Chapter 5 Anesthesia for the Surgeon

INTRODUCTION

Perioperative management has changed significantly since the early 1980s. Specifically, many operations that historically required preoperative hospitalization are now performed as same-day admission, outpatient, or office-based procedures. An estimated 400,000 outpatient surgical procedures were performed in 1984, compared with 8.3 million procedures in 2000.¹ Because of this, surgeons must be familiar with anesthesia techniques, risks, and pitfalls.

Persons older than age 65 make up the fastest-growing segment of the population in the United States and are expected to account for 20% of the population by 2025.² As expected, this segment of the population has many comorbidites that must be accounted for when evaluating perioperative risk and the safety of outpatient procedures requiring conscious sedation. Familiarity with methods used to assess operative risk can make preoperative evaluation and preparation smooth and cost effective.

Utilizing an organ system–based approach, this chapter discusses anesthetic pitfalls with which the surgeon should be familiar. The chapter is further divided into issues related to surgery in the outpatient/office-based setting and those related to more invasive inpatient procedures. For the latter, an organ system–based discussion is used to discuss pitfalls in the preoperative, intraoperative, and postoperative settings.

OUTPATIENT AND OFFICE-BASED ANESTHETIC PITFALLS

Neurologic System

Tables 5-1 and 5-2 list many of the commonly used analgesic and amnestic/anxiolytic agents, their doses, and reversal agents.

Meperidine-Related Seizure

Meperidine (Demerol) has a unique profile in that it has a toxic metabolite, normeperidine, that has a longer half-life than the parent drug but no analgesic effects. Normeperidine can accumulate to toxic levels in patients with hepatic or renal dysfunction.

• Consequence

Persistent dosing of meperidine can cause accumulation of normeperidine to toxic levels that can lead to lifethreatening seizures. These seizures are extremely difficult to control.

Grade 4/5 complication

• Repair

• Prevention

The use of meperidine for analgesia should be avoided entirely or minimized in all patients because this agent does not have a favorable analgesic profile in comparison with morphine, hydromorphone (Dilaudid), or fentanyl and has the potential to cause seizures in those patients with renal and hepatic impairment. If meperidine must be used, only small, incremental doses should be administered, especially in the outpatient setting. This agent is contraindicated in those with significant renal or hepatic dysfunction.

Local Anesthetic–Related Seizure

• Consequence

Intravascular administration of local anesthetic or overdose into the interstitium can cause lifethreatening seizures.³ Bier blocks are whole extremity blocks performed by intravenous injection of high doses of local anesthetic in an extremity that has been isolated via a tourniquet. Such blocks can cause seizures if the tourniquet is released before the injected anesthetic has dissipated to nontoxic levels or is not sufficiently tight to prevent systemic exposure. Table 5-3 lists the commonly used local anesthetics, doses, and duration of effect.

Grade 4/5 complication

Table 5-3 Commonly Used Local Anesthetics

Agent	Max Dose (Interstitial)	Duration
Lidocaine (plain)	5 mg/kg	30–60 min
Lidocaine with 100 mcg epinephrine^*	7 mg/kg	1.5–2 hr
Bupivacaine (Marcaine/Sensorcaine)	3 mg/kg	3–4 hr
Chloroprocaine^†	15 mg/kg	30–60 min
Tetracaine^†	2 mg/kg	3 hr

* Contraindicated in organs supplied by end-arterioles.

† Ester class agent that can cause allergic reaction in patients allergic to para-aminobenzoic acid (PABA).

From Rutter T, Tremper K. Anesthesiology and pain management. In Greenfield L, Mulholland M, Oldham K, et al (eds): Surgery: Scientific Principles and Practice, 2nd ed. Philadelphia: Lippincott-Raven, 1997; pp 438–454; and Salam GA. Regional anesthesia for office procedures: part I: head and neck surgeries. Am Fam Physician 2004;69:585–590.

• Repair

Local anesthetic–related seizures should be treated immediately with barbiturates. Generally, phenytoin is not required for long-term prophylaxis or treatment, but all patients require intensive care unit admission for observation and treatment of recurrent seizures. No specific reversal agents are available for local anesthetic seizures.

• Prevention

Surgeons must be familiar with the particular local anesthetic used, its toxic profile, and dosing limitations. Needle aspiration should be performed prior to injecting the local anesthetic to ensure interstitial (as opposed to intravascular) injection. Finally, bier blocks are best performed under the direction of a trained anesthesiologist.

Inadequate Analgesia

Inadequate Amnesia/Anxiolysis

• Consequence

As with inadequate analgesia, inadequate anxiolysis and amnesia cause an increase in catecholamine release and cardiac work.

Grade 1 complication

• Repair

Although high doses of narcotic can cause anxiolysis, this feeling is best controlled with benzodiazepines or propofol. Of note, both agents can cause significant dose-related respiratory depression and hypotension, as discussed later.

• Prevention

Although small doses of benzodiazepines can be used to provide both anxiolysis and amnesia before and during the start of a procedure, propofol is now the preferred agent owing to its rapid onset/offset profile.⁴ Increasingly, automated infusion of propofol or other sedatives is being used to ensure a constant blood concentration of agent. Studies have shown that patients prefer such dosing regimens and require less total drug than regimens utilizing bolus doses.⁵^–⁷

Respiratory System

One of the most common serious adverse events associated with surgeon-delivered anesthesia is airway compromise.⁸ This is most commonly seen in patients receiving conscious sedation.

Delay in Control of the Airway and Failure to Recognize Respiratory Compromise

• Consequence

Inability to recognize oversedation, hypoxemia, or hypercapnea causes a delay in obtaining expedient control of the airway. This can result in aspiration, altered blood gases, hypoxic brain injury, or cardiac failure. Furthermore, persistent bag-valve ventilation and inability to quickly intubate patients increase the risk of vomiting and aspiration.

Respiratory depression can result in impaired oxygenation and/or ventilation. Either of these results can lead to depressed mental status and inability to protect the airway. Furthermore, circulatory derangement (hypotension, bradycardia) can occur if carbon dioxide levels increase or oxygen levels decrease rapidly.

Grade 4/5 complication

• Repair

All surgeons administering conscious sedation should be trained and comfortable with orotracheal intubation and must have all necessary equipment and medications readily available. At a minimum, all surgeons must have a bag-mask and either oropharyngeal or nasopharyngeal airway immediately available to temporarily control ventilation while arrangements are made for more definitive airway management.

• Prevention

Both the surgeon and the staff should be trained in recognizing signs of inadequate ventilation. These signs may include increased work of breathing, which often manifests as paradoxical movement of the chest and abdomen or use of accessory muscles; agitation or confusion; and decreased sensorium. The surgeon should not wait for hypoxemia (desaturation) to develop before intervening and should be familiar with the dose and duration of effect of reversal agents (see Tables 5-1 and 5-2). Ultimately, it is critical to remember that the decision to intubate a sedated patient is a clinical one and the surgeon should not wait for confirmatory tests or maneuvers prior to intervening if she or he feels that the airway or respiratory system is compromised.

Table 5-1 Commonly Used Analgesics

Table 5-2 Commonly Used Amnestic/Anxiolytic Agents

It is important for the surgeon to assess the adequacy of the patient’s airway and pulmonary reserve prior to administering a sedative or analgesic agent. Assessment of the airway should include the Mallampati score (ability to visualize the tonsillar pillars), ability to open the mouth fully, submental distance, degree of neck mobility, and presence of facial hair. It has been shown that increasing Mallampati score, inability to open the mouth more than two finger widths, and submental distance less than three finger widths are associated with difficulty with orotracheal intubation.⁹ Furthermore, facial hair can make bag-mask ventilation difficult by preventing the mask from sealing around the mouth adequately.

Medication-Related Respiratory Depression

• Consequence

As noted previously, respiratory depression can result in impaired oxygenation and/or ventilation with resultant circulatory collapse and altered mental status.

Grade 1/4 complication

• Repair

The narcotic antagonist naloxone can be used to reverse the respiratory effects of narcotics, and flumazenil (Romazicon) can be used to reverse the effects of benzodiazepines. However, the half-life of either agent is much shorter than the drug against which it is directed. Therefore, patients need to be monitored very carefully for recurrence of the side effects. Also, rapid administration of either reversal agent can induce withdrawal and, in the case of flumazenil, seizures. Patients who continue to require reversal agent owing to significant overdose should be intubated and mechanically ventilated until the respiratory depressive effects of the medication(s) have fully resolved.

• Prevention

Most medications used for analgesia and amnesia/anxiolysis can cause respiratory depression. This lifethreatening complication can be prevented most effectively by using only small, incremental dose of medications and being mindful of the synergistic (not additive) effects of opioids and benzodiazepines.

Cardiovascular System

Hypotension

Opioid medications provide mainly analgesia with little to no cardiac depression. However, they cause varying degrees of histamine release. Histamine release is primarily caused by morphine, followed by hydromorphone, and is least likely to occur with fentanyl. Other commonly used sedatives, such as propofol and benzodiazepines, have a direct vasodilatory effect.

• Consequence

Histamine release can result in peripheral vasodilatation and hypotension in the preload-dependent (hypovolemic) patient. Similarly, benzodiazepines and propofol can cause hypotension if given quickly or in high doses, especially in volume-depleted patients.

Grade 1 complication

• Repair

• Prevention

The vasodilatory effects of medications can be minimized by slow administration of small doses. Furthermore, adequate hydration prior to administration of moderate to high doses will further decrease the hypotensive effects of the medication(s), although this scenario is most often addressed in the inpatient setting, in which deeper sedation is often required.

Hematologic System

Methemoglobinemia

A common anesthetic pitfall that can acutely affect the surgical patient hematologically is methemoglobinemia resulting from aerosolized anesthetic used for endoscopic procedures. Lidocaine; benzocaine, tetracaine, and butamben (Cetacaine); have been associated with methemoglobinemia, with Cetacaine implicated most often.^10,¹¹

• Consequence

Because methemoglobin cannot transport oxygen, peripheral tissues are rendered ischemic, and profound acidosis with cardiovascular collapse can occur quickly.¹² Patients will become cyanotic, and the pulse oximeter will show low-normal oxygen saturation despite the finding of high dissolved oxygen on an arterial blood gas sample.

Grade 1/2 complication

• Repair

The most effective treatment for methemoglobinemia is intravenous methylene blue (1–2 mg/kg; maximal dose is 7 mg/kg). This reduces the iron in the heme molecule back into a state at which it can once again transport oxygen. Reversal of cyanosis and recovery of cardiovascular instability should be noted in 20 to 40 minutes. Of note, intubation and mechanical ventilation with high inspired oxygen levels will not be of assistance.

• Prevention

The most effective way to prevent this occurrence is to use as little topical anesthetic as possible. Although the exact mechanism underlying this disorder is not known, most reports suggest it is a dose-dependent phenomenon.

PITFALLS FOR SPECIFIC BLOCKS ¹³

The landmarks for each of the blocks discussed later are summarized in Table 5-4. In addition, Figures 5-1 to 5-4 depict the anatomic location for each injection.

Table 5-4 Landmarks for Regional Blocks

Type of Block	Landmarks	Comments
Finger	1 cm distal to the webspace, along the radial and ulnar sides of the finger	Epinephrine-containing anesthetics are contraindicated
Median nerve	Deep to the flexor retinaculum, between the tendons of the flexor carpi radialis and the palmaris longus or just lateral to the tendon of the flexor carpi radialis	Aspirate prior to injection to avoid inadvertent arterial injection
Ulnar nerve	Deep to the flexor retinaculum, medial to the tendon flexor carpi ulnaris tendon, and also along the styloid process of the ulna	Usually requires two separate injections to anesthetize the dorsal and volar branches
Radial nerve	Wide area extending from the snuff box toward the ulnar aspect of the wrist
Posterior ankle	1 cm above the posterior aspect of the medial and lateral malleoli, deep to the flexor retinaculum	Anesthetizes sole of foot. Aspirate prior to injection to avoid injection into the posterior tibial artery/vein
Anterior ankle	1 cm above the anterior aspect of the medial and lateral malleoli	Anesthetizes the dorsum of the foot

From Salam GA. Regional anesthesia for office procedures: part II: extremity and inguinal area surgeries. Am Fam Physician 2004;69:896–900.

Figure 5-1 Ilioinguinal nerve block. Excessive injection of anesthetic can result in femoral nerve palsy, whereas inappropriately placed injectate will manifest as ineffectual analgesia postoperatively.

Figure 5-2 Digital block. Note the proximity of the vessels to the digital nerves. Epinephrine-containing solutions are absolutely contraindicated because they can result in profound arteriole spasm and digital ischemia. Furthermore, the volume of injectate should be limited to minimize compression of the vessels.

Figure 5-3 Median and ulnar nerve blocks. Care must be taken to prevent either intraneural or intra-arterial injection.

Figure 5-4 Ankle block.

Ilioinguinal Nerve Block

The addition of ilioinguinal nerve block to the anesthetic regimen used for inguinal herniorrhaphy is associated with a lower cost and higher patient satisfaction score than those of general anesthesia or systemic sedation with local anesthesia alone.^14,¹⁵ A 10- to 20-ml mixture of 0.25% bupivacaine and 1% lidocaine is injected through all layers of the anterior abdominal wall approximately 1.5 cm medial to the anterior superior iliac spine (see Fig. 5-1). This block is not intended to be used as the sole modality for analgesia during inguinal herniorrhaphy; rather, it is meant to supplement an overall regimen so as to provide better postoperative pain control and facilitate discharge from the recovery area.

• Consequence

Failure to anesthetize the ilioinguinal nerve can result from poor injection technique. This can be due to failure to inject deep to the oblique muscles of the anterior abdominal wall or to failure to inject a sufficient amount of agent.

Although it is possible to injure the cecum or sigmoid colon during this procedure, there are no reports of bowel injury resulting from this injection—most likely because a small-bore needle is used, and unintentional injection into the bowel is innocuous. The consequence of such an injection will be inadequate analgesia and postoperative pain.

Grade 1 complication

• Repair and Prevention

Because the purpose of this block is postoperative pain control, it is very difficult to assess whether proper technique has been used intraoperatively. Deep infiltration with 20 ml of local anesthetic injected along the needle tract during needle withdrawal is the best method to try to ensure adequate neural blockade.

Inadvertent Femoral Nerve Block

• Consequence

Injection of an excessive amount of local anesthetic or injection in the incorrect plane at the time of attempted placement of ilioinguinal nerve block can result in transient femoral nerve palsy. This complication has been reported in 5% of adults and 10% of children undergoing elective inguinal herniorrhaphy.^16,¹⁷ Until the block resolves, patients will complain of significant weakness or inability to bear weight on the affected extremity.

Grade 1 complication

• Repair

This block is most often detected in the recovery room after the patient attempts to ambulate, and it cannot be reversed once it occurs. The duration of the block depends on the type and amount of anesthetic administered.

• Prevention

The plane between the transversus abdominis and the transversalis fascia fuses laterally with the iliacus fascia, which contains the femoral nerve.¹⁸ It is not possible to avoid injection between these muscles because the surgeon cannot discriminate between them during a percutaneous injection. However, this complication can be avoided by limiting the volume of injectate and thus limiting the amount of anesthetic that can pool around the femoral nerve.