Diagnostic and therapeutic implications of transesophageal echocardiography in medical ICU patients with unexplained shock, hypoxemia, or suspected endocarditis

Indications, Clinical Impact, and Complications of Critical Care Transesophageal Echocardiography: A Scoping Review

BACKGROUND

Critical care transesophageal echocardiography (ccTEE) is an increasingly popular tool used by intensivists to characterize and manage hemodynamics at the bedside. Its usage appears to be driven by expanded diagnostic scope as well as the limitations of transthoracic echocardiography (TTE) - lack of acoustic windows, patient positioning, and competing clinical interests (eg, the need to perform chest compressions). The objectives of this scoping review were to determine the indications, clinical impact, and complications of ccTEE.

METHODS

MEDLINE, EMBASE, Cochrane, and six major conferences were searched without a time or language restriction on March 31^st, 2021. Studies were included if they assessed TEE performed for adult critically ill patients by intensivists, emergency physicians, or anesthesiologists. Intraoperative or post-cardiac surgical TEE studies were excluded. Study demographics, indication for TEE, main results, and complications were extracted in duplicate.

RESULTS

Of the 4403 abstracts screened, 289 studies underwent full-text review, with 108 studies (6739 patients) included. Most studies were retrospective (66%), performed in academic centers (84%), in the intensive care unit (73%), and were observational (55%). The most common indications for ccTEE were hemodynamic instability, trauma, cardiac arrest, respiratory failure, and procedural guidance. Across multiple indications, ccTEE was reported to change the diagnosis in 52% to 78% of patients and change management in 32% to79% patients. During cardiac arrest, ccTEE identified the cause of arrest in 25% to 35% of cases. Complications of ccTEE included two cases of significant gastrointestinal bleeding requiring intervention, but no other major complications (death or esophageal perforation) reported.

CONCLUSIONS

The use of ccTEE has been described for the diagnosis and management of a broad range of clinical problems. Overall, ccTEE was commonly reported to offer additional diagnostic yield beyond TTE with a low observed complication rate. Additional high quality ccTEE studies will permit stronger conclusions and a more precise understanding of the trends observed in this scoping review.

Feasibility, utility, and safety of fully incorporating transesophageal echocardiography into emergency medicine practice

INTRODUCTION

Transthoracic echocardiography (TTE) is a standard procedure for emergency physicians (EPs). Transesophageal echocardiography (TEE) is known to have great utility in patients who are critically ill or in cardiac arrest and has been used by some EPs with specialized ultrasound (US) training, but it is generally considered outside the reach of the majority of EPs. We surmised that all of our EPs could learn to perform focused TEE (F-TEE), so we trained and credentialed all of the physicians in our group.

METHODS

We trained 52 EPs to perform and interpret F-TEEs using a 4-h simulator-based course. We kept a database of all F-TEE examinations for quality assurance and continuous quality feedback. Data are reported using descriptive statistics.

RESULTS

Emergency physicians attempted 557 total F-TEE examinations (median = 10, interquartile range = 5-15) during the 42-month period following training. Clinically relevant images were obtained in 99% of patients. EPs without fellowship or other advanced US training performed the majority of F-TEEs (417, 74.9%) and 94.3% (95% confidence interval [CI] = 91.4%-96.3%) had interpretable images recorded. When TTE and TEE were both performed (n = 410), image quality of TEE was superior in 378 (93.3%, 95% CI = 89.7%-95%). Indications for F-TEE included periarrest states (55.7%), cardiac arrest (32.1%), and shock (12.2%). There was one case of endotracheal tube dislodgement during TEE placement, but this was immediately identified and replaced without complication.

CONCLUSION

After initiating a mandatory group F-TEE training and credentialing program, we report the largest series to date of EP-performed resuscitative F-TEE. The majority of F-TEE examinations (75%) were performed by EPs without advanced US training beyond residency.

Three-dimensional critical care transesophageal echocardiography: A bedside tool in the diagnosis and management of shock

Critical care echocardiography has become fundamental in diagnosis, management, and monitoring of patients in shock. Transesophageal echocardiography has gained importance, particularly in critically ill patients under mechanical ventilation. We describe echocardiographic findings concerning a patient admitted with confusion, pulmonary edema, hypotension, and systolic murmur at apex.

Transesophageal echocardiography instead or in addition to transthoracic echocardiography in evaluating haemodynamic problems in intubated critically ill patients

Background

Transesophageal echocardiography (TEE) performed by intensivists is increasingly used in critically ill patients. However, TEE is usually not the preferred monitoring tool, especially when transthoracic echocardiography (TTE) appears to have addressed the clinical problems. As a result, it remains largely unknown whether TEE is a clinically valuable replacement or supplement for TTE as a primary tool in evaluating haemodynamic problems in critically ill surgical patients. The purpose of this study was to assess the diagnostic and therapeutic value of TEE instead or in addition to TTE in critically ill surgical patients with hemodynamic instability.

Methods

A prospective observational study was conducted. A total of 68 consecutive patients were enrolled from December 2016 to February 2018. TEE was routinely performed in addition to TTE, and the imaging data from TTE and TEE were successively disclosed to two different primary physicians, who reported any resulting changes in management. The two physicians were required to reach a consensus if there was any disagreement. The results of the additional TEE examination were compared with the clinical findings and TTE information. The image quality of TTE views was classified as a good (score 2), suboptimal (score 1) or poor view (score 0). According to the scores of TTE images, the patients were divided into two groups: patients with adequate TTE views (score ≥6) and inadequate TTE views (score <6).

Results

The results of additional TEE examination were classified into four categories. TEE failed to provide additional information about the initial diagnosis and therapy (class 1) in 26 patients (38.2%). Of the remaining 42 patients (61.8%), TEE instead or in addition to TTE revealed new findings or led to significant changes in therapy, as TTE supplied inadequate information. TEE used in addition to TTE led to a new diagnosis without therapeutic implications (class 2) in 11 patients (16.2%) and made a major clinical contribution leading to a therapeutic change (class 3) in 23 patients (33.8%). TEE used instead of TTE determined the diagnosis and therapy in 8 patients (11.8%) whose haemodynamic problems could not be addressed by TTE (class 4). In total, TEE had critical therapeutic benefits (class 3 and 4) that was not provided by TTE in 31 patients (45.6%). Of particular concern was that TEE had a higher proportion of therapeutic benefits to patients with inadequate TTE views than those with adequate TTE views (54.3% vs. 27.3%, P=0.036).

Conclusions

TEE as a feasible clinical tool is useful for critically ill surgical patients with hemodynamic instability, especially for the patients with inadequate TTE views. TEE instead or in addition to TTE could provide valuable information for diagnosis, which may bring significant therapeutic benefits.

Hemodynamic monitoring using trans esophageal echocardiography in patients with shock

Circulatory shock is a life-threatening condition responsible for inadequate tissue perfusion. The objectives of hemodynamic monitoring in this setting are multiple: identifying the mechanisms of shock (hypovolemic, distributive, cardiogenic, obstructive); choosing the adequate therapeutic intervention, and evaluating the patient's response. Echocardiography is proposed as a first line tool for this assessment in the intensive care unit. As compared to trans-thoracic echocardiography (TTE), trans-esophageal echocardiography (TEE) offers a better echogenicity and is the best way to evaluate deep anatomic structures. The therapeutic implication of TEE leads to frequent changes in clinical management. It also allows depicting sources of inaccuracy of thermodilution-based hemodynamic monitoring. It is a semi invasive tool with a low rate of complications. The first step in the hemodynamic evaluation of shock is to characterize the mechanisms of circulatory failure among hypovolemia, vasoplegia, cardiac dysfunction, and obstruction. Echocardiographic evaluation includes evaluation of LV systolic and diastolic function, as well as RV function, pericardium, measure of stroke volume and cardiac output, and evaluation of hypovolemia and fluid responsiveness. TEE can be used as a semi-continuous monitoring tool and can be repeated before and after therapeutic interventions (vasopressors, inotropes, fluid therapy, specific treatment such as pericardial effusion evacuation) to evaluate efficacy and tolerance of therapeutic interventions. In conclusion, TEE plays an important role in the management of circulatory failure when TTE is not enough to answer to the questions, although it is not a continuous tool of monitoring. TEE results must be integrated in a global evaluation, the first step being clinical examination. Whether TEE-directed therapy and close hemodynamic monitoring of shock has an impact on outcome remains debated.

Diagnostic Accuracy of Critical Care Transesophageal Echocardiography vs Cardiology-Led Echocardiography in ICU Patients

BACKGROUND

Critical care transesophageal echocardiography (ccTEE) performed by intensivists is increasingly used to investigate cardiorespiratory failure in the ICU. Validation of the accuracy of TEE in the hands of intensivists remains largely unknown. The goal of this study was to characterize the diagnostic accuracy of ccTEE.

METHODS

This study was a two-center, retrospective comparison between TEE studies performed and interpreted by intensivists and cardiology-led TEE or transthoracic echocardiography (TTE) performed and/or interpreted by cardiologists. The study period was December 2012 to December 2016 for all consecutive ICU patients who received an initial ccTEE and either a cardiology TEE or TTE within 72 h. Using the cardiology-conducted examination as the gold standard, we reported sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of ccTEE.

RESULTS

Comparisons between ccTEE and cardiology TEE/TTE performed yielded 56 patients (five ccTEE vs cardiology TEE and 51 ccTEE vs cardiology TTE). The comparison between ccTEE and cardiology TEE showed 100% sensitivity, specificity, PPV, NPV, and accuracy for the primary diagnosis and other major findings. For the combined ccTEE and cardiology TEE/TTE comparison, there was a high sensitivity/specificity/PPV/NPV/accuracy for the primary diagnosis (90%-100% range), as well as other major diagnoses (88%-100% range).

CONCLUSIONS

This study showed that ccTEE has a high sensitivity, specificity, PPV, NPV, and accuracy compared with the gold standard cardiology TEE or TTEs in critically ill patients, when performed by advanced echocardiogram-trained/experienced intensivists.

Better With Ultrasound: Transesophageal Echocardiography

Transesophageal echocardiography (TEE) is a safe and minimally invasive tool that can routinely provide high-quality anatomic and hemodynamic information in the severely ill. Despite its potential for frontline acute care clinicians, TEE use has typically been reserved for diagnostic experts in the cardiac-surgical milieu. With the continued evolution of point-of-care ultrasound into increasingly sophisticated domains, TEE has gained steady uptake in many nontraditional environments for both advanced echocardiographic assessment as well as answering more goal directed, fundamental questions. This article introduces the workings of the TEE transducer, presents a systematic approach to a goal-directed hemodynamic assessment, and includes a series of illustrative figures and narrated video presentations to demonstrate the techniques described.

Impact of Critical Care Transesophageal Echocardiography in Medical-Surgical ICU Patients: Characteristics and Results From 274 Consecutive Examinations

OBJECTIVE

Critical care echocardiography has become an integral tool in the assessment and management of critically ill patients. Critical care transesophageal echocardiography (TEE) offers diagnostic reliability, superior image quality, and an expanded diagnostic scope to transthoracic echocardiography. Despite its favorable attributes, TEE use in North American intensive care units (ICUs) remains relatively undescribed. In this article, we seek to characterize the feasibility, indications, and clinical impact of a critical care TEE program.

DESIGN

Retrospective, observational study.

SETTING

Tertiary care, academic critical care program consisting of 2 hospitals in Ontario, Canada.

PARTICIPANTS

Consecutive critical care TEE examinations on ICU patients performed between December 2012 and December 2016.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Consecutive critical care TEE studies on ICU patients from December 1, 2012, to December 31, 2016, were reviewed. The TEEs performed on cardiac surgery patients and those without reports were excluded. Examination details, including indications, complications, examination complexity (number of views, Doppler techniques), and clinical recommendations were aggregated and analyzed. Two hundred seventy-four TEE studies were performed by 38 operators. Common indications for TEE studies were hemodynamic instability (45.2%), assessment for infective endocarditis (22.2%), and cardiac arrest (20.1%). A change in patient management was proposed following 79.5% of TEE studies. Thirty-eight percent of TEE studies were performed during evening hours or on weekends. There were no mechanical complications.

CONCLUSIONS

Our observational data support intensivist-performed TEE as being safe and therapeutically influential across a broad range of indications. Our program's demonstrated feasibility and impact may act as a model for TEE adoption in other North American ICUs.

Initial clinical experience with a miniaturized transesophageal echocardiography probe in a cardiac intensive care unit

OBJECTIVE

To investigate the safety of a novel, miniaturized, monoplane transesophageal echocardiography probe (mTEE) and its potential as a hemodynamic monitoring tool.

DESIGN

This was a retrospective analysis of the clinical evaluation of a disposable mTEE in ventilated patients with severe cardiogenic shock requiring hemodynamic support. mTEE assessment was performed by operators with mixed levels of TEE training. Information on hemodynamic interventions based on mTEE findings was recorded.

SETTING

A tertiary university cardiac critical care unit.

PARTICIPANTS

Male and female critical care patients admitted to the unit with severe hemodynamic instability.

INTERVENTIONS

Insertion of miniaturized disposable TEE probe and hemodynamic and other critical care interventions based on this and conventional monitoring.

MEASUREMENTS AND MAIN RESULTS

In 41 patients (51.2% female, 73.2% after cardiac surgery), hemodynamic support probe insertion was accomplished without major complications. A total of 195 mTEE studies were performed, resulting in changes in therapy in 37 (90.2%) patients based on mTEE findings, leading to an improvement in hemodynamic parameters in 33 (80.5%) patients. Right ventricular (RV) failure was diagnosed in 25 patients (67.6%) and mTEE had a direct therapeutic impact on management of RV failure in 17 patients (68 %).

CONCLUSIONS

Insertion and operation of a novel, miniaturized transoesophageal echocardiography probe can be performed for up to 72 hours without major complications. Repeated assessment using this device provides complementary information to invasive monitoring in the majority of patients and has an impact on hemodynamic management.

Technological advances in perioperative monitoring: Current concepts and clinical perspectives

Minimal mandatory monitoring in the perioperative period recommended by Association of Anesthetists of Great Britain and Ireland and American Society of Anesthesiologists are universally acknowledged and has become an integral part of the anesthesia practice. The technologies in perioperative monitoring have advanced, and the availability and clinical applications have multiplied exponentially. Newer monitoring techniques include depth of anesthesia monitoring, goal-directed fluid therapy, transesophageal echocardiography, advanced neurological monitoring, improved alarm system and technological advancement in objective pain assessment. Various factors that need to be considered with the use of improved monitoring techniques are their validation data, patient outcome, safety profile, cost-effectiveness, awareness of the possible adverse events, knowledge of technical principle and ability of the convenient routine handling. In this review, we will discuss the new monitoring techniques in anesthesia, their advantages, deficiencies, limitations, their comparison to the conventional methods and their effect on patient outcome, if any.

Cardiac ultrasound and abdominal compartment syndrome

This review focuses on the available literature published about the evaluation of haemodynamic consequences of the abdominal compartment syndrome (ACS). Animal and clinical studies described decreased venous return, systemic vasoconstriction, systolic and diastolic dysfunction of left and right ventricles. Doppler echocardiography is a non-invasive bedside procedure which provides a complete haemodynamic evaluation of patients with ACS. Despite numerous evaluations in anesthesia during laparoscopic surgery, the use of echocardiography remains scarce in critically ill patients with ACS.

Prospective assessment of a score for assessing basic critical-care transthoracic echocardiography skills in ventilated critically ill patients

Background

We studied a score for assessing basic transthoracic echocardiography (TTE) skills exhibited by residents who examined critically ill patients receiving mechanical ventilation.

Methods

We conducted a prospective study in the 16 residents who worked in our medical-surgical ICU between 1 May 2008 and 1 November 2009. The residents received theoretical teaching (two hours) then performed supervised TTEs during their six-month rotation. Their basic TTE skills in mechanically ventilated patients were evaluated after one (M1), three (M3), and six (M6) months by two experts, who used a scoring system devised for the study. After scoring, residents gave their hemodynamic diagnosis and suggested a treatment.

Results

The 4 residents with previous TTE skills obtained a significantly higher total score than did the 12 novices at M1 (18 (16 to 19) versus 13 (10 to 15), respectively, P = 0.03). In the novices, the total score increased significantly during training (M1, 13 (10 to 14); M3, 15 (12 to 16); and M6, 17 (15 to 18); P < 0.001) and correlated significantly with the number of supervised TTEs (r = 0.68, P < 0.0001). In the overall population, agreement with experts regarding the diagnosis and treatment was associated with a significantly higher total score (17 (16 to 18) versus 13 (12 to 16), P = 0.002). A total score ≥ 19/20 points had 100% specificity (95% confidence interval, 79 to 100%) for full agreement with the experts regarding the diagnosis and treatment.

Conclusions

Our results validate the scoring system developed for our study of the assessment of basic critical-care TTE skills in residents.

Hemodynamic assessment of critically ill patients using a miniaturized transesophageal echocardiography probe

INTRODUCTION

Hemodynamic management in intensive care patients guided by blood pressure and flow measurements often do not sufficiently reveal common hemodynamic problems. Trans-esophageal echocardiography (TEE) allows for direct measurement of cardiac volumes and function. A new miniaturized probe for TEE (mTEE) potentially provides a rapid and simplified approach to monitor cardiac function. The aim of the study was to assess the feasibility of hemodynamic monitoring using mTEE in critically ill patients after a brief operator training period.

METHODS

In the context of the introduction of mTEE in a large ICU, 14 ICU staff specialists with no previous TEE experience received six hours of training as mTEE operators. The feasibility of mTEE and the quality of the obtained hemodynamic information were assessed. Three standard views were acquired in hemodynamically unstable patients: 1) for assessment of left ventricular function (LV) fractional area change (FAC) was obtained from a trans-gastric mid-esophageal short axis view, 2) right ventricular (RV) size was obtained from mid-esophageal four chamber view, and 3) superior vena cava collapsibility for detection of hypovolemia was assessed from mid-esophageal ascending aortic short axis view. Off-line blinded assessment by an expert cardiologist was considered as a reference. Inter-rater agreement was assessed using Chi-square tests or correlation analysis as appropriate.

RESULTS

In 55 patients, 148 mTEE examinations were performed. Acquisition of loops in sufficient quality was possible in 110 examinations for trans-gastric mid-esophageal short axis, 118 examinations for mid-esophageal four chamber and 125 examinations for mid-esophageal ascending aortic short axis view. Inter-rater agreement (Kappa) between ICU mTEE operators and the reference was 0.62 for estimates of LV function, 0.65 for RV dilatation, 0.76 for hypovolemia and 0.77 for occurrence of pericardial effusion (all P<0.0001). There was a significant correlation between the FAC measured by ICU operators and the reference (r=0.794, P (one-tailed)<0.0001).

CONCLUSIONS

Echocardiographic examinations using mTEE after brief bed-side training were feasible and of sufficient quality in a majority of examined ICU patients with good inter-rater reliability between mTEE operators and an expert cardiologist. Further studies are required to assess the impact of hemodynamic monitoring by mTEE on relevant patient outcomes.

A pilot study on safety and clinical utility of a single-use 72-hour indwelling transesophageal echocardiography probe

PURPOSE

To evaluate the hemodynamic monitoring capability and safety of a single-use miniaturized transesophageal echocardiography (TEE) probe left in place in ventilated critically ill patients.

METHODS

The probe was inserted in 94 patients and designed to be left in place for up to 72 h. Three views were obtained: the superior vena caval transverse, the mid-esophageal four-chamber, and the transgastric mid-papillary short-axis views. Observational data on the feasibility of insertion, complications, image quality, and influence on management were recorded and analyzed.

RESULTS

No failure of probe insertion was observed. The nasogastric tube had to be removed in 17 % of cases. Image quality was judged as adequate or optimal in 91/94 (97 %) of cases in the superior vena caval view, 89/94 (95 %) of cases in the four-chamber view, and 86/94 (91 %) of cases in the short-axis view. The duration of monitoring was 32 ± 23 h, allowing 2.8 ± 1.6 hemodynamic evaluations per patient that led to a mean of 1.4 ± 1.5 therapeutic changes per patient. Among the 263 hemodynamic assessments, 132 (50 %) had a direct therapeutic impact in 62 patients (66 %). Two patients developed lip ulceration from the probe, and two patients had self-limited gastric bleeding.

CONCLUSION

The single-use miniaturized probe could be inserted in all patients. Image quality was acceptable in the majority of cases, and the information derived from the device was useful in making management decisions in patients with hemodynamic failure on ventilatory support. Further studies are needed to confirm the good tolerance and to compare the new device with other hemodynamic monitoring techniques.

Core review: physician-performed ultrasound: the time has come for routine use in acute care medicine

The use of ultrasound in the acute care specialties of anesthesiology, intensive care, emergency medicine, and surgery has evolved from discrete, office-based echocardiographic examinations to the real-time or point-of-care clinical assessment and interventions. "Goal-focused" transthoracic echocardiography is a limited scope (as compared with comprehensive examination) echocardiographic examination, performed by the treating clinician in acute care medical practice, and is aimed at addressing specific clinical concerns. In the future, the practice of surface ultrasound will be integrated into the everyday clinical practice as ultrasound-assisted examination and ultrasound-guided procedures. This evolution should start at the medical student level and be reinforced throughout specialist training. The key to making ultrasound available to every physician is through education programs designed to facilitate uptake, rather than to prevent access to this technology and education by specialist craft groups. There is evidence that diagnosis is improved with ultrasound examination, yet data showing change in management and improvement in patient outcome are few and an important area for future research.

Transesophageal Echocardiography–Guided Hemodynamic Assessment and Management

Hemodynamic instability (shock) poses a major challenge in intensive care and is associated with increased mortality, morbidity, length of stay, and costs. The purpose of hemodynamic assessment and management is to detect the cause of hemodynamic instability in a given patient, provide actionable information for the physician, and thus help guide the management and resolution of hemodynamic instability. Although transesophageal echocardiography (TEE) has been the gold standard for hemodynamic assessment and management in the cardiac operating room, the invasive nature of conventional TEE has limited its use as a management tool in intensive care. Instead, one has seen a variety of indirect hemodynamic monitors used, despite now well understood limitations as described in a previous Critical Conversation in the July 2011 issue of this journal. Here we describe the use of TEE in intensive care as well as a new TEE system (the ImaCor hTEE system, ImaCor, Garden City, NY) with a miniaturized (approximately nasogastric tube sized), indwelling probe designed specifically for TEE-guided hemodynamic assessment and management in intensive care (hemodynamic TEE).

French survey on current use of ultrasound in the critical care unit: ECHOREA

INTRODUCTION

Over the last ten years, ultrasound became standard procedure in the intensive care unit (ICU).

STUDY DESIGN

A national survey to evaluate the use of this technique in French ICUs.

METHODS

Three hundred and twenty-seven units were contacted from the listing of the Société de réanimation de langue française (SRLF). A survey containing 20 questions addressing the availability, the training for, and the use of ultrasound was sent to the ICUs. Collection of data took place over a period of three months.

RESULTS

We received 132 completed surveys out of the 327 sent out (40%). Seventy-nine percent of the public community and private centers and 94% of the university centers had an available device in the unit. Forty percent of the units carried out five to ten examinations per week. Seventy-two percent had staff trained in echocardiography. Fifty-five percent used association of monitoring techniques for the haemodynamic assessment of patients with shock. Only 73% carried out formalized reports after examination. In more than 80%, the echocardiograph was also used for the evaluation of other organs.

CONCLUSION

Ultrasound, and particularly echocardiography, has taken on a more prominent role in the routine assessment of critically ill patients. The availability of equipment and of training has increased over the last ten years, but the demand for training in this area remains strong. This French survey confirms this technique became the "extension of the hand" of the intensivist in ICU.

Safety of transesophageal echocardiography

Since its introduction into the operating room in the early 1980s, transesophageal echocardiography (TEE) has gained widespread use during cardiac, major vascular, and transplantation surgery, as well as in emergency and intensive care medicine. Moreover, TEE has become an invaluable diagnostic tool for the management of patients with cardiovascular disease in a nonoperative setting. In comparison with other diagnostic modalities, TEE is relatively safe and noninvasive. However, the insertion and manipulation of the ultrasound probe can cause oropharyngeal, esophageal, or gastric trauma. Here, the authors review the safety profile of TEE by identifying complications and propose a set of relative and absolute contraindications to probe placement. In addition, alternative echocardiographic modalities (e.g., epicardial echocardiography) that may be considered when TEE probe placement is contraindicated or not feasible are discussed.

Echocardiography for hemodynamic evaluation in the intensive care unit

The use of echocardiography in the intensive care unit for patients in shock allows the accurate measurement of several hemodynamic variables in a noninvasive way. By using echocardiography as a hemodynamic monitoring tool, the clinician can evaluate several aspects of shock states, such as cardiac output and fluid responsiveness, myocardial contractility, intracavitary pressures, and biventricular interactions. However, to date, there have been few guidelines suggesting an objective hemodynamic-based examination in the intensive care unit, and most intensivists are usually not familiar with this tool. In this review, we describe some of the most important hemodynamic parameters that can be obtained at the bedside with transthoracic echocardiography.

Echocardiography in the Intensive Care Unit: Current Position, Future Directions

There are many indications for the use of echocardiography in the critically ill and little consensus about how best to provide training for intensivists in its use. There are a profusion of opinions, courses and accreditation pathways available for training in the UK. The National Point of Care Ultrasound working group aims to facilitate learning and training in both echocardiography and ultrasound. In this article, an intermediate level of training suitable for most general UK-based intensivists, that provides more depth than focused resuscitation-based protocols but less depth than British Society of Echocardiography accreditation pathways, is proposed which, if endorsed by Royal Colleges and specialist societies, could be developed into a viable national training programme within five years.

Inadequate visualization and reporting of ventricular function from transthoracic echocardiography after cardiac surgery

OBJECTIVES

The purpose of this study was to determine the incidence of and risk factors for inadequate reporting of ventricular function from transthoracic echocardiography after cardiac surgery.

DESIGN AND SETTING

A retrospective study of cardiac surgical patients at 1 university hospital.

PATIENTS

The first 300 consecutive patients who had transthoracic echocardiogram within the first 7 days after cardiac surgery.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The primary outcomes for this study were inadequate visualization of the left ventricle, the right ventricle, or both ventricles. Analysis of data from 300 patients identified inadequate imaging of the left ventricle in 50 (17%) cases, inadequate imaging of the right ventricle in 112 (37%) cases, inadequate imaging of both ventricles in 37 (12%) cases, and inadequate imaging of either the left or right ventricle in 125 (42%) cases. Increasing age, earlier postoperative day, male sex, and median sternotomy were associated with inadequate imaging.

CONCLUSIONS

Transthoracic imaging is often inadequate in patients who have undergone recent cardiac surgery. Patient and surgical characteristics influence reporting of right and left ventricular function.

Bedside ultrasonic detection of massive hemothorax due to superior vena cava perforation after hemodialysis catheter insertion

Hemothorax resulting from perforation of a great vessel is an uncommon but life-threatening complication which may occur during central venous insertion of a hemodialysis catheter. We describe a 78-year-old uremic female who developed unexplained and refractory shock on the completion of percutaneous placement of a hemodialysis catheter in the right subclavian vein under general anesthesia. Bedside transthoracic ultrasound revealed a large anechoic area above the right hemidiaphragm, suggestive of the presence of extensive hemothorax. The diagnosis was further confirmed by prompt drainage of fresh blood from the right thoracostomy tube. Emergent thoracotomy was performed and perforation of the superior vena cava was identified. Hemodynamic stability was restored after surgical repair of the injured vessel, aggressive volume resuscitation and inotropic/vasopressor treatment. This case suggests that portable ultrasonography is an invaluable bedside tool which allows anesthesiologists to made reliable and prompt diagnosis of potentially fatal complications, such as perforation of great central vein due to inadvertent cannulation.

Is a 4 days transoesophageal training course sufficient to diagnose shock related pathologies?

INTRODUCTION

Echocardiography is a useful tool in patients suffering from shock of unknown origin to evaluate cardiac function and volume status in order to decide on further treatment. The aim of the study was to evaluate how well participants could identify function, preload and regional wall motion abnormalities after attending a 4-day transoesophageal echocardiography (TOE) seminar.

METHODS

In this prospective educational trial, participants of six TOE seminars from 2005 to 2006 were evaluated. On the basis of seven echocardiographic studies, evaluations by participants concerning cardiac function, preload and regional wall motion were analyzed. Moreover, specific causes of undifferentiated hypotension were to be judged in three cases by the participants.

RESULTS

A total of 115 participants of the TOE seminars from 2005 to 2006 were evaluated. Correct sectional plane was recognized by more than 76% of the participants. Left ventricular function, preload, and regional wall abnormalities were assessed correctly by the participants in 98%, 96%, and 84%, respectively. Moreover, more than 70% of the participants recognized the correct cause of hemodynamic instability.

CONCLUSION

The results of the investigation show that participants of a 4-day TOE seminar can interpret left ventricular function, preload and regional wall motion abnormalities correctly at a very high rate. TOE seminars seem to be effective in teaching basic theoretical knowledge of TOE.

Transesophageal echocardiography and noncardiac surgery

The use of transesophageal echocardiography (TEE) for monitoring during cardiac and noncardiac surgery has increased exponentially over the past few decades. TEE has evolved from a diagnostic tool to a monitoring device and a procedural adjunct. The close proximity of the TEE transducer to the heart generates high-quality images of the intracardiac structures and their spatial orientation. The use of TEE in noncardiac and critical care settings is not well studied, and the evidence of the benefits of its use in these settings is lacking. Despite the widespread availability of TEE equipment in US hospitals, less than 30% of anesthesiologists are formally trained in the use of perioperative TEE. In this review, the safety and indications of TEE are reviewed and detailed analysis of the best available evidence in this regard is presented. Landmark trials evaluating the use of TEE and its therapeutic impact in noncardiac surgical setting are critically reviewed. This article details recommendations to familiarize anesthesiologists with TEE technology to exploit it to its fullest potential to achieve better patient monitoring standards and eventually improve outcome. Training of greater numbers of anesthesiologists in TEE is needed to increase awareness of the indications and contraindications. Until relatively inexpensive TEE equipment is available, the initial cost of equipment acquisition remains a significant prohibitive factor limiting its widespread use.

Echocardiography practice, training and accreditation in the intensive care: document for the World Interactive Network Focused on Critical Ultrasound (WINFOCUS)

Echocardiography is increasingly used in the management of the critically ill patient as a non-invasive diagnostic and monitoring tool. Whilst in few countries specialized national training schemes for intensive care unit (ICU) echocardiography have been developed, specific guidelines for ICU physicians wishing to incorporate echocardiography into their clinical practice are lacking. Further, existing echocardiography accreditation does not reflect the requirements of the ICU practitioner. The WINFOCUS (World Interactive Network Focused On Critical UltraSound) ECHO-ICU Group drew up a document aimed at providing guidance to individual physicians, trainers and the relevant societies of the requirements for the development of skills in echocardiography in the ICU setting. The document is based on recommendations published by the Royal College of Radiologists, British Society of Echocardiography, European Association of Echocardiography and American Society of Echocardiography, together with international input from established practitioners of ICU echocardiography. The recommendations contained in this document are concerned with theoretical basis of ultrasonography, the practical aspects of building an ICU-based echocardiography service as well as the key components of standard adult TTE and TEE studies to be performed on the ICU. Specific issues regarding echocardiography in different ICU clinical scenarios are then described. Obtaining competence in ICU echocardiography may be achieved in different ways - either through completion of an appropriate fellowship/training scheme, or, where not available, via a staged approach designed to train the practitioner to a level at which they can achieve accreditation. Here, peri-resuscitation focused echocardiography represents the entry level--obtainable through established courses followed by mentored practice. Next, a competence-based modular training programme is proposed: theoretical elements delivered through blended-learning and practical elements acquired in parallel through proctored practice. These all linked with existing national/international echocardiography courses. When completed, it is anticipated that the practitioner will have performed the prerequisite number of studies, and achieved the competency to undertake accreditation (leading to Level 2 competence) via a recognized National or European examination and provide the appropriate required evidence of competency (logbook). Thus, even where appropriate fellowships are not available, with support from the relevant echocardiography bodies, training and subsequently accreditation in ICU echocardiography becomes achievable within the existing framework of current critical care and cardiological practice, and is adaptable to each countrie's needs.

Echocardiographic assessment of pulmonary artery occlusion pressure in ventilated patients: a transoesophageal study

Background

Non-invasive evaluation of left ventricular filling pressure has been scarcely studied in critically ill patients. Accordingly, we prospectively assessed the ability of transoesophageal echocardiography (TEE) Doppler to predict an invasive pulmonary artery occlusion pressure (PAOP) ≤ 18 mmHg in ventilated patients.

Methods

During two consecutive 3-year periods, TEE Doppler parameters were compared to right heart catheterisation derived PAOP used as reference in 88 ventilated patients, haemodynamically stable and in sinus rhythm (age: 63 ± 14 years; simplified acute physiologic score (SAPS) II: 45 ± 12). During the initial period (protocol A), threshold values of pulsed-wave Doppler parameters to predict an invasive PAOP ≤ 18 mmHg were determined in 56 patients. Derived Doppler values were prospectively tested during the subsequent period (protocol B) in 32 patients.

Results

In protocol A, Doppler parameters had similar area under the receiver operating characteristic (ROC) curve. In protocol B, mitral E/A ≤ 1.4, pulmonary vein S/D > 0.65 and systolic fraction > 44% best predicted an invasive PAOP ≤ 18 mmHg. Lateral E/E' ≤ 8.0 or E/Vp ≤ 1.7 predicted a PAOP ≤ 18 mmHg with a sensitivity of 83% and 80%, and a specificity of 88% and 100%, respectively. Areas under ROC curves of lateral E/E' and E/Vp were similar (0.91 ± 0.07 vs 0.92 ± 0.07: p = 0.53), and not significantly different from those of pulsed-wave Doppler indices.

Conclusion

TEE accurately predicts invasive PAOP ≤ 18 mmHg in ventilated patients. This further increases its diagnostic value in patients with suspected acute lung injury/acute respiratory distress syndrome.

Importance of transesophageal echocardiography in the critically ill and injured patient

Echocardiography, particularly transesophageal echocardiography (TEE), is a vital diagnostic and monitoring imaging modality for the intensivist. The field of echocardiography spans different venues and pathologies, ranging from surface transthoracic echocardiography and portable hand-held echocardiography, to contrast echocardiography, stress echocardiography, and TEE, among others. Numerous investigations have proven the worth of echocardiography, especially TEE, in the critically ill and injured patient, changing lives with the identification of obvious and subtle cardiothoracic diseases. Because this powerful imaging tool is immediately available and portable, crucial delays in diagnosis are not commonplace; rather than echocardiography, TEE, specifically, should be (and is in some institutions) the standard of care and management in assisting the intensivist in diagnosis of a variety of maladies. The effect of TEE technology is quite formidable, and numerous investigations have borne this out. The therapeutic effect of TEE ranges from 10% to 69%, with the majority of investigations falling into the 60% to 65% range. The diagnostic yield of TEE is far greater, approaching 78%. This article will detail the importance of echocardiography, its efficacy, and its high-yield imaging capability, particularly when compared with other imaging modalities, even transthoracic echocardiography.

Diagnosis of central hypovolemia by using passive leg raising

OBJECTIVE

Suspected central hypovolemia is a frequent clinical situation in hospitalized patients, and no simple bedside diagnostic test in spontaneously breathing patients is available. We tested the value of passive leg raising to predict hemodynamic improvement after fluid expansion in patients with suspected central hypovolemia.

DESIGN AND SETTING

Prospective study in four intensive care units at the Amiens university hospital. Thirty-four spontaneously breathing patients with suspected hypovolemia were included and were classified as responders (cardiac output increased by 12% or more after fluid expansion) or nonresponders. Patients were analyzed in the supine position during 30 degrees leg raising and after fluid expansion.

MEASUREMENTS AND RESULTS

Stroke volume and cardiac output determined by echocardiographic and Doppler techniques and heart rate and blood pressure were measured at baseline, during passive leg raising and after fluid expansion. An increase of cardiac output or stroke volume by 12% or more during passive leg raising was highly predictive of central hypovolemia (AUC 0.89+/-0.06, 95% CI 0.73-0.97 for cardiac output and AUC 0.9+/-0.06, 95% CI 0.74-0.97 for stroke volume). Sensitivity and specificity values were 63% and 89% for cardiac output and 69%, 89% for stroke volume respectively. A close correlation (r=0.75; p<0.0001) was observed between cardiac output changes during leg raising and changes in cardiac output after fluid expansion.

CONCLUSIONS

Bedside measurement of cardiac output or stroke volume by Doppler techniques during passive leg raising was predictive of a positive hemodynamic effect of fluid expansion in spontaneously breathing patients with suspected central hypovolemia.

Echocardiographic measurement of ventricular function

PURPOSE OF REVIEW

We review new findings concerning ventricular function in patients in intensive care units with shock or unexplained respiratory distress syndrome analyzed using echocardiography.

RECENT FINDINGS

Bedside echocardiography is not only an imaging technique but should be considered as a hemodynamic method. Left-ventricular systolic function can be assessed in daily clinical practice by measuring shortening fraction, fraction area change and ejection fraction. But these indices are dependent on load conditions. Index of myocardial performance can be also used. Rate of left-ventricular pressure increase may be measured from mitral regurgitation. Other indices such a maximal elastance and preload-adjusted maximal power were developed to evaluate myocardial systolic function but are not still used in clinical practice in patients in intensive care. Cardiac output measurement can be calculated easily from aortic annulus diameter and the velocity time integral of aortic blood flow. To complete the assessment of ventricular function, left-ventricular diastolic function and pressure as well as right ventricular size, septal movement and right pressures should be analyzed.

SUMMARY

Using echocardiography the intensivist can examine both the mechanism and the cause of shock or pulmonary edema. It is time to increase the use of this technique in intensive care units.

A New Window of Opportunity in Echocardiography

BACKGROUND

Improvements in echocardiographic technology have made technically difficult studies a rare entity. However, physical barriers such as bandages, inability for patients to turn because of intubation, arterial lines, and organ and life support machines make echocardiographic imaging challenging.

METHODS

We performed echocardiographic imaging from left and right posterior thoracic approach using acoustic properties of pleural fluid to assist in obtaining good imaging windows in patients who had pleural effusion (PE). In this study we describe one author's (T. Z. N.) experience with the mid to lower posterior thoracic window in 18 patients who had PE and in whom conventional transthoracic windows either provided suboptimal images or incomplete clinical information.

RESULTS

The posterior approach allowed excellent differentiation of pericardial effusion versus PE, detection of pericardial disease and pericardial infiltration, and excellent endocardial border definition of left and right ventricle in those with poor anterior transthoracic windows. Native and prosthetic aortic valve gradients could be assessed adequately as a result of perfectly parallel Doppler alignment beam to left ventricular outflow tract and aortic valve. In addition, right posterior thoracic window provided views comparable with subcostal view and allowed visualization of inferior vena cava, right atrium, and liver.

CONCLUSION

In patients with PE, imaging from low to midposterior thorax can provide additional diagnostic echocardiographic images and should be used in patients in whom conventional images are technically difficult or require additional information.

Sonography as an alternative to radiography for nasogastric feeding tube location

OBJECTIVE

To evaluate bedside sonographic confirmation of weighted-tip nasogastric feeding tube position, by comparison to radiography.

DESIGN AND SETTING

Single-center, double-blind prospective study in a 14-bed medical intensive care unit (ICU) in a 780-bed teaching hospital.

PATIENTS

Thirty-three ICU patients undergoing nasogastric tube insertion for enteral feeding.

INTERVENTIONS

The tip of the nasogastric tube was located both by sonography and standard radiography.

MEASUREMENTS AND RESULTS

The accuracy and procedure times of sonography and radiography for nasogastric tube tip location were compared during 35 procedures in 33 patients. The nasogastric tube tip was visualized by sonography in 34 of 35 procedures (sensitivity 97%) and by radiography in all procedures. The median length of the entire procedure was 24 min and 180 min with sonography and radiography, respectively.

CONCLUSIONS

Bedside sonography performed by nonradiologists is a sensitive method for confirming the position of weighted-tip feeding nasogastric feeding tubes. It is more rapid than conventional radiography and can easily be taught to ICU physicians. Conventional radiography could be reserved for cases in which sonography is inconclusive.

Bedside ultrasonography in the ICU: part 1

Ultrasonography has become an invaluable tool in the management of critically ill patients. Its safety and portability allow for use at the bedside to provide rapid, detailed information regarding the cardiovascular system and the function and anatomy of certain internal organs. Echocardiography can noninvasively elucidate cardiac function and structure. This information is vital in the management hemodynamically unstable patients in the ICU. In addition, ultrasonography has particular value for the assessment and safe drainage of pleural and intra-abdominal fluid and the placement of central venous catheters. A new generation of portable, battery-powered, inexpensive, hand-carried ultrasound devices have recently become available; these devices can provide immediate diagnostic information not assessable by physical examination alone and allow for ultrasound-guided thoracocentesis, paracentesis, and central venous cannulation. This two-part article reviews the application of bedside ultrasonography in the ICU.

Transthoracic echocardiography to identify or exclude cardiac cause of shock

BACKGROUND

Transesophageal echocardiography (TEE) is often still considered the echocardiographic test of choice in the general ICU patient population to establish the presence or absence of cardiac cause of shock, and is often requested and performed as the initial and only echocardiographic test. This premise is based on older studies in which transthoracic echocardiography (TTE) commonly offered inadequate images in ICU patients.

STUDY OBJECTIVES

We hypothesized that current TTE imaging alone is adequate to identify or exclude cardiac cause of shock in the great majority of cases.

METHODS

One hundred consecutive shock cases in which an echocardiogram was requested were prospectively analyzed by two blinded echocardiographers for image adequacy, and the absence or presence of cardiac cause of shock (defined as one or more of the following: severe left ventricular (LV) or right ventricular systolic dysfunction, tamponade, severe left-sided valve disease, or a postinfarction mechanical complication), and compared to a clinical standard of presence/absence of cardiac cause of shock as determined by autopsy, surgery, or objective testing. Shock was defined as systolic BP < 100 mm Hg or fall in BP >/= 25%, and inotrope use or evidence of low output or venous congestion. Cardiac output was determined by the LV outflow tract (LVOT) Doppler method.

RESULTS

Sixty-three percent of cases had a cardiac cause of shock. TTE image quality was adequate in 99% cases. Among the 99% of cases in which the imaging was adequate, the sensitivity of TTE for cardiac cause of shock was 100%, the specificity was 95%, the positive predictive value was 97%, and the negative predictive value was 100%. There were relative contraindications to TEE in 15% of cases. Stroke volume index (15 +/- 6 mL/m(2) vs 31 +/- 7 mL/m(2) [mean +/- 1 SD]; p < 0.001) and cardiac index (1.6 +/- 0.5 mL/min/m(2) vs 2.9 +/- 0.9 mL/min/m(2); p < 0.001) were significantly less in the group with a cardiac cause of shock than in the group with a noncardiac cause of shock.

CONCLUSIONS

In the general critical care population, current TTE imaging identifies the great majority of cardiac causes of shock. TTE should be considered not only the initial, but also the principal echocardiographic test in the critical care environment.

Methods of monitoring shock

Intensive monitoring is a crucial component of the management of shock. However, there is little consensus about optimal strategies for monitoring. Although the pulmonary artery catheter has been widely used, conflicting data exist about the utility of this device. A variety of other techniques have been developed in hopes of providing clinically useful information about myocardial function, intravascular volume, and indices of organ function. In addition, there is evolving evidence that targeting and monitoring certain physiological goals may be most important early in the course of shock. In this chapter, we examine many of the available monitoring techniques and the evidence supporting their use.

Transthoracic echocardiography does not improve prediction of outcome over APACHE II in medical-surgical intensive care

PURPOSE

To examine the hypothesis that transthoracic echocardiographic findings predict mortality in critically ill patients.

METHODS

A retrospective analysis of concurrently collected data for consecutive patients from May 1996 to May 1998 who had transthoracic echocardiography on or within six months of admission to the medical surgical intensive care (MSICU). We examined the role of physiologic, clinical, and echocardiography variables in predicting the mortality of patients admitted to the MSICU. Three logistic regression models were developed: 1) clinical; 2) echocardiographic; and 3) combined clinical with echocardiographic. Univariate and multivariate analyses were performed and the relative strength of clinical and echocardiographic predictors was compared using odds ratio (OR) and receiver-operator-characteristic (ROC).

RESULTS

Of 4,070 MSICU patient admissions, 1,093 patients had transthoracic echocardiography; the study group comprised 942 patients with complete clinical and echocardiographic data. The MSICU mortality was 28%. For the combined model, analyses identified left ventricular systolic function (LVSF), [OR 1.26; confidence interval (CI) 1.01-1.57], severe tricuspid regurgitation (TR) (OR 3.72; CI 1.04-13.24), medical diagnosis (OR 1.91; CI 1.15-3.19), and acute physiology and chronic health evaluation (APACHE) II score (OR 1.27; CI 1.23-1.31), as predictors of MSICU mortality. The combined model yielded an area under ROC curve of 0.913. For the clinical model, analyses identified age (OR 1.04; CI 1.02-1.05) and APACHE II (OR 1.32; 1.26-1.35) as predictors of mortality with an area under ROC curve of 0.917. For the echocardiography model, TR (OR 2.40; 1.08-5.38), severe aortic insufficiency (AI) (OR 4.13; CI 1.17-16.29) and pulmonary hypertension (OR 2.05; 1.01-4.09) were identified as predictors of outcome with an ROC curve of 0.536 for this model.

CONCLUSION

Statistical models utilizing clinical variables are predictive of mortality in MSICU. Models that include diagnostic transthoracic echocardiography variables do not provide incremental value to predict ICU mortality. These findings may have implications for non-invasive hemodynamic assessment of critically ill patients, and raise the hypothesis that echocardiography-guided interventions may not alter outcome in ICU.

Crossing atrial thrombus in a patient with recurrent pulmonary embolism

OBJECTIVES

To report the detection of a thrombus entrapped in a patent foramen ovale by echocardiography in a patient with recurrent pulmonary embolism.

DESIGN

Case report.

SETTING

Intensive care unit of a university hospital.

PATIENT

A 62-yr-old man with initial deep venous thrombosis and recurrent minor pulmonary embolism followed by a severe embolic event with transitory hemiparesis 10 days after prostatectomy.

INTERVENTION

Systemic anticoagulation, surgical removal of a crossing atrial thrombus, closure of a patent foramen ovale, and venous thrombectomy.

MEASUREMENTS AND MAIN RESULTS

Transesophageal echocardiography revealed a large thrombus entrapped in a patent foramen ovale with portions in all four heart chambers. Intraoperatively, a 19-cm-long thrombus, shaped like the pelvic veins, was found. The patient was successfully weaned from cardiopulmonary bypass, requiring temporary positive inotropic support because of right ventricular dysfunction. Within 24 hrs of the operation, the patient was discharged to the intermediate care unit.

CONCLUSIONS

Recurrent pulmonary embolism can potentially result in paradoxic embolism in patients with a patent foramen ovale. In such patients, it may be crucial to monitor right ventricular function and exclude right-to-left shunts by transesophageal echocardiography, regardless of clinical symptoms. The patent foramen ovale should be closed. This case emphasizes an important indication for transesophageal echocardiography in critically ill patients.

The hemodynamically unstable patient in the intensive care unit: hemodynamic vs. transesophageal echocardiographic monitoring

OBJECTIVE

Transesophageal echocardiography is a diagnostic and monitoring modality. The objectives of our study were to compare the diagnoses obtained with continuous transesophageal echocardiography and hemodynamic monitoring in the intensive care unit, to determine interobserver variability of diagnosis obtained with both modalities, and to evaluate its impact.

DESIGN

Prospective cohort study.

SETTING

Surgical intensive care unit.

PATIENTS

Consecutive hemodynamically unstable patients after cardiac surgery.

INTERVENTIONS

At admission, unstable patients were monitored during 4 hrs with transesophageal echocardiography and standard hemodynamic monitoring. The critical care physician evaluated the patients based on all information except the transesophageal echocardiography at 0, 2, and 4 hrs and formulated a hypothesis on the most likely cause of hemodynamic instability. Transesophageal echocardiography information was provided after each evaluation. To evaluate interobserver variability, all the hemodynamic and echocardiographic information was gathered, randomized, and evaluated by five clinicians for the hemodynamic data and five echocardiographers for the transesophageal echocardiography data. The evaluators were blinded to all other information. Kappa statistics were used to evaluate agreement. Impact of transesophageal echocardiography was assessed retrospectively by using the Deutsch scale.

RESULTS

Twenty patients qualified for the study. The agreement between the hemodynamic and echocardiographic diagnosis showed a kappa at admission, 2 hrs, and 4 hrs of 0.33, 0.47, and 0.28. The interobserver agreement for the initial diagnosis (p =.014) and between all evaluators (p <.001) was significantly higher in the echocardiographic compared with the hemodynamic group. The transesophageal echocardiographic information was considered retrospectively to be essential in 34% and valuable in 34% of cases.

CONCLUSIONS

These observations support the belief that transesophageal echocardiographic monitoring in the intensive care unit is associated with higher interobserver agreement in diagnosing and excluding significant causes of hemodynamic instability for postoperative cardiac surgical patients.