Ensuring proper placement of the needle/drain in the pericardium is imperative. There are several methods to do this.
Direct visualization of needle/drain tip on ultrasound.
Inject small amount of agitated saline under direct ultrasound visualization and evaluate location of bubbles.
Place small amount of aspirated fluid into a container and evaluate for development of clots.
Pericardial fluid will not clot secondary to intrinsic pericardial fibrinolytic activity.
However, a rapidly-developing effusion can overwhelm this fibrinolytic activity, causing the fluid to clot.
Send pericardial fluid for blood gas analysis
Pericardial fluid will have low pH, low pO2, high pCO2 compared to arterial, venous or mixed venous blood.
Pericardial fluid will not clot secondary to intrinsic pericardial fibrinolytic activity.
However, a rapidly-developing effusion can overwhelm this fibrinolytic activity, causing the fluid to clot.
Pericardial fluid will have low pH, low pO2, high pCO2 compared to arterial, venous or mixed venous blood.
Pericardiocentesis
Thoracotomy 
Thoracotomy
Thoracentesis
Thoracic lavage
Vasopressors
Transvenous pacing
Needle cricothyrotomy