CURRENT Essentials of Critical Care.pdf

10 Current Essentials of Critical Care■■Essential ConceptsEnd-Tidal PCO 2 Monitoring• In spontaneously breathing normal patients, end-tidal PCO 2(PETCO 2 ) approximates arterial PCO 2 (PaCO 2 )• Difference between PETCO 2 and PaCO 2 widens in patients withlung disease (pneumonia, asthma, COPD, ARDS, pulmonaryembolism)• Increased PaCO 2 –PETCO 2 difference associated with high deadspace/tidalvolume ratio (VD/VT)• Unpredictable PaCO 2 PETCO 2 differences with irregularbreathing, tachypnea, prolonged exhalation• PETCO 2 cannot be substituted for PaCO 2 when making ventilatorchanges or determining hyper- or hypoventilation• Capnography looks at expiratory CO 2 concentration continuously;may be useful for estimating endotracheal tube cuff leakEssentials of Management• Measure arterial PCO 2 to determine PaCO 2 PETCO 2 difference• Normal PaCO 2 PETCO 2 2 to 0 mm Hg• Use PETCO 2 to confirm endotracheal tube placement• High PaCO 2 PETCO 2 difference predicts high VD/VT, potentialdifficulty with weaning• If PaCO 2 PETCO 2 difference remains constant (only rarely),changes in PETCO 2 may be used for adjusting minute ventilation.• Increased PaCO 2 PETCO 2 difference may be sign of pulmonaryembolism• Attach CO 2 monitoring probe to end of endotracheal or tracheostomytube according to directions■ PearlPETCO 2 reflects perfusion of the lungs, which is related to cardiac output,much more than the arterial PCO 2 , which reflects ventilation.ReferenceAnderson CT et al: Carbon dioxide kinetics and capnography during criticalcare. Crit Care 2000; 4:207 [PMID: 11094503]