True Learn Main points 2 Flashcards
Which of the following is a design feature to prevent rebreathing of carbon dioxide in a traditional semi-closed circle system?
Placement of the adjustable pressure limiting (APL) valve, commonly called the pop-off valve, between the patient and the inspiratory valve can lead to rebreathing. Avoiding this valve location is one of the three design features to prevent rebreathing
n order to prevent rebreathing in a semi-closed circle system unidirectional valves must be placed between the patient and the inspiratory and expiratory limbs, the fresh gas inlet cannot be placed between the patient and the expiratory valve, and the APL valve cannot be placed between the patient and the inspiratory valve.
TrueLearn Insight : The circle system can be used three different ways depending on the fresh gas flow.
- Semi-open system: high fresh gas flows with no rebreathing
- Semi-closed system: lower fresh gas flows with some rebreathing
- Closed system: fresh gas flow matches patient consumption with complete rebreathing
General endotracheal anesthesia is being delivered to a patient with a combination of oxygen, nitrous oxide, and isoflurane. As the gas flow through a bobbin rotameter is increased, which of the following will increase?
A bobbin flowmeter is structured with a weighted bobbin within a tapered cylindrical tube. As the flow and pressure beneath the bobbin increases, it will rise until reaching equilibrium. Due to the shape of the cylinder, as the bobbin rises the cross-sectional area around it will increase as well.
A 64-year-old woman is undergoing general anesthesia for a total left knee arthroplasty. The sevoflurane is currently at 4%. If the anesthesiologist lowers it to 1%, how will the concentration in the blood change when it has reached equilibrium with the alveoli?
Henry’s law states that, at a constant temperature, the concentration (C) of a gas dissolved in a solution is directly proportional to the partial pressure (P) of that gas: C = kP (where k is a solubility constant) or C ∝ P.
Why are desflurane vaporizers heated?
Desflurane has an extremely high vapor pressure and is significantly vaporized at room temperature; therefore desflurane requires a heated vaporizer to maintain constant vaporizer output concentration as the vapor pressure would decrease significantly from evaporative cooling.
Which of the following is a requirement of pressure support ventilation (PSV)?
PSV is used during spontaneous ventilation to offload the work of respiratory muscle.
Fresh gas flow must be equal to at least which of the following parameters to prevent rebreathing during spontaneous ventilation while using a Mapleson A circuit?
Fresh gas flow must be equal to minute ventilation in the Mapleson A circuit in order to prevent rebreathing of exhaled gas during spontaneous ventilation.
Which of the following is most likely to be the cause of an adverse outcome related to anesthesia equipment?
Adverse outcomes secondary to equipment-related malfunction or misuse occur, with misuse being the primary issue. Proper training and upkeep of the equipment can help decrease the risk. This is most likely secondary to human error, however, which cannot be completely eliminated
Which of the following will decrease the accuracy of pulse oximetry?
Hypothermia decreases the accuracy of a pulse oximeter.
Aside from nitrous oxide, weight is more reliable than pressure for determining the amount of gas remaining in an E cylinder of which of the following medical gases?
It is more reliable to determine the amount of nitrous oxide remaining in an E cylinder based on cylinder weight rather than pressure, as the pressure gauge will read “full” until nearly 75% of the gas has been used. Carbon dioxide also requires cylinder weight to determine remaining volume.
Which of the following should be the initial step in providing patient care if a power failure occurs in the modern operating room?
If a power failure occurs in the operating room the provider should switch to the red plate electrical supply system, which is the emergency power system in the United States. Nearly all life-support devices, including the anesthesia machine, have battery backup capability and will continue to function.
A variable bypass vaporizer is being used to administer sevoflurane (saturated vapor pressure = 160 mm Hg) to a patient at sea level. A fresh gas flow of 2.5 L/min of 100% oxygen is being used, of which, 100 mL passes through the vaporizer chamber. What is the approximate sevoflurane concentration being delivered to the patient?
The following chart can be used to get an estimated vaporizer output. PP is partial pressure or saturated vapor pressure, ATM is atmospheric pressure. Agent SVP or PP PP % PP / (ATM - PP) Sevoflurane 160 mm Hg 21% ~ 1/4 Enflurane 175 mm Hg 23% ~ 1/3 Isoflurane 238 mm Hg 32% ~ 1/2 Halothane 241 mm Hg 32% ~ 1/2 Desflurane 669 mm Hg 88% N/A
For example, if 100 mL/min of inflow oxygen goes through a sevoflurane vaporizer you can say ~1/4 of that flow will be sevoflurane (about 25 mL). For the above question, this would be 25 mL sevoflurane in 2500 mL (2500 mL + 25 mL total output), which is about 1%.
A 62-year-old patient with chronic obstructive pulmonary disease (COPD) due to longstanding tobacco abuse presents in a COPD exacerbation. Noninvasive positive pressure ventilation is initiated and initial blood gasses demonstrate a PaO2 ranging between 90 and 100 mmHg on room air while on 5 cmH2O expiratory positive airway pressure (EPAP) and 10 cmH2O inspiratory positive airway pressure (IPAP). Which of the following errors in the handling of a subsequent arterial blood gas sample would be MOST likely to result in an artificially increased PaO2?
Delays in analysis and exposure of a sample to room air are the two most common sources of error in blood gas analysis. A delay will result in decreased PaO2, pH, and base excess values and an increase in PaCO2. Entrainment of room air will tend to cause the PaO2 value of the sample to approach the PO2 of room air (159 mmHg at sea level) and result in a decreased measured PaCO2.
Which of the following could help to decrease the risk of intraoperative awareness?
One of the most reliable ways to prevent awareness is use of at least 0.5 MAC volatile agent, avoidance of muscle relaxation, and a balanced anesthetic with the use of opioids. Clinical signs of awareness include autonomic signs such as hypertension and tachycardia, pupillary dilation, lacrimation, sweating, and patient movement. Patient use of certain medications may block these signs and the clinician should be aware of this. Some examples are beta-blockers or calcium channel blockers which might dampen the tachycardia or hypertension.
A 60-year-old male with a history of sick sinus syndrome and placement of pacemaker is undergoing right thoracotomy and lobectomy for lung cancer. If the electrosurgical unit (cautery) were faulty and had a current leak, which of the following is MOST likely to prevent microshock to the patient?
The equipment ground wire is the most reliable means to prevent microshock. The ground fault interrupter can prevent macroshocks, but does not reliably prevent microshocks
An otherwise healthy, 5’9”, 70 kg, 30-year-old male is in the intensive care unit after emergent external fixation of bilateral open tibial fractures following a motor vehicle accident with multiple orthopedic injuries. He is intubated and has an arterial line. Which of the following ventilator settings will BEST facilitate the use of pulse pressure variation on the arterial line to aid ongoing fluid resuscitation?
In order for PPV to most accurately predict volume response, several conditions need to be met.
1) The patient is on controlled, positive pressure ventilation.
2) Tidal volume is >7-8 mL/kg (ideal body weight).
3) PEEP is not used.
4) The patient does not have cardiac arrhythmias.
5) Significant changes in chest wall or lung compliance must be avoided. For example, PPV may not be accurate in the setting of laparoscopic surgery due to abdominal insufflation or in the setting of an open chest.
A patient will likely be volume responsive when the PPV is >13%. A patient is typically not volume responsive when PPV < 9%. Volume responsiveness is not reliably predicted with PPV between 9-13%.
