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The relationship between arterial P o 2 and mixed venous P o 2 in response to changes in positive end‐expiratory pressure in ventilated patients
Author(s) -
Groeneveld A. B. J.,
Schneider A. J.
Publication year - 2008
Publication title -
anaesthesia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.839
H-Index - 117
eISSN - 1365-2044
pISSN - 0003-2409
DOI - 10.1111/j.1365-2044.2007.05409.x
Subject(s) - medicine , mechanical ventilation , positive end expiratory pressure , oxygenation , anesthesia , cardiac index , cardiac output , cardiology , hemodynamics
Summary The response of arterial P o 2 ( P a o 2 ) to airway pressure has been used as a measure of recruitment in mechanically ventilated patients. We hypothesised that mixed venous P o 2 ( P mv o 2 ) directly affects P a o 2 . Sixteen patients with acute lung injury (ALI, lung injury score ≥ 1) on volume‐controlled mechanical ventilation ( F I o 2 0.40) were studied. Positive end‐expiratory pressure (PEEP) was increased and decreased. Incremental PEEP increased median values of P a o 2 , diminished venous admixture ( Q va / Q t ) and cardiac index, but maintained arterial P co 2 and tissue O 2 uptake. These changes were reversed during decremental PEEP. However P a o 2 did not increase in 37% of PEEP steps and changes in P a o 2 correlated to those in P mv o 2 ( r s = 0.45, p < 0.001). Changes in P mv o 2 contributed to changes in Q va / Q t in determining changes in P a o 2 (p < 0.05). P mv o 2 may be an independent determinant of P a o 2 during mechanical ventilation for ALI, so that dosing PEEP to recruit the lung should not be guided by arterial blood oxygenation alone. Arterial hypoxaemia with increasing PEEP may improve by reducing PEEP (or increasing tissue O 2 delivery), when the fall in P mv o 2 is greater than about 0.133 kPa.