Intensive care bedside echocardiography: true or a distant dream?

Flato, Uri Adrian Prync; Campos, André Luis de; Trindade, Matheus Ribas; Guimarães, Hélio Penna; Vieira, Marcelo Luiz Campos; Brunori, Fernando

doi:10.1590/S0103-507X2009000400015

Abstracts

During the last few years, technological development and acquired experience advanced and the echocardiogram has become an important and useful tool in intensive care unit environment. Data obtained from semi quantitative Doppler echocardiography (transthoracic and transesophageal) evaluation has contributed to an appropriate patient monitoring and management. Echocardiography as a diagnostic, prognostic and monitoring method for fluid responsiveness assessment has become available nowadays since hand-carried ultrasound devices are portable and cheaper. Adequate training and development of appropriateness criteria for use of echocardiography in intensive care unit may lead to a standard use as a bedside tool.

Echocardiography; Intensive care; Heart arrest; Inservice training; Point-of-care systems

Nos últimos anos, com o avanço tecnológico e a experiência adquirida, o ecocardiograma tem se tornado uma ferramenta importante e cada vez mais utilizada no ambiente de terapia intensiva. As informações obtidas, através da ecocardiografia transtorácica e da ecocardiografia transesofágica corroboraram com o monitoramento e o cuidado centrado no paciente. Seu papel como ferramenta de diagnóstico, prognóstico e monitoramento da resposta à infusão de fluidos (fluído-responsividade) tornaram-se disponíveis nos dias de hoje, em razão da portabilidade e diminuição dos custos na aquisição dos equipamentos. O treinamento adequado, assim como o desenvolvimento de diretrizes relacionadas à utilização do ecocardiograma na unidade de terapia intensiva, possibilitarão a padronização deste método assim como sua implementação à beira do leito.

Ecocardiografia; Cuidados intensivos; Parada cardíaca; Capacitação em serviço; Sistemas automatizados de assistência junto ao leito

REVIEW ARTICLE

^IPhysician - Intensive Care Unit - Instituto Dante Pazzanese de Cardiologia - São Paulo (SP), Brazil

^IIPhysician - Intensive Care Unit - Hospital Universitário da Universidade de Marília - UNIMAR - Marília (SP), Brazil

^IIIPhysician - Internal Medicine Intensive Care Unit - Universidade Federal de São Paulo - UNIFESP - São Paulo (SP), Brazil

^IVPhysician - Echocardiography Service - Instituto do Coração (InCor) da Faculdade de Medicina da Universidade de São Paulo - USP - São Paulo (SP), Brazil

^VPhysician - Intensive Care Unit - Hospital Leforte - São Paulo (SP), Brazil

Author for correspondence

ABSTRACT

During the last few years, technological development and acquired experience advanced and the echocardiogram has become an important and useful tool in intensive care unit environment. Data obtained from semi quantitative Doppler echocardiography (transthoracic and transesophageal) evaluation has contributed to an appropriate patient monitoring and management. Echocardiography as a diagnostic, prognostic and monitoring method for fluid responsiveness assessment has become available nowadays since hand-carried ultrasound devices are portable and cheaper. Adequate training and development of appropriateness criteria for use of echocardiography in intensive care unit may lead to a standard use as a bedside tool.

Keywords: Echocardiography; Intensive care; Heart arrest; Inservice training; Point-of-care systems

INTRODUCTION

In the last 10 years the systematic introduction of semi-continued echocardiography in intensive care units and in some services has made this method a valuable tool for severely ill patients management. Conditions where early diagnosis is sometimes decisive for a patient management, e.g. in cardiac tamponade and/or aortal dissecation, reiterate its implementation relevance and need.^(1-2) Currently available equipments portability, and patient-focused training (point of care echocardiography) justify its use by intensivist physicians. Some recommendations suggested for its use are in chart 1.

Appropriate perfusion and optimized oxygen supply are the major intensive care objectives in circulatory dysfunction patients. Cardiac output (CO) is a variable closely related to venous return, which is defined as the difference between right atrium pressure and mean systemic filling pressure (MSFP). Consequently, the CO should be proportional to the blood flow arriving the heart, and, depending on the Frank-Starling curve patient's situation,⁽³⁾ preload increase by a volume test may either increase or not the cardiac output. In hypovolemic conditions, probably the increased venous return will increase right ventricle preload, and consequently the left ventricle's, thus optmizing the systolic volume. This situation is said preload dependent, and the patient will be considered as a volume test responder. A frequent intensive care question is knowing the patients' "volume status", and how to evaluate if tissue perfusion targeted therapeutic interventions are towards the right direction, i.e. if they are beneficial to the patient. With such questions, we perform CO monitoring as a valuable tool for critically ill patients evaluation. A fundamental aspect in these patients is the CO determination, which can't be reliably determined by physical examination. The Swan Ganz catheter remains as the current gold standard, however its use has been reduced based on the last two years published scientific evidence.⁽⁴⁾ Thus, new non-invasive, safe, reliable and reproducible CO monitoring technologies, among them echocardiography, may mean considerable advantage on these patients management in comparison with the Swan Ganz catheter use.⁽⁵⁾ Other non-invasive CO monitoring methods are listed on chart 2.

In addition to static measures evaluation, its implementation has allowed analyzing the systolic volume variation (dynamic respiratorycycle-related measurements), which is proportional to pulse-pressure (PP) and delta PP.^(6-8) Another echocardiography tool is the possibility of estimating left ventricular filling pressure (LVFP), usually correlated with pulmonary wedge capilary pressure (PWCP), in the absence of significant valve changes, such as moderate to severe mitral valve incompetence. For this, the relationship between the trans-mitral (pulsed doppler) flow measure, positioned above the mitral valve closure (ventricular cavity), wave (E), i.e. rapid filling phase, and the tissue doppler (E') measure, positioned on the septal or lateral mitral ring is used. The E/E' <8 ratio predicts a LVFP < 12 mmHg; E/E' > 15 predicts LVFP > 18 mmHg, and intermediate values are in a grey zone.⁽⁹⁾ Left atrium pressure (LAP) may be estimated calculating the mitral regurgitation velocity integral in non-mitral valve disease patients. Practically, the non-invasive and validated gradient between left ventricle and left atrium is measured (4x peak mitral regurgitation velocity) in heart failure patients.⁽¹⁰⁾

Other echocardiographic measurements may help evaluating fluid-responsiveness, such as inferior cava vein distensibililty rate (ICVD), superior cava vein collapsing rate (SCVC), right ventricular systolic pressure (RVSP), right atrium pressure (RAP), and diastolic and end-systolic left ventricle area after volume infusion (Chart 3).

The echocardiogram dynamic both pressure and/or volume measurements advantages as compared to the static ones reside on that systolic and diastolic function, and valve changes, do not significantly interact with data interpretation, and thus with therapeutic choice. By inferior vena cava collapsing rate (IVCC), the inferior vena cava (IVC) diameter by subcostal echocardiographic section, aligning the cursor on mode M (motion) 2 cm from RA, we can estimate the right atrium pressure (Chart 4 and Figure 1).⁽⁹⁾ Obviously there are situations where we can't evaluete RAP by IVC respiratory phasic range, such as in case of right ventricle (RV) dysfunction and cardiac tamponade. Inferior vena cava is a predominantly extra-thoracic vessel (intra-abdominal) related with right heart chambers suffering amplitude variation according to the respiratory cycle and systolic volume. During spontaneous inspiration there is a reduced intra-thoracic pressure and increased venous return. Its amplitude variation is related with RAP measurement, however there are not yet literature evidences for its use as fluid-responsiveness index in spontaneous breathing or mechanicaly assisted ventilation patients.

In mechanic ventilation patients, the IVC diameter variation is reversed, i.e., during the inspiratory phase there is increased intra-thoracic pressure and transference of pressures from the right atrium and, consequently, to the communicating vessels. In this case the vena cava has its diameter increased due to two main mechanisms:

1- RV preload reduction

2- RV increased post-load (positive pressure) associated with increased LV preload secondary to blood emptying from pulmonary bed and consequent systolic volume increase

This heart-lung coupling causes extra-thoracic vessels changes (both arterial and venous), which may represent volume replacement needs. In this situation, under mechanic ventilation, a percentage of inferior vena cava variation (%ΔIVC) and or superior (%ΔSVC) is used as parameter for volume infusion responsiveness and to identify them as either responders or non-responders.^(11,12)

In practice we use a %ΔIVC cutoff value above 12% according to Feissel et al.⁽¹³⁾or above 18% according to Barbier et al.⁽¹⁴⁾ Regarding the %ΔSVC,⁽¹⁵⁾ we use a higher cutoff value equal to 36% in controlled mechanic ventilation patients for fluid-responsiveness determination.

Information from echocardiographic analysis should be always considered before the patient's clinical picture.

Recently, De Backer et al. Studied the respiratory rate (RR >30) interference on systolic volume evaluation in relation to dynamic indices. Their data showed that %ΔSVC had no respiratory rate interference, and is perhaps a more suitable parameter in this settings, such e.g., in patients with acute respiratory distress syndrome (ARDS) and/or relevant metabolic acidosis patients.⁽¹⁶⁾

The CO measurement may be performed using transthoracic echocardiography (TTE) by measuring the left ventricle exit way times the Doppler measured aortal valve time-velocity integral (VTIAo). The systolic volume found with this method is then multiplied times the heart rate, thus finding the CO.^(17-18)

A growing set of evidence-based interventions is in place to guide intensive care clinical practice. As previously described, several and variable hemodynamic monitoring methods are available from echocardiogram. However, we show in the chart 5 the most consistent fluid-responsiveness related evidences, and their cutoff values.

In this context, several articles search for answers to help and study the fluid treatment effects in severely ill patients, with emphasis on echocardiography use. Despite Swan Ganz catheter use controversies, echocardiogram is a non-invasive test, easy to perform, with low morbidity and additional to other monitoring tools.⁽¹⁹⁾ A point to be highlighted is that the previously described studies had retrospectively evaluated the predictive value of hemodynamic indices after volume administration, and not necessarily the clinical outcome, which should be evaluated in prospective, randomized and larger samples trials. Second, we should bear in mind that not necessarily a patient responsive to a volume test (%IVC 25%) actually needs fluid. A practical example would be an anesthetized patient with preserved microcirculation parameters and rated as volume-responder in who excessive hydration can entail venous-capillary congestion and increased morbidity.⁽²⁰⁾ This deserves reflection as the patient's global clinical status and use of bedside echocardiographic data. Hemodynamic echocardiographic information use confirms the hospital's efforts on safety monitoring and measuring of ICU options, which can be focused on the structure, process and health care results.⁽²¹⁾

Another much useful echocardiographic fashion in the intensive care setting is transesophageal echocardiography. Its indications and diagnostic accuracy are reported on chart 6.^(22-24) In conditions, e.g. during post heart surgery period, TEE is sometimes imperative due to difficult transthoracic images acquisition. The initial choice for transthoracic or transesophageal echocardiogram depends on the heart structure to be evaluated, as well as the clinical setting involved (surgical center, intensive care unit, pre-hospital).⁽²⁵⁾

In the intensive care unit, an echocardiogram may be used as an ancillary method for cardiorespiratory arrest (CRA) differential diagnosis, specifically in pulseless electric activity (PEA) and asystolia, where spontaneous circulation return depends on reversion of the primary cause (hypovolemia, hypoxia, hiperkalemia, cardiac tamponade, pulmonary thromboembolism).

Particularly on PEA, with echocardiographic support, two forms were described: true PEA (no heart contractility associated to no pulse) and pseudo-PEA (myocardial contractility present, with no pulse) (Figure 2). This differentiation is important due to prognostic implications. The implementation of this new format during a CRA is being developed by well designed protocols, appropriate training and mainly, with no thoracic compressions interruptions.^(26-28) Perhaps, the introduction of new technologies improve the extra-hospital and hospital survival, unchanged for three decades.^(29,31) Blaivas et al.⁽³²⁾ evaluated 169 non-arrhythmic CRA patients (PEA asystolia) using echocardiogram during resuscitation maneuvers and demonstrated 100% mortality in patients with cardiac stand still. Other authors confirmed these findings, and suggested that echocardiogram cardiac stand still in non-arrhythmic CRA is, perhaps, enough to stop cardiopulmonary resuscitation efforts.^(33,34) With an agile and more accurate clinical status benefiting from a particular intervention identification, maybe resuscitation odds may be significantly improved. So far we only have some echocardiogram use in CRA cases and series reports. Nevertheless this is a field to be explored with a perspective of future guidelines implementation. Another important echocardiogram monitoring and diagnosis related point is identifying its effectiveness and clinical feasibility with specific situations protocols, such as shock, CRA and sepsis. Based on these concepts, some studies mentioned in the text may be summarized on chart 7, evidencing its feasibility. Among the studies we highlight FEER and BEAT as promising and reproducible.

Training and education in intensive care echocardiography

Echocardiography systematization and training within the intensive care unit depends on solid guidelines and continued medical education implementation. The support of national and international associations is fundamental for these principles certification conduction. Currently, in France 90% of intensive care units have echocardiography training in a 2 years-long program. Another interesting fact is that in England, 90% of intraoperative TEE are conducted by anesthesiologists. This absolutely does not mean that the intensivist physician will replace echocardiographists in the ICU, but that will use this tool to respond specific and contextualized questions. Were recently published by the World Interactive Network Focused on Critical Ultrasound (WINFOCUS) recommendations on the use of echocardiography in the intensive care settings, and also by the British Echocardiography Society and American College of Chest Physicians and French Speaking Reanimation Society.^(35-38) These guidelines recommend rational degrees of competency and training and how the echocardiogram should be performed. They propose three distinct levels of education, relating the echocardiography use in emergency conditions, as during CRA, and the need of requesting an expert evaluation when indicated and needed. The time to complete each phase depends on each institution's training, i.e., if there is a formal ICU echocardiography training during intensive medicine specialization, presence of preceptor echocardiography-expert cardiologists, and the ways of measuring students' performance based on different international associations' rules. WINFOCUS suggested a 2-year supervised training period, with at least 50 cases recorded yearly to achieve Level 2 competence (Chart 8). It is important highlighting the activity limits for different medical professionals, and the different horizons of echocardiography techniques use in intensive care and emergency settings. So far we have no Brazilian regulation on use of echocardiography for non-habilitated medical professionals, according to the Brazilian Society of Cardiology Echocardiography Department (DEPECO/SBC).

FINAL COMMENTS

The use of echocardiography in the intensive care and emergency settings is nowadays real in some European countries and North American centers. Possibly in a near future we can have the same rational in Latin American intensive care and emergency centers, such as predicting fluid responsiveness in critical ill patient.^(39-41) The both theoretical and practical qualifications and appropriate training are fundamental stones for this tool implementation. By scientific research and cooperation between both national and international medical associations, we can improve our daily practice, offering our patients better treatment and hoping our dream comes true.

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