Cardiac Surgery Clinical Trial
Official title:
Oxygenation Targets in Cardiac Surgery Patients - a Before-and-after Study
During surgery high concentrations of supplementary oxygen are routinely administrated. However, there is increasing evidence of potential harm with liberal oxygen therapy. The hypothesis of the present study is that oxygen therapy adjusted to a normal arterial oxygen target is feasible and will attenuate the side effects of supplementary oxygen therapy. The study design is a before-and-after study in which 25 patients will follow the standard regime with high concentrations of oxygen therapy and 25 patients will be treated with oxygen to achieve a normal value of arterial oxygenation.
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.
Hypothesis The hypothesis is that oxygenation targeting is feasible and that changing the
supplementary oxygen therapy to a oxygenation targeting within the normal range will reduce
the FiO2 and thus the PaO2/FiO2 ratio.
Outcomes Primary outcome is the PaO2/FiO2 ratio on the third postoperative day. Secondary
outcomes will be changes in metabolic profiles in exhaled breath condensates and serum
samples, changes in oxygenation parameters, PaO2 and oxygen saturation, changes in time to
weaning from the ventilator in the ICU, changes in FiO2 and in supplementary oxygen therapy
after weaning from the ventilator, and changes in postoperative complications defined as
pneumonia, arrhythmias, re-operation, and re-admission to the ICU.
Statistical analyses This is a pilot study being a feasibility before-and-after study. Based
on institutional data a power calculation is performed estimating an increase in the
PaO2/FiO2 ratio from 30 ± 7 kPa with the standard regime for oxygen therapy to 36 ± 7 kPa
with a oxygenation targeting approach and with an alpha of 0,05 and a power of 80% (1-beta),
23 patients are needed in each group. To cover to dropouts at total of 50 patients, 25
patients in each group, will be recruited.
Data will be assessed for normality. Continuous normally distributed variables will be
compared using Student t tests and reported as mean and standard deviation, while
non-normally distributed data will be compared using Wilcoxon rank-sum tests and reported as
median and interquartile range. All analyses will be performed by using Stata (Metrika
Consulting AB, Stockholm, Sweden), Matlab.
The composition of metabolomics will be compared by multivariable analysis. For multivariate
analysis, various unsupervised and supervised analyses will be carried out in Matlab (The
MathWorks Inc., Natick, United States) and Python (Python Software Foundation, Delaware,
United States) software with in-house scripts. Principal component analysis will be used to
obtain a preliminary outlook of the data, to screen for outliers and detect clusters.
Eventually, partial least squares discriminant (PLS-DA) analyses coupled to different vv rs
selections algorithms will be employed to perform data reduction and classification of
treatments. For validation purposes, the Venetian-Blinds cross-validation approach will be
applied.
Ethics Patients will be included after an informed signed content is obtained. FiO2 of 0.60
is given routinely to patients undergoing cardiac surgery with CPB at Aalborg University
Hospital. Targeting a physiological PaO2 level between 10 and 12 kPa is considered to be
safe. Patients undergoing cardiac surgery is routinely maximal monitored during surgery and
in the ICU. The cardiac anaesthetist in charge can charge the PaO2 target at any time.
The collection of exhaled breath condensate is painless and without any discomfort for the
patient. The arterial blood sample on the third postoperative day will be performed by a
cardiac anaesthetist experienced in this procedure, who will apply a subcutaneous analgesia
with Lidocain 1% prior to the puncture and thus avoiding pain during the procedure.
Thereafter, a manual compression will be performed for 2 minutes to minimise the risk of a
haematoma. In total, four extra blood samples are collected for the metabonomics and one
extra blood gas analyses. The total amount of blood extracted in the study is 12.5 mL.
All other procedures and treatments follow the standard regimes.
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