Physiological considerations and patient positioning during anesthesia for thoracic surgery
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Physiological considerations and patient positioning during anesthesia for thoracic surgery
- 1. Abeer elnakera Lecturer of anesthesia 2012
- 2. Objectives To Explain normal Ventilation/Perfusion Relationships define The advantages and disdvantages of using the lateral decubitus position Ventilation /perfusion mismatch with Describe The effect of lateral decubitus ,anesthesia, PPV and open pneumothorax on Ventilation /perfusion mismatch Enumerate the complications of lateral decubitus and how to prevent them
- 3. Ventilation/Perfusion Relationships . Minute ventilation=RR X VT VA = RR X (VT – VD ) Anatomic dead space : gases in nonrespiratory airways Alveolar dead space : gases in alveoli that are not perfused. Physiological dead space= Anatomic + Alveolar dead spaces = 150 mL for most adults (approximately 2 mL/kg) In the upright position, and is nearly all anatomic .
- 10. The advantages of using the lateral decubitus position (a) it permits the most complete access to the hemithorax, (b) the length of the intercostal incision can be easily extended as needed (c) the patient can be tilted forward or backward, providing optimal access to the ipsilateral mediastinum, pericardium, hilum of the lung, and descending thoracic aorta (d) it permits intraoperative pericardial control of the hilar vessels when needed.
- 11. The disadvantages of the lateral decubitus position (a) the opposite hemithorax is relatively inaccessible, (b) ventilation / perfusion mismatch (c) the dependent lung is exposed to the risk of contamination through the tracheobronchial tree with blood and/or purulent material (d) the dependent lung has a decreased FRC, which promotes airway closure, and atelectasis (e) positioning injuries caused by abnormal pressure to muscles, eyes, ears, and stretching of nerves are more likely than if the patient were supine.
- 12. Closed chest The effect of the lateral Decubitus awake position on lung compliance
- 13. Closed chest The effect of anesthesia on lung compliance in the lateral decubitus position Anesthetized
- 14. The effect of Positive-Pressure Ventilation on lung in the lateral decubitus position
- 16. . Mediastinal shift in a spontaneously breathing patient in the lateral decubitus position
- 17. Paradoxical respiration in spontaneously breathing patients on their side
- 18. Complications of lateral thoracotomy position patients undergoing thoracotomy have a 28% incidence of acid GER, which leads to tracheal acid aspiration in 27% of patients. (Agnew et al, 2002) unwanted movement of the double-lumen tube
- 19. Complications of lateral thoracotomy position The lateral decubitus position is inherently unstable and places the relaxed, anesthetized patient at considerable risk for pressure and stretch damage brachial plexus injury An entrapment neuropathy of the suprascapular nerve The median and ulnar nerves can also be damaged lateral popliteal nerve is the most frequently injured nerve in the lower extremity The sciatic nerve may be injured
- 20. Properly positioned patients have their head supported, an axillary role in place, and pillows between their legs with the bottom leg slightly flexed at the hip and knee
- 22. Vascular complications lateral thoracotomy position Venous thrombosis Peripheral gangrene with Hyperabduction of the arm that is up, as might occur when it is suspended from the anesthesia screen Rotation of the head in an elderly arthritic patient has been suggested as a cause of central nervous system damage caused by occlusion of the vertebral artery The dependent eye is at risk of damage and permanent blindness from retinal artery thrombosis. Controlled or prolonged hypotension may reduce retinal perfusion and accentuate the possibility of thrombosis
- 24. Summary normal Ventilation/Perfusion Relationships The advantages ( surgical field exposure) and disdvantages (liability for pressure or stretch injury) of using the lateral decubitus position The effect of lateral decubitus , anesthesia, PPV and open pneumothorax on Ventilation /perfusion mismatch Complications of lateral decubitus and how to prevent them (peripheral nerve and vascular injuries)
- 25. Thank you
Hinweis der Redaktion
- Airway resistance can also contribute to regional differences in pulmonary ventilation. Final alveolar inspiratory volume is solely dependent on compliance only if inspiratory time is unlimited. In reality, inspiratory time is necessarily limited by the respiratory rate and the time necessary for expiration; consequently, an excessively short inspiratory time will prevent alveoli from reaching the expected change in volume. Moreover, alveolar filling follows an exponential function that is dependent on both compliance and airway resistance. Therefore, even with a normal inspiratory time, abnormalities in either compliance or resistance can prevent complete alveolar filling.Airway resistance can also contribute to regional differences in pulmonary ventilation. Final alveolar inspiratory volume is solely dependent on compliance only if inspiratory time is unlimited. In reality, inspiratory time is necessarily limited by the respiratory rate and the time necessary for expiration; consequently, an excessively short inspiratory time will prevent alveoli from reaching the expected change in volume. Moreover, alveolar filling follows an exponential function that is dependent on both compliance and airway resistance. Therefore, even with a normal inspiratory time, abnormalities in either compliance or resistance can prevent complete alveolar filling.
- Pulmonary blood flow is also not uniform. Regardless of body position, lower (dependent) portions of the lung receive greater blood flow than upper (nondependent) areas. This pattern is the result of a gravitational gradient of 1 cm H2O/cm lung height. The normally low pressures in the pulmonary circulation (see Chapter 19) allow gravity to exert a significant influence on blood flow. For simplification, each lung can be divided into three zones, based on alveolar (PA), arterial (Pa), and venous (Pv) pressures (Figure 22–15). Zone 1 is the upper zone and represents alveolar dead space because alveolar pressure continually occludes the pulmonary capillaries. In the middle zone (zone 2), pulmonary capillary flow is intermittent and varies during respiration according to the arterial–alveolar pressure gradient. Pulmonary capillary flow is continuous in zone 3 and is proportional to the arterial–venous pressure gradient.
- Controlled positive-pressure ventilation favors the upper lung in the lateral position because it is more compliant than the lower one. Neuromuscular blockade enhances this effect by allowing the abdominal contents to rise up further against the dependent hemidiaphragm and impede ventilation of the lower lung. Using a rigid "bean bag" to maintain the patient in the lateral decubitus position further restricts movement of the dependent hemithorax. Finally, opening the nondependent side of the chest further accentuates differences in compliance between the two sides because the upper lung is now less restricted in movement. All these effects worsen ventilation/perfusion mismatching and predispose to hypoxemia.
- During spontaneous ventilation in the lateral position, inspiration causes pleural pressure to become more negative on the dependent side but not on the side of the open pneumothorax. This results in a downward shift of the mediastinum during inspiration and an upward shift during expiration (Figure 24–3). The major effect of the mediastinal shift is to decrease the contribution of the dependent lung to the tidal volume.
- Spontaneous ventilation in a patient with an open pneumothorax also results in to-and-fro gas flow between the dependent and nondependent lung (paradoxical respiration [pendeluft]). During inspiration, the pneumothorax increases, and gas flows from the upper lung across the carina to the dependent lung. During expiration, the gas flow reverses and moves from the dependent to the upper lung
- unwanted movement of the double-lumen tube. Flexion of the neck moves the endotracheal tube distally, whereas extension of the neck leads to movement of the endotracheal tube proximally and risks extubation. Proper location of endotracheal and double-lumen tubes must be determined after anesthesia induction and again immediately after the lateral decubitus position has been established. We routinely use fiberoptic endoscopy to reconfirm the position of these tubes.
- The lateral decubitus position is inherently unstable and places the relaxed, anesthetized patient at considerable risk for pressure and stretch damage. Complications of surgical positioning are usually attributed to abnormal pressure, stretch, or both. In the lateral decubitus position, compression is the leading cause of brachial plexus injury. Ischemia of the intraneuralvasonervosum is the principal cause of positional nerve injuries. Compression of the brachial plexus may occur when the lower shoulder and arm are allowed to remain directly under the rib cage after turning the patient into the lateral position. A properly placed axillary roll reduces the risk of compression injury to the brachial plexus. An entrapment neuropathy of the suprascapular nerve is an infrequent, easily overlooked source of pain after a surgical procedure in the lateral decubitus position. Stretch of the nerve apparently occurs by circumduction of the upper extremity across the chest or by lateralization of the neck toward the opposite shoulder. The median and ulnar nerves can also be damaged if allowed to hang over the edge of the operating table. The radial nerve is susceptible to damage in the lateral position if the extended dependent arm is pushed cephalad against the vertical bar of the anesthesia screen, thereby compressing the nerve between the humerus and the bar. The common peroneal nerve (lateral popliteal nerve) is the most frequently injured nerve in the lower extremity. Damage occurs if the patient is placed in the lateral position on a poorly padded operating table and the nerve is compressed as it courses around the lateral aspect of the proximal fibula. The sciatic nerve may be injured in an emaciated patient if compressed between the operating table and the ischiopubicramus or if tight hip straps or strap buckles are used.