Lessons from aviation - the role of checklists in minimally invasive cardiac surgery

We describe an adverse event during minimally invasive cardiac surgery that resulted in a multi-disciplinary review of intra-operative errors and the creation of a procedural checklist. This checklist aims to prevent errors of omission and communication failures that result in increased morbidity and mortality. We discuss the application of the aviation - led “threats and errors model” to medical practice and the role of checklists and other strategies aimed at reducing medical errors.

Development of our TAVI protocol for emergency initiation of cardiopulmonary bypass

All transcatheter aortic valve implantation (TAVI) cases are done in our hybrid operating room with a multidisciplinary team and a primed cardiopulmonary bypass (CPB) circuit on pump stand-by. We decided that we would resuscitate all patients undergoing a TAVI procedure via a transfemoral, transapical or transaortic approach, if required. Perfusion plays an essential role in providing rescue CPB for patient salvage when catastrophic complications occur. To coordinate the multidisciplinary effort, we have developed a written safety checklist that assigns a pre-determined role for team members for the rapid sequence initiation of CPB. Although many TAVI patients are not candidates for conventional aortic valve replacements, we feel strongly that rescue CPB should be offered to all TAVI patients to allow the correction of potentially reversible complications. This protocol is included in every surgical "Time Out" involving a TAVI procedure (Figure 1). The protocol has led to rapid and safe CPB initiation in less than five minutes of cardiac arrest. It has also led to a coordinated and consistent team, with pre-specified roles and improved communication. We discuss a case series of four TAVI patients who required emergent use of CPB. The first few cases did not have a written protocol. The experience from these cases led to the development of our protocol. We identified a lack of coordination, wasted movements, unnecessary delayed resuscitation and overall chaos, each of which was targeted for correction with the protocol. We will discuss the merits of the protocol in two recent TAVI cases which required emergent CPB.

Hepatitis E virus in Scottish blood donors

BACKGROUND AND OBJECTIVES

Published prevalence figures for hepatitis E virus (HEV) reveal significant regional differences. Several studies have reported virus transmission via blood transfusion. The aim of this study was to establish HEV seroprevalence and investigate a potential HEV RNA presence in Scottish blood donors.

MATERIALS AND METHODS

IgG and IgM were determined in individual serum samples. HEV RNA was investigated in plasma mini-pools corresponding to 43 560 individual donations using nested PCR. Samples amenable to reamplification with primers from a different region were considered confirmed positives, sequenced and analysed.

RESULTS

A total of 73 of 1559 tested individual sera (4·7%) were IgG positive, none tested positive for IgM. Plasma mini-pool testing revealed an HEV RNA frequency of 1 in 14 520 donations. Three confirmed positives belonged, as expected to genotype 3.

CONCLUSIONS

HEV IgG and RNA figures in Scottish blood donors are lower than those published for the rest of the UK, but sufficiently high to prompt further studies on potential transmission rates and effects of HEV infection, especially for immunosuppressed individuals.

Clinical and biochemical outcomes for additive mesenteric and lower body perfusion during hypothermic circulatory arrest for complex total aortic arch replacement surgery

Surgical repair of transverse aortic arch aneurysms frequently employ hypothermia and antegrade cerebral perfusion as protective strategies during circulatory arrest. However, prolonged mesenteric and lower limb ischemia can lead to significant lactic acidosis and end organ dysfunction, which remains a significant cause of post-operative morbidity and mortality. We report our experience with additive warm mesenteric and lower body perfusion (1-3 L/min, 30°C) in addition to continuous cerebral and myocardial perfusion in 5 patients who underwent total aortic arch replacement with trifurcated head vessel re-implantation and distal elephant trunk reconstruction. Concomitant surgical procedures included re-operations (2), aortic root operations (2), coronary artery bypass (2) and descending thoracic aortic replacement (1). Serum lactate levels demonstrated a rapid decline from a peak 9.9±2.6 post circulatory arrest to 3.4±2.0 in the intensive care unit (ICU). The lowest serum bicarbonate levels were 19.3±3.5 mmol/L, intra-operatively, which normalized to 28.4±2.4 mmol/L on return to the ICU. The lowest pH levels were 7.25±0.10, corrected to 7.43±0.04 on return to the ICU. Mean cardiopulmonary bypass and aortic cross-clamp times were 361±104 and 253±85 minutes, respectively. Mean cerebral and lower body circulatory arrest times were 0 (0) and 50±35 minutes, respectively. The mean time required for systemic rewarming was 95±66 minutes. There were no in-hospital mortalities and no patient experienced any neurological, mesenteric, renal or lower limb ischemic complications. Two patients required mechanical ventilation >24 hours, and one patient returned for reoperation for bleeding. Median intensive care unit and total hospital lengths of stay were 5 and 16 days, respectively. Our results suggest early serum lactate clearance, normalization of acidosis, and metabolic recovery when utilizing a simultaneous cerebral perfusion and warm body protection strategy for complex aortic arch surgery. This additive perfusion strategy may attenuate visceral and lower body ischemia that normally develops during periods of deep hypothermic circulatory arrest.

Prevalence and genetic heterogeneity of SEN virus genotypes D and H in blood donors from Central and Western Europe and West Africa

OBJECTIVES

To establish prevalence and phylogenetic relationship of SEN virus (SENV) D and H in blood donors from Scotland, Czech Republic and Ghana.

AIM

To compare the data between three regions with differing prevalence of blood-borne viruses.

BACKGROUND

Anelloviruses are a ubiquitous group of viruses without a clear disease association. Although there is little evidence that they are pathogenic per se, they may have the ability to modify ongoing disease processes. They have a high degree of heterogeneity both within populations and across geographic regions.

MATERIALS AND METHODS

Three sets of donor samples were analysed by nested polymerase chain reaction (PCR) and hybridisation. A proportion of amplified samples were sequenced and phylogenetic analysis was carried out.

RESULTS

The prevalence figures (including mixed D + H infection) were established for SENV D: 1·0, 8·4 and 25·2% and H: 12·5, 34·8 and 61·0% in Scottish, Czech and Ghanaian blood donors, respectively. The compilation of prevalence figures indicates the changing ratio of SENV D/H in west-east direction, most obvious between Western Europe (D/H < 1) and far East Asia (D/H > 1). Phylogenetic analysis grouped the samples mostly in accordance with geographic origin, despite the variability of short sequence analysed. The previously indicated link between SENV prevalence and age was statistically significant in this study, only for SENV H in Czech samples.

CONCLUSION

SENV D and H appear to reflect the incidence of other blood-borne viruses in these locations. SENV H prevalence of 45·4% in Ghana represents the highest single-SENV-genotype prevalence described in blood donors to date.

What is optimal flow using a mini-bypass system?

The purpose of this study is to determine the appropriate arterial pump flow /cardiac index (CI) utilizing a mini-bypass system. The unique feature of most mini-bypass systems is that the centrifugal pump combines the function of kinetic venous drainage with arterial pump flow. Therefore, if drainage is reduced, arterial pump flow is also reduced. Managing this system can present challenges to the clinical perfusionist. We reviewed fifteen cases, using the Medtronic Resting Heart System (RHS). This retrospective study examined the arterial pump flow, measured as cardiac index (CI), mean arterial pressure, inlet venous saturation, urine output, vasopressor use, and lactate production during routine cardiac surgery. The mean cardiac index for all patients was 1.90 +/- 0.14, range 1.63-2.08 L/min/m(2). The mean hemoglobin on cardiopulmonary bypass (CPB) was 10.6 +/- 1.2, with a range of 9.2-13.3 g/dL. The lactate produced on CPB was 2.03 +/-0.67 with a range of 1.5-3.5 mmol/L. The mean change in lactate measured from pre CPB to post CPB was 0.85 +/- 0.71 with a median lactate of 0.6 mmol/L. The venous saturation was 65.53 +/- 6.03% with a median of 65% and a range of 57-82%. The mean arterial pressure was 67.04 +/- 10.45 mmHg with a median of 62.5 mmHg. The median urine output was 125 mls. The vasopressor median was 2200 microg. All patients were maintained on CPB with a mean nasopharyngeal temperature of 35.43 degrees Celsius. Despite using lower than predicted flows, it would appear that adequate perfusion is provided. The higher hemoglobin content achieved through reduced hemodilution and reduced inflammation appears to enable this system to deliver adequate flow and perfusion at reduced cardiac indices. This research provides evidence which challenges longstanding beliefs that a cardiac index of 2.4 L/min/m(2) is required for all cases.

The use of a mini bypass circuit for minimally invasive mitral valve surgery

Introduction: The purpose of the study is to clinically evaluate minimally invasive mitral valve surgeries (MIMVS) using a mini bypass circuit. The challenge to perfusion is to keep pace with MIMVS, with demonstrated improvements in perfusion-related technologies.

Methods: From October 28, 2005 to September 10, 2008, we retrospectively evaluated thirty-four elective cases which used the mini-circuit (Medtronic Resting Heart System®), with respect to safety, efficacy, cannulation technique, blood usage, resultant hemoglobin, length of ICU and hospital stay, and complications.

Conclusion: The Medtronic Resting Heart System® alleviates many factors, such as high shear stress, turbulence, air to blood interface and decreased oncotic pressure caused by hemodilution, providing more efficient perfusion to our MIMVS patients. We demonstrate, with minor circuit modifications and attention to venous air issues, that this mini-circuit can be used safely and effectively, while being associated with improvements in patient outcomes.

Detection of HCV and HIV-1 antibody negative infections in Scottish and Northern Ireland blood donations by nucleic acid amplification testing

BACKGROUND AND OBJECTIVES

To reduce the risk of transfusion-transmissible viruses entering the blood supply, the nucleic acid amplification testing (NAT) was implemented to screen Scottish and Northern Irish blood donations in minipools. After 5 years of NAT for hepatitis C virus (HCV) and 2 years for human immunodeficiency virus-1 (HIV-1), the yield of serologically negative, nucleic acid positive 'window donations' and cost-benefit of NAT is under review.

MATERIALS AND METHODS

When the Scottish National Blood Transfusion Service (SNBTS) implemented NAT in 1999, a fully automated 'black box' system was not available. Therefore, an 'in-house' assimilated NAT assay was developed, validated and implemented. The system is flexible and allows testing for additional viral markers to be introduced with relative ease.

RESULTS

The HCV and HIV NAT assays have 95% detection levels of 7.25 IU/ml and 39.8 IU/ml, respectively, as determined by probit analysis. One HCV (1 in 1.9 million) and one HIV (1 in 0.77 million) window donation have been detected in 5 and 2 years, respectively, of NAT.

CONCLUSION

The SNBTS NAT assays are robust and have performed consistently over the last 5 years. The design of the in-house system allowed HIV NAT to be added in 2003 at a relatively small additional cost per sample, although for both assays, the royalty fee far exceeds the cost of the test itself. Clearly NAT has a benefit in improving the safety of the blood supply although the risks of transfusion-transmitted viral infections, as reported in the Serious Hazards of Transfusion (SHOT) report, are extremely low. Also, in UK the yield of HCV antibody negative, NAT positive donations is far lower than predicted although the early detection of an HIV window period donation and the increase of HIV in the blood donor and general populations may provide a stronger case for HIV NAT. SUMMARY SENTENCE: The yield of HCV and HIV NAT in UK is significantly less than that anticipated from statistical models.

Acute hepatitis C virus seroconversion in a Scottish blood donor: HCV antigen is not comparable with HCV nucleic acid amplification technology screening

BACKGROUND AND OBJECTIVES

This study was conducted to analyse the usefulness of hepatitis C virus (HCV) core antigen tests for the confirmation of HCV infection in a donor presenting as nucleic acid amplification technology (NAT) positive but negative for antibodies to HCV (anti-HCV).

MATERIALS AND METHODS

Blood donations were screened, in parallel, for anti-HCV using the Abbott PRISM HCV Chemiluminescent immunoassay (ChLIA) and an 'in-house' HCV NAT (pools of up to 95 donations). An HCV NAT-positive antibody-negative donor was identified. Twelve follow-up samples were obtained and tested with various HCV antigen (including the recently marketed Trak-C second-generation assay) and HCV antibody assays.

RESULTS

The single HCV NAT-positive, antibody-negative donation was identified from 1 117 681 donations screened in the 4-year period, July 1999 to June 2003. The index donation was positive by Ortho HCV core antigen enzyme immunoassay (EIA) and Ortho Trak-C (second-generation HCV core antigen EIA). An archive sample, taken 127 days prior to the index donation, was negative for all HCV markers. Subsequent samples demonstrated a loss of reactivity in the Ortho HCV core antigen EIA and reduced activity in the Ortho Trak-C until day 69. Immunoblot (Ortho RIBA-3) and HCV PRISM became positive on day 62, whilst Ortho HCV ELISA was not positive until day 132 or Biorad HCV ELISA until day 160. An alternative immunoblot (Innogenetics Innolia III) was positive from day 55. RNA levels fluctuated considerably during the follow-up period, being completely undetectable by routine screening methods at the time-point around seroconversion; subsequently, antibody was detected using all assays investigated.

CONCLUSIONS

This HCV-converting blood donor provided a unique panel of samples for using to assess current (and future) HCV assay systems. The overall test results led to the conclusion that individual HCV antigen testing should not be considered as equivalent to HCV NAT minipool screening. Trak-C antigen testing may be considered as a suitable confirmatory assay for isolated HCV NAT reactivity.

Development of multiplexed nucleic acid testing for human immunodeficiency virus type 1 and hepatitis C virus

BACKGROUND AND OBJECTIVES

In most Western countries, blood donations are routinely screened for hepatitis C virus (HCV) RNA by polymerase chain reaction (PCR) or other nucleic acid tests. We describe the development of a multiplexed assay for human immunodeficiency virus type 1 (HIV-1) and HCV in an internally controlled PCR suitable for large-scale blood donor screening.

MATERIALS AND METHODS

The HIV/HCV multiplexed PCR used primers from highly conserved regions in the long terminal repeat region. The National Institute for Biological Standards and Controls (NIBSC) International HIV-1 RNA standard, run control and HIV-1 subtype panel were used for assay evaluation.

RESULTS

The HIV-1 PCR showed a sensitivity of 24 IU/ml for HIV-1 RNA (a dilution where 95% of replicate reactions were positive), which was at least five times more sensitive than the Roche Monitor version 1.5 (using the ultrasensitive extraction protocol) and Organon NASBA assays. The assay was capable of detecting all subtypes of HIV-1 (A to H), as well as the more divergent group N and O variants. The sensitivity of the PCR was unaffected by multiplexing with HCV primers and by the presence of a bovine viral diarrhoea virus (BVDV) internal control.

CONCLUSION

We have developed a highly sensitive multiplexed PCR for HIV-1 and HCV RNA screening that can be introduced into current PCR-based blood donor screening at minimal cost and without significant operational changes.

Use of bovine viral diarrhoea virus as an internal control for amplification of hepatitis C virus

BACKGROUND AND OBJECTIVES

Screening for hepatitis C virus (HCV) by polymerase chain reaction (PCR) will be mandatory for screening blood and plasma donors in Europe and elsewhere. This study describes an internally controlled, highly sensitive PCR method designed for screening blood donations in pools.

MATERIAL AND METHODS

RNA extracted from bovine viral diarrhoea virus (BVDV) was used as an internal control to monitor the efficiency of extraction, reverse transcription and amplification steps in HCV PCR.

RESULTS

Sensitivity of PCR for single molecules of HCV in the presence of 33 genome equivalents of BVDV RNA was achieved by reducing the efficiency of BVDV amplification. BVDV could be recovered at high efficiency from large volume pools (2-5 ml) by ultracentrifugation and by the NucliSens extraction method.

CONCLUSION

Detection of BVDV validates the extraction, reverse transcription and amplification methods used for HCV detection in plasma pools and provides valuable quality assurance for negative results.

Independent evolution of the env and pol genes of HIV-1 during zidovudine therapy

OBJECTIVE

To determine the effect that selection for antiviral resistance in the HIV-1 pol gene has on the level of variation and pattern of evolution in the V3 region of env.

DESIGN

Proviral genomes obtained from two patients before, during and after the termination of zidovudine (ZDV) therapy (approximately 2 years) were amplified and sequenced in pol and env, and the evolution of the V3 hypervariable region compared with that of the reverse transcriptase domain of pol.

METHODS

Gene fragments were polymerase chain reaction-amplified from patients' peripheral blood mononuclear cells. Nucleotide sequencing was carried out using T7 DNA polymerase and dye-labelled terminators on an automated DNA sequencer. Sequences were analysed using maximum likelihood phylogenetic techniques.

RESULTS

Both patients showed multiple resistance-associated mutations after 1 year of ZDV therapy. Sequence diversity in V3 showed no reduction during the period of treatment. Substantial change continued to occur in this region and multiple lineages were present in both patients, in contrast to the single lineage observed in the pol gene of one (patient 74), a difference confirmed by likelihood ratio tests.

CONCLUSIONS

There is no evidence from this study that selection due to antivirals has any significant impact on the evolution of the env gene. The independence in the evolution of these genes implies that recombination was occurring between the two genes during the study period. Such independent evolution should be allowed for in developing strategies for HIV therapy involving multiple target genes.

Evolution of zidovudine resistance-associated genotypes in human immunodeficiency virus type 1-infected patients

Substantial differences have been described in the response of individual patients to zidovudine (ZDV) therapy, both in the clinical impact and in virus load. Genotypic changes associated with the appearance of drug resistance may also be different or occur at different rates. We have obtained the nucleotide sequence of the RT domain of individual HIV-1 genomes extracted from 10 plasma and peripheral blood mononuclear cell (PBMC) samples donated by two haemophiliac patients before, during, and after long-term ZDV therapy. Although the plasma virus load was similar throughout, the order and timing of appearance of resistance-associated substitutions differed in the two patients. In patient p74, K70R appeared after 4 months, T215Y at 5.5 months, and M41L at 13 months. In p87, K70R also appeared at 4 months, but T215Y and K219Q were not observed until 18 months and M41L not at all. Much greater sequence change overall occurred in p74. The evolution of the viral population in that patient was dominated by the unique appearance of T215Y and subsequently M41L, with all sequences from the last time point being descended by a single path from the pretreatment samples. However, in p87, several different lineages of RT sequences were found to persist throughout treatment. We propose that these differences in outcome may be determined by differences in genetic background at sites other than the five generally considered to be associated with ZDV sensitivity.

The molecular epidemiology of human immunodeficiency virus type 1 in Edinburgh

Human immunodeficiency virus (HIV) type 1 sequences obtained from HIV-infected persons in different risk groups in Edinburgh were studied to determine the number and origin of virus variants and patterns of virus transmission. Phylogenetic analysis revealed that 12 of 14 hemophiliac patients who had been exposed to a single common batch of factor VIII had closely related gag gene sequences. Sequences from intravenous drug users and patients infected through heterosexual contact formed another distinct group, and 2 other hemophiliacs formed a third group. However, epidemiologic relationships inferred from analysis of the V3 region of the env gene were less conclusive, especially when the V3 loop was taken in isolation. This appears to be due to the length of time since infection and the action of selection, which has favored the independent appearance of similar V3 loop variants.

Selection for specific sequences in the external envelope protein of human immunodeficiency virus type 1 upon primary infection

Viral RNA was extracted from plasma samples collected from five individuals during the period of viremia before seroconversion in primary infection with human immunodeficiency virus type 1 (HIV-1) and amplified by polymerase chain reaction. Nucleotide sequence analysis of amplified DNA from the V3 and V4 hypervariable regions indicated that the initial virus population of each acutely infected individual was completely homogeneous in sequence. No intrasample variability was found among the 44,090 nucleotides sequenced in this region of env, contrasting with the high degree of variability normally found in seropositive individuals. Paradoxically, substantial sequence variability was found in the normally high conserved gag gene (encoding p17) in most of the preseroconversion samples. The diversity of p17 sequences in samples that were homogeneous in V3 and V4 can most readily be explained by the existence of strong selection for specific env sequences either upon transmission or in the interval between exposure and seroconversion in the exposed individual. Evidence that localizes the selected region upon transmission to V3 is provided by the similarity or identity of V3 loop sequences in five individuals with epidemiologically unrelated HIV-1 infections, while regions flanking the V3 loop and the V4 hypervariable region were highly divergent. The actual V3 sequences were similar to those associated with macrophage tropism in primary isolates of HIV, irrespective of whether infection was acquired by sexual contact or parenterally through transfusion of contaminated factor VIII. Proviral DNA sequences in peripheral blood mononuclear cells remained homogeneous in the V3 and V4 regions (and variable in p17gag) for several months after seroconversion. The persistence of HIV sequences in peripheral blood mononuclear cells identical to those found at primary infection in the absence of continued virus expression provides an explanation for the previously observed differences in the composition of circulating DNA and RNA populations in sequential samples from seropositive individuals.

Neuromuscular blockade significantly decreases systemic oxygen consumption during hypothermic cardiopulmonary bypass

The design limits of cardiopulmonary bypass (CPB) equipment and the performance characteristics of membrane oxygenators may place the patient with a very large body surface area at risk for incurring an oxygen debt during CPB. The influence of resting muscle tone on systemic oxygen consumption (VO2) during hypothermic (25 to 28 degrees C) nonpulsatile CPB was calculated using the Fick equation prior to, and following, neuromuscular blockade (pancuronium, 0.15 mg/kg, n = 10; or succinylcholine, 1.5 mg/kg, n = 7). During hypothermic CPB, initial VO2 was 70 +/- 30 mL/min/m2, which was significantly reduced (by 30%) to 49 +/- 13 mL/min/m2 after onset of neuromuscular blockade, with a concomitant increase in mixed venous O2 saturation from 73% +/- 18% to 83% +/- 14%. Choice of muscle relaxant did not influence the change in VO2. With succinylcholine there was a return of VO2 to control values with recovery of neuromuscular function. This study demonstrates that in the unconscious and unmoving patient during hypothermic CPB, administration of muscle relaxants to achieve complete neuromuscular blockade can significantly reduce systemic oxygen consumption.