Anesthesia and analgesia
-
Anesthesia and analgesia · Oct 2013
ReviewUnderstanding the Mechanism: Mediation Analysis in Randomized and Nonrandomized Studies.
In comparative clinical studies, a common goal is to assess whether an exposure, or intervention, affects the outcome of interest. However, just as important is to understand the mechanism(s) for how the intervention affects outcome. For example, if preoperative anemia was shown to increase the risk of postoperative complications by 15%, it would be important to quantify how much of that effect was due to patients receiving intraoperative transfusions. ⋯ We discuss the proper design and analysis of studies investigating mediation, including the importance of distinguishing mediator variables from confounding variables, the challenge of identifying potential mediators when the exposure is chronic versus acute, and the requirements for claiming mediation. Simple designs are considered, as well as those containing multiple mediators, multiple outcomes, and mixed data types. Methods are illustrated with data collected by the National Surgical Quality Improvement Project (NSQIP) and utilized in a companion paper which assessed the effects of preoperative anemic status on postoperative outcomes.
-
Anesthesia and analgesia · Oct 2013
ReviewMeasuring Mitochondrial Oxygen Tension: From Basic Principles to Application in Humans.
The protoporphyrin IX-triplet state lifetime technique (PpIX-TSLT) has been recently introduced as the first method to measure mitochondrial oxygen tension (mitoPO2) in living cells and tissues. The current implementation of the technique is based on oxygen-dependent quenching of the delayed fluorescence lifetime of 5-aminolevulinic-acid-enhanced mitochondrial PpIX. It represents a significant step forward in our ability to comprehensively measure tissue oxygenation. ⋯ Clinical measurements of mitoPO2 are possible as demonstrated by cutaneous measurements in healthy volunteers. Applications of PpIX-TSLT in anesthesiology and intensive care medicine might, e.g., be monitoring mitoPO2 as a resuscitation end point, targeting oxygen homeostasis in the critically ill, and assessing mitochondrial function at the bedside. PpIX-TSLT likely also has applications in other fields also, e.g., providing an oxygen-related feedback signal in photodynamic therapy of malignant tumors.
-
Anesthesia and analgesia · Oct 2013
Sevoflurane End-Tidal to Effect-Site Equilibration in Women Determined by Response to Laryngeal Mask Airway Insertion.
End-tidal concentrations (CET) have been used to guide delivery of inhaled anesthetic drugs for many years. Effect-site concentrations (Ceff) are a frequently used guide to therapy with IV drugs and should also be of benefit with inhaled drugs, especially during periods of rapid change. For Ceff to be useful, the appropriate levels required for any given end point, and the delay between central compartment and effect, need to be defined. In this study, we explored these relationships for the effect of response to insertion of the classic laryngeal mask airway (cLMA) and compared the utility of CET and Ceff-guided cLMA insertion. ⋯ This study confirmed that real-time calculation and display of Ceff based on measured CET values are feasible. We determined the optimum t(1/2)ke0 for sevoflurane for the effect of cLMA insertion as 2.25 minutes, similar to that determined for loss of consciousness using the raw electroencephalogram. We also showed that Ceff is a more reliable (P < 0.05) guide to successful cLMA insertion than CET.