Epidural Analgesia for Pain Management in the Intensive Care Unit

Abstract

The pain of patients admitted into the ICU remains poorly reported and managed. It has been reported that about half of patients admitted to both medical and surgical ICU experienced significant pain during their stay in the unit. Most of these patients tend to develop psycho-traumatic experiences both while in the unit and after discharge. This chapter thus highlights the drawback of poor pain management of critically ill patients and the role of epidural analgesia in contributing to better pain control in the ICU.

1. Introduction

Pain, as defined by the International Association for the study of pain, is an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage [1]. It is common among patients in the intensive care unit (ICU). Previously, a prospective study reported that about half of patients admitted to both medical and surgical ICU experienced significant pain during their stay in the unit [2]. Although most ICU patients cannot self-report pain, its presence often leads to deleterious consequences during and after discharge from the unit. Adequate pain control in the ICU is essential and adds to optimal patient care with improved outcomes.

The pain of patients admitted into the ICU remains poorly reported and managed. Most of these patients as a result tend to develop psycho-traumatic experiences both while in the unit and after discharge. This chapter thus highlights the drawback of poor pain management of critically ill patients and the role of epidural analgesia in contributing to better pain control in the ICU.

2. Aetiology of pain in ICU

The aetiology of pain among ICU patients ranges from injuries sustained prior to admission, postoperative pain, pain due to patient’s pathology and pain during routine nursing procedures such as turning, wound dressing and suctioning. A significant increase in pain intensity during patient turning in the ICU compared to when they were lying down at rest has also been documented [3].

3. Impact of pain on ICU patients

Poor or inadequate pain relief in the intensive care unit has a multi-systemic impact on the critically ill patient. Suboptimal pain management in the ICU can lead to anxiety, delirium and sleep deprivation. Anxiety leads to agitation, patient-ventilator asynchrony and difficulty in weaning from the ventilator [4]. Inadequate pain relief can lead to improper sleep, and lack of adequate sleep can increase pain response in ICU patients.

Furthermore, inadequate analgesia in the ICU is associated with increased oxygen consumption and sympathetic responses with increased poor outcomes. In mechanically ventilated patients, pain may lead to retained pulmonary secretions, resulting in secondary bacteria colonisation and the development of ventilator-associated pneumonia (VAP) [5]. Ventilator-associated pneumonia complicates ICU management, with an increased risk of morbidity and mortality.

In addition, poor pain control in the ICU can often lead to post-traumatic stress disorder (PTSD). Granja and colleagues found that about two out of ten ICU patients experience severe pain six months after being discharged from the unit [4]. This can lead to chronic pain with its attendant psychosocial and economic burden on the patients, family members and the health care system.

The stress response following, for example, surgical intervention causes an increase in stress hormones in the circulation. This can result in arteriolar vasoconstriction, impair tissue perfusion, and reduce tissue-oxygen partial pressure [6]. The consequences include poor wound healing and surgical wound infection [7], resulting in poor patient outcomes in the ICU.

4. Pain assessment in the ICU

Most patients admitted to the ICU cannot correctly communicate the intensity of their pain. This may be due to a reduced level of consciousness and the different interventions provided, such as airway and ventilatory support [8]. Since the inability to report pain does not exclude its presence [9], the need to properly assess pain intensity among ICU patients cannot be overemphasised.

Due to patients’ inability to communicate their pain, behavioural and physical responses have been used to assess pain in the ICU. The two commonly employed behavioural pain assessment tools used in sedated and ventilated patients are the Behavioural Pain Scale (BPS) and Critical-Care Pain Observation Tool (CPOT) [10]. The BPS is a clinical observational score depending upon the patient’s facial expressions, upper limb posturing, and tolerance of the controlled mechanical ventilation. The score ranges from 3 to 12, and a score of >6 requires pain management [10].

SeeTable 1 below:

	Relaxed	1
Facial expressions	Partially tightened	2
	Fully tight	3
	Grimacing	4
	No movements	1
	Partially bent	2
Upper limbs	Fully bent with fingers flexion	3
	Permanently retracted	4
	Tolerating movements	1
Compliance with mechanical ventilation	Coughing but tolerating ventilation most of the time	2
	Fighting with ventilator	3
	Unable to control the ventilation	4

Table 1.

Behavioural pain scale (BPS).

The Critical-care Pain Observation Tool is a pain assessment tool with four clinical components, facial expressions, body movements and muscle tension and compliance with invasive mechanical ventilation. The score ranges from 2 to 8, and a score of more than 2 requires pain management intervention. See Table 2:

Sub-scale	Description	Score
	Relaxed, neutral	0
Facial expression	Tense	1
	Grimacing	2
	Absence of movements	0
Body movements	Protection	1
	Restlessness	1
	Relaxed	0
Muscle tension	Tense, rigid	1
	Very tense or rigid	2
	Tolerating ventilator or movement	0
Compliance with ventilation	Coughing but tolerating	1
	Fighting ventilator	2
	Talking in normal tone or no sound	0
Vocalisation (extubated patients)	Sighing, moaning	1
	Crying out, sobbing	2

Table 2.

Critical-care pain observation tool (CPOT).

In our setting, the Behavioural Pain Scale (BPS) is easier to use and, when combined with other clinical observations, helps to determine the adequacy of analgesia in our patients.

5. Pain management in the ICU

One of the methods of achieving pain control in the ICU is via epidural analgesia. Epidural analgesia/anaesthesia is a form of neuraxial block where local anaesthetic agents and other adjuvants, such as opioids, are deposited into the epidural space. This may be done as a single-shot technique or with a catheter or continuous infusion. It offers a wide range of applications and may be performed at the cervical, thoracic, lumbar and sacral levels.

In a survey conducted in England, 89% of ICUs use epidurals for pain relief [11]. There are, however, some concerns about “the safety of placing epidural catheters in sedated patients, and confirmation of a good catheter position can be difficult in the critically ill patient if sensory level testing is not reliable” [12]. Apart from the safety concerns raised with epidural analgesia in the ICU, placing an epidural catheter in critically ill patients is sometimes difficult. This may be due to difficulty with properly positioning patients for the procedure, presence of contraindications such as sepsis and coagulopathy, common in ICU patients and the haemodynamic complications following the procedure. With the availability of trained personnel and improved monitoring, epidural analgesia can be safely done for appropriate patients in the ICU.

6. Anatomy of the epidural space

The epidural space is a potential space between the dural sheath and the spinal canal. It is continuous within the vertebral column and extends from the foramen magnum to the sacrococcygeal membrane of the sacral canal [13]. The foramen magnum occupies the superior boundary, and the sacral hiatus occupies the inferior boundary. The posterior longitudinal ligament and ligamentum flavum form the anterior and posterior boundaries, respectively. The vertebral laminae, pedicles and intervertebral foramen form the lateral boundary.

Some of the contents of the epidural space include semi-liquid fats (extra-dural fats), lymphatics, arteries and large thin-walled veins. The capacity of the epidural space is far greater than the capacity of the subarachnoid space. It requires 1.5–2.0 mls of LA to block a spinal segment via the epidural route against 0.3 mls via the subarachnoid space.

The veins within the epidural space constitute a close network which runs vertically. They form four (4) main trunks, namely: two (2) on either side of the posterior longitudinal ligament and two (2) posteriorly in front of the vertebral arches. The epidural veins anastomose freely with extra-dural veins, the azygous veins and the intracranial veins. The veins are called valveless venous plexus of Bateson.

The epidural space has a negative pressure transmitted intra-pleural pressure via the thoracic paravertebral space. This negative pressure may also be due to the relative overgrowth of the vertebral canal compared with the dural sac. Artefactual or transient negative pressure results from the needle’s anterior dimpling of the dural. It can also arise from the anterior indentation of the ligamentum flavum by the epidural needle. In addition, back flexion causes stretching of the dural sac and pushes CSF out.

7. Indications for epidural Analgesia in the ICU

Indications for epidural Analgesia in the ICU include [12]:

• Blunt trauma with or without rib fractures

• Surgical such as thoracic, abdominal, orthopaedic, cardiac and vascular surgeries

• Non-surgical indications such as intractable angina pectoris and acute pancreatitis

8. Contraindications for epidural Analgesia

These could be absolute or relative. Absolute contraindications include:

• Patient refusal

• Infection at the proposed catheter insertion site

• Sepsis

• Hypovolemia (shock)

• Allergy to local anaesthetic agents and opioids.

Relative contraindications include:

• Coagulopathy

• Increased intracranial pressure

• Neurological disorder

• Spine deformity

9. Technique for epidural Analgesia

Three methods can be used to administer epidural analgesia in the ICU: single-injection and intermittent boluses, continuous infusion via an indwelling catheter or patient-controlled epidural analgesia (PCEA). Continuous infusion via an indwelling catheter is often preferred in the ICU because it offers a constant plasma level of administered analgesics, thus providing better and more efficacious pain relief [13].

The following are steps to performing an epidural in the ICU.

Patient selections: Most surgical patients admitted to the intensive care units postoperatively in which epidural anaesthesia was provided would have an epidural catheter in situ. Others who do not already have one are selected based on a careful assessment of patient status, risks, benefits, indications and contraindications of epidural analgesia.

Patient consent: After careful patient selection, informed consent should be obtained from the patient if awake or from the relative before proceeding with the technique. Informed consent should involve a careful explanation of the procedure and the risks and benefits of the procedure. Consent may be in the form of written or verbal.

Positioning: epidural analgesia can be done with the patient sitting or lateral decubitus. However, in the ICU, the commoner position for an epidural is the lateral decubitus position due to the peculiarities of ICU patients. With the patient in the appropriate position, an epidural needle, typically a Tuohy needle, is inserted into the appropriate intervertebral space to the epidural space aseptically. Correct placement is confirmed with a loss of resistance or hanging drop technique.

Placement of catheter: Following confirmation of the correct needle placement in the epidural space, an epidural catheter may be threaded into the epidural space through the Touhy or spinal needle for a continuous top-up. The epidural catheter is advanced 2–3 cm into the epidural space [14], after which the needle is carefully removed. A slide-lock adapter may be attached to the end of the catheter to allow the attachment of an injection port or infusion tubing. A filter can also be attached to the infusion tubing to ensure sterility. The placement of an epidural catheter is determined by the dermatome innervating the area of pain to be treated. On the other, an epidural catheter can be placed directly at the site of injury or at the site of surgical incision.

Prevention of intrathecal or vascular injection: Two techniques are used to prevent the intrathecal and/or vascular placement of an epidural catheter, namely, aspiration and the use of a test dose. For the aspiration method, a syringe filled with two millilitres of preservative-free sterile normal saline is attached to the end of the catheter and gently aspirated for 30 seconds. A bloody tap implies that the catheter is in an epidural vein. In addition, an increase in heart rate or blood pressure following a test dose of a local anaesthetic with 1:200,000 adrenaline indicates that the tip of the catheter may be in an epidural vein. More than one millilitre of clear fluid which is positive for cerebrospinal fluid shows that the catheter is in the subarachnoid space. Following a satisfactory placement, a transparent sterile dressing is applied over the catheter site, while the other length is secured with a plaster [15].

10. Drugs which are injected into the epidural space

Local anaesthetic agents are the most commonly used medications for epidural analgesia in the ICU. The commonest LA for epidural analgesia is plain bupivacaine, an amide which is approximately 95% protein bound and is metabolised primarily in the liver via conjugation with glucuronic acid [16]. It comes in three different concentrations: 0.25%, 0.5%, and 0.75%. Bupivacaine for use in the ICU for analgesia is the plain formulation (plain Marcaine), and it is usually administered via an epidural catheter either as intermittent boluses or as a continuous infusion. A dose of 10–15 mg may be administered bolus after a test dose as described above. The drug may be repeated PRN at 3–5 mg.

While administering epidural bupivacaine, monitoring for the motor block using the Modified Bromage scale [17] and watching out for local anaesthetic toxicity is necessary.

The scale is as follows:

Score	Criteria
1	Complete block (unable to move feet or knees)
2	Almost complete block (able to move feet only)
3	Partial block (just able to move knees)
4	Detectable weakness of hip flexion while supine (full flexion of knees)
5	No detectable weakness of hip flexion while supine
6	Able to perform partial knee bend

No block or partial block is desirable for ICU patients on epidural bupivacaine for pain relief.

Signs of local anaesthetic toxicity (LAST) may not be easily detectable in the sedated patient in the ICU, and thus, a high index of suspicion is required. Despite this, “the incidence of LAST in sedated patients is not higher than in others” [18].

Signs of LAST include:

• Light-headedness

• Agitation

• Tremor

• Tingling sensation around the mouth

• Convulsion

• Slurred speech

• Coma

• Cardiac arrest.

Early recognition and prompt intervention are advocated in order to prevent unfavourable outcomes.

Opioids are the main medications used for Analgesia in ICU patients due to their potency and a concomitant mild sedative and anxiolytic effects. It can be administered by multiple routes. The commonly used opioids include fentanyl, remifentanil, and morphine. Morphine is usually administered as a 2–5 mg bolus or at 1–20 mg/h via continuous infusion. Epidural administration of 5 mg of morphine sulphate can provide adequate postoperative [19] analgesia for up to 24 hours. Lower doses are however, recommended in patients with hepatic or renal insufficiency which is common among ICU patients.

One of the most common side effects of epidural morphine is respiratory depression, with an overall risk of less than 1%. This is nonetheless, similar to that of opioids administered via the parenteral route [20, 21]. Others are miosis, constipation, urinary retention, pruritus, hypotension, nausea and vomiting. The sedative effect of morphine is beneficial in patients in whom sedation is indicated, such as mechanically ventilated patients and those in whom invasive procedures need to be performed.

Other analgesic adjuvants may be administered via the epidural route to improve pain relief in critically ill patients in the ICU. These include α2-agonists, such as clonidine and dexmedetomidine. In addition to providing analgesia, dexmedetomidine infusion has been shown to reduce the prevalence and duration of confusion and delirium [22]. The side-effect profile of both α2-agonists includes bradycardia, cardiac asystole and hypotension. Although rare, it can cause rebound hypertension and can cause withdrawal syndrome [22].

11. Conclusion

Pain relief is an integral part of the management of critically ill patients in the intensive care unit. Epidural analgesia is a helpful component of a multimodal analgesia approach to patients in the ICU. Careful patient selection, availability of trained personnel and increased patient monitoring will ensure the safe delivery of epidural analgesia in the ICU.