Table 1.

Etiologies of a flat arterial line waveform. BP, blood pressure; CAD, coronary artery disease; SVR, systemic vascular resistance; TEE, transesophageal echocardiography. US, ultrasound.

Etiology	Conditions	Causes	Confirmation
Occlusion	Dissection	Fragile intimal tissue Aorta cross-clamp Poor BP control	TEE Angiography
	Thrombosis	Thrombi migration	Angiography
	Surgical compression/manipulation	Surgical needs or inadvertent compression	Observe the surgical field
Hypotension	Poor cardiac output	Delayed recovery from cardioplegia Hypovolemia Unaddressed arrhythmia Myocardial ischemia Protamine induced hypotension	TEE Compare with aorta main trunk or femoral artery pressure
	Low SVR	Deep anesthesia Vasodilatory agents in use Allergy Protamine induced hypotension Sepsis	As above
Device malfunction	Catheter kink	Folded wrist or skin folds	Exposure Direct examination
	Occluded pressure transducer line Pressure set dysfunction	Inadvertent clamping of transducer line Physical impact on sensor	Check entire set
Vasospasm	Constriction of small diameter arteries	Multiple insertion attempts Prolonged catheter placement time	Peripheral US
Local swelling	Tissue edema	Over flushing of arterial line set	Exposure Peripheral US
	Hematoma	Multiple insertion attempts	Exposure Peripheral US