From the Guidelines
Tidal volume typically decreases in obese patients. According to the most recent guidelines for perioperative care in bariatric surgery, lung volume does not increase proportionally with body weight in patients with obesity 1. This suggests that obesity causes mechanical restrictions on the respiratory system, limiting the normal expansion of the lungs during breathing. The use of low tidal volumes (6-8 ml/kg of predicted body weight) is recommended to reduce pulmonary complications in patients with healthy lungs, regardless of obesity 1. Key points to consider include:
- Obesity causes mechanical restrictions on the respiratory system, with excess adipose tissue around the chest wall and abdomen limiting lung expansion
- Lung compliance is reduced, and diaphragmatic movement is restricted, resulting in lower tidal volumes
- Obese individuals often compensate by increasing their respiratory rate, adopting a pattern of rapid, shallow breathing
- The reduction in tidal volume can lead to areas of atelectasis in dependent lung regions, worsening ventilation-perfusion matching
- Careful attention to ventilation parameters is necessary during medical procedures to prevent respiratory complications in obese patients, with the use of low tidal volumes and individualized PEEP settings recommended 1.
From the Research
Tidal Volume in Obese Patients
- Tidal volume (TV) is affected by obesity, with studies suggesting that obese patients tend to have lower tidal volumes 2.
- A study published in 2012 found that obese patients have higher respiratory rates and lower tidal volumes, with total respiratory system compliance reduced due to various reasons 2.
- Another study published in 2020 investigated the effect of obesity on the topographical distribution of ventilation and found that obesity alters the distribution of ventilation, with a greater diversion of ventilation to the upper lung zone 3.
- However, it is essential to note that the relationship between tidal volume and obesity is complex and influenced by various factors, including lung compliance, chest wall compliance, and respiratory system mechanics 4.
Ventilation Strategies
- Ventilation strategies using low tidal volumes have been shown to reduce mortality in critically ill patients with acute lung injury and acute respiratory distress syndrome 5, 6.
- A randomized controlled trial published in 2008 compared a low-tidal-volume ventilation strategy with an experimental strategy combining low tidal volume, lung recruitment maneuvers, and high positive-end-expiratory pressure, and found no significant difference in all-cause hospital mortality or barotrauma between the two groups 6.
- The use of low tidal volumes in ventilation strategies is crucial in minimizing ventilator-induced lung injury, and adjustments for elastic characteristics in morbid obesity are necessary to optimize ventilation 4.