Other Causes of Hypoxemia

Other Causes of Hypoxemia

Hassan Mashbari

Ahmed Al Hazmi

Osaid Alser

Matthew Mueller

Christopher R. Tainter

1. A 75-year-old woman with a history of chronic obstructive pulmonary disease (COPD) and recent viral upper respiratory tract infection presents to the Emergency Department (ED) with shortness of breath. She reports that her breathing has become more labored over the last 24 hours and she is using her inhaler more frequently than usual. Her vital signs are significant for HR 120 bpm, BP 150/85 mm Hg, RR 24/min, SpO2 90% on 4 L/min by nasal cannula, and a temperature of 38.3°C. On examination, breath sounds are diminished over the left lower lobe and diffuse expiratory wheezes are appreciated. Point-of-care ultrasound is performed and demonstrates Figure 59.1 (relevant structures marked by the white arrows) from her left lateral chest wall.

What is the most likely diagnosis?

A. Pleural effusion

B. Community-acquired pneumonia

C. Pulmonary edema

D. Pneumothorax

View Answer

1. Correct Answer: B. Community-acquired pneumonia Rationale/Critique: Older patients and those with underlying lung disease, such as COPD, are at an increased risk for developing community-acquired pneumonia. Pneumonia may not be present on chest radiography early in its course, but can be visualized by ultrasound with >95% sensitivity and >90% specificity. Areas of focal consolidation appear as a hypoechoic disruption of the pleural line. Fluid-filled consolidated lung causes a heterogeneous appearance on ultrasound, similar to liver tissue, which is termed “hepatization.” Air bronchograms (white arrows in Figure 59.1) can also be seen (as in the image above), which are scattered small hyperechoic structures caused by focal areas of aeration reflecting the ultrasound waves.

A pleural effusion (Answer A) will appear as a hypoechoic region in dependent lung regions. The presence of B-lines suggests pulmonary edema (Answer C). The absence of lung sliding or the presence of a lung point suggests a pneumothorax.

Selected References

1. Chavez MA, Shams N, Ellington LE, et al. Lung ultrasound for the diagnosis of pneumonia in adults: a systematic review and meta-analysis. Respir Res. 2014;15(1):50. doi:10.1186/1465-9921-15-50.

2. Ellington LE, Gilman RH, Chavez MA, et al. Lung ultrasound as a diagnostic tool for radiographically-confirmed pneumonia in low resource settings. Respir Med. 2017;128:57-64. doi:10.1016/j.rmed.2017.05.007.

2. A 32-year-old woman with an elevated body mass index (BMI) presents to the ED with shortness of breath, hemoptysis, and calf pain 1 day after returning home from international travel. On presentation, her vital signs are significant for HR 115 bpm, BP 90/55 mm Hg, RR 22/min, SpO2 92% on room air, and temperature 37.9°C. On examination, she is tachypneic, her lungs are clear to auscultation bilaterally, and her right lower extremity is tender, erythematous, and has 2+ pitting edema. A point-of-care echocardiogram is performed (Figure 59.2).

Given the most likely etiology of her presentation, what additional ultrasound finding is likely to be present?

A. Tricuspid annular plane systolic excursion (TAPSE) 1.5 cm

B. Septal motion toward the right ventricle during diastole

C. Right ventricular (RV):left ventricular (LV) ratio 0.6

D. RV apical hypokinesis, sparing the base

View Answer

2. Correct Answer: A. Tricuspid annular plane systolic excursion (TAPSE) 1.5 cm

Rationale: Point-of-care ultrasound can support the diagnosis of pulmonary embolism (PE) in a patient with a high pretest probability, such as this patient. Sonographic findings suggestive of PE include:

  • RV dilatation

  • End-diastolic RV:LV ratio ≥1 visualized in the apical four- or five-chamber view

  • McConnell sign: RV free wall akinesis/hypokinesis sparing the apex, suggesting acute regional ventricular dysfunction

  • D-sign: interventricular septal flattening can be visualized on the parasternal short-axis view of the heart.

  • Paradoxical motion of the interventricular septum

  • RV hypokinesis: TAPSE <1.6 cm

Selected Reference

1. Dudzinski DM, Hariharan P, Parry BA, Chang Y, Kabrhel C. Assessment of right ventricular strain by computed tomography versus echocardiography in acute pulmonary embolism. Acad Emerg Med. 2017;24(3):337-343. doi:10.1111/acem.13108.

3. A 65-year-old man with a history of hypertension, hyperlipidemia, and insulin-dependent diabetes presents to the ED with chest pain and shortness of breath that awoke him from sleep. On presentation, his vital signs are significant for HR 115 bpm, BP 190/105 mm Hg in his right arm and 160/90 in his left arm, RR 18/min, temperature 37.2°C, and SpO2 88% on 5 L by nasal cannula. Physical examination demonstrates an anxious, pale, and diaphoretic man with asymmetric radial pulses. A point-of-care echocardiogram demonstrates the finding shown in Figure 59.3.

The acute, severe valvulopathy associated with this condition can be diagnosed by which of the following criteria?

A. Peak velocity > 4 m/s

B. Vena contracta width > 5 mm

C. Central jet ≥65% of the LV outflow tract (LVOT)

D. Mean pressure gradient >50 mm Hg

View Answer

3. Correct Answer: C. Central jet ≥ 65% of the LV outflow tract (LVOT)

Rationale: According to the Stanford classification of aortic dissection, a Type A dissection involves the ascending aorta and may also involve the descending aorta, while a Type B dissection includes only the descending aorta. Type A dissections can cause acute, severe aortic insufficiency, which can be diagnosed by measuring the central jet as ≥65% of the LVOT (Answer C). Other findings include:

  • Vena contracta >6 mm

  • Regurgitant volume >60 mL/beat

  • Regurgitant fraction >50%

  • Effective regurgitant orifice area ≥0.30 cm2

Peak velocity and mean gradient are typically used to evaluate stenotic lesions.

Selected References

1. Orde S. Valvulopathy quantification. In: Slama M, eds. Echocardiography in ICU. Springer; 2020. doi.org/10.1007/978-3-030-32219-9_22.

2. Sobczyk D, Nycz K. Feasibility and accuracy of bedside transthoracic echocardiography in diagnosis of acute proximal aortic dissection. Cardiovasc Ultrasound. 2015;13:15. doi:10.1186/s12947-015-0008-5.

3. von Homeyer P, Oxorn DC. Aortic regurgitation: echocardiographic diagnosis. Anesth Analg. 2016;122(1):37-42. doi:10.1213/ANE.0000000000001013.

4. You are called to evaluate a 27-year-old man with a history of intravenous (IV) drug abuse for worsening dyspnea. He presented to the ED the prior day with chest pain and shortness of breath. He was diagnosed with infective endocarditis, started on broad-spectrum antibiotics, and admitted to the hospital, although he eloped overnight. On evaluation, the patient is in respiratory distress and has audible crackles. A point-of-care echocardiogram is performed demonstrating Figure 59.4.

Which of the following structures is the most likely to be impacted?

A. Chordae tendineae

B. Pectinate muscles

C. Moderator band

D. Trabeculae carneae

View Answer

4. Correct Answer: A. Chordae tendineae

Rationale: Acute mitral regurgitation can occur as a result of rupture of the chordae tendineae (Answer A) or papillary muscles and can be a result of infective endocarditis, acute myocardial infarction, cardiac disease (eg, rheumatic heart disease), or may occur spontaneously. Acute mitral regurgitation can result in the rapid progression of pulmonary edema secondary to cardiogenic shock. Echocardiographic findings consistent with severe mitral regurgitation are:

  • Jet area: >8 cm2

  • Jet area: left atrial area: >40%

  • Vena contracta: >7 mm

  • Estimated orifice area: >0.4 cm2

Selected References

1. Grigioni F, Russo A, Pasquale F, et al. Clinical use of Doppler echocardiography in organic mitral regurgitation: from diagnosis to patients’ management. J Cardiovasc Ultrasound. 2015;23(3):121-133. doi:10.4250/jcu.2015.23.3.121.

2. Orde S. Valvulopathy quantification. In: Slama M, eds. Echocardiography in ICU. Springer; 2020. doi.org/10.1007/978-3-030-32219-9_22.

5. A 34-year-old man with a history of IV drug use and bioprosthetic tricuspid valve presents to the ED with shortness of breath and fatigue. His vital signs are significant for HR 105 bpm, BP 105/55 mm Hg, RR 22/min, temperature 38.2°C, and SpO2 87% on room air. A point-of-care echocardiogram is shown in Figure 59.5.

Which of the following is the most likely additional ultrasonographic finding?

A. Mitral valve mean gradient >10 mm Hg

B. LV end-diastolic pressure >25 mm Hg

C. Pulmonary artery pressure 60 mm Hg

D. Hepatic vein flow reversal

View Answer

5. Correct Answer: D. Hepatic vein flow reversal

Rationale: IV drug use can lead to tricuspid endocarditis and subsequently to tricuspid regurgitation. Valvular vegetations appear as echogenic masses that may be loose and mobile throughout the cardiac cycle. Ultrasonographic findings consistent with severe tricuspid regurgitation are:

  • Regurgitant jet area: >10 cm2

  • Vena contracta: >7 mm

  • Regurgitant volume: >45 mL

  • Tricuspid inflow E-wave velocity: >1 m/s

  • Hepatic vein systolic flow reversal

Of the answer choices listed, tricuspid regurgitation would only lead to hepatic vein flow reversal.

Selected References

1. Badano LP, Muraru D, Enriquez-Sarano M. Assessment of functional tricuspid regurgitation. Eur Heart J. 2013;34(25): 1875-1885. doi:10.1093/eurheartj/ehs474.

2. Yuan XC, Liu M, Hu J, Zeng X, Zhou AY, Chen L. Diagnosis of infective endocarditis using echocardiography. Medicine (Baltimore). 2019;98(38):e17141. doi:10.1097/MD.0000000000017141.

6. A 72-year-old man with a history of COPD and group 3 pulmonary hypertension is admitted to the intensive care unit (ICU) for respiratory failure and hypotension. The patient is started on nebulized bronchodilators and noninvasive positive pressure ventilation. Point-of-care echocardiography is performed and demonstrates Figure 59.6.

Which of the following is most consistent with right heart failure?

A. Pulsed-wave Doppler S-wave >9.5 cm/s

B. TAPSE < 17 mm

C. RV fractional area change <45%

D. RV myocardial performance index (MPI) 0.8

View Answer

6. Correct Answer: B. TAPSE < 17 mm

Rationale: COPD and PE are common causes of cor pulmonale, which is defined as enlargement of the right ventricle with resultant RV failure. Echocardiogram demonstrates RV hypertrophy or dilatation, and right atrial enlargement, and in most cases pulmonary hypertension and tricuspid regurgitation can be seen. RV dysfunction can be diagnosed on echocardiography by measuring TAPSE on an apical four-chamber view (Answer B). Findings consistent with RV dysfunction include:

  • TAPSE <17 mm

  • Pulsed-wave Doppler S-wave <9.5 cm/s

  • Tissue Doppler S-wave <6 cm/s

  • RV fractional area change <35%

  • RV ejection fraction <45%

  • Pulsed-wave Doppler MPI >0.43

  • Tissue Doppler MPI >0.54

  • E-wave deceleration time <119 or >242 msec

  • E/A <0.8 or >2.0

  • e′/a′ <0.52

  • e′ <7.8

  • E/e′ >6.0

Selected References

1. Lang RM, Badano LP, Mor-Avi V, et al. Recommendations for cardiac chamber quantification by echocardiography in adults: an update from the American Society of Echocardiography and the European Association of Cardiovascular Imaging [published correction appears in Eur Heart J Cardiovasc Imaging. 2016;17(4):412 [published correction appears in Eur Heart J Cardiovasc Imaging. 2016;17 (9):969]. Eur Heart J Cardiovasc Imaging. 2015;16(3):233-270. doi:10.1093/ehjci/jev014

2. Vieillard-Baron A, Prin S, Chergui K, Dubourg O, Jardin F. Echo-Doppler demonstration of acute cor pulmonale at the bedside in the medical intensive care unit. Am J Respir Crit Care Med. 2002;166(10):1310-1319. doi:10.1164/rccm.200202-146CC.

7. A 70-year-old woman with COPD and a 50 pack-year smoking history presents to the ED with shortness of breath. She reports that her dyspnea is worsened on exertion, her cough is newly productive of green sputum, and she is using inhaled bronchodilators every hour with minimal relief. On presentation, she is tachypneic, has audible wheezes, and breath sounds are diminished at the right lung base. Nebulized bronchodilators and oral glucocorticoids are administered for presumed COPD exacerbation. Point-of-care ultrasound is performed to further evaluate the etiology of the auscultatory finding. What is the smallest volume of pleural fluid that can be visualized on thoracic ultrasound?

A. 5 mL

B. 50 mL

C. 150 mL

D. 200 mL

View Answer

7. Correct Answer: A. 5 mL

Rationale: Thoracic ultrasound can detect as little as 5 mL of pleural fluid (Answer A), but sensitivity and specificity are improved when ≥ 20 mL is present. Posteroanterior radiographs require 200 mL of pleural fluid to be detected, while lateral views can detect effusions when at least 50 mL of pleural fluid is present.

Selected References

1. Brogi E, Gargani L, Bignami E, et al. Thoracic ultrasound for pleural effusion in the intensive care unit: a narrative review from diagnosis to treatment. Crit Care. 2017;21(1):325. doi:10.1186/s13054-017-1897-5

2. Miles MJ, Islam S. Point of care ultrasound in thoracic malignancy. Ann Transl Med. 2019;7(15):350. doi:10.21037/atm.2019.05.53.

3. Soni NJ, Franco R, Velez MI, et al. Ultrasound in the diagnosis and management of pleural effusions. J Hosp Med. 2015;10(12):811-816. doi:10.1002/jhm.2434.

8. A 25-year-old woman with a past medical history of severe persistent asthma presents to the ED with sudden-onset shortness of breath and wheezing. On presentation, she is in respiratory distress and is brought to the resuscitation bay for immediate evaluation. Vital signs are significant for HR 130 bpm, RR 30/min, BP 80/50 mm Hg, temperature 38.0°C, and SpO2 88% on 15 L via non-rebreather mask. Point-of-care ultrasound demonstrates Figure 59.7.

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Jun 9, 2022 | Posted by in CARDIOLOGY | Comments Off on Other Causes of Hypoxemia

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