Francesco Zadek

Background: Intravenous fluids modify acid–base balance by changing plasma strong ion difference (SID_PL) and total non-volatile weak acids. Experimental data suggest that pre-infusion plasma bicarbonate (HCO₃⁻) may further modulate these effects. We tested this hypothesis in a large cohort of postoperative ICU patients receiving intravenous fluids. Methods: We retrospectively analyzed all-consecutive post-operative ICU admissions over a 21-month period who received fluid therapy. Fluid inputs/outputs, plasma electrolytes, and arterial blood gases were collected from admission to 9:00 A.M. of postoperative day one. Average SID of infused fluids (SID_INF) was calculated, and SID_PL and standard base excess variations (ΔSBE) were assessed. Patients were stratified by SID_INF tertiles (low, 3⁻ (24.3 [22.4–26.3] mmol/L), and tertiles of SID_INF-HCO₃⁻ difference. Results: Among 650 admissions, 641 were included (83% elective surgery). Pre-infusion acid–base was, as average, within normal ranges. Total infused volume averaged 2327 ± 1111 mL. Across SID_INF tertiles, ΔSBE increased from 1.2 ± 3.4 to 3.0 ± 3.0 and 3.4 ± 3.0 mmol/L (p < 0.001), paralleled by ΔSID_PL rise (0.6 ± 2.3, 1.3 ± 2.4 and 1.4 ± 2.3 mEq/L, respectively; p = 0.004). For any given SID_INF, patients with lower pre-infusion HCO₃⁻ showed greater ΔSBE and ΔSID_PL (p < 0.001). When analyzed by tertiles of SID_INF-HCO₃⁻ difference, ΔSBE rose from 1.0 ± 3.2 to 2.7 ± 2.9 and 4.0 ± 3.0 mmol/L (p < 0.001), with amplified effects at higher infused volume (>2500 mL). Conclusions: In postoperative ICU patients, fluid-induced acid–base changes are largely driven by SID_INF-HCO₃⁻ difference, supporting individualized fluid selection based on baseline HCO₃⁻.

Background: This in-vitro and in-vivo study investigates the Gibbs-Donnan effect across the filter during continuous veno-venous hemofiltration (CVVH). In particular, we assessed its acid–base implications, applying the physical–chemical approach. Methods: A prospective, single-center study was conducted using the PrismaMax machine (Baxter). Two sets of in-vitro CVVH experiments (with and without albumin) were performed to quantify the Gibbs-Donnan effect. Electrolytes, glucose, and osmolarity changes were measured across the filter and in the ultrafiltrate. Strong ion difference and sieving coefficients of the main solutes were calculated. Similar measurements were performed in oligo-anuric critically ill patients undergoing CVVH. Results: In-vitro experiments without albumin showed a sieving coefficient of 1 for both positive and negative ions. On the contrary, when albumin was added, the sieving coefficient for sodium and chloride changed linearly with albumin concentration ( r = −0.94, p < 0.001 for sodium, r = 0.88, p < 0.001 for chloride), resulting in a progressive linear increase in post-filter strong ion difference ( β = 1.1, r = 0.77, p = 0.003). In 22 studied patients, calculated albumin concentration increased across the filter (2.2 ± 0.5 g/dL vs. 3.1 ± 0.7 g/dL), leading to sodium retention (138 ± 6 vs. 141 ± 6 mmol/L, p < 0.001) and chloride excretion (100 ± 5 vs . 97 ± 5 mmol/L, p < 0.001), thus resulting in a higher post-filter strong ion difference (46 ± 4 vs. 40 ± 4 mmol/L, p < 0.001). Conclusions: These in-vitro and in-vivo studies demonstrate that albumin linearly affects the sieving coefficient of ions, increasing the strong ion difference of plasma water during its passage through the filter and thus having a systemic alkalizing effect. Graphic

Background/Objectives: Effective pain management in polytrauma patients with rib fractures is essential, particularly in the critical care setting. While epidural analgesia is considered the gold standard, it is not always feasible, necessitating alternative locoregional approaches. We present the case of a polytrauma patient with multiple, bilateral rib fractures and severe chest pain that hindered weaning from mechanical ventilation. A bilateral Serratus Anterior Plane Block (SAPB) was performed, with catheters placed for continuous administration of local anesthetics. Pain relief was immediate, enabling a rapid weaning from mechanical ventilation, safe extubation, and subsequent discharge to rehabilitation. A review of the literature on this technique in critically ill patients with thoracic trauma and multiple rib fractures is also presented. Methods: We conducted a literature search up to November 2024, identifying studies evaluating the use of SAPB in critically ill patients with chest trauma and rib fractures. Results: Eight studies were identified, including a total of 197 cases, of which only 3 involved a bilateral SAPB. Studies and published case reports demonstrated significant variability in analgesic protocols and reported outcomes. Notably, only two papers addressed specifically its role in facilitating weaning from mechanical ventilation. Conclusions: Pain control is fundamental in managing severe chest trauma. This case and the reviewed literature suggest that the SAPB is a promising option when epidural analgesia is contraindicated or impractical. However, further studies are needed to define its place in clinical practice and optimize its use in critically ill patients.

Continuous positive airway pressure (CPAP) is frequently used to treat patients with acute respiratory failure in out-of-hospital settings. Compared to a facemask, the helmet has many advantages for the patient but requires a minimum gas flow of 60 L/min to avoid CO₂ rebreathing. The aim of the present bench study was to evaluate the performance of four Venturi devices, connected to a single oxygen cylinder, in delivering helmet-CPAP with clinically relevant gas flow, fraction of inspired oxygen (FiO₂)_, and positive end-expiratory pressure (PEEP) values. Three double-inlet Venturi systems (EasyVent, Ventuplus, Compact-HAR) were connected to full 5-L oxygen cylinders using a double flowmeter, and their oxygen requirements to reach different setups (flow 60-80 L/min; FiO₂ 0.4-0.5-0.6, PEEP 7.5-10-12.5 cmH₂O) were tested. The fourth Venturi system (O2-MAX) was directly attached to the tank, and the flow and FiO₂ delivered at preset FiO₂ 0.3 and 0.6 were recorded. The runtime of the cylinder was assessed. EasyVent, Ventuplus, and O2-MAX were able to deliver helmet-CPAP with clinically useful setups when connected to a single oxygen cylinder, while Compact-HAR did not. The runtime of the cylinders ranged between 28 and 60 minutes according to the preset flow and FiO₂. The delivered gas flow decreased slowly and linearly with the drop in cylinder pressure until its exhaustion. Helmet-CPAP might be provided using portable Venturi systems connected to an oxygen cylinder, but not all of them are able to deliver it. The use of a double flowmeter allows delivery of both high flow and high FiO₂ when double-inlet Venturi systems are used. Due to the flow drop observed during the cylinder consumption, a flow >60 L/min should be set when helmet-CPAP is started. Considering the flow drop phenomenon, the estimated duration of the tank runtime can be used with a margin of safety when planning patient transport.

Continuous venovenous hemofiltration (CVVH) is frequently performed in critically ill patients using diluted citrate for regional anticoagulation. The impact of this renal replacement strategy on plasma sodium has not been evaluated yet. Our aim was therefore to assess the period prevalence of hyponatremia (sodium p < 0.001. Sodium concentrations of employed dialysis bags were confirmed using ion chromatography. However, ionized sodium of Regiocit measured with a direct-ion selective electrode (ISE) resulted lower (~118 mmol/L), suggesting the presence of sodium-to-citrate complexes. Possible mechanisms explaining the hyponatremia development could therefore include: i) plasma water dilution; ii) a reduced Gibbs-Donnan effect, given the low albumin concentration (2.6 ± 0.8 g/dl) of our critically ill patients; iii) a negative sodium balance due to the loss of sodium-to-citrate complexes across the filter. The clinical implications of the described hyponatremia and the different contributions of the hypothesized mechanisms need to be addressed in future studies.

This paper challenges the assumed equivalence between changes in plasma strong ion difference (SID) and whole blood base excess (BE) during in vitro acidosis. We highlight that redistribution of strong ions, in the form of albumin ionic-binding and transerythrocyte shifts, alters SID without affecting BE. We demonstrate that these expected SID alterations are predictable from albumin and hemoglobin’s charges, or from the noncarbonic whole blood buffer value, allowing a better interpretation of SID and BE during in vitro acidosis.