4. Causes of acute pain in patients with OSA

Patients with OSA may experience acute pain in a nonsurgical or a surgical setting. Listed below in Table 1 are some of the common causes:

5.1.2. Opioid-induced sleep disturbances

exacerbate already disturbed sleep in OSA patients.

5.1.3. Opioid effects on the cardiovascular system

Patients without OSA who are on chronic opioid therapy have been reported to have sleep disturbances, impaired self-reported sleep and poor sleep quality [36]. These effects might

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Opioids have unfavorable hemodynamic effects in OSA patients such as hypotension, orthostatic hypotension, and syncope of various degrees. The negative hemodynamic effects are due to central vasomotor depression, direct myocardial depression, and arteriovenous dilatation in higher doses [37]. In general, cautious use of opioids should be considered in patients with severe OSA associated with hypertension, arrhythmias and heart failure. Fentanyl has a relatively favorable cardiovascular profile compared to other opioids. For anesthetic management, it has modest effects on blood pressure and myocardial contractility. It is well tolerated as an analgesic regarding cardiovascular adverse effects compared with other opioids. Morphine has the greatest potential for histamine release, compared to other opioids, resulting in hypotension. Hydromorphone can cause a greater drop-in blood pressure compared to equipotent doses of morphine. Tramadol has a lower risk of cardiovascular adverse events, but it can lead to serotonin syndrome and cardiac arrhythmias. Meperidine administration leads to significant decrease in blood pressure and cardiac output due to direct myocardial depressant effects and peripheral vasodilatation. It can predispose patients to serotonin crisis [38]. Methadone is recently becoming popular in chronic pain management. However, it has

been associated with QTc prolongation with a risk of torsade de pointes [35, 39].

These are foundational analgesics and highly effective as they have lower numbers needed to treat (NNT) comparable with other medications. Ketorolac and Ibuprofen are the commonly used NSAIDs in a perioperative setting. The American Society of Anesthesiologists (ASA) taskforce recommends the use of perioperative NSAIDs to decrease narcotic consumption [40]. A reduction in narcotic consumption in the postsurgical period was achieved by regular administration of Ketorolac in morbidly obese patients [41, 42]. Likewise, intravenous intraoperative Ketorolac infusion has been shown to reduce pain scores in the same population [42]. NSAIDs should be used with caution in patients with hypertension, arrhythmias, heart failure and chronic kidney disease. They can increase the risk of serious cardiovascular events, myocardial ischemia, and stroke and the risk is proportional to the duration of their use. Selective COX 2 inhibitors carry a higher risk than nonselective COX inhibitors. If NSAIDs use is necessary for high-risk patients, it is advisable to use the lowest dose possible for the shortest duration. NSAIDs could precipitate acute kidney injury in patients with compensated heart failure or diabetic nephropathy and also further worsen underlying chronic kidney disease (CKD) [43, 44]. The hyperkalemia is mild, but could be critical in patients with elevated K<sup>+</sup> serum levels due to CKD or with concomitant use of ACE inhibitors. The inhibition of platelet aggregation through decreased production of thromboxane A2 could potentially

5.2. Nonsteroidal anti-inflammatory drugs (NSAIDs)

increase bleeding in patients already on anticoagulants.


Table 1. Some common causes of acute pain in patients with OSA.

## 5. Drug treatment options

The choice of one analgesic over the others is dependent on its safety profile and the interaction with OSA and its complications. Interestingly, the systemic effects of OSA like chronic hypoxemia and systemic inflammation can increase analgesic sensitivity to opioids [31]. Chronic intermittent hypoxemia activates hypoxemia inducible factor-1 alpha which in turn increases expression of mu opioid receptor and delta opioid receptor expression, augmenting opioid sensitivity [32].

#### 5.1. Opioid medications

#### 5.1.1. Opioid effects on ventilation

Opioids depresses the respiratory drive by inhibition of respiratory centers in the brain stem, thus decreasing the respiratory rate and the tidal volume [33]. Opioids could also obstruct the upper airway through loss of muscle tone due to sedation or through direct inhibition of central neurons responsible for maintaining upper airway muscle tone [34]. Moreover, it alters the upper airway reflexes and responses to ventilatory depression [35].

The respiratory depression results in hypoventilation with subsequent increase in PaCO2 [33]. These effects are dose-dependent and could be life-threatening with higher doses of opioids or multiple boluses that are commonly used in perioperative period or after major trauma. Those additive risks in OSA patients with already depressed ventilation and airway obstruction could increase the risk of respiratory events and mortality after recovery from anesthesia. Therefore, it is prudent to start with the lowest dose recommended and carefully titrate to effect.

#### 5.1.2. Opioid-induced sleep disturbances

4. Causes of acute pain in patients with OSA

below in Table 1 are some of the common causes:

116 Pain Management in Special Circumstances

cause.

[30].

Table 1. Some common causes of acute pain in patients with OSA.

2. Uvulopalatoplasty: [29].

5. Drug treatment options

sensitivity [32].

Common surgical

causes

effect.

5.1. Opioid medications

5.1.1. Opioid effects on ventilation

Patients with OSA may experience acute pain in a nonsurgical or a surgical setting. Listed

Nonsurgical causes 1. Headache: mostly morning headache, very common, 50% of OSA patients [25], unknown

3. Tonsillitis: pain and difficulty in swallowing [27].

2. Coronary artery disease (CAD): OSA is associated with higher thrombotic risk [26].

3. Bariatric surgery: laparoscopic bariatric surgeries which are less painful than open surgeries

1. Tonsillectomy: "Post-tonsillectomy pain" due to disruption of mucosa and glossopharyngeal nerve irritation the pharyngeal muscles spasms [28].

The choice of one analgesic over the others is dependent on its safety profile and the interaction with OSA and its complications. Interestingly, the systemic effects of OSA like chronic hypoxemia and systemic inflammation can increase analgesic sensitivity to opioids [31]. Chronic intermittent hypoxemia activates hypoxemia inducible factor-1 alpha which in turn increases expression of mu opioid receptor and delta opioid receptor expression, augmenting opioid

Opioids depresses the respiratory drive by inhibition of respiratory centers in the brain stem, thus decreasing the respiratory rate and the tidal volume [33]. Opioids could also obstruct the upper airway through loss of muscle tone due to sedation or through direct inhibition of central neurons responsible for maintaining upper airway muscle tone [34]. Moreover, it alters

The respiratory depression results in hypoventilation with subsequent increase in PaCO2 [33]. These effects are dose-dependent and could be life-threatening with higher doses of opioids or multiple boluses that are commonly used in perioperative period or after major trauma. Those additive risks in OSA patients with already depressed ventilation and airway obstruction could increase the risk of respiratory events and mortality after recovery from anesthesia. Therefore, it is prudent to start with the lowest dose recommended and carefully titrate to

the upper airway reflexes and responses to ventilatory depression [35].

Patients without OSA who are on chronic opioid therapy have been reported to have sleep disturbances, impaired self-reported sleep and poor sleep quality [36]. These effects might exacerbate already disturbed sleep in OSA patients.

#### 5.1.3. Opioid effects on the cardiovascular system

Opioids have unfavorable hemodynamic effects in OSA patients such as hypotension, orthostatic hypotension, and syncope of various degrees. The negative hemodynamic effects are due to central vasomotor depression, direct myocardial depression, and arteriovenous dilatation in higher doses [37]. In general, cautious use of opioids should be considered in patients with severe OSA associated with hypertension, arrhythmias and heart failure. Fentanyl has a relatively favorable cardiovascular profile compared to other opioids. For anesthetic management, it has modest effects on blood pressure and myocardial contractility. It is well tolerated as an analgesic regarding cardiovascular adverse effects compared with other opioids. Morphine has the greatest potential for histamine release, compared to other opioids, resulting in hypotension. Hydromorphone can cause a greater drop-in blood pressure compared to equipotent doses of morphine. Tramadol has a lower risk of cardiovascular adverse events, but it can lead to serotonin syndrome and cardiac arrhythmias. Meperidine administration leads to significant decrease in blood pressure and cardiac output due to direct myocardial depressant effects and peripheral vasodilatation. It can predispose patients to serotonin crisis [38]. Methadone is recently becoming popular in chronic pain management. However, it has been associated with QTc prolongation with a risk of torsade de pointes [35, 39].

#### 5.2. Nonsteroidal anti-inflammatory drugs (NSAIDs)

These are foundational analgesics and highly effective as they have lower numbers needed to treat (NNT) comparable with other medications. Ketorolac and Ibuprofen are the commonly used NSAIDs in a perioperative setting. The American Society of Anesthesiologists (ASA) taskforce recommends the use of perioperative NSAIDs to decrease narcotic consumption [40]. A reduction in narcotic consumption in the postsurgical period was achieved by regular administration of Ketorolac in morbidly obese patients [41, 42]. Likewise, intravenous intraoperative Ketorolac infusion has been shown to reduce pain scores in the same population [42]. NSAIDs should be used with caution in patients with hypertension, arrhythmias, heart failure and chronic kidney disease. They can increase the risk of serious cardiovascular events, myocardial ischemia, and stroke and the risk is proportional to the duration of their use. Selective COX 2 inhibitors carry a higher risk than nonselective COX inhibitors. If NSAIDs use is necessary for high-risk patients, it is advisable to use the lowest dose possible for the shortest duration. NSAIDs could precipitate acute kidney injury in patients with compensated heart failure or diabetic nephropathy and also further worsen underlying chronic kidney disease (CKD) [43, 44]. The hyperkalemia is mild, but could be critical in patients with elevated K<sup>+</sup> serum levels due to CKD or with concomitant use of ACE inhibitors. The inhibition of platelet aggregation through decreased production of thromboxane A2 could potentially increase bleeding in patients already on anticoagulants.

#### 5.3. Acetaminophen

Acetaminophen is a commonly used foundational analgesic with perioperative opioid sparing properties. It offers the distinct advantage of being relatively safe and devoid of sedative properties. Addition of acetaminophen to an intravenous opioid PCA regimen was associated with a 20% opioid sparing effect in a meta-analysis of mixed surgical population [45]. Similar opioid dose reduction expected in patients with OSA could therefore potentially reduce opioid-induced ventilator problems. Obese bariatric surgical patients receiving postoperative intravenous acetaminophen 1 gram every 6 hours required fewer morphine equivalents [46]. Acetaminophen lowers cumulative narcotic consumption, regardless of the route of administration [47, 48]. It has the most favorable effect on blood pressure and should be considered as the first line treatment option in patients with hypertension or cardiovascular disease.

and tachycardia. It may also reduce atrial fibrillation (AF) induction among adult patients with

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Ketamine, an N-methyl-d-aspartate (NMDA) antagonist has recently received increasing attention as a relatively safe adjuvant analgesic. In patients with morbid obesity, low-dose Ketamine added to intravenous Morphine PCA resulted in a significant reduction in opioid consumption. Importantly, subjects receiving ketamine in addition to morphine had fewer episodes of desaturation postoperatively [9]. A preinduction dose of ketamine of 0.5 mg kg<sup>1</sup> together with Clonidine significantly lowered pain scores and perioperative opioids consumed [58]. Intra-operative Ketamine at doses up to 1 mg kg<sup>1</sup> was shown to decrease opioid consumption

It is an analgesic of intermediate potency with possible advantages in OSA patients due to its

6. Multimodal strategies for pain management in obese patients with OSA

Multimodal analgesia is the use of a combination of different analgesic medications and techniques with an aim to provide optimal pain control, thus allowing reduction in opioid requirements. They may have additive or synergistic effects by acting through diverse mechanisms either peripherally or centrally in the nervous system [61]. Multimodal analgesia with a combination of IV Paracetamol and IV Ketorolac in bariatric surgery was found to reduce the postoperative opioid consumption by about 70% [62]. A nonopioid analgesic regimen that employed a combination of nonopioid analgesics (Ketorolac, Clonidine, Ketamine, Lidocaine and Magnesium) in thirty morbidly obese patients undergoing bariatric surgery resulted in lesser PACU opioid consumption and less sedation [63]. The opioid-sparing multimodal

Magnesium, intravenous local anesthetic infusions (lidocaine), and Clonidine are some additional drugs that have been used perioperatively in patients with morbid obesity to enhance analgesia [64, 65] but more scientific evidence is needed before adopting these agents into

Narcotic-based pain regimens for OSA patients have a risk of opioid-induced respiratory depression. Hypoxia, sleep disturbance, pain, and disturbed opioid responses in OSA contribute to that risk [66, 67]. Neuraxial techniques and peripheral nerve blocks are effective

6.1. Regional analgesia techniques in patients with obstructive sleep apnea

multimodal mechanism and a relatively lower risk of respiratory depression [60].

history of paroxysmal AF.

in recovery but at the cost of significant drowsiness [59].

techniques are summarized in Table 2.

routine clinical use.

5.6. Ketamine

5.7. Tramadol

#### 5.4. Anticonvulsant agents

Anticonvulsant agents in clinical use for their analgesic benefits include Pregabalin and Gabapentin. The preoperative use of Pregabalin as premedication significantly lowered immediate postoperative requirement of pain medications among bariatric surgical patients. [49] Preoperative Gabapentin has also significantly lowered immediate postoperative pain scores in morbidly obese bariatric surgical patients [50]. However, the most common side effects of these drugs are dizziness and somnolence, which potentially add to the OSA induced somnolence. Postoperative respiratory depression with the use of Pregabalin has been reported in a patient with undiagnosed obstructive sleep apnea [51]. Concomitant opioid use could increase the risk of respiratory depression and caution should be considered. The Ottawa hospital algorithm for Pregabalin use recommends either avoiding or cautiously titrating low doses depending on the clinical setting and patient characteristics [51]. Pregabalin and Gabapentin could cause peripheral edema which is not related to cardiac, hepatic or kidney failure [52].

#### 5.5. Alpha <sup>2</sup> agonists

Alpha <sup>2</sup> agonists such as Clonidine and Dexmedetomidine are used in perioperative setting for their analgesic properties. A meta-analysis conducted in a mixed general surgical population suggested that perioperative alpha <sup>2</sup> agonists reduce narcotic consumption in the postoperative period [53]. However, very limited data is available regarding their use in obese patients with OSA. Nonopioid anesthetic with Dexmedetomidine in obese patients with OSA resulted in low pain scores in Post Anesthesia Care Unit (PACU) and no perioperative events [54]. Among patients with morbid obesity, substitution of intraoperative opioids with an intraoperative Dexmedetomidine infusion resulted in reduced perioperative opioid requirements [55]. Also, perioperative Dexmedetomidine infusion were found to significantly reduce postoperative opioid consumption (24-hours) as compared to conventional perioperative analgesic regimens [56]. Alpha <sup>2</sup> agonists can cause sedation which could interfere with arousal in OSA patients. However, their opioid sparing benefits may offer greater benefit than the risks. Clonidine causes adverse effects like hypotension, bradycardia, sinus and AV nodal block [57]. Dexmedetomidine causes hypotension and bradycardia more often than hypertension and tachycardia. It may also reduce atrial fibrillation (AF) induction among adult patients with history of paroxysmal AF.

#### 5.6. Ketamine

5.3. Acetaminophen

118 Pain Management in Special Circumstances

5.4. Anticonvulsant agents

5.5. Alpha <sup>2</sup> agonists

Acetaminophen is a commonly used foundational analgesic with perioperative opioid sparing properties. It offers the distinct advantage of being relatively safe and devoid of sedative properties. Addition of acetaminophen to an intravenous opioid PCA regimen was associated with a 20% opioid sparing effect in a meta-analysis of mixed surgical population [45]. Similar opioid dose reduction expected in patients with OSA could therefore potentially reduce opioid-induced ventilator problems. Obese bariatric surgical patients receiving postoperative intravenous acetaminophen 1 gram every 6 hours required fewer morphine equivalents [46]. Acetaminophen lowers cumulative narcotic consumption, regardless of the route of administration [47, 48]. It has the most favorable effect on blood pressure and should be considered as

the first line treatment option in patients with hypertension or cardiovascular disease.

Anticonvulsant agents in clinical use for their analgesic benefits include Pregabalin and Gabapentin. The preoperative use of Pregabalin as premedication significantly lowered immediate postoperative requirement of pain medications among bariatric surgical patients. [49] Preoperative Gabapentin has also significantly lowered immediate postoperative pain scores in morbidly obese bariatric surgical patients [50]. However, the most common side effects of these drugs are dizziness and somnolence, which potentially add to the OSA induced somnolence. Postoperative respiratory depression with the use of Pregabalin has been reported in a patient with undiagnosed obstructive sleep apnea [51]. Concomitant opioid use could increase the risk of respiratory depression and caution should be considered. The Ottawa hospital algorithm for Pregabalin use recommends either avoiding or cautiously titrating low doses depending on the clinical setting and patient characteristics [51]. Pregabalin and Gabapentin could cause peripheral edema which is not related to cardiac, hepatic or kidney failure [52].

Alpha <sup>2</sup> agonists such as Clonidine and Dexmedetomidine are used in perioperative setting for their analgesic properties. A meta-analysis conducted in a mixed general surgical population suggested that perioperative alpha <sup>2</sup> agonists reduce narcotic consumption in the postoperative period [53]. However, very limited data is available regarding their use in obese patients with OSA. Nonopioid anesthetic with Dexmedetomidine in obese patients with OSA resulted in low pain scores in Post Anesthesia Care Unit (PACU) and no perioperative events [54]. Among patients with morbid obesity, substitution of intraoperative opioids with an intraoperative Dexmedetomidine infusion resulted in reduced perioperative opioid requirements [55]. Also, perioperative Dexmedetomidine infusion were found to significantly reduce postoperative opioid consumption (24-hours) as compared to conventional perioperative analgesic regimens [56]. Alpha <sup>2</sup> agonists can cause sedation which could interfere with arousal in OSA patients. However, their opioid sparing benefits may offer greater benefit than the risks. Clonidine causes adverse effects like hypotension, bradycardia, sinus and AV nodal block [57]. Dexmedetomidine causes hypotension and bradycardia more often than hypertension Ketamine, an N-methyl-d-aspartate (NMDA) antagonist has recently received increasing attention as a relatively safe adjuvant analgesic. In patients with morbid obesity, low-dose Ketamine added to intravenous Morphine PCA resulted in a significant reduction in opioid consumption. Importantly, subjects receiving ketamine in addition to morphine had fewer episodes of desaturation postoperatively [9]. A preinduction dose of ketamine of 0.5 mg kg<sup>1</sup> together with Clonidine significantly lowered pain scores and perioperative opioids consumed [58]. Intra-operative Ketamine at doses up to 1 mg kg<sup>1</sup> was shown to decrease opioid consumption in recovery but at the cost of significant drowsiness [59].

#### 5.7. Tramadol

It is an analgesic of intermediate potency with possible advantages in OSA patients due to its multimodal mechanism and a relatively lower risk of respiratory depression [60].

## 6. Multimodal strategies for pain management in obese patients with OSA

Multimodal analgesia is the use of a combination of different analgesic medications and techniques with an aim to provide optimal pain control, thus allowing reduction in opioid requirements. They may have additive or synergistic effects by acting through diverse mechanisms either peripherally or centrally in the nervous system [61]. Multimodal analgesia with a combination of IV Paracetamol and IV Ketorolac in bariatric surgery was found to reduce the postoperative opioid consumption by about 70% [62]. A nonopioid analgesic regimen that employed a combination of nonopioid analgesics (Ketorolac, Clonidine, Ketamine, Lidocaine and Magnesium) in thirty morbidly obese patients undergoing bariatric surgery resulted in lesser PACU opioid consumption and less sedation [63]. The opioid-sparing multimodal techniques are summarized in Table 2.

Magnesium, intravenous local anesthetic infusions (lidocaine), and Clonidine are some additional drugs that have been used perioperatively in patients with morbid obesity to enhance analgesia [64, 65] but more scientific evidence is needed before adopting these agents into routine clinical use.

#### 6.1. Regional analgesia techniques in patients with obstructive sleep apnea

Narcotic-based pain regimens for OSA patients have a risk of opioid-induced respiratory depression. Hypoxia, sleep disturbance, pain, and disturbed opioid responses in OSA contribute to that risk [66, 67]. Neuraxial techniques and peripheral nerve blocks are effective

#### Nonopioid analgesics include Nonsteroidal anti-inflammatory drugs (NSAIDs), Acetaminophen, Analgesic adjuvants such as Ketamine, Dexmedetomidine, and Clonidine may also decrease postoperative opioid requirements.

studies showed not much of a difference in success rate between obese and nonobese and proved that success mainly depends on experience of anesthesiologist and the use of ultrasound-guided techniques [46]. Upper extremity blocks include brachial plexus block that could be performed at different levels. It offers good analgesia for patients with OSA who have a respiratory compromise. Phrenic nerve block is a theoretical risk with inter-scalene block. There is insufficient evidence to recommend its use in this group of patients [79]. Ultrasound-guided transversus abdominis plane (TAP) block is performed in laparoscopic and open abdominal surgeries as it effectively blocks T10 to L1 segments. A successful bilateral TAP block is effective for abdominal midline incisions, especially in nonobese and in situations of failed or difficult epidurals [63]. Paravertebral block is another option for thoracoabdominal surgeries. It could be administered as a single shot or continuous technique, either intra or postoperatively. Multilevel paravertebral block has shown to be successful and opioid-sparing in obese females undergoing breast surgery [80]. The erector spinae plane block (ESP) is a recently evolved simple technique that could be performed under ultrasound guidance. It is gaining popularity for its effective pain relief for somatic and visceral pain. However, further clinical investigation is needed to clearly establish its efficacy in OSA patients. Perioperative analgesia for OSA patients could be carefully planned in the perioperative period. Many effective regional analgesia modalities are currently available for

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Preemptive analgesia could obtund nociceptive responses prior to surgical stimulus and possibly decrease postoperative pain. Moreover, it could possibly decrease the probability of conversion of acute pain to chronic pain [81]. Postoperative patient-controlled intravenous analgesia (PCA) or epidural analgesia (PCEA) have been shown to decrease narcotic consumption and provide a high degree of patient satisfaction [82]. Other techniques like long-acting local anesthetic infusions at the surgical wound site or even intraperitoneal infusion have

Poor pain management of morbidly obese patients increases postoperative complications [85]. Therefore, the use of multimodal analgesia can solve this problem, consequently improving

Developing an optimal evidence-based pain management protocol tailored to obese patients with OSA is a challenging task. The majority of current recommendations are either based on studies with small sample size or lacking a scientifically rigorous study design. Given the paucity of literature in obese patients with sleep apnea, it is difficult to draw a definitive conclusion. Yet, the obvious benefits of multimodal analgesic regimen make it popular in regular clinical practice.

intraoperative and postoperative.

shown promising results [83, 84].

7. Combined strategies for analgesia

patient satisfaction and reduce postoperative morbidity.

8. Nonpharmacological options to pain management

The nonpharmacological options are summarized in Table 3:

Regional analgesia with local anesthetic (e.g., peripheral nerve blocks, epidural analgesia)

Table 2. Opioid-sparing techniques include a combination of the following.

interventions and superior alternatives in pain management toolkits. It offers a superior analgesic effect and minimizes the need for systemic analgesics [68, 69].

Perioperative management by regional analgesic techniques rather than systemic opioids has been recommended by the American Society of Anesthesiologists since 2014, with an aim to reduce the likelihood of OSA-related perioperative adverse outcomes. The beneficial effects of perioperative regional analgesic techniques on patient outcomes have been proved in general surgical population [70, 71]. Still, the evidence in OSA patients is inconclusive as it was driven mainly from case reports or small retrospective case–control studies [67, 72].

#### 6.2. Neuraxial analgesia techniques

Neuraxial analgesia is a modality with high efficacy and can be used effectively as a sole analgesic approach. Its beneficial effects on respiratory functions such as superior spirometry in the immediate postoperative period and lower postoperative pulmonary complications have been consistently documented in many studies [73, 74]. The risks in morbidly obese patients include respiratory depression secondary to a rostral spread of neuraxial opioids that could lead to a postoperative respiratory arrest [75, 76]. Therefore, the ASA task force recommends that expected benefits should be weighed against the potential risks.

Technical difficulty with procedure failure has been proposed as another challenge in OSA patients, who are often obese. Yet, these concerns lack conclusive evidence, and most have been driven from opinion-based reports. Studies in obese pregnant have showed that the incidence of technical difficulty for epidural anesthesia is overrated. The success was correlated with optimal positioning prior to placement and good quality of palpable surface landmarks [77]. Preprocedural ultrasonography (US) of the spine could accurately identify the intervertebral space and predict the needle insertion depth in intrathecal space thus facilitating placement of an epidural catheter. Systematic review and meta-analysis have shown that spine US has a greater accuracy than manual palpation of surface anatomical landmarks [78]. This could lead to a decreased risk of technical failures and the number of needle punctures.

#### 6.3. Peripheral nerve blocks (PNB)

PNB modality is another pillar of opioid-sparing analgesic techniques. It includes upper extremity, lower extremity, and planar blocks such as transversus abdominis plane (TAP) block, paravertebral block, and erector spinae plane block (ESP). Initially, studies showed that obesity (BMI > 25 kg/m2 ) is independent risk factor for block failure. [45] However, other studies showed not much of a difference in success rate between obese and nonobese and proved that success mainly depends on experience of anesthesiologist and the use of ultrasound-guided techniques [46]. Upper extremity blocks include brachial plexus block that could be performed at different levels. It offers good analgesia for patients with OSA who have a respiratory compromise. Phrenic nerve block is a theoretical risk with inter-scalene block. There is insufficient evidence to recommend its use in this group of patients [79]. Ultrasound-guided transversus abdominis plane (TAP) block is performed in laparoscopic and open abdominal surgeries as it effectively blocks T10 to L1 segments. A successful bilateral TAP block is effective for abdominal midline incisions, especially in nonobese and in situations of failed or difficult epidurals [63]. Paravertebral block is another option for thoracoabdominal surgeries. It could be administered as a single shot or continuous technique, either intra or postoperatively. Multilevel paravertebral block has shown to be successful and opioid-sparing in obese females undergoing breast surgery [80]. The erector spinae plane block (ESP) is a recently evolved simple technique that could be performed under ultrasound guidance. It is gaining popularity for its effective pain relief for somatic and visceral pain. However, further clinical investigation is needed to clearly establish its efficacy in OSA patients. Perioperative analgesia for OSA patients could be carefully planned in the perioperative period. Many effective regional analgesia modalities are currently available for intraoperative and postoperative.
