What is a PM (post meridiem) capsule used for?

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Understanding PM Capsules in Sleep Medicine

PM (post meridiem) capsules are primarily used for the diagnosis of obstructive sleep apnea (OSA) in adult patients with high pretest probability of moderate to severe OSA who do not have comorbid medical conditions or other sleep disorders. 1

What is a PM Capsule?

In sleep medicine, PM refers to "Portable Monitoring" devices that are used as an alternative to in-laboratory polysomnography (PSG) for diagnosing sleep disorders, particularly OSA. These devices:

  • Must record at minimum airflow, respiratory effort, and blood oxygenation 1
  • Are classified as Type 3 devices in sleep medicine terminology 1
  • Should use the same types of biosensors as in-laboratory PSG, including oronasal thermal sensors, nasal pressure transducers, and oximetry 1

Appropriate Uses for PM Devices

PM devices are indicated in the following scenarios:

  • For diagnosis of OSA in patients with high pretest probability of moderate to severe OSA 1
  • For patients without significant comorbid medical conditions 1
  • For patients without other suspected sleep disorders 1
  • For patients for whom in-laboratory PSG is not possible due to immobility, safety concerns, or critical illness 1
  • To monitor response to non-CPAP treatments for OSA, including oral appliances, upper airway surgery, and weight loss 1

Contraindications for PM Devices

PM devices should NOT be used in:

  • Patients with significant comorbid medical conditions that may affect accuracy, including moderate to severe pulmonary disease, neuromuscular disease, or congestive heart failure 1
  • Patients suspected of having other sleep disorders, including central sleep apnea, periodic limb movement disorder, insomnia, parasomnias, circadian rhythm disorders, or narcolepsy 1
  • Pediatric populations or older adults (>65 years) without careful consideration, as most validation studies have been done in middle-aged adults 1

Clinical Implementation

When using PM devices:

  • They should be used only as part of a comprehensive sleep evaluation supervised by a practitioner with board certification in sleep medicine 1
  • Application of PM sensors should be performed by an experienced sleep technician or appropriately trained healthcare practitioner 1
  • PM testing should be performed under the auspices of an AASM accredited comprehensive sleep medicine program 1
  • The diagnosis of OSA is confirmed if the number of obstructive events is greater than 15 events/hour or greater than 5/hour in a patient with relevant symptoms 1

Important Considerations and Pitfalls

  • PM devices tend to underestimate the severity of sleep apnea compared to full PSG because they measure events per recording time rather than per sleep time 1
  • Technical failures can occur with PM devices (reported failure rates up to 19% in some studies) 1
  • Clinical judgment remains the best method for determining OSA risk and interpreting PM results 1
  • PM results should be combined with clinical evaluation to determine whether additional testing is required or treatment should be initiated 1

Note: PM in this context refers specifically to portable monitoring devices used in sleep medicine, not to be confused with evening (post meridiem) medication dosing.

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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