Predicting volume responsiveness

One of the current Holy Grails of ED critical care is to find a reliable measure of fluid responsiveness in those patients with impaired organ perfusion, such as those with severe sepsis. This would enable us to identify those patients whose cardiac output would be improved by fluid therapy, and avoid subjecting ‘non-responders’ to the risks associated with fluid overload. Thanks to the uptake of early goal-directed therapy in sepsis, under-resuscitation is now much less common in the ED. However a growing evidence base reveals the dangers of over-resuscitation. We have a responsibility to optimise fluid therapy as best we can with the equipment we have, according to the latest evidence.

Inferior Vena Cava Ultrasound
Some tests of fluid responsiveness rely on the effect of respiration-induced changes in pleural pressure on the circulation. Inferior vena cava (IVC) size and degree of inspiratory collapse correlate with central venous pressure (CVP), but CVP is not a reliable predictor of volume status or responsiveness. Skinny, collapsing IVCs detected on ultrasound suggest volume responsiveness, but the lack of this finding does not exclude fluid responsiveness. IVC size and measurement can be affected by patient position, probe position, and a variety of health states from athleticism to increased abdominal pressure.

Pulse Pressure Variation
Respiratory pulse pressure variation derived from an arterial line trace in mechanically ventilated patients who are adequately sedated and receiving large tidal volumes can predict fluid responsiveness too. Variability in tidal volume, the presence of spontaneous breathing activity in a ventilated patient, and cardiac dysrhythmia can all confound the usefulness of this method.

End expiratory occlusion
Another test in mechanically ventilated patients is the end expiratory occlusion test. A positive pressure inspiratory breath cyclically decreases the left cardiac preload. Occluding the circuit at end-expiration prevents this cyclic impediment in left cardiac preload and acts like a fluid challenge. A 15 second expiratory occlusion is performed and an increase in pulse pressure or (if you can measure it) cardiac index predicts fluid responsiveness with a high degree of accuracy. The patient must be able to tolerate the 15 second interruption to ventilation without initiating a spontaneous breath.

Passive Leg Raise
Passive leg raising (PLR) involves measuring cardiac output (or its surrogate, velocity-time integral, or VTI) before and after tilting the semirecumbent patient supine and raising the legs to 45 degrees. This ‘autotransfuses’ blood from the lower limbs to the core and acts as a reversible fluid challenge. An increase in VTI identifies fluid responders. It would be nice if a PLR-induced increase in blood pressure revealed the answer, but BP does not reliably inform us of changes in cardiac output.

All these tests have limitations. Pulse pressure variation fails in patients with low respiratory system compliance, such as is found in ARDS(1). End-expiratory occlusion and PLR work in low respiratory system compliance, but the former still requires mechanical ventilation, and the latter requires a means of estimating cardiac output or a surrogate – oesophageal Doppler, the velocity-time integral measured by transthoracic echocardiography, and femoral artery flow (measured by arterial Doppler) have all been used. Non-invasive cardiac output monitors that are not operator dependent exist, such as the NICOM(TM) bioreactance device. Bioreactance cardiac output measurement is based on an analysis of relative phase shifts of an oscillating current that occurs when this current traverses the thoracic cavity. Its advantages are that it is noninvasive, it does not require endotracheal intubation or an arterial line, and it provides a good estimate of stroke volume in patients with atrial fibrillation.

A recent study evaluating the combination of PLR with NICOM(TM) bioreactance monitoring revealed that another tool could indicate volume responsiveness: an increase in carotid blood flow after PLR, as measured by carotid Doppler flow imaging(2). A threshold increase in carotid Doppler flow imaging of 20% for predicting volume responsiveness had a sensitivity and specificity of 94% and 86%, respectively. This was studied in a heterogenous group of hemodynamically unstable patients, suggesting applicability to the kind of patients who present to the ED, although numbers were small so more validation is required.

End-tidal carbon dioxide
End-tidal carbon dioxide (ETCO2) levels depend on cardiac output. Increasing cardiac output with a fluid challenge or PLR increases ETCO2,as long as ventilatory and metabolic conditions remain stable. In a recent small study, a PLR-induced increase in ETCO2 ≥ 5 % predicted a fluid-induced increase in cardiac index ≥ 15 % with sensitivity of 71 % (95 % confidence interval: 48-89 %) and specificity of 100 (82-100) %(3). The maximal effects of PLR on CI and ETCO2 were observed within 1 min.

So what can I use?
In summary, differentiating fluid responders from non-responders in the ED remains a challenge. The method used depends on available equipment and expertise, and whether the patient is spontaneously breathing or mechanically ventilated. The NICOM(TM) shows great promise but until your department can afford one, ultrasound is the way to go; small collapsing IVCs suggest fluid responders. Learning to measure a VTI on transthoracic echo or carotid Doppler flow will help you assess the response to a PLR in spontaneously ventilating patients. If they’re mechanically ventilated, then looking for an ETCO2 rise after PLR could be a simpler alternative.

 
I look forward to more studies on these modalities, and to trying some of them in the resus room at every available opportunity.

 

1. Passive leg-raising and end-expiratory occlusion tests perform better than pulse pressure variation in patients with low respiratory system compliance
Crit Care Med. 2012 Jan;40(1):152-7
Abstract

2. The use of bioreactance and carotid doppler to determine volume responsiveness and blood flow redistribution following passive leg raising in hemodynamically unstable patients
Chest. 2013 Feb 1;143(2):364-70
Abstract

3. End-tidal carbon dioxide is better than arterial pressure for predicting volume responsiveness by the passive leg raising test
Intensive Care Med. 2013 Jan;39(1):93-100
Abstract

Swallow a camera in GI bleed

Two recent studies evaluate the use of a novel ingestable camera to diagnose upper gastrointestinal bleeding in emergency department patients.

The potential advantages of video capsule endoscopy over traditional endoscopy could include immediate availability, avoidance of sedation, patient tolerance, and the ability to rule out active bleeding in the emergency department.

The device used was the PillCam ESO2 – shown here in this animation:

Further research is needed. These small interesting studies demonstrate the potential for this imaging technology to be used in stable patients presenting to emergency departments. Since it can only diagnose rather than treat, it would not appear to have any role in unstable patients.

Video capsule endoscopy in the emergency department: a prospective study of acute upper gastrointestinal hemorrhage.
Ann Emerg Med. 2013 Apr;61(4):438-443
Abstract

Capsule endoscopy in acute upper gastrointestinal hemorrhage: a prospective cohort study
Endoscopy. 2013 Jan;45(1):12-9
Abstract

Point of care analysis of intraosseous samples

Some good news for remote, rural, prehospital, and retrieval medicine clinicians who rely on point of care testing with the i-STAT® device. An animal study confirmed the reliability of testing aspirates from intraosseous samples taken from the tibia(1).

This is also good news for hospital practitioners when it comes to the acquisition of blood gas results, since there are concerns over the potential damage to blood gas analysers by bone marrow contents in the samples.

The researchers tested blood gases, acid–base status, lactate, haemoglobin, and electrolytes, and compared these with results from an arterial sample.

There was no malfunction of the equipment. Most of the acid–base parameters showed discrepancies between arterial and osseous samples: the average pH and base excess were consistently lower whilst pCO2 and lactate were higher in the intraosseous samples compared to the arterial. However the overall small degree and predictable direction of discrepancy in these values should preserve the clinical usefulness of intraosseous gases if these findings can be replicated in human subjects. pO2 was obviously very different between osseous and arterial samples.

They noted that aspiration of intraosseous samples was generally straightforward, especially immediately after placement of the cannulae, but on a few occasions more forceful aspiration was needed. They point out that this could possibly cause cellular lysis and affect the potassium analysis.

The authors consider the issue of how much aspirate should be discarded before taking a sample after intraosseous cannula insertion, and refer to a prior study which suggested that 2mL is adequate.

Summary

• Intraosseous aspirate can be tested on an i-STAT® point-of-care analyser
• Haemoglobin and electrolytes show good correlation with arterial samples
• Acid-base, pCO2, and lactate differ slightly from arterial results but in a predictable direction and results are still likely to be clinically useful in an emergency
• It may be worth discarding the first 2 ml of aspirate
• These results require validation in human subjects

Analysis of intraosseous samples using point of care technology–an experimental study in the anaesthetised pig
Resuscitation. 2012 Nov;83(11):1381-5
Click to read abstract

Infectious biomarkers in the critically ill

A study examining patterns of procalcitonin in a group of critically ill patients(1) showed some interesting findings:

Shock was associated with higher procalcitonin values independent of the presence of infection

Procalcitonin (PCT) levels were less in patients who developed infections later during their ICU stay compared with those who had infections when admitted to ICU.

The accompanying editorial(2) reminds us about commonly used inflammatory biomarkers.

White blood cells are influenced by almost every inflammatory stimulus, rendering them unhelpful in the management of severely ill patients.

Daily monitoring of CRP levels can identify ICU-acquired infections early, and some prognostic information can be provided by how rapidly CRP levels respond to treatment.

PCT rises early in severe sepsis, mainly by pneumonia and bloodstream infections, and can reflect the severity of the systemic inflammatory response syndrome to infection. PCT is more specific than CRP for infection compared with non-infectious causes of systemic inflammatory response syndrome. However PCT can also be increased in noninfectious diseases such as acute pancreatitis and cardiogenic shock.

1. Longitudinal changes in procalcitonin in a heterogenous group of critically ill patients
Crit Care Med. 2012 Oct;40(10):2781-2787
Click for Abstract

2. The many facets of procalcitonin in the critically ill population
Crit Care Med. 2012 Oct;40(10):2903-5

COPD and heart disease interactions

Ischaemic heart disease (IHD) and chronic obstructive pulmonary disease (COPD) often affect the same patient; in fact, more than one-third of patients with angiography-proven IHD also have COPD on spirometry(1).
A recent study suggests COPD exacerbations in patients with IHD were associated with longer (5 more days) recovery times and suffered more severe breathlessness between exacerbations(2).

An accompanying editorial highlights some important points:

• Patients admitted with COPD exacerbations are more susceptible to myocardial infarction during the admission.

• Infective COPD exacerbations may contribute to heart failure through systemic inflammation, autonomic activation, and increased fluid in the lung. Lung infection can increase ventilation/perfusion mismatch and increased work of breathing, further straining the heart.

• Heart failure can be very difficult to diagnose during a COPD exacerbation because cough, dyspnoea and wheeze are common to both disorders. Physical examination may not be discriminatory, and chest radiography is insensitive to milder degrees of heart failure.

The authors recommed a high index of suspicion combined with consideration of biomarkers (BNP or pro-BNP) and imaging such as echocardiography or even nuclear medicine scans, cardiac MRI, and cardiac catheterisation.

So, next time you’re managing a COPD exacerbation, ask yourself:

• Could there be concomitant heart failure contributing to symptoms?

• If not, is the patient at risk of cardiac events during this admission, for which we need to be vigilant?

• Do I need to consider additional laboratory (BNP) or imaging (echo) investigations? Remember BNP may be elevated in pneumonia and other non-cardiac critical illness, although a normal BNP rules out heart failure.

• Should I add empiric anti-failure therapy to the acute treatment regimen?

• If there is combined COPD exacerbation and heart failure, are there any conflicting priorities in therapy (eg. the pros and cons of beta-agonists, anticholinergics, and steroids)?

1. The complex relationship between ischemic heart disease and COPD exacerbations
Chest. 2012 Apr;141(4):837-8

2. The impact of ischemic heart disease on symptoms, health status, and exacerbations in patients with COPD
Chest. 2012 Apr;141(4):851-7

Click to read abstract

Lung ultrasound for pneumothorax by paramedics

This UK study showed that paramedics could successfully acquire and identify lung ultrasound images after a two day course. The course covered the identification and management of patients who present with serious thoracic injury, with a specific focus on the use of thoracic ultrasound during early prehospital assessment. Standard 2D images for pleural sliding and comet tails and M-Mode for the ‘seashore sign’ were acquired, and colour Doppler was also used to assist in the identification of pleural sliding.

Objective This trial investigated whether advanced paramedics from a UK regional ambulance service have the ability to acquire and interpret diagnostic quality ultrasound images following a 2-day programme of education and training covering the fundamental aspects of lung ultrasound.

Method The participants were tested using a two-part examination; assessing both their theoretical understanding of image interpretation and their practical ability to acquire diagnostic quality ultrasound images. The results obtained were subsequently compared with those obtained from expert physician sonographers.

Results The advanced paramedics demonstrated an overall accuracy in identifying the presence or absence of pneumothorax in M-mode clips of 0.94 (CI 0.86 to 0.99), compared with the experts who achieved 0.93 (CI 0.67 to 1.0). In two-dimensional mode, the advanced paramedics demonstrated an overall accuracy of 0.78 (CI 0.72 to 0.83), compared with the experts who achieved 0.76 (CI 0.62 to 0.86). In total, the advanced paramedics demonstrated an overall accuracy at identifying the presence or absence of pneumothorax in prerecorded video clip images of 0.82 (CI 0.77 to 0.86), in comparison
with the expert users of 0.80 (CI 0.68 to 0.88). All of the advanced paramedics passed the objective structured clinical examination and achieved a practical standard considered by the examiners to be equivalent to that which would be expected from candidates enrolled on the thoracic module of the College of Emergency Medicine level 2 ultrasound programme.

Conclusion This trial demonstrated that ultrasound-naive practitioners can achieve an acceptable standard of competency in a simulated environment in a relatively short period of time.

Acquisition and interpretation of focused diagnostic ultrasound images by ultrasound-naive advanced paramedics: trialling a PHUS education programme
Emerg Med J, 2012 vol. 29 (4) pp. 322-326

Only when I laugh

A middle-aged martial arts enthusiast was training in Krav Maga, and participated in a high-contact punching and grappling sparring exercise in which his (younger, heavier) partner threw him to the ground and landed on him. During the throw the patient felt a ‘pop’ in his right side, and wondered whether he’d fractured a rib. During the subsequent five rounds against two additional sparring partners he noticed a clicking in the same area every time he was grappling, and pain in the right side when pushing up off the floor with his right arm. As a trained emergency physician, he assessed his own level of breathing comfort throughout the training to reassure himself he didn’t have a significant pneumothorax, and therefore elected to continue to fight in the interests of assessing his ability to defend himself while injured.

Pain on deep inspiration, coughing, and squeezing the chest suggested a fractured rib, so out of curiosity at work the next day he ultrasounded the area of maximum tenderness:

Examination of the lung confirmed pleural sliding, B-lines, and ‘pearls on a string’, which excluded pneumothorax.

Sonography is more sensitive than radiography for the detection of rib fractures and may also detect costochondral junction injuries and disruption of costal cartilage¹. This video from Hennepin County Medical Centre takes you through the simple procedure:

Although the management of rib fractures is no different from that of chest wall contusion, knowledge of the presence of fracture in this case is helpful to this patient in deciding when to return to the questionably sane ‘hobby’ of fighting bigger guys half his age.

The patient’s consent was obtained prior to the publication of the ultrasound image.

1. Sonography Compared with Radiography in Revealing Acute Rib Fracture
AJR Am J Roentgenol. 1999 Dec;173(6):1603-9.
Full text article
Click to read abstract

International recommendations for lung ultrasound

A multidisciplinary panel of 28 experts from eight countries reviewed the literature and came up with consensus guidelines in point-of-care lung ultrasound. There were some big names involved – all the big players in emergency/critical care ultrasound from around the World. Conspicuously absent were Matt and Mike from the Emergency Ultrasound Podcast, but maybe there was a maximum awesomeness limit or something.

Here are some snippets, taken out of context and without the grade of recommendation attached. Try to get hold of the original if you can, which might not be easy. I never understand it when ‘international recommendations’ are published as subscription-only articles. Either they want people to follow them or not. Oh well – here are some of their recommendations:

Pneumothorax

• The sonographic signs of pneumothorax include the following: Presence of lung point(s); Absence of lung sliding; Absence of B-lines; Absence of lung pulse
• The lung pulse refers to the subtle rhythmic movement of the visceral upon the parietal pleura with cardiac oscillations and is a rule-out sign for pneumothorax
• In the supine patient, the sonographic technique consists of exploration of the least gravitationally dependent areas progressing more laterally.
• Bedside lung ultrasound is a useful tool to differentiate between small and large pneumothorax, using detection of the lung point.

Interstitial syndrome

• B-lines are defined as discrete laser-like vertical hyperechoic reverberation artifacts that arise from the pleural line (previously described as ‘‘comet tails’’), extend to the bottom of the screen without fading, and move synchronously with lung sliding.
• The presence of multiple diffuse bilateral B-lines indicates interstitial syndrome. Causes of interstitial syndrome include the following conditions: Pulmonary edema of various causes; Interstitial pneumonia or pneumonitis; Diffuse parenchymal lung disease (pulmonary fibrosis)

Lung consolidation

• The sonographic sign of lung consolidation is a subpleural echo-poor region or one with tissue-like echotexture.
• Lung ultrasound is a clinically useful tool to rule in pneumonia; however, lung ultrasound does not rule out consolidations that do not reach the pleura.
• In mechanically ventilated patients lung ultrasound should be considered as it is more accurate than portable chest radiography in the detection of consolidation.

Pleural effusion

• Both of the following signs are present in almost all free effusions: A space (usually anechoic) between the parietal and visceral pleura; Respiratory movement of the lung within the effusion (‘‘sinusoid sign’’)
• In opacities identified by chest radiography, lung ultrasound should be used because it is more accurate than chest radiography in distinguishing between effusion and consolidation.
• Visualization of internal echoes, either of mobile particles or septa, is highly suggestive of exudate or hemothorax

BACKGROUND: The purpose of this study is to provide evidence-based and expert consensus recommendations for lung ultrasound with focus on emergency and critical care settings.

METHODS: A multidisciplinary panel of 28 experts from eight countries was involved. Literature was reviewed from January 1966 to June 2011. Consensus members searched multiple databases including Pubmed, Medline, OVID, Embase, and others. The process used to develop these evidence-based recommendations involved two phases: determining the level of quality of evidence and developing the recommendation. The quality of evidence is assessed by the grading of recommendation, assessment, development, and evaluation (GRADE) method. However, the GRADE system does not enforce a specific method on how the panel should reach decisions during the consensus process. Our methodology committee decided to utilize the RAND appropriateness method for panel judgment and decisions/consensus.

RESULTS: Seventy-three proposed statements were examined and discussed in three conferences held in Bologna, Pisa, and Rome. Each conference included two rounds of face-to-face modified Delphi technique. Anonymous panel voting followed each round. The panel did not reach an agreement and therefore did not adopt any recommendations for six statements. Weak/conditional recommendations were made for 2 statements, and strong recommendations were made for the remaining 65 statements. The statements were then recategorized and grouped to their current format. Internal and external peer-review processes took place before submission of the recommendations. Updates will occur at least every 4 years or whenever significant major changes in evidence appear.

CONCLUSIONS: This document reflects the overall results of the first consensus conference on “point-of-care” lung ultrasound. Statements were discussed and elaborated by experts who published the vast majority of papers on clinical use of lung ultrasound in the last 20 years. Recommendations were produced to guide implementation, development, and standardization of lung ultrasound in all relevant settings.

International evidence-based recommendations for point-of-care lung ultrasound
Intensive Care Med. 2012 Apr;38(4):577-91

Spinal imaging for the adult obtunded blunt trauma patient

‘You can’t clear the cervical spine until the patient wakes up!’ How often have you heard this said about a patient with severe traumatic brain injury who may not ‘wake up’ for weeks, if at all?

A controversial area, but many institutions now allow collar removal if a neck CT scan is normal. Does this rule out injury with 100% sensitivity? No – but it probably pushes the balance of risk towards removing the collar – an intervention with no evidence for benefit and plenty of reasons why it may be harmful to ventilated ICU patients. For example, clearing the cervical spine based on MDCT was associated with less delirium and less ventilator associated pneumonia, both of which have been associated with increased mortality in critically ill patients (this is referenced in the paper below).

The UK’s Intensive Care Society has had pragmatic guidelines along these lines since 2005, which can be found here. This month’s Intensive Care Medicine publishes an updated literature review providing some further support to this approach.

PURPOSE: Controversy exists over how to ‘clear’ (we mean enable the clinician to safely remove spinal precautions based on imaging and/or clinical examination) the spine of significant unstable injury among clinically unevaluable obtunded blunt trauma patients (OBTPs). This review provides a clinically relevant update of the available evidence since our last review and practice recommendations in 2004.

METHODS: Medline, Embase. Google Scholar, BestBETs, the trip database, BMJ clinical evidence and the Cochrane library were searched. Bibliographies of relevant studies were reviewed.

RESULTS: Plain radiography has low sensitivity for detecting unstable spinal injuries in OBTPs whereas multidetector-row computerised tomography (MDCT) approaches 100%. Magnetic resonance imaging (MRI) is inferior to MDCT for detecting bony injury but superior for detecting soft tissue injury with a sensitivity approaching 100%, although 40% of such injuries may be stable and ‘false positive’. For studies comparing MDCT with MRI for OBTPs; MRI following ‘normal’ CT may detect up to 7.5% missed injuries with an operative fixation in 0.29% and prolonged collar application in 4.3%. Increasing data is available on the complications associated with prolonged spinal immobilisation among a population where a minority have an actual injury.

CONCLUSIONS: Given the variability of screening performance it remains acceptable for clinicians to clear the spine of OBTPs using MDCT alone or MDCT followed by MRI, with implications to either approach. Ongoing research is needed and suggestions are made regarding this. It is essential clinicians and institutions audit their data to determine their likely screening performances in practice.

Clinical review: spinal imaging for the adult obtunded blunt trauma patient: update from 2004
Intensive Care Med. 2012 Mar 10. [Epub ahead of print]

Prehospital echo predicts arrest outcome

In hospital, the detection of cardiac standstill with ultrasound predicts a fatal outcome from cardiac arrest with a high degree of accuracy. A similar finding has been made in the prehospital setting. Interestingly, it was a better predictor than other commonly recognised factors associated with outcome: the presence of asystole, down time, bystander CPR, or end-tidal CO₂ levels.

Introduction. The prognostic value of emergency echocardiography (EE) in the management of cardiac arrest patients has previously been studied in an in-hospital setting. These studies mainly included patients who underwent cardiopulmonary resuscitation (CPR) by emergency medicine technicians at the scene and who arrived at the emergency department (ED) still in a state of cardiac arrest. In most European countries, cardiac arrest patients are normally treated by physician-staffed emergency medical services (EMS) teams on scene. Transportation to the ED while undergoing CPR is uncommon. Objective. To evaluate the ability of EE to predict outcome in cardiac arrest patients when it is performed by ultrasound-inexperienced emergency physicians on scene.

Methods. We performed a prospective, observational study of nonconsecutive, nontrauma, adult cardiac arrest patients who were treated by physician-staffed urban EMS teams on scene. Participating emergency physicians (EPs) received a two-hour course in EE during CPR. After initial procedures were accomplished, EE was performed during a rhythm and pulse check. A single subxiphoid, four-chamber view was required for study enrollment. We defined sonographic evidence of cardiac kinetic activity as any detected motion of the myocardium, ranging from visible ventricular fibrillation to coordinated ventricular contractions. The CPR had to be continued for at least 15 minutes after the initial echocardiography. No clinical decisions were made based on the results of EE.

Results. Forty-two patients were enrolled in the study. The heart could be visualized successfully in all patients. Five (11.9%) patients survived to hospital admission. Of the 32 patients who had cardiac standstill on initial EE, only one (3.1%) survived to hospital admission, whereas four out of 10 (40%) patients with cardiac movement on initial EE survived to hospital admission (p = 0.008). Neither asystole on initial electrocardiogram nor peak capnography value, age, bystander CPR, or downtime was a significant predictor of survival. Only cardiac movement was associated with survival, and cardiac standstill at any time during CPR resulted in a positive predictive value of 97.1% for death at the scene.

Conclusion. Our results support the idea of focused echocardiography as an additional criterion in the evaluation of outcome in CPR patients and demonstrate its feasibility in the prehospital setting.

Cardiac Movement Identified on Prehospital Echocardiography Predicts Outcome
Prehosp Emerg Care. 2012 Jan 11. [Epub ahead of print]

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