Current Commonly Used Dynamic Parameters and Monitoring Systems for Perioperative Goal-Directed Fluid Therapy: A Review.

Goal-directed fluid therapy (GDFT) is usually recommended in patients undergoing major surgery and is essential in enhanced recovery after surgery (ERAS) protocols. This fluid regimen is usually guided by dynamic hemodynamic parameters and aims to optimize patients' cardiac output to maximize oxygen delivery to their vital organs. While many studies have shown that GDFT benefits patients perioperatively and can decrease postoperative complications, there is no consensus on which dynamic hemodynamic parameters to guide GDFT with. Furthermore, there are many commercialized hemodynamic monitoring systems to measure these dynamic hemodynamic parameters, and each has its pros and cons. This review will discuss and review the commonly used GDFT dynamic hemodynamic parameters and hemodynamic monitoring systems.

Transesophageal echocardiography identification of aortic dissection during cardiac arrest and cessation of ECMO initiation.

Cardiac arrest is a challenging clinical presentation that emergency medicine providers often encounter. Aortic dissection is an uncommon etiology in all-comers presenting in cardiac arrest. The use of bedside point of care echocardiography to aid in resuscitative efforts is expanding, particularly with the increasing use of transesophageal echocardiography (TEE) by emergency medicine providers. Additionally, emergency department initiation of extracorporeal membrane oxygenation (ECMO) is a relatively newer development in emergency department practice. We report the case of a 64-year old male presenting to the emergency department in cardiac arrest with TEE identification of aortic dissection as the etiology resulting in discontinuation of ECMO initiation attempts.

Phenytoin Serum Concentrations in Patients With Left Ventricular Support Devices: A Case Series.

PURPOSE: Achieving therapeutic levels of phenytoin is critical to its efficacy and safety. Free serum levels represent pharmacologically active phenytoin due to the high protein binding of the drug. Predicting free serum levels in patients with left ventricular support devices can be challenging, as the pharmacokinetics (PK) can be significantly altered, and equations to correct total levels have not been validated in this population. The aim of this case series was to describe serum phenytoin concentrations in critically ill patients requiring left ventricular support devices. METHODS: A retrospective chart review was performed including patients who received phenytoin therapy and had at least 1 set of simultaneously measured free and total serum phenytoin levels during left ventricular support with a mechanical device. Corrected total phenytoin levels were calculated using Sheiner-Tozer equations. RESULTS: Three patients were included in this case series. Patients 1 and 2 required venoarterial extracorporeal membrane oxygenation (ECMO) during phenytoin therapy, and patient 3 had a durable left ventricular assist device (LVAD). Measured phenytoin levels ranged from 4.1 to 11.4 µg/mL, and calculated corrected levels were 6.8 to 18.4. Measured free phenytoin levels ranged from 1.2 to 3.6 µg/mL, which correlated with free fractions of 15.8% to 37.9%. CONCLUSION: This case series demonstrates a higher percentage of free phenytoin compared to the total serum level than would be predicted and an inability to rely on corrected total phenytoin level to predict whether it is within therapeutic range. Monitoring of free serum phenytoin concentrations should be strongly considered in critically ill patients requiring LVAD or ECMO support.

Combined use of a Total Control Introducer and a hyperangulated video laryngoscope to place a left-sided double lumen endotracheal tube in a patient with a history of difficult laryngoscopy.

We describe the use of a Total Control Introducer (TCI) in combination with video laryngoscopy (VL) to place a left-sided double-lumen endotracheal tube (DLT) in a patient with a history of difficult laryngoscopy undergoing video-assisted thoracoscopic surgery (VATS). VL was used to obtain visualisation of the glottis and a TCI articulating introducer was used to dynamically navigate the airway and access the trachea. A 39 French DLT was subsequently passed over the TCI shaft and into the trachea under indirect visualisation. The TCI shaft was removed and the DLT was gently guided into the left main bronchus. Successful endobronchial intubation was confirmed with capnography, auscultation and fibreoptic bronchoscopy. We propose that the combined use of VL and a TCI can facilitate placement of a DLT in a patient with a known difficult airway who may otherwise be limited to a bronchial blocker placement for lung isolation during VATS.

Stabilin receptors clear LPS and control systemic inflammation.

Lipopolysaccharides (LPSs) cause lethal endotoxemia if not rapidly cleared from blood circulation. Liver sinusoidal endothelial cells (LSEC) systemically clear LPS by unknown mechanisms. We discovered that LPS clearance through LSEC involves endocytosis and lysosomal inactivation via Stabilin-1 and 2 (Stab1 and Stab2) but does not involve TLR4. Cytokine production was inversely related to clearance/endocytosis of LPS by LSEC. When exposed to LPS, Stabilin double knockout mice (Stab DK) and Stab1 KO, but not Stab2 KO, showed significantly enhanced systemic inflammatory cytokine production and early death compared with WT mice. Stab1 KO is not significantly different from Stab DK in circulatory LPS clearance, LPS uptake and endocytosis by LSEC, and cytokine production. These data indicate that (1) Stab1 receptor primarily facilitates the proactive clearance of LPS and limits TLR4-mediated inflammation and (2) TLR4 and Stab1 are functionally opposing LPS receptors. These findings suggest that endotoxemia can be controlled by optimizing LPS clearance by Stab1.

Auditory response properties of neurons in the tectal longitudinal column of the rat.

The newly-discovered tectal longitudinal column (TLC) spans the paramedian region of the mammalian tectum. It has connections with several nuclei of the auditory system. In this report, we provide the first detailed description of the responses of TLC neurons to auditory stimuli, including monaural and binaural tones and amplitude modulated tones. For comparison, responses in the inferior colliculus (IC) were also recorded. Neurons in the TLC were sensitive to similar ranges of frequency as IC neurons, could have comparably low thresholds, and showed primarily excitatory responses to stimulation of the contralateral ear with either phasic or sustained response patterns. Differences of TLC compared to IC neurons included broader frequency tuning, higher average threshold, longer response latencies, little synchronization or rate tuning to amplitude modulation frequency and a smaller degree of inhibition evoked by stimulation of the ipsilateral ear. These features of TLC neurons suggest a role for the TLC in descending auditory pathways.

Detection of interaural correlation by neurons in the superior olivary complex, inferior colliculus and auditory cortex of the unanesthetized rabbit.

A critical binaural cue important for sound localization and detection of signals in noise is the interaural time difference (ITD), or difference in the time of arrival of sounds at each ear. The ITD can be determined by cross-correlating the sounds at the two ears and finding the ITD where the correlation is maximal. The amount of interaural correlation is affected by properties of spaces and can therefore be used to assess spatial attributes. To examine the neural basis for sensitivity to the overall level of the interaural correlation, we identified subcollicular neurons and neurons in the inferior colliculus (IC) and auditory cortex of unanesthetized rabbits that were sensitive to ITDs and examined their responses as the interaural correlation was varied. Neurons at each brain level could show linear or non-linear responses to changes in interaural correlation. The direction of the non-linearities in most neurons was to increase the slope of the response change for correlations near 1.0. The proportion of neurons with non-linear responses was similar in subcollicular and IC neurons but increased in the auditory cortex. Non-linear response functions to interaural correlation were not related to the type of response as determined by the tuning to ITDs across frequencies. The responses to interaural correlation were also not related to the frequency tuning of the neuron, unlike the responses to ITD, which broadens for neurons tuned to lower frequencies. The neural discriminibility of the ITD using frozen noise in the best neurons was similar to the behavioral acuity in humans at a reference correlation of 1.0. However, for other reference ITDs the neural discriminibility was more linear and generally better than the human discriminibility of the interaural correlation, suggesting that stimulus rather than neural variability is the basis for the decline in human performance at lower levels of interaural correlation.