To evaluate the value of US-guided Stellate ganglion block for improving radial arterial blood flow and peripheral perfusion in Septic shock patients on vasopressor support with an indwelling radial arterial cannula, which can result in reduced incidence premature failure of the catheter (due to vasospasm or thrombosis) and incidence of ischemic complications in the cannulated arm.

Radial artery cannulation is a well-established procedure in the ICU, especially in critically ill hemodynamically unstable patients. The first description of arterial cannulation in humans dates back to 1856, when the blood pressure was measured int the femoral artery. It can be used for continuous blood pressure monitoring, obtaining func¬tional hemodynamic parameters derived from the arterial waveform, to predict the physiologic response to fluid resuscitation and also for blood sampling.

The most common complications for the procedure are temporary radial artery occlusion (19.7%), in addition to hematoma (14.4%), infection at the arterial site (0.72%), hemorrhage (0.53%) or bacteremia (0.13%), pseudoaneurysm (0.09%) and finally ischemic damage (0.09%). Larger catheter diameter, presence of vasospasm, female sex (probably related to smaller vessel diameter) increase the risk of ischemic complications. Inadequate experience (high number of attempts, multiple arterial sticks and hematoma formation) can also increase the complication rate.

In a recent study by Numaguchi et al, they found that radial artery cannulation decreases the distal arterial blood flow measured by power Doppler ultrasound. In another study by Kim et al, they found that after radial artery cannulation ulnar artery diameters were significantly increased (compensatory) and radial artery diameters were decreased after cannulation compared with pre-cannulation values, then returned to pre-cannulation values 5 min after cannulation. They detected radial artery vasospasm in 12 patients with 20-G cannulas used (31.5%) and in 2 patients with 22-G cannulas used (5.3%) (p < 0.05), which was observed immediately after cannulation, and had mostly disappeared after 5 min. There was no data regarding the follow up of the patients afterwards. In both studies the subjects were not critically ill patients (and not on vasopressors).

Peripheral limb ischemia in ICU patients can be the result of iatrogenic injury, thrombotic complications or hypoperfusion related to the underlying disease state. The patients at greatest risk for acute ischemia are those with underlying peripheral artery disease (PAD), but limb ischemia can also be the consequence of embolism, injury, dissection, or severe vasoconstriction, even in the absence of preexisting occlusive disease. Repeated arterial punctures may result in extensive hematoma formation and arterial spasm, The thick muscular coat and abundance of alpha adrenoreceptors make it prone to develop spasm when traumatized. Attempts to control bleeding following cannulation through local hemostasis only complicate matters. While, normally, the likelihood of serious ischemia is minimized by the presence of the palmar arterial arch.

The use of vasopressors especially nor-epinephrine with its potent α1-adrenergic receptor agonist activity can aggravate the condition more. We didn't find in the literature any reliable data regarding the effect of using vasopressors (particularly nor-epinephrine) in any dosage on the incidence of peripheral arterial vasospasm or ischemic complications following arterial cannulation. But there were mixed case reports linking both or one of them: high dose vasopressors and arterial cannulation, to ischemic complications. Such as developing peripheral gangrene after starting high dose vasopressors, or developing complex regional pain syndrome (CRPS) following radial artery cannulation.

It is believed that blocking the Stellate ganglion with Local anesthetics can interfere with the sympathetic out flow to the upper limb resulting in abolishing its vasoconstrictor action on the arteries thus decreasing arterial spasm and promoting better blood flow in the peripheral circulation.

Inclusion Criteria:

• Age range of 18-80 years.
• Septic shock patients on vasopressor support (Nor-epinephrine or epinephrine).
• Presence of an indication for an arterial cannula.

Exclusion Criteria:

• Coagulopathies (with prothrombin concentration less than 60% or international normalized ratio INR more than 1.5)
• In-ability to postpone anti-coagulation medications.
• Infection or injury or a lesion at the block site.
• Suspected cervical vertebral column injury necessitating using a neck collar.
• Bradycardia with heart rate less than 60 beat per minute.
• A compromised lung on the contralateral side of the arterial cannula (Pneumothorax, hemothorax or Pneumonectomy).
• Recent cardiac insult (cardiogenic shock) (Due to blockage of the sympathetic cardiac accelerator fibers by the block).
• Traumatic vascular injuries or operative interventions (Surgical harvesting) involving arteries of the upper limb on either side.
• Peripheral vascular disease, atherosclerosis, atrial fibrillation, previous history of ischemic injuries, hypercoagulable syndromes.