Observation of ventilation-induced Spo₂ oscillations in pigs: first step to noninvasive detection of cyclic recruitment of atelectasis?

ABSTRACT

High arterial partial oxygen pressure (Pao₂) oscillations within the respiratory cycle were described recently in experimental acute lung injury. This phenomenon has been related to cyclic recruitment of atelectasis and varying pulmonary shunt fractions. Noninvasive detection of Spo₂ (oxygen saturation measured by pulse oximetry) as an indicator of cyclic collapse of atelectasis, instead of recording Pao₂ oscillations, could be of clinical interest in critical care. Spo₂ oscillations were recorded continuously in three different cases of lung damage to demonstrate the technical feasibility of this approach. To deduce Pao₂ from Spo₂, a mathematical model of the hemoglobin dissociation curve including left and right shifts was derived from the literature and adapted to the dynamic changes of oxygenation. Calculated Pao₂ amplitudes (derived from Spo₂ measurements) were compared to simultaneously measured fast changes of Pao₂, using a current standard method (fluorescence quenching of ruthenium). Peripheral hemoglobin saturation was capable to capture changes of Spo₂ within each respiratory cycle. For the first time, Spo₂ oscillations due to cyclic recruitment of atelectasis within a respiratory cycle were determined by photoplethysmography, a technology that can be readily applied noninvasively in clinical routine. A mathematic model to calculate the respective Pao₂ changes was developed and its applicability tested.

KEYWORDS :

• acute lung injury
• cyclic recruitment of atelectasis
• oxygen oscillations
• varying pulmonary shunt fractions
• venous admixture
• ventilator-associated lung injury