Home  >  Related Knowledge  >  Monitoring During Ventilatory Support
Cardiac monitor, blood pressure, and pulse oximetry (SaO2) are recommended. The authors�� practice with stable patients is to titrate down FiO2 to the minimum value necessary to maintain maximal SaO2. An arterial blood gas (ABG) measurement is frequently obtained 10-15 minutes after the institution of mechanical ventilation. The measured arterial PaO2 should verify the transcutaneous pulse oximetry readings and direct the reduction of FiO2 to a value less than 0.5. The measured PaCO2 can suggest adjustments of minute ventilation but should be interpreted in light of the patient's overall acid-base status. For example, full correction of PaCO2 in a chronically hypercarbic COPD patient will lead to unopposed metabolic alkalosis.
 
Reasonable alternatives to arterial blood gas measurement in more stable patients include measuring the venous blood gas, which will give values close to arterial pH and PaCO2 or monitoring an end-tidal CO2. An additional advantage of end-tidal CO2 monitoring is that it can detect acute ventilator dysfunction such as endotracheal tube obstruction or dislodgement. 
 
Peak inspiratory and plateau pressures should be assessed frequently, although it should be recognized that both pressures will be increased by extrapulmonary pressure, for example from stiff chest walls or a distended abdomen, and do not reflect the true risk of barotrauma. In general, however, parameters may be altered to limit pressures to less than 35 cm H2 O. Expiratory volume is checked initially and periodically (continuously if ventilator is capable) to ensure that the set tidal volume is delivered. Any indication of an air leak must prompt a search for underinflated tube cuffs, open tubing ports, or worsening pneumothorax. In patients with airway obstruction, monitor auto-PEEP.