Does fluid overload increase the incidence of phrenic nerve palsy in supraclavicular brachial plexus block?

Fluid Overload and Phrenic Nerve Palsy in Supraclavicular Brachial Plexus Block

Fluid overload does not directly increase the incidence of phrenic nerve palsy in supraclavicular brachial plexus block; however, fluid overload can worsen the clinical consequences of phrenic nerve palsy when it occurs, particularly by compromising respiratory mechanics through pulmonary edema and splanchnic edema. 1

Understanding the Relationship

Phrenic Nerve Palsy Mechanism in Supraclavicular Blocks

• Phrenic nerve palsy occurs in supraclavicular brachial plexus blocks due to backward diffusion of local anesthetic within the neural sheath, not due to fluid status. 2
• The incidence of hemidiaphragmatic paralysis is volume-dependent, with higher local anesthetic volumes (30 mL) causing phrenic nerve blockade in 45% of cases compared to lower volumes. 2
• Ipsilateral phrenic nerve paralysis can cause acute hypercapnic respiratory distress and loss of consciousness, particularly in patients with compromised respiratory reserve. 3, 4

How Fluid Overload Exacerbates the Problem

Fluid overload creates a dangerous synergy with phrenic nerve palsy by independently impairing respiratory function:

• Fluid overload causes pulmonary edema, which impairs pulmonary gas exchange and tissue oxygenation, reducing the patient's ability to compensate for hemidiaphragmatic paralysis. 1
• Even modest fluid overload of 2.5 L can cause adverse effects including increased postoperative complications and prolonged hospital stay. 1
• Splanchnic edema from fluid overload increases abdominal pressure, which further compromises diaphragmatic function and can lead to abdominal compartment syndrome. 1

Clinical Risk Assessment

High-Risk Patients Requiring Special Caution

Avoid supraclavicular blocks entirely in favor of alternative approaches (axillary or infraclavicular) in patients with:

• Preexisting cardiorespiratory dysfunction, where even unilateral diaphragmatic paralysis may not be tolerated. 1, 2
• Morbid obesity, which already compromises respiratory mechanics and increases risk of acute respiratory failure. 4
• Chronic obstructive pulmonary disease or restrictive lung disease. 1
• Congestive heart failure, where fluid tolerance is already reduced. 1

Volume Management Strategy

Maintain near-zero to mildly positive fluid balance (+1-2 L maximum by end of procedure) to protect against both fluid overload complications and preserve respiratory reserve: 1

• Administer maintenance fluids at 25-30 mL/kg/day with no more than 70-100 mmol sodium/day. 1
• Avoid indiscriminate fluid boluses; use vasopressors for hypotension after ensuring normovolemia. 1
• Monitor for signs of fluid overload including increased jugular venous pressure and pulmonary crackles. 1

Block Technique Modifications to Reduce Phrenic Nerve Palsy

Use the lowest effective volume of local anesthetic (20 mL or less of 0.375% bupivacaine) to reduce phrenic nerve blockade incidence: 2

• Ultrasound guidance is mandatory to reduce local anesthetic systemic toxicity and allow precise needle placement. 1
• Consider modified supracostal approach with needle-tip placement in the visceral or dorsal area of the first rib, which significantly reduces forced vital capacity decline compared to standard approach. 5
• The bent needle technique for continuous supraclavicular blocks can reliably avoid phrenic nerve blockade when performed correctly. 6

Monitoring and Emergency Preparedness

Have emergency intubation equipment immediately available when performing supraclavicular blocks, as respiratory distress can develop within minutes: 4

• Use bedside M-mode ultrasonography to detect hemidiaphragmatic paralysis by assessing diaphragmatic excursion and velocity before and 20 minutes after block placement. 3, 2
• Monitor oxygen saturation continuously; target 94-98% in patients without hypercapnic risk. 7
• Obtain arterial blood gases if acute dyspnea or oxygen desaturation occurs to assess for hypercapnic respiratory acidosis. 4

Common Pitfalls to Avoid

• Do not assume supraclavicular blocks spare the phrenic nerve—the incidence of hemidiaphragmatic paralysis ranges from 25-47.5% depending on volume used. 2
• Do not administer aggressive fluid resuscitation to hypotensive patients receiving epidural or regional anesthesia—use vasopressors instead after confirming normovolemia. 1
• Do not reduce pre-procedural sedation doses without considering respiratory compromise risk—patients with potential phrenic nerve palsy need minimal sedation. 1
• Do not overlook fluid management as a modifiable risk factor—fluid overload worsens respiratory mechanics independent of the block itself. 7