Sean D. Galvin

Influence of Changes in Blood Pressure on Cerebral Perfusion and Oxygenation

Cerebral autoregulation (CA) is a critical process for the maintenance of cerebral blood flow and oxygenation. Assessment of CA is frequently used for experimental research and in the diagnosis, monitoring, or prognosis of cerebrovascular disease; however, despite the extensive use and reference to static CA, a valid quantification of “normal” CA has not been clearly identified. While controlling for the influence of arterial Pco2, we provide the first clear examination of static CA in healthy humans over a wide range of blood pressure. In 11 healthy humans, beat-to-beat blood pressure (radial arterial), middle cerebral artery blood velocity (MCAv; transcranial Doppler ultrasound), end-tidal Pco2, and cerebral oxygenation (near infrared spectroscopy) were recorded continuously during pharmacological-induced changes in mean blood pressure. In a randomized order, steady-state decreases and increases in mean blood pressure (8 to 14 levels; range: ≈40 to ≈125 mm Hg) were achieved using intravenous infusions of sodium nitroprusside or phenylephrine, respectively. MCAvmean was altered by 0.82±0.35% per millimeter of mercury change in mean blood pressure (R2=0.82). Changes in cortical oxygenation index were inversely related to changes in mean blood pressure (slope=−0.18%/mm Hg; R2=0.60) and MCAvmean (slope=−0.26%/cm · s−1; R2=0.54). There was a progressive increase in MCAv pulsatility with hypotension. These findings indicate that cerebral blood flow closely follows pharmacological-induced changes in blood pressure in otherwise healthy humans. Thus, a finite slope of the plateau region does not necessarily imply a defective CA. Moreover, with progressive hypotension and hypertension there are differential changes in cerebral oxygenation and MCAvmean.

Initial orthostatic hypotension is unrelated to orthostatic tolerance in healthy young subjects

The physiological challenge of standing upright is evidenced by temporary symptoms of light-headedness, dizziness, and nausea. It is not known, however, if initial orthostatic hypotension (IOH) and related symptoms associated with standing are related to the occurrence of syncope. Since IOH reflects immediate and temporary adjustments compared with the sustained adjustments during orthostatic stress, we anticipated that the severity of IOH would be unrelated to syncope. Following a standardized period of supine rest, healthy volunteers [n=46; 25+/-5 yr old (mean+/-SD)] were instructed to stand upright for 3 min, followed by 60 degrees head-up tilt with lower-body negative pressure in 5-min increments of -10 mmHg, until presyncope. Beat-to-beat blood pressure (radial arterial or Finometer), middle cerebral artery blood velocity (MCAv), end-tidal PCO2, and cerebral oxygenation (near-infrared spectroscopy) were recorded continuously. At presyncope, although the reductions in mean arterial pressure, MCAv, and cerebral oxygenation were similar to those during IOH (40+/-11 vs. 43+/-12%; 36+/-18 vs. 35+/-13%; and 6+/-5 vs. 4+/-2%, respectively), the reduction in end-tidal CO2 was greater (-7+/-6 vs. -4+/-3 mmHg) and was related to the decline in MCAv (R2=0.4; P<0.05). While MCAv pulsatility was elevated with IOH, it was reduced at presyncope (P<0.05). The cardiorespiratory and cerebrovascular changes during IOH were unrelated to those at presyncope, and interestingly, there was no relationship between the hemodynamic changes and the incidence of subjective symptoms in either scenario. During IOH, the transient nature of physiological changes can be well tolerated; however, potentially mediated by a reduced MCAv pulsatility and greater degree of hypocapnic-induced cerebral vasoconstriction, when comparable changes are sustained, the development of syncope is imminent.

A Database-driven Decision Support System: Customized Mortality Prediction

We hypothesize that local customized modeling will provide more accurate mortality prediction than the current standard approach using existing scoring systems. Mortality prediction models were developed for two subsets of patients in Multi-parameter Intelligent Monitoring for Intensive Care (MIMIC), a public de-identified ICU database, and for the subset of patients >80 years old in a cardiac surgical patient registry. Logistic regression (LR), Bayesian network (BN) and artificial neural network (ANN) were employed. The best-fitted models were tested on the remaining unseen data and compared to either the Simplified Acute Physiology Score (SAPS) for the ICU patients, or the EuroSCORE for the cardiac surgery patients. Local customized mortality prediction models performed better as compared to the corresponding current standard severity scoring system for all three subsets of patients: patients with acute kidney injury (AUC = 0.875 for ANN, vs. SAPS, AUC = 0.642), patients with subarachnoid hemorrhage (AUC = 0.958 for BN, vs. SAPS, AUC = 0.84), and elderly patients undergoing open heart surgery (AUC = 0.94 for ANN, vs. EuroSCORE, AUC = 0.648). Rather than developing models with good external validity by including a heterogeneous patient population, an alternative approach would be to build models for specific patient subsets using one’s local database.

Desmopressin for reducing postoperative blood loss and transfusion requirements following cardiac surgery in adults.

A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was, in adult patients undergoing cardiac surgery requiring extracorporeal cardiopulmonary bypass (CPB), does administration of desmopressin acetate (DDAVP) reduce postoperative blood loss and transfusion requirements? Altogether 38 papers were found using the reported search, of which 19 represented the best evidence to answer the clinical question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. Perioperative administration of DDAVP in adult patients undergoing cardiac surgery requiring CPB may result in a small but significant reduction in postoperative blood loss. However, this does not translate into a reproducible, clinically significant reduction in exposure to transfusion in unselected patients exposed to CPB. Several sub-groups of patients have been identified in whom DDAVP reduces postoperative blood loss and transfusion requirements. These sub-groups include patients who have received preoperative aspirin within 7 days of surgery, patients with CPB times in excess of 140 min and patients with demonstrable pre- or perioperative platelet dysfunction as determined by TEG analysis or platelet function assays. Platelet dysfunction at the time of surgery may be secondary to preoperative administration of antiplatelet medications, the result of pathological processes such as von Willebrands disease, uraemia or aortic stenosis with its associated sheer stress, as well as operative variables such as prolonged exposure to CPB. The evidence does not support the routine use of DDAVP in all cardiac surgery; indeed, it is clear that there is no significant reduction in postoperative blood loss or transfusion requirements with the administration of DDAVP in patients undergoing isolated coronary artery bypass grafting (CABG) in the absence of the features noted above. Given the absence of a clinically significant reduction in exposure to blood transfusion in unselected patients, we cannot recommend the routine use of DDAVP in patients exposed to CPB. However, DDAVP may reduce postoperative bleeding in patients who have received preoperative aspirin within 7 days of surgery, patients with CPB times in excess of 140 min and patients with demonstrable platelet dysfunction and should be used selectively in these subgroups.

Benign Metastasizing Leiomyoma: A Rare Metastatic Lesion in the Right Ventricle

Cardiac tumors require resection for diagnostic purposes and to avoid complications associated with an intracardiac mass. We present the case of a 41-year-old woman with a known uterine leiomyoma who presented 3 months after elective cesarian section and hysterectomy with a right ventricular mass that was confirmed histologically to be a benign leiomyoma of the same pathologic type as the uterine primary. Benign metastasizing leiomyoma is a rare pathologic entity occurring in women with a history of a uterine leiomyoma. This is the second reported case of cardiac metastasis from a benign uterine leiomyoma.

Identical pattern of cerebral hypoperfusion during different types of syncope

Syncope is caused by insufficient oxygen supply to the brain. There have been attempts to classify syncope on the basis of defects in the venous system, arterial system (that is impaired systemic vascular resistance) or a combination of the two (that is mixed). We examined the hypothesis that a comparable decrease in cerebral perfusion would be evident at pre-syncope irrespective of the category of dysfunction. Young healthy volunteers (N=37) participated. The protocol consisted of 15 min supine rest, followed by 60° head-up tilt and lower body suction in increments of −10 mm Hg for 5 min each until pre-syncope. Beat-to-beat blood pressure (BP) (Finometer or intra-arterial), cardiac output (Finometer), middle cerebral artery blood velocity (MCAv), end-tidal CO2 and cerebral oxygenation were monitored continuously. At pre-syncope, mixed dysfunction was common (21 out of 37 participants), followed by venular dysfunction (15 out of 37 participants). In the venular and mixed groups, comparable orthostatic tolerance and declines in BP (−37 vs −43% from baseline, respectively), end-tidal PCO2, MCAv (−35 vs −38%) and cerebral oxygenation (−5 vs −7%) were evident despite distinct mechanisms purportedly being responsible for the hypotension. Although different determinants of hypotension do exist, cerebral hypoperfusion occurs to a similar extent.

Magnetic Resonance Imaging of Partial Segmental Priapism (Segmental Thrombosis of Corpus Cavernosum)

Partial segment priapism or segmental thrombosis of the corpus cavernosum is a rare urologic condition reported 23 times in the world literature. We present the clinical and radiologic findings of a 22-year-old man who presented 7 days after the onset of symptoms in whom the diagnosis was confirmed with magnetic resonance imaging. He was treated conservatively with a nonsteroidal anti-inflammatory drug and aspirin with full restoration of erectile function. On the basis of previous reports and our own experience, we suggest that the management of partial segment priapism should include diagnosis with magnetic resonance imaging and conservative treatment with analgesics and an anti-inflammatory drug to control symptoms.

Branch-first continuous perfusion aortic arch replacement and its role in intra-operative cerebral protection.

Surgery of the aortic arch remains one of the most challenging areas of cardiac surgery. Despite the advancements and refinements in surgical and perfusion techniques over the last 30 years, mortality, morbidity, and in particular the incidence of cerebral injury, remains higher than that reported in procedures performed on the more proximal aorta. The brain is the most oxygendependent organ in the body and many steps during aortic arch replacement have the potential to cause cerebral injury, either as a result of temporary interruption to its blood supply or the introduction of gaseous or particulate emboli. Traditional approaches have focused on the use of two concepts to limit cerebral injury during arch replacement. Firstly, the use of profound hypothermia to reduce cerebral metabolic demands combined with surgical haste to minimize periods of cerebral ischemia; and secondly, the addition of various techniques of cerebral perfusion (antegrade and/or retrograde) in an attempt to prolong the period of “safe” circulatory arrest.

Continuous perfusion "Branch-first" aortic arch replacement: a technical perspective.

The following video, along with the in-depth perspective article published elsewhere in this issue, aims to take you through the significant steps and the theoretical aspects of aortic arch replacement using the “Branch-first” continuous perfusion technique (Video 1). Video 1 Continuous perfusion “Branch-first” aortic arch replacement: a technical perspective In essence the procedure consists of 5 major steps: Establishment of cardiopulmonary bypass using femoral inflow and moderate hypothermia; Serial disconnection and reconstruction of each arch branch (proceeding from innominate to left subclavian) using a trifurcation arch graft with a perfusion side arm port (TAPP graft, Vascutek Ltd., Renfrewshire, Scotland, UK). Following completion of the innominate anastomosis, the perfusion side arm port is used for selective antegrade cerebral perfusion for the remainder of the procedure; Clamping of the proximal descending aorta and construction of the distal arch anastomosis; Completion of aortic root reconstruction; Connection of the common stem of the trifurcation graft to the ascending aortic graft. Collateral network and individual proximal arch branch clamping A basic principle of the “Branch-first” technique is the richness of the collateral network that exists between the 3 arch branches and between the arch branches and the upper and lower body. Apart from the circle of Willis, there are a number of extra-cranial collateral channels that augment cerebral perfusion during individual clamping of each branch vessels (1,2). These collateral channels include: Those between the external and internal carotid arteries; The right and the left carotid arteries; The upper and lower body; The subclavian and carotid arteries. These extracranial collaterals allow for a short period of occlusion of one branch while the other two branches perfuse its territory. Typically with this technique, anastomotic times for each individual branch vessel are performed in approximately 10 minutes and we rarely see changes in ipsilateral cerebral oxygenation during this period. On the infrequent occasion that this does occur, alteration of systemic or head circuit flows generally brings cerebral oxygenation back to baseline levels.

The history of arterial revascularization: from Kolesov to Tector and beyond

Coronary artery bypass grafting (CABG) is the one of the most effective revascularization strategies for patients with obstructive coronary artery disease. Total arterial revascularization using one or both internal thoracic and radial arteries has been shown to improve early outcomes and reduce long-term cardiovascular morbidity. Although CABG has evolved from an experimental procedure in the early 1900s to become one of the most commonly performed surgical procedures, there is still significant variation in grafting strategies amongst surgeons. We review the history and development of CABG with a particular emphasis on the early pioneers and the evolution of arterial grafting.