Predicting Fluid Responsiveness

Dr. Trivedi

Monnet X, Dres M, Ferré A, Le Teuff G, Jozwiak M, Bleibtreu A, Le Deley MC, Chemla D, Richard C, Teboul JL. Prediction of fluid responsiveness by a continuous non-invasive assessment of arterial pressure in critically ill patients: comparison with four other dynamic indices. Br J Anaesth. 2012 Sep;109(3):330-8. Epub 2012 Jun 26.

            A debate within the realm of anesthesia continues over the best hemodynamic monitoring tool. Traditional static measures such as central venous pressure and pulmonary artery occlusion pressures are now being replaced by dynamic indices. Monnet and colleagues sought to compare non invasive arterial pulse pressure variation (PPV) to invasive PPV, respiratory variation of pulse contour-derived stroke volume, and changes in cardiac index induced by passive leg raising (PLR) and end-expiratory occlusion (EEO) tests. The PPV, the respiratory variation of arterial pulse pressures induced by mechanical ventilation, estimates stroke volume with relatively good accuracy. PLR acts as a “self volume challenge” and the effects of PLR on the cardiac output can predict fluid responsiveness. The EEO is a newer tool which involves  occluding the respiratory circuit for a few seconds at end-expiration interrupting the venous return that occurs at each mechanical inspiration resulting increase in cardiac preload.  Patient populations which may have the greatest benefit from new dynamic indices, the critically ill with hemodynamic failure, were chosen as the focus for this study. 47 critically ill patients were chosen. Baseline non-invasive and invasive PPVs, stroke volume variation, and changes in cardiac index induced by PLR and EEO were recorded. The patient was then administered 500 ml of saline and the response recorded. CNAP could not record arterial pressures in 8 patients which the authors attribute to severe vasoconstriction from vasopressors and/or micro thrombi. Fluid increased cardiac index by ≥15% in 17 'responders' out of the remaining 39 patients. A limitation is that in patients with low tidal volumes the changes in intrathoracic pressure might be so low that changes in cardiac preload could be too low to challenge the preload-dependent stroke volume. The PLR may be useful in this case since it would allow testing for fluid responsiveness even in ventilated patients with low tidal volumes and lung compliance. The authors found that combing multiple dynamic indices did not prove to have higher accuracy in terms of fluid responsiveness and that non-invasive assessment of PPV appears to be of great utility in this patient population. 

Estimating fluid status in the post surgical ICU can be challenging as patients indices are increasingly challenged by failing organs and influenced by measures such as dialysis. In addition to the influence of ventilation, the PPV can also be invalidated by developed arrhythmias which are frequent in this population. In addition to the use of PPV and other static and dynamic measures, I found the use of transthoracic ultrasound to be of great utility in a situation of uncertainty. A quick look at the heart by the anesthesiologist at bedside can reveal valuable information about the overall function/contractility of the heart as well as fluid status as the heart may appear overfilled/ volume overloaded or under filled/ “kissing.”

Fluid Resuscitation in Septic Shock

Dr. Perz,

Boyd, J.H., Forbes, J., Nakada, T., Walley, K., Russell, J.A. Fluid Resuscitation in septic shock: A positive fluid balance and elevated central venous pressure are associated with increased mortality. Critical Care Medicine: Volume 39, Issue 2 (Feb 2011).

The objective of this study was to determine when central venous pressure (CVP) and fluid balance after resuscitation for septic shock are associated with mortality by doing a retrospective review of the use of IV fluids during the first 4 days of care.  The study concluded that a more positive fluid balance both early in resuscitation and cumulatively over four days is associated with an increased risk of mortality in septic shock.  CVP may be used to gauge fluid balance <12 hours into septic shock but becomes an unreliable indicated of fluid balance thereafter.  The study referenced a VASST study (Vasopressin in Septic Shock Trial), which noted that optimal survival occurred with a positive fluid balance of approximately 3L at 12 hours.

This study was a retrospective review of 778 patients from the VASST, all of whom were in septic shock and receiving at least 5mcg of norepinephrine per minute; they analyzed whether a positive fluid balance in the first 12 hours of resuscitation and during the next 4 days was associated with an increase in 28-day mortality. Using the Surviving Sepsis guidelines from 2008, the study grouped patients into those who fell into the recommended range (CVP = 8-12), those with CVP < 8 and those with a CVP >12 and analyzed whether a CVP of 8-12 had a survival advantage.  In this VASST, the patients at 12 hours with a CVP <8 had a lower mortality over those with CVPs of 8-12 and those with CVPs >12.  However, the study also concluded that there is a point when too little fluid is also detrimental.  It also concluded that CVP may be useful along with other measures to gauge adequacy of fluid resuscitation <12 hours into septic shock but becomes an unreliable marker of fluid balance thereafter.  Optimal survival in the VASST study occurred with a positive fluid balance of appx. 3L at 12 hours.  

Hypotensive Resuscitation and Mortality

Dr. Dong

Hypotensive Resuscitation during Active Hemorrhage: Impact on In-Hospital Mortality

Dutton MD, Mackenzie MD, Scalea MD

J Trauma 2005

This article focuses on the latest strategies to improve the outcomes of patients suffering from acute hemorrhagic shock as a result of trauma. It aims to support findings from a study done in the early 1990’s from Houston which proposed the idea of holding intravenous crystalloids and allowing permissive hypotension until the active source of bleeding is located and resolved. However the authors at the University of Maryland Shock Trauma Center noted multiple shortcomings from the previous study and embarked on a mission to re-create the aforementioned trend. 110 patients were reenrolled over 20 months, in which 55 were placed in a group with an average SBP being 114mmHg and the other 100mmHg. Variables such as injury severity score, and duration of hemorrhage were similar between the groups. In the end however, both groups demonstrated similar outcomes in which survivability was 92.7% in each group with 4 deaths each. The article mentions that the possible reasons for the lack of differentiation could have been improvements in the overall diagnostic and theurapeutic technology, short duration of the study, major difference in the mechanism of trauma and the imprecision of manual SBP readings. 

Lactate/Pyruvate as a marker of tissue hypoxia

Dr. Perz

Lactate/Pyruvate Ratio as a Marker of Tissue Hypoxia in Circulatory and Septic Shock

Rimachi, R., Bruzzi de Carvahlo, F., Orellano-Jimenez, C., Cotton, F., Vincents, J.L., De Backer, D.  Anesth Intensive Care 2012; 40:427-423.

                This article described a prospective, observational study which measured arterial lactate and pyruvate concentrations within the first four hours of shock and at four hour intervals during the first 24 hours in 26 patients with septic shock and 13 patients with cardiogenic shock.    The basis for this study is based on the fact that several authors have suggested that lactate in itself may not be an accurate measure of hypoxia.  Increased blood lactate concentrations may also, especially in patients with sepsis, result from impaired clearance of lactate, inhibition of pyruvate dehydrogenase, and accelerated aerobic glycolysis due to the activation of the Na/K ATPase by catecholamines.  These authors suggest that lactate should be measured with pyruvate, to attempt to distinguish between hypoxic and non-hypoxic sources of lactate.  In anaerobic conditions, pyruvate is transformed to lactate and thus, the lactate/pyruvate (L/P) ratio increases.  So, this study attempted to use the L/P ratio to assess the contribution of hypoxic and non-hypoxic causes to hyperlactataemia.

The lactate/pyruvate ratio was measured in each of these patients, and several observations were noted.  Blood lactate values were higher at shock onset and remained higher in the non-survivors in relation to the survivors; the lactate/pyruvate ratio at shoch onset was significantly higher in the non-survivors.  All patients with cardiogenic shock had hyperlactataemia at the onset of shock and 69% had a high lactate/pyruvate ratio, and of the septic shock patients, 65% had hyperlactataemia and 76% had a high lactate/pyruvate ratio.  Eighteen percent of patients died during the first 24 hours, thirty one percent of patients died later in the ICU and fifty four percent were discharged alive from the ICU.  Ultimately, the study concluded that the L/P ratio confirms that hyperlactataemia is frequently, but not solely due to hypoxia, especially at the onset of shock.

Update on Transfusion Medicine

Dr. T. Chon

Anesthesiology. Goodhough LT, Shander A. 2012 June;116(6):1367-1376. Patient Blood Management

It is the collaboration of a multidisciplinary team consisting of transfusion medicine specialists, surgeons, anesthesiologists, and critical care specialist to optimize the appropriate use of blood and blood components for patients when needed. Multiple steps are outlined to guide clinicians the decision to transfuse keeping in mind the risks of exposing the patient to known blood risks, unknown blood risks, preservation of the national blood inventory, and constraints from escalating costs. The multimodal decision to transfuse are based on, but not limited to, 1) appropriate anemia management and work-up in the pre operative setting; 2) blood availability and compatibility testing; 3) blood administration and documentation; 4) alternatives to allogeneic blood; and 5) indications for blood transfusion.

A thorough anemia workup must be complete before (at least 30days) scheduled elective surgery. Anemia can be due to iron deficiency secondary to occult blood loss or malignancy, chronic inflammation, chronic kidney disease, Vitamin B12/Folic acid deficiency.

If the patient is suspected to undergo transfusion, preparation must include a completed type and screen/cross. To ensure availability of the blood products, clinicians should confirm that the appropriate blood work is completed before proceeding to the operating room.

In order to decrease error of blood product administration, blood products must have a patient identification with transfusion order confirmed, date and time of transfusion, and vitals before and after transfusion.

To help with decreasing the introduction of allogeneic blood, autologous transfusions are a good option for patients, but not without risks. In preoperative autologous donation, patients donate their own blood over a period of weeks, but risks include acquired storage lesions, depletion of 2,3-DPG, and impaired ability for erythrocytes to unload oxygen to tissues. Acute normovolemic hemodilution allows preoperative dilution of blood loss, most effective in procedures with large blood loss, but efficacy on its use is mixed due to low acceptance secondary to the lack of standardized protocols, variations in target hemoglobin, types of fluids used, heterogeneity in surgical blood losses by procedure, and patient selection criteria. Lastly cell salvage helps with the reduction of allogeneic blood transfusions but can increase loss of platelets and plasma in washed blood leading to dilutional coagulopathy or thrombocytopenia, and is a relative contraindication in patients with cancer or obstetric/bowel surgeries involving contamination.

Consensus for blood transfusion has been debated, using hemoglobin levels as a threshold.

Generally, transfusion is not of benefit when hemoglobin is greater than 10 g/dl, and are beneficial when less than 6 g/dl. Multiple trials show that patients can tolerate hemoglobin between 7 and 8 g/dl, with equivalent clinical outcomes, and a higher threshold for elderly patients with coronary risks undergoing surgery with anticipated blood loss.

Blood transfusions are at times necessary but do carry risks. The decision to transfuse must be based on a thorough workup, preparation, alternative options, and optimization of patient safety

Goal Directed Fluid Management During High Risk Surgery, Dr. Perz

Katie Perz, D.O.

Goal Directed Fluid Management Based on Pulse Pressure Variation Monitoring During High Risk Surgery: A Pilot Randomized Controlled Trial

Lopes, M., Oliveira, M., Pereira, V., Lemos, I., Auler, J., Michard, F.  J Crit Care, v.11 (5); 2007.

Several studies have shown that maximizing stroke volume by volume loading during high-risk surgery may improve post operative outcome.  The goal of this study was to determine whether this goal could be achieved by simply by minimizing the variation in arterial pulse pressure induced by mechanical ventilation.  In this study, thirty three patients undergoing high-risk surgery were randomized; the intervention group was continuously monitored during surgery by a multiparameter bedside monitor and minimized to 10% or less by volume loading.  The study was done in Brazil, and the “multiparameter bedside monitor” was made by a company called Dixtal, and the monitor was referred to as the DX2020.  The arterial pressure curve was recorded via a specific module (IBPplus; Dixtal), allowing calculation of the change in pulse pressure.  The study concluded that monitoring and minimizing the change in pulse pressure by fluid loading during high-risk surgery decreases the incidence of post operative complications and also the duration of mechanical ventilation, stay in the ICU, and stay in the hospital.

Hemodynamic Parameters to Guide Fluid Therapy, Dr. Perz

Katie Perz, DO

Hemodynamic Parameters to Guide Fluid Therapy

Paul E Marik, Xavier Monney, Jean-Louis Teboul

Journal Ann Intensive Care, 2011

Introduction: The cornerstone of treating patients with shock remains as it has for decades: IV fluids.  Surprisingly, dosing IV fluid during resuscitation of shock remains largely empirical.  Multiple studies have demonstrated that only approximately 50% of hemodynamically unstable patients in the ICU and OR respond to a fluid challenge.  Cardiac filling pressures, including CVP and PAOP have been traditionally used to guide fluid management, but studies during the past 30 years have demonstrated that cardiac filling pressures are unable to predict fluid responsiveness.  During the past decade, a number of dynamic test of volume responsiveness have been reported.  This article outlines a recommendation for assessing hemodynamic management with consideration of useful parameters for volume status and ventilatory status of the patient (mechanically vs. spontaneous vs. combination).

Recommendations for accurately assessing volume status:

1.     Pulse Pressure Variation (PPV):

a.     Derived from analysis of arterial waveform

b.     Some authors predict that PPV was a reliable predictor of fluid responsiveness only when tidal volumes are >8mL/kg

2.     Stroke Volume Variation (SVV):

a.     Derived from pulse contour analysis

3.     Pulse Oximeter Plethysmographic Waveform Amplitude Variation

a.     Dynamic changes of this waveform with positive pressure ventilation have shown a significant correlation and good agreement with the PPV and have accurately predicted fluid responsiveness in the OR in ICU

4.     Doppler Echocardiography

a.     Respiratory changes in aortic blood velocity as measure by TEE can predict fluid responsiveness in mechanically ventilated patients

b.     Changes in vena-caval diameter can be measured to predict fluid responsiveness

5.     End Expiratory Occlusion Test

a.     Interrupting mechanical ventilation during an end-expiratory occlusion can increase cardiac preload sufficiently for such a test being used to predict fluid responsiveness

6.     Passive Leg Raising

a.     Can be used in patients who are mechanically ventilated or those who have a spontaneous component to their mechanical ventilation

b.     The change in aortic blood flow, measured by esophageal Doppler, during a 45 degree  leg elevation was shown to predict the changes in aortic blood flow produced by a 500mL fluid challenge even in patients with arrhythmias and/or spontaneous ventilator triggering (a situation when PPV loses its predictive ability)

c.     Can be assessed with use of Flo-trac Vigileo, PiCCO, or NICOM devices

                                               i.     Less invasive than PA catheterization but not ideally suited to resuscitate in the ER or ward.

Conclusion: All these methods have a useful place in the continuum of the resuscitation process.  This article recommends that CVP no longer be used to guide fluid management in the OR, ICU or ER.

Is NPO after Midnight Archaic? Dr. Trivedi

Puja Trivedi, DO

Time to Abolish “NPO After Midnight” by Mark Singleton MD

Dr. Singleton highlights an archaic term, "NPO after midnight," which
was coined with patient safety at heart but in the modern day context
can actually harm our patients. In the past, patients were asked not
to eat or drink anything after midnight to ensure an empty stomach.
However. this led to both binge eating at 11:45pm (which may lead to a
bloated, uncomfortable, sleep deprived patient the morning of surgery)
or conversely, starvation due to case delays or cancellations. As
surgical care transitions from a solely in patient practice where all
surgical patients had been admitted in the past to more of an emphasis
on outpatient, ambulatory surgical centers, patients are scheduled and
asked to arrive at specifc times. For example, a patient scheduled for
an elective procedure at 3pm should be allowed to eat a light
breakfast. Unfortunately this is only one part of the battle. The
notion of NPO after midnight is often echoed by surgical team members,
pre op nursing and hospital staff. It is for this reason that Dr.
Singleton advocates the concept of having an anesthesiologist contact
the patient the night before to answer and address the issue of "NPO."

Meta-Analysis of Fluid Management Strategies, Dr. Mjos

Bahar Mjos, DO

Perioperative Fluid Management Strategies in Major Surgery: A Stratified Meta-Analysis

This article reviewed the outcome of goal directed fluid therapy versus liberal fluid therapy intraoperative. Many previous studies focus on perioperative fluid therapy. However, the optimal strategy remains controversial and uncertain. Most current studies center around the type of fluids administered (colloid versus crystalloid), the total volume administered (restrictive versus liberal [LVR]), and whether the administration of fluids should be guided by hemodynamic goals (goal directed [GD] versus not goal directed. In this paper it was hypothesized that liberal use of perioperative fluid therapy without hemodynamic goals is not equivalent to GD fluid therapy, and a meta-analysis was conducted to compare these 2 approaches of managing perioperative fluid therapy and how they many have different end results. 

Studies were grouped into 2 strata, standard therapy with hemodynamic goals versus GD and liberal versus restrictive in this meta-analysis. The primary outcome was postoperative mortality. Secondary outcomes were organ-specific complications, recovery of bowel function (time to first flatus, time to first bowel movement, and return to oral diet), and length of hospital stay.

The findings:

1)    “ GD fluid therapy reduced renal complications, pneumonia, time to first bowel movement, resumption of normal diet and length of stay compared to non-GD therapy”

2)    “Restrictive fluid strategy reduced the incidence of pulmonary edema and pneumonia, time to first bowel movement, and the length of stay compared to liberal fluid therapy without using hemodynamic goals”

3)    “Both patients randomized to have GD fluid strategy and liberal fluid therapy without hemodynamic goals received more perioperative fluid than those managed with non-GD therapy and a restrictive fluid strategy, respectively.”

4)     “Although both GD and liberal fluid therapy both used a large amount of perioperative fluid, their effects on perioperative outcomes were different; patients in the GD groups had a shorter length of stay, time to recovery of gastrointestinal function, and a lower incidence of pneumonia compared to those in the liberal groups;

5)     “No specific fluid management strategy was associated with an improvement in mortality”

6)     “Significant heterogeneity in continuous outcome was observed, but publication bias was not apparent.”

This study showed that both methods of GD fluid therapy and liberal use of fluid w/o hemodynamics goals ended up using a large amount of fluid intraop. But the end outcomes still favored the use of hemodynamic monitoring. With the limited data available, significant uncertainty remains concerning the relative benefits of GD and restrictive fluid strategies, or the superiority of one modality of hemodynamic monitoring over another.