What are the steps to rule out the Hs (hypovolemia, hypoxia, hyperkalemia, hypokalemia, hypothermia, hydrogen ions acidosis) and Ts (tamponade, tension pneumothorax, toxins, thrombosis) in cardiac arrest?

Systematic Approach to Rule Out Hs and Ts in Cardiac Arrest

Bedside cardiac ultrasonography (BCU) should be performed during cardiac arrest to rapidly identify and address potentially reversible causes of pulseless electrical activity (PEA) and asystole, as this can significantly impact patient survival. 1

Initial Assessment (During CPR)

Immediate Diagnostic Steps

• Perform BCU during cardiac arrest with minimal interruption to chest compressions (≤10 seconds) 1
• Use waveform capnography to monitor CPR quality and detect ROSC 1
• Obtain 12-lead ECG as soon as possible after ROSC 2

Systematic Evaluation of Hs

1. Hypovolemia

   • BCU findings: Small, hyperdynamic left ventricle, collapsed IVC 1
   • Clinical indicators: History of blood loss, dehydration, excessive diuresis
   • Management: Rapid IV/IO crystalloid administration; blood transfusion for hemorrhage 1

2. Hypoxia

   • Monitor: Low SpO2, low PETCO2 despite adequate CPR
   • Clinical indicators: History of respiratory distress, airway obstruction
   • Management: Ensure proper airway management, ventilation with 100% oxygen 1

3. Hydrogen ion (Acidosis)

   • Laboratory: Arterial blood gas showing pH <7.2
   • Clinical indicators: History of diabetic ketoacidosis, renal failure, sepsis
   • Management: Treat underlying cause; ensure adequate ventilation 1

4. Hyperkalemia/Hypokalemia

   • ECG findings: Tall, peaked T waves, widened QRS (hyperkalemia); U waves, flattened T waves (hypokalemia)
   • Laboratory: Serum potassium levels
   • Management: Calcium, insulin/glucose, sodium bicarbonate for hyperkalemia; potassium replacement for hypokalemia 1

5. Hypothermia

   • Clinical indicators: Cold skin, history of environmental exposure
   • Core temperature measurement
   • Management: Active internal rewarming; continue resuscitation until core temperature >32°C 1

Systematic Evaluation of Ts

1. Tamponade (Cardiac)

   • BCU findings: Pericardial effusion with right atrial/ventricular diastolic collapse 1
   • Clinical indicators: Distended neck veins, muffled heart sounds
   • Management: Pericardiocentesis (echocardiography-guided if available) 1

2. Tension Pneumothorax

   • BCU/chest ultrasound findings: Absence of lung sliding, absence of B-lines, lung point sign 1
   • Clinical indicators: Decreased breath sounds, tracheal deviation, distended neck veins
   • Management: Immediate needle decompression followed by chest tube placement 1

3. Thrombosis (Coronary)

   • ECG findings: ST-segment elevation, new LBBB
   • BCU findings: Regional wall motion abnormalities 1
   • Management: Consider fibrinolytic therapy or immediate coronary intervention after ROSC 2

4. Thrombosis (Pulmonary)

   • BCU findings: Right ventricular dilation and dysfunction, McConnell's sign 1
   • Clinical indicators: History of immobilization, cancer, recent surgery
   • Management: Consider fibrinolytic therapy when pulmonary embolism is suspected 1

5. Toxins

   • Clinical indicators: History of ingestion, medication overdose, specific toxidromes
   • Management: Specific antidotes when available; supportive care 1

Advanced Diagnostic Techniques

Bedside Cardiac Ultrasonography (BCU)

• Perform during brief pauses in chest compressions (≤10 seconds) 1
• Views to obtain:
  • Subcostal four-chamber view (first choice during CPR)
  • Parasternal long-axis view
  • Apical four-chamber view 1

Point-of-Care Testing

• Arterial blood gas: Assess for acidosis, hypoxemia
• Electrolytes: Particularly potassium, calcium, magnesium
• Lactate: Marker of tissue hypoperfusion
• Toxicology screening when indicated 3

Post-ROSC Evaluation

1. Obtain 12-lead ECG immediately to detect ST elevation or new LBBB 2
2. Perform comprehensive BCU to assess cardiac function 1
3. Consider emergency coronary angiography for:
   • Patients with ST-elevation
   • Patients with high clinical suspicion of cardiac etiology
   • Patients with initial VF/pulseless VT 2
4. Evaluate for other causes using the H's and T's framework 1

Common Pitfalls to Avoid

• Delaying BCU assessment: BCU should be integrated into resuscitation with minimal interruption to chest compressions 1
• Misinterpreting PEA: True PEA must be differentiated from pseudo-PEA (cardiac activity without palpable pulse) 1
• Overlooking non-traditional causes: Consider intracranial hemorrhage and non-ischemic cardiac disorders, which occur with similar frequency to some traditional H's and T's 4
• Excessive ventilation: Avoid hyperventilation which can decrease cerebral blood flow; target 10-12 breaths/minute 1
• Prolonged pulse checks: Limit pulse checks to <10 seconds to minimize interruptions to chest compressions 1

By systematically evaluating for these reversible causes during cardiac arrest resuscitation, providers can identify and treat the underlying etiology, potentially improving survival outcomes and neurological recovery.