True Learn Main points 12 Flashcards
Isoflurane is being used for maintenance of general anesthesia at 1% along with 4 L/min fresh gas flow. In an open system (no rebreathing), approximately how much liquid isoflurane would be used in 5 minutes?
The volume of inhalational anesthetic vapor delivered by a vaporizer at a particular dialed setting can be calculated: V = (%V * FG) / (1 - %V). One milliliter of liquid anesthetic is converted to approximately 200 mL vapor at room temperature. A shortcut for calculating the volume of liquid anesthetic consumed in one hour is: Liquid volatile anesthetic (mL/hr) ≈ 3 * FGF (L/min) * % anesthetic vapor.
Which of the following gas properties influences the flow rate around the annular space of a conventional flowmeter at low fresh gas flows?
The annular space towards the bottom of a conventional flowmeter is considered to be tubular. Laminar flow is present around the flowmeter float when the FGF is low. Laminar flow is primarily affected by gas viscosity (Hagen-Poiseuille equation). The annular space towards the top of a conventional flowmeter is considered to be orificial. Turbulent flow, affected primarily by gas density (Graham’s law), is present around the flowmeter when the FGF is high.
Which of the following has the LEAST error when comparing SpO2 to arterial blood gas oxygen saturation?
Pulse oximetry measures the relative absorbance of infrared and red light to reflect arterial oxygen saturation, however, inaccuracy occurs with dyes, nail polish, vasoconstriction, hypothermia, methemoglobinemia, carboxyhemoglobin, and artifact such as movement, but is not affected by fetal hemoglobin
Using an anesthesia machine with a circle system and a tight-fitting mask, you are providing preoxygenation to a 70 kg 30-year-old non-smoking male with normal cardiopulmonary function and oxygen consumption. The machine is set to deliver 100% O2 at 15 L/min. Which of the following techniques is the LEAST LIKELY to induce rebreathing of exhaled gases?
Whenever minute ventilation (calculated as tidal volume * respiratory rate) exceeds fresh gas flow, rebreathing of exhaled gases will occur, leading to a lower FiO2, compared to the dialed O2 concentration.
TrueLearn Insight : Adding nasal cannula oxygen can improve pre-oxygenation before rapid sequence induction and can also provide apneic oxygenation during laryngoscopy.
Which of the following is INCREASED with the use of a closed circuit anesthetic technique?
Advantages of using a closed circuit or low-flow anesthetic technique include decreased use of fresh gas, decreased volatile anesthetic use, conservation of heat and humidity, improved mucociliary function, and decreased occurrence of microatelectasis. Rebreathing of noxious gases, such as acetone or carbon monoxide, increases the risk of postoperative nausea and vomiting.
Which of the following is an appropriate INITIAL intervention for an incompetent inspiratory valve?
The most important initial step in management of an incompetent inspiratory valve is to increase fresh gas flow such that rebreathing will be minimized or eliminated. The faulty inspiratory unidirectional valve should then be replaced as soon as possible.
While delivering an anesthetic to a 34-year-old obese female for laparoscopic cholecystectomy, the oxygen supply alarm sounds and the oxygen analyzer detects a decreasing FiO2 delivery. Which of the following steps is the most appropriate NEXT STEP in management of this patient?
If an oxygen supply line fails the oxygen cylinder on the anesthesia machine needs to be fully opened and the anesthesia machine disconnected from the hospital oxygen supply pipeline.
TrueLearn Insight : If 2 oxygen cylinders are open on an anesthesia machine it is possible that 1 tank will become depleted and divert some flow from the other tank decreasing the oxygen reserve. Additionally, the tank being used should be fully open so that flow from the tank is not restricted. If the tank is not fully opened it may quit delivering oxygen before the tank is empty.
In a patient receiving volume controlled ventilation, breaths are triggered by which of the following preset milestones?
Mechanical ventilation can be categorized by three variables – trigger, limit, and cycle. The trigger variable is what initiates the breath and depends on the ventilatory drive. The limit variable is the algorithm that governs the positive pressure delivery and depends on the ventilatory requirements related to how much flow and volume are required to satisfy the metabolic demands of the patient. The cycle variable is what terminates the inspiratory phase and depends on the duration and ratio of inspiratory time to total breath cycle duration.
Volume controlled ventilation is a total ventilator controlled mode of ventilation where the clinician sets the tidal volume to be delivered and the rate at which it should be delivered. The pressure required to deliver this tidal volume will depend on pulmonary compliance.
Desflurane is being delivered by a Datex-Ohmeda Tec 6 vaporizer in an environment where atmospheric pressure is 380 mm Hg. Which of the following vaporizer dial settings should be used to administer 1 MAC of desflurane (assume 1 MAC = 6% at sea level)?
Most desflurane vaporizers deliver the anesthetic at a constant percent concentration at a given dial setting and not a constant partial pressure. In order to deliver a constant partial pressure of desflurane when changes in altitude or atmospheric pressure occur, the dial should be adjusted according to the formula below. Variable bypass vaporizers will mostly compensate for changes in altitude/atmospheric pressure automatically.
Required dial setting = desired % x (760 mm Hg / current atmosphere mm Hg)
Which of the following approximates the percentage of acetylcholine receptors occupied by rocuronium if there are 2 twitches elicited on train-of-four stimulation (TOF)?
When assessing the degree of neuromuscular blockade using TOF stimulation after nondepolarizing NMBD administration:
1 palpated twitch indicates >90% suppression.
2 palpated twitches indicate 80-90% suppression.
3 palpated twitches indicate 70-80% suppression.
4 palpated twitches indicate up to 65-75% suppression.
Palpation of twitches using TOF testing cannot detect the percentage of receptors bound at < 65%.
A T4:T1 height ratio of 0.75 typically guarantees (1) a sustained head lift for 5 seconds, (2) the ability to generate a vital capacity of 15-20 ml/kg, (3) an effective cough to clear secretions, and (4) a negative inspiratory force of -25 cm H2O.
A patient is being transported to the post-anesthesia care unit after general anesthesia with supplemental oxygen via facemask at 10 L/min. The oxygen E-cylinder pressure gauge reads 500 PSIG. Which of the following BEST estimates the time left before the cylinder is depleted?
A full E-cylinder oxygen tank contains 660 L oxygen at a pressure of 1900 or 2200 PSIG (depending on the reference source). If a tank is partially filled, that amount is divided by the full amount, in either liters or PSIG. The time remaining in an oxygen E-cylinder can also be approximated by dividing the pressure left by 3 and then dividing by the flow rate. For example, if there is 600 PSI in the tank at a flow rate of 5 L/min, it would be (600 / 3) / 5 ≈ 40 minutes.
Which of the following condition will MOST LIKELY increase the plateau pressure during positive-pressure mechanical ventilation?
An increase in Pplat reflects decreased CRS, while an isolated elevation in Ppeak represents increased airway resistance. Examples of issues that will increase plateau pressure include pulmonary edema, acute respiratory distress syndrome, transfusion-related acute lung injury, pneumothorax, pleural effusion, chest wall rigidity, fluid overload, obesity, abdominal insufflation, and abdominal compartment syndrome. Examples of issues that will increase peak pressure include kinked circuit, endotracheal tube obstruction, acute asthma attack, and bronchospasm.
A 60-year-old female is emergently brought to the operating room for suspected splenic rupture after blunt abdominal trauma during a motor vehicle accident. The patient is hypotensive and is actively being transfused multiple units of PRBC’s. Urine output is minimal at 0.1 mL/kg/hour. Which of the following is MOST likely true in regards to temperature monitoring?
Core body temperature is best measured at nasopharyngeal, pulmonary artery, tympanic, and esophageal sites. Esophageal temperature probes should be placed in the distal one-third of the esophagus to accurately reflect core temperature.
Which of the following intravenous dyes is LEAST likely to cause falsely low pulse oximetry readings?
Blue or blue-green intravenous dyes such as methylene blue, indocyanine green, and indigo carmine can cause falsely low oxygen saturations to be displayed by standard two-wave pulse oximeters. False readings occur due to interference with the differential absorption of 660 and 940 nm light.
TrueLearn Insight : A mnemonic to help recall light absorption by wavelength is SeXy DARLing: at SiX hundred wavelength, Deoxyhemoglobin Absorbs Red Light.
A 68-year-old male is scheduled to undergo right total hip arthroplasty. His supine blood pressure is 148/90 mm Hg with an appropriately sized cuff on the right forearm. An arterial line is also present in the right radial artery. If the patient is turned to the left lateral decubitus position with the right arm now 30 cm above his heart and the arterial line transducer is adjusted to the level of the heart, which of the following is MOST likely correct
An arterial line does not require blood pressure conversion with changes in height of the intra-arterial catheter as long as the transducer is at the point of reference (e.g. the level of the heart), unlike the blood pressure cuff which does require such a conversion. The conversion is 0.75 mm Hg per 1 cm change in height relative the reference point (e.g. the level of the heart), adding when the cuff is below and subtracting when the cuff is above the level of the point of reference.
TrueLearn Insight : A mnemonic to help is “pH 15 20” to remember the pressure of 15 mm Hg is equal to a change in height of 20 cm.
