(see also Capnography; Lung Volumes; Ventilator Management; Ventilator Modes)
Both premature extubation and prolonged intubation places the patient at risk. Prolonged intubation may cause increased stress and delirium as well as other complications such as ventilator-induced lung injury, venous thromboembolism, pneumonia, or atrophy/dysfunction of the diaphragm. Extubating too early may result in loss of airway, respiratory failure, and/or aspiration. The primary goal for patients requiring mechanical ventilation is to decrease the total time on this support by extubating promptly and at an optimal point.
Spontaneous Awakening Trial (SAT) and Spontaneous Breathing Trial (SBT)
Daily assessment of the readiness for extubation is available via the use of both the SAT and SBT, which, in combination, has proven to reduce mechanical ventilator time and overall length of hospital stay. Known as the “Wake up and breathe protocol,” these trials are an essential daily first step to achieving timely extubation.
Other Elements to Wean
The Tobin Index
The Tobin Index, also known as the Rapid Shallow Breathing Index (RSBI), is an additional tool to help predict success versus failure of extubation. However, it should not be the sole determinant of extubation and is not meant to answer the question of whether a patient is ready for extubation. Rather, it is designed to help predict the outcome after extubation and be used as additional supporting data. It is only applicable to patients who are clinically ready for weaning as evidenced by meeting other clinical criteria.
To calculate RSBI min/L use the formula: Respiratory rate ÷ Tidal volume (in liters)
<105 breaths/min/L (positive) Successful extubation likely
>105 breaths/min/L (negative) Failed extubation likely
EtCO2 (Capnography)
End-tidal CO2 offers an additional parameter to assist in determining the adequacy of alveolar ventilation during weaning. Data suggests that EtCO2 offers a reasonable estimate of the PaCO2 associated with weaning and is useful to detect hypercapnia due to hypoventilation or hypocapnia due to hyperventilation. However, EtCO2 is less sensitive to patients with parenchymal disease (particularly emphysema), and while it can give information about the trends and efficiency of ventilation and perfusion, its use is limited due to this sensitivity. Target EtCO2 is 35 to 45 mm Hg.