pH Gradient Liposomes Extract Protein Bound Amitriptyline in Peritoneal Dialysis-Exploratory Work.

Poisoning is a significant cause of injury-related death worldwide. Dialysis is usually ineffective in removing the toxin once it has been absorbed because of drug protein binding and high volumes of distribution. In this work, we explore whether the addition of liposomes to peritoneal dialysate could extract protein bound amitriptyline. Liposomes were prepared using the thin film hydration method. In the in vitro experiment, 3 mL of 20% albumin with a concentration of 6000 nmol/L amitriptyline in a proprietary dialysis cartridge was dialysed against 125 mL of phosphate-buffered saline with and without 80 mg 1,2-dioleoyl-sn-glycero-3-phosphoglycerol (DOPG) liposomes. In the in vivo arm, peritoneal dialysis was undertaken in 6 rats with pH gradient liposome augmented dialysate after intravenous amitriptyline injection. Peritoneal blood flow was estimated by CO2 extraction. Total amitriptyline extracted was compared to freely dissolved (non-protein bound) and total amitriptyline perfusing the membrane during the peritoneal dwell. Mean liposome size for DOPG and acidic centre pH gradient liposomes was 119 nm and 430 nm, respectively. In the in vitro experiment, more amitriptyline was extracted into the liposome containing dialysate than the control dialysate (40 +/- 2 nmol/L vs. 27 +/- 1 nmol/L). In the in vivo experiment, the total amitriptyline in dialysate was 5240 +/- 2750 nmol. Mean total free amitriptyline perfusing the peritoneal membrane was 93 +/- 46 nmol. Mean total blood amitriptyline perfusing the peritoneal membrane was 23,920 +/- 6920 nmol. Two of the six animals were excluded due to overestimation of peritoneal blood flow. This exploratory work suggests the addition of liposome nanoparticles to peritoneal dialysate extracted protein bound amitriptyline from blood.

Liposome supported peritoneal dialysis in rat amitriptyline exposure with and without intravenous lipid emulsion.

Liposome supported peritoneal dialysis is a recently described technique which may eventually be applicable in the clinical scenario of the intoxicated patient. We evaluated the hypothesis that intravenous injection of lipid emulsion (ILE) would augment acidic pH gradient liposome supported peritoneal dialysis (LSPD). Orogastrically amitriptyline dosed rats were treated with either Sodium bicarbonate (NaHCO3) intravenously and standard intraperitoneal dialysate (Group A); NaHCO3 intravenously and LSPD (Group B); or ILE and LSPD (Group C). The primary endpoint was dialysate amitriptyline concentration after a 60 min dwell. Secondary analysis included an estimate of extraction ratio for peritoneal blood flow (ERs). There were significantly higher intraperitoneal concentrations of amitriptyline and ERs in the two groups treated with LSPD (Group B, p = 0.02, Group C, p < 0.01 vs. Group A). There was no observed effect for ILE on intraperitoneal amitriptyline concentration or ERs (p > 0.20). LSPD increased the amitriptyline concentration in peritoneal dialysate. No further increase was demonstrated with ILE. This may be either because such an effect is absent, or type II error. Exploratory analysis suggests LSPD may be driven by total rather than free drug concentrations.

Lipid emulsion in local anesthetic toxicity.

PURPOSE OF REVIEW: Enthusiasm for regional anesthesia has been driven by multimodal benefits to patient outcomes. Despite widespread awareness and improved techniques (including the increasing use of ultrasound guidance for block placement), intravascular sequestration and the attendant risk of local anesthetic systemic toxicity (LAST) remains. Intravenous lipid emulsion (ILE) for the treatment of LAST has been endorsed by anesthetic regulatory societies on the basis of animal study and human case report data. The accumulated mass of reporting now permits objective interrogation of published literature. RECENT FINDINGS: Although incompletely elucidated the mechanism of action for ILE in LAST seemingly involves beneficial effects on initial drug distribution (i.e., pharmacokinetic effects) and positive cardiotonic and vasoactive effects (i.e., pharmacokinetic effects) acting in concert. Recent systematic review by collaborating international toxicologic societies have provided reserved endorsement for ILE in bupivacaine-induced toxicity, weak support for ILE use in toxicity from other local anesthetics, and largely neutral recommendation for all other drug poisonings. Work since publication of these recommendations has concluded that there is a positive effect on survival for ILE when animal models of LAST are meta-analyzed and evidence of a positive pharmacokinetic effect for lipid in human models of LAST. SUMMARY: Lipid emulsion remains first-line therapy (in conjunction with standard resuscitative measures) in LAST. Increasing conjecture as to the clinical efficacy of ILE in LAST, however, calls for high-quality human data to refine clinical recommendations.

Should we consider the infusion of lipid emulsion in the resuscitation of poisoned patients?

The use of intravenous lipid emulsions (ILEs) as antidote in local anaesthetic systemic toxicity has gained widespread support following convincing data from animal models, and successful case reports in humans. Proposed beneficial mechanisms of action for ILEs include intravascular sequestration of intoxicant and subsequent enhanced redistribution to biologically inert tissues, augmentation of fatty acid utilisation for ATP synthesis in the context of metabolic poisoning, and direct cardiotonic and ion channel effects. The evidence base for use of ILEs in acute drug intoxication is evolving. The present evidence supports use of ILEs only in local anaesthetic systemic toxicity and in lipophilic cardiotoxin intoxication when there is an immediate threat to life, and other therapies have proven ineffective.

Comparison of the onset and offset times of two available formulations of rocuronium bromide in an animal model.

Rocuronium bromide is a neuromuscular blocker in widespread use in anaesthesia, emergency and intensive care. Reports of reduced efficacy of a new different formulation of rocuronium bromide were submitted to Medsafe, the New Zealand Medicines and Medical Devices Safety Authority, in 2020. Given the requirement for rapid and predictable paralysis for patient safety the efficacy of the two available formulations of rocuronium bromide was investigated in an animal model. After ethics committee approval, 19 rats were anaesthetised and paralysis, defined as loss of tibialis anterior flexion on direct electrical stimulation of the sciatic nerve, was assessed by mechanomyography in response to ED90 doses of rocuronium.Paralysis was observed at a median of 12 seconds for the new different formulation: A, Hameln Pharma (interquartile range (IQR) 6-106 seconds) and 28 seconds for formulation B: Pfizer (IQR 12-68 seconds) P = 0.48. Offset of paralysis was observed after 293 seconds for formulation A (IQR 250-372 seconds) and 241 seconds for formulation B (IQR 220-263 seconds). While the differences observed were substantial, they were not statistically significant. Moreover, the direction of observed difference was towards a shorter median onset and longer offset for the newer formulation, a finding in the opposite direction to the initial clinical concern.Relevance to the clinical situation is indeterminate given the study was stopped at low numbers for futility and limitations around the clinical applicability of animal pharmacokinetics and dynamics. Nevertheless our findings provide some reassurance that the newly available different formulation of this critical use medication does not exhibit a substantial increase in time to onset.

Premorbid beta blockade in sepsis is associated with a lower risk of a lactate concentration above the lactate threshold, a retrospective cohort study.

Sepsis and septic shock represent a significant worldwide mortality burden. A lactate greater than 4 mmol/L is associated with increased mortality in septic patients. This is the concentration at the "lactate threshold" where serum lactate concentrations rise markedly with increased workload in exercise. Hyperlactatemia in both sepsis and exercise is contributed to by adrenergic agonism which stimulates aerobic glycolysis, increasing lactate production and decreasing lactate clearance. Our hypothesis is that in patients with sepsis, treatment with beta blockers in the community will be associated with a lower probability of initial lactate ≥ 4 mmol/L. This was single centre retrospective cohort study. We used an in-house SQL Database for all admissions to ICU/HDU for the 2017-2020 calendar years. The dataset was filtered for an APACHE III Diagnosis of sepsis. T-tests were used for continuous data, Chi squared and Fisher's exact test were used as appropriate to compare proportions. Logistic regression was used to investigate covariate effects. Of the 160 patient records analysed, 49 were prescribed beta blockers. A greater proportion of patients not prescribed beta blockers in the community had a first lactate ≥ 4 mmol/L (p = 0.049). This was robust to regression analysis. There was no difference in the proportion of patients with lactate ≥ 2 mmol/L (p = 0.52). In our cohort patients previously prescribed beta blockers were less likely to have a lactate of ≥ 4 mmol/mL. This supports the proposed mechanism that treatment with beta blockers increases the lactate threshold in sepsis. Further study is warranted.

Trending peripheral venous PCO2 in patients with respiratory failure using mathematically arterialised venous blood gas samples.

BACKGROUND: Trending venous blood gases (VBGs) has been suggested as an alternative to arterial blood gases (ABGs) in patients with respiratory failure, but there are limits to its utility. The aim of this study was to compare the trending of venous carbon dioxide partial pressure (pCO2) (pCO2v) with mathematically arterialised pCO2 (pCO2ca) and to further evaluate whether pCO2ca follows change in arterial pCO2 (pCO2a) more accurately. METHODS: We analysed two data sets. The first was a retrospective study of patients with respiratory failure admitted to the intensive care unit. Venous samples were mathematically arterialised using the vTAC method. The change in pCO2 between two consecutive samples (ΔpCO2) for pCO2v was compared with the change in calculated pCO2ca values. In the second data set taken from previously published work, we analysed 82 trend points (difference between consecutive samples) for change in pCO2. There were pCO2v, pCO2a and pCO2ca values for each trend point. The primary outcome measures were the 95% limits of agreement (LOAs) between different sampling methods for ΔpCO2. RESULTS: In the first data set, 46 patients had 203 VBG results giving 157 trend points for ΔpCO2 analysis. The 95% LOAs for ΔpCO2ca and ΔpCO2v were -9.28 to 11.12 mm Hg.In the second data set, 95% LOAs for ΔpCO2 were -9.46 to 9.48 mm Hg for ΔpCO2a and ΔpCO2v, -8.94 to 8.58 mm Hg for ΔpCO2ca and ΔpCO2v, and -4.54 to 4.91 mm Hg for ΔpCO2a and ΔpCO2ca. CONCLUSION: This study suggests that trending pCO2v is not an accurate way to trend pCO2a in patients with respiratory failure. ΔpCO2ca via vTAC trended differently to ΔpCO2v. Our data suggest pCO2ca more accurately trends pCO2a.

How Much PEEP Does High Flow Deliver via Tracheostomy? A Literature Review and Benchtop Experiment.

BACKGROUND: High flow tracheostomy (HFT) is a commonly used weaning and humidification strategy for tracheostomised patients, but little is known as to how much PEEP or mechanical benefit it offers. Patient anatomy and device characteristics differentiate it from high flow nasal cannula and the physiological effects observed. OBJECTIVES: (1) To review the available literature on the effects of HFT on airway pressure and indices of gas exchange. (2) To quantify PEEP generated by a HFT circuit. METHODS: A randomised benchtop experiment was conducted, with a size 8 uncuffed Portex tracheostomy connected to an Optiflow™ with Airvo 2™ humidifier system. The tracheostomy tube was partially immersed in water to give rise to a column of water within the inner surface of the tube. An air fluid interface was generated with flows of 40 L/min, 50 L/min, and 60 L/min. The amount of potential PEEP (pPEEP) generated was determined by the distance the water column was pushed downward by the flow delivered. Findings. Overall 40 L/min, 50 L/min, and 60 L/min provided pPEEP of approximately 0.3 cmH2O, 0.5 cmH2O, and 0.9 cmH2O, respectively. There was a statistically significant change in pPEEP with change in flows from 40-60 L/min with an average change in pPEEP of 0.25-0.35 cmH2O per 10 L/min flow (p value <0.01). Interpretation. HFT can generate measurable and variable PEEP despite the open system used. The pPEEP generated with HFT is minimal despite statistically significant change with increasing flows. This pPEEP is unlikely to provide mechanical benefit in weaning patients off ventilatory support.

Liposomes to Augment Dialysis in Preclinical Models: A Structured Review.

In recent years, a number of groups have been investigating the use of "empty" liposomes with no drug loaded as scavengers both for exogenous intoxicants and endogenous toxic molecules. Preclinical trials have demonstrated that repurposing liposomes to sequester such compounds may prove clinically useful. The use of such "empty" liposomes in the dialysate during dialysis avoids recognition by complement surveillance, allowing high doses of liposomes to be used. The "reach" of dialysis may also be increased to molecules that are not traditionally dialysable. We aim to review the current literature in this area with the aims of increasing awareness and informing further research. A structured literature search identified thirteen papers which met the inclusion criteria. Augmenting the extraction of ammonia in hepatic failure with pH-gradient liposomes with acidic centres in peritoneal dialysis is the most studied area, with work progressing toward phase one trials. Liposomes used to augment the removal of exogenous intoxicants and protein-bound uraemic and hepatic toxins that accumulate in these organ failures and liposome-supported enzymatic dialysis have also been studied. It is conceivable that liposomes will be repurposed from the role of pharmaceutical vectors to gain further indications as clinically useful nanomedical antidotes/treatments within the next decade.

Is lactate lower in septic patients who are prescribed beta blockers? Retrospective cohort study of an intensive care population.

OBJECTIVE: Elevated serum lactate has long been considered an important marker of sepsis severity. Increasing evidence supports catecholamine-stimulated aerobic glycolysis being a major contributor to the hyperlactataemia seen in sepsis. Beta-blockade may blunt such catecholamine mediated rise in lactate analogous to the way it can mask tachycardia. This could impact the way we evaluate sepsis severity and adequacy of initial treatment. The objective of this study is to investigate whether septic patients who were on beta-blocker treatment at presentation have lower serum lactate level. METHODS: Using a retrospective cohort design we gathered data on patients admitted to our base hospital intensive care unit with APACHE III diagnosis of sepsis and septic shock during the 2017 calendar year. Serum lactate, current medications, presenting vital signs, illness severity scores, laboratory data and mortality outcome were extracted from patients' medical record and the unit's clinical database. RESULTS: Of 189 records analysed, 49 patients were concurrently prescribed beta-blockers. More beta-blocked patients were male, beta-blocked patients were older, and a greater proportion of beta blocked patients had their first lactate measured as an inpatient. After regression to correct for identified significant covariates mean serum lactate was 0.87 (95% confidence interval 0.05-1.69) mmol/L lower in those prescribed beta blockers. CONCLUSIONS: In our cohort pre-existing beta blocker treatment was associated with lower serum lactate measurements in patients presenting with sepsis. Pre-existing beta blocker treatment may reduce serum lactate at presentation in patients with sepsis.

Epinephrine injection in lipid-based resuscitation from bupivacaine-induced cardiac arrest: transient circulatory return in rabbits.

BACKGROUND: IV lipid emulsion has demonstrated to be effective therapy for bupivacaine-induced cardiotoxicity. However, the role of epinephrine when coadministered with lipid emulsion in toxin-induced cardiac arrest is unclear. We postulated superior resuscitation outcome in the absence of epinephrine in a rabbit model of bupivacaine-induced cardiac arrest resuscitated with IV lipid emulsion. METHODS: Twenty sedated, instrumented New Zealand White rabbits received 10 mg/kg IV bupivacaine producing asystole. Mechanical ventilation and external chest compressions were commenced at 30 seconds. At 1 minute, animals received 5 mL/kg 20% lipid emulsion in addition to 1 of 4 additional IV treatments (n = 5 all groups): 0.9% saline, 2.5 microg/kg epinephrine, 10 microg/kg epinephrine, 100 microg/kg epinephrine; all at 1 mL/kg. Lipid emulsion bolus was repeated at 4 minutes. Return of spontaneous circulation and hemodynamic metrics were obtained to 15 minutes. Saline group animals additionally received high-dose epinephrine (100 microg/kg) treatment at 15 minutes, and were monitored to 20 minutes. RESULTS: High-dose epinephrine administration was associated with increased rate of return of spontaneous circulation compared with saline control (0 of 5 saline-treated animals; 0 of 5 animals in the 2.5 microg/kg epinephrine group; 3 of 5 in the 10 microg/kg group [P = 0.167]; and 4 of 5 in the 100 microg/kg group [P = 0.048]). Spontaneous but decreasing circulation was maintained at 15 minutes in 4 of 5 animals in the 100 microg/kg group alone (P = 0.048); mean arterial blood pressure at 15 minutes was 12.8 (SEM 2.8) mm Hg saline, 12.0 (2.5) mm Hg 2.5 microg/kg epinephrine, 20.6 (2.7) mm Hg 10 microg/kg epinephrine, and 26.4 (3.9) mm Hg 100 microg/kg epinephrine (P = 0.008). Four of five animals in the saline-treated group exhibited return of spontaneous circulation after delayed epinephrine treatment (P = 0.048). High-dose epinephrine administration was associated with a significant increase in coronary perfusion pressure before return of spontaneous circulation. CONCLUSIONS: Epinephrine seemed to be necessary for return of spontaneous circulation, but was subsequently associated with declining hemodynamic variables in this rabbit model of bupivacaine-induced cardiac arrest. Further study is required to define the role of epinephrine in lipid-based resuscitation from local anesthetic-induced cardiac arrest.

A novel method to assist gastric tube insertion: a case series.

Gastric tube insertion in the intubated patient can prove both difficult and frustrating. A simple modification to the standard gastric tube and corresponding technique of insertion is described which enables directional manoeuvring of the tube tip. Experience with the technique is described in a case series of 10 patients.

Intralipid infusion diminishes return of spontaneous circulation after hypoxic cardiac arrest in rabbits.

BACKGROUND: Infusion of lipid emulsion has been shown to reverse lipophilic drug-induced cardiovascular collapse in laboratory models and humans. The effect of high dose lipid in nondrug-induced cardiac arrest is, however, uncertain. In a rabbit model of asphyxial pulseless electrical activity (PEA) we compared lipid augmented with standard advanced cardiac life support (ACLS) resuscitation. METHOD: Adult New Zealand White rabbits underwent hypoxic PEA via tracheal clamping. After 2 min of cardiac arrest, basic life support cardiopulmonary resuscitation was commenced and 3 mL/kg 20% Intralipid or 3 mL/kg 0.9% saline solution infused. Adrenaline (100 microg/kg) was administered at 4 and 5 min. Return of spontaneous circulation (ROSC), hemodynamic metrics, and survival to 50 min were recorded. RESULTS: Seven of 11 saline-treated rabbits developed ROSC versus 1 of 12 Intralipid-treated animals; P = 0.009. No significant difference in survival to 50 min was observed (3/11 saline vs 0/12 Intralipid; P = 0.211). CONCLUSION: In this model of hypoxia-induced PEA, standard ACLS resulted in greater coronary perfusion pressure and increased ROSC compared with ACLS plus lipid infusion. Lipid emulsion may be contraindicated in cardiac arrest complicated by significant hypoxia.

Magnetic extraction of toxin binding liposomes; a method to ameliorate drug toxicity? Preliminary in vitro/ in vivo study.

AIM: Removal of a toxin from the body once absorbed is usually not possible. We describe the use of magnetite containing pH gradient 'MagnepH' liposomes to overcome limitations preventing removal. METHODS: MagnepH liposomes were added to albumin solution containing amitriptyline and dosed intravenously in rats prior to amitriptyline injection. Albumin solution or drawn blood was exposed to a magnet and sampled. RESULTS: One third of amitriptyline was extracted in vitro. In vivo amitriptyline concentrations were 1830 nmol/l (controls) and 10870 nmol/l (MagnepH; n = 2). Amitriptyline extraction increased from 0.6% (control) to 10.4% (MagnepH; 95% CI for difference 2.0-17.6%). CONCLUSION: MagnepH liposomes sequestered amitriptyline and could then be extracted. This method has potential to ameliorate limitations to extracorporeal removal of toxins in poisoning.

Intralipid outperforms sodium bicarbonate in a rabbit model of clomipramine toxicity.

STUDY OBJECTIVE: Previous investigators have demonstrated amelioration of lipid-soluble drug toxidromes with infusion of lipid emulsions. Clomipramine is a lipid-soluble tricyclic antidepressant with significant cardiovascular depressant activity in human overdose. We compare resuscitation with Intralipid versus sodium bicarbonate in a rabbit model of clomipramine toxicity. METHODS: Thirty sedated and mechanically ventilated New Zealand White rabbits were infused with clomipramine at 320 mg/kg per hour. At target mean arterial pressure of 50% initial mean arterial pressure, animals were rescued with 0.9% NaCl 12 mL/kg, 8.4% sodium bicarbonate 3 mL/kg, or 20% Intralipid 12 mL/kg. Pulse rate, mean arterial pressure, and QRS duration were sampled at 2.5-minute intervals to 15 minutes. In the second phase of the experiment, 8 sedated and mechanically ventilated rabbits were infused with clomipramine at 240 mg/kg per hour to a mean arterial pressure of 25 mm Hg. Animals received either 2 mL/kg 8.4% sodium bicarbonate or 8 mL/kg 20% Intralipid as rescue therapy. External cardiac compression and intravenous adrenaline were administered in the event of cardiovascular collapse. RESULTS: Mean difference in mean arterial pressure between Intralipid- and saline solution-treated groups was 21.1 mm Hg (95% confidence interval [CI] 13.5 to 28.7 mm Hg) and 19.5 mm Hg (95% CI 10.5 to 28.9 mm Hg) at 5 and 15 minutes, respectively. Mean difference in mean arterial pressure between Intralipid- and bicarbonate-treated groups was 19.4 mm Hg (95% CI 18.8 to 27.0 mm Hg) and 11.5 mm Hg (95% CI 2.5 to 20.5 mm Hg) at 5 and 15 minutes. The rate of change in mean arterial pressure was greatest in the Intralipid-treated group at 3 minutes (6.2 mm Hg/min [95% CI 3.8 to 8.6 mm Hg/min] Intralipid versus -0.25 mm Hg/min [95% CI -1.9 to 1.4 mm Hg/min] saline solution) and 5 minutes (4.4 mm Hg/min [95% CI 3.0 to 5.9 mm Hg/min] Intralipid versus 0.06 mm Hg/min [95% CI -0.9 to 1.1 mm Hg/min] saline solution). In the second phase of the experiment spontaneous circulation was maintained in all Intralipid-treated rabbits (n=4). All animals in the bicarbonate-treated group developed pulseless electrical activity and proved refractory to resuscitation at 10 minutes (n=4, P=.023). CONCLUSION: In this rabbit model, Intralipid infusion resulted in more rapid and complete reversal of clomipramine-induced hypotension compared with sodium bicarbonate. Additionally, Intralipid infusion prevented cardiovascular collapse in a model of severe clomipramine toxicity.

Reversal of lipophilic weak bases using pH gradient acidic centre liposomes: demonstration of effect in dabigatran-induced anticoagulation.

INTRODUCTION: Liposomes have recently emerged as rational vehicles for drug detoxification. Modification of the core pH may further enhance the ability of liposomes to sequester lipophilic toxins that are weak bases. Dabigatran, a reversible inhibitor of thrombin, has been widely promoted as a novel oral anticoagulant. As a lipophilic weak-base, it provides a rational target for reversal with acidic-centred liposomal preparations. The present study tests the hypothesis that acidic centre liposomes will reverse dabigatran induced anticoagulation. METHOD: Following enteric dabigatran dosing in vitro assessment of thrombin clotting times (TCT) was undertaken in rabbit plasma spiked with incremental liposome concentrations. Tail vein bleeding was assessed following intravenous liposome injection in rats after enteric dabigatran administration. RESULTS: Liposomes achieved reversal of TCT to baseline at low levels of thrombin inhibition, and partial reversal of TCT at higher levels. Liposomes completely reversed the effects of dabigatran on rat tail vein bleeding time (134.0 (6.7) s liposomes vs. 410 (37.8) s control; p < 0.01). CONCLUSION: Dabigatran-induced coagulopathy was reversed in vitro and in vivo by acidic-centred liposomes. pH-modified liposomes are a promising investigational entity in the antidotal treatment of pharmacologic weak bases that are lipid soluble at physiologic pH.