Ventilation and O2 Delivery Systems MCQs

Invasive ventilation uses gadgets which pass beyond vocal cords and achieve a definitive airway. In mechanical ventilation, artificial airways provide a vital link between the ventilator and the patient. Two common artificial airways used in conjunction with mechanical ventilators are the endotracheal (ET) and tracheostomy tubes. Reference: Clinical Application of Mechanical Ventilation, Fourth Edition by David W. Chang, page no 151

While resuscitation devices such as Ambu bags or bag-mask units have nonrebreathing valves, neither the Mapleson (only has adjustable pressure-limiting valve) nor the circle system (only has unidirectional valves and does allow rebreathing) has this component. Ambu resuscitation bags do allow for positive pressure ventilation as the intake valve closes during bag compression. The patient valve has low resistance, but can become obstructed by exhaled moisture. Ambu bags have a reservoir system to prevent room air entrapment and are able to deliver nearly 100% oxygen. Reference: Lippincott's ANESTHESIA REVIEW: 1,001 QUESTIONS AND ANSWERS Paul Sikka, MD, PhD

One gram of hemoglobin can combine with 1.34 mL of O2. None of the other choices in this question will do as much to increase the O2-carrying capacity of this patient's blood as a transfusion Reference: Stoelting: Pharmacology and Physiology in Anesthetic Practice, ed 4, pg 787, 849.

They are fixed performers HAFOE stands for 'high air flow oxygen enriched' devices. The Bernoulli principle is used with a venturi device to cause entrainment of air around an oxygen jet venturi. These devices are constant in performance and require masks with holes to enable high volumes of air to be entrained. Reference: Yentis S, Hirsch N, Smith G. Anaesthesia A to Z. Butterworth-Heinemann, 1995.

During spontaneous breathing the maximum inspiratory flow rate can exceed 30L/min for brief periods. A standard Hudson-type mask will therefore not supply a constant fraction of inspired oxygen (FiO2) unless the flow rate of oxygen through the connecting tubing exceeds 30L/min, since air will be entrained at a variable ratio throughout the respiratory cycle. Masks such as the Venturi and Hudson are loose fitting and have holes permitting ready elimination of waste gases; they do not significantly increase dead space. Anaesthetic face masks have a tight seal with the patient's face and may be bulky, increasing dead space, although this is not usually clinically significant in adult practice. Reference: Masks. In: Essentials of Anaesthetic Equipment, 2nd Ed. Al-Shaikh B, Stacey S. London: Churchill-Livingstone, 2002: 73-9.

PEEP increases FRC and decreases the work of breathing. Compliance is increased, and the lung volume is increased. Positive end-expiratory pressure (PEEP) increases the end-expiratory or baseline airway pressure to a value greater than atmospheric pressure. It is often used to improve the patient’s oxygenation status, especially in hypoxemia that is refractory to high level of FiO 2 . Reference: Clinical Application of Mechanical Ventilation, Fourth Edition by David W. Chang, page no 87

Double-lumen Endobronchial tube: A special airway for independent lung ventilation. It has two separate lumens, two cuffs, and two pilot balloons. Independent lung ventilation is done via a DLT to facilitate lung isolation, surgical procedure, and Broncho pleural/Broncho cutaneous fistulas. They are used to provide independent lung ventilation where isolation of the lungs is desirable in order to prevent lung-to-lung spillage of blood or pus. They are also used to provide one-lung ventilation so that the non-ventilated lung may undergo surgical procedure on the thoracic structures with minimal movement. Reference: Clinical Application of Mechanical Ventilation, Fourth Edition by David W. Chang, page no 141

The normal physiological respiration is a process of generation of negative pressures inside the thoracic cavity during inspiration and expiration is passive .In contrast mechanical ventilation involves positive pressure to inflate the lungs during inspiration. There are opposite mechanisms. During positive pressure ventilation, gas flow is delivered to the lungs under a positive pressure gradient (i.e., airway pressure is greater than alveolar pressure). When positive pressure is used for ventilation, the pressures in the airways, alveoli, and pleura are increased during inspiration. Under normal conditions, the pressure gradient and tidal volume are directly related. Reference: Clinical Application of Mechanical Ventilation, Fourth Edition by David W. Chang, page no 28