The evolution and current use of invasive hemodynamic monitoring for predicting volume responsiveness during resuscitation, perioperative, and critical care

Anesthetic Considerations for Patients on Renal Replacement Therapy

The number of patients presenting for surgery with renal dysfunction requiring renal replacement therapy (RRT) is expected to increase as the population ages and improvements in therapy continue to be made. Every aspect of the perioperative period is affected by renal dysfunction, its associated comorbidities, and altered physiology secondary to RRT. Most alarming is the increased risk for perioperative cardiac morbidity and mortality seen in this population. Perioperative optimization and management aims to minimize these risks; however, few definite guidelines on how to do so exist.

Miniaturized Echocardiography in the Cardiac Intensive Care Unit

Miniaturized transesophageal echocardiography has become more common in cardiac intensive care units. There are potential benefits to this mode of technology, many of which have been described in the literature. However, image acquisition and quality have been cited as being less optimal when compared to traditional transesophageal echocardiography. This review will discuss the current options available for miniaturized transesophageal echocardiography along with a literature review of this emerging assessment modality.

Mini-fluid challenge can predict arterial pressure response to volume expansion in spontaneously breathing patients under spinal anaesthesia

INTRODUCTION

The objective of this study was to test whether stroke volume (SV) variations in response to a fixed mini-fluid challenge (ΔSV100) measured by impedance cardiography (ICG) could predict an increase in arterial pressure with volume expansion in spontaneously breathing patients under spinal anaesthesia.

METHODS

Thirty-four patients, monitored by ICG who required intravenous fluid to expand their circulating volume during surgery under spinal anaesthesia, were studied. Haemodynamic variables and bioimpedance indices (blood pressure, SV, cardiac output [CO]) were measured before and after fluid challenge with 100mL of crystalloid, and before/after volume expansion. Responders were defined by ≥15% increase in systolic arterial pressure (SAP) after infusion of 500 mL of crystalloid solution.

RESULTS

SAP increased by ≥15% in 20 (59%) of the 34 patients. SAP, SV, and CO increased and HR decreased only in responders. SV variations in response to mini-fluid challenge and volume expansion differed between patients who showed arterial responsiveness and those in whom SAP did not increase with volume expansion (11.6% [9.1-19.3] versus 2.5% [1.3-7], P<0.001, and 22.4% [11.7-36.6] versus 0.9 [0-5.5], P<0.001, respectively). ΔSV100 predicted an increase of arterial pressure with an area under the receiver operating characteristic (AUC) curve of 0.89 (CI95%: 0.73-0.97, P<0.001). The cut-off was 5%. Baseline SAP and HR were not predictive of arterial responsiveness (P>0.05).

CONCLUSION

A ΔSV100 over 5% accurately predicted arterial pressure response to volume expansion during surgery.

Diuretic response to colloid and crystalloid fluid loading in critically ill patients

AIMS

In the critically ill patient, fluid loading is commonly done to stabilise hemodynamics and increase diuresis, whereas the absence of diuresis may predispose to harmful overloading. The goal of the current study was to evaluate the diuretic response and determinants thereof upon crystalloid and colloid fluid loading.

SUBJECTS AND METHODS

This is a substudy on 42 clinically hypovolemic, septic or non-septic patients without acute kidney injury, who were randomly assigned, after stratification for sepsis, to a 90-min fluid loading protocol with either 0.9% saline or a colloid solution (gelatin, hydroxyethyl starch 200/0.5 or albumin). Hemodynamics, biochemical parameters and diuresis were recorded. A response was defined by an increase in diuresis of >10% during fluid loading.

RESULTS

Diuresis increased more during saline than colloid infusion, together with a decline in colloid osmotic pressure (COP) of plasma and less increase in plasma volume and global hemodynamics with saline, at similar fluid balance. Nine patients (82%) receiving saline had a diuretic response, compared to 13 patients (42%) receiving colloids (P = 0.04), and the response was not predicted by underlying condition, global hemodynamics, volume of fluid infused and COP.

CONCLUSION

In critically ill patients with clinical hypovolemia, diuresis increases more during saline than colloid fluid loading, only partly dependent of a fall in plasma COP.

The maintenance and monitoring of perioperative blood volume

The assessment and maintenance of perioperative blood volume is important because fluid therapy is a routine part of intraoperative care. In the past, patients undergoing major surgery were given large amounts of fluids because health-care providers were concerned about preoperative dehydration and intraoperative losses to a third space. In the last decade it has become clear that fluid therapy has to be more individualized. Because the exact determination of blood volume is not clinically possible at every timepoint, there have been different approaches to assess fluid requirements, such as goal-directed protocols guided by invasive and less invasive devices.

This article focuses on laboratory volume determination, capillary dynamics, aspects of different fluids and how to clinically assess and monitor perioperative blood volume.