ACE inhibition does not exaggerate the blood pressure decrease in the early phase of spinal anaesthesia

BACKGROUND: This study investigates whether long-term treatment with an angiotensin converting enzyme inhibitor (ACEI) impairs the hemodynamic regulation during the early phase of spinal anaesthesia. METHODS: Forty-two patients undergoing minor surgery were studied. Twenty-one patients were long-term treated (ACEI group), while the other patients served as controls (nonACEI group). All patients received a balanced electrolyte solution (6 ml kg(-1)) 20 min before spinal anaesthesia. RESULTS: Mean arterial blood pressure decreased 19% in both groups within 20 min after spinal anaesthesia. Heart rate did not change in either group. Plasma renin concentration increased from 7.3 +/- 2.1 to 12.8 +/- 4 pg ml(-1) during spinal anaesthesia in nonACEI patients (P < 0.05), whereas an elevated plasma renin level remained unchanged in the nonACEI group. The angiotensin II concentration increased in both groups during spinal anaesthesia (P < 0.05). The vasopressin concentration did not change during spinal anaesthesia in the ACEI group, but increased from 1.2 +/- 0.3 to 2.2 +/- 0.5 pg ml(-1) in patients with ACEI treatment (P < 0.05). The norepinephrine concentration increased transiently 5 min after spinal anaesthesia in both groups, and returned to baseline levels within 15 min. CONCLUSION: Long-term ACEI treatment does not further exaggerate the blood pressure decrease in the early phase of spinal anaesthesia. The increase in vasopressin concentrations in ACEI treated patients seems to be sufficient to compensate for the inhibited renin-angiotensin system. In addition, the transient increase in plasma norepinephrine, which occurs independent of preoperative ACEI treatment, seems to be involved in blood pressure regulation during spinal anaesthesia.     

Epidural clonidine produces antinociception, but not hypotension, in sheep

Intrathecally administered clonidine produces analgesia, but also produces hypotension. To assess the effects of epidural administration, the authors inserted lumbar epidural catheters in seven nonpregnant ewes, and injected, on separate days, clonidine (50-750 mcg), morphine (5-10 mg), and a clonidine-morphine combination (clonidine 150 mcg + morphine 5 mg). Clonidine produced dose-dependent antinociception and sedation, with the lowest maximally effective antinociceptive dose being 300 mcg. Morphine produced less intense antinociception than clonidine, and did not potentiate clonidine's effect. Antinociception, but not sedation, following clonidine injection was reversed by epidural injection of the alpha 2-adrenergic antagonist, idazoxan. Epidurally administered naloxone and prazosin did not reverse clonidine's antinociceptive effect, nor did intravenously administered idazoxan. Epidurally administered clonidine did not decrease blood pressure or heart rate or affect arterial blood gas tensions or spinal cord histology. These data suggest that epidurally administered clonidine produces analgesia by a local, alpha 2-adrenergic mechanism. In sheep, epidurally administered clonidine does not produce hypotension.     

Subarachnoid clonidine reduces spinal cord blood flow and glucose utilization in conscious rats

The authors investigated the spinal blood flow and metabolic effects of subarachnoid clonidine in conscious rats prepared with chronically implanted subarachnoid catheters. For the blood flow experiments, rats received saline (n = 7) or clonidine 20 nmol (7 micrograms; n = 6), 100 nmol (27 micrograms; n = 5), or 400 nmol (107 micrograms; n = 7) intrathecally. Another group of rats received clonidine 400 nmol intravenously (n = 4). Spinal glucose utilization was measured in rats that received either saline (n = 5) or clonidine 100 nmol (n = 5) intrathecally. Spinal cord blood flow (SCBF) and glucose utilization were measured in five gray and three white matter areas of lumbar spinal cord 15 min after drug administration with the autoradiographic iodo-[14C]-antipyrine and 2-[14C]-deoxyglucose methods, respectively. Physiologic differences between the groups were minor. Rats in the blood flow experiments that received clonidine 100 nmol had a slightly lower arterial PO2 level (70 +/- 1 vs. 82 +/- 3 mmHg; P less than 0.05), whereas those in the glucose utilization group were mildly hypocarbic (PCO2 27 +/- 1 vs. 32 +/- 2 mmHg; P less than 0.01) relative to control animals. Only animals that received 400 nmol clonidine intrathecally had significant analgesia, as assessed by the tail-flick test. One control animal for the metabolism experiments was technically unsatisfactory and was excluded from data analysis. Subarachnoid clonidine reduced both SCBF and glucose utilization. In spinal gray matter, the largest decreases in flow (32-44%; P less than 0.01) occurred with 20 nmol clonidine, whereas flow decreased least (12-27%) with the 400-nmol dose.(ABSTRACT TRUNCATED AT 250 WORDS)     

Coronary blood flow does not decrease during allograft rejection in heterotopic heart transplants

To evaluate changes in coronary blood flow during allograft rejection, 16 beagles with cervical cardiac allografts from mongrel donors were immunosuppressed postoperatively for 7 days with cyclosporine (20 mg/kg orally) and prednisone (0.5 mg/kg orally). They were weaned from immunosuppression over 3 days and then treated with methylprednisolone (30 mg/kg/day IV), cyclosporine (20 mg/kg orally), and prednisone (0.5 mg/kg orally) for 4 days. Previous experiments with this model have suggested the utility of phosphorus 31 nuclear magnetic resonance spectroscopy (31P NMR) in the diagnosis of rejection. Therefore in 10 dogs (NMR group) bioenergetic changes during rejection were assessed using the 31P NMR index of the ratio of phosphocreatine to inorganic phosphate (PCr/Pi). To correlate coronary blood flow and graft ischemia with allograft rejection, six dogs (FLOW group) underwent placement of a magnetic flow probe on the left anterior descending coronary artery to determine mean and peak coronary flow. In both NMR and FLOW groups, grafts were evaluated by endomyocardial biopsy (grading 0 to 8 for increasing rejection), and measurement of lactate production and left ventricular end-diastolic pressure. During the initial 7 days of immunotherapy, cellular rejection was effectively suppressed, and the bioenergetic status of the grafts remained stable (day 7: PCr/Pi = 70% of baseline, biopsy score = 2.0). During weaning of immunotherapy, however, the metabolic profile of the grafts decayed (day 10: PCr/Pi = 45% of baseline, biopsy score = 5.8; p less than 0.05 vs day 0). After 4 days of augmented immunosuppression, PCr/Pi recovered to 83% of baseline; this metabolic recovery corresponded with an improvement in mean biopsy score to 3.2.(ABSTRACT TRUNCATED AT 250 WORDS)     

Perioperative blood transfusion does not decrease survival after surgical treatment of spinal metastases

Purpose

To assess whether perioperative allogenic blood transfusions in patients undergoing surgical treatment for spinal metastases independently influence patient survival.

Methods

A retrospective study including 170 consecutive patients undergoing surgical treatment for spinal metastases in 2009 and 2010 at a tertiary referral center. Variables related to postoperative survival were all included in the same multivariable logistic regression analysis with either 3- or 12-month survival as the dependent variable. The independent variables were: transfusion of allogenic red blood cells, age at surgery, gender, preoperative hemoglobin, revised Tokuhashi score and no. of instrumented levels.

Results

Perioperative allogenic blood transfusion of 1–2 units was associated with increased 12-month survival [p = 0.049, odds ratio 2.619 (confidence interval 1.004–6.831)], but not with 3-month survival. Larger transfusion volumes did not significantly influence survival.

Conclusion

The results of the present study support that perioperative blood transfusion of <5 units does not decrease survival in patients operated for spinal metastases. Transfusion of 1–2 units seems to be associated with increased 12-month survival. Future studies should assess if a liberal transfusion regime can be applied to this group of patients; thereby, prioritizing early postoperative mobilization.     

Epidural clonidine analgesia in obstetrics: sheep studies

Epidural clonidine administration produces analgesia by a nonopiate, spinal mechanism, and offers advantages over other epidural agents for labor analgesia. To examine clonidine's acute maternal and fetal effects, the authors injected clonidine, 300 micrograms, epidurally in seven chronically prepared, near term ewes. Unlike epidural saline injection, clonidine increased maternal and fetal serum glucose (by 178 +/- 30% and 190 +/- 30%, respectively; mean +/- SEM, P less than .01) 1 h following injection. Maternal and fetal serum cortisol and arterial blood gas tensions were unchanged following clonidine. Epidural clonidine injection produced minor decreases (10-15%) in heart rate in ewe and fetus, without altering maternal and fetal blood pressure, intra-uterine pressure, or uterine blood flow. Maternal and fetal serum clonidine concentrations peaked at 58 +/- 8 and 73 +/- 5 min following injection, respectively, and declined with similar half-lives. Heart rate correlated negatively with serum clonidine concentration in both ewe and fetus (P less than .05). Apart from hyperglycemia, which does not occur in humans, these results in sheep suggest that epidurally administered clonidine does not adversely affect the fetus and may be evaluated as an analgesic in obstetrics.     

Effects of a contusion injury on spinal cord blood flow in the sheep

The effect of experimental trauma on the blood flow in the central (essentially gray matter) and peripheral (essentially white matter) regions of the sheep's spinal cord was studied using a radioactive microsphere technique. In seven out of eight animals, a progressive fall in blood flow occurred in both the peripheral and central regions of the cord within 2 hours following injury and remained reduced over the period of recording (up to 12 hours). Changes in local vascular resistance indicated that in approximately 60% of our animals, changes in arterial pressure alone contributed highly significantly to the decreased spinal blood flow. There remains the possibility that early therapeutic intervention could sustain neuronal function where local blood flow would otherwise be inadequate in the damaged spinal cord.     

Successful improvement of blood pressure, cardiac output, and spinal cord blood flow after experimental spinal cord injury

Thirty-seven rats were anesthetized and ventilated and had continuous monitoring of mean systemic arterial pressure (MSAP) and central venous pressure (CVP). The animals underwent a 60-g clip compression injury at T-1 for 1 minute. Fifteen minutes after injury, microspheres were used to measure cardiac output (CO) and spinal cord blood flow (SCBF). Each animal was then randomized into one of five groups. Four groups received intravenous infusions for 1 hour each of 5% albumin, autologous packed cells, low molecular weight dextran, or autologous whole blood to maintain the MSAP. The fifth group served as a control group and received an infusion of normal saline. Seventy-five minutes after injury, CO and SCBF were measured. The posttraumatic reduction in CO was significantly improved by all four treatment infusions. However, only autologous whole blood and dextran successfully reversed the posttraumatic hypotension. Dextran significantly elevated the CVP (P less than 0.01) and reduced the hematocrit (P less than 0.01). Whole blood improved SCBF in all segments of the spinal cord by nearly 100% (P less than 0.05), and dextran increased SCBF by 200% (P less than 0.01). Thus, the most marked improvements in MSAP, CO, and SCBF were produced by hypervolemia and hemodilution associated with dextran infusion. The therapeutic implications of this reversal of local and systemic changes in acute spinal cord injury are discussed.     

Elevated coronary sinus pressure does not alter myocardial blood flow or left ventricular contractile function in mature sheep. Implications after the Fontan operation

The hypothesis that elevation of coronary sinus pressure affects coronary blood flow and ventricular function was tested in this study of seven adult ewes placed under pentobarbital anesthesia. Coronary sinus pressure was elevated by partial balloon occlusion. Right atrial, left atrial, and aortic mean pressures and rate of rise of left ventricular pressure were measured. Coronary blood flow was determined with radioactive microspheres. Studies were performed at control and at moderate (15 to 20 mm Hg) and marked (30 to 35 mm Hg) elevation of coronary sinus mean pressures. Despite increase of coronary sinus pressure from a control value of 2 mm Hg +/- 1 to levels of 19 mm Hg +/- 1 and 34 mm Hg +/- 1, no significant changes were observed in right atrial, left atrial, or aortic mean pressure or rate of rise of left ventricular pressure. Both endocardial and epicardial blood flows were unaffected. The endocardial/epicardial flow ratio at moderate coronary sinus pressure elevation was significantly increased, which suggested local subendocardial vasodilation in the absence of changes in transmural perfusion. The findings suggest that isolated increase in coronary sinus pressure is not a major determinant of myocardial blood flow or ventricular performance in the normal ewe.     

Effect of epidural clonidine on spinal cord blood flow and regional and central hemodynamics in pigs

Epidural clonidine is reported to produce analgesia in humans. To investigate the effect of epidural injection of this alpha 2-adrenoceptor agonist on spinal cord blood flow as well as on regional and central blood flow and hemodynamics, 11 anesthetized pigs were studied. Each pig received clonidine in increments of 3, 10 and 30 micrograms/kg, each dose given in a volume of 5 ml via a lumbar epidural catheter. The tip of the catheter was located in the lumbar epidural space. The microsphere method was used to measure regional circulation. The measurements were made 45 min after each dose. Each pig served as its own control. The lowest dose of epidural clonidine (3 micrograms/kg) did not affect regional blood flow to the spinal cord or to any other organ. The intermediate and high doses were associated with local vasoconstriction in the lumbar and thoracic parts of the spinal cord that produced a statistically significant reduction in flow of 25-35% (P less than 0.05). Blood flow to the brain, cerebellum and the cervical parts of the spinal cord was not significantly changed, nor was renal blood flow. In the adrenal and in skeletal muscles a marked reduction of the blood flow occurred after the high dose, 61% and 78%, respectively. These findings indicate that epidural clonidine 3 micrograms/kg, a dose of clinical interest, is not likely to produce dangerous vasoconstriction in the spinal cord.     

Static intra-access pressure ratio does not correlate with access blood flow

BACKGROUND: Access flow (Qa) measurement is recommended by Kidney Disease Outcomes Quality Initiative (K/DOQI) as the preferred method for access surveillance. Static intra-access pressure ratio (SIAPR) measurement is the second surveillance method of choice. The purpose of this prospective multicenter study was to investigate the relationship between SIAPR and Qa and to examine the premise upon which SIAPR surveillance is based-namely, that high SIAPR is a surrogate for low Qa associated with hemodynamically significant stenosis. METHODS: SIAPR and Qa (HD01; Transonic Systems, Inc., Ithaca, NY, USA) were simultaneously measured monthly in 242 patients [146 prosthetic arteriovenous bridge grafts (AVG), 96 autogenous arteriovenous fistulas (AVF)] from three centers. SIAPR was measured according to the K/DOQI protocol. RESULTS: There was no correlation between Qa and venous or arterial SIAPR in AVGs (R(2)= 0.0037 and R(2)= 0.006, respectively, N= 730), or in AVFs (R(2)= 0.0247 and R(2)= 0.0329, respectively, N= 431). Of the high SIAPR measurements in AVGs, 81% and 50% were associated with Qa > or =600 and Qa > or =1000 mL/min, respectively. Of the AVGs studied, 41% (60/146) had consistently high Qa > or =1000 mL/min. Seventy percent (42/60) of these high-Qa AVGs had at least two consecutive sessions with high SIAPR measurements, thereby meeting the K/DOQI SIAPR criteria for referral. In addition, 78% (14/18) of new AVGs with Qa > or =1000 mL/min, and 86% (6/7) of AVGs with the highest Qa (> or =2000 mL/min), had high SIAPR. As a result, these high-Qa AVGs, which represented the best functioning AVGs by K/DOQI Qa standards, were erroneously targeted for referral based on SIAPR measurements. CONCLUSION: SIAPR does not correlate with Qa or discriminate between high and low Qa. Therefore, because the utility of SIAPR surveillance for detection of clinically significant stenosis depends on a correlation with Qa, the current use of absolute K/DOQI SIAPR thresholds for intervention based on the presumption that such thresholds are indicative of low Qa is not justified, and should be discontinued. Studies need to be done to examine the utility of SIAPR for trend analysis.     

Epidural anaesthesia for elective Caesarean section does not influence fetal umbilical artery blood flow indices

This prospective study was completed to determine the influence of epidural anaesthesia on the fetoplacental circulation of normal subjects. Thirty-seven normal pregnant patients at term, undergoing elective Caesarean section, had Doppler measurements of the fetal umbilical artery blood flow velocity before and after epidural anaesthesia using lidocaine 2% without epinephrine. There were no differences in systolic/diastolic, resistance or pulsality indices following epidural anaesthesia. These results suggest that this technique has no adverse effect on fetoplacental circulation in normal non-labouring subjects. Cette étude prospective a pour but de déterminer l’influence de l’anesthésie épidurale sur la circulation foeto-placentaire dans le contexte d’une grossesse normale. Des indices de vélocité du flot de l’artère ombilicale foetale ont été mesurés par Doppler chez trentesept patientes gravides à terme, sans complications, programmées pour une césarienne élective, avant et après une anesthèsie épidurale utilisant la lidocaine 2% sans épinéphrine. Les indices de rapport systole/diastole, de résistance et de pulsatilité sont demeurés inchangés après l’induction de l’anesthésie épidurale. Ces constatations suggèrent que l’anesthésie épidurale n’a pas d’influence sur la circulation foetoplacentaire chez des patientes enceintes normales à terme qui ne sont pas en travail.     

Cervical spinal cord injury associated with near-drowning does not increase pneumonia risk or mortality

Body surfing accidents (BSA) can cause cervical spinal cord injuries (CSCIs) that are associated with near-drowning (ND). The submersion injury from a ND can result in aspiration and predispose to pulmonary complications. We predicted a worse outcome (particularly the development of pneumonia) in patients with CSCIs associated with ND. A retrospective review was performed of patients who were treated at Eastern Virginia Medical School for a CSCI resulting from a blunt mechanism. Data collected included basic demographic data, data regarding injury and in-hospital outcomes, and discharge data, including discharge disposition. Statistics were performed using χ(2) and Student t test. In 2003 to 2008, 141 patients were treated for CSCIs with inclusion criteria. Thirty patients (21%) had an associated ND (BSA) and 111 patients (79%) did not (BLT). The cohorts were similar in mean age (BSA, 45 years; BLT, 50 years; P = 0.16) and male gender distribution (BSA, 93%; BLT, 79%; P = 0.13). The cohorts were similar in injury severity using Injury Severity Score (BSA, 22; BLT, 24; P = 0.65). The cohorts were similar in rates of developing pneumonia (BSA, 3%; BLT, 12%; P = 0.31). The rate of infection was significantly higher in the cohort without an associated near-drowning (BSA, 10%; BLT, 32%; P = 0.033). The mean intensive care unit stay (BSA, 3.5 days; BLT, 11.3 days; P = 0.057) and the rate of mortality were similar (BSA, 10%; BLT, 10% P = 0.99). Those patients with an associated ND had a shorter hospital stay (BSA, 5.7 days; BLT, 22.2 days; P = 0.007) and a better chance of being discharged home (BSA, 57%; BLT, 27%; P = 0.004). CSCIs after a BSA do better than their counterparts without an associated ND. CSCIs associated with ND appear to be isolated injuries with minimal pulmonary involvement despite submersion injuries.     

Cerebral and spinal cord blood flow in awake and fentanyl-N2O anesthetized rats: evidence for preservation of blood flow autoregulation during anesthesia

Blood flow responses to alterations in mean arterial blood pressure (MABP) were measured in the cerebral cortex, subcortex, midbrain, and spinal cord of awake rats. Data were compared with those of rats anesthetized with an i.v. fentanyl infusion and inspired nitrous oxide (N2O). Regional cerebral blood flow was measured using radioactive microspheres in the following blood pressure ranges: (a) <40 mm Hg; (b) 40-60; (c) 60-80; (d) 80-100; (e) 100-120; (f) 120-140; (g) 140-160; and (h) >160. Blood pressure was increased with phenylephrine or decreased with trimethaphan combined with blood withdrawal. Cerebral blood flow was not measured when MABP was less than 60 mm Hg in awake rats. Autoregulation was seen in all brain areas between 60 and 140 mm Hg in both treatment groups. Although regional cerebral blood flow was not different between the two treatment groups, PaCO2 was 2-4 mm Hg lower in awake rats. This suggests that PaCO2-corrected cerebral blood flow may be 10-20% lower with fentanyl-N2O anesthesia.     

Spinal cord stimulation does not change peripheral skin blood flow in patients with neuropathic pain

BACKGROUND AND OBJECTIVE: Spinal cord stimulation has been used successfully for many years in the management of neuropathic pain. Nociceptive pathways are closely integrated into many autonomic reflexes. The aim was to test the hypothesis that pain relief caused by spinal cord stimulation is related to changes in peripheral skin blood flow. METHODS: Twelve patients with spinal cord stimulators implanted as a treatment for neuropathic pain were entered into the study. Laser Doppler perfusion scanning was used as a direct method for selective measurement of changes in skin (peripheral) blood flow. Measurements were taken before and after the onset of spinal cord stimulation over the site of its sensory projection. The degree of pain relief due to spinal cord stimulation and the skin temperature of each patient were also recorded. RESULTS: Apart from one patient, spinal cord stimulation did not change skin blood flow in a statistically significant manner. CONCLUSIONS: Pain relief due to spinal cord stimulation is not related to changes of skin blood flow.     

Effects of aortic occlusion on regional spinal cord blood flow and somatosensory evoked potentials in sheep

Somatosensory evoked potentials (SEPs) were recorded continuously during aortic occlusion in sheep, with simultaneous measurement of spinal cord blood flow (SCBF) by radiolabeled microspheres. Aortic occlusion was associated with disappearance of the SEPs in seven of nine sheep in 7.8 +/- 4.1 (SD) minutes. SCBF at the time of initial cross clamping and 30 minutes after the onset of ischemia revealed a severe reduction in white and gray matter flow in the thoracolumbar cord. Release of the aortic clamp was associated with reactive hyperemia in these ischemic regions. In two animals, the SEP persisted during aortic cross clamping. The total SCBF in the thoracic and lumbar regions of these two animals exceeded 20 ml/100 g/min after 30 minutes of ischemia and was significantly greater than the flow recorded in sheep whose evoked response disappeared. The relation between spinal cord ischemia and evoked potential alterations is discussed in detail.     

急性脊髓损伤中脊髓血流量与神经功能损害的关系

目的 :观察脊髓损伤 (SCI)后伤段脊髓血流量的动态变化 ,探讨其与脊髓神经功能损害的关系。方法 :Allen′s法致伤大鼠脊髓 ,于伤前和伤后 1、4、8、2 4、72、1 6 8h和 1个月 ,采用氢清除法测量脊髓血流量 ,参照Konrad的方法记录脊髓运动诱发电位 (MEP) ,应用斜板试验评价大鼠的运动功能。结果 :SCI后伤段脊髓血流量明显下降 (P <0 0 5或 0 0 1 ) ,与脊髓MEP的变化和运动功能的损害呈显著相关关系。结论 :脊髓损伤后缺血在脊髓神经功能损害中有重要意义 ,可能是SCI后继发性损伤形成的主要因素之一。