Anesthetic Equipment and Monitoring Practice Questions

Q: Anaesthetic circuit that prevents rebreathing of CO2 –

Circle system. ***Circle system*** - The **circle system** incorporates a **carbon dioxide absorber** (soda lime or barium hydroxide lime) which chemically removes CO2 from exhaled gases, preventing rebreathing. - It uses both inspiratory and expiratory limbs with one-way valves to ensure unidirectional flow of gases through the CO2 absorber and to the patient. *Ayre's piece* - This is a modification of the **Mapleson F (Jackson-Rees) circuit** and is a non-rebreathing system for pediatric use. - It **prevents rebreathing** by having high fresh gas flow but does not contain a CO2 absorber. *Mapleson D circuit* - The **Mapleson D circuit** prevents rebreathing by using a high fresh gas flow to flush exhaled gases out of the system, not via a CO2 absorber. - It is classified as an **open non-rebreathing system** and effectively prevents CO2 rebreathing if fresh gas flow is sufficient (typically 2-3 times minute ventilation). *Magill's circuit* - The **Magill's circuit** (Mapleson A) is designed to prevent rebreathing at fresh gas flows approximately equal to minute ventilation, but it relies on separating fresh gas flow from exhaled gas, not CO2 absorption. - Rebreathing can occur if the fresh gas flow is not adequate or if there is insufficient emptying of the reservoir bag during expiration.

Q: What is the name of this test to be done before drawing an arterial blood gas sample:

Allen test. ***Allen test*** - The **Allen test** is performed to assess the patency of the **ulnar artery** and ensure adequate collateral blood flow to the hand before an **arterial blood gas (ABG) sample** is drawn from the **radial artery**. - This prevents **ischemic complications** in case the radial artery is damaged during the procedure. *Both radial & ulnar artery are occluded* - While both arteries are initially occluded during the Allen test, this statement describes only a **partial step** of the complete procedure, not the name of the test itself. - The crucial part of the test involves releasing one artery to observe **reperfusion**. *Trendelenburg test* - The **Trendelenburg test** is used to evaluate **venous insufficiency**, typically in the **lower limbs**, and is unrelated to arterial blood sampling. - It involves assessing the filling pattern of **varicose veins** after leg elevation. *Ulnar artery kept occluded, Radial artery released; These are steps of Allen's test* - This statement describes a specific step within the Allen test; however, for the test to be valid, the radial artery is typically the one from which the sample is drawn, thus the **ulnar artery's patency is being assessed**. - The correct sequence for assessing radial artery patency after initial occlusion is to release the ulnar artery, not the radial artery, to observe hand reperfusion; an alternative sequence is used if the sample is taken from the ulnar artery.

Q: The Penaz technique:

Uses plethysmography. ***Uses plethysmography*** - The **Penaz technique**, also known as **Finapres** or volume-clamp method, continuously measures blood pressure using **photoplethysmography** to detect arterial wall movements. - This method maintains a constant transmural pressure across the arterial wall, providing beat-to-beat pressure readings in a **non-invasive** manner. *Requires a pneumatic cuff* - While it uses a cuff-like device on the finger, this is a **small occluding cuff** used to maintain a constant arterial volume and not a standard pneumatic cuff for intermittent oscillometric measurements. - The cuff inflates and deflates to counterbalance arterial pressure, unlike the complete occlusion and slow deflation of a conventional cuff. *Is suitable in presence of peripheral vascular disease* - The Penaz technique relies on intact peripheral arteries to function accurately. **Peripheral vascular disease** can affect arterial compliance and blood flow, leading to **inaccurate readings**. - Its use may be limited in conditions that significantly alter peripheral arterial hemodynamics, such as severe atherosclerosis or Raynaud's phenomenon. *Is invasive* - The Penaz technique is a **non-invasive** method for continuous blood pressure monitoring, relying on external sensors applied to the finger. - **Invasive blood pressure monitoring** involves catheter insertion directly into an artery, which is a fundamentally different procedure.

Q: All true about interaction of SpO2 reading and methemoglobinemia, except:

Does not get affected in Methemoglobinaemia. ***Correct: Does not get affected in Methemoglobinemia*** - This statement is **FALSE**, making it the correct answer for this EXCEPT question - **Methemoglobinemia significantly affects SpO2 readings** due to MetHb's optical properties - Pulse oximeters cannot distinguish methemoglobin from oxyhemoglobin and deoxyhemoglobin, leading to **inaccurate measurements** - As MetHb levels rise, the SpO2 reading tends to **plateau around 85%** regardless of true oxygen saturation *Incorrect: Increase in MetHb produces an overestimation when true SpO2 <85%* - This statement is TRUE - When **actual SpO2 is below 85%** and MetHb is elevated, the pulse oximeter reads **higher than the true value** (overestimation) - This occurs because MetHb absorption characteristics cause the reading to gravitate toward 85% *Incorrect: MetHb absorbs red and infrared wavelength of light in a 1:1 ratio* - This statement is TRUE - **Methemoglobin** has similar extinction coefficients at both **660 nm (red)** and **940 nm (infrared)** wavelengths - This 1:1 absorption ratio corresponds to an SpO2 reading of approximately **85%** on conventional pulse oximeters - This is why SpO2 readings plateau at 85% in methemoglobinemia regardless of true saturation *Incorrect: Increase in MetHb produces an underestimation when true SpO2 >85%* - This statement is TRUE - When **actual SpO2 is above 85%** and MetHb is elevated, the pulse oximeter reads **lower than the true value** (underestimation) - The reading is pulled down toward the 85% plateau created by MetHb's absorption characteristics

Q: If an anesthetist at high altitude uses plenum vaporizers, what will be the delivered vapor concentration?

Higher than the concentration at same partial pressure. ***Higher than the concentration at same partial pressure*** - Plenum vaporizers are calibrated at **sea level** and deliver a constant *volume percent* of volatile anesthetic. At high altitude, ambient pressure is lower, meaning a given volume percent represents a **higher partial pressure** of anesthetic. - While the *anesthetic partial pressure* might be what the anesthetist aims for, the *delivered concentration* (volume percent) will be higher than the concentration that would achieve the same partial pressure at sea level because the total pressure is lower. *Lower than concentration at same partial pressure* - This statement is incorrect because a plenum vaporizer will deliver a **higher partial pressure** at altitude for a given dial setting, due to the reduced ambient pressure. - A lower partial pressure for the same set concentration would only occur if the ambient pressure were higher than calibration. *Lower than the concentration at lower partial pressure* - This option is vaguely worded and does not accurately describe the behavior of plenum vaporizers at altitude. When total pressure drops, the *partial pressure* delivered by a plenum vaporizer at a given dial setting will increase, not decrease. - A lower vapor concentration leading to a lower partial pressure is generally true, but it doesn't address the specific issue of a plenum vaporizer's performance at high altitude. *Higher than the original concentration at high partial pressure* - This option is confusing as it refers to "original concentration at high partial pressure" which isn't a standard comparison. The key is that a plenum vaporizer's *delivered volume % remains constant*, regardless of altitude. - However, this constant volume % translates to a higher *partial pressure* when the **ambient atmospheric pressure is lower**, as is the case at high altitude.

Q: Gas cylinder with single pin index ?

Entonox. **Entonox** - Entonox cylinders have a unique **single pin index** safety system to prevent accidental connection to incorrect gas lines. - This distinct pin configuration ensures the delivery of the correct 50% nitrous oxide and 50% oxygen mixture. *Nitrogen* - Nitrogen cylinders typically use a **double pin index** system (7-2 configuration) for connection. - This gas is primarily used for powering surgical equipment and is not a breathing gas. *Oxygen* - Oxygen cylinders are easily identifiable by their **white colour** and use a **double pin index** system (2-5 configuration) for connection. - This prevents interchangeability with other medical gases that have different pin configurations. *Air* - Medical air cylinders are grey and white and use a **double pin index** safety system (1-5 configuration). - This ensures only medical air is connected and used for patient ventilation or nebulization.

Q: A 25 year old male is undergoing incision and drainage of abscess under general anaesthesia with spontaneous respiration. Which of the following is the most efficient anaesthetic circuit which can be used in this patient?

Mapleson A. ***Mapleson A*** - This circuit is highly efficient for **spontaneous respiration** due to its design, which effectively sweeps away exhaled CO2 with a low fresh gas flow. - The **reservoir bag** is close to the patient, and the APL valve is at the machine end, preventing rebreathing of carbon dioxide during spontaneous breathing. *Mapleson D* - While versatile, the Mapleson D circuit is considered far more efficient for **controlled ventilation** rather than spontaneous respiration, requiring higher fresh gas flows in the latter. - It features the **APL valve near the patient** and a longer expiratory limb, leading to potential rebreathing of CO2 if fresh gas flows are not sufficiently high during spontaneous breathing. *Mapleson B* - This circuit is generally considered **inefficient for both spontaneous and controlled ventilation** compared to other Mapleson systems. - The fresh gas inlet and APL valve are both near the patient, leading to significant rebreathing unless very high fresh gas flows are used. *Mapleson C* - Similar to Mapleson B, the Mapleson C circuit is also considered **inefficient for spontaneous respiration**, requiring high fresh gas flows to prevent CO2 rebreathing. - It has a very short expiratory limb and the APL valve near the patient, making it less effective for maintaining normocapnia during spontaneous breathing compared to Mapleson A.

Q: The pulse oximetry reading is affected in:

Dark skin. ***Dark skin*** - **Dark skin pigmentation**, especially in individuals with very dark complexions, can cause **underestimation of oxygen saturation** by pulse oximetry. - This is due to the increased absorption of light by **melanin**, which can interfere with the device's ability to differentiate between oxygenated and deoxygenated hemoglobin. *Jaundice* - **Jaundice** primarily involves the accumulation of **bilirubin**, which typically does not significantly interfere with the absorption spectra used by pulse oximeters. - While **severe jaundice** might theoretically have a minor effect, it is not considered a primary or common cause of pulse oximetry inaccuracy. *Anemia* - **Anemia** is a reduction in **hemoglobin concentration**, which affects the oxygen-carrying capacity of blood. - Pulse oximeters measure the **percentage of hemoglobin saturated with oxygen**, not the absolute amount of hemoglobin, thus a low hemoglobin count alone does not directly alter the SpO2 reading. *Red nail polish* - **Red nail polish** can absorb and scatter light, especially the red light wavelengths used by pulse oximeters, leading to a falsely low or erroneous SpO2 reading. - This interference can prevent the sensor from accurately detecting the pulsatile blood flow and light absorption characteristics of hemoglobin.

Q: The Pin Index Safety System (PISS) number for nitrous oxide (N2O) is

3,5. ***3,5*** - The **Pin Index Safety System (PISS)** is designed to prevent incorrect gas tank connections by using specific arrangements of pins on the cylinder yoke. - For **nitrous oxide (N2O)**, the pins are located at positions **3 and 5** on the cylinder valve. *2,6* - This pin configuration corresponds to **air**, which is a mixture of nitrogen and oxygen. - Using this for nitrous oxide would be a **misconnection**, potentially leading to patient harm. *1,6* - This specific pin index combination is associated with **oxygen**. - Incorrectly connecting a nitrous oxide tank to an oxygen yoke position would be a serious **safety breach**. *2,5* - This is the PISS configuration for **carbon dioxide (CO2)**. - Misconnection with nitrous oxide could lead to **hypoxia** or other adverse events due to incorrect gas delivery.

Q: According to standard medical gas cylinder color coding, the colour of ethylene cylinder is:

Purple. ***Purple*** - Ethylene gas cylinders are **color-coded purple** to ensure quick and accurate identification in medical settings. - This standardized color coding helps prevent dangerous mix-ups of medical gases. *Orange* - **Orange** is the standard color for **cyclopropane** gas cylinders in many medical gas color-coding systems. - Cyclopropane is an anesthetic agent rarely used today, but its color code differs from ethylene. *Blue* - **Blue** is typically used to identify **nitrous oxide** cylinders, a common anesthetic and analgesic gas. - Mistaking nitrous oxide for ethylene could have significant clinical consequences. *Grey* - **Grey** is commonly associated with **carbon dioxide (CO2)** cylinders, used for insufflation during surgery and as a respiratory stimulant. - This color is distinct from ethylene's purple cylinder.

Question 1

Anaesthetic circuit that prevents rebreathing of CO2 –

Accepted Answer

Circle system

Answer

Ayre's piece

Answer

Mapleson D circuit

Answer

Magill's circuit

Question 2

What is the name of this test to be done before drawing an arterial blood gas sample:

Accepted Answer

Allen test

Answer

Both radial & ulnar artery are occluded

Answer

Trendelenburg test

Answer

Ulnar artery kept occluded, Radial artery released; These are steps of Allen's test

Question 3

The Penaz technique:

Accepted Answer

Uses plethysmography

Answer

Requires a pneumatic cuff

Answer

Is suitable in presence of peripheral vascular disease

Answer

Is invasive

Question 4

All true about interaction of SpO2 reading and methemoglobinemia, except:

Accepted Answer

Does not get affected in Methemoglobinaemia

Answer

Increase in MetHb produces an overestimation when true SpO2 <85%

Answer

MetHb absorbs red and infrared wavelength of light in a 1:1 ratio corresponding

Answer

Increase in MetHb produces an underestimation when true SpO2 >85%

Question 5

If an anesthetist at high altitude uses plenum vaporizers, what will be the delivered vapor concentration?

Accepted Answer

Higher than the concentration at same partial pressure

Answer

Lower than concentration at same partial pressure

Answer

Lower than the concentration at lower partial pressure

Answer

Higher than the original concentration at high partial pressure

Question 6

Gas cylinder with single pin index ?

Accepted Answer

Entonox

Answer

Nitrogen

Answer

Oxygen

Answer

Air

Question 7

A 25 year old male is undergoing incision and drainage of abscess under general anaesthesia with spontaneous respiration. Which of the following is the most efficient anaesthetic circuit which can be used in this patient?

Accepted Answer

Mapleson A

Answer

Mapleson D

Answer

Mapleson B

Answer

Mapleson C

Question 8

The pulse oximetry reading is affected in:

Accepted Answer

Dark skin

Answer

Jaundice

Answer

Anemia

Answer

Red nail polish

Question 9

The Pin Index Safety System (PISS) number for nitrous oxide (N2O) is

Accepted Answer

3,5

Answer

2,6

Answer

1,6

Answer

2,5

Question 10

According to standard medical gas cylinder color coding, the colour of ethylene cylinder is:

Accepted Answer

Purple

Answer

Orange

Answer

Blue

Answer

Grey

Anesthetic Equipment and Monitoring — MCQs

Anesthetic Equipment and Monitoring — MCQs

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