True learn main points

Question 1

Which of the following is the CORRECT order of structures encountered when performing a lumbar paramedian approach for spinal anesthesia?

Answer 1

The correct order of structures encountered when performing a paramedian approach for spinal anesthesia is skin -> subcutaneous tissue -> muscle -> ligamentum flavum -> epidural space -> dura mater -> arachnoid mater -> subarachnoid space.

Question 2

What is the BEST initial treatment for post spinal backache?

Answer 2

Post-spinal backache is a relatively common occurrence with generally self-limited symptoms. Initial treatment is reassurance and mild analgesics.

Question 3

Isolated unilateral recurrent laryngeal nerve injury would cause which of the following?

Answer 3

Unilateral recurrent laryngeal nerve injury results in weak voice, hoarseness, and paramedian (adduction) position of the ipsilateral vocal cord. Bilateral injury results in airway obstruction requiring tracheostomy.
Left unilateral vocal cord paralysis may occur after PDA ligation as the left recurrent laryngeal nerve loops under the aortic arch in the same vicinity.

Question 4

Which of the following will MOST AFFECT the epidural spread of local anesthetics?

Answer 4

Local anesthetic spread during epidural injection is affected by several patient- and procedure-related factors. Increased volume of the injectate, positive airway pressure, lateral/Trendelenburg position, and increased age all generally increase the epidural spread of local anesthetics. Of these, the volume of injection has the most significant impact. Dura mater is more permeable in the elderly due to the increased number of arachnoid villi. This allows local anesthetic to more easily reach the spinal nerve roots. Accordingly, epidural dosing should be reduced in the elderly.

Question 5

73yr old in septic shock with MODS requiring debridement of infected wound - ASA 5

Answer 5

Despite debate about variability between clinicians with regard to ASA PS classification, following the ASA language for each class will help you to designate the most appropriate physical status. When differentiating between class 2 and 3, recall that ASA PS 3 patients have disease that is either poorly controlled or limiting to their activities of daily living. When differentiating between class 3 and 4, recall that ASA PS 4 patients have disease that is a “constant threat to life”.

Question 6

A 74-year-old female is undergoing repair of an anterior cerebral artery ruptured aneurysm. Preoperative imaging suggested the patient had a cerebrovascular accident involving the preoptic anterior hypothalamus, without significant localized swelling or midline shift. Which of the following would MOST likely be expected during the perioperative period?

Answer 6

The hypothalamus is comprised of a large number of distinct nuclei that are responsible for numerous homeostatic functions. The preoptic anterior hypothalamus plays a key role in temperature homeostasis and thermoregulation. The medial tuberal hypothalamus contains neurons that extend into the posterior pituitary and secrete vasopressin and oxytocin.

Question 7

Ventilation plays an important role in the speed of inhaled anesthetic uptake and induction (FA/FI). With which of the following agents does a high minute ventilation MOST improve the FA/FI?

Answer 7

The rate of inhaled anesthetic induction (FA/FI) is increased with increased minute ventilation. This effect is greatest with the agents with high solubility, including halothane and isoflurane.

Question 8

Which of the following statements regarding the rate of induction of anesthesia in the setting of intracardiac shunts is TRUE?

Answer 8

Intrapulmonary right to left shunt decreased speed of induction of inhalational agents with minimal effects on induction with IV agents
Intracardiac right to left - inhalational agents decreased induction speed but increased IV induction
Intracardiac Left to right minimal to no effect on either forms of induction

Question 9

Which of the following BEST describes a Grade 3 view according to the modified Cormack-Lehane grading system?

Answer 9

Grade 1 - complete glottis visible
Grade 2a - partial view of the glottis
Grade 2b - Only posterior arytenoids and epiglottis are visible
Grade 3 - only epiglottis visible
Grade 4 - neither the glottis nor the epiglottis are visible

Question 10

A 42-year-old female undergoes general anesthesia for a laparoscopic cholecystectomy. She receives rocuronium for muscle relaxation at induction and during the case. At the completion of the surgery, the patient displays 2 out of 4 twitches at 50 Hz. Antagonism of the rocuronium is obtained using neostigmine and glycopyrrolate. Which option below is NOT a side effect of neostigmine?

Answer 10

Cardiac: bradycardia, hypotension
Pulmonary: bronchospasm, increased respiratory secretions
GI: increased peristalsis, increased salivation and GI secretions
Ophthalmic: miosis, decreased intraocular pressure

Question 11

During laparoscopic surgery, which of the following is LEAST likely to occur secondary to carbon dioxide embolism?

Answer 11

Discontinuation of N2O does not improve hemodynamic stability with 100% CO2 embolus. However, it should be discontinued to provide 100% oxygen during cardiopulmonary compromise. Decreased ETCO2 is more commonly seen, but increased ETCO2 may occur in CO2 embolus even in cardiovascular collapse.

Question 12

Which of the following conditions will MOST likely increase end-tidal carbon dioxide?

Answer 12

Factors that affect EtCO2 include:

Increase EtCO2 Decrease EtCO2
Malignant hyperthermia Disconnect from or loose sampling line
Hyperthermia Malpositioned endotracheal tube
Hyperthyroidism Hyperventilation
Hypoventilation Hypoperfusion (hypotension, cardiac arrest)
Rebreathing Hypothermia
Sepsis Hypothyroidism
Shivering Pulmonary embolism

Question 13

Oculocardiac reflex

Answer 13

Stimuli at the eye -> ciliary ganglion -> ophthalmic division of trigeminal nerve -> Gasserian ganglion -> trigeminal nucleus -> vagus nerve -> bradycardia.

Question 14

Mechanism of action of propofol

Answer 14

To differentiate GABAA from GABAB, remember Baclofen for GABAB and Anesthetics for GABAA.

Question 15

Which of the following is NOT a cause of hypoxemia in the head-down (Trendelenburg) position?

Answer 15

Trendelenburg position reduces FRC, TLC, lung compliance, and chest wall compliance. Abdominal contents are shifted cephalad, which may potentially relocate the end of a fixed ETT into the right mainstem bronchus.

Question 16

Researchers want to determine whether daily supplementation with multivitamins plays a role in postoperative nausea and vomiting in laparoscopic gynecological surgery. the researchers assessed clinical records and grouped patients into 2 groups: patients who had daily multivitamin supplementation and those who did not have daily multivitamin supplementation. The researchers then determine whether these groups of patients developed postoperative nausea and vomiting and calculate a relative risk. What type of study is performed?

Answer 16

Authors of cohort studies seek to determine the incidence rate and whether an exposure or risk factor is associated with the outcome or disease of interest. Cohort studies help to determine whether an exposure plays a role in the outcome of interest. Relative risk can be calculated in cohort studies.

Question 17

In the setting of a viral respiratory pandemic, a previously healthy 22-year-old woman underwent uncomplicated open-reduction and internal fixation of a right distal radius fracture. After ensuring the return of spontaneous respiration, deep extubation is performed. Following removal of the endotracheal tube, the anesthesiologist smells sevoflurane through the N95 designated mask that she is wearing. Which of the following is MOST TRUE regarding this situation?

Answer 17

N95 masks only filter 95% of 0.3-micrometer particles, allowing smaller particles and substances to more freely pass through the mask. All patients, even asymptomatic patients, during a viral respiratory pandemic should be considered carriers of the pathogen, and the anesthesiologist must take precautions and modify their practice to ensure that there is minimal aerosolization of particles from the patient’s airway during intubation and extubation. If sevoflurane or any other volatile anesthetic can be smelled, it is likely that the environmental concentration of that agent is orders of magnitude greater than stated NIOSH safety limits.

Question 18

Chloroprocaine’s rapid onset of action is secondary to what characteristic of the drug?

Answer 18

While pKa is generally closely related to the onset time of local anesthetics, 2-chloroprocaine has a very rapid onset despite a high pKa. This is due to the high concentration of 2-chloroprocaine that can be safely given secondary to its rapid metabolism and low systemic toxicity.

Question 19

The Tec 9 Datex-Ohmeda vaporizer heats desflurane to 2 atmospheres in order to ensure reliability of the dialed concentration. This is because desflurane is near boiling point at room temperature, which means an unpredictable amount is in liquid form, while the rest of it may be in gaseous form. This heated vaporizer reliably converts desflurane to the gaseous form.

Answer 19

Isoflurane is a potent volatile anesthetic with a MAC near 1.1%. In terms of inhalational anesthetic potency, isoflurane (MAC ~1%) > sevoflurane (MAC ~2%)&raquo_space; desflurane (MAC ~6%)&raquo_space;> nitrous oxide (MAC ~104%).

Question 20

Administration of fresh frozen plasma is NOT recommended for management of which of the following situations?

Answer 20

Fresh frozen plasma may be transfused to manage multiple coagulation factor deficiencies, microvascular bleeding, and massive or trauma-related blood loss. It is also used for urgent reversal of warfarin therapy and treatment of heparin resistance, TTP, or HUS.

Question 21

A 63-year-old woman is undergoing laparoscopic sigmoid colectomy for diverticulitis. At the end of the procedure, the end-tidal carbon dioxide continues to increase. The patient’s vital signs and ventilator values remain stable with a pulse rate of 68/min, blood pressure of 125/68 mm Hg, and pulse oximetry of 99%. Which of the following is the MOST likely reason for this change?

Answer 21

Subcutaneous emphysema can be a complication of CO2 insufflation with laparoscopic surgery. A sudden rise in ETCO2 following the initial rise that occurs with insufflation (first 15-30 min) should raise suspicion of subcutaneous emphysema. Abdominal compartment syndrome or intra-abdominal hypertension is seen with increased intra-abdominal pressure. As pressure increases over 10 mm Hg, tissue perfusion begins to decrease. Abdominal hypertension results in decreased preload, decreased renal perfusion, and increased airway pressures (both peak and plateau). Intra-abdominal hypertension is graded on a 1-4 scale, with grade 1 being pressures of 10-15 mm Hg, grade 2 pressures of 16-25, grade 3 pressures of 26-35, and grade 4 pressures more than 35. Organ dysfunction can be seen in susceptible patients with pressures as low as 10 mm Hg. However, organ dysfunction is generally not seen till pressures are above 20 mm Hg.

Question 22

You are called to see a patient in the PACU that is two hours post-op from a left tibia fracture repair. He is complaining of pain and tingling in the operative leg. On exam, the left leg appears more pale than the right and you are unable to palpate pulses in either of the left dorsalis pedis or the posterior tibial arteries. Which of the following is the MOST appropriate next step?

Answer 22

Peripheral compartment syndrome is diagnosed using the 5 Ps’s: pulselessness, paralysis, pallor, paresthesia, and pain. Treatment is emergent fasciotomy.

Question 23

Which of the following tests is most useful to diagnose acute abnormalities in hepatic synthesis?

Answer 23

The liver is a synthetic organ that produces most of the proteins in the body (with the exception of a few). Albumin can be used to monitor long-term liver synthetic function, however it must be noted that many other diseases can cause hypoalbuminemia. Monitoring prothrombin time gives the clinician a better understanding of acute hepatic protein synthesis capabilities.

Question 24

A 36-year-old female has just undergone a laparoscopic cholecystectomy and is not awakening from anesthesia in the post-anesthesia recovery unit despite an adequate amount of time for recovery. The patient has a history of symptomatic cholelithiasis, type I diabetes, and obesity. This is the patient’s first surgery, but she has no family history of any problems with anesthesia. The patient underwent a rapid sequence induction with intravenous lidocaine, fentanyl, succinylcholine, and propofol. She was maintained under anesthesia with isoflurane, vecuronium for paralysis, and morphine for analgesia. Paralysis was antagonized at the end of surgery with neostigmine and glycopyrrolate. The anesthesiologist would like to begin a workup to determine the cause of the patient’s delayed emergence. Which of the following should NOT be included in the INITIAL workup of this patient?

Answer 24

The differential for delayed emergence can be categorized into drug effects, metabolic derangements, and neurologic disorders. Initial workup should include vital signs with temperature, neurologic exam, peripheral nerve stimulation, ABG with electrolytes, and blood glucose level.

TrueLearn Insight : Hypoventilating patients may have adequate SpO2 values if they are receiving high-flow oxygen as this can provide apneic oxygenation. Hypercarbia in these patients will prolong awakening, highlighting the importance of ETCO2 monitoring. In one case, an apneic patient received high flow oxygen through an endotracheal tube and delayed emergence was not recognized for over three hours, at which point an ABG was drawn and showed: 6.65 / 213 / 265 / 29.

Question 25

A 60-year-old male with no significant past medical history is in the PACU after an uneventful total knee arthroplasty under general anesthesia. You are called to evaluate the patient for declining SpO2 which is currently 85% on a 2L nasal cannula. He is awake and following commands, breathing at a respiratory rate of 10 breaths per minute, and does not appear to be breathing deep or shallow. An arterial blood gas is drawn which reveals the following values:

pH: 7.28
PaCO2: 60 mm Hg
PaO2: 55 mm Hg
HCO3: 27 mEq/L

Which of the following statements is MOST likely true?

Answer 25

The carotid body chemoreceptors increase ventilation when PaO2 (not PAO2, CaO2, or SaO2) decreases through afferent impulses via the glossopharyngeal nerve to CNS ventilation centers. Their function is impaired by opioids, benzodiazepines, volatile anesthetics (as low as 0.1 MAC), and bilateral carotid endarterectomy.Do not confuse carotid bodies and carotid sinuses. Both are located at the carotid bifurcation, and impulses from both are transmitted via a branch of the glossopharyngeal (Hering’s nerve) but carotid bodies are chemoreceptors while carotid sinuses are baroreceptors.

Question 26

Which of the following is a gastrointestinal effect of succinylcholine?

Answer 26

Succinylcholine increases both LES tone and intragastric pressure. The former effect is greater than the latter, so the risk of aspiration is not increased. The increase in intragastric pressure can be offset by a priming dose of a nondepolarizing neuromuscular blocker.

Question 27

Which of the following induction agents primarily works by blocking glutamate?

Answer 27

Ketamine is primarily a potent NMDA receptor antagonist. The NMDA receptors are a class of excitatory glutamate receptor.

Question 28

When the placement of a central line in the left internal jugular vein versus the right internal jugular vein is compared, which complication occurs MORE often with left-sided placement?

Answer 28

The thoracic duct drains into the venous system on the left side, making chylothorax a complication of central line placement on the left side only. Pleural fluid analysis for triglyceride content helps to confirm a diagnosis of chylothorax. Definitive diagnosis of chylothorax is made by analyzing the suspected chylous fluid (eg, via thoracentesis). A high fat content, specifically triglycerides, and high T-lymphocyte count are diagnostic of chyle.

Question 29

An otherwise healthy patient is undergoing laparoscopic cholecystectomy. Which of the following will be the first sign that the pipeline oxygen supply was switched with nitrous oxide?

Answer 29

The oxygen analyzer will be the first device to detect a hypoxic mixture in the event of a pipeline crossover or mix-up where oxygen is replaced. A key step in the management of a pipeline supply issue is disconnecting the pipeline supply gases.

Question 30

Which choice BEST describes the effect that 1.5 MAC isoflurane has on cerebral blood flow (CBF) and cerebral metabolic rate (CMRO2) in a normal brain?

Answer 30

All volatile anesthetics are thought to cause an “uncoupling” of the CBF and CMRO2. They decrease CMRO2 while increasing CBF via a direct cerebral vasodilating effect. All intravenous anesthetics except ketamine cause a decrease in CMRO2 and a decrease in CBF. Fentanyl has no effect on CMRO2 or CBF.

Question 31

Capnogram of incompetent inspiratory valve. The expiratory alveolar plateau is extended due to inspiration of CO2-rich gas at the beginning of inspiration. The blue arrows above indicate where inspiration actually began in the patient. The inspiratory phase is shortened, has a blunted downstroke, and the CO2 nadir may or may not reach zero.

Answer 31

Capnogram of incompetent expiratory valve. The capnograph shows a markedly elevated inspiratory segment which does not return to zero, representative of rebreathing of CO2. Over time, the EtCO2 will rise, but the shape of the tracing is otherwise essentially normal.

Question 32

A patient becomes mildly hypotensive and has increased oxygen requirements three hours after receiving two units PRBCs; PaO2 is 100 mm Hg with an FiO2 of 40%. Which of the following is NOT an appropriate treatment option?

Answer 32

Transfusion related acute lung injury is the leading cause of death related to blood product transfusion. Anti-granulocyte antibodies in the donor plasma attack activated leukocytes sequestered in the pulmonary vasculature of recipient’s lungs leading to pulmonary inflammation and injury. Diagnosis is made by sudden onset of hypoxemia < 6 hrs following the conclusion of transfusion, bilateral infiltrates on CXR, no evidence of cardiogenic pulmonary edema, and exclusion of other sources of acute lung injury. The PaO2:FiO2 ratio is typically 200-300. Treatment is largely supportive and includes ventilatory strategies aimed at reducing further alveolar damage while promoting oxygenation.

TrueLearn Insight : The most common source of anti-leukocyte antibodies in cases of TRALI-related mortality have come from multiparous female donors. The SHOT surveillance system in the UK actually switched to using male plasma donors only beginning in 2004. A precipitous decline in TRALI and TRALI-related deaths was then observed. The mechanism is likely due to alloimmunization during previous pregnancies.

Question 33

A 40-year-old 80 kg male is undergoing an open cholecystectomy. The patient is a non-smoker with no other medical history. He is maintained on 2% sevoflurane with rocuronium for relaxation. His intraoperative ventilator settings are 60% FiO2 with a tidal volume of 400 mL and a respiratory rate of 6 breaths per minute. Over the next 20 minutes, ETCO2 increases to 65 mm Hg and SpO2 decreases from 99 to 93%. His temperature is 37.1 degrees Celsius. An arterial blood gas is performed and shows:

pH: 7.20
PaCO2: 70 mm Hg
PaO2: 76 mm Hg
Bicarbonate:  26 mEq/L
Base deficit: -1 mEq/L

Which of the following gas laws MOST likely explains this patient’s arterial hypoxemia?

Answer 33

he Dalton law of partial pressures states that the total gas pressure in a system is equal to the sum of the partial pressures of the component gases. Arterial hypoxemia as a result of hypoventilation is one example of the Dalton law applied clinically.

TrueLearn Insight : Another example of the Dalton Law applies to an E-cylinder of air. If an E-cylinder of air is full and reads 1900 psi and air is composed of ~20% oxygen and 80% nitrogen, then the partial pressures of each gas should equal the total gas pressure. Oxygen partial pressure is 20% * 1900 psi and nitrogen partial pressure is 80% * 1900 psi.

Question 34

Fresh gas flow must be greater than or equal to which of the following parameters to prevent rebreathing during controlled ventilation when using a Mapleson D semi-open circuit?

Answer 34

The FGF must be equal to 1-2 times minute ventilation in the Mapleson D circuit in order to prevent the rebreathing of exhaled gas during controlled ventilation.

TrueLearn Insight : The advantages of a Bain circuit (coaxial version of a Mapleson D system) include (1) conservation of moisture due to partial rebreathing, (2) warming of fresh gas inflow by surrounding expiratory gas, (3) scavenging waste is easier from the APL valve, and (4) advantageous when access to the patient is limited.

Question 35

A healthy 29-year-old, 70 kg woman is admitted for a diagnostic laparoscopy. Anesthesia is induced and intubated without complication and the patient is maintained on inhaled isoflurane. Following intubation, she is placed on a standard semi-closed anesthesia delivery circuit and provided positive pressure ventilation with 100% FIO2. Fresh gas flow is decreased from 2.5 L/min to 0.25 L/min. Which of the following is MOST likely to occur following this change?

Answer 35

A closed circle system injects only the required amount of fresh gas to meet a patient’s metabolic demand. In doing so, no gas is scavenged and all inhaled gas is rebreathed except for CO2 which is absorbed by the CO2 absorbent. A closed circle system results in the maximal amount of heat and moisture conservation, as well as the minimum amount of inhaled anesthetic agent usage.

Question 36

Which of the following is used to measure the partial pressure of oxygen and requires a power source (e.g. battery) for operation?

Answer 36

Clark, galvanic, and paramagnetic electrodes measure oxygen. Severinghaus electrode measures CO2. Sanz electrode measures pH.

TrueLearn Insight : In an arterial blood gas, pH, pO2, and pCO2 are all directly measured using the electrodes mentioned above. The HCO3 is calculated.

Question 37

Which of the following is a correct pairing of standard United States color codes for gas cylinders?

Answer 37

The following are the gas type and required cylinder color pairings in the United States: oxygen = green, carbon dioxide = gray, nitrous oxide = blue, nitrogen = black, air = yellow, helium = brown.

Question 38

The bellows are completely collapsed on an ascending (standing) bellows ventilator during mechanical ventilation of an anesthetized patient. Which of the following is MOST likely to have occurred?

Answer 38

In a typical ascending (standing) bellows ventilator, the bellows rise during patient exhalation. The bellows can act as an indicator of a leak or a disconnection of the circuit from the patient because the patient’s exhaled gasses will exit the system and will not be able to elevate the bellows, leaving them collapsed.

TrueLearn Insight : The negative pressure leak test may check for leaks in the low-pressure system of the anesthesia machine. A suction bulb is inserted into the fresh gas outlet while the flowmeter or vaporizer being checked is opened. The suction bulb is then compressed. The flowmeter or vaporizer is considered safe if the bulb remains compressed for at least 10 seconds. This process is repeated for each flowmeter and vaporizer.

Question 39

A 49-year-old man with a history of a congenital bicuspid aortic valve and aortic stenosis is undergoing an aortic valve replacement with cardiopulmonary bypass. During bypass, the patient is cooled to 34 °C. Which of the following is MOST TRUE regarding the acid-base and blood gas measurements that are obtained after the analyzer warms the patient’s blood sample to 37 °C compared to the true blood gas composition of the cooled patient?

Answer 39

The warming of blood will result in decreased gas solubility in the blood sample. This results in higher gas partial pressures, and more availability of the gas to participate in chemical reactions. This results in higher oxygen and carbon dioxide partial pressures, as well as lower serum pH levels in warm blood compared to a cold sample from the same patient.

TrueLearn Insight : The generally accepted uses for pH-stat and alpha-stat acid-base management strategies in hypothermic cardiac bypass surgeries can be remembered with the following acronym: pH-stat = Pediatric; alpha-stat = Adult.

Question 40

Which of the following statements about the effects of high altitude on anesthetic delivery is MOST accurate?

Answer 40

Most commercially-available variable-bypass vaporizers for isoflurane and sevoflurane deliver fixed partial pressures of volatile anesthetics based on their dialed settings. Dial settings do not generally need to be changed to compensate for changes in altitude. Desflurane vaporizers deliver fixed percent concentrations of desflurane. The dialed inspired concentration must be increased at higher altitudes to maintain an appropriate alveolar partial pressure of desflurane.

Question 41

Which of the following breathing systems is the most efficient user of fresh gas flow during spontaneous ventilation?

Answer 41

Among the Mapleson breathing systems, Mapleson A is the most efficient user of FGF during spontaneous ventilation, but is the least efficient for controlled ventilation.
All Dogs Can Bite (spontaneously): A > D > C > B
Dead Bodies Can’t Argue (controlled): D > B > C > A

Question 42

An increase in the fraction of inspired oxygen from 20% to 40% will change the pressure of inspired oxygen by what magnitude?

Answer 42

PiO2 = FiO2 x (PBar - PH2O). If PBar and PH2O remain constant, increasing FiO2 by a factor of 2 will increase PiO2 by a factor of 2. In other words, PiO2 and FiO2 are directly proportional.

Question 43

A patient is brought emergently to an operating room for an exploratory laparotomy following a gunshot wound to the lower abdomen. The anesthesia workstation is currently powered off. Which of the following capabilities is MOST likely to be nonfunctional until the machine is fully powered up?

Answer 43

In the setting of a power failure or if using a powered down anesthesia workstation, the oxygen delivery and manual positive pressure ventilation capabilities of the workstations are almost always still functional. If vaporizers are mechanical (e.g. variable-bypass, flow-over) they are also likely to be functional. Monitoring is always fully dependent on electricity.

Question 44

Which of the following is the MOST likely cause of the distortion in this ECG tracing?

Answer 44

A wandering baseline artifact on ECG tracings can be caused by a loose ECG electrode, poor skin contact, or patient movement.

Question 45

Which of the following is an advantage of double-burst stimulation over train-of-four stimulation?

Answer 45

Assessment of fade with peripheral stimulators is inaccurate in the clinical setting. Double-burst stimulation was developed to allow clinicians to use tactile or visual methods to detect fade. Double-burst stimulation is more painful for the patient than train-of-four (TOF) stimulation, and less accurate than objective TOF measurements.

TrueLearn Insight : Depolarizing block, also called phase I block, is preceded by muscle fasciculation. It has no fade during repetitive stimulation (tetanic or train of four [TOF]), no post-tetanic potentiation, and is characterized by a decrease in twitch tension. With prolonged administration of succinylcholine or in patients with abnormal genetic variants of butyrylcholinesterase, the block can change to a phase II block. Phase II block has fade during TOF and tetanic stimulation, and also has post-tetanic potentiation. It is similar to what is seen with a nondepolarizing muscle relaxant. Use of antagonists (e.g., neostigmine) gives an unpredictable response in phase II block and is generally not recommended.

Question 46

Which of the following would MOST likely result in an abrupt drop of end-tidal carbon dioxide to zero on capnography?

Answer 46

Capnography Waveform Etiologies
Sudden drop to zero Circuit disconnect
Acute ETT obstruction (D)
Esophageal intubation
Sudden drop
(value above zero) Partial airway obstruction
Circuit leak
Rapid decrease Pulmonary embolism
Circulatory arrest (C)
Gradual decrease Hypothermia
Hyperventilation (A)
Sudden increase Release of tourniquet
Sodium bicarbonate injection
Gradual increase Decrease in minute ventilation
Faulty unidirectional valve
CO2 absorbent exhausted
Thyroid storm
Malignant hyperthermia
Insufficient fresh gas flow

Question 47

A 10 kg 1-year-old child has just completed an abdominal MRI scan under volatile general anesthesia using a circle system. They will now be transported to the CT scanner with a modified Mapleson D system to undergo a needle-guided drainage. Which of the following is TRUE of the change to this new system?

Answer 47

the Bain circuit allows for more rapid changes in inspired gas concentration compared to the circle system. However, this is one of the only advantages over a circle system.

Question 48

You are taking a patient for an emergency cesarean section under spinal anesthesia and her only significant medical history is for palpitations. Which ECG lead would be the best to monitor for atrial dysrhythmias?

Answer 48

Lead II is the most appropriate lead for monitoring atrial dysrhythmias due to P-wave size. Lead V1 is the second most sensitive.

TrueLearn Insight : After initial adoption of the use of lead II for intraoperative monitoring for arrhythmia, London et al validated the use of leads II and V5 together to improve the sensitivity of detection of myocardial ischemia. Schwartz and Barash later proposed the use of leads II and V4 for preserved sensitivity but improved specificity over the II/V5 combination.

Question 49

Which of the following carbon dioxide absorbents produces the highest potential for formation of carbon monoxide when used with desflurane?

Answer 49

Baralyme is the most likely to cause carbon monoxide formation with desflurane.A potential hazard of carbon dioxide absorbents is toxic byproducts, specifically carbon monoxide and compound A. The risk depends on the chemical composition of the absorbent, the dryness of the material, and the type of volatile anesthetic used.

TrueLearn Insight : Other toxic inhalational anesthetic reactions include:
Nitrous oxide: can react with and inactivate vitamin B12, which can disrupt pathways that are dependent on it. B12 deficiency results in hematologic and neurologic dysfunction (megaloblastic anemia, myelopathy, neuropathy, and encephalopathy). These risks are higher in patients with pernicious anemia, GI malabsorption, extremes of age, malnutrition, and strict vegans. Bone marrow changes are rare in healthy individuals unless exposure is very prolonged (> 12hours), however in critically ill patients changes may be seen after only a few hours.
Methoxyflurane: can cause polyuric renal insufficiency secondary to high plasma fluoride concentrations. Methoxyflurane is extremely lipophilic and has a very long residence in tissues, which contributes to its toxicity.
Halothane: 20% of adults will develop subclinical hepatotoxicity that is reversible and innocuous, fulminant hepatotoxicity (known as halothane hepatitis) develops rarely but is fatal 50-75% of the time. Usually results from multiple exposures and is likely due to an immune response.

Question 50

Acoustic impedance during ultrasonography is the product of which of the following two characteristics?

Answer 50

Acoustic impedance is the product of the density of a medium and the propagation speed of sound through that medium. Ultrasound reflections that occur at the interface of different mediums are due to the changes in acoustic impedance. Since propagation speed changes slightly between biological mediums, acoustic impedance is primarily dependent upon density.