Comparison of differences in cohort (forwards) and case control (backwards) methodological approaches for validation of the Hypotension Prediction Index.

BACKGROUND: The Hypotension Prediction Index (the index) software is a machine learning algorithm that detects physiological changes that may lead to hypotension. The original validation used a case control (backwards) analysis that has been suggested to be biased. We therefore conducted a cohort (forwards) analysis and compared this to the original validation technique. METHODS: We conducted a retrospective analysis of data from previously reported studies. All data were analysed identically with 2 different methodologies and receiver operating characteristic curves (ROC) constructed. Both backwards and forwards analyses were performed to examine differences in area under the ROC for HPI and other haemodynamic variables to predict a MAP < 65mmHg for at least 1 minute 5, 10 and 15 minutes in advance. RESULTS: Two thousand and twenty-two patients were included in the analysis, yielding 4,152,124 measurements taken at 20 second intervals. The area-under-the-curve for the index predicting hypotension analysed by backward and forward methodologies respectively was 0.957 (95% CI, 0.947-0.964) vs 0.923 (95% CI, 0.912-0.933) 5 minutes in advance, 0.933 (95% CI, 0.924-0.942) vs 0.923 (95% CI, 0.911-0.933) 10 minutes in advance , and 0.929 (95% CI, 0.918-0.938) vs. 0.926 (95% CI, 0.914-0.937) 15 minutes in advance. No other variable had an area-under-the-curve > 0.7 except for MAP. Area-under-the-curve using forward analysis for MAP predicting hypotension 5, 10, and 15 minutes in advance was 0.932 (95% CI, 0.920-0.940), 0.929 (95% CI, 0.918-0.938), and 0.932 (95% CI, 0.921-0.940). The R 2 for the variation in the index due to MAP was 0.77. CONCLUSION: Using an updated methodology, we found the utility of the HPI index to predict future hypotensive events is high, with an area under the receiver-operating-characteristics curve similar to that of the original validation method.

Intraoperative hypotension in ambulatory surgery centers.

STUDY OBJECTIVES: To measure the incidence of intraoperative hypotension (IOH) during surgery in ambulatory surgery centers (ASCs) and describe associated characteristics of patients and procedures. DESIGN: Retrospective analysis. SETTING: 20 ASCs. PATIENTS: 16,750 patients having non-emergent, non-cardiac surgery; ASA physical status 2 through 4. INTERVENTIONS: None. MEASUREMENTS: We assessed incidence of IOH using the definition from the Centers for Medicare & Medicaid Services (CMS) Merit-based Incentive Payment System (MIPS)-mean arterial pressure (MAP) < 65 mmHg for at least 15 cumulative minutes-and three secondary definitions: minutes of MAP <65 mmHg, area under MAP of 65 mmHg, and time-weighted average MAP <65 mmHg. MAIN RESULTS: 30.9% of ASC cases had a MAP <65 mmHg for at least 15 min. The incidence of IOH varied significantly, and was higher among younger adults (age 18-39; 36.2%), females (35.2%), and patients with ASA physical status 2 (32.8%). IOH increased with increasing surgery length, even when time-weighted, and was higher among low complexity (30.6%) than moderate complexity (28.8%) procedures, and highest among high complexity procedures (44.1%). CONCLUSIONS: There was substantial occurrence of IOH in ASCs, similar to that described in academic hospital settings in previous literature. We hypothesize that this may reflect clinician preference not to intervene in perceived healthy patients or assumptions about ability to tolerate lower blood pressures on behalf of these patients. Future research will determine whether IOH in ACSs is associated with adverse outcomes to the same extent as described in more complex hospital-based surgeries.

Adult Cardiac Surgery-Associated Acute Kidney Injury: Joint Consensus Report.

OBJECTIVES: Acute kidney injury (AKI) is increasingly recognized as a source of poor patient outcomes after cardiac surgery. The purpose of the present report is to provide perioperative teams with expert recommendations specific to cardiac surgery-associated AKI (CSA-AKI). METHODS: This report and consensus recommendations were developed during a joint, in-person, multidisciplinary conference with the Perioperative Quality Initiative and the Enhanced Recovery After Surgery Cardiac Society. Multinational practitioners with diverse expertise in all aspects of cardiac surgical perioperative care, including clinical backgrounds in anesthesiology, surgery and nursing, met from October 20 to 22, 2021, in Sacramento, California, and used a modified Delphi process and a comprehensive review of evidence to formulate recommendations. The quality of evidence and strength of each recommendation were established using the Grading of Recommendations Assessment, Development, and Evaluation methodology. A majority vote endorsed recommendations. RESULTS: Based on available evidence and group consensus, a total of 13 recommendations were formulated (4 for the preoperative phase, 4 for the intraoperative phase, and 5 for the postoperative phase), and are reported here. CONCLUSIONS: Because there are no reliable or effective treatment options for CSA-AKI, evidence-based practices that highlight prevention and early detection are paramount. Cardiac surgery-associated AKI incidence may be mitigated and postsurgical outcomes improved by focusing additional attention on presurgical kidney health status; implementing a specific cardiopulmonary bypass bundle; using strategies to maintain intravascular euvolemia; leveraging advanced tools such as the electronic medical record, point-of-care ultrasound, and biomarker testing; and using patient-specific, goal-directed therapy to prioritize oxygen delivery and end-organ perfusion over static physiologic metrics.

Incidence of intraoperative hypotension during non-cardiac surgery in community anesthesia practice: a retrospective observational analysis.

BACKGROUND: Intraoperative hypotension (IOH) is well-described in the academic setting but not in community practice. IOH is associated with risk of postoperative morbidity and mortality. This is the first report of IOH in the community setting using the IOH measure definition from the Centers for Medicare and Medicaid Services Merit-based Incentive Payment System program. OBJECTIVES: To describe the incidence of IOH in the community setting; assess variation in IOH by patient-, procedure-, and facility-level characteristics; and describe variation in risk-adjusted IOH across clinicians. METHODS: Design Cross-sectional descriptive analysis of retrospective data from anesthesia records in 2020 and 2021. Setting Forty-five facilities affiliated with two large anesthesia providers in the USA. Participants Patients aged 18 years or older having non-emergent, non-cardiac surgery under general, neuraxial, or regional anesthesia. Cases were excluded based on criteria for the IOH measure: baseline mean arterial pressure (MAP) below 65 mmHg prior to anesthesia induction; American Society of Anesthesiologists (ASA) physical status classification of I, V, or VI; monitored anesthesia care only; deliberate induced hypotension; obstetric non-operative procedures; liver or lung transplant; cataract surgery; non-invasive gastrointestinal cases. Main outcomes IOH, using four definitions. Primary definition: binary assessment of whether the case had MAP < 65 mmHg for 15 min or more. Secondary definitions: total number of minutes of MAP < 65 mmHg, total area under MAP of 65 mmHg, time-weighted average MAP < 65 mmHg. RESULTS: Among 127,095 non-emergent, non-cardiac cases in community anesthesia settings, 29% had MAP < 65 mmHg for at least 15 min cumulatively, with an overall mean of 12.4 min < 65 mmHg. IOH was slightly more common in patients who were younger, female, and ASA II (versus III or IV); in procedures that were longer and had higher anesthesia base units; and in ambulatory surgery centers. Incidence of IOH varied widely across individual clinicians in both unadjusted and risk-adjusted analyses. CONCLUSION: Intraoperative hypotension is common in community anesthesia practice, including among patients and settings typically considered "low risk." Variation in incidence across clinicians remains after risk-adjustment, suggesting that IOH is a modifiable risk worth pursuing in quality improvement initiatives.

Fluid Optimisation in Emergency Laparotomy (FLO-ELA) Trial: study protocol for a multi-centre randomised trial of cardiac output-guided fluid therapy compared to usual care in patients undergoing major emergency gastrointestinal surgery.

INTRODUCTION: Postoperative morbidity and mortality in patients undergoing major emergency gastrointestinal surgery are a major burden on healthcare systems. Optimal management of perioperative intravenous fluids may reduce mortality rates and improve outcomes from surgery. Previous small trials of cardiac-output guided haemodynamic therapy algorithms in patients undergoing gastrointestinal surgery have suggested this intervention results in reduced complications and a modest reduction in mortality. However, this existing evidence is based mainly on elective (planned) surgery, with little evaluation in the emergency setting. There are fundamental clinical and pathophysiological differences between the planned and emergency surgical setting which may influence the effects of this intervention. A large definitive trial in emergency surgery is needed to confirm or refute the potential benefits observed in elective surgery and to inform widespread clinical practice. METHODS: The FLO-ELA trial is a multi-centre, parallel-group, open, randomised controlled trial. 3138 patients aged 50 and over undergoing major emergency gastrointestinal surgery will be randomly allocated in a 1:1 ratio using minimisation to minimally invasive cardiac output monitoring to guide protocolised administration of intra-venous fluid, or usual care without cardiac output monitoring. The trial intervention will be carried out during surgery and for up to 6 h postoperatively. The trial is funded through an efficient design call by the National Institute for Health and Care Research Health Technology Assessment (NIHR HTA) programme and uses existing routinely collected datasets for the majority of data collection. The primary outcome is the number of days alive and out of hospital within 90 days of randomisation. Participants and those delivering the intervention will not be blinded to treatment allocation. Participant recruitment started in September 2017 with a 1-year internal pilot phase and is ongoing at the time of publication. DISCUSSION: This will be the largest contemporary randomised trial examining the effectiveness of perioperative cardiac output-guided haemodynamic therapy in patients undergoing major emergency gastrointestinal surgery. The multi-centre design and broad inclusion criteria support the external validity of the trial. Although the clinical teams delivering the trial interventions will not be blinded, significant trial outcome measures are objective and not subject to detection bias. TRIAL REGISTRATION: ISRCTN 14729158. Registered on 02 May 2017.

Indicators of haemodynamic instability and left ventricular function in a porcine model of esmolol induced negative inotropy.

To investigate if the Hypotension Prediction Index was an early indicator of haemodynamic instability in a negative inotropy porcine model, and to assess the correlation of commonly measured indicators of left ventricular systolic function. Eight anaesthetised pigs were volume resuscitated and then underwent an incremental infusion of esmolol hydrochloride (0-3000 mg/hr), following which it was then reduced in a stepwise manner. Full haemodynamic measurements were taken at each stage and measurements of left ventricular systolic function including left ventricular stroke work index, ejection fraction and peripheral dP/dT were obtained. At an infusion rate of 500 mg/hr of esmolol there were no significant changes in any measured variables. At 1000 mg/hr MAP was on average 11 mmHg lower (95% CI 1 to 11 mmHg, p = 0.027) with a mean of 78 mmHg, HPI increased by 33 units (95% CI 4 to 62, p = 0.026) with a mean value of 63. No other parameters showed significant change from baseline values. Subsequent increases in esmolol showed changes in all parameters except SVV, SVR and PA mean. Correlation between dP/dt and LVSWI was 0.85 (95% CI 0.77 to 0.90, p < 0.001), between LVEF and dP/dt 0.39 (95% CI 0.18 to 0.57, p < 0.001), and between LSWI and LVEF 0.41 (95% CI 0.20 to 0.59, p < 0.001). In this model haemodynamic instability induced by negative inotropy was detected by the HPI algorithm prior to any clinically significant change in commonly measured variables. In addition, the peripheral measure of left ventricular contractility dP/dt correlates well with more established measurements of LV systolic function.

Association of Upper Gastrointestinal Surgery of Great Britain and Ireland (AUGIS)/Perioperative Quality Initiative (POQI) consensus statement on intraoperative and postoperative interventions to reduce pulmonary complications after oesophagectomy.

BACKGROUND: Pulmonary complications are the most common morbidity after oesophagectomy, contributing to mortality and prolonged postoperative recovery, and have a negative impact on health-related quality of life. A variety of single or bundled interventions in the perioperative setting have been developed to reduce the incidence of pulmonary complications. Significant variation in practice exists across the UK. The aim of this modified Delphi consensus was to deliver clear evidence-based consensus recommendations regarding intraoperative and postoperative care that may reduce pulmonary complications after oesophagectomy. METHODS: With input from a multidisciplinary group of 23 experts in the perioperative management of patients undergoing surgery for oesophageal cancer, a modified Delphi method was employed. Following an initial systematic review of relevant literature, a range of anaesthetic, surgical, and postoperative care interventions were identified. These were then discussed during a two-part virtual conference. Recommendation statements were drafted, refined, and agreed by all attendees. The level of evidence supporting each statement was considered. RESULTS: Consensus was reached on 12 statements on topics including operative approach, pyloric drainage strategies, intraoperative fluid and ventilation strategies, perioperative analgesia, postoperative feeding plans, and physiotherapy interventions. Seven additional questions concerning the perioperative management of patients undergoing oesophagectomy were highlighted to guide future research. CONCLUSION: Clear consensus recommendations regarding intraoperative and postoperative interventions that may reduce pulmonary complications after oesophagectomy are presented.

Delivery of drinking, eating and mobilising (DrEaMing) and its association with length of hospital stay after major noncardiac surgery: observational cohort study.

BACKGROUND: Enhanced recovery pathways are associated with improved postoperative outcomes. However, as enhanced recovery pathways have become more complex and varied, compliance has reduced. The 'DrEaMing' bundle re-prioritises early postoperative delivery of drinking, eating, and mobilising. We investigated relationships between DrEaMing compliance, postoperative hospital length of stay (LOS), and complications in a prospective multicentre major surgical cohort. METHODS: We interrogated the UK Perioperative Quality Improvement Programme dataset. Analyses were conducted in four stages. In an exploratory cohort, we identified independent predictors of DrEaMing. We quantified the association between delivery of DrEaMing (and its component variables) and prolonged LOS in a homogenous colorectal subgroup and assessed generalisability in multispecialty patients. Finally, LOS and complications were compared across hospitals, stratified by DrEaMing compliance. RESULTS: The exploratory cohort comprised 22 218 records, the colorectal subgroup 7230, and the multispecialty subgroup 5713. DrEaMing compliance was 59% (13 112 patients), 60% (4341 patients), and 60% (3421), respectively, but varied substantially between hospitals. Delivery of DrEaMing predicted reduced odds of prolonged LOS in colorectal (odds ratio 0.51 [0.43-0.59], P<0.001) and multispecialty cohorts (odds ratio 0.47 [0.41-0.53], P<0.001). At the hospital level, complications were not the primary determinant of LOS after colorectal surgery, but consistent delivery of DrEaMing was associated with significantly shorter LOS. CONCLUSIONS: Delivery of bundled and unbundled DrEaMing was associated with substantial reductions in postoperative LOS, independent of the effects of confounder variables. Consistency of process delivery, and not complications, predicted shorter hospital-level length of stay. DrEaMing may be adopted by perioperative health systems as a quality metric to support improved patient outcomes and reduced hospital length of stay.

Dietary Nitrate Supplementation Does Not Alter Exercise Efficiency at High Altitude - Further Results From the Xtreme Alps Study.

Introduction: Nitrate supplementation in the form of beetroot juice (BRJ) ingestion has been shown to improve exercise tolerance during acute hypoxia, but its effect on exercise physiology remains unstudied during sustained terrestrial high altitude exposure. We hypothesized that performing exercise at high altitude would lower circulating nitrate and nitrite levels and that BRJ ingestion would reverse this phenomenon while concomitantly improving key determinants of aerobic exercise performance. Methods: Twenty seven healthy volunteers (21 male) underwent a series of exercise tests at sea level (SL, London, 75 m) and again after 5-8 days at high altitude (HA, Capanna Regina Margherita or "Margherita Hut," 4,559 m). Using a double-blind protocol, participants were randomized to consume a beetroot/fruit juice beverage (three doses per day) with high levels of nitrate (∼0.18 mmol/kg/day) or a nitrate-depleted placebo (∼11.5 µmoles/kg/day) control drink, from 3 days prior to the exercise trials until completion. Submaximal constant work rate cycle tests were performed to determine exercise efficiency and a maximal incremental ramp exercise test was undertaken to measure aerobic capacity, using breath-by-breath pulmonary gas exchange measurements throughout. Concentrations of nitrate, nitrite and nitrosation products were quantified in plasma samples collected at 5 timepoints during the constant work rate tests. Linear mixed modeling was used to analyze data. Results: At both SL and HA, plasma nitrate concentrations were elevated in the nitrate supplementation group compared to placebo (P < 0.001) but did not change throughout increasing exercise work rate. Delta exercise efficiency was not altered by altitude exposure (P = 0.072) or nitrate supplementation (P = 0.836). V̇O2peak decreased by 24% at high altitude (P < 0.001) and was lower in the nitrate-supplemented group at both sea level and high altitude compared to placebo (P = 0.041). Dietary nitrate supplementation did not alter other peak exercise variables or oxygen consumption at anaerobic threshold. Circulating nitrite and S-nitrosothiol levels unexpectedly rose in a few individuals right after cessation of exercise at high altitude. Conclusion: Whilst regularly consumed during an 8 days expedition to terrestrial high altitude, nitrate supplementation did not alter exercise efficiency and other exercise physiological variables, except decreasing V̇O2peak. These results and those of others question the practical utility of BRJ consumption during prolonged altitude exposure.

Physiological responses during ascent to high altitude and the incidence of acute mountain sickness.

Acute mountain sickness (AMS) occurs when there is failure of acclimatisation to high altitude. The aim of this study was to describe the relationship between physiological variables and the incidence of AMS during ascent to 5300 m. A total of 332 lowland-dwelling volunteers followed an identical ascent profile on staggered treks. Self-reported symptoms of AMS were recorded daily using the Lake Louise score (mild 3-4; moderate-severe ≥5), alongside measurements of physiological variables (heart rate, respiratory rate (RR), peripheral oxygen saturation (SpO2 ) and blood pressure) before and after a standardised Xtreme Everest Step-Test (XEST). The overall occurrence of AMS among participants was 73.5% (23.2% mild, 50.3% moderate-severe). There was no difference in gender, age, previous AMS, weight or body mass index between participants who developed AMS and those who did not. Participants who had not previously ascended >5000 m were more likely to get moderate-to-severe AMS. Participants who suffered moderate-to-severe AMS had a lower resting SpO2 at 3500 m (88.5 vs. 89.6%, p = 0.02), while participants who suffered mild or moderate-to-severe AMS had a lower end-exercise SpO2 at 3500 m (82.2 vs. 83.8%, p = 0.027; 81.5 vs. 83.8%, p < 0.001 respectively). Participants who experienced mild AMS had lower end-exercise RR at 3500 m (19.2 vs. 21.3, p = 0.017). In a multi-variable regression model, only lower end-exercise SpO2 (OR 0.870, p < 0.001) and no previous exposure to altitude >5000 m (OR 2.740, p-value 0.003) predicted the development of moderate-to-severe AMS. The Xtreme Everest Step-Test offers a simple, reproducible field test to help predict AMS, albeit with relatively limited predictive precision.

Hemodynamic and Intestinal Microcirculatory Changes in a Phenylephrine Corrected Porcine Model of Hemorrhage.

BACKGROUND: Intraoperative hypotension is a common event, and a recent study suggests that maintenance of blood pressure may reduce complications. The splanchnic circulation provides a reservoir of blood that can be mobilized during hemorrhage; hence, intestinal microcirculation is sensitive to volume changes. The aim of this study was to assess the impact of hemorrhage on intestinal microcirculation and hemodynamics, and the effects of phenylephrine on these parameters. METHODS: Eight anesthetized, mechanically ventilated Yorkshire/Landrace crossbreed pigs were studied. Graded hemorrhage was performed with the removal of 20% of blood volume in 5% increments. Hemodynamic and intestinal microcirculatory measurements were performed at each stage with side-stream dark field microscopy, following which mean arterial pressure (MAP) was corrected with phenylephrine to baseline values and measurements repeated. A repeated measurement 1-way analysis of variance (ANOVA) was used to compared changes from baseline measurements. RESULTS: The mean baseline microcirculation score was 42 (standard deviation [SD] = 5). A 5% hemorrhage decreased the microcirculation score by a mean difference of 19 (95% confidence interval [CI], 12-27; P < .0001), and an additional 5% hemorrhage further reduced the microcirculation score by a mean difference of 12 (95% CI, 4-19; P = .0001). Subsequent hemorrhage or administration of phenylephrine did not significantly change the microcirculation scores except when phenylephrine was administered at the 15% hemorrhage stage, which increased the microcirculation score by a mean difference of 7 (95% CI, 1-13; P = .003). All hemodynamic variables were returned to baseline values following hemorrhage by the phenylephrine infusion. CONCLUSIONS: Intestinal microcirculatory flow is reduced early in hemorrhage and is uncorrected by phenylephrine infusion. Hemodynamic changes associated with hemorrhage are corrected by phenylephrine and do not reflect microcirculatory flow status.

Association between perioperative fluid management and patient outcomes: a multicentre retrospective study.

BACKGROUND: Postoperative complications increase hospital length of stay and patient mortality. Optimal perioperative fluid management should decrease patient complications. This study examined associations between fluid volume and noncardiac surgery patient outcomes within a large multicentre US surgical cohort. METHODS: Adults undergoing noncardiac procedures from January 1, 2012 to December 31, 2017, with a postoperative length of stay ≥24 h, were extracted from a large US electronic health record database. Patients were segmented into quintiles based on recorded perioperative fluid volumes with Quintile 3 (Q3) serving as the reference. The primary outcome was defined as a composite of any complications during the surgical admission and a postoperative length of stay ≥7 days. Secondary outcomes included in-hospital mortality, respiratory complications, and acute kidney injury. RESULTS: A total of 35 736 patients met the study criteria. There was a U-shaped pattern with highest (Q5) and lowest (Q1) quintiles of fluid volumes having increased odds of complications and a postoperative length of stay ≥7 days (Q5: odds ratio [OR] 1.51 [95% confidence interval {CI}: 1.30-1.74], P<0.001; Q1: OR 1.20 [95% CI: 1.04-1.38], P=0.011) compared with Q3. Patients in Q5 had greater odds of more severe acute kidney injury compared with Q3 (OR 1.52 [95% CI: 1.22-1.90]; P<0.001) and respiratory complications (OR 1.44 [95% CI: 1.17-1.77]; P<0.001). CONCLUSIONS: Both very high and very low perioperative fluid volumes were associated with an increase in complications after noncardiac surgery.

A national survey of anaesthetists' preferences for their own end of life care.

OBJECTIVES: To describe individual views, wishes, and preferences for end of life care and to report UK anaesthetists' personal perspectives. METHODS: The 'bigconversations' questionnaire was developed by modifying an existing framework for end of life discussions. An online cross-sectional survey of UK anaesthetists was then conducted using the questionnaire in January 2019. RESULTS: The bigconversations questionnaire was validated as measuring the important aspects of end of life care by an expert panel and was found to have moderate test-retest reliability. Responses were received from 760/1913 (40%) of those invited to take part. Overall, 698/760 (92%) of respondents wished to be well informed about their condition and prognosis and 518/760 (68%) wanted to be heavily involved in decision-making about their health. Meanwhile, 639/760 (84%) of respondents would choose to forego treatment aimed at prolonging life should that life be of poor quality. The desire to spend time with family was a theme which arose from the qualitative analysis. CONCLUSION: This study provides the first systematic description of UK doctors', specifically anaesthetists', personal preferences for end of life care. Broad trends were identified: to be well informed; to avoid high-intensity medical treatments if terminally unwell; to spend remaining time with family and friends; and to be symptom-free and well cared for. However, a substantial minority expressed different, indeed opposite, opinions. This variation highlights that good quality end of life care must be driven by discussion of an individual's values, wishes, and preferences.

Intravenous fluid therapy in the perioperative and critical care setting: Executive summary of the International Fluid Academy (IFA).

Intravenous fluid administration should be considered as any other pharmacological prescription. There are three main indications: resuscitation, replacement, and maintenance. Moreover, the impact of fluid administration as drug diluent or to preserve catheter patency, i.e., fluid creep, should also be considered. As for antibiotics, intravenous fluid administration should follow the four Ds: drug, dosing, duration, de-escalation. Among crystalloids, balanced solutions limit acid-base alterations and chloride load and should be preferred, as this likely prevents renal dysfunction. Among colloids, albumin, the only available natural colloid, may have beneficial effects. The last decade has seen growing interest in the potential harms related to fluid overloading. In the perioperative setting, appropriate fluid management that maintains adequate organ perfusion while limiting fluid administration should represent the standard of care. Protocols including a restrictive continuous fluid administration alongside bolus administration to achieve hemodynamic targets have been proposed. A similar approach should be considered also for critically ill patients, in whom increased endothelial permeability makes this strategy more relevant. Active de-escalation protocols may be necessary in a later phase. The R.O.S.E. conceptual model (Resuscitation, Optimization, Stabilization, Evacuation) summarizes accurately a dynamic approach to fluid therapy, maximizing benefits and minimizing harms. Even in specific categories of critically ill patients, i.e., with trauma or burns, fluid therapy should be carefully applied, considering the importance of their specific aims; maintaining peripheral oxygen delivery, while avoiding the consequences of fluid overload.

Perioperative Quality Initiative (POQI) consensus statement on fundamental concepts in perioperative fluid management: fluid responsiveness and venous capacitance.

BACKGROUND: Optimal fluid therapy in the perioperative and critical care settings depends on understanding the underlying cardiovascular physiology and individualizing assessment of the dynamic patient state. METHODS: The Perioperative Quality Initiative (POQI-5) consensus conference brought together an international team of multidisciplinary experts to survey and evaluate the literature on the physiology of volume responsiveness and perioperative fluid management. The group used a modified Delphi method to develop consensus statements applicable to the physiologically based management of intravenous fluid therapy in the perioperative setting. DISCUSSION: We discussed the clinical and physiological evidence underlying fluid responsiveness and venous capacitance as relevant factors in fluid management and developed consensus statements with clinical implications for a broad group of clinicians involved in intravenous fluid therapy. Two key concepts emerged as follows: (1) The ultimate goal of fluid therapy and hemodynamic management is to support the conditions that enable normal cellular metabolic function in order to produce optimal patient outcomes, and (2) optimal fluid and hemodynamic management is dependent on an understanding of the relationship between pressure, volume, and flow in a dynamic system which is distensible with variable elastance and capacitance properties.

Effects of dietary nitrate supplementation on microvascular physiology at 4559 m altitude - A randomised controlled trial (Xtreme Alps).

Native highlanders (e.g. Sherpa) demonstrate remarkable hypoxic tolerance, possibly secondary to higher levels of circulating nitric oxide (NO) and increased microcirculatory blood flow. As part of the Xtreme Alps study (a randomised placebo-controlled trial of dietary nitrate supplementation under field conditions of hypobaric hypoxia), we investigated whether dietary supplementation with nitrate could improve NO availability and microvascular blood flow in lowlanders. Plasma measurements of nitrate, nitrite and nitroso species were performed together with measurements of sublingual (sidestream dark-field camera) and forearm blood flow (venous occlusion plethysmography) in 28 healthy adult volunteers resident at 4559 m for 1 week; half receiving a beetroot-based high-nitrate supplement and half receiving an identically-tasting low nitrate 'placebo'. Dietary supplementation increased plasma nitrate concentrations 4-fold compared to the placebo group, both at sea level (SL; 19.2 vs 76.9 µM) and at day 5 (D5) of high altitude (22.9 vs 84.3 µM, p < 0.001). Dietary nitrate supplementation also significantly increased both plasma nitrite (0.78 vs. 0.86 µM SL, 0.31 vs. 0.41 µM D5, p = 0.03) and total nitroso product (11.3 vs. 19.7 nM SL, 9.7 vs. 12.3 nM D5, p < 0.001) levels both at sea level and at 4559 m. However, plasma nitrite concentrations were more than 50% lower at 4559 m compared to sea level in both treatment groups. Despite these significant changes, dietary nitrate supplementation had no effect on any measured read-outs of sublingual or forearm blood flow, even when environmental hypoxia was experimentally reversed using supplemental oxygen. In conclusion, dietary nitrate supplementation does not improve microcirculatory function at 4559 m.

Barriers to advance care planning with patients as perceived by nurses and other healthcare professionals: A systematic review.

INTRODUCTION: Advance care planning is a means for patients to communicate their wishes, fears and desires for future health decisions should they lose the ability to consider or communicate these. Despite being supported by governments and healthcare leaders, uptake amongst the general population remains low. Nurses play a crucial role in promoting and engaging with these discussions given their close relationship with patients and families in a range of clinical settings. AIM: To describe the barriers that nurses and healthcare professionals believe prevent them from exploring advance care planning with their patients. METHOD: We carried out a systematic review of peer-reviewed journal articles from the databases MEDLINE, Embase, CINAHL Plus, Web of Science and ProQuest Central, guided by the PRISMA checklist. RESULTS: Eleven articles were identified: all were self-reporting surveys using a mix of open and closed questions. They originated in the USA, Canada, Australia and Ireland. The participants included various healthcare professionals, with the majority of studies focussing on nurses. The two most important barriers to advance care planning are lack of education and insufficient time. Advance care planning appears to be well supported, and nurses and healthcare professionals report themselves to be comfortable and confident to take on the responsibility. CONCLUSION: There is a need for greater education and training for nurses and healthcare professionals. In particular, there needs to be better understanding of professional and legal responsibilities. The need for sufficient time to be made available to allow these conversations, in often busy settings, will need institutional and financial support. RELEVANCE TO CLINICAL PRACTICE: Increased training and knowledge are likely to lead to more positive attitudes and greater confidence for nurses, and other healthcare professionals, which should help support and encourage patient engagement with advance care planning.