What are the acceptable durations for Deep Hypothermic Circulatory Arrest (DHCA) and Selective Cerebral Perfusion (SCP)?

Acceptable Time Periods for Deep Hypothermic Circulatory Arrest and Selective Cerebral Perfusion

Deep hypothermic circulatory arrest (DHCA) should be limited to 30-40 minutes maximum, while selective cerebral perfusion (SCP) can safely extend this time to 40-50 minutes or longer when properly implemented.

Deep Hypothermic Circulatory Arrest (DHCA) Duration

Safe Duration Limits

• DHCA without cerebral perfusion should be limited to a maximum of 30 minutes to prevent neurological complications 1, 2
• The impact of DHCA on neurodevelopmental outcomes is nonlinear, with adverse effects becoming significant when duration exceeds 41 minutes 1
• Studies have shown that DHCA duration >30 minutes is predictive of higher rates of neurological events (25.2% vs. 2.0%) 3
• Quality of life is significantly decreased in patients with DHCA between 20-34 minutes compared to those with DHCA <20 minutes, with further significant deterioration when DHCA exceeds 35 minutes 4

Temperature Considerations

• DHCA typically involves cooling patients to temperatures ranging from 12° to 30°C using extracorporeal circulation 1, 5
• Deep hypothermia reduces cerebral metabolic rate by approximately 6% for every 1°C reduction in brain temperature, which is the primary neuroprotective mechanism during circulatory arrest 5
• Moderate or profound hypothermia is an essential component of the operative technique for open surgical repairs of the ascending aorta and/or aortic arch 1

Selective Cerebral Perfusion (SCP) Duration

Antegrade Cerebral Perfusion (ACP)

• When aortic surgery requires DHCA longer than 30 minutes, antegrade cerebral perfusion (ACP) should be instituted 3
• ACP is usually performed at a perfusion pressure of 50 to 80 mm Hg and may be instituted by direct cannulation of the brachiocephalic arteries, side-graft anastomosis to the axillary artery, or direct cannulation of graft material 1
• ACP significantly reduces the incidence of neurological events compared to straight DHCA when DHCA exceeds 30 minutes (16.5% vs. 30.5%) 3
• ACP can safely extend the circulatory arrest time to approximately 40-50 minutes 3, 6

Retrograde Cerebral Perfusion (RCP)

• Retrograde brain perfusion is usually performed at a perfusion pressure of 20 to 40 mm Hg at a mildly or profoundly hypothermic temperature 1
• There is controversy regarding the ability of retrograde brain perfusion to support brain metabolic function and improve neurological outcomes 1
• RCP can maintain brain hypothermia but may not be as effective as ACP for extending safe DHCA duration 1

Optimizing Cerebral Protection During Circulatory Arrest

Bilateral vs. Unilateral Perfusion

• For DHCA exceeding 40 minutes, bilateral antegrade cerebral perfusion provides superior mid-term quality of life compared to unilateral right axillary antegrade cerebral perfusion 6
• Bilateral selective antegrade cerebral protection (SACP) provides the best cerebral protection for prolonged DHCA (>40 minutes) 6

Cold Reperfusion Technique

• A 10-minute period of cold perfusion (20°C) preceding rewarming significantly reduces the incidence of neurological events (7.7% vs. 18.7%) 3
• This cold reperfusion technique can extend the safe period of DHCA to approximately 40 minutes 3

Monitoring and Adjuncts

• Monitoring of brain function and metabolic suppression by electroencephalography, evoked potentials, bispectral index, noninvasive cerebral oximetry, and jugular bulb oxyhemoglobin saturation can help guide the timing of circulatory arrest 1
• Some centers use barbiturates, calcium channel blockers, or steroids for added protection, but no prospective randomized trials have confirmed their efficacy 1

Clinical Considerations and Pitfalls

Risk Factors for Adverse Outcomes

• Predictors of higher early mortality include acute aortic disease, longer DHCA duration, lack of ACP when DHCA >30 minutes, prompt rewarming without cold reperfusion, and postoperative stroke 3
• The experience and outcomes of the operating surgeon and institution are important considerations in selecting a brain protection strategy 1

Common Pitfalls to Avoid

• Exceeding the safe duration limits for DHCA (>30-40 minutes) without appropriate cerebral perfusion strategies 3, 2
• Failure to implement cold reperfusion before rewarming, which can significantly reduce neurological events 3
• Using retrograde cerebral perfusion for very prolonged cases when antegrade perfusion would be more beneficial 6
• Selecting unilateral rather than bilateral perfusion techniques for cases requiring prolonged DHCA (>40 minutes) 6

In conclusion, the acceptable duration for DHCA without cerebral perfusion is generally limited to 30 minutes, while selective cerebral perfusion techniques can safely extend this time to 40-50 minutes or longer. The implementation of appropriate cerebral protection strategies, including bilateral antegrade cerebral perfusion and cold reperfusion before rewarming, is critical for optimizing outcomes in procedures requiring prolonged circulatory arrest.