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# Tidal Volume The initial tidal volume is usually set between 10 and 12 mL/kg of predicted body weight. Typically, the patient's actual weight can be used for selecting the tidal volume unless the patient is significantly underweight or overweight. Table 8-6 shows a method to calculate the patie...

# Tidal Volume The initial tidal volume is usually set between 10 and 12 mL/kg of predicted body weight. Typically, the patient's actual weight can be used for selecting the tidal volume unless the patient is significantly underweight or overweight. Table 8-6 shows a method to calculate the patient's predicted body weight. The lower end of the acceptable tidal volume range (e.g., around 10 mL/kg) might be appropriate for certain patients. Tidal volumes as low as 6 mL per kg of predicted body weight have been recommended for ARDS patients (de Durante et al., 2002). Lower tidal volumes are often used to minimize airway pressures and the risk of barotrauma (Feihl et al., 1994). However, low tidal volume ventilation can lead to complications such as acute hypercapnia, increased deadspace ventilation, and work of breathing, dyspnea, severe acidosis, and atelectasis (Kallet et al., 2001a, 2001b). COPD patients may benefit from a reduced tidal volume setting. These patients have reduced expiratory flow rates due to decreased alveolar elastic recoil. Therefore, a longer expiratory time is needed for complete exhalation. If there's not enough time for complete exhalation, air trapping, V/Q mismatch, hypoxemia, and hypercapnia may result. Decreasing the tidal volume by 100–200 mL in COPD patients reduces expiratory time requirements and helps prevent air trapping. A higher flow rate can also shorten inspiratory time. For patients with reduced lung volumes due to lung resection, lower tidal volumes may be necessary. Table 8-7 provides examples of clinical conditions where lower tidal volume settings might be beneficial or necessary. # Gas Leakage and Circuit Compressible Volume The actual tidal volume delivered to the patient's lungs is usually lower than the set tidal volume. This is primarily due to: 1. Gas leakage in the ventilator circuitry 2. Gas leakage in the cuff 3. Circuit compressible volume loss.