Different Ventilatory Modes During One Lung Anesthesia

Abstract

SUMMARY O ne lung anesthesia is defined as a technique in which one lung is separated from the other in ventilation during surgery. Lung isolation techniques are primarily designed to facilitate OLV in patients undergoing cardiac, thoracic, mediastinal, vascular, osophageal, or orthopedic procedures involving the chest cavity. The concept of endobronchial intubation had its roots in the late nineteenth century. Pulmonary ventilation means the inflow and outflow of air between the atmosphere and the lung alveoli. Distribution of ventilation is different between each lung segment according to the position, pleural pressure and transpulmonary pressure. Pulmonary perfusion serves three purposes which are; delivering oxygen to the body, removing CO2 from the alveoli, and providing left heart preload to support systemic cardiac output. Lung perfusion can be affected by gravitational and non-gravitational factors. Hypoxic pulmonary vasoconstriction is the constriction of the small arterioles in response to alveolar hypoxia. There are various modifiers to HPV such as; inhalation anesthetics, intravenous anesthetics, other drugs, surgical retraction, and positioning of the patient. Thoracic surgery represents a unique set of physiological problems that require special considerations. These include lateral decubitus position, opening of the chest, and the frequent need for OLV. There are various indications for OLA; some are absolute and others are relative. Lung isolation techniques can be achieved by one of three methods: DLT, BB, or SLT. DLT is the most frequently used technique; whether it is left or right. DLTs shouldn't be placed in patients with excessive distortion of the tracheobronceal anatomy. There are various types of DLTs. Placement and confirmation of DLT is an important issue. This is done either blindly or using the FOB. DLTs shouldn't be placed in patients with excessive distortion of the trachea broncheal anatomy. BB technique involves the blockade of a main-stem bronchus to allow lung collapse distal to the occlusion. BB are either within a modified SLT (Univent tube) or used independently with a conventional SLT. Each type has its advantage, placement technique and disadvantge. SLTs are used in practice in cases of emergency, difficult airways, or in infants and children. Monitoring lung separation is essential to make hypoxemia less likely. Fluid management is crucial during OLA. Monitoring during OLA includes inspired and expired gas, blood pressure, temperature and pharmacological manipulation. Ventilation strategy is important to decrease the incidence of hypoxemia during OLV. The best ventilation strategy in an individual patient should be tailored according to the patient's condition, physiologic reasoning, and the best clinical evidence. Ventilation strategies for the ventilated lung include respiratory acid-base status, FiO2, PEEP, tidal volume, and ventilatory mode. Ventilatory mode whether PCV or VCV is an essential choice that the anesthesiologist must make to ensure the best outcome. The non- ventilated lung may present a unique operative consideration that must be taken into account when selecting a management plan. CPAP, partial ventilation methods, or intermittent re-inflation of the non-ventilated lung may be needed. Despite all modern endoscopes, tubes, and ventilatory machines, various complications can occur. Those complications could be of anesthetic origin or surgical origin. Anesthetic complications include high inflation pressure during OLA, trauma, cardiovascular disturbances, failure of deflation of the non-ventilated lung, and hypoxemia. On the other hand, surgical complications include bleeding, nerve injury, or pneumothorax.