Impact of normocapnic and permissive hypercapnic one-lung ventilation on arterial oxygenation

Introduction

Physiologically, an approximately 5 to 10 mmHg difference exists between end-tidal carbon dioxide (EtCO₂) and arterial carbon dioxide (PaCO₂) measured during double-lung ventilation (DLV) that may increase during one-lung ventilation (OLV) especially if low tidal volume is applied. There is no evidence that during OLV the EtCO₂ or PaCO₂ should be kept in the normal range. The aim of the present work was to test whether different ventilatory strategies to maintain EtCO₂ or PaCO₂ in the normal range during OLV have any impact on arterial oxygenation (PaO₂).

Methods

Data were obtained from 100 patients undergoing thoracic surgery necessitating OLV. Patients were randomized into two groups. In GrEtCO₂ (n = 50) the OLV was guided by capnography, and the respiratory rate (RR) was adjusted to maintain EtCO₂ in the normal range. In GrPaCO₂ (n = 50) the OLV was guided by arterial blood gas analysis (ABG) and RR was adjusted to maintain PaCO₂ in the normal range. ABG was performed in a supine position after induction and in a lateral decubitus position during DLV and every 15 minutes during OLV. During OLV 5 ml/kg tidal volume with 5 cmH₂O PEEP, I:E = 1:2 ratio and FiO₂ 1.0 was used.

Results

There were no significant differences in PaO₂ values between groups during DLV and at the 15th minute of OLV. There were significant differences in PaO₂ at the 30th and 45th minutes between groups. In GrPaCO₂ mean airway pressure and RR was higher, and the inspiratory and expiratory time was shorter than in GrEtCO₂.

Conclusions

The relatively high RR impairs the emptying of alveoli and results in increased functional residual capacity. So the normocapnic lung-protective OLV results in significantly higher PaO₂ than permissive hypercapnic OLV.