Regional anesthesia for management of acute pain in the intensive care unit.

Pain is a major problem for Intensive Care Unit (ICU) patients. Despite numerous improvements it is estimated that as many as 70% of the patients experience moderate-to-severe postoperative pain during their stay in the ICU. Effective pain management means not only decreasing pain intensity, but also reducing the opioids' side effects. Minimizing nausea, vomiting, urinary retention, and sedation may indeed facilitate patient recovery and it is likely to shorten the ICU and hospital stay. Adequate postoperative and post-trauma pain management is also crucial for the achievement of effective rehabilitation. Furthermore, recent studies suggest that effective acute pain management may be helpful in reducing the development of chronic pain. When used appropriately, and in combination with other treatment modalities, regional analgesia techniques (neuraxial and peripheral nerve blocks) have the potential to reduce or eliminate the physiological stress response to surgery and trauma, decreasing the possibility of surgical complications and improving the outcomes. Also they may reduce the total amount of opioid analgesics necessary to achieve adequate pain control and the development of potentially dangerous side effects.

INTRODUCTION

The aim of this review is to describe the most commonly used regional analgesia techniques for the management of acute pain in ICU patients, and how a pain management strategy that includes the correct use of regional analgesia techniques (appropriate indication and timing of the intervention) can be effectively implemented in the overall treatment plan.

Pain is a major problem for Intensive Care Unit (ICU) patients. Despite numerous improvements it is estimated that as many as 70% of the patients experience moderate-to-severe postoperative pain during their stay in the ICU.[1234]

Pain is frequently treated inappropriately because of fears of depressing spontaneous ventilation, inducing opioid dependence, and precipitating cardiovascular instability. Moreover, many clinicians do not clearly understand the methods for assessing pain, the techniques for optimally treating it, and the potential long-term benefits of effective pain management. Effective pain management not only means decreasing the pain intensity, but also improving the functionality. Minimizing opioid side effects such as nausea, vomiting, urinary retention, and sedation may indeed facilitate patient recovery and is likely to shorten the ICU and hospital stay.[567] Adequate perioperative pain control has also been reported to decrease the recurrence of certain types of cancer.[89]

Adequate postoperative and post-trauma pain management is also crucial for the achievement of effective rehabilitation. Furthermore, recent studies suggest that effective acute pain management may be helpful in reducing the development of chronic pain.[10]

When used appropriately, and in combination with other treatment modalities, regional analgesia techniques (neuraxial and peripheral nerve blocks) have the potential to reduce or eliminate the physiological stress response to surgery and trauma, decreasing the possibility of surgical complications and improving the outcomes. Also they may reduce the total amount of opioid analgesics necessary to achieve adequate pain control and the development of potentially dangerous side effects.

The use of the regional anesthesia technique in the ICU, however, can, in part, be limited by the presence of hemodynamic instability, bleeding diathesis, and by the fear of the performing procedures potentially associated with significant side effects in heavily sedated patients.

Whether or not it is safe to perform the regional anesthesia / analgesia techniques in heavily sedated patients continues to be a matter of debate. However, in an article published in 2008,[11] Bernards et al. state that based on the evidence available, an appropriate local anesthetic solution test dose, containing a marker of intravascular injection (e.g., epinephrine, isoproterenol), properly applied and monitored for an objective cardiovascular response, is a reliable method to detect or prevent intravascular injections that may lead to systemic toxicity, minimizing the importance of the patient's report of symptoms to detect an intravascular injection.

The concern associated with the potential placement of an epidural catheter in the intrathecal space always requires a high level of suspicion. The introduction of new laboratory techniques (beta 2 transferrin test)[12] can be very helpful in detecting the inadvertent placement of an epidural catheter in the subarachnoid space.

Concern about the risk of nerve injury is also one of the reasons often cited for not performing peripheral nerve blocks in heavily sedated patients. In the same article the authors recommend that blocks should not be performed in heavily sedated patients as a routine. However, it may be reasonable, after careful consideration of the risk-to-benefit ratio, to place regional analgesia blocks if the clinical situation warrants it.[11]

The recent introduction of ultrasound-guided (USG) techniques allows an easier and more reliable identification of neural structures, the safe administration of lower doses of local anesthetic,[13] and the insertion of nerve catheters, even in heavily sedated ICU patients. High success rates with reduced onset time until complete analgesia have been reported.[1415] Effective identification of the needle allows for the reduction of the amount of administered drug volumes, which might be of importance in critically ill patients, who may need more than one block, especially those who have undergone multi-site surgery, or sustained multi-trauma.[16]

Other important factors, such as the presence of an infectious process and / or the patient's coagulation status must be considered when planning the use of regional analgesia techniques in ICU patients. Careful consideration of the risk-to-benefit ratio, correct indication and timing of the intervention, and a strict adherence to the American Society of Regional Anesthesia and Pain Medicine Guidelines, published in 2006 (regarding infectious complications in Regional Anesthesia)[17181920] and 2010 (anticoagulation and Regional Anesthesia),[21] will always guide the practitioner and are strongly recommended.

It is our opinion that performing regional analgesia intervention at the appropriate time is of utmost importance. For example placement of a thoracic epidural in a patient mechanically ventilated with chest wall trauma and rib fractures when he / she may not be ready to be weaned from the ventilator is inappropriate and can expose the patient to unnecessary risks. Furthermore, it is imperative to fully assess the full impact of the potential side effects associated with the use of regional anesthesia techniques on the patients’ clinical condition; the reduction of the sympathetic tone associated with most neuraxial and peripheral nerve blocks can cause a deterioration of the patient's clinical status, which could negatively affect a potentially favorable outcome.[22] However, it is also extremely important to consider the positive impact that epidural analgesia may have in reducing the risks of unnecessary intubation and prolonged ventilation in patients with chest wall trauma. Furthermore the positive cardioprotective effects of thoracic epidural analgesia,[2324] and the reduction in the incidence of deep vein thrombosis, reported in patients in whom a regional anesthesia / analgesia technique has been utilized, cannot be emphasized enough.[25]

Regional Analgesia for Thoracic and Abdominal Trauma and Surgery

Blunt chest wall trauma is frequently associated with rib fractures and lung injury. Pain associated with chest wall trauma is very intense and may lead to ineffective coughing and shallow breathing, and the consequent development of atelectasis, pneumonia, and consolidation and respiratory failure.[26] Mechanical ventilation may be necessary and can potentially be associated with increased morbidity and mortality. Providing adequate analgesia can help these patients with respiratory care, improving pulmonary mechanics, and respiratory parameters, especially in older patients (> 65 years of age) and in patients with more than three rib fractures.[27]

Thoracic epidural analgesia is associated with better pain scores and side effect profile, in patients with blunt thoracic trauma, and after thoracic surgery, when compared to systemic analgesia.[2829] However, the impact of epidural analgesia on mortality, duration of mechanical ventilation, and length of ICU and hospital stay is controversial. Although a recent meta-analysis[22] has not found a statistically significant difference, another one including more than 5,000 surgical patients[30] has shown that postoperative epidural analgesia reduces the time to extubation, length of ICU stay, incidence of renal failure, morphine consumption during the first 24 hours, maximal glucose, and cortisol blood concentrations, and improves forced vital capacity. Many of these benefits may be relevant to ICU patients and have been demonstrated to be beneficial in cardiac surgery,[31] as well as in patients with severe acute pancreatitis.[32]

Thoracic paravertebral blocks have been found to be as effective as thoracic epidurals in providing adequate analgesia in patients with chest wall trauma and unilateral rib fractures,[33] after a thoracotomy,[34] and in patients in whom epidural anesthesia may be contraindicated. Technically they are less challenging to perform[35] and are associated with minimal hypotension, making them appealing to patients with hemodynamic instability. Other side effects (urinary retention and pruritus) are also less frequent. A small risk of pneumothorax, the inadvertent administration of the drug in the epidural and intrathecal space, and a more rapid absorption of local anesthetic must always be considered when performing paravertebral blocks.[36]

Intercostal nerve blocks are associated with risk of pneumothorax and systemic local anesthetic toxicity. As with all regional analgesia techniques, the patient's coagulation status must always be checked, to prevent the risk of bleeding and hematoma formation, subsequent to the laceration of an intercostal vessel.

Continuous intercostal nerve blockade after thoracotomy using an extrapleural catheter results in better pain relief and preservation of pulmonary function than the use of systemic opioids, and appears to be at least as effective as the relief provided by the epidural approach.[37] The ease of the extrapleural approach and the low incidence of complications, suggest that this technique should be used more frequently. The use of a multifaceted approach to post-thoracotomy analgesia, which includes the intercostal nerve blockade, has been shown to be beneficial in the immediate postoperative period and seems to be associated with a reduction in the incidence of chronic pain.[38] Major pulmonary resections, which have been managed with a mini-thoracotomy and intrapleural intercostal nerve blocks have been shown to be associated with reduced postoperative pain and improved outcome.[39]

Although not frequently used, multilevel intercostal nerve blocks can be extremely useful in ICU patients, especially when used as a single injection for painful procedures (e.g., placement of chest tubes), or as an infusion when the patient's hemodynamic conditions do not allow the use of thoracic epidural analgesia[40]

Interpleural blockade is a technique by which an amount of local anesthetic is injected into the thoracic cage between the parietal and visceral pleura, to produce an ipsilateral somatic block of multiple thoracic dermatomes. Local anesthetic solutions can be administered as single or intermittent boluses, or as continuous infusions via an indwelling catheter.[4142] It has been shown to provide safe, high quality analgesia after cholecystectomy, thoracotomy, renal surgery, breast surgery, and for some invasive radiological procedures of the renal and hepatobiliary system. It has also been used successfully in the treatment of pain from multiple rib fractures, herpes zoster, Complex Regional Pain Syndromes (CRPS), thoracic and abdominal cancer, and pancreatitis.[42]

There are several methods proposed for the detection of the entry of the needle into the pleural space and all of them involve detection of the ‘negative pressure’ of the intrapleural space.[42] If a posterior approach is not possible, an anterior approach can be used. The catheter also may be positioned in the interpleural space under direct vision, during surgery.

The risk of pneumothorax is 2%[42] and the risk of systemic local anesthetic toxicity is 1.3%. Pleural inflammation increases the risk of toxicity.

It has been suggested that the local anesthetic solution diffuses outward with the interpleural technique, blocking multiple intercostal nerves, the sympathetic chain of the head, neck, and upper extremity, the brachial plexus, splanchnic nerves, the phrenic nerve, the celiac plexus, and the ganglia. As the injected local anesthetic diffuses out through both layers of the pleura, direct local effects on the diaphragm, lung, pericardium, and peritoneum may also contribute to some of its analgesic activity.[42] However, given the high and rapid absorption of the local anesthetic, which could be associated with systemic toxicity, the bolus doses and the infusion rates of medication through interpleural catheters must be carefully monitored.

Transversus Abdominis Plane Block

Incisional pain represents a considerable portion of postoperative pain following abdominal operations.[43]

The abdominal wall consists of three muscle layers; external oblique, internal oblique, transversus abdominis, and their corresponding fascial sheaths. Nerves supplying the skin, muscles, and parietal peritoneum of the anterior abdominal wall are derived from T6 to L1, and pass through the transversus abdominis plane, before supplying to the anterior abdominal wall.[4445] The anterior primary rami of these nerves exit their respective intervertebral foramina and extend over the vertebral transverse process. Subsequently, they pierce the musculature of the lateral abdominal wall, to travel through a neuro-fascial plane between the internal oblique and transversus abdominis muscles. Deposition of local anesthetic dorsal to the mid-axillary line, blocks both the lateral cutaneous branch and the lateral cutaneous afferents, thus facilitating blockade of the entire anterior abdominal wall. The transversus abdominis plane (TAP), thus provides a space into which the local anesthetic can be deposited to achieve a myocutaneous sensory blockade. An approach to this neurofascial plane, through the lumbar triangle of Petit, by using a loss of resistance technique is described in an article published by McDonnell et al., in 2007.[43]

This regional analgesia technique has been shown to provide good postoperative analgesia for a variety of procedures involving the abdominal wall.[464748] Use of a fine-gauge, blunt-tipped, short bevel needle and USG have been proposed, to reduce the incidence of possible complications (intraperitoneal injection with bowel injury / hematoma, liver laceration, transient femoral nerve palsy, accidental intravascular injection, infection, and catheter breakage).[495051] In addition, with the USG techniques, the upper and lower portions of the abdominal wall can be preferentially blocked.[52]

Single shot bolus TAP blocks, with standard volumes of different solutions of local anesthetic (ropivacaine 0.25%, 0.5%), have been reported to be significantly more effective than placebo infusions of normal saline in a group of healthy women undergoing outpatient gynecological laparoscopic surgery.[53] Furthermore, in a case series (three patients) published in 2010, Heil et al.[54] have reported the possibility of using an ultrasound-guided TAP block and catheter for the ambulatory infusion of local anesthetic, for prolonged postoperative analgesia, after outpatient inguinal hernia repair, with promising results. Data from these studies require further confirmation with larger randomized controlled trials, however, the application of this regional technique in ICU patients seems warranted.

Peripheral Nerve Blocks for the Upper Extremities

Severe trauma to the shoulders and arms is frequently present in acutely injured ICU patients. These injuries usually augment overall pain, especially during positioning of the patient.[55] If the orthopedic injury is associated with a closed head injury, causing alterations of the mental status, which limit the use of opioid-based analgesia regimens, adequate analgesia can be provided with blocks of the brachial plexus.

Continuous brachial plexus blocks consistently provide superior analgesia with minimal side effects, while promoting earlier hospital discharge, and possibly improving rehabilitation after a major surgery.[5657]

Peripheral nerve injury is a rare complication of regional anesthesia for the upper extremities. A large study from France has reported 0.04% overall risk of a serious adverse event after peripheral nerve block.[58] Several retrospective studies have reported the incidence of peripheral nerve injury to be between 0.5 and 1.0%, while prospective studies published higher incidence rates, between 10 and 15%.[5960]

The current evidence suggests that peripheral nerve blocks should not be routinely performed in most adults during general anesthesia or heavy sedation, especially when the interscalene approach to the brachial plexus is used. However, the risk-to-benefit ratio of performing a peripheral nerve block under these conditions versus utilizing high doses of opioids, to maintain adequate analgesia, should be carefully considered in select ICU patients.[11]

Furthermore the advent of ultrasound techniques,[616263] in combination with injection pressure monitoring, and electric nerve stimulation, might help to significantly minimize possible serious complications in heavily sedated patients, with an increased success rate and potential benefits overall.

Peripheral Nerve Blocks for the Lower Extremities

Lower extremity injuries are also commonly present in critically ill ICU patients.

Recent literature has reported that when USG is utilized, the accuracy and the success rate associated with the performance of lower extremity nerve blocks are higher and the complication rate is lower, as compared to similar blocks performed with the help of peripheral nerve stimulation only.[57] It is our opinion that a peripheral nerve block performed with a combined approach (ultrasound-guidance and peripheral nerve stimulation) may improve the overall quality of the analgesia provided and reduce the complication rate even further.

The femoral nerve block (FNB) is the preferred analgesic technique following injuries of the knee. Compared to epidural analgesia, it has a favorable morbidity profile, it allows early mobilization, and there is no need for urinary catheterization. In addition, with ultrasound guidance, the technique is simple and easy to perform compared to epidural blocks.[6465] FNBs and catheters are helpful in the management of acute pain following femoral fractures as well as after surgical stabilization.[666768]

Easy visualization of the sciatic nerve proximal to the popliteal fossa, before it divides into the common peroneal nerve medially and the tibial nerve laterally with the USG, makes the lateral approach to the sciatic nerve an ideal approach for the management of pain, secondary to distal tibia, ankle, and foot fractures.[69] This block can be conveniently performed in the supine position and enables more secure placement of a peripheral nerve catheter, with a high success rate.

CONCLUSIONS

Pain control in critically ill patients is of paramount importance. Achieving adequate levels of analgesia in trauma and surgery patients decreases the stress response and improves morbidity and mortality.

Lack of education, fear of possible side effects, and inappropriate use of medications contribute to the ineffective treatment of pain in critically ill ICU patients. The expertise of pain management specialists and anesthesiologists is often necessary.

Choosing the treatment plan that best fits the patient's clinical conditions is mandatory. A potentially favorable outcome can be altered if inappropriate pain modalities are chosen and used.

A rational multimodal approach including the use of non-pharmacological, pharmacological, and regional analgesia techniques is desirable, and often needed. The continued use of these techniques extended into the postoperative period may shorten the recovery time and speed up the discharge.

Regional analgesia techniques (neuraxial and peripheral nerve blocks), although proven to be safe and effective, are underused in the management of pain, in critically ill patients. They allow a decrease in the overall use of opioid analgesics and sedatives and reduce the possibility of developing potentially dangerous side effects, associated with the use of these medications. A correct indication as well as an appropriate timing for their use is required in order to increase their beneficial effects.

The availability of new technologies (e.g., ultrasonography) improves the quality and safety of the neuraxial, upper, and lower extremity peripheral nerve blocks, even in heavily sedated ICU patients.