Laurie K. Davies

cerebral Microembolism Diagnosed by Transcranial Doppler during Total Knee Arthroplasty : Correlation with Transesophageal Echocardiography

BACKGROUND Tourniquet deflation following total knee arthroplasty (TKA) frequently results in release of emboli into the pulmonary circulation. Small emboli may gain access to the systemic circulation via a transpulmonary route or through a patent foramen ovale. This study examined the incidence of cerebral microembolism after tourniquet release by transcranial Doppler (TCD) ultrasonography and its correlation with echogenic material detected in the left atrium. METHODS Twenty-two adult patients (9 men, 13 women) undergoing TKA were studied with simultaneous TCD ultrasonography and transesophageal echocardiography. Data were recorded after anesthesia induction and tourniquet inflation and during tourniquet deflation. Emboli counts were performed manually off-line. Echogenic material in the left atrium was qualitatively assessed and correlated with TCD data. Patients were examined postoperatively for focal neurologic deficits. RESULTS Fifteen patients had unilateral TKA (six left, nine right) and seven had bilateral TKA. Cerebral emboli were detected in 9 of 15 patients (60%) with unilateral TKA and in 4 of 7 patients (57%) with bilateral TKA. Echogenic material was identified in the left atrium in eight patients (two through a patent foramen ovale and six from the pulmonary veins). Emboli counts were significantly higher in patients with bilateral TKA compared with those with unilateral TKA (P<0.05). Duration of tourniquet time in patients with emboli was longer only during bilateral TKA (P<0.05). All patients with echogenic material in the left atrium detected by transesophageal echocardiography had emboli as assessed by TCD ultrasonography. No focal neurologic deficits were identified. CONCLUSIONS Cerebral microembolism occurs frequently during tourniquet release, even in the absence of a patient foramen ovale. This passage most likely occurs through the pulmonary capillaries or the opening of recruitable pulmonary vessels.

Acute Neuropsychological Functioning Following Cardiosurgical Interventions Associated With the Production of Intraoperative Cerebral Microemboli

Coronary artery bypass graft (CABG) and valve replacement (VR) surgical patients underwent neuropsychological assessment 1–2 days prior to surgery; 7–10 days postsurgery; and 1 month following hospital discharge. A group of matched healthy controls was tested at identical intervals. Cerebral microemboli in both middle cerebral arteries were quantified during surgery using Doppler sonography. Neuropsychological testing results revealed that the CABG and VR groups did not differ from one another at any assessment point. However, surgical patients performed more poorly than healthy controls across all assessments. Surgical patients, as a group, demonstrated a mild decline in attentional functioning and learning efficiency at the 7–10 day follow-up, but these difficulties essentially returned to baseline by the 1-month follow-up. Intraoperative microemboli counts were not significantly associated with postsurgical neuropsychological functioning in either the CABG or VR group.

Unilateral vs. bilateral ultrasound in the monitoring of cerebral microemboli

We used bilateral transcranial Doppler to monitor the number of microembolic events (ME) in the left and right middle cerebral arteries of 29 patients during cardiac surgery that required extracorporeal circulation. Based on a previously published study, we hypothesized that the commonly used method of doubling unilateral ME counts to obtain an estimated bihemispheric load would result in significant errors of estimation. In our sample, estimated bihemispheric counts were inaccurate by an average of 18% (range 0--80%). Despite this large range of error, calculation of Cronbachs alpha revealed that actual error due to unreliability (4%) was small relative to the large variation in ME counts across subjects in this patient series. These findings suggest that unilateral monitoring is sufficient when the goal is to characterize a given subjects ME load within the context of the other subjects in the sample. However, when precise ME counts are required, bilateral monitoring is essential.

End-of-life discussions: Who's doing the talking?

Purpose: To determine, in a tertiary academic medical center, the reported frequency of end‐of‐life discussions among nurses and the influence of demographic factors on these discussions. Methods: Survey of nurses on frequency of end‐of‐life discussions in two urban academic medical centers. Chi‐square tests were used to separately assess the relationship between age, gender, specialty, and experience with responses to the question, “Do you regularly talk with your patients about end‐of‐life wishes?” Results: Overall, more than one‐third of respondents reported rarely or never discussing end‐of‐life wishes with their patients. Only specialty expertise (p < 0.001) was statistically significantly associated with discussing end‐of‐life issues with patients. Over half of nurses specializing in critical care responded that they have these discussion “always” or “most of the time.” However, for the specialties of surgery (59%) and anesthesiology (56%), the majority of respondents reported rarely or never having end‐of‐life discussions with patients. Conclusions: In a survey conducted in two tertiary care institutions, more than one‐third of nurses from all disciplines responded that they never or almost never discuss end‐of‐life issues with their patients. Specialty influenced the likelihood of discussing end‐of‐life issues with patients.

Diagnosis and Management of Arrhythmias in Children After Cardiac Surgery

Arrhythmias that lead to hemodynamic deterioration and sudden death are one of the most challenging problems in children after cardiac surgery. In infants with congenital heart disease, disorders of impulse conduction are more frequent than those of impulse generation. Various factors that include anatomic or physiologic abnormalities of the conduction system, damage as a result of hemodynamic stress or chronic hypoxia, and injury occurring at the time of surgery interact to produce dysrhythmias. During the post operative period, supraventricular tachycardia rarely causes sudden death in children. However, junctional ectopic tachy cardia and Wolff-Parkinson-White syndrome are 2 that have been associated with a high mortality rate. In general, ven tricular tachycardia carries a more serious prognosis than supraventricular tachycardia because it typically occurs in abnormal myocardium with suboptimal function, which may also be vulnerable to degeneration into ventricular fi brillation. A practical approach to the most common intra operative and postoperative arrhythmias in pediatric cardiac patients is discussed. Patients at risk, the types of arrhyth mias likely to occur after specific cardiac operations, and the most effective current therapies are reviewed.

Physiologic Principles and Clinical Use of Hypothermia

Hypothermia has been used to treat a wide variety of diseases for centuries. Lowered body temperature has been used to combat cancer, infections, trauma, central nervous system diseases and as a regional method to produce anesthesia for amputation. {1,2} Although Bigelow demonstrated in 1950 that tolerance to inflow occlusion in hypothermic animals was longer than in their normothermic counterparts, the first clinical application of hypothermia in cardiac surgery was reported by Lewis and Taufic who used surface cooling to 28°C with 5.5 minutes of inflow occlusion to facilitate successful closure of an atrial septal defect in a 5 year old child.{3,4} Despite the introduction of the pump oxygenator in clinical practice by Gibbon in 1954 it was not until 1958 that hypothermia was used in conjunction with the cardiopulmonary bypass circuit for intracardiac repairs.{5,6} The use of the pump oxygenator and hypothermia has allowed the repair of more and more complex cardiac lesions with remarkably low mortality. A better understanding of the underlying physiologic principles of hypothermia will increase its safe clinical application.