# Point-of-Care Ultrasound (POCUS) in Internal Medicine

## Introduction

**Point-of-care ultrasound (POCUS)** is a focused, bedside imaging modality performed and interpreted by the treating clinician to answer specific clinical questions. In internal medicine, POCUS has transformed the physical examination by enabling real-time visualization of anatomy and physiology, improving diagnostic accuracy, and guiding procedures.

## Core POCUS Applications in Internal Medicine

### Cardiac Ultrasound

- **Parasternal long axis (PLAX)**: assess LV function, pericardial effusion, mitral and aortic valves
- **Parasternal short axis (PSAX)**: evaluate RV strain (D-sign), regional wall motion
- **Apical four-chamber**: compare RV and LV size, assess global function
- **Subxiphoid**: best view for pericardial effusion; evaluate IVC for volume assessment
- Qualitative **LV ejection fraction** (hyperdynamic, normal, reduced, severely reduced) is reliable with training

### Lung Ultrasound

| Finding | Appearance | Clinical Significance |
|---------|------------|---------------------|
| A-lines | Horizontal reverberation artifacts | Normal aeration (or pneumothorax if no sliding) |
| B-lines (≥3/zone) | Vertical laser-like artifacts | Interstitial syndrome (edema, ILD) |
| Lung sliding present | Shimmering at pleural line | Rules out pneumothorax at that location |
| Lung sliding absent + barcode sign | No shimmering; M-mode stratospheric | Pneumothorax |
| Anechoic space above diaphragm | Dark fluid collection | Pleural effusion |
| Hepatization / tissue sign | Lung looks like liver | Consolidation / atelectasis |

- **A-lines**: horizontal reverberation artifacts indicating normal aeration or pneumothorax
- **B-lines**: vertical laser-like artifacts from pleural line; 3+ per intercostal space indicates interstitial syndrome (pulmonary edema, interstitial lung disease)
- **Lung sliding**: rules out pneumothorax at that location; absent sliding with barcode sign on M-mode suggests pneumothorax
- **Pleural effusion**: anechoic fluid above the diaphragm; estimate size and guide thoracentesis
- The **BLUE protocol** rapidly differentiates causes of acute dyspnea

![POCUS lung ultrasound findings and clinical correlations](images/lung-ultrasound-findings.png)

### Abdominal Ultrasound

- **FAST exam (Focused Assessment with Sonography for Trauma)**: detects free fluid in Morrison's pouch, splenorenal recess, and pelvis
- **Aorta**: screen for abdominal aortic aneurysm; measure AP diameter at three levels
- **Renal**: identify hydronephrosis; assess bladder volume to guide catheterization
- **Gallbladder**: detect gallstones, wall thickening, pericholecystic fluid, sonographic Murphy sign

### Vascular Ultrasound

- **IVC assessment**: IVC diameter and collapsibility index to estimate volume status
- IVC < 2.1 cm with > 50% collapse suggests low CVP; IVC > 2.1 cm with < 50% collapse suggests elevated CVP
- **DVT assessment**: two-point compression at common femoral and popliteal veins; non-compressibility indicates thrombus
- **Peripheral IV access**: ultrasound-guided peripheral IV placement increases first-attempt success

## Volume Status Assessment: The Integrated Approach

- No single POCUS finding should be used in isolation to determine volume status
- Combine **IVC assessment**, **lung B-lines**, **LV function**, and **pleural effusion** for a comprehensive picture
- The **VExUS score** (Venous Excess Ultrasound Score) evaluates venous congestion through hepatic vein, portal vein, and renal vein Doppler
- Integrate POCUS findings with clinical assessment, vital signs, and laboratory data

![Integrated POCUS volume status assessment framework](images/pocus-volume-assessment.png)

## Procedural Guidance

- **Central venous catheterization**: real-time ultrasound guidance is standard of care; reduces complications and improves success
- **Thoracentesis**: ultrasound marking or real-time guidance reduces pneumothorax risk
- **Paracentesis**: identify optimal entry site and avoid inferior epigastric vessels
- **Arthrocentesis**: improves accuracy particularly for small or difficult joints
- **Lumbar puncture**: identify midline, interspace level, and depth to posterior complex

## Training and Competency

- The **Society of Hospital Medicine (SHM)** POCUS certificate program includes cardiac, lung, abdominal, vascular, and procedural modules
- Minimum recommended training: **25-50 supervised scans per application** for basic competency
- **Image archival and quality assurance** programs should be established
- POCUS does not replace comprehensive imaging but answers focused clinical questions
- Document findings in the medical record including images

![POCUS training competency milestones](images/pocus-training-milestones.png)

## Limitations and Pitfalls

- **Operator-dependent**: quality varies with training and experience
- **Body habitus**: obesity and subcutaneous emphysema limit image quality
- **Overconfidence**: POCUS answers binary questions; complex pathology requires formal imaging
- **Incidental findings**: must be followed up with appropriate confirmatory studies
- Cannot replace echocardiography for valvular quantification or diastolic function assessment

## Key Clinical Pearls

- POCUS transforms the physical examination by adding real-time visual data to clinical assessment.
- Lung ultrasound is more sensitive than chest X-ray for detecting pleural effusion, pneumothorax, and pulmonary edema.
- IVC assessment should be integrated with other POCUS findings rather than used in isolation for volume assessment.
- Ultrasound-guided procedures are standard of care for central lines and strongly recommended for thoracentesis and paracentesis.
- Competency requires structured training, supervised scanning, and ongoing quality assurance.

## References

1. Defined the Core Point-of-Care Ultrasound Competencies. Society of Hospital Medicine Position Statement on POCUS. *Journal of Hospital Medicine*. 2019;14:E1-E6.
2. Lichtenstein DA, Meziere GA. Relevance of Lung Ultrasound in the Diagnosis of Acute Respiratory Failure: The BLUE Protocol. *Chest*. 2008;134(1):117-125.
3. Defined the Core Competencies for Internal Medicine Residency. Soni NJ, Arntfield R, Kory P. *Point-of-Care Ultrasound*. 2nd ed. Philadelphia: Elsevier; 2019.
4. Defined the Core Competencies. Franco-Sadud R, Schnobrich D, Engel D, et al. A Focused Cardiac Ultrasound Curriculum for Internal Medicine Residents. *Journal of Graduate Medical Education*. 2021;13(4):474-482.