Oxygenation Targets in Cardiac Surgery Patients - a Before-and-after Study

Background Oxygen is essential to life and supplementary oxygen therapy is routinely administrated during surgery to avoid life-threatening hypoxemia. Supplementary oxygen therapy is often given as a high and fixed fraction of inspired oxygen (FiO2) ranging from 0.60 to 1.00. As a consequence, the partial pressure of arterial oxygen (PaO2) often exceeds normal levels. There is increasing evidence of potential harm with liberal administrated oxygen therapy. Therefore, the standard regimes for oxygen therapy during surgery have to be further investigated.

The purpose of the study is to evaluate whether a regime for oxygen therapy targeting normal levels of PaO2 during elective cardiac surgery with use of cardiopulmonary bypass (CPB) and in the first postoperative day in the intensive care unit (ICU) is feasible. Additionally, metabolic changes in exhaled breath condensate and in arterial blood collected prior to surgery, before and after CPB, the first postoperative day in the ICU and the third postoperative day at the surgical ward will be evaluated.

Study Design The study design is a before-and-after study in patients scheduled for elective cardiac surgery being coronary artery bypass grafting or valve replacement or a combination of both. The first 25 patients will follow our institutional the standard regime for supplementary oxygen therapy; i.e. a minimum FiO2 of 0.60 during mechanical ventilation and at least 3 liters oxygen per minute after weaning from the ventilator in the ICU. Thereafter, another 25 patients will receive supplementary oxygen therapy to achieve a normal PaO2 defined as 10-12 kPa (75-120 mmHg) during surgery and in the ICU.

Exhaled breath condensates will be collected via a mouthpiece during spontaneous breathing prior to surgery, first and third postoperative day while the condensates will be collected via the tracheal tube during mechanical ventilation. Arterial blood samples will be collected simultaneously. Exhaled breath condensates and serum samples will be divided into aliquots and stored in a -80 degree Celsius freezer until final analyses after all patients have been included.

Metabolic changes in exhaled breath condensates and in serum samples will be analyzed using nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS). The spectra's will give a snapshot of all metabolites in a given sample and elucidate changes in the metabolic profiles in response to oxygen exposures.