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Background: According to the "three-compartment" model of ventilation-perfusion (VA/Q) inequality, increased VA/Q scatter in the lung under general anesthesia is reflected in increased alveolar deadspace fraction (VDA/VA) customarily measured using end-tidal to arterial (A-a) partial pressure gradients for carbon dioxide. A-a gradients for anesthetic agents such as isoflurane are also significant but have been shown to be inconsistent with those for carbon dioxide under the three-compartment theory. The authors hypothesized that three-compartment VDA/VA calculated using partial pressures of four inhalational agents (VDA/VAG) is different from that calculated using carbon dioxide (VDA/VACO2) measurements, but similar to predictions from multicompartment models of physiologically realistic "log-normal" VA/Q distributions.Methods: In an observational study, inspired, end-tidal, arterial, and mixed venous partial pressures of halothane, isoflurane, sevoflurane, or desflurane were measured simultaneously with carbon dioxide in 52 cardiac surgery patients at two centers. VDA/VA was calculated from three-compartment model theory and compared for all gases. Ideal alveolar (PAG) and end-capillary partial pressure (Pc'G) of each agent, theoretically identical, were also calculated from end-tidal and arterial partial pressures adjusted for deadspace and venous admixture.Results: Calculated VDA/VAG was larger (mean ± SD) for halothane (0.47 ± 0.08), isoflurane (0.55 ± 0.09), sevoflurane (0.61 ± 0.10), and desflurane (0.65 ± 0.07) than VDA/VACO2 (0.23 ± 0.07 overall), increasing with lower blood solubility (slope [Cis], -0.096 [-0.133 to -0.059], P < 0.001). There was a significant difference between calculated ideal PAG and Pc'G median [interquartile range], PAG 5.1 [3.7, 8.9] versus Pc'G 4.0[2.5, 6.2], P = 0.011, for all agents combined. The slope of the relationship to solubility was predicted by the log-normal lung model, but with a lower magnitude relative to calculated VDA/VAG.Conclusions: Alveolar deadspace for anesthetic agents is much larger than for carbon dioxide and related to blood solubility. Unlike the three-compartment model, multicompartment VA/Q scatter models explain this from physiologically realistic gas uptake distributions, but suggest a residual factor other than solubility, potentially diffusion limitation, contributes to deadspace. : WHAT WE ALREADY KNOW ABOUT THIS TOPIC: General anesthesia increases the inhomogeneity (scatter) of the distribution of ventilation-perfusion ratios in the lung, widening alveolar to arterial partial pressure gradients for respired gasesThis inhomogeneity is reflected in increased alveolar deadspace fraction in the traditional three-compartment model of ventilation-perfusion scatterThe alveolar to arterial partial pressure difference for isoflurane is inconsistent with that measured simultaneously using end-tidal and arterial carbon dioxide partial pressures WHAT THIS ARTICLE TELLS US THAT IS NEW: Alveolar deadspace fraction calculated for volatile anesthetic agents is much larger than that calculated simultaneously for carbon dioxide, and its magnitude increases as blood solubility decreasesPhysiologically realistic multicompartment modeling of ventilation-perfusion scatter explains the relative differences between inhalational agents in alveolar to arterial partial pressure gradients and alveolar deadspace. [ABSTRACT FROM AUTHOR]

What is known and objective: Physicians' response to moderate and severe hypokalaemia in hospitalized patients is frequently suboptimal, leading to increased risk of cardiac arrhythmias and sudden death. While actively alerting physicians on all critical care values using telephone or electronic pop‐ups can improve response, it can also lead to alert fatigue and frustration due to non‐specific and overdue alerts. Therefore, a new method was tested. A clinical rule built into a clinical decision support system (CDSS) generated alerts for patients with a serum potassium level (SPL) <2.9 mmol/L without a prescription for potassium supplementation. If the alert was deemed clinically relevant, a pharmacist contacted the physician. The aim of this study was to evaluate the impact of the clinical rule‐guided pharmacists' intervention compared to showing passive alerts in the electronic health records on outcome in patients who developed hypokalaemia (<2.9 mmol/L) during hospitalization. Methods: A before (2007‐2009) and after (2010‐2017) study with time series design was performed. Pre‐intervention, physicians were shown passive alerts for hypokalaemia in the electronic health records. During the intervention period, in addition to these passive alerts, a pharmacist provided the physician with a specific advice on patients with untreated hypokalaemia, guided by the generated alerts. Unique patients >18 years with SPL <2.9 mmol/L measured at least 24 hours after hospitalization in whom no potassium supplementation was initiated within 4 hours after measurement and normalization of SPL was not achieved within these 4 hours were included. Haemodialysis patients were excluded. The percentage of hypokalaemic patients with a subsequent prescription for potassium supplementation, time to subsequent potassium supplementation prescription, the percentage of patients who achieved normokalaemia (SPL ≥ 3.0 mmol/L), time to achieve normokalaemia and total duration of hospitalization were compared. Results and discussion: A total of 693 patients were included, of whom 278 participated in the intervention phase. The percentage of patients prescribed supplementation as well as time to prescription improved from 76.0% in 31.1 hours to 92.0% in 11.3 hours (P <.01). Time to achieve SPL ≥3.0 mmol/L improved, P <.009. No changes, however, were observed in the percentage of patients who achieved normokalaemia or time to reach normokalaemia, 87.5% in 65.2 hours pre‐intervention compared to 90.2% (P =.69) in 64.0 hours (P =.71) in the intervention group. A non‐significant decrease of 8.2 days was observed in the duration of hospitalization: 25.4 compared to 17.2 days (P =.29). What is new and conclusion: Combining CDSS alerting with a pharmacist evaluation is an effective method to improve response rate, time to supplementation and time to initial improvement, defined as SPL ≥3.0 mmol/L. However, it showed no significant effect on the percentage of patients achieving normokalaemia, time to normokalaemia or hospitalization. The discrepancy between rapid supplementation and improvement on the one hand and failure to improve time to normokalaemia on the other warrants further study. [ABSTRACT FROM AUTHOR]