Pulse Oximetry
This law explains how a pulse oximeter calculates oxygen saturation, based on light absorption being proportional to the concentration of the absorbing substance and the path length.
What is the Beer-Lambert Law?
This sampling method aspirates gas through tubing to a remote sensor, creating a built-in 1- to 3-second delay compared with a real-time reading.
What is sidestream sampling?
This is the blood pressure measurement method used in the OR that detects arterial pulsations with a cuff.
What is the oscillometric method?
This stimulation mode delivers four stimuli at 2 Hz over 2 seconds.
What is Train of Four (TOF)?
This is the core temperature threshold that defines hypothermia.
What is 36 degrees Celsius (96.8°F)?
This hemoglobin type absorbs more of the 940 nm infrared wavelength used by a standard pulse oximeter.
What is oxyhemoglobin?
This is the phase of the capnogram made up mostly of alveolar gas, where the CO2 concentration levels off into a plateau.
What is Phase III (the alveolar plateau)?
Of the values displayed on an oscillometric blood pressure monitor, this is the one measured directly rather than calculated.
What is mean arterial pressure (MAP)?
This is the TOF ratio considered the objective threshold for adequate neuromuscular recovery.
What is 0.9?
This is the optimal placement of an esophageal temperature probe for the closest correlation to core blood temperature.
What is the distal third of the esophagus?
This is the SpO2 value that marks the inflection point on the oxyhemoglobin dissociation curve — below this number, small further drops in PaO2 cause large, steep drops in saturation.
What is 90%?
This is the specific point on the capnogram where the ETCO2 value is actually read.
What is the end of Phase III (right before the inspiratory downstroke)?
This is the type of reading you get if the blood pressure cuff is too small for the patient's arm.
What is a falsely high reading?
This monitoring mode is used when the TOF count is 0 to estimate how soon TOF responses will return as the block lightens.
What is Post-Tetanic Count (PTC)?
Heat is lost as infrared energy to cooler surrounding surfaces, and this is the most significant heat-loss mechanism early in a case in the operating room.
What is radiation?
Decreased CO2, decreased temperature, decreased 2,3-DPG, and increased pH together cause this change in the oxyhemoglobin dissociation curve, increasing hemoglobin's affinity for oxygen.
What is a left shift?
This is the normal difference between PaCO2 and ETCO2, with PaCO2 running higher due to dead space dilution.
What is 2 to 5 mmHg?
This ECG lead is best for detecting rhythm and arrhythmias, such as atrial fibrillation and junctional rhythms.
What is Lead II?
This stimulation mode is more sensitive than TOF for detecting fade by feel, making it useful for tactile assessment of residual block when no quantitative monitor is available.
What is Double Burst Stimulation (DBS)?
Along with delayed emergence, this is a consequence of hypothermia related to how long anesthetic drugs stay active in the body.
What is prolonged drug clearance (prolonged drug effect)?
This abnormal hemoglobin species, elevated after carbon monoxide exposure, causes the pulse oximeter to read falsely normal or high — around 98% — despite the patient being severely hypoxic.
What is carboxyhemoglobin?
Bronchospasm, COPD, and airway obstruction all produce this change in the angle between Phase II and Phase III of the capnogram.
What is an increased alpha angle?
This combination of two ECG leads is most commonly monitored together in the OR, covering both rhythm and ischemia detection.
What are Lead II and V5?
This is the approximate percentage of receptors occupied when the TOF count is 1 out of 4 twitches.
What is 90%?
This process is impaired under general anesthesia, causing the hypothalamic set point to reset and the body to lose its normal ability to respond to cold.
What is thermoregulation?