Does a plethysmograph have any practical uses in emergency medicine?

Plethysmography in Emergency Medicine: Limited Practical Utility

Plethysmography has minimal practical use in emergency medicine, as it has largely fallen out of favor due to lack of reliable and reproducible quantitative data, and has been replaced by more accurate and clinically useful modalities.

Current Status in Acute Care Settings

Peripheral Vascular Assessment

• Plethysmography and pulse volume recording (PVR) are no longer recommended for routine use in evaluating peripheral arterial disease because they lack reliable and reproducible quantitative data 1
• These techniques have been superseded by ankle-brachial index (ABI), duplex ultrasound, and cross-sectional imaging (CTA/MRA) for assessing limb ischemia 1
• While plethysmography can be used for initial evaluation in patients with chronic limb-threatening ischemia, its accuracy is limited and it provides inferior diagnostic information compared to modern alternatives 1

Respiratory Monitoring

• Respiratory inductive plethysmography has specific but narrow applications in monitoring thoracoabdominal motion, primarily in research settings and specialized pediatric respiratory assessments 1
• The American Journal of Respiratory and Critical Care Medicine notes that respiratory inductive plethysmography is valuable for assessing chest wall motion and detecting asynchronous breathing patterns, but it is a nonspecific indicator that must be interpreted in clinical context 1
• This technique is particularly problematic in infants with highly compliant chest walls, where calibration for volume is difficult and phase angles may be hard to interpret 1

The One Potentially Useful Emergency Application

Pulse Oximetry Plethysmography

• The plethysmographic waveform available on modern pulse oximeters represents the only clinically relevant form of plethysmography in emergency settings 2
• This provides real-time assessment of peripheral perfusion and can detect:
  • Heart rate and rhythm abnormalities 2
  • Pulsus paradoxus 2
  • Peripheral vasoconstriction and developing shock 2
  • Myocardial and valvular dysfunction 2
• However, this remains an underutilized data source despite widespread availability 2

Critical Limitations for Emergency Use

Technical and Practical Constraints

• Body plethysmography requires sealed chambers with rigid walls and is designed for pulmonary function testing, not acute care 3
• Strain-gauge plethysmography is rarely used because it requires invasive catheters and drug infusion 1
• Respiratory inductive plethysmography has significant baseline drift (over 10-fold when warm) that precludes long-term monitoring 4
• Only approximately one-third of individual measurements of functional residual capacity changes are accurate to within ±10% of reference standards 5

Why Other Modalities Are Superior

• For cardiovascular emergencies: Echocardiography (including focused cardiac ultrasound) provides superior diagnostic information and is now recommended for cardiac arrest management where trained practitioners are available 1
• For peripheral vascular emergencies: ABI testing, duplex ultrasound, and point-of-care ultrasound provide more actionable information more rapidly 1
• For respiratory emergencies: Direct pressure measurements, spirometry, and modern ventilator monitoring provide more reliable data 1

Bottom Line for Emergency Practice

Plethysmography should not be considered a standard tool in emergency medicine. The only exception is the passive monitoring of the plethysmographic waveform already displayed on pulse oximeters, which can provide supplementary hemodynamic information but should never replace standard monitoring or more definitive diagnostic modalities 2. For any clinical question that might historically have been addressed with plethysmography, superior alternatives now exist that provide faster, more accurate, and more clinically actionable information in the emergency setting 1.