Anesthesia Literature Review

J. Lance Lichtor, M.D., Editor 

Stroke is a common complication of coronary artery bypass graft surgery (CABG). A long-term, prospective, propensity-matched study at a single institution was conducted to assess the prevalence, temporal trends, and longitudinal outcomes of stroke after CABG. Overall, 1.6% of patients experienced stroke after undergoing CABG surgery. The prevalence decreased to 0.62% during the 28-yr period from 1982 to 2009. Stroke occurred more often after CABG (see fig. below). The risk of postoperative stroke peaked at 40 h after surgery and was reduced to a constant hazard of 0.055% per day by day 6. Mortality, prolonged ventilation, renal failure, and length of intensive care unit stay were significantly worse for patients who had a stroke than for those who did not. The risk of death was similar in patients who had strokes but survived for more than 3 months and those who did not experience stroke.

This 28-yr study evaluated adverse neurologic events after CABG at a single institution. Despite an increasing patient risk profile, the overall stroke occurrence declined after 1988. Continued identification of risk factors for intraoperative and postoperative strokes may contribute to additional reductions in stroke.

Methicillin-resistant Staphylococcus aureus  (MRSA) infections contribute significantly to morbidity and mortality after surgery. This study describes a single center's experience implementing an MRSA intervention program. The intervention included screening of personnel; preoperative screening and treatment with mupirocin of all cardiac surgery patients; and treatment with vancomycin prophylaxis for identified carriers. Two of 98 surgical staff members were MRSA carriers and subsequently decolonized. Only 2.2% of patients tested positive for MRSA and were treated. During the 3-yr follow-up after intervention, postoperative MRSA wound infections decreased by 93% (see fig. below).

The authors instituted a quality improvement program designed to eliminate MRSA for patients undergoing cardiac surgery through a median sternotomy. MRSA surgical-site infection rates were reduced by more than 90%. The accompanying editorial discusses the need for additional studies to elucidate which components of the intervention are critical for successful reduction of MRSA.

A definitive study has not been conducted to evaluate the role of increased cardiac enzyme concentrations in the first 24 h after coronary artery bypass graft (CABG) surgery. Therefore, a review of primary data and longitudinal outcomes from 18,908 patients enrolled in seven different studies of CABG was conducted. Higher creatine kinase or troponin concentrations were associated with increasing 30-day and 1-yr mortality after CABG. Creatine kinase was a strong predictor of mortality regardless of baseline risk factors. The 30-day mortality rate for a creatine kinase ratio of 4 or 5 was double that of a creatine kinase ratio of 1.

In this large retrospective study, increased cardiac enzyme concentrations within 24 h after CABG were associated with 30-day and 1-yr mortality. The authors note that in future clinical trials, cardiac enzyme concentrations within the first 24 h after CABG could be used as an early endpoint for therapies that may improve long-term prognoses.

Healthcare-associated infections (HAI) result in severe economic burden to surgical and nonsurgical patients and the healthcare system. A retrospective analysis of a 2004 survey in 100 Swiss acute care hospitals was performed to compare the burden of HAIs in these patients. Surgery was an independent predictor of increased risk of HAI (odds ratio, 2.43). Regardless of hospital size, patients exposed to surgery were significantly more likely to experience HAIs than were those not exposed to surgery (10.6% vs.  4.2%; P < 0.001). Surgical site infections accounted for 5.4% of HAIs. Surgical patients had significantly more extrinsic risk factors for infection than did nonsurgical patients (such as catheters, mechanical ventilation, and intensive care unit stay).

The authors assessed the overall burden of HAI in a large nationwide patient population. The overall HAI burden was 2-fold greater in patients exposed to surgery than in patients with HAIs who did not undergo surgery.

The Pneumonectomy Project is the first descriptive longitudinal study of changes in cardiorespiratory function in patients who underwent pneumonectomy for lung cancer. Nineteen percent (117 of 523) of patients remained eligible for follow-up at the end of the 5-yr study. Survivors generally were younger and more likely to have advanced tumors but had preoperative cardiorespiratory function similar to that of nonsurvivors. Most patients had no, mild, or moderate dyspnea (see fig. below). Dyspnea severity was associated with age but not time since surgery, postoperative lung function (forced expiratory volume), or pulmonary artery pressure. There was a wide range of values for forced expiratory volume and forced vital capacity among patients. However, overall reductions of predicted values in forced expiratory volume and forced vital capacity were 30% and 14%, respectively. Thirty-six percent of patients had pulmonary hypertension, mostly mild to moderate in severity.

Previous studies of lung function after pneumonectomy have included patients with benign disease such as tuberculosis and had few patients or a follow-up that was limited. In this study, 117 patients who underwent pneumonectomy for lung cancer and survived to 5 yr were evaluated. Pulmonary hypertension was not associated with significant changes in lung function or exercise capacity. This study demonstrates the potential survival benefits of patients after pneumonectomy.

Jean Mantz, M.D., Ph.D., Editor 

The rate of cardiac arrests characterized by initial ventricular fibrillation or pulseless ventricular tachycardia has decreased by nearly 50% in the past 30 yr. To determine the role of public access automated external defibrillators (AEDs) in this reduction, a prospective, multicenter, population-based cohort study was conducted. Cardiac arrests were more likely to occur in public than in the home (P < 0.001) and were more likely to be associated with bystander-applied AED and improved survival to hospital discharge (see table above). The improvements occurred regardless of whether or not emergency medical services personnel witnessed the arrest or the AED was administered.

This study indicates that the proportion of cardiac arrests with initial ventricular fibrillation or pulseless ventricular tachycardia is much greater in public settings than at home. The survival rate at hospital discharge was threefold greater in patients resuscitated in public. These results support the utility of AED located in public places when correctly and promptly used by bystanders and also suggest further improving the public's knowledge on use of AED rather than wide deployment of these devices at home.

Overall survival rates for out-of-hospital cardiac arrests are as low as 5%. Augmentation of negative intrathoracic pressure during cardiopulmonary resuscitation (CPR) may provide additional survival benefit in these patients compared with standard CPR. A randomized, multicenter trial was conducted to compare standard CPR and augmented CPR (“intervention”) performed by emergency medical personal in patients experiencing out-of-hospital cardiac arrest. Patients who received the augmented CPR had improved survival rates (see fig. below) with equivalent secondary outcomes, such as cognitive skills and disability at hospital discharge. Although edema was more prevalent in the intervention group, the overall adverse event rate was similar between groups.

Overall compression-decompression CPR resulted in improved survival compared with standard CPR after out-of-hospital cardiac arrest. These results support that compression-decompression CPR should be considered a potentially promising alternative to standard CPR in out-of-hospital cardiac arrest.

Patients with traumatic brain injury are at high risk for development of venous thromboembolism (VTE) and other thrombotic complications, but the risk may be reduced through the use of pharmacologic thromboprophylaxis (PTP). A two-center retrospective cohort study was conducted to assess the optimal timing of PTP administration in patients with traumatic brain injury. Approximately 53% (255 of 480) of patients received PTP during their hospital stay, and these patients were generally younger and more severely injured. VTE occurred in 15 patients overall, and the overall mortality rate was 4.18%.

Neither the administration of PTP (OR = 0.36) nor timing of administration (OR = 0.19) altered the risk of VTE administration. Furthermore, mortality and hemorrhage progression did not differ in patients who received PTP compared with those who did not. However, PTP administration was interrupted in 67 patients and was associated with an increased risk of VTE (see fig. below).

Pharmacologic thromboprophylaxis is frequently interrupted in traumatic brain injury patients, and this study clearly identifies interruption of PTP as a risk factor associated with VTE. As a retrospective cohort study, these results have limitations; however, they suggest the importance of continuous thromboprophylaxis in patients with traumatic brain injury.

Despite the demonstrated advantages of quality improvement interventions in academic centers, the rate of implementation of such interventions at community hospitals is low because of limited financial and personnel resources. A cluster-randomized pragmatic trial was conducted to test the rate of adoption of six evidence-based care practices at 15 community intensive care units (ICUs) in Canada. Overall, patients in targeted care practices were more likely to receive an active intervention than were those in control ICUs (odds ratio = 2.79; P = 0.05). The odds ratios favored intervention for semirecumbent positioning (to prevent ventilator-associated pneumonia) and prevention of catheter-related bloodstream infection. Rates of adherence for semirecumbent positioning increased to approximately 90% in intervention and control ICUs after 4 months of intervention, and remained high (96%) for as long as 3 additional months in intervention ICUs.

For improved quality of care, this study highlights the impact of programs shared concomitantly by several ICUs versus  programs initiated in individual ICUs. The shared program noted an increase in the observance of the procedures for prevention of ventilation-acquired pneumonias and bloodstream catheter-related infections. Although the impact of this intervention on mortality was not the primary goal of the study, considerations for programs using ICU networks for improving quality of care are highlighted.

Timothy J. Brennan, Ph.D., M.D., Editor 

Routine spinal imaging of patients with low back pain is commonly reported by 40% of family practice physicians and 13% of internal medicine physicians; in addition, as many as 62% of physicians report conducting imaging for patients with low back pain and sciatica. However, routine imaging has not been shown to improve clinical outcomes. This article reviews the American College of Physicians/American Pain Society guidelines to promote a rational and cost-conscious diagnostic approach to spinal imaging.

Summaries of six randomized trials revealed routine lumbar magnetic resonance imaging or computed tomography did not provide any benefit over usual care without imaging in terms of pain, function, quality of life, or overall patient-rated improvement. The American College of Physicians/American Pain Society guidelines recommend a thorough history and physical examination to identify patients with low back pain in need of lumbar imaging (the guidelines are briefly summarized in the table on the next page).

This article reviews criteria for patients in whom diagnostic spine imaging is indicated. Imaging is immediately indicated for patients with major risk factors for cancer, spinal infection, acute neurologic deficit, or severe progressive neurologic deficit. Imaging does not need to be completed immediately in patients with minor risk factors for these diseases. Imaging patients without these indications does not improve outcomes.

The incidence of vertebral compression fractures may be as high as 24% for patients with specific cancers. Balloon kyphoplasty is a minimally invasive technique used in conjunction with injection of viscous cement to restore lost bone. The Cancer Patient Fracture Evaluation (CAFE) study is the first randomized multicenter trial to compare the safety and efficacy of kyphoplasty (n = 70) with standard nonsurgical management (n = 65) in patients with cancer who have vertebral compression fractures. At 1-month follow-up, patients in the kyphoplasty group had significant (P < 0.0001) reductions in Roland-Morris disability scores and Kamofksy performance scores, whereas the control group remained unchanged. Kyphoplasty also significantly (P < 0.0001) improved quality of life measured by the short form (SF-36) survey. Patients in the kyphoplasty group also had significantly (P < 0.0001) fewer reduced activity and bed rest days at the 1-month follow-up compared with baseline. Patients in the kyphoplasty group also had significantly reduced pain scores, and fewer of them were using analgesics. The rate and type of adverse events were similar between the groups.

There has been increased interest in vertebral augmentation techniques to treat vertebral compression fractures in patients with cancer and noncancer patients. The accompanying editorial notes the limitations of a study that enrolls patients as indicated by the treating physician rather than strict inclusion criteria. The lack of a placebo controlled group is noted as a limitation. Nevertheless, this study demonstrated reduced disability 1 month after the augmentation treatment in patients with cancer.

In an attempt to identify novel targets for analgesics, a whole-genome screen was conducted in Drosophila  fruit flies and supported by knockout mice studies and single-nucleotide polymorphism analysis in human volunteers. This multispecies study identified genes that may play a role in nociceptive behaviors, many of which had no known function. The family of α2δ genes was implicated in heat nociception in flies. Mice with mutations in the α2δ3 gene, a mammalian calcium channel subunit, exhibited diminished pain responses.

Analysis of 189 healthy volunteers subjected to a battery of pain sensitivity tests revealed a minor allele of α2δ3, single-nucleotide polymorphism rs6777055, was significantly associated with reduced thermal pain sensitivity. In addition, this single-nucleotide polymorphism was associated with reduced pain in a previous prospective study of surgical discectomy patients for persistent lumbar root pain.

This large group of investigators identified pain-related genes in fruit flies. Deletion of one of these pain-related genes, the α2δ3 calcium channel in mice, decreased pain sensitivity. Genetic variations in this channel were associated with less chronic pain after spine surgery in patients. The authors suggests that the α2δ3 calcium channel may be a target for new analgesic drugs.