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Monitoring of Oxygenation and Ventilation
Introduction
During anesthesia for a thoracic surgical procedure, many alterations in physiology occur, including changes in oxygenation and ventilation. Whether the patient is receiving monitored anesthesia care (MAC), regional anesthesia, or general anesthesia, it is essential that the anesthesiologist monitor each patient diligently to optimize management and avoid complications. (“Vigilance” is the motto of the American Society of Anesthesiologists [ASA]). Monitoring of oxygenation and ventilation are of vital importance, particularly in thoracic anesthesia, where one-lung ventilation (OLV) is necessary in most cases. The anesthesiologist should be familiar with the various methods available to monitor oxygenation and ventilation, and how to correctly interpret data.
American Society of Anesthesiologists Standards for Basic Anesthetic Monitoring
The ASA has adopted two standards for basic anesthetic monitoring. Standard I requires that qualified anesthesia personnel be present in the procedural room over the entirety of all general anesthetics, regional anesthetics, and MAC. Standard II ( Box 11.1 ) requires continual evaluation of a patient’s oxygenation, ventilation, circulation, and temperature during all anesthetics. This chapter will explore the various methods of monitoring oxygenation and ventilation and will emphasize their importance during thoracic anesthesia.
• Box 11.1
American Society of Anesthesiologists Standards for Basic Anesthetic Monitoring
2. STANDARD II
During all anesthetics, the patient’s oxygenation, ventilation, circulation, and temperature shall be continually evaluated.
2.1 Oxygenation
2.1.1 Objective
To ensure adequate oxygen concentration in the inspired gas and the blood during all anesthetics.
2.2 Methods
2.2.1 Inspired gas: During every administration of general anesthesia using an anesthesia machine, the concentration of oxygen in the patient breathing system shall be measured by an oxygen analyzer with a low oxygen concentration limit alarm in use. a
2.2.2 Blood oxygenation: During all anesthetics, a quantitative method of assessing oxygenation, such as pulse oximetry, shall be used. a When the pulse oximeter is used, the variable pitch pulse tone and the low threshold alarm shall be audible to the anesthesiologist or the anesthesia care team personnel. a Adequate illumination and exposure of the patient are necessary to assess color. a
3. VENTILATION
3.1 Objective
To ensure adequate ventilation of the patient during all anesthetics.
3.2 Methods
3.2.1 Every patient receiving general anesthesia shall have the adequacy of ventilation continually evaluated. Qualitative clinical signs, such as chest excursion, observation of the reservoir breathing bag, and auscultation of breath sounds are useful. Continual monitoring for the presence of expired carbon dioxide shall be performed unless invalidated by the nature of the patient, procedure, or equipment. Quantitative monitoring of the volume of expired gas is strongly encouraged. a
3.2.2 When an endotracheal tube or laryngeal mask is inserted, its correct positioning must be verified by clinical assessment and by identification of carbon dioxide in the expired gas. Continual end-tidal carbon dioxide analysis, in use from the time of endotracheal tube/laryngeal mask placement, until extubation/removal or initiating transfer to a postoperative care location, shall be performed using a quantitative method, such as capnography, capnometry, or mass spectroscopy. a When capnography or capnometry is used, the end-tidal CO 2 alarm shall be audible to the anesthesiologist or the anesthesia care team personnel. a
3.2.3 When ventilation is controlled by a mechanical ventilator, there shall be in continuous use a device that is capable of detecting disconnection of components of the breathing system. The device must give an audible signal when its alarm threshold is exceeded.
a Under extenuating circumstances, the responsible anesthesiologist may waive the requirements marked ( a ); it is recommended that when this is done, it should be so stated (including the reasons) in a note in the patient’s medical record.
Oxygenation
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