Alistair Nichol

Critical care services and 2009 H1N1 influenza in Australia and New Zealand

BACKGROUND Planning for the treatment of infection with the 2009 pandemic influenza A (H1N1) virus through health care systems in developed countries during winter in the Northern Hemisphere is hampered by a lack of information from similar health care systems. METHODS We conducted an inception-cohort study in all Australian and New Zealand intensive care units (ICUs) during the winter of 2009 in the Southern Hemisphere. We calculated, per million inhabitants, the numbers of ICU admissions, bed-days, and days of mechanical ventilation due to infection with the 2009 H1N1 virus. We collected data on demographic and clinical characteristics of the patients and on treatments and outcomes. RESULTS From June 1 through August 31, 2009, a total of 722 patients with confirmed infection with the 2009 H1N1 virus (28.7 cases per million inhabitants; 95% confidence interval [CI], 26.5 to 30.8) were admitted to an ICU in Australia or New Zealand. Of the 722 patients, 669 (92.7%) were under 65 years of age and 66 (9.1%) were pregnant women; of the 601 adults for whom data were available, 172 (28.6%) had a body-mass index (the weight in kilograms divided by the square of the height in meters) greater than 35. Patients infected with the 2009 H1N1 virus were in the ICU for a total of 8815 bed-days (350 per million inhabitants). The median duration of treatment in the ICU was 7.0 days (interquartile range, 2.7 to 13.4); 456 of 706 patients (64.6%) with available data underwent mechanical ventilation for a median of 8 days (interquartile range, 4 to 16). The maximum daily occupancy of the ICU was 7.4 beds (95% CI, 6.3 to 8.5) per million inhabitants. As of September 7, 2009, a total of 103 of the 722 patients (14.3%; 95% CI, 11.7 to 16.9) had died, and 114 (15.8%) remained in the hospital. CONCLUSIONS The 2009 H1N1 virus had a substantial effect on ICUs during the winter in Australia and New Zealand. Our data can assist planning for the treatment of patients during the winter in the Northern Hemisphere.

Inhibition of Rho-kinase attenuates hypoxia-induced angiogenesis in the pulmonary circulation.

Pulmonary hypertension (PH) is a common complication of chronic hypoxic lung diseases, which increase morbidity and mortality. Hypoxic PH has previously been attributed to structural changes in the pulmonary vasculature including narrowing of the vascular lumen and loss of vessels, which produce a fixed increase in resistance. Using quantitative stereology, we now show that chronic hypoxia caused PH and remodeling of the blood vessel walls in rats but that this remodeling did not lead to structural narrowing of the vascular lumen. Sustained inhibition of the RhoA/Rho-kinase pathway throughout the period of hypoxic exposure attenuated PH and prevented remodeling in intra-acinar vessels without enlarging the structurally determined lumen diameter. In chronically hypoxic lungs, acute Rho kinase inhibition markedly decreased PVR but did not alter the alveolar to arterial oxygen gap. In addition to increased vascular resistance, chronic hypoxia induced Rho kinase–dependent capillary angiogenesis. Thus, hypoxic PH was not caused by fixed structural changes in the vasculature but by sustained vasoconstriction, which was largely Rho kinase dependent. Importantly, this vasoconstriction had no role in ventilation-perfusion matching and optimization of gas exchange. Rho kinase also mediated hypoxia-induced capillary angiogenesis, a previously unrecognized but potentially important adaptive response.

Relative hyperlactatemia and hospital mortality in critically ill patients: a retrospective multi-centre study

IntroductionHigher lactate concentrations within the normal reference range (relative hyperlactatemia) are not considered clinically significant. We tested the hypothesis that relative hyperlactatemia is independently associated with an increased risk of hospital death.MethodsThis observational study examined a prospectively obtained intensive care database of 7,155 consecutive critically ill patients admitted to the Intensive Care Units (ICUs) of four Australian university hospitals. We assessed the relationship between ICU admission lactate, maximal lactate and time-weighted lactate levels and hospital outcome in all patients and also in those patients whose lactate concentrations (admission n = 3,964, maximal n = 2,511, and time-weighted n = 4,584) were under 2 mmol.L-1 (i.e. relative hyperlactatemia).ResultsWe obtained 172,723 lactate measurements. Higher admission and time-weightedlactate concentration within the reference range was independently associated with increased hospital mortality (admission odds ratio (OR) 2.1, 95% confidence interval (CI) 1.3 to 3.5, P = 0.01; time-weighted OR 3.7, 95% CI 1.9 to 7.00, P < 0.0001). This significant association was first detectable at lactate concentrations > 0.75 mmol.L-1. Furthermore, in patients whose lactate ever exceeded 2 mmol.L-1, higher time-weighted lactate remained strongly associated with higher hospital mortality (OR 4.8, 95% CI 1.8 to 12.4, P < 0.001).ConclusionsIn critically ill patients, relative hyperlactataemia is independently associated with increased hospital mortality. Blood lactate concentrations > 0.75 mmol.L-1 can be used by clinicians to identify patients at higher risk of death. The current reference range for lactate in the critically ill may need to be re-assessed.

A multicenter randomized trial of atorvastatin therapy in intensive care patients with severe sepsis

RATIONALE Observational studies link statin therapy with improved outcomes in patients with severe sepsis. OBJECTIVES To test whether atorvastatin therapy affects biologic and clinical outcomes in critically ill patients with severe sepsis. METHODS Phase II, multicenter, prospective, randomized, double-blind, placebo-controlled trial stratified by site and prior statin use. A cohort of 250 critically ill patients (123 statins, 127 placebo) with severe sepsis were administrated either atorvastatin (20 mg daily) or matched placebo. MEASUREMENTS AND MAIN RESULTS There was no difference in IL-6 concentrations (primary end point) between the atorvastatin and placebo groups (P = 0.76) and no interaction between treatment group and time to suggest that the groups behaved differently over time (P = 0.26). Baseline plasma IL-6 was lower among previous statin users (129 [87-191] vs. 244 [187-317] pg/ml; P = 0.01). There was no difference in length of stay, change in Sequential Organ Failure Assessment scores or mortality at intensive care unit discharge, hospital discharge, 28- or 90-day (15% vs. 19%), or adverse effects between the two groups. Cholesterol was lower in patients treated with atorvastatin (2.4 [0.07] vs. 2.6 [0.06] mmol/L; P = 0.006). In the predefined group of 77 prior statin users, those randomized to placebo had a greater 28-day mortality (28% vs. 5%; P = 0.01) compared with those who received atorvastatin. The difference was not statistically significant at 90 days (28% vs. 11%; P = 0.06). CONCLUSIONS Atorvastatin therapy in severe sepsis did not affect IL-6 levels. Prior statin use was associated with a lower baseline IL-6 concentration and continuation of atorvastatin in this cohort was associated with improved survival. Clinical trial registered with the Australian New Zealand Clinical Trials Registry (ACTRN 12607000028404).

Sustained hypercapnic acidosis during pulmonary infection increases bacterial load and worsens lung injury

Objective:Hypercapnic acidosis is commonly permitted in patients with acute respiratory distress syndrome during the use of protective ventilation strategies. Hypercapnic acidosis is also a common complication of multiple lung diseases and is associated with a poor prognosis, although the mechanisms by which it leads to increased mortality is not known. Previous studies using noninfective models of lung injury show that acute (<6 hrs) hypercapnic acidosis reduced lung damage by an anti-inflammatory effect. We hypothesized that this anti-inflammatory effect would be detrimental in vivo in the presence of untreated bacterial infection and sustained hypercapnia (>48 hrs) and, furthermore, that if bacterial reproduction were controlled by antibiotic therapy, then the anti-inflammatory effects of hypercapnic acidosis would no longer prove detrimental. Design:This study was a prospective, randomized animal study. Setting:This study was conducted at a university research laboratory. Subjects:Study subjects were adult male Wistar-Kyoto rats. Interventions:After intratracheal instillation of Escherichia coli under general anesthesia, rats were housed in normocapnic (21% O2, 0% CO2) or hypercapnic (21% O2, 5% CO2) environments for 2 days. Rats were then reanesthetized for assessment of physiological and quantitative stereologic indices of lung damage, quantitative bacterial counts, and neutrophil phagocytosis. Measurements and Main Results:Hypercapnic acidosis was associated with higher lung bacterial colony counts, more structural damage, and lower static lung compliance than normocapnia. Neutrophils isolated from hypercapnic rats demonstrated impaired phagocytosis. In a further separate series of experiments, in which rats were given antibiotic therapy, lung damage was not different between normocapnic and hypercapnic acidosis groups. Conclusions:Prolonged hypercapnic acidosis worsened bacterial infection-induced lung injury. Our findings suggest an immunosuppressive effect of hypercapnic acidosis and have important implications for protective ventilation strategies that permit hypercapnic acidosis in patients with adult respiratory distress syndrome and in the management of hypercapnic acidosis during infective exacerbations of chronic obstructive pulmonary disease and other lung diseases.

Age of red blood cells and transfusion in critically ill patients

Red blood cells (RBC) storage facilitates the supply of RBC to meet the clinical demand for transfusion and to avoid wastage. However, RBC storage is associated with adverse changes in erythrocytes and their preservation medium. These changes are responsible for functional alterations and for the accumulation of potentially injurious bioreactive substances. They also may have clinically harmful effects especially in critically ill patients. The clinical consequences of storage lesions, however, remain a matter of persistent controversy. Multiple retrospective, observational, and single-center studies have reported heterogeneous and conflicting findings about the effect of blood storage duration on morbidity and/or mortality in trauma, cardiac surgery, and intensive care unit patients. Describing the details of this controversy, this review not only summarizes the current literature but also highlights the equipoise that currently exists with regard to the use of short versus current standard (extended) storage duration red cells in critically ill patients and supports the need for large, randomized, controlled trials evaluating the clinical impact of transfusing fresh (short duration of storage) versus older (extended duration of storage) red cells in critically ill patients.

Therapeutic hypothermia: Benefits, mechanisms and potential clinical applications in neurological, cardiac and kidney injury

Therapeutic hypothermia involves the controlled reduction of core temperature to attenuate the secondary organ damage which occurs following a primary injury. Clinicians have been increasingly using therapeutic hypothermia to prevent or ameliorate various types of neurological injury and more recently for some forms of cardiac injury. In addition, some recent evidence suggests that therapeutic hypothermia may also provide benefit following acute kidney injury. In this review we will examine the potential mechanisms of action and current clinical evidence surrounding the use of therapeutic hypothermia. We will discuss the ideal methodological attributes of future studies using hypothermia to optimise outcomes following organ injury, in particular neurological injury. We will assess the importance of target hypothermic temperature, time to achieve target temperature, duration of cooling, and re-warming rate on outcomes following neurological injury to gain insights into important factors which may also influence the success of hypothermia in other organ injuries, such as the heart and the kidney. Finally, we will examine the potential of therapeutic hypothermia as a future kidney protective therapy.

Measuring functional and quality of life outcomes following major head injury: Common scales and checklists

Traumatic brain injury (TBI) is a major public health issue, which results in significant mortality and long term disability. The profound impact of TBI is not only felt by the individuals who suffer the injury but also their care-givers and society as a whole. Clinicians and researchers require reliable and valid measures of long term outcome not only to truly quantify the burden of TBI and the scale of functional impairment in survivors, but also to allow early appropriate allocation of rehabilitation supports. In addition, clinical trials which aim to improve outcomes in this devastating condition require high quality measures to accurately assess the impact of the interventions being studied. In this article, we review the properties of an ideal measure of outcome in the TBI population. Then, we describe the key components and performance of the measurement tools most commonly used to quantify outcome in clinical studies in TBI. These measurement tools include: the Glasgow Outcome Scale (GOS) and extended Glasgow Outcome Scale (GOSe); Disability Rating Scale (DRS); Functional Independence Measure (FIM); Functional Assessment Measure (FAM); Functional Status Examination (FSE) and the TBI-specific and generic quality of life measures used in TBI patients (SF-36 and SF-12, WHOQOL-BREF, SIP, EQ-5D, EBIQ, and QOLIBRI).

A randomised controlled trial of an open lung strategy with staircase recruitment, titrated PEEP and targeted low airway pressures in patients with acute respiratory distress syndrome

IntroductionTidal volume and plateau pressure minimisation are the standard components of a protective lung ventilation strategy for patients with acute respiratory distress syndrome (ARDS). Open lung strategies, including higher positive end-expiratory pressure (PEEP) and recruitment manoeuvres to date have not proven efficacious. This study examines the effectiveness and safety of a novel open lung strategy, which includes permissive hypercapnia, staircase recruitment manoeuvres (SRM) and low airway pressure with PEEP titration.MethodTwenty ARDS patients were randomised to treatment or ARDSnet control ventilation strategies. The treatment group received SRM with decremental PEEP titration and targeted plateau pressure < 30 cm H2O. Gas exchange and lung compliance were measured daily for 7 days and plasma cytokines in the first 24 hours and on days 1, 3, 5 and 7 (mean ± SE). Duration of ventilation, ICU stay and hospital stay (median and interquartile range) and hospital survival were determined.ResultsThere were significant overall differences between groups when considering plasma IL-8 and TNF-α. For plasma IL-8, the control group was 41% higher than the treatment group over the seven-day period (ratio 1.41 (1.11 to 1.79), P = 0.01), while for TNF-α the control group was 20% higher over the seven-day period (ratio 1.20 (1.01 to 1.42) P = 0.05). PaO2/FIO2 (204 ± 9 versus 165 ± 9 mmHg, P = 0.005) and static lung compliance (49.1 ± 2.9 versus 33.7 ± 2.7 mls/cm H2O, P < 0.001) were higher in the treatment group than the control group over seven days. There was no difference in duration of ventilation (180 (87 to 298) versus 341 (131 to 351) hrs, P = 0.13), duration of ICU stay (9.9 (5.6 to 14.8) versus 16.0 (8.1 to 19.3) days, P = 0.19) and duration of hospital stay (17.9 (13.7 to 34.5) versus 24.7 (20.5 to 39.8) days, P = 0.16) between the treatment and control groups.ConclusionsThis open lung strategy was associated with greater amelioration in some systemic cytokines, improved oxygenation and lung compliance over seven days. A larger trial powered to examine clinically-meaningful outcomes is warranted.Trial registrationACTRN12607000465459

Long-term quality of life in patients with acute respiratory distress syndrome requiring extracorporeal membrane oxygenation for refractory hypoxaemia

IntroductionThe purpose of the study was to assess the long term outcome and quality of life of patients with acute respiratory distress syndrome (ARDS) receiving extracorporeal membrane oxygenation (ECMO) for refractory hypoxemia.MethodsA retrospective observational study with prospective health related quality of life (HRQoL) assessment was conducted in ARDS patients who had ECMO as a rescue therapy for reversible refractory hypoxemia from January 2009 until April 2011 in a tertiary Australian centre. Survival and long-term quality of life assessment, using the Short-Form 36 (SF-36) and the EuroQol health related quality of life questionnaire (EQ5D) were assessed and compared to international data from other research groups.ResultsTwenty-one patients (mean age 36.3 years) with ARDS receiving ECMO for refractory hypoxemia were studied. Eighteen (86%) patients were retrieved from external intensive care units (ICUs) by a dedicated ECMO retrieval team. Eleven (55%) had H1N1 influenza A-associated pneumonitis. Eighteen (86%) patients survived to hospital discharge. Of the 18 survivors, ten (56%) were discharged to other hospitals and 8 (44%) were discharged directly home. Sequelae and health related quality of life were evaluated for 15 of the 18 (71%) long-term survivors (assessment at median 8 months). Mean SF-36 scores were significantly lower across all domains compared to age and sex matched Australian norms. Mean SF-36 scores were lower (minimum important difference at least 5 points) than previously described ARDS survivors in the domains of general health, mental health, vitality and social function. One patient had long-term disability as a result of ICU acquired weakness. Only 26% of survivors had returned to previous work levels at the time of follow-up.ConclusionsThis ARDS cohort had a high survival rate (86%) after use of ECMO support for reversible refractory hypoxemia. Long term survivors had similar physical health but decreased mental health, general health, vitality and social function compared to other ARDS survivors and an unexpectedly poor return to work.