Today our topic of discussion is Respiratory Parameters as Criteria for Weaning.
Respiratory Parameters as Criteria for Weaning
Respiratory Parameters as Criteria for Weaning (Huba)
- Ability to oxygenate: The arterial tension during mechanical ventilation should be greater than 70 mm of Hg with an FIO, of 40%.
- The above condition should exist with a level of PEEP that is less that 10 cm H O When PEEP is greater than 10 cm H,O weaning is contraindicated .
- Arterial blood gas Pao, >55 mm Hg with FiO, and CPAP <5 cm H O Oximetry-Hb. Saturation >90% Corresponds to Pao, >55 mm of Hg.
- Spontaneous resting ventilatory needs: Ventilation is a given amount of gas exchange required to eliminate carbon dioxide adequately.
- The necessary level of minute ventilation (VT x RR) is determined by CO, production and dead space ventilation.
- The dead space to tidal volume ratio defines the percentage of tidal volume that does not participate in CO, elimination and can be considered as wasted ventilation.
- This dead space ratio is increased in disease that affect the lung parenchyma and distribution of gas flow as in adult respiratory distress syndrome, pulmonary embolism, chronic obstructive pulmonary disease and hypovolemia. If VD/VT is 0.6, i.e. 60% of tidal volume or more, the minute volume required to eliminate CO, is sufficient to allow total weaning.
- Minute ventilation of 10 liters/minute or less during mechanical ventilation indicates that patient can be safely weaned.
- Respiratory mechanical capability to sustain spontaneous respiration, the patient’s mechanical function is assessed by measuring the vital capacity, inspiratory force and the spontaneous rate.
- The vital capacity should be 10-15 mL/kg of actual body weight to institute weaning. Inspiratory force (the amount of negative pressure generated against occluded airway) is the measurement of muscle strength.
- The respiratory rate should not exceed 35 breaths/minute as it results in fatigue, CO retention and respiratory acidosis.
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