Original article
Viviane G Nasr, James A DiNardo. Pulse Oximetry. Pediatr Rev. 2019 Nov;40(11):605-608. PMID: 31676537
Back when I was in college, my friends and I would argue endlessly over the question: “If you were stranded on a desert island and could have only one vinyl album (OK for most of you, that’s now a streamed electronic album) what would it be”? Beatles or the Stones? Hendrix or Garcia? Davis or Bird? You get the idea. The August 25th PAAD, “CO2 monitoring review” unleashed a flood of emails: What’s the desert island anesthesia monitor? pulse oximeter or capnograph”? I picked the best of these for your enjoyment. I’ve also asked Charlie Cote to submit a remembering the classics PAAD to describe the background of his historic papers on this topic…it should appear in the next 2-3 weeks. Myron Yaster MD
Alan Jay Schwartz, MD, MSEd, recently retired professor of anesthesiology at Children’s Hospital of Philadelphia, stated unequivocally: Pulse oximetry. “Before the advent of pulse oximetry, during clinical care of patients under anesthesia, our clues to hypoxia included the 1) surgeon's comment or our own observation of "black blood" in the field-desaturation that had progressed way too far and 2) bradycardia, also a sign of how far gone hemoglobin oxygen desaturation had progressed with organ dysfunction and very little time to get the patient "out of the soup"!
“I have always encouraged residents and fellows in my clinical education to make it simple,” he wrote. “I suggested they make a problem list for every patient. I recommended they categorize each problem in the following manner; if the problem is mismanaged, would it harm the patient in seconds, minutes, hours, days or weeks? With this approach, I believe pulse oximetry monitoring will avoid patient harm (potentially occurring in seconds or minutes) much sooner than monitoring information from ETCO2. From a purely clinical safety standpoint, I believe pulse oximetry monitoring has immense short term safety value”.
Justin L. Lockman, MD, MSEd, associate professor of anesthesiology at Children’s Hospital of Philadelphia, and a frequent PAAD contributor, is equally unequivocal: Capnography. “Pulse oximetry is a valuable monitoring tool in any clinical situation associated with hypoxemia. As such, changes in SpO2 are a sensitive indicator of disease severity and response to treatment in conditions associated with ventilation/perfusion mismatch and intrapulmonary or intracardiac shunt, such as asthma, bronchopulmonary dysplasia, bronchiolitis, pneumonia, and congenital heart disease. However, conditions associated with hypercarbia due to reduced alveolar ventilation (hypoventilation) as a result of partial airway obstruction or depression of ventilation (endotracheal tube kinking or disconnect, ventilator failure, drugs) will not be associated with significant changes in SpO2, particularly if supplemental oxygen is administered, until partial pressure of carbon dioxide in arterial blood is extremely elevated. Hence, use of pulse oximetry could result in a delay of diagnosis in these conditions – especially in the PACU or PICU or in sedated patients in whom oxygen supplementation is standard practice. Moreover, there is only one monitor that we use than can singlehandedly provide data about all 3 of the ABCs: Capnography. If any one of airway, breathing, or circulation are not intact, there is a change (or loss) of EtCO2.”
Fortunately, we don’t have to make a choice….however, in many resource poor countries of the world they do have to make such choices; they often lack the resources to buy either device. I would urge all of you, either individually or as a group, to consider buying pulse oximeters through LIFEBOX – an international non-profit working to make surgery and anesthesia safer on a global scale. https://www.lifebox.org/purchase-oximeter
Another interesting comment that arose from the CO2 Monitoring Review PAAD comes from Dr. Jeff Gross, chairman of the Department of Anesthesiology, University of Connecticut School of Medicine. As you may recall, in that PAAD, I told the story of how in the old anesthesia machines, there was a knob that when unscrewed, removed the CO2 cannister from the anesthesia circuit to cause CO2 rebreathing and hasten wake up. Jeff writes: “Despite the fact that modern anesthesia circle systems lack a CO2 absorber bypass "knob" I have been using a similar strategy with slow-to-awaken patients. On GE Avance anesthesia machines equipped with the "EZ Change" option, the circuit remains sealed if you physically remove the CO2 absorber from the circuit, so with low oxygen flows (<200 ml/min) you can get rapid CO2 to build up. To rid the circuit of volatile anesthetics, I put an activated charcoal adsorber, designed for use in MH patients (Vapor-Clean, Dynasthetics, Salt Lake City, UT) in the inspiratory limb of the breathing circuit. Within minutes, the PICO2 is above 20 mmHg and the spontaneous minute ventilation is greater than 10 l/min while the inspired concentration of volatile anesthetic is zero. The combination of increased minute ventilation and increased cerebral blood flow, gets patients awake in a hurry. There is a commercial device (ANEclear, Salt Lake City, UT) which accomplishes the same goal by using an activated charcoal adsorber and imposing a variable amount of dead space between the Y-piece and the endotracheal tube”.
I would caution all of you though: “don’t do this at home”…Jeff is one of the world’s experts on CO2, anesthesia machines and circuits and the control of ventilation. His technique works for him and may be dangerous for many of you who are not as familiar with these techniques as he is. Anesthesia safety mechanisms are in place for good reasons! In the meantime, visit https://www.lifebox.org/purchase-oximeter- and let’s talk about how/whether to build a similarly inexpensive EtCO2 monitor, too!
Myron Yaster MD
PS: When I was a Penn anesthesia resident in the 1970s, Jeff was my fellow; when I was a CHOP pediatric anesthesia fellow, Alan was my teacher; and when I was an attending at Hopkins, Justin was my fellow. Will the circle be unbroken? MY