Changes of microvascular vasomotion and oxygen metabolism during cooling and rewarming period of cardiopulmonary bypass

Microcirculation plays an important role in keeping a stable tissue metabolism during cardiopulmonary bypass (CPB). The relationship between microvascular vasomotion (MV) and total body's oxygen metabolism with temperature alteration during CPB remains unclear. Is there a relationship, or is the autoregulation a consequence of CO2, pressure and/or blood flow? The purpose of this study was to investigate the effect of temperature alteration on cutaneous MV and the total body's oxygen metabolism during CPB. Sixteen consecutive patients scheduled for elective cardiac valve replacement surgery were included in this study. The pump flow varied from 1.8-3.0 L/m(-2)min(-1) to maintain venous oxygen saturation above 65% and mean arterial blood pressure above 60 mmHg. At a nasopharyngeal temperature of 30 degrees C, oxygen consumption (VO2) and oxygen extraction (O2 ext) were measured during the cooling and rewarming periods. MV and skin microcircular flow (SMF) were monitored dynamically at the middle of two sides of the eyebrow with a laser Doppler flowmeter simultaneously VO2 and O2 ext at 30 degrees C were significantly lower during the cooling period (VO2, 49.9 +/- 17.7 mL/m(-2)/min(-1); O2 ext, 19.3 +/- 6.2%) than that during the rewarming period (VO2, 133.3 +/- 40.0 mL/m(-2)/min(-1); O2 ext, 35.2 +/- 9.2%) (p < .05). SMF was significantly depressed during CPB (p < .05). SMF during the cooling period (50.2% +/- 10.1%) was significantly less than that during the rewarming period (79.5% +/- 12.3%) (p < .05). MV was significantly less active during CPB than that before CPB (5.8 +/- 1.2 cyc/min) (p < .05), whereas there was no significant difference in MV between the cooling (3.7 +/- 1.8 cyc/min) and the rewarming period (4.1 +/- 1.5 cyc/min) and (p > .05). SMF and MV were depressed during hypothermic CPB, and there was some recovery during the rewarming period. Compared to baseline, SMF and MV were still significantly reduced during the warming period, indicating microvascular function was abnormal. Some measures should be taken for improvement of microvascular function during CPB.     

Erweitertes zerebrales Monitoring mit transkranieller Doppler-Sonographie und zerebrovenöser Oxymetrie während einer Reanimation

This case report describes cerebral monitoring of intracranial haemodynamics using transcranial Doppler sonography (TCD) and jugular bulb oxygen saturation (SjO₂) by fiberoptic jugular bulb oximetry during cardiac arrest following cardiac surgery involving cardiopulmonary bypass (CPB). CPB for aortic valve replacement and coronary artery bypass grafting was performed in a 63-year-old patient previously operated upon for heart disease. Mean blood flow velocity was measured in the middle cerebral artery using a bidirectional 2?MHz TCD system. SjO₂ was measured using a fiberoptic thermodilution catheter placed in the right jugular bulb via the right internal jugular vein under radiographic control. At the end of the operation, low cardiac output syndrome and cardiac arrest occurred, which required reopening of the thorax and cardiopulmonary resuscitation (CPR) until CPB could be resumed. Following extrathoracic cardiac resuscitation, systolic “spikes”, loss of the diastolic flow profile, and no increase in SjO₂ were recorded by the monitors, indicating cerebral circulatory arrest. However, a normal flow profile with increasing diastolic portions and an increase in SjO₂ to 52% were seen following optimisation of the open thorax cardiac resuscitation. This monitoring may be able to give information to optimise therapy during CPR to avoid ischaemic cerebral injury.     

The Benefits of High‐flow Management in Children With Pulmonary Atresia

The high‐flow management of cardiopulmonary bypass (CPB; ≥2.4 L/min/m²) is a standard strategy used at this institute for children with pulmonary atresia (PA) due to a fear that the blood flow may be diverted by the major/minor aortopulmonary‐collateral‐arteries and hypervascularization due to long‐term hypoxia. The purpose of this study was to describe the validity of high‐flow management in children with PA. The CPB records of 23 children with PA who underwent a definitive biventricular repair between Feb 2006 and Nov 2008 were retrospectively reviewed. The mean age at the operation was 33 ± 22 months. The blood‐pressure during bypass was controlled with the same protocol. The mean cooling‐temperature was 28.4 ± 3.7°C. The mean minimum hematocrit was 25.0 ± 3.4%. The mean maximum bypass flow index at the initiation, the mean maximum flow index during aortic cross‐clamping, the mean minimum flow index during aortic cross‐clamping, and the mean maximum flow index after rewarming were 3.1 ± 0.5, 3.1 ± 0.5, 2.6 ± 0.4, and 3.2 ± 0.4 L/min/m², respectively. The higher bypass flow indexes significantly correlated with the lower serum lactate levels. The lowest oxygen delivery during CPB had significant influences on the urine output during bypass (R = 0.547, P = 0.007), the serum lactate levels at the end of CPB (R = ?0.442, P = 0.035), and the postoperative thoracic effusion (R = ?0.459, P = 0.028). A bypass flow index of 2.4 L/min/m² may not be sufficient and the maximum requirement of bypass flow index may be 3.2 L/min/m² or more in this patient population.     

Beneficial effect of balloon-induced pulsatility on brain oxygenation in hypothermic cardiopulmonary bypass

BACKGROUND: Sufficient O2 delivery to meet the demand is an important factor for protecting the brain during cardiopulmonary bypass (CPB). This study was designed to investigate the influences of temperature, pulsatility of blood flow (intra-aortic balloon pump-induced) and flow rate during CPB on the cerebral oxygenation. METHODS: Patients were divided into five groups. Normothermia (36 degrees C): pulsatile (n=8, 2.5 L/min/m2), nonpulsatile (n=12, 2.5 L), and nonpulsatile perfusion (n=12, 2.8 L); hypothermia (30 degrees C): pulsatile (n=9, 2.5 L) and nonpulsatile perfusion (n=11, 2.5 L). The oxygen saturation (SjVO2), lactate and CPK-BB levels in the jugular venous blood were measured. RESULTS: In all of the normothermic groups, the SjVO2 value decreased during the CPB (p<0.1-0.01). No remarkable change was observed in the hypothermic groups, with the exception during the rewarming period in the nonpulsatile group. A higher SjVO2 and a lower frequency of SjVO2 values <50% were observed in the hypothermic pulsatile group, as compared with those in the normothermic groups (p<0.05). The levels of CPK-BB were nearly the same, however the levels of lactate were higher in the normothermic pulsatile and nonpulsatile (2.5 L) groups (p<0.05). CONCLUSIONS: We concluded that the hypothermic CPB was advantageous over normothermic CPB in regard to the SjVO2 levels and lactate production. The beneficial effect of intra-aortic balloon pump assist was only obtained in the hypothermic CPB.     

Persistent low cerebral blood flow velocity following profound hypothermic circulatory arrest in infants

Acute neurological morbidity following repair of congenital heart disease (CHD) in infancy is well recognized, particularly with the modalities of hypothermic cardiopulmonary bypass (CPB) and profound hypothermic circulatory arrest (PHCA). Reduced O₂ delivery (perfusion defect) during rewarming following PHCA has been shown in the operating room. This reduction in cerebral blood flow coincides with disordered cerebral metabolism and oxygen utilisation after PHCA. The objective of this study was to extend the period of investigation of cerebral blood flow velocity (CBFV) behaviour in infants following PHCA to determine if hypoperfusion persisted in the paediatric intensive care unit (PICU). Ten patients undergoing CHD surgery were divided, based on the pump modality employed, into either mild hypothermic CPB or profound hypothermic CPB with circulatory arrest. Following admission to the PICU, sequential recordings of the mean CBFV in the middle cerebral artery, anterior fontanelle pressure, haemodynamic variables, tympanic membrane temperature, haematocrit and PaCO₂ were performed. The PHCA group had a consistently reduced CBFV compared with the control group (P < 0.05). The CBFV values at one, two and four hours were 60 ± 11, 51.8 ± 11.4 and 52.6 ± 11.9 respectively in the mild hypothermic CPB group. The CBFV values at one, two and four hours were 26.6 ± 6.8, 32.6 ± 10 and 34 ± 8 respectively in the PHCA group. There was no difference in cerebral perfusion pressure between both groups. Tympanic temperature, haematocrit and PaCO₂ did not vary between groups at any interval. This study demonstrates a sustained reduction in the CBFV pattern following PHCA into the postoperative period despite adequate cerebral perfusion pressures. This abnormality correlates with electroencephalographic aberrations documented after PHCA. It supports the concept of a prolonged unreactive cerebrovascular bed which could potentially contribute to the acute neurological morbidity following PHCA in neonates.     

Cerebral oxygen metabolism during total body flow and antegrade cerebral perfusion at deep and moderate hypothermia

The aim of this study is to evaluate the effect of temperature on cerebral oxygen metabolism at total body flow bypass and antegrade cerebral perfusion (ACP). Neonatal piglets were put on cardiopulmonary bypass (CPB) with the initial flow rate of 200 mL/kg/min. After cooling to 18°C (n = 6) or 25°C (n = 7), flow was reduced to 100 mL/kg/min (half‐flow, HF) for 15 min and ACP was initiated at 40 mL/kg/min for 45 min. Following rewarming, animals were weaned from bypass and survived for 4 h. At baseline, HF, ACP, and 4 h post‐CPB, cerebral blood flow (CBF) was measured using fluorescent microspheres. Cerebral oxygen extraction (CEO₂) and cerebral metabolic rate of oxygen (CMRO₂) were monitored. Regional cranial oxygen saturation (rSO₂) was continuously recorded throughout the procedure using near‐infrared spectroscopy. At 18°C, CBF trended lower at HF and ACP and matched baseline after CPB. CEO₂ trended lower at HF and ACP, and trended higher after CPB compared with baseline. CMRO₂ at ACP matched that at HF. Cranial rSO₂ was significantly greater at HF and ACP (P < 0.001, P < 0.001) and matched baseline after CPB. At 25°C, CBF trended lower at HF, rebounded and trended higher at ACP, and matched baseline after CPB. CEO₂ was equal at HF and ACP and trended higher after CPB compared with baseline. CMRO₂ at ACP was greater than that at HF (P = 0.001). Cranial rSO₂ was significantly greater at HF (P = 0.01), equal at ACP, and lower after CPB (P = 0.03). Lactate was significantly higher at all time points (P = 0.036, P < 0.001, and P < 0.001). ACP provided sufficient oxygen to the brain at a total body flow rate of 100 mL/kg/min at deep hypothermia. Although ACP provided minimum oxygenation to the brain which met the oxygen requirement, oxygen metabolism was altered during ACP at moderate hypothermia. ACP strategy at moderate hypothermia needs further investigation.     

Combined effects of propofol and mild hypothermia on cerebral metabolism and blood flow in rhesus monkey: a positron emission tomography study

Purpose Propofol reduces the cerebral metabolic rate for oxygen (CMRO₂), regional CMRO₂ (rCMRO₂), cerebral blood flow (CBF), and regional CBF (rCBF), but maintains the coupling of cerebral metabolism and blood flow. Under mild to moderate hypothermia, the coupling is maintained, while rCBF is reduced, but no direct measurement of rCMRO₂ has yet been reported. This study aimed to evaluate the effects of propofol under normothermic and mild hypothermic temperatures upon rCMRO₂, rCBF, and their regional coupling, through direct measurement by positron emission tomography. Methods Rhesus monkeys were anesthetized with 65% nitrous oxide and propofol. Then rCBF and rCMRO₂ were measured under four sets of conditions: infusion of a low-propofol dose (12 mg·kg⁻¹·h⁻¹) at normothermic temperatures (38°C), a high dose (25 mg·kg⁻¹·h⁻¹) at normothermic temperatures, a low dose under mild hypothermia (35°C), and a high dose under mild hypothermia. The ratio of rCBF/rCMRO₂ was calculated from these data. Results Reductions in CMRO₂ and rCMRO₂ in most regions were associated with two factors: the higher propofol dose and the induction of hypothermia, but there was no interaction between these factors. Concerning blood flow, no significant reduction was observed, except for CBF by the induction of hypothermia. The ratio of rCBF/rCMRO₂ was constant in this study setting. Conclusion During propofol anesthesia, it is possible to reduce cerebral metabolism throughout the entire brain as well as in any brain region by increasing the propofol dose or inducing hypothermia. The concurrent use of these two interventions has an additive effect on metabolism, and can be considered as safe, as their combination does not impair the coupling of cerebral metabolism and blood flow.     

Comparative analysis of alpha-stat and pH-stat strategies with a membrane oxygenator during deep hypothermic circulatory arrest in young pigs

Using young pigs, this study compared the strategies of alpha-stat and pH-stat during deep hypothermic circulatory arrest (DHCA) for the cooling time of brains during the induction of hypothermia and rewarming time with cardiopulmonary bypass (CPB); the cerebral perfusion rate and metabolism rate, and the ratio of these 2 rates; and the extent of the cerebral edema development after circulatory arrest. Fourteen young pigs were assigned to 1 of 2 strategies of gas management. Cerebral blood flow was measured with a cerebral venous outflow technique. With CPB, core cooling was initiated and continued until the nasopharyngeal temperature fell below 20 degrees C. The flow rate was set at 2,500 ml/min. Once the temperature reached below 20 degrees C, the animals were subjected to DHCA for 40 min. During the cooling period, the acid-base balance was maintained using either alpha-stat or pH-stat strategy. After DHCA, the body was rewarmed to the normal body temperature. The animals then were sacrificed, and we measured the brain water content. The cerebral perfusion and metabolism rates were measured before the onset of CPB, before cooling, before DHCA, 15 min after rewarming, and upon the completion of rewarming. The cooling time was significantly shorter with alpha-stat than with pH-stat strategy while no significant differences were observed in the rewarming time between groups. Also, no significant differences were found in cerebral blood flow volume, metabolic rate, or flow/metabolic rate ratio between groups. In each group, the cerebral blood flow volume, metabolic rate, and flow/metabolic rate ratio showed significant differences in body temperature. Brain water content showed no significant differences between the 2 groups. In summary, this study found no significant differences between alpha-stat and pH-stat strategies, except in the cooling time. The cooling time was rather shorter with the alpha-stat than with the pH-stat strategy.     

异丙酚对体外循环中脑氧代谢的影响

目的：探讨异丙酚对体外循环（ＣＰＢ）各阶段脑氧及乳酸代谢的影响。方法：选择心内直视手术病人３１例，随机分为异现酚组（Ａ组）１６例，对照组（Ｂ组）１５例。分别于ＣＰＢ前、降温及３３℃和３０℃，低温期，复温至３０℃和３３℃以及ＣＰＢ后１５分钟七个时点动脉，颈内静脉血气及乳酸值（ＬＡ）并计算脑摄氧率（Ｏ２Ｅｘｔ）及动脉－颈内静脉乳酸差值。     

Hemodilution elevates cerebral blood flow and oxygen metabolism during cardiopulmonary bypass in piglets

BACKGROUND: Hemodilution continues to be widely used during cardiopulmonary bypass (CPB) for both adults and children. Previous studies with nonbypass models have suggested that an increase in cerebral blood flow (CBF) compensates for the reduced oxygen-carrying capacity; however, this increased CBF is achieved by an increase in cardiac output. We hypothesized that even with the fixed-flow perfusion of CPB, CBF would be increased during hemodilution. METHODS: Two experiments were conducted and analyzed separately. In each experiment, 10 piglets were randomized to two different groups, one with a total blood prime yielding a high hematocrit (25% or 30%), and the other with a crystalloid prime resulting in a low hematocrit (10% or 15%). Animals were cooled with pH-stat strategy at full flow (100 or 150 mL.kg(-1).min(-1)) to a nasopharyngeal temperature of 15 degrees C, a period of low flow (50 mL.kg(-1).min(-1)) preceding deep hypothermic circulatory arrest (45 or 60 minutes), and a period of rewarming at full flow. Cerebral blood flow was measured at the beginning of CPB, at the end of cooling, at the end of low flow, 5 minutes after the start of rewarming, and at the end of rewarming by injection of radioactive microspheres. RESULTS: Mean arterial pressure was significantly greater with higher hematocrit at each time point (p< 0.05). Cerebral blood flow and the cerebral metabolic rate of oxygen decreased during cooling and further during low flow bypass but were significantly greater with lower hematocrit during mild hypothermia and at the end of rewarming (p< 0.05). CONCLUSIONS: Hemodilution is associated with decreased perfusion pressure, increased CBF and increased the cerebral metabolic rate of oxygen during hypothermic CPB.     

Evaluation of cerebral circulation during cardiopulmonary bypass using near-infrared spectroscopy

Cerbral oxygenation level during cardiopulmonary bypass (CPB) was measured using near-infrared spectroscopy as a monitor of cerebral circulation in 30 patients. Six adult cases with thoracic aortic aneurysm were operated on using selective cerebral perfusion (SCP). CPB was established under moderate hypothermic temperature in 9 adult cases (hypothermic group, lowest blood temperature during CPB; 25°C) and under normothermic temperature in 9 adult cases (normothermic group, lowest blood temperature during CPB; 34°C). In congenital cases (n=6), CPB was established under moderate hypothermic temperature (congenital grpoup, lowest blood temperature; 25°C). The oxyhemoglobin (HbO₂) level showed a significant positive correlation with cerebral blood flow during SCP (r = 0.715). There was no significant correlation between SjO₂ and HbO₂ in the SCP group. The HbO₂ levels in the hypothermic group after 30 and 60 min. from the initiation of CPB and 30 min. before the weaning of CPB were significant lower than the control level (p<0.05). HbO₂ levels in the congenital group after 0, 30 and 60 min. from the initiation of CPB and 30 min. before the weaning of CPB were significantly lowr than the control level (p<0.01). The deoxyhemoglobin (HbR) level in the hypothermic group after 30 and 60 from the initiation of CPB and 30 min. before the weaning of CPB were significantly higher than the pre level (p<0.05). The mixed venous saturation (SvO₂) in the normothermic group showed significant lower levels than those in the hypothermic group (p<0.01). However, there was no significant difference in HbO₂ levels between the two groups. In conclusion, these results suggest that near-infrared spectroscopy may be a noninvasive and useful technique for the cerebral circulation monitorin during CPB.     

A comparative analysis of the effects of sevoflurane and propofol on cerebral oxygenation during steep Trendelenburg position and pneumoperitoneum for robotic-assisted laparoscopic prostatectomy

Purpose

Steep Trendelenburg position and pneumoperitoneum during robotic-assisted laparoscopic prostatectomy (RALP) increase intracranial pressure (ICP) and may alter cerebral blood flow (CBF) and oxygenation. Volatile anesthetics and propofol have different effects on ICP, CBF, and cerebral metabolic rate and may have different impact on cerebral oxygenation during RALP. In this study, we measured jugular venous bulb oxygenation (SjO₂) and regional oxygen saturation (SctO₂) in patients undergoing RALP to evaluate cerebral oxygenation and compared the effects of sevoflurane and propofol. We also verified whether SctO₂ may be an alternative to SjO₂.

Methods

Fifty patients scheduled for RALP were randomly assigned to undergo sevoflurane (group S) or propofol (group P) anesthesia. SjO₂, SctO₂, mean arterial pressure (MAP), heart rate (HR), cardiac index (CI), central venous pressure (CVP), partial pressures of arterial oxygen (PaO₂) and carbon dioxide (PaCO₂), hemoglobin concentration (Hb), Bispectral Index (BIS) and nasopharyngeal temperature (BT) were recorded 5 min before surgery commencement, 5 min after pneumoperitoneum, 5, 30, 60, 90, and 120 min after pneumoperitoneum in a Trendelenburg position, and after desufflation in a supine position.

Results

SjO₂ was significantly higher in group S than in group P at all measurement points [group S vs. group P: 77 % (11) vs. 65 % (13), mean of all measurement points (1SD); p < 0.01]. Linear regression analysis (β = 0.106; r ² = 0.065; p = 0.004) shows a weak relationship between SjO₂ and SctO₂.

Conclusions

Sevoflurane maintains higher SjO₂ levels than propofol during RALP. SctO₂ does not accurately reflect SjO₂.

     

The effect of bloodless pump prime on cerebral oxygenation in paediatric patients

BACKGROUND: In paediatric patients, crystalloid prime for cardiopulmonary bypass (CPB) causes further haemodilution in comparison with blood-containing prime. Thus it may affect the cerebral oxygen supply/demand balance. The purpose of the study was to compare the effect of bloodless pump prime with that of blood-containing prime on cerebral oxygenation in children. METHODS: Thirty-six paediatric patients scheduled for elective repair of atrial or ventricular septal defect were enrolled. In Group C (n = 18), the CPB circuit was primed only with crystalloid. In Group B (n = 18), red blood cells were added to achieve a haematocrit (Hct) of 20% during CPB. The regional cerebral oxygen saturation (rSO(2)) value measured by near-infrared spectroscopy was compared between the two groups. RESULTS: In both groups, rSO(2) decreased below baseline at the start of CPB and during rewarming (P < 0.001, for both groups during each period). At the start of CPB, haemodilution was greater in Group C than in Group B (Hct 16.1 +/- 0.7% vs. 20.7 +/- 0.5%; P < 0.01), and there was a greater reduction in rSO(2) in Group C (49.0 +/- 5.4% vs. 59.2 +/- 7.0%; P < 0.01). During rewarming, rSO(2) was significantly lower in Group C than in Group B (57.8 +/- 5.3% vs. 62.8 +/- 6.2%; P < 0.01). CONCLUSIONS: In paediatric patients, the haemodilution associated with crystalloid priming causes a greater reduction in rSO(2) than with blood-containing prime at the starting period of CPB and the rewarming period.     

Cerebral physiology and outcome after hypothermic circulatory arrest followed by selective cerebral perfusion

BACKGROUND: This study explored the impact of an interval of hypothermic circulatory arrest (HCA) preceding selective cerebral perfusion (SCP) on cerebral physiology and outcome. This protocol allows use of SCP during aortic surgery without the threat of embolization inherent in balloon catheterization of often severely atherosclerotic cerebral vessels. METHODS: In this blinded study, 30 pigs (20 to 22 kg) were randomized after cooling to 20 degrees C. Pigs in the HCA-CPB group (n = 10) underwent 30 minutes of HCA followed by 60 minutes of total body perfusion (CPB); HCA-SCP pigs (n = 10) underwent 30 minutes of HCA followed by 60 minutes of SCP, and SCP pigs (n = 10) had 90 minutes of SCP without prior HCA. Fluorescent microspheres enabled calculation of cerebral blood flow during perfusion and recovery. Hemodynamics, intracranial pressure, cerebrovascular resistance, and cerebral oxygen consumption were also monitored. Daily behavioral scores were obtained for 7 days postoperatively. RESULTS: In all groups, cerebral oxygen consumption fell significantly with cooling (p < 0.0001), remained low during perfusion, and rebounded promptly with rewarming; cerebral oxygen consumption was significantly (p = 0.027) greater during SCP than during HCA-CPB. Cerebral blood flow was significantly higher throughout SCP in the HCA-SCP group (p < 0.0001) than with CPB. Cerebrovascular resistance during SCP and HCA-SCP was significantly lower (p = 0.036) than during CPB. Behavioral scores were significantly better with SCP than with HCA-CPB throughout recovery, but did not differ between SCP and HCA-SCP. CONCLUSIONS: This study suggests that a short period of HCA preceding SCP provides global cerebral protection comparable to continuous SCP, implying that in clinical practice, a short period of HCA to reduce risk of embolization will not compromise the superior cerebral protection provided by SCP.     

The effects of cardiopulmonary bypass on postoperative oxygen metabolism

The relationships between oxygen delivery (DO₂), oxygen consumption (VO₂), and the extraction rate (ER=VO₂/DO₂x100) in patients undergoing cardiopulmonary bypass (CPB) may differ from the normal physiologic state due to the oxygen debt acquired during CPB. Blood gas analysis and hemodynamic parameters were repeatedly measured for the determination of DO₂ and VO₂ in 40 patients undergoing CPB, every 8h during the first 48h postoperatively. As a control, 20 patients who had suffered acute myocardial infarction (AMI) were also studied using the same protocol. In the CPB group, a regression analysis showed that VO₂ was significantly dependent on DO₂, even within the physiologic range of DO₂ (>500 ml/min per m²); VO₂=121.4+0.0844×DO₂ (r=0.254,P=0.023). Conversely, in the AMI group, no such supply-dependent consumption was observed within the same range of DO₂. At an ER of 30%, which is the optimal value in general, the DO₂ of the CPB group was 575 ml/min per m² and that of the AMI group was 493 ml/min per m². All these results suggest that patients undergoing CPB need a much higher oxygen supply to recover from the oxygen debt acquired during open heart surgery.     

Per- and postoperative changes in the arterio-venous oxygen content difference (AVDO2) in patients subjected to craniotomy for cerebral tumours

Summary Sixteen patients with supratentorial cerebral tumours were subjected to craniotomy under thiopentone, fentanyl, nitrous oxide, halothane anaesthesia during moderate hypocapnia (PaCO₂ level 4.0 kPa). The arterio-venous oxygen content difference (AVDO₂) was measured peroperatively, and repeatedly during the first three hours after extubation.Peroperatively the level of AVDO₂ averaged 8.0 vol% during opening of the dura, and decreased to 7.0 vol% during closure of the dura (P<0.05). Immediately after extubation the AVDO₂ decreased to 4.3 vol% (P<0.05), and during the next 3 hours a gradual increase to 5.8 vol% (P<0.05) was disclosed. In individual cases the postoperative changes in AVDO₂ correlated fairly well with changes in mean arterial blood pressure (MABP), but other factors including duration of the operation, age of the patients, size of the tumour, level of PaCO₂ and adaptation to prolonged hyperventilation during operation are supposed to be responsible for the low levels of AVDO₂ observed in the postoperative period.     

Effect of rewarming speed during hypothermic cardiopulmonary bypass on cerebral pressure-flow relation

BACKGROUND: Cerebral blood flow is less dependent on arterial blood pressure during hypothermic cardiopulmonary bypass (CPB) compared to warm CPB. Fast rewarming has a more pronounced effect on cognitive performance in the elderly and causes an increased arterio-jugular oxygen content difference. We studied the effect of rewarming and rewarming speed on cerebral pressure-flow relation in adult patients undergoing elective coronary artery bypass surgery with mild hypothermic CPB. METHODS: Fifty patients were randomly assigned to either a slow rewarming strategy (0.24 degrees C/min) or a fast rewarming strategy (0.5 degrees C/min). Cerebral pressure-flow relation was assessed by a transcranial Doppler derived index for cerebral pressure-flow relation (Pressure-flow Index, PFI). The effect of rewarming speed on cerebral pressure-flow relation was assessed by comparing the absolute PFI value after rewarming between the two treatment groups. RESULTS: The mean PFI decreased significantly from 0.73 (standard deviation: 0.28) before rewarming to 0.54 (0.35) after rewarming in the slow rewarming group and from 0.63 (0.29) to 0.48 (0.30) in the fast rewarming group. Absolute PFI after rewarming was not significantly different (mean PFI difference = 0.06; 95% CI = - 0.13; 0.26) between both rewarming strategies. CONCLUSION: Rewarming from mild hypothermic CPB might result in pressure-dependent cerebral blood flow velocity but rewarming speed did not aggravate the effect of rewarming on pressure-flow dependency.     

Dynamic changes in cerebral oxygenation related to deep hypothermia and circulatory arrest evaluated by near-infrared spectroscopy

BACKGROUND: Total circulatory arrest in deep hypothermia, which is used in corrective surgery of complex cardiovascular malformations, has been said to cause brain injury. Near-infrared spectroscopy (NIRS) is a new non-invasive method that potentially monitors changes in cerebral oxygenation and tissue oxygen utilisation. The aim of this experimental study in rabbits was to evaluate the change in intravascular and intracellular oxygenation patterns during cooling, deep hypothermic circulatory arrest and rewarming using a commercially available NIRS-cerebral oximeter. METHODS: Ten New Zealand White male rabbits (weight, 3.1+/-0.25 kg BW) were included in this study. All animals underwent cardiopulmonary bypass (CPB), cooling to a rectal temperature below 15 degrees C, 60 min of deep hypothermic circulatory arrest (DHCA) followed by reperfusion and rewarming. Cerebral oxyhaemoglobin (HbO2), deoxyhaemoglobin (HHb) and cytochrome oxidase aa3 (CytOxaa3) concentrations were continuously measured during the entire procedure using the Cerebral RedOx Monitor 2020 (Criticon cerebral redox monitor 2020, Johnson & Johnson Medical). Total haemoglobin concentration (tHb) and regional cerebral oxygen saturation (rSO2) values were calculated by integrated algorithm. RESULTS: In all animals an initial increase of oxygenated haemoglobin (HbO2, rSO2) and a fall in deoxygenated haemoglobin (HHb) were found during cooling on bypass. A slight decrease in CytOxaa3 signal was observed in response to initial cooling. Variation in intravascular haemoglobin oxygenation parameters (HbO2, HHb) were related to haemodynamic changes associated with fluid loading, initiation and termination of CPB, bypass flow rate and cooling and rewarming. When the pump flow was stopped all NIRS parameters, except the HHb value, decreased precipitously during the DHCA-period (P<0.01). After reperfusion and rewarming, all haemoglobin oxygen saturation readings returned nearly to pre-CPB levels (P=0.09), but the CytOxaa3 was still significantly lower than the pre-CPB levels (P<0.05). CONCLUSION: The change in the NIRS-derived haemoglobin oxygenation parameters may reflect physiological changes in systemic and cerebral haemodynamics. CytOxaa3 values may represent related effects on cellular oxygenation. Thus, continuous, real-time NIRS-monitoring may identify critical periods with inadequate brain tissue oxygenation, particularly during DHCA. The neurological implications of the observed changes in NIRS oxygenation parameters, however, require further quantitative morphological evaluation of the brain in animals surviving a longer reperfusion and observation period.     

Retrograde arterial perfusion and its outcome in robotic mitral-valve surgery

ObjectiveRetrograde arterial perfusion is frequently used in minimally invasive cardiac surgery. However, there are concerns about its safety.MethodsA prospective observational cohort study was conducted in a tertiary university affiliated medical center during 2016–2018. Right side femoral artery and femoral vein are used for bypass route. We set cardiopulmonary bypass flow to 2.5–3.0 L/min/m², and adjust pump flow rate to achieve adequate cerebral oxygenation. The upper limit of arterial cannula pressure was 250 mmHg. We divided our patients into four groups by average pump flow 2.2 L/min/m² and average mean arterial pressure 45 mmHg. Compared outcomes included surgical mortality, hospital stay, ventilator use, neurological outcomes, acute kidney injury, distal limb saturations, and post-operative clinical complications.ResultsWe included 117 patients in this study, and all participants had successful mitral valve repair or replacement. Our longest CPB duration was 210 minutes. Surgical mortality was 1.7%. Hemorrhagic stroke rate was 1.7%, and there was no ischemic stroke event. CPB flow did not affect survival rate, hospital stay, intensive care unit stay, or serum lactate in post-operative day 1, but serum creatinine (mg/dL) level increased transiently in patients with low pump flow group(0.9 ± 0.4 vs 1.3 ± 0.7,p < 0.05). Cannulation limb had decreased oxygenation during CPB, but their oxygenation all recovered after surgery. No limb ischemia event happened.ConclusionRetrograde arterial perfusion is a safe method for minimally invasive cardiac surgery less than 3.5 hours under mild hypothermic status.     

Clinical evaluation of cerebral oxygen balance during cardiopulmonary bypass: on-line continuous monitoring of jugular venous oxyhemoglobin saturation.

To prevent brain damage during cardiopulmonary bypass (CPB), adequate cerebral perfusion for cerebral oxygen demand should be maintained. We monitored jugular venous oxyhemoglobin saturation (SjO2), which reflects the overall balance of cerebral oxygen supply and demand, continuously in 12 patients undergoing cardiac surgery. We examined whether this balance is disrupted during CPB, and if so, analyzed critical factors that affect this phenomenon. At the initiation of CPB, in spite of a significant decrease in mean arterial pressure, SjO2 did not change, and it was stable during the hypothermic period of CPB. On the other hand, a significant reduction in SjO2 was observed during the rewarming period, and SjO2 had an inverse linear correlation with nasopharyngeal temperature. Furthermore, the percent decrease of SjO2 was significantly related to "rewarming speed" (an average increase in temperature per minute). Our results indicate that temperature change during the rewarming period is a critical factor affecting the balance of cerebral oxygen supply and demand during CPB.