Imaging in Critical Care Case File

Imaging in Critical Care Case File

Eugene C. Toy, MD, Manuel Suarez, MD, FACCP, Terrence H. Liu, MD, MPH

Case 6

A 44-year-old man with a  subarachnoid hemorrhage and a Glasgow coma score (GCS) of 9  is admitted  to  the  ICU after  initial assessment  in the emergency department, where he was intubated and placed on a ventilator. ACT of the brain revealed a   subarachnoid and an intracerebral hemorrhage. Several hours after his arrival to the ICU, the patient is noted to have increased ventilatory pressures and decreased breath sounds on the left. His O2 saturation remains at 100%.

⯈What are the possible causes for the patient's change in condition? 

⯈What imaging modalities can you use to further assess the patient's problem?

ANSWER TO CASE

Imaging in Critical Care

Summary: An intubated 44-year-old man with a subarachnoid hemorrhage develops increased ventilatory pressures and decreased left-sided breath sounds.

Possible causes for the patient's condition: Right mainstem intubation or left pneumothorax.

Confirmatory studies: Portable chest radiograph to determine whether the patient has developed a pneumothorax and/or if the endotracheal tube has advanced into the right mainstem bronchus. Bedside ultrasound can also be used to determine the presence (or absence) of visceral/parietal pleural sliding. The presence of this tissue interface would confirm a fully expanded left lung and exclude the diagnosis of left pneumothorax.

ANALYSIS

Objectives

1. To learn the values and indications of portable chest radiographs in the ICU.
2. To learn the indications and applications of bedside ultrasound in the ICU (diagnostic and procedure guidance) .
3. To learn to apply echocardiography and CT scans for the management of patients in the ICU.

Considerations

This is a 44-year-old patient who is receiving positive pressure ventilation and has been recently transported from the emergency department to the CT scanner and then to the intensive care unit. Additionally, patients with traumatic brain injuries often undergo invasive procedures such as placement of central venous catheters for central venous pressure monitoring. Such events place them at risk for both malpositioning of the endotracheal tube into the right mainstem bronchus and the development of pneumothorax. Both of these conditions can present clinically with decreased left-sided breath sounds.

Approach To:

Imaging in ICU Patients

DEFINITIONS

PORTABLE CHEST RADIOGRAPHY: A modality for performing chest radiographs at the patient's bedside. Patients are often supine or semi-supine for these studies. Portable radiographs are performed using antero-posterior technique, where x-ray beams penetrate from the anterior position. This orientation decreases the quality of the image and impairs detection of small pneumothoraces and hemothoraces due to the supine position. Portable x-rays are helpful for confirmation of endotracheal tube positions and infiltrates or effusions that may signify pathology.

ULTRASOUND: Tissue interfaces reflect sound waves. These "acoustic signals" can be translated into 2-dimensional images that represent the anatomy beneath the ultrasound probe. The images are displayed with those structures closest to the probe at the top of the image whereas those farthest away from the probe appear at the bottom of the image. Subcutaneous air and dense structures ( eg, bones, gallstones, foreign bodies ) can create artifacts that distort the ultrasound images. Body habitus and lack of skin-to-probe interface secondary to surgical dressings or wounds can also limit visibility and quality of images. Ultrasonography in the ICU is useful for diagnostic purposes (detection of pneumothorax, intraperitoneal fluid, bladder filling) or for the guidance of bedside procedures (central venous catheter placement, arterial line placement, peripheral venous catheter placement, drainage of intraperitoneal or intrapleural fluid collections ) .

ECHOCARDIOGRAPHY: Ultrasound that i s used specifically to evaluate cardiac anatomy and function. Modem day echocardiography adds computerized functions such as color flow Doppler and waveform analysis to quantify flow patterns across ( and within) anatomic regions of the heart. The addition of flow analysis and volume measurement software enhances the diagnostic range of echocardiograms. As with other forms of ultrasound, subcutaneous air, wounds, and body habitus all play a role in the quality of images obtainable in individual patients. Echocardiography is useful for the determination of cardiac performance and intravascular volume statuses, especially in patients with clinical shock.

CLINICAL APPROACH

Portable Chest Radiography in the ICU

Portable chest radiographs allow for assessment of ICU patients with acute or progressive respiratory changes. One of the major advantages of these bedside procedures is that transport during instability is avoided. Despite a reduction in image quality, bedside chest radiographs are helpful in determining many different conditions that warrant prompt intervention (Table 6-1 ) .

Portable chest radiographs are less helpful in determining if respiratory decompensation is due to pulmonary embolism (PE) . Patients with seemingly "normal" radiographs can have venous embolic disease as the source of their ventilation/perfusion mismatch. If the findings on portable chest films do not elucidate a cause and the patient is at risk for PE, CT angiography can be helpful to rule in or out embolic disease.

Historically, the practice of daily "routine" chest films was common in the ICU. In a recent meta-analysis, this practice was compared to the practice of only performing chest radiographs when clinically indicated ( ie, "on demand" ) . There was no difference in mortality, ICU length of stay, or days on the ventilator between the 2 groups. Patients who received studies only when clinically indicated were exposed to less radiation and had lower hospital costs.

Bedside Ultrasound in the ICU

The advent of small, portable ultrasound machines with improved image resolution and greater depth capabilities has made bedside ultrasonography a valuable tool in the intensive care setting. In comparison to CT scans, ultrasonography does not require the transport of critically ill patients, is not associated with radiation or intravenous contrast exposure. It is more often available and can be repeated more easily than computed tomography. Accessibility and ease of use have made ultrasound an extension of the physical examination for the assessment of critically ill patients.

Ultrasound can be used for almost all anatomic regions. In the thorax, ultrasound assessment of pleural approximation can reliably rule out pneumothorax. Cardiac function can be evaluated in a number of ways, including estimates of ejection fraction and qualitative assessment of wall motion symmetry. In the abdomen, visualization of inferior vena cava diameter changes during the respiratory cycle can give an estimate of a patient's central venous volume status. The focused assessment with sonography for trauma (FAST) allows for initial and serial assessments for increases in intraperitoneal fluid that can represent ongoing hemorrhage after abdominal trauma (Table 6--2 ) .

Ultrasound also offers therapeutic options. Real-time visualization of central venous structure during catheter insertions is associated with lower procedure related complications and is a practice endorsed by most professional organizations. Fluid in the pericardium can more safely be sampled using ultrasound guidance for pericardiocentesis. Infectious source control can sometimes be accomplished by ultrasound-guided drainage of fluid collections in the thorax, pericardium, abdomen, or soft tissues (Figures 6-1 to 6-4 ) .

Figure 6-1. Pleural sliding to rule out pneumothorax: the bright white line represents apposition of visceral and parietal pleura. The arrows represent "comet tails" artifacts created by the inter­face of pleural layers. When these findings are absent, the likelihood of pneumothorax increases. (Courtesy of Arun  Ngdev,  M.D., Emergency  Medicine Residency  Program, Alameda Health System.) 

Figure 6-2. Inferior vena cava (IVC) anatomy on ultrasound. Visualization of the IVC during the respiratory cycle yields a  reliable estimate of volume status. In the normovolemic state, the IVC will narrow during inspiration and distend during expiration. In severe hypovolemia, the IVC will collapse. In hypervolemia, the IVC diameter will not change throughout the respiratory cycle. (Courtesy of Arun  Ngdev,  M.D., Emergency  Medicine Residency  Program, Alameda Health System.)

Figure 6-3. Line placement under ultrasound guidance. Real-time visualization for catheter place­ment: the white arrows point to a  needle entering the internal jugular vein for central venous access. (Courtesy of Arun Ngdev,  M.D., Emergency Medicine Residency Program, Alameda Health System.) 

Learn to Apply Echocardiography and CT Scans for the Management of Patients in the ICU

When patients in the ICU are hemodynamically unstable and ongoing resuscitative efforts do not appear to correct perfusion, one must consider whether cardiac

Figure 6-4. Abscess image on ultrasound. Subcutaneous abscess. (Courtesy of Arun Ngdev,  M.D., Emergency Medicine Residency Program, Alameda Health System.) 

dysfunction is contributing to the clinical presentation. Bedside echocardiography offers a real-time assessment of the patient's cardiac function. Echocardiography can be used to estimate left ventricular wall motion, ejection fractions, right heart filling volumes, and pulmonary venous pressures. Information gleaned from such assessments can direct the initiation of inotropic agents, further volume resuscitation, or addition of vasoconstrictors.

Left ventricular function: Bedside echocardiography can qualitatively assess left ventricular wall motion and estimate ventricular function. These qualitative estimates can be performed with most ultrasound machines by clinicians with basic ultrasound training. More sophisticated quantitative measurements can be performed with slightly more advanced ultrasound machines that can be found in many modern day ICUs. Such machines must be able to clearly image the endocardial layer and obtain ventricular areas or volumes during the cardiac cycle. By noting the change in measured areas or volumes of the ventricle during diastole and during systole, fractional area change or ejection fraction can be calculated.

Right ventricular function: The right ventricle is normally a compliant, thin-walled chamber with low pressures. In critical illness, however, factors such as increased pulmonary vascular resistance, left ventricular dysfunction, or marked fluid overload may alter the pressures routinely found in the right ventricle. An acute increase in right ventricular pressures leads to right ventricular dysfunction and if severe, right ventricular failure. Just as in the assessment of the left ventricle, echocardiography can assess the right ventricle qualitatively or quantitatively. Qualitative findings of right ventricular enlargement and septal "bulging" toward the left ventricle suggest severe right ventricular dysfunction. For quantitative measurements, image resolution must be adequate to assess chamber volumes and Doppler flow measurements. Whether clinicians are armed with basic skills and equipment or more advanced training with slightly more sophisticated equipment, bedside echocardiography offers an accessible, noninvasive adjunct for diagnosis of unstable, critically ill patients.

Volume status: Assessment of adequate resuscitation is crucial in the management of patients in shock. Echocardiography offers several noninvasive options for assessment of preload ( ie, volume status) . As mentioned previously, IVC diameter change during the respiratory cycle can reliably estimate central venous pressure (CVP) . Equipment capable of measuring Doppler flow patterns can further elucidate preload by measuring flow across the mitral valve and within the pulmonary artery. Likewise, echocardiographic assessment of left ventricular volumes during the cardiac cycle can estimate left ventricle preload by measuring left ventricular end diastolic volumes. Doppler technology can be used to measure flow across the left ventricular outflow tract to estimate cardiac output.

Anatomic pathology: In addition to wall motion abnormalities, bedside echocardiography can be used to diagnose valvular vegetations, papillary muscle rupture, and ventricular aneurysms. Defects in the ventricular or atrial septum and valvular regurgitation can be visualized with flow Doppler. Increased fluid in the pericardium and its effect on filling of the ventricles during diastole will identify tamponade physiology if preload is compromised by the amount of fluid in the pericardia! space. Additionally, therapy for cardiac tamponade can be initiated with ultrasound-guided pericardiocentesis.

Computed tomography: Computed tomography ( CT) requires patient transport to radiology; however in some instances, the information gained is worth the risk of transport. CT arteriograms are the study of choice to diagnose pulmonary emboli. Thoracic, abdomen, and pelvic CT scans can determine sources for sepsis that are too deep for detection or obscured by artifact with bedside ultrasonography. CT scans can guide placement of percutaneous drainage catheters for source control, a key component of treatment in the septic patient.

Source identification: When patients experience clinical decline, imaging plays a key role in identifying the source of the problem (see Table 6-3 ) . Portable radiographs and ultrasound are easily accessible and do not require IV contrast and radiation exposure. These studies can be nonspecific and in the case of ultrasound, operator-dependent. Additionally, there are regions of the abdomen, mediastinum, and cranium that are difficult to image with portable ultrasound due to the density of adjacent structures, especially bone. Computed tomography offers a more sensitive and specific way to evaluate the brain, thorax, and abdomen. CT scans can identify fluid collections, areas of active bleeding, inflammation, or edema.

When the acute decline is neurologic, noncontrast computed tomography is used to assess for intracranial pathology, such as worsening traumatic brain injuries, hemorrhagic stroke, or ischemia strokes. Noncontrast CT is less sensitive in determining

ischemic strokes; however, CT perfusion imaging (when available) improves accuracy in detection of irreversible cerebral ischemia. Although magnetic resonance imaging (MRI ) is the most sensitive for assessment of cerebral ischemia, this study is less feasible in critically ill patients since it requires them to be isolated in the scanning cylinder for a period of time while the study is performed. Patients who require mechanical ventilation, close monitoring, and frequent interventions are poor candidates for this diagnostic modality.

CLINICAL CASE CORRELATION

• See also Case 13 (DVT/Pulmonary Emboli), Case 16 (Acute Cardiac Failure), and Case 28 (Blunt Trauma) .

COMPREHENSION QUESTIONS

6.1 Which of the following methods provides the safest approach for placement of internal jugular central venous catheters?

A. Using an ultrasound to mark the vein position prior to applying sterile skin prep

B. Portable chest radiograph before and after the procedure

C. Echocardiogram to visualize catheter in right atrium

D. Ultrasound imaging of vein at time of venipuncture

E. Ultrasound of lung apices during procedure to avoid pneumothorax

6.2 A 22-year-old woman has just arrived to the intensive care unit from an uneventful femur fixation in the operating room. During transport, her oxygen saturations dropped to 82%. The respiratory therapist reports that she became more difficult to ventilate with the Ambu-bag ( transport ventilation device). On your preliminary examination, she has absent breath sounds on the right and her respiratory rate is 34 breaths/minute and her oxygen saturations are now 87% with an increase to 100% inspired oxygen on the ventilator. The patient's blood pressure is 115/70 mm Hg and heart rate is 110 beats/minute. Which of the following diagnostic test is most likely to be helpful?

A. Ultrasound of the abdomen

B. Computed tomography of the chest

C. Portable chest film

D. MRI of the chest

E. Nuclear medicine scan of the chest

6.3 A 67-year-old man is brought to the emergency department after being found unconscious in his backyard. On initial evaluation, he is unresponsive, his skin is ashen, extremities are cool, and he is perspiring. His blood pressure is 80/65 mm Hg, heart rate is 102 beats/minute, and he has distended neck veins. He is intubated and has bilateral breath sounds. There are several trauma resuscitations on other patients occurring simultaneously and you are given one choice of diagnostic machine to use (because all the equipment is being shared ) .

Which instrument would you choose?

A. Portable chest radiograph machine

B. ECG machine

C. Ultrasound machine with echocardiography probe and Doppler flow

D. CT scan

E. Ultrasound with thoracic and abdomen soft tissue probe

6.4 A hospital has recently identified that transporting critically ill patients to the CT imaging has inherent hazards. Which of the following patients is most appropriate to have a CT scan?

A. A 87 -year-old woman, BP 110/70 mm Hg, HR 90 beats/minute, RR 14 breaths/minute, O2sat 95 % with ipsilateral decreased breath sounds after sat central line placement.

B. A 3 70-lb man, with a subhepatic abscess and extensive subcutaneous emphysema. He is fully resuscitated but remains on 2 vasopressor agents and has a mean arterial pressure of 72 mm Hg.

C. A 43 -year-old man on the ventilator with increased peak airway pressures, increased work of breathing, and diminished breath sounds on the left.

D. A 92-year-old woman with BP 86/48 mm Hg, HR 105 beats/minute, RR 18 breaths/minute, serum creatinine of 2.1 mg/dL, and distended neck veins.

E. A 22-year-old man, who was stabbed with a 3 -in knife in the third intercostal space, lateral to the right nipple, BP 128/78 mm Hg, HR 82 beats/ minute, RR 12 breaths/minute.

ANSWERS TO QUESTIONS

6.1 D. "Real-time" imaging of the internal jugular vein while it is being cannulated has been shown to be the safest approach when compared to the anatomic landmark technique and when compared to pre-procedure vein location marking.

6.2 C. Chest Radiograph is most appropriate. Although thoracic computed tomography can give valuable information on chest pathophysiology, the patient presented with acute respiratory decompensation and signs worrisome for right pneumothorax. Transport to the CT scanner in such a tenuous patient would invite catastrophe. Modalities such as bedside thoracic ultrasound to evaluate presence or absence of pleural sliding and portable chest radiograph (performed in a timely manner) could both identify a clinically significant pneumothorax. Right needle thoracostomy can be performed in patients in whom you have a high index of suspicion for pneumothorax. This procedure, when performed appropriately, is of relatively low risk and transient therapeutic benefit. Repeating auscultation once a room quiets down is quick, easy, and can help confirm presence or absence of breath sounds. The important point here is if a patient is unstable and diagnosis can be made at the bedside, it is safest not to transport the patient elsewhere for diagnostics.

6.3 C. The patient presents in shock with no available history. Clinical findings suggest cardiac dysfunction with severe malperfusion and distended neck veins. Although an ECG can give some information that can help rule in or out a potential infarction, a bedside echocardiogram can quickly identify anatomic and functional abnormalities such as pericardia! tamponade, papillary muscle

rupture, severe wall motion abnormalities, septal rupture, and so on. With echocardiography, the patient's volume status can also be estimated, as can the presence of increase pulmonary vascular pressures. In the instance of tamponade, echocardiography can be used real-time for a safer method of pericardiocentesis.

6.4 B. Of the patients listed, the obese man with subcutaneous emphysema will likely be technically challenging for bedside ultrasound-guided drainage of his subhepatic abscess. His body habitus and the subcutaneous air will increase artifacts and lessen the safety of the ultrasound-guided technique. CT-guided abscess drainage offers a much safer route for patients who have limited ultrasound views. Patients "A, C, and E" all have suspected pulmonary diagnoses that can be evaluated with either portable radiographs or thoracic ultrasound. Patient "D" has a likely cardiac source for her symptoms and can be evaluated with bedside echocardiography.

References

Beaulieu Y, Marik PE. Bedside ultrasound in the ICU: Part 1 . Chest . 2005 ; 1 28:88 1 -895 . 

Guillory RK, Gunter OL. Ultrasound in the surgical intensive care unit. Curr Opin Crit Care . 2008 ; 1 4 : 4 1 5 -422. 

McLean AS, Needham A, Stewart D, et al. Estimation of cardiac output by noninvasive echocardiographic techniques in critically ill subj ects. Anaesth Intensive Care . 1997;25 :250-254. 

Oba Y, Zaza T. Abandoning daily routine chest radiography in the intensive care unit: meta-analysis. Radiology. 2 0 1 0 ; 2 5 5 :386-395 . 

Vigno P, Mucke F, Bellec F, et al. Basic critical care echocardiography: validation of a curriculum dedicated to noncardiologist residents. Crit Care Med . 2 0 1 1 ;3 9 : 63 6-642.

HomeCritical Care Case FileImaging in Critical Care Case File