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ORIGINAL ARTICLE |
Department of Cardiovascular Surgery, Yokkaichi Municipal Hospital, Yokkaichi, Japan
Masashi Toyama, MD, Tel: +81 59 3541111 Fax: +81 59 3521565 Email: machapon{at}tg.commufa.jp, Department of Cardiovascular Surgery, Yokkaichi Municipal Hospital, 2-20-37 Shibata, Yokkaichi 510-8567, Japan.
ABSTRACT
Although hypothermic circulatory arrest with antegrade selective cerebral perfusion is used for cerebral protection, optimal perfusion characteristics are still unclear. Between May 2006 and March 2008, 26 patients (mean age, 68.9 years; 14 males) underwent thoracic aortic repair with mild hypothermic circulatory arrest (34.3°C ± 1.9°C) and antegrade selective cerebral perfusion (30°C) for various indications including 16 acute type A aortic dissections. Mean cerebral perfusion rate was 21.1 ± 4.3mL kg–1 min–1. Non-elective operations were carried out in 16 (61.5%) cases. Operative procedures were ascending aortic replacement in 16 patients, hemiarch replacement in 4, and total arch replacement in 6. Cardiopulmonary bypass time was 209 ± 61 min, cardiac ischemic time was 141 ± 45 min, cerebral perfusion time was 81 ± 67 min, and lower body circulatory arrest time was 65 ± 22 min. Mean rectal temperature drifted to 30.6°C ± 1.3°C. There was 1 (3.8%) hospital death due to rupture of a residual descending thoracic aneurysm. One patient needed reexploration for bleeding, and 2 (7.7%) suffered permanent neurologic dysfunction. No postoperative spinal cord dysfunction was observed. Mild hypothermic circulatory arrest with antegrade selective cerebral perfusion could be performed safely in our patient population.
Key Words: Aortic Diseases • Cardiopulmonary Bypass • Mild Hypothermia • Selective Cerebral Perfusion • Brain Protection
INTRODUCTION
Deep hypothermic circulatory arrest has been widely used for thoracic aortic repairs. However, the safe duration of deep hypothermic circulatory arrest is limited, and procedures for aortic repairs are occasionally too complex to accomplish within this time limit. Various cerebral protection techniques have been advocated. Hypothermic circulatory arrest is usually performed with retrograde or antegrade selective cerebral perfusion (SCP). Randomized trials have revealed no evidence of significant metabolic, neurologic, or neuropsychological benefit of retrograde SCP.1,2 In a review of cerebral protection techniques, Harrington and colleagues 3 found that antegrade SCP has become the preferred method of brain protection, but there is no consensus on the optimal temperature and flow rate. Recently, the safety of mild hypothermic circulatory arrest with antegrade SCP has been reported.4–7 The goal of this study was to analyze our results of mild hypothermic arrest with antegrade SCP to determine the safety and efficacy of our brain protection strategy.
PATIENTS AND METHODS
Between May 2006 and March 2008, 26 consecutive patients (mean age 68.9 years, range 34–79 years; 12 male) underwent thoracic aortic repair with mild hypothermic circulatory arrest (34.3°C ± 1.9°C) and antegrade SCP (30°C) for various indications including 16 acute type A aortic dissections. All patients gave written informed consent. During the study period, we did not use deep hypothermic circulatory arrest with antegrade or retrograde SCP. Urgent or emergency operations were performed in 16 cases. Among 16 patients with acute type A aortic dissection, one showed transient brain ischemia during preoperative hypotension. The patients’ demographic and preoperative data are summarized in Table 1
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The patient’s body weight was measured daily in the immediate postoperative period to evaluate fluid retention. After hemodynamic stabilization, no additional anesthetic drugs were given for neurologic evaluation. If the patient suffered oliguria and renal insufficiency, continuous hemodiafiltration was performed after consultation with a nephrologist. Permanent neurologic deficit was defined as the presence of new stroke or coma. Respiratory failure was defined as intubation for>72 h. Postoperative renal dysfunction was defined as a creatinine level>1.5 mg dL–1.
All data were collected from medical charts and expressed as mean ± standard deviation. Statistical analysis was performed with the Mann-Whitney U test or Fisher’s exact test, using SPSS software (SPSS, Inc., Chicago, IL, USA).
RESULTS
Intraoperative data are given in Table 2. Most patients underwent ascending aortic repair. Femorofemoral bypass was required in one patient who suffered preoperative leg ischemia secondary to acute type A aortic dissection. The rectal temperature drifted to 30.6°C ± 1.3°C. Postoperative morbidity and mortality are shown in Table 3. Transfusion of red blood cells comprised 8.7 ± 5.6 units intraoperatively and 1.0 ± 1.6 units on postoperative day 0 in the intensive care unit. Of the 2 patients who experienced permanent neurologic dysfunction, one who had transient cerebral ischemia preoperatively, showed mild paralysis of the right upper extremity postoperatively; the other had preoperative innominate artery occlusion due to dissection, which resulted in left hemiparesis; there was no paraplegia. The arousal time was 15.2 ± 17.8 h (range, 0.6–59.9 min) in patients without permanent neurologic dysfunction. The mean intubation time was 49 ± 44 h. Postoperative renal dysfunction was noted in 8 patients; temporary hemodiafiltration was required in 5, but none needed permanent hemodialysis. The maximal serum lactate level was 66.5 ± 23.7 mg dL–1 (range, 27–120 mg dL–1) intraoperatively. The serum lactate level on postoperative day 1 was 29.2 ± 12.8 mg dL–1 (range, 15.5–57.5 mg dL–1). There was a gain in body weight of 2.8 ± 2.0 kg (range, 0.3–6.5 kg) during the operation. The mean intensive care unit stay was 4.8 ± 5.1 days, and hospital stay was 37.9 ± 25.7 days. The single hospital death was due to a residual descending thoracic aneurysm that ruptured on postoperative day 8.
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Antegrade SCP has become the preferred method of brain protection, although its optimal perfusion characteristics are still unknown.3,9–14 Deep hypothermia (15°C) has been used to suppress cerebral metabolism during antegrade SCP, but a recent animal study reported improved cerebral metabolic outcome after antegrade SCP at 10°C–15°C compared to 20°C–25°C.15 Kazui and colleagues9 achieved excellent clinical results after antegrade SCP at 22°C. Most studies used a flow rate of 10 mL kg–1 min–1 during antegrade SCP, but this is probably significantly higher than that required with deep hypothermia.3 Further cooling below 28°C does not decrease brain oxygen consumption effectively.16 Usui and colleagues17 found that regional cerebral blood flow under antegrade SCP decreased at temperatures below 28°C because arteriovenous shunts open. Accordingly, we hypothesized that hypothermia below 28°C would not be advantageous for cerebral protection when adequate regional cerebral blood flow is achieved. Moreover, deep hypothermia causes adverse events such as coagulopathy, fluid retention, and respiratory failure.18,19 Therefore, we used mild hypothermic circulatory arrest with high-flow antegrade SCP for thoracic aortic repairs.
The Hannover group adjusted the cerebral perfusion temperature to 14°C during mild hypothermic circulatory arrest that started at nasopharyngeal temperatures of 25°C–28°C with perfusion pressure maintained at 40–60 mm Hg, corresponding to flow rates of 400–650 mL min–1.5 They concluded that their cerebral protection technique was safe. Minatoya and colleagues7 showed that antegrade SCP regulated to maintain mean pressure in the superficial temporal arteries at 60 mm Hg, allowed perfusion at 19 ± 4.2 mL kg–1 min–1 during hypothermic circulatory arrest at a nasopharyngeal temperature of 28°C for aortic arch replacement; the rate of neurologic events did not increase. Bakhtiry and colleagues6 reported good results even for aortic dissections when antegrade SCP was controlled at a perfusion pressure of 75 mm Hg, allowing a flow rate of 1,320 ± 160 mL min–1; hypothermic circulatory arrest was commenced at a rectal temperature of 30°C. In our institution, we conducted antegrade SCP with a targeted perfusion flow pressure of 75 mm Hg and flow rate of 21.1 ± 4.3 mL kg–1 min–1 during hypothermic circulatory arrest, starting at a nasopharyngeal temperature below 30°C; the lowest rectal temperature was 30.6 ± 1.3°C. Thus core temperature and cerebral perfusion flow rates were higher in our study. We cannulated the left carotid and subclavian arteries as well as the right axillary artery for all ascending aorta and aortic arch repairs because of a probable incomplete circle of Willis, although Bakhtiry and colleagues 6 reported good results of cannulation of the right axillary artery only.
In our patients, mild hypothermic circulatory arrest with antegrade SCP could be performed safely. We believe that our perfusion strategy achieves adequate regional cerebral blood flow and meets the metabolic demand of the brain, as evidenced by the low rates of hospital mortality and permanent neurological deficit, which were unrelated to the perfusion technique. Reported mortality rates after mild hypothermic circulatory arrest with antegrade SCP are 5%–11.6%, with stroke rates of 5.1%–6.0%.4–7 There was no spinal chord dysfunction in our study (reported rates are 0%–1.5%).4,7 The reason for low rate of postoperative paraplegia despite the much longer lower-body circulatory arrest time is unclear. The avoidance of deep hypothermia might prevent spasm in the spinal chord collateral circulation, and the spinal chord might be perfused via the anterior spinal artery and collateral circulation during high-flow antegrade SCP.
Five (19.2%) patients who had 62 ± 36 min of lower-body circulatory arrest, needed postoperative hemodiafiltration; none needed permanent hemodialysis. Kamiya and colleagues4 reported that 17 (6.6%) patients needed hemodialysis after mild hypothermic circulatory arrest with lower-body circulatory arrest time of 23.5 ± 15.8 min. Bakhtiary and colleagues6 noted that 15% needed postoperative continuous hemofiltration. During our study, we performed emergency total aortic arch replacement for a kidney transplant recipient; no postoperative hemodialysis was required as the maximal postoperative creatinine level was 2.0 mg dL–1 on postoperative day 1, and within the normal range on postoperative day 3. Even in patients who required postoperative continuous hemodiafiltration, appropriate medical management can reduce the permanent hemodialysis rate. However, measures to avoid renal failure are needed to improve the safety of this perfusion strategy. Morphologic and functional damage to the kidney does not occur after 60 min of circulatory arrest at 18°C to 20°C.20 The safe duration of circulatory arrest is <20 min at 37°C. Renal ischemic time should be decreased to avoid postoperative hemodiafiltration. A balloon catheter could be introduced into the descending aorta with the aid of a fiberoptic scope, and lower-body perfusion achieved with femoral artery perfusion and balloon catheter occlusion of the descending aorta. Postoperative renal dysfunction causing fluid retention and respiratory failure might be prevented by this method. We noted postoperative respiratory failure in 34.6% of patients. Kamiya and colleagues4 reported that 10.7% had respiratory insufficiency needing ventilation for>48 h, mean ventilation time was 61.7 ± 126.7 min. Bakhtiary and colleagues6 found mean ventilation time was 54 ± 22 min, and their lower-body circulatory arrest time was much shorter than in our series. Excessive fluid retention due to renal dysfunction might be the main cause of respiratory failure. Patients with postoperative respiratory failure required significantly more hemodiafiltration than those without respiratory failure (4 vs. 1, p = 0.034). Three patients needed reintubation.
The limitations of our study include the small number of cases and the lack of a control group, because we abandoned deep hypothermia from May 2006 due to hypothermia-related adverse events. More cases are needed to prove efficacy and safety; however, we could perform thoracic aortic repair during mild hypothermic circulatory arrest with antegrade SCP safely in terms of brain protection. This technique may prevent hypothermia-related adverse complications.
REFERENCES
Asian Cardiovasc Thorac Ann 2009;
17:500-504
© 2009 by SAGE Publications
DOI: 10.1177/0218492309342716
This article has been cited by other articles:
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  Z. Khabbaz Aortic Arch Surgery: Moderate or Mild Hypothermic Circulatory Arrest? Asian Cardiovasc Thorac Ann, October 1, 2010; 18(5): 495 - 495. [Full Text] [PDF]
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