Published data highlight the safety of minimally invasive procedures in the hands of adequately trained and experienced surgeons. Laparoscopic cholecystectomy results in shorter length of hos-pital stay and fewer complications compared with open cholecystectomy, and similar results have been reported for colorectal surgery. A longer termsalutary impact is achieved when laparoscopic techniques are included in ERPs. A laparoscopic approach is also associated with less morbidity in elderly surgical patients.

B. Regional Anesthesia/Analgesia Techniques

A variety of fast-track surgical procedures have taken advantage of the beneficial clinical and metabolic effects of regional anesthesia/analgesia techniques(Table 48–1). Neuraxial blockade of nocicep-tive stimuli by epidural and spinal local anesthetics has been shown to blunt the metabolic and neuroendocrine stress response to surgery. To be effective, the blockade must be established before incision and continued postoperatively. In major open abdominal and thoracic procedures, thoracic epidural blockade with local anesthetic can be a rec-ommended anesthetic component of a postoperative ERP, providing excellent analgesia, facilitating mobili-zation and physical therapy, and decreasing the inci-dence and severity of ileus. However, the advantages of neuraxial blockade are not as evident when mini-mally invasive surgical techniques are used. Lumbar epidural anesthesia/analgesia should be discouraged for abdominal surgery because it often does not pro-vide adequate segmental analgesia for an abdominal incision. In addition, it frequently causes urinary

retention and lower limb sensory and motor block-ade, increasing the need for urinary drainage cathe-ters (with accompanying increased risk of urinary tract infection), delaying mobilization and recovery, and increasing the risk of falls.

Epidural blockade using a solution of local anes-thetic and low-dose opioid provides better postopera-tive analgesia at rest and with movement thansystemic opioids (Figure 48–4 and Table 48–2). By sparing opioid use and minimizing the incidence of systemic opioid-related side effects, epidural analgesia facilitates earlier mobilization and earlier resumption of oral nutrition, expediting exercise activity and attenuating loss of body mass. Neural blockade minimizes postoperative insulin resistance, attenuating the postoperative hyperglycemic response and facilitating utilization of exogenous glucose, thereby preventing postoperative loss of amino acids and conserving lean body mass.

If spinal anesthesia is used for fast-track (and especially ambulatory) surgery, attention must be paid to delayed recovery due to prolonged motor blockade. The use of smaller doses of intrathecal local anesthetics (lidocaine, 30–40 mg; bupivacaine, 3–7 mg; or ropivacaine, 5–10 mg) with lipophilic intrathecal opioids (fentanyl, 10–25 mcg, or sufent-anil, 5–10 mcg) can prolong postoperative analgesia and minimize the motor block without delaying recovery from anesthesia. The introduction of ultra-short-acting intrathecal agents such as 2-chloropro-caine (still controversial at present) may further speed the fast-track process. Spinal opioids are asso-ciated with side effects such as nausea, pruritus, and postoperative urinary retention. Adjuvants such as clonidine are effective alternatives to intrathecal opi-oids, with the goal of avoiding untoward side effects that may delay hospital discharge. For example, intrathecal clonidine added to spinal local anesthetic

provides effective analgesia with less urinary reten-tion than intrathecal morphine. Further studies are needed to define the safety and efficacy of regional anesthesia techniques in fast-track cardiac surgery (and many clinicians avoid them due to concerns about neuraxial hematomas). Although some stud-ies have shown that spinal analgesia with intrathecal morphine decreases extubation time, decreases length of stay in the intensive care unit, reduces pul-monary complications and arrhythmias, and pro-vides analgesia with less respiratory depression, other studies have shown no benefit to this approach.

Continuous peripheral nerve blocks (CPNBs) with local anesthetics block afferent nociceptive pathways and are an excellent way to reduce the incidence of opioid-related side effects and facilitate recovery . The choice of local anes-thetic, dosage, and concentration should be made with the goal of avoiding prolonged motor blockade and delayed mobilization and discharge. Ropiva-caine, because of its lower toxicity relative to bupiva-caine, is often preferred when high volumes of local anesthetic solution are needed. CPNB after knee arthroplasty facilitates earlier discharge and rehabil-itation. Efforts must be made to minimize the motor block of the quadriceps, which can be responsible for accidental falls. Administering a lumbar plexus block along with a sciatic nerve block decreases hospital length of stay, postoperative urinary reten-tion, and ileus associated with lower extremity total joint replacement when compared with general or neuraxial anesthesia followed by intravenous opi-oids. The same benefits of fewer opioid side effects and accelerated discharge have been shown with regional anesthesia/analgesia for hand, shoulder, anorectal, and inguinal hernia repair surgery.

Advances in imaging techniques and periph-eral catheter technology have generated interest in abdominal wall blockade, facilitating the selective localization of nerves and the direct deposition of local anesthetic in proximity to the compartments where the nerves are located. Transversus abdominis plane (TAP) block  has been used for abdominal surgery to facilitate postoperative analgesia and early return of bowel function. Rectus abdominis block can be used for midline incisions. These techniques are alternatives to epidural block-ade when the latter is contraindicated.

The potential role of wound infusion of local anesthetic solution in providing analgesia for ERAS  has not been determined; nevertheless, local anes-thetic wound infusions are widely used to improve postoperative pain control and reduce the necessity for opioids.

C. Intravenous Lidocaine Infusion

Lidocaine (intravenous bolus of 100 mg or 1.5–2 mg/kg, followed by continuous intravenous infusion of 1.5–3 mg/kg/h or 2–3 mg/h) has analgesic, antihyperalgesic, and antiinflammatory properties. In patients undergoing colorectal and radical retropubic prostate surgeries, intravenous lidocaine has been shown to reduce requirements for opioids and general anesthetic agents, to provide satisfactory analgesia, to facilitate early return of bowel function, and to accelerate hospital discharge. Although lidocaine infusion potentially may replace neuraxial blockade and regional anesthesia in some circumstances, more studies are needed to confirm the advantage of this technique in the context of ERPs. The most effective dose and duration of infu-sion for various surgical procedures remains to be determined; even short duration of lidocaine infu-sion may have benefit.

D. β-Blockade Therapy

Blockers have been used to blunt the sympathetic response during laryngoscopy and intubation and to attenuate the surgical stress-induced increase in cir-culating catecholamines. They also have been shown to prevent perioperative cardiovascular events in at-risk patients undergoing noncardiac surgery and to help maintain hemodynamic stability during the intraoperative period and during emergence from anesthesia. β Blockers reduce the requirement of volatile anesthetic agents and decrease minimum alveolar concentration values; they may also have an opioid-sparing effect. They possess anticatabolic properties, which may be explained by reduced energy requirements associated with decreased adrenergic stimulation. A positive protein balance has been reported in critically ill patients whenblockade is combined with parenteral nutrition. In the context of ERPs, the anesthetic- and analgesic-sparing effects of β blockers may facilitate recovery by accelerating emergence from anesthesia and by reducing anesthetic- and analgesic-related postop-erative side effects, including PONV.

E. Intravenous α₂-Agonist Therapy

Both clonidine and dexmedetomidine have anes-thetic and analgesic properties. Clonidine decreases postoperative pain, reduces opioid consumption and opioid-related side effects, and prolongs neur-axial and peripheral nerve local anesthetic blockade. In patients undergoing cardiovascular fast-track surgery, spinal morphine with clonidine decreases extubation time, provides effective analgesia, and improves quality of recovery. Dexmedetomidine has not been extensively studied in ERP pathways.

Use of Short-Acting Intravenous & Inhalation Agents

A. Intravenous Anesthetics

Intravenous propofol is the deep sedation and general anesthesia induction agent of choice for many surgi-cal procedures, and may reduce the risk of PONV.

B. Inhalational Anesthetics

Compared with other volatile anesthetic agents, desflurane and sevoflurane can shorten anesthesia emergence, reduce length of stay in the postanesthe-sia care unit, and decrease recovery-associated costs. When compared with propofol, all inhalation agents increase the risk of PONV. Nitrous oxide, because of its anesthetic- and analgesic-sparing effects, rapid pharmacokinetic profile, and low cost, is frequently administered with other inhalation agents. However, its use may increase the risk of PONV, and nitrous oxide is frequently avoided in patients with risk fac-tors for PONV. Moreover, the use of nitrous oxide during laparoscopic surgery may distend the bowel and impair the surgeon’s view of anatomic structures .

C. Opioids

Short-acting opioids such as fentanyl, alfentanil, and remifentanil are commonly used during fast-track surgery in combination with inhalation agents or propofol, and with regional analgesia techniques. However, intraoperative administration of remi-fentanil to patients who will experience extensive postoperative pain has been associated with opioid-induced hyperalgesia, acute opioid tolerance, and increased analgesic requirements during the post-operative period.

D. Muscle Relaxants

The short-acting muscle relaxant succinylcholine and intermediate-acting muscle relaxants such as rocuronium, atracurium, and cisatracurium are commonly used to minimize the risk of unplanned and prolonged muscle relaxation. They are chosen to facilitate tracheal extubation while decreasing the risk of residual blockade during anesthesia recovery.

Maintenance of Normothermia

The inhibitory effect of anesthetic agents on ther-moregulation, exposure to the relatively cool sur-gical environment, and intraoperative loss of heat through the surgical field can lead to intraoperative hypothermia in all patients undergoing surgical procedures under general or regional anesthesia. The duration and extent of the surgical procedure directly correlate with hypothermia risk. Periop-erative hypothermia, by increasing sympathetic discharge and inhibiting immune cellular response, increases cardiovascular morbidity and wound infection risk. A decrease in core body tempera-ture of 1.9°C triples the incidence of surgical wound infection. The risk of bleeding and blood transfusion requirement are also increased with hypothermia. Furthermore, by impairing the metabolism of many anesthetic agents, hypothermia significantly pro-longs anesthesia recovery.

Maintenance of Adequate Tissue Oxygenation

Surgical stress leads to impaired pulmonary function and peripheral vasoconstriction, resulting in arterial and local tissue hypoxemia. Perioperative hypoxia can increase cardiovascular and cerebral complica-tions, and many strategies should be adopted during the perioperative period to prevent its development.

Maintenance of adequate perioperative oxygen-ation by oxygen supplementation has been associated with the improvement of some clinically relevant out-comes without increasing the risk of postoperative complications. Ensuring complete recovery of neu-romuscular blockade can reduce early postoperative hypoxemia. Intraoperative and postoperative (for 2 h) inspired oxygen concentration of 80% has been associated with increased arterial and subcutaneous oxygen tension, decreased rate of wound infection, and lower incidence of PONV, but without increas-ing potential complications associated with high oxygen fraction, such as atelectasis and hypercapnia. However, these advantages have not been confirmed in a large, randomized, multicenter trial of patients undergoing elective and emergent laparotomy. The use of regional anesthesia techniques, by decreas-ing systemic vascular resistance, can also improve superficial and deep peripheral tissue perfusion and oxygenation. Finally avoidance of bedrest, and encouraging early mobilization and physiotherapy, can also improve postoperative central and periph-eral tissue oxygenation.

PONV Prophylaxis

Postoperative nausea and vomiting (PONV) is a fre-quent complication associated with anesthetic drugs that delay early feeding and recovery from surgery. Perioperative strategies for minimizing PONV are strongly advocated for any type of surgery, and con-sensus guidelines for prevention and management of PONV are available in the current literature.

Goal-Directed Fluid & Hemodynamic Therapy

Intraoperative and postoperative fluids are com-monly infused in excess of perioperative loss. Despite numerous studies seeking to define fluid strategy (amount and type of fluid administered, crystalloid versus colloid, etc), “liberal,” “standard,” or “restrictive” fluid regimens have failed to con-sistently improve postoperative outcomes. Liberal fluid administration and sodium excess lead to fluid overload, increase postoperative morbidity, and prolong hospitalization. Fluid overload, espe-cially of crystalloid, has been associated with anas-tomotic leakage, pulmonary edema, pneumonia, wound infection, postoperative ileus, and reduced tissue oxygenation. Furthermore, excess fluids com-monly increase body weight by 3–6 kg and may impair postoperative mobilization. On the other hand, restrictive fluid management does not offer any substantial, clinically relevant advantage, except possibly improving pulmonary function and reduc-ing postoperative hypoxia. However, compared with liberal fluid management, restrictive fluid manage-ment increases the release of stress-related hor-mones such as aldosterone, renin, and angiotensin

The amount of perioperative extracellular fluid losses can be minimized with limited preoperative fasting, avoidance of mechanical bowel preparation, minimally invasive surgical techniques such as lapa-roscopic and video-assisted thoracoscopic (VAT) surgery, and early postoperative enteral nutrition.

The concept of goal-directed fluid therapy is based on the optimization of hemodynamic mea-sures such as heart rate, blood pressure, stroke vol-ume, pulse pressure variation, and stroke volume variation obtained by noninvasive cardiac output devices such as pulse-contour arterial waveform analysis, transesophageal echocardiography, or esophageal Doppler. The type of fluid infused is also important: isotonic crystal-loid should be used to replace extracellular losses, whereas iso-oncotic colloids are needed to replace intravascular volume ( Table 48–3).