- Supine
- Chest Wall Contribution: In the supine position, the contribution of the chest wall to breathing is reduced to about 10%, leading to restricted movement of the diaphragm.
- Respiratory Impact: There is a reduction in functional residual capacity (FRC) and an increase in the volume of the lungs at which they start to close off (closing volumes). This makes the anesthetized patient more prone to atelectasis and hypoxemia.
- Trendelenburg
- Abdominal Shift: This position causes the abdominal contents to move towards the chest (cephalad), which can significantly decrease lung capacity, tidal volume, pulmonary compliance, vital capacity, and FRC by about 20%.
- Respiratory Challenges: The shift in abdominal contents can compress the lungs, making breathing more difficult and potentially leading to decreased oxygenation.
- Steep Trendelenburg
- Enhanced Effects: The steep Trendelenburg position intensifies the cephalad shift of abdominal contents, potentially placing most of the lung below the level of the left atrium. This position increases the risk of pulmonary interstitial edema due to pulmonary engorgement.
- Swelling and Edema: This position can also cause increased pressure and swelling of the face and neck due to engorgement and edema. Special care is needed during extubation to ensure that airway patency is maintained, which involves checking for an air leak around the endotracheal tube (ETT). If no air leak is detected, it may be safer to leave the patient intubated until the swelling subsides.
- Prone
- Respiratory Mechanics: Prone positioning can redistribute blood and airflow more evenly across the lungs, minimally affecting respiratory mechanics or even improving them.
- Oxygenation Improvement: This position may increase FRC and oxygen tension by facilitating ventilation, as the mediastinal contents fall forward, away from the lungs, improving overall oxygenation.
- Careful Positioning: Extreme care is needed when positioning obese patients to avoid nerve damage and ventilatory impairment. Modified supine or beach-chair positions are preferred to minimize respiratory compromise.
- Positioning Risks: Muscle relaxation increases the risk of nerve damage and improper positioning, especially outside of the patient’s normal range of motion. The risk of nerve damage escalates with prolonged surgeries, especially those lasting over 3 hours.
- Nerve Damage Prevention: Ulnar neuropathy is notably prevalent among obese patients. Continuous reevaluation of the patient’s positioning, use of elbow padding, and maintaining a neutral or supinated arm position are recommended.
| Position | Respiratory effect | Consideration |
|---|---|---|
| Supine | Chest wall contributes only about 10% to breathing and diaphragm movement is restricted; functional residual capacity falls while closing volumes rise | Anesthetized patient is more prone to atelectasis and hypoxemia |
| Trendelenburg | Abdominal contents shift cephalad, decreasing lung capacity, tidal volume, pulmonary compliance, vital capacity, and functional residual capacity by about 20% | Lung compression makes ventilation harder and can reduce oxygenation |
| Steep Trendelenburg | Cephalad shift intensifies, potentially placing most of the lung below the level of the left atrium | Pulmonary engorgement risks interstitial edema; face and neck swell — check for an air leak around the endotracheal tube before extubation and consider leaving the patient intubated until swelling subsides |
| Prone | Blood and airflow redistribute more evenly; functional residual capacity and oxygen tension may increase as mediastinal contents fall forward | Respiratory mechanics are minimally affected or even improved |
