Pulse oximetry and capnography are anesthesia's peanut butter and jelly — I won't use one without the other. Why? Because capnography helps monitor respiration and pulse oximetry monitors blood oxygen levels. Those real-time readings provide reassurance that patients' respiration rates are normal and their airways are secure. The monitors also provide the earliest warning signs of respiratory depression.

It's impossible to overstate the importance of that feedback, especially in the outpatient setting, where many procedures are performed under IV sedation or monitored anesthesia care (MAC). The primary goal of anesthesia is to minimize risks. Capno- graphy and pulse oximetry do that during procedures done under light sedation or major surgeries involving general anesthetics. If your providers aren't using both, they're not providing safe patient care. It's that simple.

Here's how each monitoring modality works:

• Pulse oximetry measures the percentage of oxygen that's bound to hemoglobin. It's usually an accurate, non-invasive and reliable way to monitor the oxygen saturation level (SpO2) of a patient's blood. The measure is converted into a percentage that's displayed on the pulse oximeter, usually along with the patient's heart rate. Acceptable SpO2 ranges from 95% to 100%. Providers will take notice and begin to take action when the reading starts to decrease and creep toward 90%.

• Capnography measures the partial pressure of CO2 in each expired breath. Providers place a sample line, a very thin tube that's 3 to 4 mm in diameter, in the anesthesia machine's breathing circuit or the patient's oxygen mask. When patients breathe out, CO2 is captured in the line and the capnography monitor provides a relative reading of end tidal CO2 (ETCO2).

On a capnography monitor, you see a waveform (capnogram) that represents the real-time reading of a patient's rate of respiration. A normal waveform appears as a square-shaped or rectangular box and a numeric reading (capnometry) shows the measurement of exhaled CO2. "Normal" ETCO2 is in the range of 35 to 45 mmHg. In patients who are spontaneously breathing during deep sedation, you'd attach the capnography monitor's sample line to the oxygen mask. In that case, because it's mixed with fresh air coming into the oxygen mask, ETCO2 might only read 15 mmHg.

If the patient's respiratory rate increases (hyperventilation), the CO2 waveform becomes smaller and more frequent, and the numeric reading falls below the normal range. If respiration decreases (hypoventilation), the waveform becomes taller and less frequent, and the numeric reading rises above the normal range. If the square waveform starts to collapse, there's an airway obstruction. If the square becomes a flat line, the patient is not breathing.

Oxygenation and ventilation are not the same physiologic process. Oxygenation involves the addition of O2 from the environment to the blood, while ventilation and CO2 elimination is the movement of air into and out of the lungs. The human body actually needs to move only small amounts of air in order to be able to saturate the blood with oxygen. However, that movement may not be sufficient to eliminate proper amounts of CO2. That's why pulse oximetry and capnography are both needed to monitor the safe administration of sedation and general anesthesia.

When patients are sedated, drugs that affect the central nervous system and depress airway reflexes can compromise ventilation. In addition, the relaxed muscles of a sedated patient could lead to partial or complete airway obstruction. LMAs or endotracheal tubes manage the airways of patients under general anesthesia, but sedated patients, who do not have such devices placed, are at higher risk of airway compromise. That's why capnography is arguably more important during such cases.

There are a few features to consider when assessing your monitor options. Are the controls intuitive? Are the surfaces easy to wipe down between cases? Can you adjust the alarm settings? For example, providers can set ETCO2 parameters on a capnography monitor to a range that's appropriate for the patient being sedated. When they're monitoring a frail, elderly patient, they can set the apnea alarm to sound in 20 seconds, instead of the typical 30 to 40 seconds, if respiratory rate readings fall below the safe range. Certainly, providers should notice changes in the capnograph long before the apnea alarm sounds, but the adjustable built-in safety feature is a nice failsafe to have.

Always watching

I use the trends of pulse oximetry and capnography to avoid deteriorations in patient care, not necessarily to wait until an alarm sounds before I take action. That's the point of using the monitors — they alert you to slight changes in a patient's condition long before the situation turns critical.

Before pulse oximetry and capnography were available, providers relied on skin coloration, auscultation, manual pulse and blood pressure readings to assess vital signs. Oxygenation and ventilation were assessed less objectively in previous generations. Thankfully we've come a long way since then. I believe capnography and pulse oximetry are among the most important monitoring developments of the past 30 years and essential technologies to have in your ORs. But we can still learn from providers of the past who knew that awareness and vigilance are anesthesia's most important tools. Without them, even the most informative patient monitors are useless. OSM