Management of Postoperative Pain

Treatment of pain after thoracotomy (see Chapter 72 ) is important not only to ensure patient comfort but also to minimize pulmonary complications by enabling patients to breathe normally (without active exhalation or splinting, or both) and deeply (so that they can cough) and to ambulate. Normal and deep breathing requires stretching of the skin incision, which is painful. Postoperative patients normally try to prevent stretching of the skin incision by contracting their expiratory muscles (splinting), thus limiting the stretch on the incision during inspiration, and by actively exhaling, thus rapidly diminishing whatever stretch was caused by inspiration. Failure to inspire deeply before a forceful exhalation results in an ineffective cough. Splinting, active exhalation, and failure to cough promote retention of secretions, airway closure, and atelectasis.

Two very efficacious methods of post-thoracotomy pain treatment, cryoanalgesia and administration of epidural narcotics, have become widely used and are considered by many to be the methods of choice. In addition, interpleural regional analgesia has recently been introduced as an alternative method of treating pain after thoracotomy. This section discusses only these three methods.

Cryoanalgesia

An extremely long-lasting intercostal nerve block may be achieved by intercostal nerve freezing (cryoanalgesia).^{[435] [436] [437] [438] [439] [440] [441] [442] [443] [444] [445]} Direct application of an ice ball to the nerve causes degeneration of nerve axons without damage to the support structure of the nerve (the neurolemma), thereby reversibly disrupting nerve activity. Thus, intraneural and perineural connective tissue is preserved and provides a scaffolding for regenerating capillaries, axons, and Schwann cells.^[442] The area of anesthesia is along the dermatomes treated. During the 2 to 3 weeks after nerve freezing, nerve structure and function begin to recover in parallel, and by 1 to 3 months after freezing, they are usually fully restored, without untoward sequelae (neuritis or neuroma formation). The numbness that persists during this period is not especially bothersome. Young women, however, have admitted to some distress during the period of axonal regeneration that is due to the loss of sensation in the nipple area if the fifth and higher intercostal nerves have been frozen.^[441]

Currently used cryoprobes are about the size of a pen; the core of the instrument has an exit port that permits rapid expansion of a gas (usually nitrous oxide). This rapid expansion of gas cools a surrounding metal sheath. Because the metal sheath is in contact with a fluid, an ice ball (temperature of -60°C) forms at the tip of the cryoprobe. The intercostal nerves are approached from within the chest because the probe has to pierce the parietal pleura to reach the intercostal nerves in the subcostal groove. This is easily accomplished by the surgeon lifting the nerve out of the groove with a small nerve hook. The cryoprobe is applied directly to the nerves as far posteriorly as possible from within the chest at the level of the incision plus two or three interspaces above and below this level, just before closure of the thoracotomy wound. The cryoprobe is activated so that the center of the resultant ice ball encapsulates the nerve. During the freeze, nerve tissue temperature is approximately -20°C.^[441] If 2 to 3 mm of tissue remains between the tip of the cryoprobe and the nerve to be blocked, the nerve will not become adequately frozen, and nerve function might not be totally eliminated. If the pleura is thickened, local peeling of the pleura is advisable.^[441] Usually, two 30-second freeze cycles, separated by a 5-second thaw period, are applied to each of the nerves selected. However, recent experience with one 30-second freeze exposure has resulted in no loss of postoperative pain control with a significant reduction in the period of numbness (from 3.0 to 1.2 months).^[441]

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The use of cryoanalgesia in this way has effectively reduced postoperative narcotic requirements and improved pulmonary function.^{[434] [437] [438] [439]} Cryoanalgesia patients have had moderate pain at the end of the first postoperative day and only slight pain after that; in contrast, patients receiving intravenous narcotics experience moderate to severe pain at 24 hours. Most of the pain experienced by cryoanalgesia patients has not been incisional discomfort, but rather shoulder or arm pain secondary to irritation of the pleura by the chest tube. A further advantage of the cryoanalgesic method can be gained if the chest tubes can be placed within an intercostal space where the nerves have been subjected to cryoanalgesia.^[441] Once the chest tubes are removed, usually on the second or third postoperative day, pain in cryoanalgesia patients has become barely noticeable. Consequently, these patients are more able to cooperate with the postoperative pulmonary physiotherapy maneuvers described in Chapter 75 . Return of sensation occurs in most patients by the 30th postoperative day. Long-term follow-up for 6 months has shown that the procedure is associated with a certain worrisome incidence of dysesthesia and intercostal muscle paralysis,^[443] but it is impossible to distinguish between injury to the nerves and muscle during surgery (which does occur [e.g., 44% of patients in one long-term follow-up study had persistent post-thoracotomy pain^[444] ]) and injury from the cryoprobe^[445] as the cause of these problems.

Because cryoanalgesia has been shown to reliably and effectively relieve pain and allow significant improvement in postoperative pulmonary function, it has become an important addition to the modalities used in the treatment of post-thoracotomy pain. Cryoanalgesia may be a treatment of choice in thoracic pain situations that are expected to last a long time (e.g., pain from chest trauma) and to limit respiratory function significantly.

Epidural Analgesia (also see Chapter 43 )

Thoracic epidural analgesia is the current gold standard for post-thoracotomy analgesia because most believe that this technique produces subjectively better analgesia than any other method does. However, no randomized trials have documented a benefit of thoracic epidural over other regional anesthetic techniques, and most show no difference between a lumbar-placed epidural and a thoracic epidural when quantitative measurements are taken.^[446] Furthermore, the high block necessary for adequate analgesia when using local anesthetics is associated with systemic hypotension, bradycardia, and decreased cardiac output as a result of the consequent sympathectomy.^[447] Some prefer epidural opioids because they produce less hypotension. However, these drugs have their own set of side effects, including respiratory depression, nausea, pruritus, and urinary retention. Most acknowledge that a combined opiate and dilute local anesthetic diminishes the major toxicity of each drug type and maximizes the therapeutic benefit.^[448] We administer a combination of low-dose hydromorphone (Dilaudid) and dilute bupivacaine and achieve excellent postoperative analgesia, with rare local anesthetic- or opioid-induced side effects. However, there is still the issue of neurologic risk during placement, which is catastrophic when it occurs, even though it is rare. Because of this devastating complication, thoracic epidural catheters should be placed only in awake patients. Pediatric patients can have their epidural placed through the sacral hiatus and advanced to the thoracic level under anesthesia (but placement should be verified by radiography).

Thoracic Epidural Placement Tips

The following thoracic epidural catheter placement tips are provided in an effort to share our University of California, San Diego experience and, we hope, make your patient's experience more comfortable. The epidural catheter should be placed before induction of general anesthesia and checked for correct position by using a small dose of local anesthetic.

1. Both the midline and paramedian approaches are feasible. However, we recommend that the epidurals be placed by the paramedian approach when inexperienced in this technique because the midline approach is notorious for false loss of resistance when advancing the needle.
2. Catheters are placed above T8 to ensure coverage of the operative site. The epidural catheter is threaded a minimum of 3 cm, preferably 5 cm.
3. A test dose of 3 to 6 mL of 2% lidocaine with epinephrine 1:200,000 should be administered to rule out intravenous catheter positioning and demonstrate a band of anesthesia before inducing anesthesia.
4. If our resident is having difficulty placing the thoracic epidural, we acknowledge that it is acceptable to proceed to a more experienced faculty member for assistance.
5. Once the catheter is in place, 3 mL of 0.25% to 0.5% bupivacaine plus morphine sulfate (Duramorph) (see dosing recommendations later) should be administered, followed by 3 mL of 0.25% to 0.5% bupivacaine every 20 to 30 minutes throughout the case. Thoracic Duramorph bolus dosing recommendations are as follows:

>65 years of age: 1 mg



<65 years of age: 2 mg



6. Postoperative epidural orders should be written in the operating room and sent to the pharmacy at the beginning of the procedure so they will be available as soon as the patient leaves the operating room and enters the postanesthesia or surgical intensive care unit. Our standard orders are as follows:

Bupivacaine, 1/16%, with hydromorphone, 20 µg/mL



Continuous infusion starting at 6 to 10 mL/hr (depending on the size and age of the patient)



Patient-controlled epidural analgesia bolus dose—3 mL



Lockout—30 minutes



Clinician-activated boluses—up to 6 mL every 30 minutes



7. If the patient is not receiving adequate analgesia, immediately postoperatively we recheck the catheter position and readminister a bolus; if still not functional, a new catheter should be placed de novo or another analgesic technique used.

Thoracic Epidural Management Principles

Treatment of pain after thoracic surgery with epidural analgesia (see Chapter 72 ) consisting of a combination of

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The initial injection can be made in the operating room (most usual—see earlier), recovery room, or intensive care unit. Several important clinical points have emerged from the post-thoracotomy epidural opioid analgesia experience.

First, although the thoracic epidural route has been used, the procedure has risks (primarily dural puncture and spinal cord damage), and the lumbar area is equally satisfactory for catheter insertion if a water-soluble opiate alone (e.g., morphine) is used, although slightly larger amounts are needed when infused from the lumbar region.^{[448] [451] [452] [453] [454] [455] [456] [457]} Morphine can be used alone with a lumbar epidural injection for relief of thoracic pain because it is lipophobic and will therefore remain in and have time to spread throughout the epidural and cerebrospinal fluid (CSF) spaces. For relief of thoracic pain, instillation of 4 to 6 mg of morphine in 10 to 15 mL of diluent (preservative-free normal saline) in the lumbar epidural region has been used successfully.^{[451] [455]} Though studied to a much smaller degree, fentanyl, ^{[458] [459]} methadone, ^[460] hydromorphone,^[461] and nalbuphine^[462] may also be used by either the thoracic or lumbar epidural route. Not surprisingly, the lumbar route requires a greater diluent volume to push the narcotic into a wider distribution mechanically because these lipophilic narcotics bind too quickly to the

TABLE 49-20 -- Epidural narcotics that have been used for postoperative thoracic surgery pain management: Routes, dosages, and pharmacodynamics

Site of Incision	Epidural Route	Drug	Lipid Solubility *	Epidural Dose (Diluent Saline): Continuous Infusion	Onset (min)	Duration (hr)
Thoracotomy	Thoracic	Morphine	1.4		40–60	12–24
		Meperidine	39		10	4–8
		Methadone	116	5 mg (10 mL)	15	8–10
		Alfentanil	126	200 mg (10 mL)	10	2
		Fentanyl	813	50–100 mg (10 mL):0.5–1.5 mg/kg/hr	10	2–3
		Sufentanil	1778	20–40 mg (10 mL):5 mg/hr	5	1–5
	Lumbar	Morphine	1.4	6–8 mg (10–15 mL)	40–60	12–24
		Hydromorphone	8	1–2 mg (10–15 mL)	20	8–12
		Meperidine	39	1 mg/kg (10–15 mL)	10	4–8
		Methadone	116	5–10 mg (10–15 mL)	15	8–10
		Fentanyl	813	1–2 mg/kg (18 mL):1–2 mg/kg/hr	10	2–3
		Sufentanil	1778	30–50 mg (20 mL)	5	1–5
Abdominal	Lumbar	Morphine	1.4	6–8 mg (10 mL)	40–60	12–24
		Methadone	116	5–10 mg (10–15 mL)	15	8–10
		Fentanyl	813	1–2 mg/kg (10 mL)/1–2 mg/kg/hr	10	2–3

*Octanol/water partition coefficient.

Second, epidural morphine^[456] and fentanyl^[453] have been reported to be effective after thoracic trauma. In patients with multiple fractured ribs, epidural morphine resulted in well over 6 hours of analgesia with each dose. Alternatively, continuous epidural infusion of fentanyl (1 to 2 µg/kg/hr after a 1- to 2-µg/kg bolus) is a good choice in the thoracic trauma situation (as well as for post-thoracotomy pain) because it has a decreased likelihood of causing respiratory depression. Because there is no sympathetic blockade with epidural opioids, there is no need for the patient to lie supine for top-up doses, and patients with some degree of hypovolemia may be managed more safely than with epidural local anesthetics.

Third, in the post-thoracotomy pain relief experience, relatively few significant side effects have occurred. Urinary retention is not generally a problem because most patients have a bladder catheter in place.

Fourth, catheters have been left in situ and used for as long as 5 days without the development of tolerance.^[463]

Fifth, pain relief failures have usually been due to improper catheter localization because no pain relief could be demonstrated after injection of local anesthetics.^[463]

Sixth, the expected increase in the mean post-thoracotomy expiration flow rate, forced vital capacity,

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Finally, epidural narcotics have been used to treat intractable pain caused by thoracic tumors.^[465] A lower dosage is required, and a longer duration of analgesia with each intermittent dose is obtained for intractable cancer pain than for acute postoperative pain.^[465] However, although results have been satisfactory after the first few series of injections for intractable pain, tolerance has developed, and dosages have had to be increased because of continuous bathing of the spinal cord with a CSF concentration of opioid. ^[453] For treatment of chronic pain, permanent catheters have been implanted in the subarachnoid and epidural space and connected to reservoirs or perfusion pumps.^[453] These systems have been found to be effective, but again, tachyphylaxis has been observed.^[453]

Interpleural Regional Analgesia

Interpleural regional analgesia has been used for the treatment of pain resulting from a number of conditions, including rib fractures,^[466] pancreatitis,^[467] and postoperative pain from mastectomy, cholecystectomy, and renal operations.^{[468] [469] [470]} In addition, this technique has been evaluated in patients who have undergone thoracic procedures.^{[471] [472] [473] [474]}

Interpleural regional analgesia is the percutaneous introduction of a catheter (usually an epidural catheter) into the thoracic cage between the parietal and visceral pleura. Because the catheter tip is located and a local anesthetic is deposited between the two layers of the pleura, this technique is better termed interpleural rather than intrapleural regional analgesia.^[475]

Bupivacaine in concentrations ranging from 0.25% to 0.5%, usually containing epinephrine, is the local anesthetic that has been studied most often. Analgesia is thought to occur as a result of (1) diffusion of local anesthetic through the parietal pleura and the innermost intercostal muscles to reach the intercostal nerves where blockage occurs, (2) blockage of the intrathoracic sympathetic chain, and (3) direct action of local anesthetic on nerve endings within the pleura. A more detailed discussion of this technique can be found in Chapter 43 , Chapter 44 , and Chapter 72 .

For thoracic surgery patients, the catheter is usually placed intraoperatively by the surgeon at an interspace just below the level of the incision. ^{[471] [472] [473]} Alternatively and less commonly, a chest tube can be used for the instillation of local anesthetic.^[474] The chest tube should be clamped for 5 to 15 minutes after each administration of bupivacaine. If the chest tube is not clamped, approximately 30% to 40% of any administered dose of local anesthetic will be lost through the thoracostomy tube.^[476] The patient should be kept in a supine position during the injection and for the next 10 to 15 minutes.

Most of the many studies have had good results with interpleural analgesia^{[466] [467] [468] [469] [470] [471] [472] [473] [474] [475]} (good pain relief, increased pulmonary function, decreased narcotic requirements, or any combination of these results). However, several reports have been only mildly positive ^[476] or frankly negative.^{[472] [477] [478] [479]} The most important reason for failure to achieve adequate analgesia after interpleural administration of local anesthetics has been failure to clamp the chest tube before administration, which causes the local anesthetic to be suctioned out of the pleural space into the chest tube. Indeed, when one group^[472] changed technique to include clamping of the chest tube,^[480] negative results were converted to positive results. Other reasons for failure of the technique are posterior placement of local anesthetic, which prevents adequate analgesia for anterior thoracotomy; dilution of local anesthetic by pleural effusion, blood, or infected fluid; loculation of local anesthetic by adhesions, fibrosis, or infection; and loss of local anesthetic through a bronchopleural fistula.

A review covering a total of 703 cases has detailed the complications of interpleural analgesics.^[481] Pneumothorax was the most frequently registered complication (2.0%), followed by signs of systemic toxicity (1.2% [in one patient seizures were thought to be due to rapid uptake because of the presence of a highly inflamed pleura^[482] ]) and pleural effusion (0.42%). Horner's syndrome, pleural infections, and catheter rupture have also been reported.^[481]

Because the initial results of treating post-thoracotomy pain with interpleural regional analgesia have been mixed at best, the routine use of this technique cannot be recommended at this time. Its ultimate role in the treatment of post-thoracotomy pain will be determined by the results of further studies.