Predictors of Perioperative Vasoactive Drug Requirement During Retroperitoneal Adrenalectomy for Pheochromocytoma: A Retrospective Exploratory Study

The aim of the present study was to test a hypothesis that baseline systemic vascular resistance index (SVRI) assessed by method of transpulmonary thermodilution predicts perioperative requirement for vasoactive drugs. The primary outcomes were: (1) peak vasoactive-inotropic score (VIS) and (2) peak dose of hypotensive drugs at any stage of surgery. The main exposure variable was baseline SVRI. Hemodynamics were retrospectively assessed by transpulmonary thermodilution in 50 adults who had undergone posterior retroperitoneal surgery for pheochromocytoma. Univariate linear regression analysis showed predictive value of SVRI on VIS [regression coefficient, 95% CI; 0.024 (0.005, 0.4), p=0.015]. Other significant factors were the history of peak diastolic pressure, baseline MAP, baseline betablocker therapy, and history of coronary artery disease (CAD). After adjustment of SVRI for the history of CAD, its prognostic value became non-significant [0.018 (0.008, 0.03), p=0.063 and 29.6 (19, 40.2), p=0.007 for SVRI and history of CAD, respectively]. Requirements of vasodilators were predicted by baseline adrenergic activity [0.37 (0.005, 0.74), p=0.047]. In conclusion, baseline SVRI is associated with perioperative requirement of vasopressor drugs, but history of CAD is a stronger prognostic factor for vasopressor support. Perioperative requirement in vasodilators is associated with baseline adrenergic activity.

57Fe Mössbauer study of unusual magnetic structure of multiferroic 3R-AgFeO2

We report new results of a ⁵⁷Fe Mössbauer study of hyperfine magnetic interactions in the layered multiferroic 3R-AgFeO₂ demonstrating two magnetic phase transitions at T _N1 and T _N2. The asymptotic value β ^*  ≈  0.34 for the critical exponent obtained from the temperature dependence of the hyperfine field H _hf(T) at ⁵⁷Fe the nuclei below T _N1  ≈  14 K indicates that 3R-AgFeO₂ shows quasi-3D critical behavior. The spectra just above T _N1 (T _N1  <  T  <  T  ^*  ≈  41 K) demonstrate a relaxation behavior due to critical spin fluctuations which indicates the occurrence of short-range correlations. At the intermediate temperature range, T _N2  <  T  <  T _N1, the ⁵⁷Fe Mössbauer spectra are described in terms of collinear spin-density-waves (SDW) with the inclusion of many high-order harmonics, indicating that the real magnetic structure of the ferrite appears to be more complicated than a pure sinusoidally modulated SDW. Below T  <  T _N2  ≈  9 K, the hyperfine field H _hf reveals a large spatial anisotropy (ΔH _anis  ≈  30 kOe) which is related with a local intra-cluster (FeO₆) spin-dipole term that implies a conventional contribution of the polarized oxygen ions. We proposed a simple two-parametric formula to describe the dependence of H _anis on the distortions of the (FeO₆) clusters. Analysis of different mechanisms of spin and hyperfine interactions in 3R-AgFeO₂ and its structural analogue CuFeO₂ points to a specific role played by the topology of the exchange coupling and the oxygen polarization in the delafossite-like structures.