Breathing Systems MCQs

At concentrations of 1 MAC or less, volatile anesthetics, as well as the inhaled anesthetic N 2 O, will produce dose-dependent increases in the respiratory rate in spontaneously breathing patients. This trend continues at concentrations greater than 1 MAC for all of the inhaled anesthetics except isoflurane. With the exception of N 2 O, the evidence suggests that this effect is caused by direct activation of the respiratory center in the CNS rather than by stimulation of pulmonary stretch receptors. Additionally, volatile anesthetics decrease Vt and significantly alter the breathing pattern from the normal awake pattern of intermittent deep breaths separated by varying time intervals to one of rapid, shallow, regular, and rhythmic breathing. Reference: Miller’s Anesthesia, ed 8, pp 691-692.

The components of a circle system include: a CO 2 absorber containing CO 2 absorbent; a fresh gas inlet; an inspiratory unidirectional valve and inspiratory breathing tube; a Y-connector; an expiratory unidirectional valve and expiratory breathing tube; an APL valve; and a reservoir. Reference: Morgan, edition 4, page no 40

Advantages of the circle system include economy (low fresh gas flow rates, decreased use of volatile agents), conservation of heat and humidity, and decreased operating-room pollution. Disadvantages of circle system include greater size, decreased portability, increased risk of disconnection, and increased resistance to patient breathing. Reference: Lippincott's ANESTHESIA REVIEW: 1,001 QUESTIONS AND ANSWERS Paul Sikka, MD, PhD

Explanation: The adjustable pressure-limiting (APL) valve in a Mapleson breathing circuit is typically set at 30-40 cm H 2 O to allow appropriate control of airway pressure during manual ventilation. The Mapleson circuit is a semi-open anesthetic breathing system used in controlled and spontaneous ventilation. It consists of: Fresh gas flow inlet Corrugated tubing Reservoir bag Adjustable Pressure-Limiting (APL) valve The APL valve is crucial for: Controlling the maximum pressure delivered during manual ventilation Preventing barotrauma by allowing excess gas to escape once a set pressure is reached The typical pressure setting for the APL valve is 30-40 cm H₂O, which ensures: Adequate positive pressure during assisted breaths Protection against excessive airway pressure

During spontaneous ventilation/breathing of the patient, the Mapleson circuit providing for the most efficacy ranges from A > D > C > B (in the order of decreasing efficiency). Reference: Lippincott's ANESTHESIA REVIEW: 1,001 QUESTIONS AND ANSWERS Paul Sikka, MD, PhD

All of the statements are correct except for C. The Mapleson D system is a semiopen anesthetic system with a proximal fresh gas inflow and a distal overflow valve. To eliminate rebreathing, higher fresh gas flows are needed with spontaneous ventilation than with controlled ventilation. Note the Mapleson A system is a semiopen anesthetic system with a distal fresh gas flow and a proximal overflow valve. The Mapleson F circuit is most widely used for pediatric anesthesia. Reference: Davis: Smith's Anesthesia for Infants and Children, ed 8, pp 294-297.

While using Jackson Rees circuit, Fresh gas flows of 2-3 times minute volume should be used to prevent rebreathing during spontaneous ventilation, (But plz note, whatever be the baby's weight, a minimum flow of 3 L/min should be kept) During controlled ventilation in children, normocapnia can be maintained with a fresh gas flow of 1L + 100 mL/kg/min E.g. a 4-year-old weighing 20 kg would need a total FGF of around 3 L/min. Reference: Objective anesthesia review (Atul Kulkarni) 3rd Ed Pg. 403

In Mapleson A, just a minimum Fresh gas flow (FGF) is enough to prevent normocapnia in the circuit, making it the most efficient circuit for spontaneous respiration Reference: E Book of Morgan and Mikhail's Clinical Anaesthesiology 6th Edition Chapter 3 Page No 80