Optimal oxygen delivery in critically ill patients

Standard hemodynamic support in septic shock is to increase pulmonary capillary wedge pressure to above 15 mmHg by volume replacement and to give inotropic support if the mean arterial pressure (MAP) is not adequate. In an attempt to decrease mortality in critically ill patients, oxygen delivery (DO₂) was increased by switching inotropic support from dobutamine alone or in combination with norepinephrine to dopamine alone, or by adding dopexamine, prostacyclin, or hypertonic saline to the treatment. DO₂ increased significantly in all patients, but the increase in DO₂ was accompanied by only a 10% increase in oxygen consumption (VO₂). The increase in VO₂ was similar in survivors and nonsurvivors and in patients with and without septic shock. The results indicate that if adequate volume and inotropic support is provided for critically ill patients, the detectable oxygen debt is small and has little effect on patient outcome. When DO₂ is adequate, factors other than a tissue oxygen deficit seem to determine patient outcome.     

Dynamic lactate indices as predictors of outcome in critically ill patients

Introduction  

Dynamic changes in lactate concentrations in the critically ill may predict patient outcome more accurately than static indices. We aimed to compare the predictive value of dynamic indices of lactatemia in the first 24 hours of intensive care unit (ICU) admission with the value of more commonly used static indices.     

Pharmacokinetics and intrapulmonary diffusion of levofloxacin in critically ill patients with severe community-acquired pneumonia

OBJECTIVE: To determine the steady-state plasma and epithelial lining fluid concentrations of intravenous levofloxacin, 500 mg, administered once or twice daily in critically ill patients with severe community-acquired pneumonia. DESIGN: Prospective, open-label study. SETTING: An intensive care unit and a clinical pharmacokinetic laboratory in two university hospitals. PATIENTS: Twenty-four adult patients with severe community-acquired pneumonia and receiving mechanical ventilation were enrolled. INTERVENTIONS: All subjects received 1-hr intravenous infusions of 500 mg levofloxacin once or twice daily. The plasma and epithelial lining fluid levofloxacin concentrations were determined at steady-state after 2 days of therapy with high-performance liquid chromatography. MEASUREMENTS AND MAIN RESULTS: The median (interquartile range [IQR]) plasma and epithelial lining fluid peak levofloxacin concentrations were 12.6 (IQR, 12.0-14.1) and 11.9 (IQR, 8.7-13.7) mg/L, respectively, in the once-daily group and 19.7 (IQR, 19.0-22.0) and 17.8 (IQR, 16.2-23.5) mg/L in the twice-daily group, showing a pulmonary percentage penetration of >100% in both groups. The median (IQR) total body exposures were 151 (IQR, 137-174) and 416 (IQR, 406-472) mg.hr/L, respectively, in the once-daily and twice-daily groups. CONCLUSIONS: Our results suggest that in critically ill patients who are receiving mechanical ventilation and have severe community-acquired pneumonia and creatinine clearance of >40 mL/min, the administration of 500 mg of intravenous levofloxacin once and twice daily allows for the exceeding of pharmacodynamic thresholds predictive of outcome (i.e., peak concentration to minimum inhibitory concentration ratio of >10 or area under concentration-time curve to minimal inhibitory concentration ratio of >125 hrs) both in serum and epithelial lining fluid for pathogens with minimum inhibitory concentration values of < or =1 mg/L and >1 mg/L, respectively.     

Statistical modeling of prognostic indices for evaluation of critically ill patients

OBJECTIVE: To identify the most predictive association of variables from the usual indices of severity of illness by statistical objective analysis. DESIGN: Logistic regression analysis of the different variables of the most important indices. SETTING: A general critical care medicine group practice in a university hospital. PATIENTS: A total of 630 critical care patients age 12 to 87 yrs were evaluated. The most important indices of severity of illness and the corresponding variables were recorded and the patient's course was followed for 3 months after ICU admission. MEASUREMENTS AND MAIN RESULTS: One of our hypotheses was that the inclusion of an excessive number of variables to obtain the most common prognostic indices of mortality in critical care patients results in an underestimation of mortality and a redundancy of prognostic information. We performed a logistic regression analysis using the variables of the currently used indices of critical care prognosis: Acute Physiology Score, Simplified Acute Physiology Score, Acute Physiology Score-II, and Mortality Prediction Model. This mathematical approach resulted in a model of five variables: organ system failure, blood glucose, serum calcium, serum prothrombin activity, and serum osmolality. The score obtained from this model gave accurate prognostic criteria:sensitivity 91.2% and specificity 90%, using a cutoff point of 0.7; sensitivity 86% and, specificity 94%, using a cutoff point of 0.5. CONCLUSIONS: Our results show that suitable statistical management of the discriminant prognostic variables allows reduction of the number of variables of the severity indices currently used, obtaining five more predictive variables.     

Pharmacokinetics and intrapulmonary concentrations of linezolid administered to critically ill patients with ventilator-associated pneumonia

OBJECTIVE: To determine the steady-state plasma pharmacokinetic variables and epithelial lining fluid concentrations of linezolid administered to critically ill patients with ventilator-associated pneumonia. DESIGN: Prospective, open-label study. SETTING: An intensive care unit and research ward in a university hospital. PATIENTS: Sixteen critically ill adult patients with ventilator-associated pneumonia. INTERVENTIONS: All subjects received 1-hr intravenous infusions of linezolid 600 mg twice daily. After 2 days of therapy, the steady-state plasma pharmacokinetic variables and epithelial lining fluid concentrations of linezolid were determined by high-performance liquid chromatography. MEASUREMENTS AND MAIN RESULTS: The mean +/- sd linezolid peak and trough concentrations were 17.7 +/- 4.0 mg/L and 2.4 +/- 1.2 mg/L in plasma and 14.4 +/- 5.6 mg/L and 2.6 +/- 1.7 mg/L in epithelial lining fluid, respectively, showing a mean linezolid percentage penetration in epithelial lining fluid of approximately 100%. The mean +/- sd area under concentration-time curve during the observational period (AUC0-12) was 77.3 +/- 23.7 mg x hr/L, corresponding to a mean AUC0-24 of 154.6 mg x hr/L. CONCLUSIONS: Our study shows satisfactory results, with linezolid concentrations exceeding the susceptibility breakpoint for Gram-positive bacteria in both plasma and epithelial lining fluid. This suggests that a dosage of 600 mg administered intravenously twice daily to critically ill patients with Gram-positive ventilator-associated pneumonia would achieve success against organisms with minimum inhibitory concentrations as high as 2-4 mg/L in both plasma and epithelial lining fluid.     

危重病患者细胞因子和氧代谢指标的动态变化

多器官功能障碍综合征( MODS)已成为ICU患者死亡的主要原因〔1〕;尽管采取各种措施对危重患者积极进行器官功能支持,但其病死率仍高达70 %左右〔2〕,多数患者死于进行性MODS。全身炎症反应综合征( SIRS)是MODS发病的基础,细胞因子失控性释放是SIRS向MODS转化的关键,危重患者氧供能否得到充分保证及合理利用与MODS预后密切相关。观察危重患者SIRS期间炎症细胞因子和氧代谢指标的动态变化,旨在为临床诊断提供依据。1　资料与方法1.1　病例:2 0 0 2年6月—2 0 0 3年12月我院急诊科收治的35例危重病患者均符合SIRS诊断标准〔1〕…     

Tissue blood flow and oxygen transport in critically ill patients.

The theoretical and practical solutions to the problems of increasing oxygen transport are well understood. Unfortunately the quantitation of hypoxia, both as an absolute deficit and as a precise method of prognosis is not yet available. This may well be because regional hypoxia in a vital tissue cannot be mirrored in a total body measurement. In the low-flow state, oxygen delivery can be maintained by redistribution of cardiac output, reduction of oxygen uptake by ischemic tissue by reducing work load, by increasing oxygenation of the blood, or by decreasing the affinity of oxygen for hemoglobin. The latter provides for more oxygen to be delivered by a given amount of oxyhemoglobin before the tension falls to deleterious regions (about 20 torr). There is some evidence that pharmacologic doses of methylprednisolone may be beneficial in this respect.     

Discomfort associated with underhumidified high-flow oxygen therapy in critically ill patients

Objective  To measure (1) the discomfort in non-intubated patients under high-flow oxygen therapy (HFOT) humidified with bubble (BH) or heated humidifiers (HH), and (2) the hygrometric properties of oxygen with a BH and an HH. Design and setting  This was a randomized cross-over study in critically ill patients during a 3-day period. The humidification device used at days 1 and 3 was changed for the other at day 2. (2) It was also an experimental bench study using the psychrometric method with five randomized flows (3, 6, 9, 12 and 15 l/min) and different humidification techniques. Methods  Discomfort, particularly dryness of the mouth and throat, was measured for two humidification conditions (BH and HH) using a 0–10 numerical rating scale (NRS) by patients requiring HFOT with a face mask at a flow ≥5 l/min, in a double-blinded condition. Results  (1) In this clinical study, 30 patients treated by HFOT at a median flow of 7.8 l/min (5.1–10.9) were included. The global incidence of moderate (NRS = 4–6) and severe discomfort (NRS = 7–10) was 25 and 29%, respectively. The median intensities of both mouth and throat dryness were significantly lower with the HH than with the BH [7.8 (5.0–9.4) vs. 5.0 (3.1–7.0), P = 0.001 and 5.8 (2.3–8.5) vs. 4.3 (2.0–5.0), P = 0.005, respectively]. (2) In the bench study, the mean absolute humidity measured at an ambient temperature of 26°C with the HH was two times greater than with the BH (30 ± 1 vs. 16 ± 2 mg/l, P < 0.05) regardless of the flow rate. Conclusions  Compared to bubble humidifiers, the use of a heated-humidifier in patients with high-flow oxygen therapy is associated with a decrease of dryness symptoms mediated by increased humidity delivered to the patient. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. This article is discussed in the editorial available at: doi:. The authors declare that Fisher & Paykel Healthcare France (Courtaboeuf, France) provided technical assistance for the bench test study, including a financial aid of 3,000 €, which was used to acquire technical equipment and to present results at scientific meetings. Respironics France (Carquefou, France) provided technical assistance for the bench test.     

Monitoring of central venous oxygen saturation versus mixed venous oxygen saturation in critically ill patients

Continous monitoring of mixed venous (SvO₂) and central venous (ScO₂) oxygen saturation was compared in 7 critically-ill patients (Apache II score: 19±2.1) to determine whether or not information derived from ScO₂ were reliable in clinical practice. Patients were catheterized with both a pulmonary artery (PA) and a central venous (CV) catheter, each of them mounted with fiberoptic sensors (Opticath PA Catheter P7110 and Opticath CV Catheter U440, Abbott). A total of 580 comparative measurements were obtained during periods without and with therapeutic interventions (drug-titration, bronchial suction, use of PEEP, changes in FiO₂...). The systematic error between the 2 measurement techniques was 0.6% and 0.3% in periods with and without therapeutic interventions, respectively. The variability between the 2 techniques was 10% for both periods. Differences between the values were 5% in 49% of values during periods of stability and in 50% of values during periods with therapeutic interventions. There were poor correlations between the values during periods without (r=0.48) and with therapeutic interventions (r=0.62). Better, but still less than ideal, correlations were obtained with changes in SvO₂ and ScO₂ during periods without (r=0.70) and with therapeutic interventions (r=0.77). Although there is a need to develop a simple technique to monitor mixed venous oxygen saturation, the present study indicates that ScO₂ monitoring was not reliable in the study patients.     

Hyponatremia in critically ill patients

Disorders of sodium and water metabolism are frequently encountered in hospitalized patients. Hyponatremia in critically ill patients can cause significant morbidity and mortality. Inappropriate treatment of hyponatremia can add to the problem. The diagnosis and management of salt and water abnormalities in critically ill patients is often challenging. The increasing knowledge about aquaporins and the role of vasopressin in water metabolism has enhanced our understanding of these disorders. The authors have outlined the general approach to the diagnosis and management of hyponatremia. A systematic approach by clinicians, using a detailed history, physical examination, and relevant diagnostic tests, will assist in efficient management of salt and water problems.     

Delirium in critically ill patients

Delirium in the intensive care unit is a serious problem that has recently attracted much attention. User-friendly and reliable tools, such as the Confusion Assessment Method for the Intensive Care Unit (CAM-ICU), offer the clinician the opportunity to identify delirium in patients better. Diagnosis of delirium in a critical care population is often a difficult task because classical psychiatric evaluation is impossible for a number of reasons. The CAM-ICU makes use of nonverbal assessments to evaluate the cardinal features of delirium (i.e. acute or fluctuating onset, inattention, disorganized thinking and altered level of consciousness). Its development for use in the critical care setting represents a significant advance that could lead to better care for such patients.     

Myopathy in critically ill patients

OBJECTIVE: To review myopathic changes occurring during intensive care treatment in the light of recent information about manifestation, clinical settings, pathophysiology, and histomorphologic changes. DATA SOURCES: The computerized MEDLINE database, bibliography of pertinent articles, and the author's personal files. STUDY SELECTION: Studies were selected according to their relevance to myopathic complications in critically ill patients. DATA EXTRACTION: All applicable data were extracted. DATA SYNTHESIS: Myopathic changes occur frequently in patients treated in the intensive care unit (ICU). Three main types have been identified: critical illness myopathy, myopathy with selective loss of myosin filaments, and acute necrotizing myopathy of intensive care. These histologic types probably represent variable expressions of a toxic effect not yet identified. Candidates for such myotoxic effects are the mediators of the systemic response in sepsis and high-dose administration of corticosteroids and muscle relaxants. The influence of these latter agents appears to be particularly important in the pathogenesis of myosin loss and myonecrosis. Experimental studies suggest that axonal damage attributable to critical illness neuropathy can be an additional factor triggering myopathies in the ICU. Muscle membrane inexcitability was recently identified as an alternative mechanism of severe weakness in ICU patients. CONCLUSIONS: Myopathic changes are surprisingly frequent in critically ill patients. The clinical importance of this finding is still unknown, but it is likely that weakness caused by myopathy prolongs ICU stay and rehabilitation. Because corticosteroids and muscle relaxants appear to trigger some types of ICU myopathy, they should be avoided or administered at the lowest doses possible. Sepsis, denervation, and muscle membrane inexcitability may be additional factors. Studies addressing the pathophysiology of myopathy in critically ill patients are urgently needed.     

Hypernatremia in critically ill patients

Hypernatremia is common in intensive care units. It has detrimental effects on various physiologic functions and was shown to be an independent risk factor for increased mortality in critically ill patients. Mechanisms of hypernatremia include sodium gain and/or loss of free water and can be discriminated by clinical assessment and urine electrolyte analysis. Because many critically ill patients have impaired levels of consciousness, their water balance can no longer be regulated by thirst and water uptake but is managed by the physician. Therefore, the intensivists should be very careful to provide the adequate sodium and water balance for them. Hypernatremia is treated by the administration of free water and/or diuretics, which promote renal excretion of sodium. The rate of correction is critical and must be adjusted to the rapidity of the development of hypernatremia.     

Diarrhea in critically ill patients

The onset of diarrhea complicates the care of critically ill patients, who often have complex cardiopulmonary, renal or metabolic problems. Diarrhea further upsets fluid and electrolyte balance and creates difficulties in nutritional support. Common causes of acute diarrhea in critically ill patients include medications, enteral feedings, ischemic bowel disease, pseudomembranous colitis, short bowel syndrome, intestinal fistulas, pancreatic insufficiency and opportunistic infections in patients with AIDS.     

Hypophosphatemia in critically ill patients

Purpose

The aim of this study was to assess the association of phosphate concentration with key clinical outcomes in a heterogeneous cohort of critically ill patients.

Materials and Methods

This was a retrospective observational study at a general intensive care unit (ICU) of an Australian university teaching hospital enrolling 2730 adult critically ill patients.

Results

We studied 10?504 phosphate measurements with a mean value of 1.17 mmol/L (measurements every 28.8 hours on average). Hyperphosphatemia (inorganic phosphate [iP] concentration > 1.4 mmol/L) occurred in 45% and hypophosphatemia (iP ≤ 0.6 mmol/L) in 20%. Among patients without any episodes of hyperphosphatemia, patients with at least 1 episode of hypophosphatemia had a higher ICU mortality than those without hypophosphatemia (P = .004). In addition, ICU nonsurvivors had lower minimum phosphate concentrations than did survivors (P = .009). Similar results were seen for hospital mortality. However, on multivariable logistic regression analysis, hypophosphatemia was not independently associated with ICU mortality (adjusted odds ratio, 0.86 [95% confidence interval, 0.66-1.10]; P = .24) and hospital mortality (odds ratio, 0.89 [0.73-1.07]; P = .21). Even when different cutoff points were used for hypophosphatemia (iP ≤ 0.5, 0.4, 0.3, or 0.2 mmol/L), hypophosphatemia was not an independent risk factor for ICU and hospital morality. In addition, timing of onset and duration of hypophosphatemia were not independent risk factor for ICU and hospital mortality.

Conclusions

Hypophosphatemia behaves like a general marker of illness severity and not as an independent predictor of ICU or in-hospital mortality in critically ill patients.     

Psychoneuroimmunology in critically ill patients

Psychoneuroimmunology is the study of the interactions among behavior, neural, and endocrine functions and the immune system. The purpose of this review is to briefly summarize the evidence concerning interactions among behavior, the neuroendocrine system, and the immune system, and to show how this evidence relates to critical care patients. It has been shown that the immune function of many patients in the intensive care unit is suppressed as a result of trauma, sepsis, or profound physiologic and psychological stress. Three of the most common stressors among patients in the intensive care unit are pain, sleep deprivation, and fear or anxiety. Findings have shown each of these stressors to be associated with decreased immune functioning. Nurses have an important responsibility to protect their patients from infection and promote their ability to heal. Several actions are suggested that can help the nurse achieve these goals. It is hoped that nurses would keep these interactions in mind while caring for their patients in the intensive care unit.     

Bronchoscopy in critically ill patients

Fiberoptic bronchoscopy is a valuable diagnostic and therapeutic tool for use in carefully selected patients with serious pulmonary disease. The authors review the benefits and risks of fiberoptic bronchoscopy and discuss the essentials of nursing care before, during, and after the procedure.