Current applications of capnography in non-intubated patients

Abstract

Current clinical guidelines recommend capnography as one of the best non-invasive methods to assess adequacy of ventilation in the non-intubated patient. Alveolar hypoventilation or respiratory depression is a serious event that occurs in a variety of clinical settings where patients receive sedatives and opioids. With the large number of procedures performed outside the operating room under the effects of sedatives and the increased use of patient-controlled analgesia, the need for capnography for monitoring has dramatically increased. Despite the succesful use of capnography to monitor ventilation in the operating room over several decades, other clinical areas have been very slow adapters of the technology and still rely heavily upon pulse oximetry to detect hypoventilation. This article reviews the most current evidence for using capnography in the non-intubated patient and summarizes the results of outcome measures reported in recent clinical trials. Capnography should be routinely used for non-intubated patients at risk for respiratory depression, in particular those receiving supplemental oxygen.

Keywords::

• capnography
• carbon dioxide
• hypoventilation
• patient-controlled analgesia
• procedural sedation
• respiratory depression
• volumetric CO₂

Financial & competing interests disclosure

RD Restrepo and J Waugh are investigators for Covidien-Oridion Capnography. G Spratt is involved in marketing Covidien-Oridion Capnography. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending or royalties.

No writing assistance was utilized in the production of this manuscript.

Key issues

• Noninvasive measures of respiratory status are preferred if sufficient accuracy and reliability can be attained. Pulse oximetry, a ubiquitous noninvasive respiratory monitor, is a valuable indicator of oxygenation but cannot substitute capnography as an indicator of ventilation, given oxygenation and ventilation are distinctly different physiological processes and thus require separate but complementary monitoring methods.

• Intermittent ‘spot checks’ of oxygenation (pulse oximetry) and ventilation (visual inspection) are not adequate for reliably recognizing clinically significant drug-induced respiratory depression.

• The use of pulse oximetry as a surrogate monitor for detecting hypoventilation should be limited to patients breathing room air and without risk factors for hypercarbia and should be used selectively for patients at high risk of oxygenation problems.

• It is obvious that more and more procedures are performed far from operating rooms and under the supervision of nonanesthesiologists. The American Society of Anesthesiologists has strongly recommended capnography to reduce the likelihood of unrecognized clinically significant opioid-induced and sedative-induced respiratory depression and thus enhance patient safety.

• Staff should be educated not to rely on pulse oximetry alone because pulse oximetry can suggest adequate oxygen saturation in patients who are actively experiencing respiratory depression, especially when supplemental oxygen is being used. When pulse oximetry or capnography is used, it should be used continuously rather than intermittently.

Notes

^†If a change is noted in the patient’s ETCO₂ trend or respiratory status (increased symptoms), (P_(a−ET)CO₂) should be confirmed.