Reappearance of Motor-Evoked Potentials During the Rewarming Phase After Deep Hypothermic Circulatory Arrest.

OBJECTIVE: Although motor-evoked potentials (MEPs) disappear in deep hypothermic circulatory arrest (DHCA), MEPs have been used to confirm whether motor function is intact after DHCA. It is crucial to know the timing, body temperature, and MEP amplitude at MEP reappearance to detect spinal cord ischemia after DHCA. However, data on these parameters are sparse. The authors investigated the characteristics of MEPs at reappearance after DHCA. DESIGN: A retrospective observational study. SETTING: Single national center. PARTICIPANTS: Sixty-one patients who underwent descending aortic replacement and thoracoabdominal aortic replacement with DHCA between January 2013 and December 2015. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The authors extracted the following data: time to MEP reappearance after the end of lower extremity circulatory arrest, bladder temperature (BT) and nasopharyngeal temperature (NPT) when MEPs recovered, and %amplitude of MEPs relative to control values at MEP reappearance. The median time to MEP reappearance was approximately 70 minutes. BT at MEP reappearance ranged from 34.3°C to 34.6°C and NPT ranged from 36.2°C to 36.4°C. At MEP reappearance, %amplitude less than 50% of the control value was observed in more than 50% of patients. Time to MEP reappearance had a significant positive association with rewarming time (p < 0.01) and BT (p = 0.03). CONCLUSIONS: There was a wide variation in MEP amplitude at reappearance during the rewarming phase. BT was approximately 34°C when MEPs in the leg recovered. The time to MEP reappearance is influenced significantly by rewarming time and BT.

Rhythmic electrographic discharges during deep hypothermic circulatory arrest.

OBJECTIVE: The main objective of this study is to examine the prevalence and timing of rhythmic electrographic discharges and periodic sharp transients during aortic arch repair surgeries using DHCA as detected by continuous intraoperative encephalogram (EEG) and correlate it with outcome. METHODS: Electronic medical records and the intraoperative EEGs of 32 patients who underwent aortic arch reconstruction with DHCA were reviewed. Preoperative patient characteristics, intraoperative data, and postoperative outcomes were examined. EEGs were graded based on the frequency of sharp transients (grade 0-2) and/or the presence of rhythmic electrographic discharges (grade 3). RESULTS: Periodic sharp transients were seen in 30/32 cases. Grade 1 and grade 2 activations were more prominent during cooling at nasopharyngeal temperature of 23.9±4.01 °C (mean±SDV). Rhythmic electrographic discharges occurred in seven patients and were exclusively seen during cooling at nasopharyngeal temperatures below 28 °C except in one case during rewarming at nasopharyngeal temperatures of 22°C. No patient with rhythmic discharges developed postoperative clinical neurologic deficit or seizures. CONCLUSIONS: Periodic sharp transients occurred in almost all cases during induction of deep hypothermia. This activity was not associated with postoperative neurologic deficit. SIGNIFICANCE: Clinical neurophysiologists, technicians and surgeons need to be aware that low amplitude periodic sharp transients and rhythmic electrographic discharges are common during DHCA, yet have no apparent clinical significance.

Severity and Duration of Metabolic Acidosis After Deep Hypothermic Circulatory Arrest for Thoracic Aortic Surgery.

OBJECTIVE: To determine the severity, duration, and contributing factors for metabolic acidosis after deep hypothermic circulatory arrest (DHCA). DESIGN: Retrospective observational study. SETTING: University hospital. PATIENTS: Eighty-seven consecutive patients undergoing elective thoracic aortic surgery with DHCA. INTERVENTIONS: Regression analysis was used to test for relationships between the severity of metabolic acidosis and clinical and laboratory variables. MEASUREMENTS AND MAIN RESULTS: Minimum pH averaged 7.27±0.06, with 76 (87%) having a pH<7.35; 55 (63%), a pH<7.30; and 7 (8%), a pH<7.20. The mean duration of metabolic acidosis was 7.9±5.0 hours (range: 0.0 - 26.8), and time to minimum pH after DHCA was 4.3±2.0 hours (1.0 - 10.0 hours). Hyperchloremia contributed to metabolic acidosis in 89% of patients. The severity of metabolic acidosis correlated with maximum lactate (p<0.0001) and hospital length of stay (LOS) (r = 0.22, p<0.05), but not with DHCA time, DHCA temperature, duration of vasoactive infusions, or ICU LOS. Patient BMI was the sole preoperative predictor of the severity of postoperative metabolic acidosis. LIMITATIONS: This retrospective analysis involved short-term clinical outcomes related to pH severity and duration, which indirectly may have included the impact of sodium bicarbonate administration. CONCLUSIONS: Metabolic acidosis was common and severe after DHCA and was attributed to both lactic and hyperchloremic acidosis. DHCA duration and temperature had little impact on the severity of metabolic acidosis. The severity of metabolic acidosis was best predicted by the BMI and had minimal effects on short-term outcomes. Preventing hyperchloremic acidosis has the potential to decrease the severity of metabolic acidosis after DHCA.

Update on transient cardiac standstill in cerebrovascular surgery.

Transient cardiac standstill is a complementary procedure used with microsurgery to treat patients with particularly complex aneurysms, such as large or giant cerebral aneurysms. These procedures allow the aneurysms to be decompressed while maintaining a bloodless field and increased surgical exposure. Deep hypothermia combined with circulatory arrest provides cerebroprotection with optimal surgical conditions. However, its disadvantage is the relatively high risk of the procedure, which requires extensive expertise and infrastructure. Thus, its use is typically limited to patients with complex posterior circulation aneurysms. Adenosine-induced transient asystole is an easily applied technique in a variety of clinical situations. Its use requires minimal advanced preparation and no complex logistical coordination with other subspecialties. However, patient-specific dose-response relationships must be determined by exposure, so the relationship may not be known in an emergent situation. Persistent hypotension is a potentially major complication. Rapid ventricular pacing (RVP) has recently been reintroduced into cerebrovascular surgery. It is more predictable than adenosine in response time and, thus, can be used during unanticipated complications, such as aneurysmal rupture. It also induces a shorter period of hypotension compared with adenosine. However, RVP is more invasive and more complex from an anesthesia standpoint. Vascular neurosurgeons should be familiar with these techniques and know their applications and limitations.

New frontiers in aortic therapy: focus on deep hypothermic circulatory arrest.

There is currently a paradigm shift in the conduct of adult aortic arch repair. Although deep hypothermic circulatory arrest has been the classic perfusion platform for adult aortic arch repair, recent developments have challenged this aortic arch paradigm. There has been a gradual clinical drift towards moderate, and even mild, hypothermic circulatory arrest combined with antegrade cerebral perfusion. This paradigm shift appears to be associated with equivalent clinical outcomes, and in certain settings, with improved outcomes. The advent of endovascular therapy has challenged even further the concept that circulatory arrest is required for adult aortic arch repair. These dramatic advances have resulted in the emergence of an international aortic arch surgery study group that aims to advance this dynamic field through consensus statements, meta-analysis, clinical database analysis, prospective registries, and randomized controlled trials.

Hipotermia terapéutica en la parada cardiaca / Therapeutic hypothermia in cardiac arrest

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The history and present status of deep hypothermia and circulatory arrest in cerebrovascular surgery.

After the development of deep hypothermia and circulatory arrest for cardiothoracic procedures in the late 1950s, this technique was adopted by several neurosurgeons as an aid to complex cranial surgery. Woodhall and colleagues described its first use for a neurosurgical procedure in 1960. Although their case did not involve a cerebrovascular procedure, the technique was subsequently used for the surgical treatment of cerebrovascular lesions, especially complex and giant aneurysms as well as large and solid hemangioblastomas. At the beginning, incorporation of this technique into common neurosurgical practice was impeded by several factors. For example, postbypass coagulopathy had been a serious source of morbidity. Furthermore, the need for cooperation among multiple subspecialties and the requirements for expensive equipment had further limited the availability of this technique. Subsequent improvements in the technique and advances in the equipment designed for cardiopulmonary bypass have led to its more widespread use starting in the 1980s. Hypothermic circulatory arrest has been described in several reports as a safe and useful tool in the treatment of large and giant aneurysms. Nevertheless, improvements in endovascular procedures and further refinement in skull base surgical techniques have limited the indications for circulatory arrest and deep hypothermia. The authors describe the history of hypothermia and circulatory arrest, its implementation in cerebrovascular surgery, and the changes in indications for and results of its use over time.