Astrid Ellen Berggreen

Postoperative intubation time is associated with acute kidney injury in cardiac surgical patients

IntroductionAcute kidney injury (AKI) is a frequent complication after cardiac surgery and is associated with a poor prognosis. Mechanical ventilation is an important risk factor for developing AKI in critically ill patients. Ventilation with high tidal volumes has been associated with postoperative organ dysfunction in cardiac surgical patients. No data are available about the effects of the duration of postoperative respiratory support in the immediate postoperative period on the incidence of AKI in patients after cardiac surgery.MethodWe performed a secondary analysis of 584 elective cardiac surgical patients enrolled in an observational trial on the association between preoperative cerebral oxygen saturation and postoperative organ dysfunction and analyzed the incidence of AKI in patients with different times to extubation. The latter variable was graded in 4 h intervals (if below 16 h) or equal to or greater than 16 h. AKI was staged according to the AKI Network criteria.ResultsOverall, 165 (28.3%) patients developed AKI (any stage), 43 (7.4%) patients needed renal replacement therapy. Patients developing AKI had a significantly (P <0.001) lower renal perfusion pressure (RPP) in the first 8 hours after surgery (57.4 mmHg (95% CI: 56.0 to 59.0 mmHg)) than patients with a postoperatively preserved renal function (60.5 mmHg ((95% CI: 59.9 to 61.4 mmHg). The rate of AKI increased from 17.0% in patients extubated within 4 h postoperatively to 62.3% in patients ventilated for more than 16 h (P <0.001). Multivariate logistic regression analysis of variables significantly associated with AKI in the univariate analysis revealed that the time to the first extubation (OR: 1.024/hour, 95% CI: 1.011 to 1.044/hour; P <0.001) and RPP (OR: 0.963/mmHg; 95% CI: 0.934 to 0.992; P <0.001) were independently associated with AKI.ConclusionWithout taking into account potentially unmeasured confounders, these findings are suggestive that the duration of postoperative positive pressure ventilation is an important and previously unrecognized risk factor for AKI in cardiac surgical patients, independent from low RPP as an established AKI trigger, and that even a moderate delay of extubation increases AKI risk. If replicated independently, these findings may have relevant implications for clinical care and for further studies aiming at the prevention of cardiac surgery associated AKI.

Pharmacokinetic modeling of the transition of propofol from blood plasma to breathing gas

The anesthetic agent propofol is applied intravenously and different groups demonstrated that it is detectable in breathing gas. To quantify the propofol concentration in breathing gas (cbreath) might be a promising feedback for anesthesiologist and for potential closed loop control, yet there is no online measurement in standard clinical practice. Since the physiological relevance of the propofol concentration in breath is not entirely known it may be adverse to control the infusion with cbreath as target variable. In order to control the concentration at the plasma site (cplasma) or even at the effect site (ceffect) in the brain mathematical models can be used to describe the dependencies between cbreath and cplasma or ceffect. This contribution presents the pharmacokinetic modeling of the transition from blood to alveolar gas concentration of propofol. For characterization a model described by a gas blood partition coefficient and one time constant or an equivalent one compartment system, respectively, is taken into account. Clinical data obtained in a study with 17 patients are used for fitting. During anesthesia breathing gas was monitored continuously with an electrochemical sensor and venous blood samples were taken at given times. The use of the mentioned model structure leads to a simple and adequate characterization. A data conditioning in form of a model based interpolation was performed prior to the identification process. The identified parameters are comparable to results of other research works.

An analysis of variance type method to describe and compare steady states in clinical data

Identifying and comparing different steady states is an important task for clinical decision making. Data from unequal sources, comprising diverse patient status information, have to be interpreted. In order to compare results an expressive representation is the key. In this contribution we suggest a criterion to calculate a context-sensitive value based on variance analysis and discuss its advantages and limitations referring to a clinical data example obtained during anesthesia. Different drug plasma target levels of the anesthetic propofol were preset to reach and maintain clinically desirable steady state conditions with target controlled infusion (TCI). At the same time systolic blood pressure was monitored, depth of anesthesia was recorded using the bispectral index (BIS) and propofol plasma concentrations were determined in venous blood samples. The presented analysis of variance (ANOVA) is used to quantify how accurately steady states can be monitored and compared using the three methods of measurement.