Intensive care doctors' preferences for arterial oxygen tension levels in mechanically ventilated patients.

BACKGROUND: Oxygen is liberally administered in intensive care units (ICUs). Nevertheless, ICU doctors' preferences for supplementing oxygen are inadequately described. The aim was to identify ICU doctors' preferences for arterial oxygenation levels in mechanically ventilated adult ICU patients. METHODS: In April to August 2016, an online multiple-choice 17-part-questionnaire was distributed to 1080 ICU doctors in seven Northern European countries. Repeated reminder e-mails were sent. The study ended in October 2016. RESULTS: The response rate was 63%. When evaluating oxygenation 52% of respondents rated arterial oxygen tension (PaO2 ) the most important parameter; 24% a combination of PaO2 and arterial oxygen saturation (SaO2 ); and 23% preferred SaO2 . Increasing, decreasing or not changing a default fraction of inspired oxygen of 0.50 showed preferences for a PaO2 around 8 kPa in patients with chronic obstructive pulmonary disease, a PaO2 around 10 kPa in patients with healthy lungs, acute respiratory distress syndrome or sepsis, and a PaO2 around 12 kPa in patients with cardiac or cerebral ischaemia. Eighty per cent would accept a PaO2 of 8 kPa or lower and 77% would accept a PaO2 of 12 kPa or higher in a clinical trial of oxygenation targets. CONCLUSION: Intensive care unit doctors preferred PaO2 to SaO2 in monitoring oxygen treatment when peripheral oxygen saturation was not included in the question. The identification of PaO2 as the preferred target and the thorough clarification of preferences are important when ascertaining optimal oxygenation targets. In particular when designing future clinical trials of higher vs lower oxygenation targets in ICU patients.

Synchronizing thermodilution cardiac output measurements with spontaneous breathing does not improve precision.

INTRODUCTION: Measuring cardiac output (CO) with the pulmonary artery catheter intermittent bolus thermodilution technique (PAC-IBTD) is less precise with spontaneous breathing compared to controlled ventilation. We aimed to test if precision could be improved in spontaneous breathing by synchronizing the measurement with respiration or using instructed respiration in 18 post-operative cardiac surgery patients. METHODS: We performed eight CO measurements with PAC-IBTD using cold saline in three different situations; in random order: 1) random compared to respiration, 2) timed to the start of expiration, and 3) synchronized with a slow exhalation through a PEP-flute. We calculated the standard deviation (SD), coefficient of variation (CV), and precision in the total material and in the three situations using a linear mixed effects model. RESULTS: A total of 408 CO measurements were performed in 17 included patients. There were no differences between the three study situations regarding mean or precision. The overall CO was 6.0 ± 1.4 l/min (mean ± SD), CV 6.2% and precision 12.2% for single measurements. Averaging three measurements increased the precision to 7.0%. CONCLUSION: We could not improve the precision of PAC-IBTD in spontaneously breathing patients by synchronizing the measurements with respiration.

Post-operative myocardial dysfunction does not affect the physiological response to early mobilization after coronary artery bypass grafting.

BACKGROUND: An acute increase in oxygen demand can be compensated for either by increased cardiac index (CI) or increased oxygen extraction, resulting in reduced mixed venous oxygen saturation (SvO2). We tested the hypothesis that post-operative cardiac dysfunction may explain why oxygen extraction alone is increased during early mobilization after cardiac surgery. METHODS: Twenty patients with a pre-operative ejection fraction > 50% were included in an open prospective observational study comparing the changes in SvO2 and hemodynamics during mobilizations immediately prior to surgery and on the first post-operative morning. RESULTS: Mobilization induced an absolute reduction in SvO2 of 17.7 +/- 7.4% pre- and 19.0 +/- 5.5% post-operatively (NS). ANOVA for a series of measurements throughout the mobilization sequence identified no different effect on SvO2 between pre- and post-operative mobilizations (P = 0.567). The SvO2 level was reduced post-operatively resulting in a SvO2 during standing exercise of 55% before and 49% after the surgery (P < 0.01). Mobilization increased the heart rate (HR) and decreased the stroke volume index (SVI), leaving CI unchanged. This response was similar pre- and post-operatively (NS). Compared with pre-operative measurements, CI and HR increased post-operatively while SVI remained unchanged despite elevated cardiac filling pressures and reduced systemic vascular resistance. The left ventricular stroke work index was reduced, indicating reduced myocardial performance. CONCLUSION: Myocardial function was reduced on the first morning after coronary artery bypass grafting (CABG), but during post-operative mobilization this reduction did not significantly influence the changes in CI or SvO2.

Mixed venous oxygen desaturation during early mobilization after coronary artery bypass surgery.

BACKGROUND: Early postoperative mobilization induces a marked reduction in mixed venous oxygen saturation (S(v)O(2)) after aortic valve replacement. We investigated whether a similar desaturation occurs among coronary artery bypass grafting (CABG) patients, and if the desaturation was related to the preoperative ejection fraction (EF). METHODS: Thirty-one CABG patients with a wide range in EF were included in an open observational study. We recorded hemodynamic and oxygenation variables during mobilization on postoperative day 1 and day 2 using a pulmonary artery catheter. RESULTS: Patients with an EF ranging from 24 to 87% were mobilized without clinical problems. S(v)O(2) at rest was 65.4 +/- 4.9% (mean +/- SD) on day 1 and 64.3 +/- 5.8% on day 2 (NS). During mobilization, cardiac index and oxygen delivery were reduced while oxygen consumption was increased (P-values: 0.000, 0.007 and 0.000, respectively). Consequently, oxygen extraction increased, resulting in a marked reduction in S(v)O(2)-42.9 +/- 8.3% on day 1 and 47.4 +/- 8.5% on day 2 (P = 0.025 between days). Several pre-, intra- and postoperative factors were tested as possible predictors for S(v)O(2) during mobilization. No factor contributed substantially. CONCLUSION: Patients with CABG exhibit a marked desaturation during early postoperative mobilization. Preoperative ejection fraction did not affect S(v)O(2) during exercise. The clinical consequences and underlying mechanism require further investigation.

Mixed venous oxygen saturation during mobilization after cardiac surgery: are reflectance oximetry catheters reliable?

BACKGROUND: Oximetry catheters immediately reflect changes in mixed venous oxygen saturation (SvO2). We have used the Baxter 2-SAT system to register changes in SvO2 during early mobilizations after cardiac surgery. To assess catheter reliability, readings were compared to blood gases. METHODS: A total of 352 paired catheter and bench haemoximetry measurements were obtained at the expected highest and lowest levels of SvO2 during the mobilization procedures. The agreement between methods was explored by a Bland-Altman plot. The influence of haemoglobin (Hgb), pH, cardiac output (CO), posture, catheter identity and catheter calibration on agreement was assessed through analysis of covariance. RESULTS: Data included a substantial number of low SvO2 values, 95 paired means of SvO2 < or = 50% and 37 paired means < or = 40%. Mean oxygen saturation difference between catheter and haemoximeter readings was -1.6 +/- 5.7% (SD). Agreement between the methods depended upon the level of SvO2. At SvO2 of 65%, the two methods were virtually identical. Below 65%, the catheters increasingly underestimated the corresponding haemoximetric values by 1.5% for every 10% reduction in SvO2. Agreement was to some degree dependent on individual calibrations and catheter identity, but to a lesser extent on Hgb, CO and posture. CONCLUSION: The two methods are interchangeable for most clinical purposes. Catheter readings are, however, substantially lower than the corresponding haemoximetric measurements at low SvO2 values. Careful interpretation of the absolute values resulting from catheter measurements is recommended, especially when SvO2 readings are low.