Managing acute and critical care problems with point-of-care ultrasound

Opening Vignette #1 A 66-year-old man with known congestive heart failure presented with 1 day of fever and right-sided abdominal pain. His vital signs were as follows: blood pressure 86/30 mmHg, heart rate 117/min, respiratory rate 30/min, temperature 39°C and peripheral oxygen saturation 92% in room air. He had a distended abdomen with tenderness in the right hypochondral region with no guarding and reduced air entry in the right lower lung zone. His jugular venous pressure was not elevated, and the oral mucosa was dry. Peripheries were cold, and the capillary refill time was 4 s (normal 3 s). The urine output was minimal over the past 2 h. The chest radiograph showed a right lower zone opacification with blunting of the costophrenic angle.MANAGING CIRCULATORY FAILURE WITH POINT-OF-CARE ULTRASOUND Point-of-care ultrasound (POCUS) is the use of ultrasonography at the bedside to complement clinical assessment. It is valuable for timely diagnosis of the underlying cause for circulatory failure and screening for sources of sepsis. It is also helpful in guiding eventual management, specifically assessment of fluid responsiveness. The top differential diagnosis in this case is septic shock. Early identification of the source of sepsis is crucial for early source control and antimicrobial guidance. However, as the patient also had borderline peripheral oxygen saturation and chest radiograph findings as above, pneumonia had not been ruled out. Given the history of congestive cardiac failure, concomitant cardiogenic shock (i.e. mixed shock) needs to be considered as well. Other differentials include shock due to hypovolaemia, and obstructive shock. Fluid administration needs to be judicious, especially with the history of congestive cardiac failure. Fluid responsiveness should be assessed when shock is not due to obvious intravascular volume losses (e.g. massive haemorrhage, or intravascular depletion in the initial phases of sepsis). For these conditions, volume expansion should proceed without the need to assess fluid responsiveness. Otherwise, assessing fluid tolerance and using it to guide fluid therapy may avoid giving excessive fluids. Even without cardiac dysfunction, excess accumulated fluid balance has been shown to increase mortality in patients with sepsis.[1] Physicians are now more aware of the harmful consequences associated with excessive fluid balance in the intensive care unit. Consequently, there has been a shift towards emphasising the concept of ‘fluid tolerance’.[2] Fluid tolerance is defined as the extent to which a patient can receive fluid without causing organ dysfunction. It seeks to determine if it is safe to administer fluid to a patient, even if he/she exhibits fluid responsiveness. Fluid responsiveness indicates that a patient could potentially increase his/her cardiac output with a fluid bolus, but does not guarantee it is safe to do so. This approach primarily focuses on increasing blood flow on the arterial side of circulation and overlooks the potential problems related to venous congestion and its impact on organ function. Resuscitation aims to enhance perfusion, which involves the net pressure difference after the capillary bed, taking into consideration the venous and arterial pressure.[3] It is well established that increasing venous pressure or decreasing arterial pressure can have detrimental effects. Increasingly, excess fluid administration, which is associated with elevated central venous pressure and portal dysfunction,[4] has been shown to harm the brain[5] and kidneys.[6] Critical care echocardiography (CCE) with a low-frequency (1–5 MHz), phased array probe can be used to assess cardiac function. An obstructive cause of shock, such as pericardial tamponade, must be excluded early because it necessitates pericardial drainage. Separately, cardiac function can be assessed by looking at left ventricular systolic contraction and right ventricle (RV) dilatation (normally, RV is less than two-thirds the size of the left ventricle [LV]), and a D-shaped LV with straightening of the interventricular septum in the parasternal short-axis view is abnormal [Figure 1a and Table 1]. Presence of a D-shaped LV is a relative contraindication to aggressive fluid resuscitation because it indicates that there is RV dilatation and right heart pressure or volume overload, and further increment of right heart filling pressures in the presence of ventricular interdependency will result in impaired LV diastolic filling. With the subcostal inferior vena cava (IVC) view, measurements of IVC diameter can either be done with B-mode or M-mode ultrasound. However, recent evidence indicates that measurement of IVC diameter is an unreliable method to predict fluid responsiveness in patients who are spontaneously breathing without mechanical ventilation.[7]Figure 1: Ultrasound images show (a) an abnormal, D-shaped left ventricle with straightening of the interventricular septum (arrow) in parasternal short axis view, suggestive of right heart pressure or volume overload; (b) ‘V’ marker (cephalad), minimal–moderate pleural effusion (☆) and atelectasis (Δ); (c) ‘V’ marker (cephalad), subphrenic collection, fibrin strands (arrow labelled subphrenic collection), mild–moderate pleural effusion as seen in 1b. LV: left ventricle, RV: right ventricleTable 1: Common POCUS findings, associated clinical diagnoses and test characteristics.Alternatively, POCUS can be used to make stroke volume and cardiac output estimates with LV outflow tract velocity time integral (LVOT VTI),[8] which is part of the dynamic assessments to estimate fluid responsiveness. Carotid artery peak velocity with respiration is also reported to assess fluid responsiveness.[9] However, these are more advanced assessments that require optimal image acquisition and more advanced (Doppler) techniques for accurate estimates, and may be time-consuming for the novice. Fluid administration can also be guided by lung ultrasonography. The Fluid Administration Limited by Lung Sonography protocol[10] includes assessment of fluid status. Clinicians should recognise A-profile (predominance of horizontal equidistant echogenic lines, parallel to the pleural line, indicative of aerated lung fields in the presence of lung sliding) and B-profile (more than two B-lines in the anterior chest, which are vertical artefacts that appear as echogenic lines and extend from the pleural line to the bottom edge of the screen without fading and erasing A-lines, indicative of interstitial syndromes). For the latter, fluid boluses should be withheld or given judiciously. Even in patients who are predicted to be fluid responsive, a routine lung ultrasound should be performed to rule out contraindications to fluid administration. Should a patient who originally had an A-profile subsequently develop B-profile after fluid boluses, without improvement in haemodynamics, it is likely due to fluid-unresponsive septic shock and further fluid challenges should be withheld. At the bedside, POCUS can be easily repeated, allowing dynamic assessments of haemodynamics and fluid status pre- and post-interventions. IDENTIFYING SOURCE OF SEPSIS WITH POCUS Systematic POCUS of the lungs and abdomen can help identify the source of sepsis, as shown in our case. As the chest radiograph showed right lower zone opacification and blunting of the costophrenic angle, lung ultrasound was performed to assess for consolidation or parapneumonic effusion. It revealed bilateral aerated lungs (A-profile) and no consolidation. Lung ultrasound can be used to estimate the amount of pleural effusion, such as with the Balik formula.[11] The Balik formula measures the maximum distance (mm) between the parietal and visceral pleura at end expiration, with the patient positioned supine with mild (15°) truncal elevation. Pleural effusion volume (mL) = (measured distance) × 20. There was a moderate (estimated 800 mL) right-sided pleural effusion, which was anechoic, with underlying atelectasis [Figure 1b], suggesting it was not complicated (parapneumonic, empyema), and the right hemidiaphragm was elevated (located above the nipple line) when the patient was sitting up. Abdominal POCUS was performed with a low-frequency (2–5 MHz) curvilinear probe, starting from the right subcostal area. The liver parenchyma appeared homogeneous, except for a posterior segment showing a circumscribed intraparenchymal area of heterogeneity with perihepatic fluid. There was no fluid in the Morrison’s pouch, suggestive of free fluid. There was a subphrenic, perihepatic fluid collection with fibrin strands [Figure 1c]. There were no hyperechoic lesions in the gallbladder, with acoustic shadows suggestive of gallstones. The gallbladder was thin walled, and pericholecystic fluid was absent. Furthermore, POCUS of the kidneys revealed that both kidneys were not enlarged, and the pelvicalyceal system did not appear dilated. The bladder was not distended, thus ruling out lower urinary tract obstructive uropathy. Identifying these abnormalities early will lead to earlier decompression of obstructed systems that could be causing sepsis, using interventions like percutaneous nephrostomy or urinary catheterisation. Abdominal ultrasound should not be used alone to identify the cause of a surgical abdomen because not all pathologies (e.g. ischaemic bowel) can be identified easily with ultrasonography.Closing Vignette #1 Critical care echocardiography was done, and a cardiogenic cause was excluded because the left ventricular systolic function looked consistent with the findings in the patient’s recent outpatient transthoracic echocardiography: there was thickening and contracting of all segments except akinetic inferior segments, which were pre-existing. The RV function appeared preserved, and RV was smaller than LV, with no straightening of the interventricular septum. After a passive leg raise manoeuvre, LVOT VTI improved from 16 cm to 20 cm (normal 17–22 cm),[12] and this was an increase in more than 10%, which was suggestive of fluid responsiveness. Anteriorly, there were fewer than three B-lines on both sides of the chest, suggesting the patient would be able to tolerate a fluid bolus. After assessments for fluid tolerance and responsiveness, a fluid challenge with 250 mL lactated Ringer’s solution was given over 15 min. The blood pressure improved significantly with reduction of heart rate to 90 beats per minute. With the chest radiograph findings, there was initially a concern of pneumonia and parapneumonic effusion, and a chest drain was considered. Given the POCUS findings, chest drainage using the usual anatomical landmark in the triangle of safety (fifth intercostal space and above, lateral border of the pectoralis major anteriorly, lateral border of the latissimus dorsi posteriorly) would have been hazardous because of the elevated diaphragm. Ultrasonography of the hepatobiliary system by professional sonographers confirmed the findings of a large liver abscess with a subphrenic perihepatic collection causing diaphragmatic splinting. The abscess was urgently treated by intravenous ceftriaxone and metronidazole, and with radiologically guided percutaneous drainage. Subsequently, the patient’s blood culture and abscess fluid culture grew Escherichia coli. The patient’s condition stabilised, and computed tomography of the abdomen was done for more definitive evaluation and follow-up.Opening Vignette #2 A 70-year-old woman with history of end-stage kidney disease had acute respiratory distress and drowsiness. Her last complete haemodialysis session occurred 2 days before the current presentation. Her vital signs were as follows: blood pressure 190/100 mmHg, heart rate 100/min, respiratory rate >25/min and temperature 37.4°C. Her peripheral oxygen saturation was 90% on venturi mask with 40% oxygen. On auscultation, there were bilateral crepitations and reduced air entry at bilateral bases.MANAGING ACUTE RESPIRATORY FAILURE WITH POCUS Chest radiography is more commonly ordered in acute respiratory failure. However, in comparison, POCUS of the lungs has many benefits, such as the ability for scans to be done immediately at the bedside with no ionising radiation and its superior sensitivity for common diagnoses such as pleural effusion, pneumonia and interstitial syndromes. It can help to identify the nature and estimate the size of a pleural effusion and can be used in real time during the insertion of pleural drains to increase success and safety. Furthermore, POCUS can be repeated regularly in the course of a patient’s disease to assess progression of the condition, efficacy of treatment and any occurrence of complications, such as pneumothorax after pleural drain insertion. Point-of-care ultrasound for the lungs can be done with either the high-frequency (6–13 MHz) linear probe, to assess superficial structures such as pleural abnormalities, or with the low-frequency (2–5 MHz) curvilinear probe for deeper structures. A well-known protocol is the Bedside Lung Ultrasound in Emergency (BLUE) protocol.[13] Each hemithorax is evaluated at three standardised points: the midclavicular line, intersecting at the second intercostal space (upper lung point), anterior axillary line intersecting at the 6th–7th intercostal space (lower lung point), and posterior axillary line intersecting at the 10th–12th intercostal space (posterior and/or lateral alveolar and/or pleural syndrome point). The BLUE protocol is used to assess patients with respiratory failure and to categorise patients into pathophysiological profiles based on key findings; each profile suggests certain diagnoses. An A-profile (predominance of horizontal equidistant echogenic lines, parallel to the pleural line) suggests aerated lung fields in the presence of lung sliding, and that respiratory failure may be due to non-parenchymal causes such as pulmonary embolism (PE) or asthma. Conversely, the finding of numerous homogeneous B-lines (>2 in the anterior chest is considered abnormal: B-profile) is highly suggestive of interstitial syndromes [Table 1]. The aetiology is most likely cardiogenic rather than infectious if B-lines and anechoic pleural effusions are present bilaterally and the pleural surfaces are smooth, with no underlying consolidation. In contrast, a heterogeneous B-line distribution pattern with spared areas, localised regions of pleural pulsation with reduced sliding, pleural line abnormalities (thickening, indentation or a broken pleural line), consolidation (subpleural, multifocal or basal) and minimal or unilateral effusion would be suggestive of acute respiratory distress syndrome and pneumonia.[14] Atelectasis may be mistaken to be consolidation and can be distinguished from pneumonia by the presence of static air bronchograms (unlike dynamic air bronchograms seen in consolidation). If there are no signs of lung pathology on lung ultrasound, and an A-profile is found with lung sliding, the aetiology of a respiratory failure would less likely be due to pneumonia, pneumothorax (A-profile without lung sliding is found in pneumothorax) or pulmonary oedema, but would be possibly due to PE. To assess for deep vein thrombosis (DVT), POCUS can be performed at the V-point using a linear probe. The V-point, at the medial and lower one-third of the thigh, is where the superficial femoral vein is assessed. If the vein does not appear compressible [Figure 2], PE is likely, though sensitivity of this feature is limited to ≤50%[20] [Table 1]. However, massive PE may not have DVT at the V-point, and absence of thrombus in a lower limb DVT scan is not sufficient to exclude PE [Table 1].Figure 2: Ultrasound image shows proximal lower limb femoral vein (arrow) that was not compressible (at V point).Closing Vignette #2 The arterial blood gas showed decompensated hypercapnic respiratory failure. There were no consolidated areas in the aerated lung fields. Lung ultrasound revealed the presence of lung sliding bilaterally, excluding a spontaneous pneumothorax. The pleural surfaces were smooth and not thickened. There were numerous homogeneous B-lines bilaterally [Figure 3 and Table 1] and bilateral large pleural effusions spanning at least three rib spaces, estimated to be about 900 mL each with the Balik formula.[11] The effusions were anechoic, suggesting that they were transudative. The patient was diagnosed with cardiogenic pulmonary oedema. She was admitted to the high-dependency unit and received bilevel positive pressure ventilation. Dialysis for fluid removal was arranged urgently. Subsequently, there was only borderline improvement in the arterial partial pressure of carbon dioxide, so bilateral chest drains were inserted with significant improvement in gas exchange and wakefulness. The chest drains were safely inserted cephalad to the diaphragm, with the ultrasound image identifying landmarks above the diaphragm and subdiaphragmatic organs. Repeat lung ultrasound revealed <2 B-lines anteriorly. A formal referral for a transthoracic echocardiogram was made to assess the function of the heart.Figure 3: Ultrasound image shows numerous B-lines, which are vertical artefacts that arise from the pleural line, laser-like, slides with respiration (arrows). This is pathological as there are >2 B-lines in a single frame.TAKE HOME MESSAGES Point-of-care ultrasound can be used to distinguish between a pleural effusion and subphrenic collection and to guide drainage of these fluid collections. Abdominal ultrasound can be used as a screening tool in septic patients to look for the source of sepsis, but it cannot always detect other causes of surgical abdomen. Therefore, more definitive imaging modalities may be required. Lung ultrasound finding of numerous homogeneous B-lines (>2 is considered abnormal: B-profile) is highly suggestive of interstitial syndromes, which encompass pulmonary oedema of various causes. Locally, cardiac and lung ultrasound are the most common POCUS modalities used to guide diagnostic and therapeutic decisions in the intensive care unit.[15] We propose an algorithm integrating these modalities with abdominal and lower limb DVT POCUS in common acute clinical scenarios [Figure S1, Supplemental Digital Appendix at https://links.lww.com/SGMJ/A154]. Financial support and sponsorship Nil. Conflicts of interest See KC is a member of the SMJ Editorial Board and was thus not involved in the peer review and publication decisions of this article. SMC CATEGORY 3B CME PROGRAMME Online Quiz: https://www.sma.org.sg/cme-programme Deadline for submission: 6 pm, 10 January 2025