Evaluation of the utility of cardiac ultrasonography of patients in a surgical intensive care unit

After approval of the present observational study by our Institutional Review Board (approval No. 147/ 2015), we retrospectively reviewed the medical records of a cohort patients who underwent CUS in the SICU of King Chulalongkorn Memorial Hospital (a 1,400-bed university hospital in Bangkok, Thailand) from January 2011 to March 2013. The CUS was performed using an SSD-4000SV system (Hitachi Aloka Medical, Tokyo, Japan) by all the authors who are intensivists trained in the use of CUS. The main indications for CUS were (1) shock (a systolic blood pressure of <90 mmHg, or presence of signs of poor tissue perfusion), (2) oliguria (urine output of <0.5 mL/kg/h), and (3) baseline assessment of hemodynamic status. The CUS was used mainly to determine (1) preload, (2) cardiac contractility, and (3) other miscellaneous findings.

Preload assessment was performed by measurement of the inferior vena cava (IVC) diameter, calculating the collapsibility index of IVC (IVC_CI), or observing the ventricular wall kissing sign. The IVC diameter was measured using a subxiphoid view within 2 cm of the IVC-right atrial junction at the end of expiration in both mechanically ventilated and spontaneously breathing patients (Figure 1).

Figure 1

The IVC_CI was calculated as followed:

IVCCI=maximumIVCdiameter−maximumIVCdiameter×100%maximumIVCdiameter$${\rm{IV}}{{\rm{C}}_{{\rm{CI}}}} = {{{\rm{maximum \; IVC \; diameter - maximum \; IVC \; diameter}} \times 100\text{%}} \over {{\rm{maximum \; IVC \; diameter}}}}$$

Any patients with IVC diameter less than 1.2 cm, or IVC_CI > 50%, or a positive ventricular wall kissing sign were classified as having hypovolemia [3, 9-11],

Cardiac contractility was assessed by (1) subjective assessment (observing overall contraction and grading as poor, normal, or hyperdynamic contraction), and (2) fractional shortening (FS) as shown in Figure 2.

Figure 2

According to the FS, the patient would be classified as having poor contraction when the FS was less than 25% [4, 12]. The other findings that were sought included the presence of pericardial fluid/ cardiac tamponade and gross valvular abnormalities.

Besides the hemodynamic assessment, the authors also performed additional US to detect miscellaneous problems, e.g. fluid collection, biliary tract problems, obstructive uropathy, and deep vein thrombosis (DVT) in patients suspected of having these particular problems. The main criterion for DVT diagnosis was the absence of venous compressibility. The adjunct criteria for DVT diagnosis included the presence of a thrombus, decrease of flow, and the absence of augmentation upon calf squeezing [13].

We classified the patients into 8 groups namely: general surgery, hepatobiliary-pancreatic surgery, vascular surgery, colorectal surgery, urology, trauma, orthopedics, and miscellaneous (e.g. plastic surgery, head and neck surgery). Data collected included demographic variables, patient groups, initial Sequential Organ Failure Assessment (SOFA) score, monitoring devices used, hemodynamic parameters, indications for CUS, and results of CUS. Outcomes including ICU days, ventilator days, and mortality were recorded. Change in management was defined as “alteration of a treatment plan because of the CUS results”, and depended mainly on the clinical judgment of the intensivists.

Statistical analyses were performed using Microsoft Excel 2013, version 15.0.4420 (Microsoft Corp, Redmond, WA, USA). Descriptive ordinal data were analyzed and expressed as mean and standard deviation (SD). The linear association between the IVC diameter and central venous pressure (CVP) was analyzed using Pearson correlation coefficients and is represented by a scatter plot.

From January 2011 to March 2013, CUS was performed 190 times in 157 patients (96 male and 61 female, mean age 63.5 ± 19.4 years) in the SICU. Their demographic data, monitoring device used, and inotropic drug use are shown in Table 1 and the indications of CUS are shown in Table 2.

The CUS was performed on 137 patients (87%) on a mechanical ventilator. The most common indication was baseline assessment of hemodynamic status (78 times), followed by shock (69 times), and oliguria (35 times).

CUS of 58 patients with shock was performed 69 times in the SICU to assess the hemodynamic status and causes of shock. According to our criteria of preload assessment, hypovolemia was identified 28 times, which led to fluid challenge 26 times following the clinical judgment of the intensivists. Poor left ventricular (LV) contraction was observed 10 times, which led to administration or increment of inotropic drugs on 5 occasions. One patient with global hypokinesia of the left ventricle was subsequently diagnosed with acute myocardial infarction. Valvular abnormalities were detected 6 times, all were subsequently confirmed by formal echocardiography conducted by cardiologists (2 aortic regurgitations, 1 aortic stenosis, 2 tricuspid regurgitations, and 1 mitral valve regurgitation). No cardiac tamponade detected in the present study.

CUS was performed 35 times in 28 patients with oliguria. Preload assessment revealed hypovolemia 15 times, which led to fluid challenge on 12 occasions. Poor LV contraction was identified 2 times, both instances treated by inotropic drug administration. In addition, urinary bladder obstruction was found 2 times, which led to urinary catheter changes.

Other miscellaneous findings from the additional US leading to changes in management were as follows: (1) pleural effusions leading to placement of percutaneous drainage (8 times), (2) intra-abdominal fluid/collection leading to placement of percutaneous drainage (4 times), (3) one intracardiac thrombus and 10 DVTs leading to administration of anticoagulant, and (4) cholecystitis leading to cholecystectomy (1 times). The US was also used to confirm the diagnosis of abdominal compartment syndrome by showing a narrow, compressed IVC in a patient with intra-abdominal hypertension who subsequently required decompressive laparotomy (Figure 3).

Figure 3

Overall, there were 71 changes in management dictated by 190 instances of CUS performed (38 fluid challenges, 7 inotropic drug managements, 11 anticoagulant administrations, and 15 other procedures). During the study period 23 patients died (15% mortality). The outcomes of the patients are summarized in the Table 3.

An analysis of the correlation between CVP and IVC diameter was conducted for 109 patients who had a central venous catheter (98 mechanically ventilated and 11 spontaneous breathing). The correlation coefficient showed a weakly positive relationship between the IVC diameter (measured from CUS) and the CVP (Pearson’s r = 0.45) (Figure 4).

Figure 4

CUS performed by intensivists has played an important role in ICUs because it is a noninvasive test that provides useful hemodynamic information [1-8]. Furthermore, problem-focused US can help identify specific problems e.g., fluid collection, DVT, biliary tract diseases, and urinary tract obstruction, which are common in surgical patients as seen in the present study [13, 14]. CUS can occasionally lead to changes in management in ICU patients (18%—55%) [5, 8]. For instance, Ferrada et al. reported 55% change in management in ICU patients with trauma who underwent CUS including volume management (79%) and increase in inotropic drugs or vasopressors, or both (20%) [5]. In the present study, most common change in management was fluid challenge, followed by invasive procedures, administration of anticoagulant, and inotropic drug management. However, these changes did not depend solely on the CUS findings because the decision to change the management plan in the present study depended mainly on the clinical judgment of the intensivists.

A correlation between IVC diameter and CVP or right atrial pressure (RAP) has been demonstrated by several studies including the present study [3, 9-11, 15, 16]. In the present study, we used end-expiratory IVC diameter to assess CVP because the diameter is not affected by inspiration, either in spontaneously breathing or mechanically-ventilated patients. We used 1.2 cm as a lower normal limit of IVC diameter because IVC diameter of < 1.2 cm is often seen with intravascular volume depletion and is specific for a low RAP [9, 10, 15, 16]. The respiratory variation in IVC diameter has been used by other investigators to estimate RAP and to predict fluid responsiveness in ICU patients [11, 17, 18]. In the present study, we used the IVC_CI of >50% to define hypovolemia because this value correlates well with a low RAP and is usually associated with fluid responsiveness in patients with acute circulatory failure [9, 11].

The LV systolic function evaluation by CUS can be performed by subjective assessment and/or objective assessment. Volumetric measurement of the LV ejection fraction by Simpson’s biplane method is a preferred over linear measurement [12]. Nevertheless, a prospective study comparing 3 LV systolic function evaluation methods by CUS performed by intensivists showed that FS was more accurate than left ventricular outflow tract/velocity-time integral and Simpson’s method in estimating cardiac index [3]. Moreover, noncardiologist physicians can measure FS relatively easily. We used FS as a component of cardiac contractility assessment in the present study. However, FS and cardiac output could not be correlated because the number of patients with cardiac output monitoring was low (7.6%).

There are some limitations to the present study. First, this is a retrospective study with no clear management protocol in response to the CUS results because changes in management depended mainly on the judgment of the intensivists. Therefore, the amount of fluid administered when fluid challenge was performed or the type of inotropic drugs used were not uniform. Second, we did not have any data regarding response to treatment because there was no criterion to define response to treatment, especially in hemodynamic management (e.g., response to fluid challenge). Therefore, we could not identify the effectiveness of CUS-guided hemodynamic management.

In conclusion, we believe that CUS is a useful tool for evaluating patients in the SICU, especially those with acute hemodynamic problems (e.g., shock or oliguria) because it is a noninvasive test and is easy to perform. Along with clinical information, CUS and problem-focused US may help guide decision making in SICU patient management. Intensivists should be familiar with CUS technique so that it can be included in the ICU armamentarium.