Evaluation of oxygen consumption and resting energy expenditure in critically ill patients with systemic inflammatory response syndrome

Current Perspectives of Mitochondria in Sepsis-Induced Cardiomyopathy

Sepsis-induced cardiomyopathy (SICM) is one of the leading indicators for poor prognosis associated with sepsis. Despite its reversibility, prognosis varies widely among patients. Mitochondria play a key role in cellular energy production by generating adenosine triphosphate (ATP), which is vital for myocardial energy metabolism. Over recent years, mounting evidence suggests that severe sepsis not only triggers mitochondrial structural abnormalities such as apoptosis, incomplete autophagy, and mitophagy in cardiomyocytes but also compromises their function, leading to ATP depletion. This metabolic disruption is recognized as a significant contributor to SICM, yet effective treatment options remain elusive. Sepsis cannot be effectively treated with inotropic drugs in failing myocardium due to excessive inflammatory factors that blunt β-adrenergic receptors. This review will share the recent knowledge on myocardial cell death in sepsis and its molecular mechanisms, focusing on the role of mitochondria as an important metabolic regulator of SICM, and discuss the potential for developing therapies for sepsis-induced myocardial injury.

Mitigating Intensive Care Unit Noise: Design-Led Modeling Solutions, Calculated Acoustic Outcomes, and Cost Implications

OBJECTIVES, PURPOSE, OR AIM

The study aimed to decrease noise levels in the ICU, anticipated to have adverse effects on both patients and staff, by implementing enhancements in acoustic design.

BACKGROUND

Recognizing ICU noise as a significant disruptor of sleep and a potential hindrance to patient recovery, this study was conducted at a 40-bed ICU in Fiona Stanley Hospital in Perth, Australia.

METHODS

A comprehensive mixed-methods approach was employed, encompassing surveys, site analysis, and acoustic measurements. Survey data highlighted the importance of patient sleep quality, emphasizing the negative impact of noise on work performance, patient connection, and job satisfaction. Room acoustics analysis revealed noise levels ranging from 60 to 90 dB(A) in the presence of patients, surpassing sleep disruption criteria.

RESULTS

Utilizing an iterative 3D design modeling process, the study simulated significant acoustic treatment upgrades. The design integrated effective acoustic treatments within patient rooms, aiming to reduce noise levels and minimize transmission to adjacent areas. Rigorous evaluation using industry-standard acoustic software highlights the design's efficacy in reducing noise transmission in particular. Additionally, cost implications were examined, comparing standard ICU construction with acoustically treated options for new construction and refurbishment projects.

CONCLUSIONS

This study provides valuable insights into design-based solutions for addressing noise-related challenges in the ICU. While the focus is on improving the acoustic environment by reducing noise levels and minimizing transmission to adjacent areas. It is important to clarify that direct measurements of patient outcomes were not conducted. The potential impact of these solutions on health outcomes, particularly sleep quality, remains a crucial aspect for consideration.

OXYGEN CONSUMPTION AS AN EARLY WARNING SYSTEM IN THE CRITICALLY ILL

ABSTRACT

Introduction: In this study, we assessed whether changes in oxygen consumption (VO 2 ) and other metabolic parameters could be used as an early warning system for detecting clinical deterioration in mechanically ventilated patients. Methods: This was a prospective cohort study of adult patients requiring mechanical ventilation between February 2016 and March 2019. We looked for changes in VO 2 , carbon dioxide production (VCO 2 ), respiratory quotient (RQ), and end-tidal carbon dioxide (EtCO 2 ), occurring prior to clinical deterioration. Clinical deterioration was predefined as a requirement of vasopressor, an increase in serum lactate by 20% where at least one value was above 3 mmol/L, or a decrease in hemoglobin by 20% in the 4 hours prior to clinical deterioration. Results A total of 141 patients were included. There were no detectable changes in VO 2 , VCO 2 , and EtCO 2 within the 4 hours prior to any clinical deterioration. RQ increased significantly within the 4 hours prior to an increase in lactate as compared with no increase in lactate, but there were no detectable changes prior to other clinical deteriorations. Conclusions RQ has the potential to be an early marker of tissue hypoperfusion or mitochondrial dysfunction. However, future studies are necessary to evaluate the use of RQ as a bedside monitor in critical care settings.

Computational modeling of targeted temperature management in post-cardiac arrest patients

Our core body temperature is held around [Formula: see text]C by an effective internal thermoregulatory system. However, various clinical scenarios have a more favorable outcome under external temperature regulation. Therapeutic hypothermia, for example, was found beneficial for the outcome of resuscitated cardiac arrest patients due to its protection against cerebral ischemia. Nonetheless, practice shows that outcomes of targeted temperature management vary considerably in dependence on individual tissue damage levels and differences in therapeutic strategies and protocols. Here, we address these differences in detail by means of computational modeling. We develop a multi-segment and multi-node thermoregulatory model that takes into account details related to specific post-cardiac arrest-related conditions, such as thermal imbalances due to sedation and anesthesia, increased metabolic rates induced by inflammatory processes, and various external cooling techniques. In our simulations, we track the evolution of the body temperature in patients subjected to post-resuscitation care, with particular emphasis on temperature regulation via an esophageal heat transfer device, on the examination of the alternative gastric cooling with ice slurry, and on how anesthesia and the level of inflammatory response influence thermal behavior. Our research provides a better understanding of the heat transfer processes and therapies used in post-cardiac arrest patients.

Cardiac Metabolism in Sepsis

The mechanism of sepsis-induced cardiac dysfunction is believed to be different from that of myocardial ischemia. In sepsis, chemical mediators, such as endotoxins, cytokines, and nitric oxide, cause metabolic abnormalities, mitochondrial dysfunction, and downregulation of β-adrenergic receptors. These factors inhibit the production of ATP, essential for myocardial energy metabolism, resulting in cardiac dysfunction. This review focuses on the metabolic changes in sepsis, particularly in the heart. In addition to managing inflammation, interventions focusing on metabolism may be a new therapeutic strategy for cardiac dysfunction due to sepsis.

Association Between Obstructive Sleep Apnea and Reduced Mortality in Critically Ill Patients: A Propensity Score-Based Analysis

Background

The impact of obstructive sleep apnea (OSA) on the prognosis of intensive care unit (ICU) patients remains controversial. Thus, this study aimed to determine the association between OSA status and outcomes in ICU patients.

Methods

We conducted a retrospective cohort study composed of 38,177 critically ill patients from the Medical Information Mart for Intensive Care III (MIMIC-III) database. Propensity score matching was used to evaluate the association between OSA and mortality in ICU adults.

Results

A total of 38,177 critically ill patients were included in this study. Among them, 1428 (3.71%) patients had OSA. Before matching, patients with OSA had a significantly lower 28-day mortality (relative risk (RR), 0.47; 95% confidence interval (CI), 0.38–0.58), 90-day mortality (RR, 0.50; 95% CI, 0.43–0.60), ICU mortality (RR, 0.41; 95% CI, 0.31–0.54), and in-hospital mortality (RR, 0.46; 95% CI, 0.36–0.57). After adjusting with propensity-score matching, the findings of reduced risk of mortality remained unchanged. The RR of 28-day mortality, 90-day mortality, ICU mortality, in-hospital mortality was 0.57 (95% CI, 0.34–0.57), 0.53 (95% CI, 0.40–0.70), 0.54 (95% CI, 0.37–0.79), and 0.55 (95% CI, 0.39–0.77), respectively.

Conclusion

This study indicated that ICU patients with OSA had a significantly lower risk of mortality compared with those without OSA.

Metabolic Alterations in Sepsis

Sepsis is defined as “life-threatening organ dysfunction caused by a dysregulated host response to infection”. Contrary to the older definitions, the current one not only focuses on inflammation, but points to systemic disturbances in homeostasis, including metabolism. Sepsis leads to sepsis-induced dysfunction and mitochondrial damage, which is suggested as a major cause of cell metabolism disorders in these patients. The changes affect the metabolism of all macronutrients. The metabolism of all macronutrients is altered. A characteristic change in carbohydrate metabolism is the intensification of glycolysis, which in combination with the failure of entering pyruvate to the tricarboxylic acid cycle increases the formation of lactate. Sepsis also affects lipid metabolism—lipolysis in adipose tissue is upregulated, which leads to an increase in the level of fatty acids and triglycerides in the blood. At the same time, their use is disturbed, which may result in the accumulation of lipids and their toxic metabolites. Changes in the metabolism of ketone bodies and amino acids have also been described. Metabolic disorders in sepsis are an important area of research, both for their potential role as a target for future therapies (metabolic resuscitation) and for optimizing the current treatment, such as clinical nutrition.

Systematic review of factors associated with energy expenditure in the critically ill

BACKGROUND AND AIMS

Indirect calorimetry is the reference standard for energy expenditure measurement. Predictive formulae that replace it are inaccurate. Our aim was to review the patient and clinical factors associated with energy expenditure in critically ill patients.

METHODS

We conducted a systematic review of the literature. Eligible studies were those reporting an evaluation of factors and energy expenditure. Energy expenditure and factor associations with p-values were extracted from each study, and each factor was classified as either significantly, indeterminantly, or not associated with energy expenditure. Regression coefficients were summarized as measures of central tendency and spread. Metanalysis was performed on correlations.

RESULTS

The search strategy yielded 8521 unique articles, 307 underwent full text review, and 103 articles were included. Most studies were in adults. There were 95 factors with 352 evaluations. Minute volume, weight, age, % body surface area burn, sedation, post burn day, and caloric intake were significantly associated with energy expenditure. Heart rate, fraction of inspired oxygen, respiratory rate, respiratory disease diagnosis, positive end expiratory pressure, intensive care unit days, C- reactive protein, and size were not associated with energy expenditure. Multiple factors (n = 37) were identified with an unclear relationship with energy expenditure and require further evaluation.

CONCLUSIONS

An important interval step in the development of accurate formulae for energy expenditure estimation is a better understanding of relationships between patient and clinical factors and energy expenditure. The review highlights the limitations of currently available data, and identifies important factors that are not included in current prediction formulae of the critically ill.

The effectiveness of noise interventions in the ICU

PURPOSE OF REVIEW

Excessive noise has direct adverse physiological and psychological effects, and may also have indirect negative health consequences by reducing sleep quality and quantity. This review presents a synthesis of the epidemiology of noise in the ICU, and the potential interventions designed to attenuate noise and protect patients.

RECENT FINDINGS

Noise increases cortisol release, oxygen consumption, and vasoconstriction. ICU noise levels are excessive throughout the 24-h cycle, irrespective of level of intervention or whether the patient is in a side room or open ward. Direct measurement suggests that noise is a substantial contributor to poor sleep quantity and quality in the ICU and is frequently recalled by survivors of critical illness as a negative experience of ICU admission. Noise abatement, environmental masking and pharmacological interventions may all reduce the impact of noise on patients. However, the sustainability of behavioural interventions remains uncertain and high-quality evidence demonstrating the benefit of any intervention on patient-centered outcomes is lacking.

SUMMARY

Noise levels in the ICU are consistently reported to reach levels likely to have both direct and indirect adverse health consequences for both patients and staff. Noise reduction, abating the transmission of noise and pharmacological modulation of the adverse neural effects of noise are all potentially beneficial strategies, although definitive evidence of improved patient-centered outcomes is lacking.

Sleep in the Intensive Care Unit

Patients in the intensive care unit (ICU) are susceptible to sleep deprivation. Disrupted sleep is associated with increased morbidity and mortality in the critically ill patients. The etiology of sleep disruption is multifactorial. The article reviews the literature on sleep in the ICU, the effects of sleep deprivation, and strategies to promote sleep in the ICU. Until the impact of disrupted sleep is better explained, it is appropriate to provide critically ill patients with consolidated, restorative sleep.

Adequacy of early enteral nutrition in adult patients in the intensive care unit

AIMS AND OBJECTIVES

To evaluate the adequacy of energy and protein intake of patients in a Korean intensive care unit in the first four days after initiation of enteral feeding and to investigate the factors that had impact on adequate intake.

BACKGROUND

Underfeeding is a common problem for patients hospitalised in the intensive care unit and is associated with severe negative consequences, including increased morbidity and mortality.

DESIGN

A prospective, cohort study was conducted in a medical intensive care unit of a university hospital in Korea.

METHODS

A total of 34 adult patients who had a primary medical diagnosis and who had received bolus enteral nutrition for the first four days after initiation of enteral nutrition were enrolled in this study. The data on prescription and intake of energy and protein, feeding method and feeding interruption were recorded during the first four days after enteral feeding initiation. Underfeeding was defined as the intake <90% of required energy and protein.

RESULTS

Most patients (62%) received insufficient energy, although some (29%) received adequate energy. More than half of patients (56%) had insufficient protein intake during the first four days after enteral feeding was initiated. Logistic regression analysis showed that the factors associated with underfeeding of energy were early initiation of enteral nutrition, under-prescription of energy and prolonged interruption of prescribed enteral nutrition.

CONCLUSION

Underfeeding is frequent in Korean critically ill patients owing to early initiation, under-prescription and prolonged interruption of enteral feeding.

RELEVANCE TO CLINICAL PRACTICE

  Interventions need to be developed and tested that address early initiation, under-prescription and prolonged interruption of enteral nutrition. Findings from this study are important as they form the foundation for the development of evidence-based care that is badly needed to eliminate underfeeding in this large vulnerable Korean intensive care unit population.

Energy expenditure of critically ill neonatal foals

REASONS FOR PERFORMING STUDY

Nutritional support in critically ill neonatal foals is of great importance given their high metabolic rate and minimal stores of energy and protein. Nutrient requirements of healthy growing foals have been estimated based on daily milk intake; however, little is known about the resting energy expenditure (REE) of sick foals.

OBJECTIVES

To determine REE in critically ill neonatal foals (sepsis and/or hypoxic-ischaemic encephalopathy [HIE] and compare this with REE in control foals.

METHODS

Critically ill newborn foals admitted to the Fundació Hospital Clinic Veterinari, Universitat Autònoma de Barcelona, Spain from March 2009 to February 2011 were included in this study. Healthy neonatal foals and foals with nonsystemic conditions were used as controls. Oxygen consumption and CO2 production were measured with a respiratory monitor connected to a tight fitting facemask and REE (kcal/kg bwt/day) was calculated with the abbreviated Weir formula. Measurements were performed within 24 h of admission and repeatedly during hospitalisation.

RESULTS

Twenty-seven foals were included (16 critically ill foals and 11 controls) and a total of 47 measurements were performed. In the critically ill, REE was reduced (mean +/- s.e. 49.5 +/- 2.1 kcal/kg bwt/day) on admission relative to the controls. In surviving foals (n = 5), REE before hospital discharge was not different (68.4 +/- 7.0 kcal/kg bwt/day) from control foals (64.8 +/- 2.7 kcal/kg bwt/day).

CONCLUSIONS

REE was lower in critically ill foals upon admission (40-50 kcal/kg bwt/day) and normalised before hospital discharge (60-80 kcal/kg bwt/day).

POTENTIAL RELEVANCE

Critically ill neonatal foals tolerating enteral feeding would receive approximately their REE when given 10% of their bodyweight in mare's milk daily. For sick neonates unable to tolerate enteral nutrition, provision of 50 kcal/kg bwt/day would be a reasonable goal for parenteral nutrition.

Resting energy expenditure after Fontan surgery in children with single-ventricle heart defects

BACKGROUND

Data on resting energy expenditure (REE) and oxygen consumption (VO(2)) after pediatric cardiopulmonary bypass (CPB) will facilitate optimal nutrient prescription.

METHODS

The authors measured continuous REE and VO(2), using an in-line indirect calorimetery (IC) in 30 consecutive children with single-ventricle physiology immediately after Fontan surgery. REE during steady state at 8 hours after surgery was compared with standard equation-estimated energy expenditure (EEE). Patients were classified into 3 groups: hypermetabolic (measured REE [MREE]/EEE ratio >1.2), hypometabolic (MREE/EEE ratio <0.8), and normometabolic (MREE/EEE ratio 0.8-1.2). Demographic, anthropometric, and perioperative clinical characteristics were examined for their correlation with metabolic status.

RESULTS

In 26 of 30 patients with completed IC, mean REE at 8 hours after surgery was 57 ± 20 kcal/kg/d, and mean VO(2) was 110 ± 35 mL/min. Mean values of VO(2) and REE did not change within the first 24 hours after surgery. There was poor correlation between MREE at 8 hours and the EEE using the World Health Organization equation (r = 0.32, P = .11). Most patients (n = 19, 73%) were either normometabolic or hypometabolic. Lack of hypermetabolism was significantly associated with higher intraoperative serum lactate level and positive fluid balance compared with the rest of the group.

CONCLUSIONS

The authors report a low prevalence of hypermetabolism in children with single-ventricle defects after Fontan surgery. Measured REE had poor correlation with equation-estimated energy expenditure in a majority of the cohort. The absence of increased energy expenditure after CPB will influence energy prescription in this group.

Sleep deprivation in critical illness: its role in physical and psychological recovery

Critically ill patients frequently experience poor sleep, characterized by frequent disruptions, loss of circadian rhythms, and a paucity of time spent in restorative sleep stages. Factors that are associated with sleep disruption in the intensive care unit (ICU) include patient-ventilator dysynchrony, medications, patient care interactions, and environmental noise and light. As the field of critical care increasingly focuses on patients' physical and psychological outcomes following critical illness, understanding the potential contribution of ICU-related sleep disruption on patient recovery is an important area of investigation. This review article summarizes the literature regarding sleep architecture and measurement in the critically ill, causes of ICU sleep fragmentation, and potential implications of ICU-related sleep disruption on patients' recovery from critical illness. With this background information, strategies to optimize sleep in the ICU are also discussed.

The serotonergic anatomy of the developing human medulla oblongata: implications for pediatric disorders of homeostasis

The caudal serotonergic (5-HT) system is a critical component of a medullary "homeostatic network" that regulates protective responses to metabolic stressors such as hypoxia, hypercapnia, and hyperthermia. We define anatomically the caudal 5-HT system in the human medulla as 5-HT neuronal cell bodies located in the raphé (raphé obscurus, raphé magnus, and raphé pallidus), extra-raphé (gigantocellularis, paragigantocellularis lateralis, intermediate reticular zone, lateral reticular nucleus, and nucleus subtrigeminalis), and ventral surface (arcuate nucleus). These 5-HT neurons are adjacent to all of the respiratory- and autonomic-related nuclei in the medulla where they are positioned to modulate directly the responses of these effector nuclei. In the following review, we highlight the topography and development of the caudal 5-HT system in the human fetus and infant, and its inter-relationships with nicotinic, GABAergic, and cytokine receptors. We also summarize pediatric disorders in early life which we term "developmental serotonopathies" of the caudal (as well as rostral) 5-HT domain and which are associated with homeostatic imbalances. The delineation of the development and organization of the human caudal 5-HT system provides the critical foundation for the neuropathologic elucidation of its disorders directly in the human brain.

Using drug probes to monitor hepatic drug metabolism in critically ill patients: midazolam, a flawed but useful tool for clinical investigation of CYP3A activity?

IMPORTANCE OF THE FIELD

In the UK, acute kidney injury (AKI) occurs in 25% of patients admitted to intensive care. Outcome is worsened in the presence of AKI for reasons not easily explained. AKI unpredictably affects the pharmacokinetics and pharmacodynamics of drugs and dosing in patients with AKI is largely based on data from chronic kidney disease patients, but how appropriately is unknown.

AREAS COVERED IN THIS REVIEW

Midazolam as a drug probe of CYP3A activity is reviewed, with discussion of its limitations and alternatives in critically ill patients. Pharmacogenetics of CYP3A enzymes and their significance are discussed and emerging evidence that AKI affects liver metabolism is reviewed.

WHAT THE READER WILL GAIN

The aim is to give the reader insight into the complexities of in vivo research in critically ill patient with discussion of interaction between the kidney and liver. We explain the use of midazolam as a drug probe for the investigation of the effect of AKI on hepatic function.

TAKE HOME MESSAGE

Critically ill patients are difficult to manage but methods are now available for investigation of complex interrelationships that complicate the care and management of these patients with the potential to improve safety, efficacy and outcome, particularly for drug administration.

Oxygen consumption is depressed in patients with lactic acidosis due to biguanide intoxication

INTRODUCTION

Lactic acidosis can develop during biguanide (metformin and phenformin) intoxication, possibly as a consequence of mitochondrial dysfunction. To verify this hypothesis, we investigated whether body oxygen consumption (VO2), that primarily depends on mitochondrial respiration, is depressed in patients with biguanide intoxication.

METHODS

Multicentre retrospective analysis of data collected from 24 patients with lactic acidosis (pH 6.93 +/- 0.20; lactate 18 +/- 6 mM at hospital admission) due to metformin (n = 23) or phenformin (n = 1) intoxication. In 11 patients, VO2 was computed as the product of simultaneously recorded arterio-venous difference in O2 content [C(a-v)O2] and cardiac index (CI). In 13 additional cases, C(a-v)O2, but not CI, was available.

RESULTS

On day 1, VO2 was markedly depressed (67 +/- 28 ml/min/m2) despite a normal CI (3.4 +/- 1.2 L/min/m2). C(a-v)O2 was abnormally low in both patients either with (2.0 +/- 1.0 ml O2/100 ml) or without (2.5 +/- 1.1 ml O2/100 ml) CI (and VO2) monitoring. Clearance of the accumulated drug was associated with the resolution of lactic acidosis and a parallel increase in VO2 (P < 0.001) and C(a-v)O2 (P < 0.05). Plasma lactate and VO2 were inversely correlated (R2 0.43; P < 0.001, n = 32).

CONCLUSIONS

VO2 is abnormally low in patients with lactic acidosis due to biguanide intoxication. This finding is in line with the hypothesis of inhibited mitochondrial respiration and consequent hyperlactatemia.

Laboratory validation of the M-COVX metabolic module in measurement of oxygen uptake

A practical method of breath-by-breath monitoring of metabolic gas exchange has previously been developed by GE Healthcare and can now be easily incorporated into existing anaesthetic and critical care monitoring (M-COVX). Previous research using this device has shown good accuracy and precision between the M-COVX measurements and a traditional measurement of gas uptake at the mouth and also against the reverse Fick method during cardiac surgery and critical care, but its accuracy in the paediatric situation and across a range of ventilatory settings awaits validation. We tested the M-COVX metabolic monitor in the laboratory comparing its measurement to a traditional Haldane transformation across a wide range of oxygen consumption values, from 50 ml/minute to just under 300 ml/minute, typical of those expected in anaesthetised adults and children. The M-COVX device showed acceptable accuracy with an overall mean bias of -3.3% (range -15.1 to +4.2%, P = 0.21). Excellent linearity was found, by y = 0.96x + 0.5 ml/minute, r = 0.99. The device showed acceptable robustness to ventilatory changes examined, including changes in respiratory rate, I:E ratio, FiO2 up to 75% and simulated spontaneous breathing. However any induced leak from around the simulated endotracheal tube caused a significant error in paediatric scenarios.

Sleep and critical care

PURPOSE OF REVIEW

Sleep distortion has been studied as an independent risk factor for morbidity and mortality; however, this role in the ICU patients is unclear. These patients suffer from psychological and physiological stressors and significant disturbance in sleep. We conducted a systematic review of all recent data over the last decade to elaborate the extent and implications of sleep disruption in the ICU.

RECENT FINDINGS

Despite adequate data proving that ICU patients have poor quality of sleep over the last three decades, the implications of the sleep distortion in this patient population remains misunderstood. Recently, the Whitehall cohort trial has raised interest in sleep and mortality and substantial data have surfaced regarding prevalence of sleep disturbance in the ICU.

SUMMARY

This article discusses the available data on sleep disruption in patients in the ICU and implications with discussion of effects of ventilators and commonly used medications in the ICU. We will conclude with interventions to improve sleep in the intensive care setting.

Mitochondrial function in sepsis: acute phase versus multiple organ failure

OBJECTIVE

To describe temporal changes in mitochondrial function during the septic process, including the recovery phase.

DESIGN

Literature review.

SUBJECTS

Clinical studies and laboratory models.

MAIN RESULTS

Biochemical and ultrastructural mitochondrial abnormalities have been recognized in in vivo, ex vivo, and in vitro laboratory models of sepsis for >30 yrs. Short-term models show variable effects on mitochondrial function and structure; this is likely related to differences in model design, including species, organs studied, degree of septic insult, and degree of resuscitation. Longer-term models more consistently reveal mitochondrial dysfunction and damage. There is a rebound increase in oxygen consumption and resting energy expenditure in the recovery phase of sepsis. This could reflect mitochondrial recovery (biogenesis) that may restore the energy supply needed to fuel restorative metabolic processes and enable patient survival.

CONCLUSION

Mitochondrial dysfunction seems to be intrinsically involved in the pathogenesis of multiple organ failure. As a consequence of a progressive decrease in energy availability, metabolism must decrease or the cell will die. The interplay between adenosine 5'-triphosphate supply and demand, dictated by the degree of mitochondrial dysfunction and the level of metabolic shutdown (analogous to a hibernation-type response), seems to be crucial in determining outcome. Further studies are needed to confirm this hypothesis.

Energy expenditure in critically ill children

OBJECTIVE

To assess the measured resting energy expenditure pattern over time in a group of critically ill children who were admitted to a pediatric intensive care unit and to determine whether a hypermetabolic response, i.e., >10% above predicted, occurred in a pattern similar to that observed in adults. A secondary aim was to compare the accuracy of a newly derived prediction equation specific to the pediatric intensive care unit and the measured resting energy expenditure.

DESIGN

A prospective, clinical, observational study.

SETTING

A pediatric intensive care unit of a tertiary care medical center.

PATIENTS

Forty-four children (29 males, 15 females) ages 2 wks to 17 yrs.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

During the course of their stay in the pediatric intensive care unit, 44 patients' measured resting energy expenditure was assessed using indirect calorimetry 94 times at up to three time points. The first measurement was at a mean time of 25 +/- 10 (+/-sd) hrs after admission, the second at 73 +/- 16 hrs, and the third immediately before discharge, which occurred at a mean of 193 +/- 93 hrs after admission. Measured energy expenditure varied only slightly (7% to 10%) from the first to second and the second to third measurements. Evidence for hypermetabolism was not apparent. Generally, the prediction equations performed well. Mean measured resting energy expenditure for all measurements was 821 +/- 653 kcals/24 hrs. The Schofield equation estimate was 798 +/- 595 kcals/24 hrs and the White equation estimate was 815 +/- 564 kcals/24 hrs (p = not significant). Nineteen (20%) measurements were >110% above the age-appropriate Schofield-predicted equation, and 30 measurements (32%) were <90% below that predicted by Schofield. Consequently, 45% of measured resting energy expenditure measurements were within 90% to 110% of that predicted by the Schofield equation. The White equation was inaccurate (not within 10% of measured resting energy expenditure) in 66 of 94 measurements (70%). The discrepancy was greatest (100%) in children with measured resting energy expenditure <450 kcal/24 hrs.

CONCLUSION

The hypermetabolic response apparent in adults was not evident in these critically ill children. Currently available prediction equations cannot substitute for indirect calorimetry measurement of energy expenditure in guiding nutritional support in pediatric intensive care units.

Ventilatory changes following head-up tilt and standing in healthy subjects

Passive tilting increases ventilation in healthy subjects; however, controversy surrounds the proposed mechanism. This study is aimed to evaluate the possible mechanism for changes to ventilation following passive head-up tilt (HUT) and active standing by comparison of a range of ventilatory, metabolic and mechanical parameters. Ventilatory parameters (V (T), V (E), V (E)/VO(2), V (E)/VCO(2), f and PetCO(2)), functional residual capacity (FRC), respiratory mechanics with impulse oscillometry; oxygen consumption (VO(2)) and carbon dioxide production (VCO(2)) were measured in 20 healthy male subjects whilst supine, following HUT to 70 degrees and unsupported standing. Data were analysed using a linear mixed model. HUT to 70 degrees from supine increased minute ventilation (V (E)) (P<0.001), tidal volume (V (T)) (P=0.001), ventilatory equivalent for O(2) (V (E)/VO(2)) (P=0.020) and the ventilatory equivalent for CO(2) (V (E)/VCO(2)) (P<0.001) with no change in f (P=0.488). HUT also increased FRC (P<0.001) and respiratory system reactance (X5Hz) (P<0.001) with reduced respiratory system resistance (R5Hz) (P=0.004) and end-tidal carbon dioxide (PetCO(2)) (P<0.001) compared to supine. Standing increased V (E) (P<0.001), V (T) (P<0.001) and V (E)/VCO(2) (P=0.020) with no change in respiratory rate (f) (P=0.065), V (E)/VO(2) (P=0.543). Similar changes in FRC (P<0.001), R5Hz (P=0.013), X5Hz (P<0.001) and PetCO(2) (P<0.001) compared to HUT were found. In contrast to HUT, standing increased VO(2) (P=0.002) and VCO(2) (P=0.048). The greater increase in V (E) in standing compared to HUT appears to be related to increased VO(2) and VCO(2) associated with increased muscle activity in the unsupported standing position. This has implications for exercise prescription and rehabilitation of critically ill patients who have reduced cardiovascular and respiratory reserve.

Clinical evaluation of hormonal stress state in medical ICU patients: a prospective blinded observational study

OBJECTIVE

To evaluate whether classification of patients as having low, moderate, or high stress based on clinical parameters is associated with plasma levels of stress hormone.

DESIGN AND SETTING

Prospective, blinded, observational study in an 18-bed medical ICU.

PATIENTS

Eighty-eight consecutive patients.

INTERVENTIONS

Patients were classified as low (n=28), moderate (n=33) or high stress (n=27) on days 0 and 3 of ICU stay, based on 1 point for each abnormal parameter: body temperature, heart rate, systemic arterial pressure, respiratory rate, physical agitation, presence of infection and catecholamine administration. The stress categories were: high: 4 points or more, moderate 2-3 points, low 1 point. Plasma growth hormone (GH), insulin-like growth factor 1 (IGF-1), insulin, glucagon, cortisol were measured on days 0 and 3.

MEASUREMENTS AND RESULTS

Plasma cortisol and glucagon were significantly higher and IGF-1 lower in high vs. low stress patients on days 0 and 3. High stress patients were more likely to have high cortisol levels (odds ratio 5.8, confidence interval 1.8-18.9), high glucagon (8.7, 2.1-36.1), and low IGF-1 levels (5.9, 1.8-19.0) than low stress patients on day 0. Moderate stress patients were also more likely to have high cortisol and glucagon levels than low stress patients. Insulin and GH did not differ significantly. Results were similar for day 3.

CONCLUSIONS

Moderate and severe stress was significantly associated with high catabolic (cortisol, glucagon) and low anabolic (IGF-1) hormone levels. The hormonal stress level in ICU patients can be estimated from simple clinical parameters during routine clinical evaluation.

Complement C5 and early oxygen kinetics during murine sepsis

OBJECTIVES

Changes in oxygen consumption (VO(2)) and carbon dioxide production (VCO(2)) are common but poorly understood features of sepsis. The authors studied the role of complement C5 in the development of abnormal oxygen kinetics during sepsis in mice, arguing that as a pro-inflammatory event, complement activation might exacerbate disturbances in oxygen use during abdominal sepsis.

METHODS

An open-circuit indirect calorimeter was used to measure VO(2), VCO(2), and respiratory exchange ratio during a seven-day median lethal dose (LD(50)) murine cecal ligation and puncture (CLP) model.

RESULTS

CLP produced significant changes in oxygen kinetics within three hours of onset, although when the animals were stratified by seven-day survival, no difference in these abnormalities was seen between the survivors and the nonsurvivors. Genetic deficiency of C5 did not ameliorate the changes in oxygen utilization. Rather, the C5-deficient mice experienced more severe abnormalities in oxygen kinetics and greater mortality. Treating animals with anti-C5a antibodies at the time of injury had little effect on oxygen kinetics, indicating that C5b, rather than C5a, was predominantly acting to protect the mice during the first 24 hours of illness.

CONCLUSIONS

These findings indicate that the primary contribution of C5 to oxygen kinetics during sepsis is salutary through the host defense conveyed by generation of C5b, rather than detrimental by worsening oxygen utilization via pro-inflammatory mechanisms.

Effects of an immune-enhancing diet in endotoxemic rats

OBJECTIVE

This work compared the nutritional efficiency of a recently available enteral formula enriched with arginine, omega-3 fatty acids, and antioxidants and supplied nitrogen as peptides (Crucial, Nestle Clinical Nutrition) with that of a standard polymeric formula (Sondalis HP, Nestle Clinical Nutrition) in endotoxemic rats.

METHODS

Male Wistar rats (209 +/- 2 g) underwent catheter gastrostomy and received Sondalis HP until they recovered their preoperative weight. At that time (day 0), an endotoxemic shock was induced by an intraperitoneal injection of lipopolysaccharide (Escherichia coli, 8 mg/kg) and rats then received 290 kcal x kg(-1) x d(-1) and 3.29 g of nitrogen x kg(-1) x d(-1) in the form of Crucial (IED group, n = 7) or Sondalis HP (S group, n = 6) for 3 d. Another group underwent no treatment and was fed ad libitum (AL group). Rats were killed on day 3. Results are presented as mean +/- standard error of the mean (analysis of variance and Newman-Keuls test).

RESULTS

The endotoxemic shock induced a weight loss in group S on days 1 and 2 and a weight gain in group IED (-3.5 +/- 1.3 g in group S versus +6.0 +/- 2.2 g in group IED, P < 0.05). In the same way, atrophy of extensor digitorum longus muscle was observed in group S, whereas wasting was limited in group IED (102 +/- 4 mg in group IED versus 90 +/- 3 mg in group S versus 119 +/- 3 mg in group AL, P < 0.05). Muscular atrophy was associated with muscular glutamine depletion and correlated with hyperphenylalaninemia (R = 0.60), with the latter being blunted in group IED (57 +/- 1 microM/L in group AL versus 77 +/- 4 microM/L in group S versus 66 +/- 2 microM/L in group IED, P < 0.05). No difference was observed between the experimental groups of endotoxemic rats with respect to nitrogen balance, urinary excretion of 3-methyl histidine, or total tissue protein content.

CONCLUSION

Crucial counteracts injury-mediated weight loss, extensor digitorum longus muscle atrophy, and hyperphenylalaninemia in endotoxemic rats.

Optimum treatment of severe sepsis and septic shock: evidence in support of the recommendations

Severe sepsis and septic shock are among the most common causes of death in noncoronary intensive care units. The incidence of sepsis has been increasing over the past two decades, and is predicted to continue to rise over the next 20 years. While our understanding of the complex pathophysiologic alterations that occur in severe sepsis and septic shock has increased greatly asa result of recent clinical and preclinical studies, mortality associated with the disorder remains unacceptably high. Despite these new insights, the cornerstone of therapy continues to be early recognition, prompt initiation of effective antibiotic therapy, and source control, and goal-directed hemodynamic, ventilatory,and metabolic support as necessary. To date, attempts to reduce mortality with innovative, predominantly anti-inflammatory therapeutic strategies have been extremely disappointing. Observations of improved outcomes with physiologic doses of corticosteroid replacement therapy and activated protein C (drotrecogin alfa[activated]) have provided new adjuvant therapies for severe sepsis and septic shock in selected patients. This article reviews the components of sepsis management and discusses the available evidence in support of these recommendations. In addition, there is a discussion of some promising new strategies.

Assessment of resting energy expenditure in mechanically ventilated patients

BACKGROUND

Usual equations for predicting resting energy expenditure (REE) are not appropriate for critically ill patients, and indirect calorimetry criteria render its routine use difficult.

OBJECTIVE

Variables that might influence the REE of mechanically ventilated patients were evaluated to establish a predictive relation between these variables and REE.

DESIGN

The REE of 70 metabolically stable, mechanically ventilated patients was prospectively measured by indirect calorimetry and calculated with the use of standard predictive models (Harris and Benedict's equations corrected for hypermetabolism factors). Patient data that might influence REE were assessed, and multivariate analysis was conducted to determine the relations between measured REE and these data. Measured and calculated REE were compared by using the Bland-Altman method.

RESULTS

Multivariate analysis retained 4 independent variables defining REE: body weight (r(2) = 0.14, P < 0.0001), height (r(2) = 0.11, P = 0.0002), minute ventilation (r(2) = 0.04, P = 0.01), and body temperature (r(2) = 0.07, P = 0.002): REE (kcal/d) = 8 x body weight + 14 x height + 32 x minute ventilation + 94 x body temperature - 4834. REE calculated with this equation was well correlated with measured REE (r(2) = 0.61, P < 0.0001). Bland-Altman plots showed a mean bias approaching zero, and the limits of agreement between measured and predicted REE were clinically acceptable.

CONCLUSION

Our results suggest that REE estimated on the basis of body weight, height, minute ventilation, and body temperature is clinically more relevant than are the usual predictive equations for metabolically stable, mechanically ventilated patients.

Clinical evaluation of a continuous oxygen consumption monitor in mechanically ventilated patients

We measured oxygen consumption using a new noninvasive modular metabolic monitor, M-COVX trade mark, in ventilated critically ill patients. Oxygen consumption was measured continuously as part of routine monitoring for up to 24 h following mechanical ventilation in 27 patients admitted to a general intensive care unit. We explored several possible sources of error. Most errors related to inaccurate tidal volume measurement, which resulted in rejection of a median 14% (interquartile range 8-34%) of data. Water accumulation in the pneumotachograph was responsible and occurred more frequently with water bath humidifiers. After manual removal of erroneous data mean oxygen consumption values were virtually identical to calculated values in 24 of 27 patients. We conclude that in most ventilated patients averaging of continuous oxygen consumption data with the M-COVX module results in small errors.

Effect of sepsis syndrome on neonatal oxygen consumption and energy expenditure

OBJECTIVE

To evaluate oxygen consumption (VO2), carbon dioxide production, and energy expenditure (EE) in full-term neonates with early-onset neonatal septicemia daily for 7 days beginning at the day of clinical diagnosis of sepsis.

METHODS

A total of 17 spontaneously breathing full-term neonates, 10 with clinical signs of sepsis and 7 healthy neonates (control group), were enrolled in the study. Age at first study day was 3 +/- 0.9 days in both groups. Sepsis syndrome was defined as a systemic response to a bacterial infection with clinical signs of infection, elevated values of interleukins 6 and 8 and C-reactive protein, and abnormal white blood cell count and positive blood cultures (9 group B streptococci, 1 Escherichia coli). Measurements of VO2 and carbon dioxide production were performed daily for 7 days by means of indirect calorimetry.

RESULTS

In the septic infants, VO2 and EE were increased by about 20% at days 1 to 3 and by 15% at day 4 when compared with the controls. From days 1 to 3, EE averaged 57 +/- 3 kcal/kg/d in the septic neonates and 47 +/- 2 kcal/kg/d in the controls. At day 4, EE was 55 +/- 2 and 47 +/- 2 kcal/kg/d, respectively. Energy intake was about the same in both groups, whereas weight gain during the 7 study days was significantly lower in the sick patients than in the control group (19 +/- 2 g/d vs 33 +/- 9 g/d and 5.4 +/- 0.5 g/kg/d vs 9.4 +/- 2.6 g/kg/d, respectively). Increased EE was associated with increased heart rate (126 +/- 4 vs 112 +/- 4 min(-1) at day 1) and respiratory rate (56 +/- 6 vs 40 +/- 4 min(-1) at day 1). There were no differences in rectal temperature (37.3 +/- 0.4 degrees C vs 37.4 +/- 0.2 degrees C), skin temperature (36.5 +/- 0.4 degrees C vs 36.6 +/- 0.3 degrees C), and oxygen saturation (96 +/- 3% vs 96 +/- 3%) between the 2 groups.

CONCLUSIONS

Neonates with sepsis syndrome have elevated VO2 and EE values that could explain impaired growth during the illness period and may make the infants vulnerable to insufficient calorie supply during the acute phase of septic disease.

Nutritional support in the critically ill child

The nutritional management of a critically ill child is not a glamorous subject and seldom receives the attention that it merits despite increasing evidence that appropriate goal-oriented nutritional support is associated with improved outcome. Current nutritional management is based on rapidly emerging knowledge on the very special nutritional requirements related to the "vastly different metabolic and physiologic characteristics of the hypermetabolic and stressed" critically ill child. There has been significant changes in traditional practice particularly in the area of calorie delivery, amount of macronutrients and route of nutrient delivery in the critically ill child. The critically ill child presents with "greatly disordered nutrient metabolism" and successful nutritional support involves an initial "hypocaloric regime" with a precise mix of carbohydrates, proteins and lipids which need periodic review as the child improves. The therapeutic benefits of minimal enteral feeding (MEF) have been clearly established--MEF being associated with diminished morbidity, infection rates as well as reduced ICU and hospital stays. Immune enhancement has also been shown to be of some benefit in the critically ill but the subject needs further study.

Metabolic response and parenteral nutrition in trauma, sepsis, and burns

Trauma, sepsis, and burns cause abnormal manifestations in the body. These manifestations can cause alterations in body metabolism, which complicates nutritional management. Goals of nutrition support with assessment modifications for a constantly changing population are reviewed. Patients in such stress states as burns, trauma, and sepsis many times need altered nutrition. This article outlines guidelines for total parenteral formula modification and monitoring, and discusses other complications such as drug interactions with parenteral formulas.

Similar metabolic responses to standardized total parenteral nutrition of septic and nonseptic critically ill patients

BACKGROUND

Nutritional support is an important link between the response to injury and recovery in critical illness.

OBJECTIVE

Our goal was to evaluate energy and substrate metabolism in septic and nonseptic critically ill patients in the resting state and during the administration of standardized total parenteral nutrition.

DESIGN

This was a prospective, clinical cohort study of 25 consecutively admitted critically ill patients either with (n = 14) or without (n = 11) sepsis who received total parenteral nutrition. Resting energy expenditure was measured on days 0, 2, and 7 by indirect calorimetry. Energy and substrate balances were calculated on days 2 and 7.

RESULTS

Resting energy expenditure was not significantly different between septic and nonseptic patients on day 0 (2.65 +/- 0.49 and 2.36 +/- 0.56 kJ x min(-1) x m(-2), respectively). Energy balances were positive for both groups on days 2 (0.68 +/- 0.4 and 0.74 +/- 0.6 kJ x min(-1) x m(-2), respectively; NS) and 7 (0.65 +/- 0.3 and 0.78 +/- 0.5 kJ x min(-1) x m(-2), respectively; NS). Substrate balances were not significantly different between groups on days 0, 2, and 7. Resting energy expenditure on day 0 was negatively correlated with the severity of illness in septic patients only (r = -0.58, P < 0.05).

CONCLUSIONS

Metabolic changes were not significantly different between septic and nonseptic critically ill patients during the administration of standardized total parenteral nutrition. A disease-specific macronutrient composition of total parenteral nutrition formulas does not seem to be necessary in either septic or nonseptic critically ill patients.

Pediatric sepsis and multiple organ dysfunction syndrome

Systemic inflammatory response syndrome may be viewed as the systemic expression of cytokine signals that normally function on an autocrine or paracrine level. Sepsis is defined as systemic inflammatory response syndrome caused by an infection. Multiple organ dysfunction syndrome may represent the end stage of severe systemic inflammatory response syndrome or sepsis. Many cells are involved, including endothelial cells and leukocytes and multiple proinflammatory and antiinflammatory mediators (cytokines, oxygen free radicals, coagulation factors, and so forth). Various pathophysiologic mechanisms have been postulated. The most popular theory is that the inflammatory process loses its autoregulatory capacity; however, microcirculatory dysregulation and apoptosis may also be important, and a new paradigm posits a complex nonlinear system. Many new treatments have been studied recently. The usefulness of immune modulating diets remains to be evaluated. Molecular immunomodulation is still of unclear value. The therapy of sepsis and multiple organ dysfunction syndrome remains mainly supportive.

Oxygen consumption, carbon dioxide production and lactic acid during normothermic cardiopulmonary bypass

The objective of this study was to measure oxygen consumption, carbon dioxide production and lactic acid levels during normothermic cardiopulmonary bypass. A prospective study was undertaken in a tertiary care community hospital, involving 20 adults undergoing cardiopulmonary bypass with prolonged (>65 min) crossclamping of the aorta. O2 consumption, CO2 production, hemoglobin and lactic acid levels were measured 5, 35 and 65 min after crossclamping of the aorta. O2 consumption was 79.7 +/- 14.5, 78.8 +/- 15.4 and 81.5 +/- 14.1 ml/min/m2 at 5, 35 and 65 min after crossclamping the aorta. CO2 production was 61.8 +/- 42.9, 60.6 +/- 26.3 and 62.2 +/- 35.9 ml/min/m2 at the same times. Lactic acid levels were 1.6 +/- 0.5 mM/dl at all three times and did not correlate with O2 consumption or CO2 production. In conclusion, although oxygen consumption was low, there was no evidence of abnormal lactate or anaerobic metabolism to suggest tissue ischemia.

Nutritional support in sepsis: still skeptical?

The immediate metabolic response to a septic challenge is probably adaptive, meaning that nutritional interference, mainly via the parenteral route, during this early phase of instability can do more harm than good. During the later phases, a gradual increase in enteral nutrition, at the expense of parenteral nutrition, combined with the administration of nutraceuticals such as glutamine and omega-3 fatty acids, can counteract wasting and modulate the complex inflammatory response and immunosuppression associated with sepsis. In these times of scarce resources, there is an urgent need to clearly document the efficacy of immuno/pharmaconutrients, individually and in combination, enterally or parenterally, before proposing them for routine management of septic patients in the intensive care unit.