For a patient in the kidney rest position for Pelvolithotomy, lying on their right side, should the Non-Invasive Blood Pressure (NIBP) cuff be placed on the right or left arm?

NIBP Cuff Placement for Pelvolithotomy in Right Lateral Decubitus Position

Direct Answer

Place the NIBP cuff on the LEFT arm (non-dependent, upper arm) when the patient is lying on their right side for pelvolithotomy. 1, 2

Physiologic Rationale

The fundamental principle of accurate blood pressure measurement requires the cuff to be positioned at the exact level of the right atrium (mid-sternum/fourth intercostal space), regardless of patient position. 1, 2

When a patient lies on their right side:

• The left arm (upper, non-dependent arm) can be properly supported and positioned at right atrial level 1, 2
• The right arm (lower, dependent arm) lies below heart level, creating hydrostatic pressure errors that falsely elevate readings by approximately 2 mmHg for every inch below heart level—potentially 10 mmHg or more total error 1, 2

Critical Positioning Requirements

The left arm must be actively supported at mid-sternum level using an armboard or padded support—never allow the arm to hang unsupported or be held by the patient. 1, 2 Muscle tension from unsupported positioning creates clinically significant measurement errors. 1

Specific positioning steps:

• Position the middle of the cuff at the exact level of the right atrium (fourth intercostal space/mid-sternum) 1
• Ensure the cuff bladder encircles at least 80% of the arm circumference 1, 2
• Place the lower edge of the cuff a few centimeters above the antecubital fossa 1
• Support the entire arm on an armboard or padded surface at heart level 1, 2

Magnitude of Positioning Errors

Understanding the severity of positioning errors emphasizes why the left arm is mandatory:

• Arm below heart level (right arm in this case): Falsely HIGH readings by ~2 mmHg per inch, potentially ≥10 mmHg total 1, 2
• Arm above heart level: Falsely LOW readings by the same magnitude 1, 2
• Unsupported arm positioning: Additional elevation from isometric muscle tension 2

Device Selection

Use a validated oscillometric device appropriate for intraoperative monitoring. 1, 2 Only 6% of commercially available devices have been adequately validated according to current standards. 1 Note that oscillometric devices are not validated for use in patients with atrial fibrillation. 1

Common Pitfalls to Avoid

• Never place the cuff on the right (dependent) arm when the patient is in right lateral decubitus—this guarantees falsely elevated readings 1, 2
• Never allow the left arm to hang unsupported—this creates both hydrostatic and muscle tension errors 1, 2
• Never position the cuff above or below heart level—even small deviations create clinically significant errors 1, 2
• Never assume the patient can hold their arm in position—this creates isometric muscle tension that falsely elevates readings 2

Alternative Considerations

If bilateral arm access is restricted (extremely rare in pelvolithotomy positioning), consider lower extremity measurement with recognition that lower limb pressures are typically 10-20 mmHg higher than brachial pressures. 2 However, this should not be necessary for standard pelvolithotomy positioning where the left arm remains accessible.