Peripheral Nerve Blocks

Regional anesthesia in the form of peripheral nerve blocks has been used to decrease postoperative pain in the ICU. Peripheral nerve blocks have the benefit of being associated with less strict anticoagulant guidelines prior to performing the block and fewer side effects, while providing safe and effective analgesia. These blocks can be performed via a single injection or a continuous catheter-based technique.

Fascial plane blocks, such as the pectoralis (PECS) I and II blocks and the erector spinae block (ESPB), as well as the serratus anterior plane block (SAPB), have been used for rescue analgesia in cardiac surgical patients who have had severe postsurgical pain, and can also improve lung function by reducing splinting from severe thoracic pain.

Patients who have had sternal fractures, sternotomies, and rib fractures have also benefited from ultrasound-guided transversus thoracis plane block (TTPB), which can also decrease pain scores and ultimately improve lung function by reducing splinting secondary to severe pain.

Neuraxial Analgesia

Patients who have suffered rib fractures, as well as those undergoing thoracic and upper and mid-abdominal surgeries, can benefit from neuraxial analgesia, in particular, thoracic epidural analgesia.

Benefits include reduced pain scores, improved pulmonary function, increased gastric motility, decreased risk of deep vein thrombosis (DVT), which may assist in early extubation in patients who are intubated, reduced time to initial bowel movement, and reduced morbidity and mortality.

Side effects of neuraxial anesthesia include, but are not limited to, nausea, vomiting, urinary retention, and lower extremity weakness (especially in the case of lumbar epidural). If opiates are added to the local anesthetic administered via these routes, opioid-induced pruritus can also occur. In addition, the choice of using these techniques must be weighed against their possible side effects.

Contraindications to neuraxial interventional techniques include patient refusal, hemodynamic instability, true allergy to local anesthetic drugs, and active anticoagulation (guided by the anticoagulation guidelines from the American Society of Regional Anesthesia).

Opiates

Opiates used for acute perioperative pain management include morphine, hydromorphone, fentanyl, buprenorphine, methadone, remifentanil, sufentanil, alfentanil, and ketamine. These medications can be administered via the oral, intravenous, sublingual, intramuscular, and rectal routes. All of these medications provide excellent analgesia; however, many have unwanted side effects, as well as significant abuse potential. Adverse side effects include nausea, vomiting, sedation, opioid-induced respiratory depression, opioid-induced constipation, opioid-induced pruritus, and urinary retention. In addition, they can result in hypoventilation and hypercarbia, and can lead to cardiopulmonary compromise in critically ill patients, which may result in these patients requiring respiratory support or prolonged intubation in some of these patients.

Methadone is generally administered to patients who have a history of opiate abuse and are attempting to overcome their addiction. In addition, it can also be used as part of an anesthetic plan to reduce perioperative pain. This drug is generally administered orally or intravenously. Administration of methadone, in particular, can prolong the QTc interval and can lead to torsades de pointes, which may result in ventricular tachycardia and fibrillation in patients with a history of prolonged QT interval. A careful review of medications must be performed prior to reducing the risk of increasing the QTc interval.

Remifentanil may be used as a continuous intravenous infusion at a low rate, with a patient-controlled bolus, as part of patient-controlled analgesia (PCA) for acute pain management. Remifentanil is unique of all the opiates in that it has a very short half-life and a context-sensitive half-time of approximately 10 minutes, resulting in complete clearance of the opiate from blood. This is due to the fact that it is metabolized by red blood cell esterases which rapidly break down the drug in the bloodstream.

Sufentanil may be administered via the neuraxial or intravenous route (as a bolus or a continuous infusion) for acute pain management. It is an excellent adjuvant in local anesthetic solutions for neuraxial analgesia and has also been used as an adjuvant to prolong the duration of a spinal anesthetic when used for surgical anesthesia; however, it is associated with opioid-induced pruritus, nausea, and vomiting when used as an intrathecal adjuvant. Sufentanil, when used as an infusion, has a longer context-sensitive half-time when compared to remifentanil, and care must be taken with regard to administration of large doses of this medication.

Buprenorphine is another medication used in the perioperative period in patients with a history of opiate abuse. It is generally combined with naloxone to produce buprenorphine/naloxone (naloxone added to reduce the abuse potential of this drug). Buprenorphine is a partial opioid μ-agonist and a kappa antagonist with a half-life of approximately 37 hours. When buprenorphine is administered, the drug provides a ceiling effect with regard to analgesia and does not produce as much respiratory depression compared to more potent opiates. This drug is commonly used for withdrawal of opiates in those who have a history of opiate abuse and is generally administered as an oral formulation and, in some instances, as a transdermal patch for this purpose. It has also been approved for pain management. In addition, it can be combined with local anesthetic solutions as an adjuvant, given that it possesses some local anesthetic properties by blocking voltage-gated sodium channels, and can thus be administered via the epidural or intrathecal routes. In this regard, buprenorphine can be effective in treating drug cravings in opioid-dependent patients in the ICU.

Meperidine is an opioid with an atropine-like structure and local anesthetic-like properties. Meperidine has been used intrathecally to prolong the duration of spinal anesthesia; however, it has unpleasant side effects of opioid-induced pruritus, constipation, sedation, nausea, and vomiting. When compared to other commercially available opioids used as adjuvants in intrathecal local anesthetic solutions, meperidine has a greater rate of side effects. Currently, meperidine is most commonly used in the ICU for treatment of postoperative shivering, as well as shivering in patients undergoing hypothermia after sudden cardiac arrest. It can also be used to provide analgesia; however, other agents, such as fentanyl, can provide superior analgesia in comparison.

Tramadol is an opiate with both serotonin and norepinephrine reuptake inhibitor properties that can be administered via the oral, intravenous, intramuscular, and intrathecal routes. Side effects include increased risk of seizures in those with a history of seizures and increased risk of serotonin syndrome (especially in patients who take medications that increase serotonin levels). It can be considered as an analgesic agent in the ICU; however, there are other agents that can provide better quality of analgesia.