Write a short note on perioperative use of pocus for My MD Anaesthesiology exam
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I now have comprehensive, exam-grade content from Barash Clinical Anesthesia 9e. Let me write the exam note.
Perioperative Use of POCUS (Point-of-Care Ultrasound) in Anaesthesia
(Barash Clinical Anesthesia 9e; Miller's Anesthesia 10e)
Definition
Point-of-care ultrasound (POCUS) is the use of ultrasonography at the bedside to rapidly answer specific, goal-oriented diagnostic questions or guide acute care procedures. It differs fundamentally from consultative (radiologist/cardiologist) ultrasonography in that it is:
- Narrower in scope (goal-directed, not comprehensive)
- Performed and interpreted by the treating clinician
- Repeated serially to monitor response to therapy
- Mostly limited to 2D imaging
Why POCUS for Anaesthesiologists?
POCUS spans the entire perioperative spectrum - preoperative assessment, intraoperative monitoring, postoperative care, and ICU. The American Board of Anesthesiology (ABA) content guidelines and ASA educational programs now include POCUS as a key clinical competency. It represents a "disruptive innovation" that is cheaper, faster, and more accessible than formal echocardiography.
Perioperative Phases and POCUS Applications
1. Preoperative
- Identify severe LV systolic dysfunction (LV wall thickening <30%; LV emptying <50%; MAPSE <8 mm)
- Detect significant valvular disease (aortic stenosis, MR, AR) before high-risk surgery
- Assess RV size and function - RV dilation, interventricular septal deviation (D-sign) suggestive of RV pressure/volume overload
- Assess IVC collapsibility as a surrogate for volume status
- Predict difficult airway: pre-tracheal soft tissue thickness >2.8 cm at vocal cord level predicts difficult laryngoscopy
- Identify gastric contents to guide aspiration risk (antral cross-section area >9.6 cm² in supine = at-risk stomach; Grade 0/1/2 classification)
2. Intraoperative
- Hemodynamic monitoring: detect cause of intraoperative hypotension rapidly
- Hypovolemia: small, hyperdynamic LV, collapsible IVC
- LV failure: severely reduced LV systolic function
- RV failure: dilated RV with septal shift, plethoric IVC
- Obstructive shock (tamponade, massive PE): specific POCUS signs
- Distributive shock: hyperdynamic LV with preserved function
- Tamponade features on POCUS:
- IVC plethora (>2 cm, non-collapsing)
- Diastolic RV collapse (best on M-mode, PLAX view)
- RA collapse >1/3 of cardiac cycle
- Exaggerated respiratory variation: mitral inflow >25%, tricuspid >40%
- Lung POCUS:
- Pneumothorax: absent lung sliding ("barcode sign" on M-mode); confirmed absence of B-lines or lung pulse
- Pulmonary edema: bilateral B-lines (>3 in multiple zones)
- Pleural effusion: hypoechoic areas in posterior costophrenic angles
- Consolidation: tissue-like (hepatised) lung, shred sign for focal subpleural disease
- Airway POCUS:
- Confirm endotracheal tube position (bilateral lung sliding) - especially valuable in low cardiac output states where capnography may be unreliable
- Identify cricothyroid membrane for emergency front-of-neck access
- Vascular access: Ultrasound-guided CVC insertion (IJV, subclavian, femoral) - now the standard of care; real-time guidance reduces complications
3. Postoperative / Critical Care
- Reassess volume status and cardiac function post-resuscitation
- Serial monitoring of treatment response (fluid, inotrope, vasopressor)
- FAST exam (Focused Assessment with Sonography for Trauma): four standard views - subxiphoid (pericardial), RUQ (Morrison's pouch), LUQ (perisplenic), suprapubic; sensitivity 74-82%, specificity 96-99% for blunt thoracoabdominal trauma
- E-FAST: adds anterior thoracic views for pneumothorax detection (sensitivity 91%, specificity 99% vs. CXR sensitivity 47%)
Focused Cardiac POCUS - Core Clinical Questions
| Clinical Question | Key POCUS Finding |
|---|---|
| Severe LV systolic dysfunction? | Wall thickening <30%; chamber emptying <50%; MAPSE <8 mm |
| Severe RV dilation/dysfunction? | Decreased RV free wall motion; septal deviation toward LV; RV emptying <35% |
| Cardiac tamponade? | IVC plethora; diastolic RV collapse; RA collapse; respiratory valvular variation |
| Hypovolemia? | IVC <2 cm with >50% collapse; small hyperkinetic LV |
| LVOT obstruction (SAM)? | Systolic anterior motion of anterior mitral leaflet on PLAX or A5C |
| Elevated LA pressure? | B-lines bilaterally; interatrial septal bowing right; E/A >2 or E/e' >14 |
| Aortic dissection? | Dissection flap in ascending aorta on PLAX/suprasternal views |
| Stroke volume assessment? | LVOT VTI (A5C/A3C) × LVOT area (PLAX) |
| Fluid responsiveness? | LVOT VTI change >15-20% with therapeutic maneuver |
| Pulmonary hypertension? | TR Vmax with CVP to calculate PAP |
Lung POCUS - Key Signs
| Sign | Meaning |
|---|---|
| Lung sliding | Normal aerated pleura; rules out ipsilateral pneumothorax |
| A-lines | Horizontal reverberation artifacts; normal aerated lung |
| B-lines | Vertical comet-tail artifacts reaching screen edge; indicate interstitial fluid; ≥3 per zone = significant |
| Barcode/stratosphere sign (M-mode) | Absent lung sliding = pneumothorax |
| Seashore sign (M-mode) | Normal lung sliding |
| Shred sign | Irregular border between consolidated and aerated lung |
| Hepatisation | Consolidated lung resembling liver texture |
| Diaphragm thickening | >30% thickening with inspiration = normal function |
Gastric POCUS (Aspiration Risk Assessment)
- Right lateral decubitus position (gastric antrum moves anteriorly)
- Grade 0: empty in both supine and RLD - low risk
- Grade 1: fluid only in RLD - low risk
- Grade 2: fluid in both supine and RLD - high risk; antral cross-sectional area >9.6 cm² in supine = at-risk stomach (>1.5 mL/kg)
- Useful before emergency/non-fasted surgery and obstetric anaesthesia
POCUS-Guided Procedures in Anaesthesia Practice
- Central venous cannulation - IJV, subclavian, femoral; reduces accidental arterial puncture and pneumothorax
- Arterial line insertion - radial, femoral
- Peripheral venous access (difficult IV)
- Regional anaesthesia / nerve blocks (covered separately - brachial plexus, femoral, sciatic, etc.)
- Thoracentesis and pericardiocentesis guidance
- Nasogastric tube confirmation
- Cricothyroid membrane identification (emergency airway)
POCUS vs. Consultative Echocardiography
| Feature | POCUS | Consultative Echo |
|---|---|---|
| Scope | Goal-directed, limited | Comprehensive |
| Training needed | Less extensive | Extensive (cardiology/radiology) |
| Imaging modalities | Primarily 2D | 2D, 3D, Doppler, strain |
| Purpose | Answer specific clinical question | Diagnose and grade a range of pathologies |
| Performed by | Treating clinician (anaesthesiologist) | Sonographer + specialist |
| Setting | Bedside, intraoperative, ICU | Echo lab |
| Repeatability | Yes, serially | Not always practical |
POCUS Protocols in Anaesthesia
- FAST/E-FAST - Trauma
- RUSH (Rapid Ultrasound in SHock) - undifferentiated shock
- BLUE (Bedside Lung Ultrasound in Emergency) - acute respiratory failure
- FALLS (Fluid Administration Limited by Lung Sonography) - fluid management
- HIMAP - Heart, IVC, Morrison's pouch, Aorta, Pleura
Training and Certification
- USA: National Board of Echocardiography (NBE) - Basic/Advanced Perioperative TEE; Critical Care Echo - requires documented number of examinations under supervision + cognitive exam
- ABA expects echocardiographic recognition of normal cardiac anatomy (TEE) in residency; ACGME requires TEE placement/use as a competency
- European Society of Intensive Care Medicine (2020): framework of 15 echocardiographic competencies + thoracic/abdominal/vascular US
- Society of Cardiovascular Anesthesiologists (SCA) and ASE joint guidelines (2013): basic perioperative TEE training objectives
- Handheld/portable devices have accelerated POCUS adoption worldwide
Limitations of POCUS
- Operator-dependent (skill and knowledge)
- Visual information must be interpreted in clinical context
- Mainly 2D; cannot fully replace comprehensive echo (Doppler, 3D, strain)
- Image quality limited by obesity, subcutaneous emphysema, chest deformity, dressings
- Cannot diagnose retroperitoneal, diaphragmatic, pancreatic, or bowel injuries reliably (FAST)
- Negative FAST does not exclude significant injury when clinical suspicion is high
High-Yield Exam Summary
"POCUS for the anaesthesiologist goes beyond assessment of cardiac function and hemodynamic status, and includes assessment of lung pathology, gastric contents, and airway." - Barash Clinical Anesthesia 9e
- Preop: cardiac function, valve disease, volume status, aspiration risk, airway prediction
- Intraop: hemodynamic monitoring, cause of hypotension, tamponade, lung pathology, tube confirmation, vascular access
- Postop/ICU: FAST, E-FAST, serial reassessment
- Lung US B-lines = interstitial fluid (pulmonary edema/ARDS/pneumonia)
- Absent lung sliding = pneumothorax until proven otherwise
- Gastric antral area >9.6 cm² supine = full/at-risk stomach
- Fluid responsiveness: LVOT VTI change >15-20%
Sources: Barash, Cullen, and Stoelting's Clinical Anesthesia, 9e (Ch. 27, 53); Miller's Anesthesia, 10e (Ch. 26)
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