Neutral red is a lysosomal probe and a biological pH indicator. In aqueous solutions, the protonated (NRH) and neutral (NR) forms of monomeric neutral red exhibit distinct absorption maxima (535 and 450 nm, respectively) but have the same fluorescence with a maximum at 637 nm and a quantum yield of 0.02. The similarity of the fluorescence spectra at acidic and basic pH suggests deprotonation of cationic species in the first singlet excited state. The NR fluorescence strongly depends on the solvent polarity as shown by addition of increasing amounts of water to pure dioxane, which gradually shifts the fluorescence maximum from 540 nm in pure dioxane to 637 nm in water. The fluorescence quantum yield increases from 0.17 in dioxane to 0.3 upon addition of 7% water and then decreases, reaching 0.02 in pure water. Immediately after incubation of human skin fibroblasts with neutral red, excitation with 435 nm light produces a fluorescence whose maximum is recorded at 575 nm. This fluorescence is located in the perinuclear region and originates from large fluorescent intracytoplasmic spots, suggesting staining of the endoplasmic reticulum-Golgi complex. At longer times, this fluorescence is shifted to 606 nm, suggesting slow diffusion of the lysosomotropic dye toward the more hydrated and acidic interior of lysosomes. Addition of a lysosomotropic detergent to cells previously incubated with neutral red shifts the fluorescence to the blue. Thus, in complex biological systems, this probe cannot be a good pH indicator but is a very sensitive probe of lysosomal microenvironments.
Background
Sepsis is one of the most frequent reasons for acute intensive care unit (ICU) admission of very old patients and mortality rates are high. However, the impact of pre-existing physical and cognitive function on long-term outcome of ICU patients ≥ 80 years old (very old intensive care patients (VIPs)) with sepsis is unclear.
Objective
To investigate both the short- and long-term mortality of VIPs admitted with sepsis and assess the relation of mortality with pre-existing physical and cognitive function.
Design
Prospective cohort study.
Setting
241 ICUs from 22 European countries in a six-month period between May 2018 and May 2019.
Subjects
Acutely admitted ICU patients aged ≥80 years with sequential organ failure assessment (SOFA) score ≥ 2.
Methods
Sepsis was defined according to the sepsis 3.0 criteria. Patients with sepsis as an admission diagnosis were compared with other acutely admitted patients. In addition to patients’ characteristics, disease severity, information about comorbidity and polypharmacy and pre-existing physical and cognitive function were collected.
Results
Out of 3,596 acutely admitted VIPs with SOFA score ≥ 2, a group of 532 patients with sepsis were compared to other admissions. Predictors for 6-month mortality were age (per 5 years): Hazard ratio (HR, 1.16 (95% confidence interval (CI), 1.09–1.25, P < 0.0001), SOFA (per one-point): HR, 1.16 (95% CI, 1.14–1.17, P < 0.0001) and frailty (CFS > 4): HR, 1.34 (95% CI, 1.18–1.51, P < 0.0001).
Conclusions
There is substantial long-term mortality in VIPs admitted with sepsis. Frailty, age and disease severity were identified as predictors of long-term mortality in VIPs admitted with sepsis.
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