Feature | April 08, 2008| Devjani Saha, M.D., and Girish P. Joshi, M.D., MB, BS, FFARCSI

Monitoring Capnography Helps Prevent Respiratory Complications

Monitoring CO2 offers a quick assessment of ventilation.

Nihon Kohden's capONE mainstream CO2 sensor can be used on nonintubated patients. It's airway adapter catches oral as well as nasal expired CO2 to help increase accuracy.

Nihon Kohden's capONE mainstream CO2 sensor can be used on nonintubated patients. It's airway adapter catches oral as well as nasal expired CO2 to help increase accuracy.

As obesity continues to be a widening problem in the U.S., anesthesiologists face more issues involving drug-induced respiratory depression and airway obstruction, but capnography provides a reliable means of assessing these complications during procedural sedation to prevent associated catastrophic adverse respiratory complications.

The development of new surgical techniques and sophisticated sedatives has allowed more practitioners to perform procedures outside of the operating room arena. However, increasing complexity of not only these medical procedures but also of patient profiles, make administration of sedation/analgesia more challenging. Airway obstruction is becoming increasingly common during sedation and analgesia because of the trend toward obesity in modern times. It is well appreciated amongst anesthesiologists, that the increasing frequency of obesity and associated obstructive sleep apnea (OSA) has increased the presentation of perioperative airway complications. These patients are sensitive to sedative and analgesic drugs and extremely prone to upper airway obstruction. Obesity causes changes in the patency and compliance of the airway, changes in the pharyngeal tissues and changes in central respiratory control centers.1 Complications associated with sedation appear to be more prevalent in recent times secondary to these factors. 2.3

The American Society of Anesthesiology (ASA) Practice Guidelines for Sedation and Analgesia by Non-Anesthesiologists state the primary causes of morbidity associated with sedation/analgesia are drug-induced respiratory depression and airway obstruction. 4 In fact, hypoventilation in the form of bradypnea and airway obstruction is a serious and often underappreciated problem in patients receiving sedation/analgesia outside of the operating room. A recent review of closed claims of anesthesia for procedures outside of the operating room revealed a higher incidence of adverse events, one third of which were felt to be largely preventable with better monitoring. 3

In this review, we highlight how patients outside of the operating room arena are commonly monitored in respect to oxygenation alone versus oxygenation and ventilation. We advocate the use of capnography, a standard tool used in the operating room, in order to provide a more reliable means of assessing airway obstruction and ventilation during procedural sedation, thereby preventing associated catastrophic adverse respiratory complications.

Pulse oximetry is routinely used during sedation as a means of monitoring blood oxygenation. While monitoring oxygenation is crucial during sedation, it is important to consider that pulse oximetry does not serve as a reliable indicator of adequate ventilation, or the exchange of gases between the lungs and the atmosphere. Since hypoventilation, in the forms of bradypnea and most importantly airway obstruction, is extremely common during sedation, capnography serves as a useful adjunct to pulse oximetry. Reliance on pulse oximetry alone as an indicator of patient well-being during sedation can lead to failure of timely detection hypoventilation/airway obstruction because arterial deoxygenation is often delayed especially in patients breathing supplemental oxygen. 5,7

The role for capnography in the detection of inadequate ventilation, namely bradypnea and airway obstruction, has been well established in the operating room and should be considered for use in other areas where sedation is administered. The ASA guidelines have helped direct anesthesiologists in the use of capnography in distinguishing problems with ventilation from those of oxygenation. By providing a noninvasive method to assess ventilation through a continuous graphic display of expired or end-tidal carbon dioxide (EtCO2) concentrations over time, capnography provides the practitioner with data regarding the exchange of air between the patient’s lungs and the atmosphere in real time. Capnography can be easily adapted for use with nasal cannula or facemask oxygen delivery devices and can assist in detecting adverse respiratory outcomes. The graphic display of EtCO2 over time can serve as a valuable tool in recognizing partial or complete airway obstruction. A visual change or disappearance in the EtCO2 waveform can signal an airway obstruction to the practitioner, and airway maneuvers such as a chin lift, jaw thrust or placement of an oral airway are needed immediately. Of note, while capnography provides important data regarding ventilation, it is necessary to keep in mind that EtCO2 may not always reflect arterial partial pressure of carbon dioxide (PaCO2).

Monitoring Patient On-Demand Pain Control

Like sedation, patient-controlled analgesia is being increasingly examined as a potential area of medicine where respiratory complications can occur. Numerous studies have shown increased risk of respiratory events such as respiratory depression and even respiratory arrest associated with intravenous patient-controlled analgesia (IV-PCA) administration of opioids in normal, elderly and obese patients. 8,12 In addition, IV-PCA can be affected by programming errors and device malfunctions, adding an additional layer of complexity in the administration of patient controlled analgesia. 11,12

Given these risks, it is important to consider the use of capnography in the safe administration of IV-PCA opioids, especially in select high-risk populations (e.g., frail elderly patients, obese patients and patients with OSA). In fact, a recent study showed that continuous respiratory monitoring in the form of combined oximetry and capnometry/capnography can prove optimal for the safe administration of IV-PCA. 8
Recent studies and ASA guidelines have delineated that patients with OSA receiving postoperative opioids for analgesia are at risk for postoperative respiratory depression even days into the postoperative recovery period. 1, 13-14 This prolonged period of risk for respiratory depression is attributed in part to the re-establishment of sleep patterns several days after surgery, and the exacerbation of natural REM- induced respiratory depression by opioid analgesics. 1, 13

Diminishing Sedation-Related Respiratory Events

The number of more complex procedures in the U.S. is increasing, and as the number of patients with significant co-morbidities increases, the need to perform more procedures outside of the operating room with deeper levels of sedation also rises. As the need for sedation in these arenas continues, the role for extra vigilance and monitoring increases. The use of capnography as a means of monitoring ventilation has been well established by anesthesiologists in the operating room and its use has greatly diminished anesthesia- and sedation-related adverse perioperative respiratory events. 15 By providing a means to quickly assess ventilation, and by decreasing reliance on the pulse oximeter as the sole monitor of respiratory status, capnography can increase the margin of safety when administering sedation and analgesia.


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12. Institute for Safe Medication Practices, “Misprogram a PCA pump? It's easy!” Institute for Safe Medication Practices Web Site. www.ismp.org/Newsletters/acutecare/articles/20040729_asp. Accessed Feb 8, 2008.
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