Oxygen consumption in the early postinjury period: use of continuous, on-line indirect calorimetry

Extremity trauma exacerbates acute kidney injury following prolonged hemorrhagic hypotension

BACKGROUND

The incidence of and mortality due to acute kidney injury is high in patients with traumatic shock. However, it is unclear how hemorrhage and trauma synergistically affect renal function, especially when timely volume resuscitation is not available.

METHOD

We hypothesized that trauma impairs renal tolerance to prolonged hemorrhagic hypotension. Sprague-Dawley rats were randomized into six groups: control, extremity trauma (ET), hemorrhage at 70 mm Hg (70-H), hemorrhage at 55 mm Hg (55-H), ET + 70 mm Hg (70-ETH), and ET + 55 mm Hg (55-ETH). Animals were anesthetized, and ET was induced via soft tissue injury and closed fibula fracture. Hemorrhage was performed via catheters 5 minutes after ET with target mean arterial pressure (MAP) clamped at 70 mm Hg or 55 mm Hg for up to 3 hours. Blood and urine samples were collected to analyze plasma creatinine (Cr), Cr clearance (CCr), renal oxygen delivery (DO2), urinary albumin, and kidney injury molecule-1 (KIM-1).

RESULTS

Extremity trauma alone did not alter renal hemodynamics, DO2, or function. In 70-H, CCr was increased following hemorrhage, while Cr, renal vascular resistance (RVR), KIM-1, and albumin levels remained unchanged. Compared with 70-H, ET + 70 mm Hg exhibited increases in Cr and RVR with decreases in CCr and DO2. In addition, ET decreased the blood volume loss required to maintain MAP = 70 mm Hg by approximately 50%. Hemorrhage at 55 mm Hg and ET + 55 mm Hg exhibited a marked and similar decrease in CCr and increases in RVR, Cr, KIM-1, and albumin. However, ET greatly decreased the blood volume loss required to maintain MAP at 55 mm Hg and led to 50% mortality.

CONCLUSION

These results suggest that ET impairs renal and systemic tolerance to prolonged hemorrhagic hypotension. Thus, traumatic injury should be considered as a critical component of experimental studies investigating outcomes and treatment following hemorrhagic shock.

LEVEL OF EVIDENCE

This is an original article on basic science and does not require a level of evidence.

Energy Expenditure and Protein Requirements After Traumatic Injury

Traumatic injury induces hypermetabolism. The degree of hypermetabolism can be variable, depending on the type of injury, the degree of inflammation, body composition, age, and treatment regimens. To estimate metabolic rate in some types of injury, predictive equations have been published. Some of these equations have been tested in validation studies. For other types of injury, equations do not exist. Some expert panels have recommended measuring in lieu of estimating metabolic rate, though studies have not been performed to determine whether clinical outcome is affected by the method used to determine energy requirements. Traumatically injured patients are usually catabolic, but protein needs after traumatic injury continue to be debated. Some suggest that 1.5 g protein per kg body weight is adequate and that any additional protein is simply oxidized, adding to the nitrogen load to be excreted. Alternately, protein intake >2.0 g/kg body weight increases the absolute rate of body protein synthesis, and achievement of nitrogen balance has been associated with survival. Thus, provision of high-protein feeding to achieve nitrogen balance might be worthwhile, even if that balance is achieved at the cost of additional nitrogen production.

Coagulopathy and traumatic shock: characterizing hemostatic function during the critical period prior to fluid resuscitation

AIMS

Identifying early changes in hemostatic clot function as a result of tissue injury and hypoperfusion may provide important information regarding the mechanisms of traumatic coagulopathy. A combat-relevant swine model was used to investigate the development of coagulopathy during trauma by monitoring hemostatic function during increasing severity of shock.

METHODS

Swine were injured (soft tissue+femur fracture) and hemorrhaged while continuously monitoring Oxygen Debt (OD) by indirect calorimetry at the airway. Hemostatic function was assessed by Thrombelastography (TEG), Prothrombin Time (PT), Partial Thromboplastin Time (PTT), and fibrinogen concentration and compared before hemorrhage (D0) and during shock when OD=40 and 80 ml/kg. An instrumented sham group was used for comparison.

RESULTS

N=23 swine (N=18 hemorrhage, N=5 sham) weighing 45+/-6 kg were studied after removing an average of 34+/-14% of blood volume during hemorrhage. Hgb, Hct, platelet counts, PT and PTT did not change with increasing OD (p<0.05). Fibrinogen was reduced significantly by OD=40 ml/kg (mean diff.=-59.9 mg/dl, 95% CI diff. [-95.1, -24.6]). TEG parameters representing clot initiation (R) and polymerization (K and Alpha Angle) did not change with increasing OD during shock (p>0.053). Clot strength (MA) was reduced in the hemorrhage group by OD=80 ml/kg (mean diff.=-4.1mm, 95% CI diff. [-7.4, -0.8]).

CONCLUSION

In this swine model of traumatic shock, fibrinogen was significantly reduced and an isolated reduction in clot strength (MA) was found with increasing OD. Fibrinogen consumption and altered platelet function may account for the earliest changes in hemostatic function during traumatic shock.

Influence of different ventilator modes on Vo(2) and Vco(2) measurements using a compact metabolic monitor

OBJECTIVE

We assessed the influence of different ventilator modes on carbon dioxide elimination (Vco(2)) and oxygen uptake (Vo(2)) using a new compact modular metabolic monitor (E-COVX) and its impact on calculated respiratory quotient (RQ) and resting energy expenditure (REE) in critically ill children.

METHODS

Sequential 30-min ventilation by pressure-regulated volume controlled ventilation (PRVC), synchronized intermittent mandatory ventilation (SIMV), and biphasic intermittent positive airway pressure/airway pressure release ventilation (BiVent) in mechanically ventilated critically-ill children was assessed. To determine within- or between-day variations, 30-min Vo(2) and Vco(2) measurements were repeated at four separate occasions.

RESULTS

A total of 3960pulmonary 1-min gas exchange measurements were recorded in the 44 sessions for the three ventilator modes. Vo(2), Vco(2), and REE did not differ significantly among the PRVC, SIMV, and BiVent sequence of measurements. RQ (0.86+/-0.1) in the SIMV and Vco(2) (113+/-55mL/min) in the BiVent mode had a higher trend compared with PRVC (0.82+/-0.01, P<0.05, and 103+/-49mL/min, P<0.2, respectively). All three modes displayed good agreement and there were no significant differences between the first and second same-day or between the first- and second-day measurements or sequentially changed ventilator modes. Bland-Altman plots comparing the means of sequential REE, Vo(2), Vco(2), and RQ during the PRVC, SIMV, and BiVent modes of ventilation indicated that the average paired differences were <-5.5%.

CONCLUSION

The influence of different ventilator modes on Vo(2) and Vco(2) measurements in adequately sedated critically ill children is not significant. The E-COVX metabolic module is suitable for repeated measurements in well-sedated mechanically ventilated children with stable respiratory patterns using the PRVC, SIMV, or BiVent modes of ventilation.

Acute trauma with multiple injuries

Trauma with multiple injuries is a leading cause of death. It presents a diversity of challenges and requires many healthcare workers to care for its victims. Advances continue in the organization of pre-hospital care, the techniques of trauma surgery and critical care, and understanding the pathophysiology of traumatic injuries.

Management of the critically ill geriatric patient

OBJECTIVE

To review the effect of an aging society on the utilization of critical care services and the physiology of aging as it applies to critical illness and prognosis and management issues in the intensive care unit (ICU).

DATA SOURCE

MEDLINE, Embase, and citation review of relevant primary and review articles.

DATA SYNTHESIS

Elderly patients (age of >65 yrs) currently account for 42-52% of ICU admissions and for almost 60% of all ICU days. Aging is associated with decreased cardiopulmonary and renal reserve and with a high rate of co-morbidities, increasing the risks of the elderly developing progressive organ failure. Elderly ICU patients are at a particularly high risk of developing delirium, which is associated with significant morbidity. Severity of illness and age are the important factors determining ICU survival. Age and functional status before ICU admission are the major determinants of survival at 6 and 12 months after ICU discharge. Age alone should not be used to triage ICU patients; the decision to admit an elderly patient to an ICU should be based on the patients co-morbidities, acuity of illness, prehospital functional status, and preferences with regard to life-sustaining treatment.

CONCLUSIONS

The management of critically ill elderly patients is a complex issue and involves an understanding of the changing demographics of our society and the physiology of aging. The reality of our aging society dictates that we must focus on how to best care for the elderly who develop critical illness.

Comparison of metabolic monitors in critically ill, ventilated patients

OBJECTIVE

We compared the Deltatrac II, the M-COVX, and the Evita 4 metabolic monitoring devices under clinical conditions.

METHODS

A prospective simultaneous clinical comparison was performed in a general intensive care department of a tertiary university hospital in 43 ventilated, critically ill patients. The monitors were compared simultaneously. After 30 min of steady state, oxygen consumption per unit time, carbon dioxide consumption per unit time, resting energy expenditure, and respiratory quotient were recorded for the Deltatrac II; the same parameters in addition to end-tidal carbon dioxide and fraction of inspired oxygen were recorded for the M-COVX; and carbon dioxide consumption per unit time, end-tidal carbon dioxide, and fraction of inspired oxygen were recorded for the Evita 4. Pulmonary gas-exchange measurements from the Deltatrac II and resting energy expenditure and respiratory quotient from the M-COVX were obtained after 30 min. The other parameters were calculated from the last five measurements obtained at the end of the study period.

RESULTS

A good correlation was found between oxygen consumption per unit time and resting energy expenditure as obtained from the Deltatrac II and the M-COVX (r = 0.76 and 0.75, respectively; P < 0.001), but the correlation was lower between carbon dioxide consumption per unit time as obtained from the Deltatrac II and the M-COVX or Evita 4 (r = 0.67 and 0.48, respectively). Agreement between the different methods did not reach clinical acceptability, exceeding a 20% difference using the Bland-Altman statistical methods.

CONCLUSION

Poor agreement was found between the Deltatrac II and M-COVX or Evita 4 metabolic monitors, despite a good correlation between measurements, leading to the conclusion that the M-COVX and Evita 4 provide less accurate measurements of metabolic gas exchange in stable ventilated patients. These devices can be used for daily nutritional assessment and continuous monitoring, but the Deltatrac II remains the method of choice for metabolic measurement.

Energy expenditure in children with severe head injury: lack of agreement between measured and estimated energy expenditure

BACKGROUND

The purpose of this study was to test the hypotheses that estimates of resting energy expenditure (REE) vary significantly from measured energy expenditure in a population of head-injured children and are not accurate for use in determining nutrition needs in this population.

METHODS

This is a retrospective study of 30 children with severe head injury, with Glasgow Coma Scale (GCS) score of <8 and needing mechanical ventilation. Measured REE was obtained using indirect calorimetry. Estimated REEs were calculated using Harris-Benedict, World Health Organization (WHO), Schofield, and White formulas. Severity of illness was calculated using Pediatric Risk of Mortality (PRISM) score. Agreement between measured REE and estimated REE was tested using the Bland-Altman method. Correlation coefficient between PRISM score and measured REE was calculated using Spearman test.

RESULTS

More than half of the estimates of REE differed from measured REE by >10%. Significant disagreement between estimated REE and measured REE was demonstrated using the Bland-Altman method. There was no correlation between severity of illness and measured REE to explain the inaccuracies of REE estimates.

CONCLUSION

Energy expenditure in critically ill children cannot be estimated accurately; hence, nutrition for critically ill children with head injury should be provided according to measurement of REE to avoid the consequences of overfeeding or malnutrition.

Assessment and management of the geriatric patient

OBJECTIVE

To describe the potential critical care problems that arise as a result of aging and to identify some of the methods that may be used to minimize these problems.

DATA SYNTHESIS

The population of the United States is aging. This is reflected in the age of our surgical patients. Aging is associated with myriad physiologic changes and an increased susceptibility to disease, all of which renders older patient more susceptible to the negative sequela of anesthetic and surgical stress. Minimizing the effects of aging begins preoperatively by assessing the impact of these changes on the individual patient. Once deficits are identified, efforts can be made to correct what is correctable preoperatively and to address what is not by designing an intra- and postoperative plan that limits additional stress to the compromised system. Although good data regarding optimal perioperative management of the elderly patient are presently lacking, awareness of the areas of potential vulnerability allows the anesthesiologist and surgeon to design their treatment plans with these limitations in mind.

CONCLUSION

By identifying the limitations imposed by aging, critical care problems in elderly patients can be anticipated and addressed, and surgical outcomes can be improved.

Predicted versus measured energy expenditure by continuous, online indirect calorimetry in ventilated, critically ill children during the early postinjury period

OBJECTIVE

Compare the energy expenditure, predicted by anthropometric equations, with that measured by continuous on-line indirect calorimetry in ventilated, critically ill children during the early postinjury period.

DESIGN

Prospective, clinical study.

SETTING

Pediatric intensive care unit of a pediatric university hospital.

PATIENTS

A total of 43 ventilated, critically ill children during the first 6 hrs after injury.

INTERVENTIONS

An indirect calorimeter was used to continuously measure the energy expenditure for 24 hrs.

MEASUREMENTS AND MAIN RESULTS

Clinical data collected were age, gender, actual and ideal weight, height, and body surface. Nutritional status was assessed by Waterlow and Shukla Index. Severity of illness was determined by Pediatric Risk of Mortality, Physiologic Stability Index, and Therapeutic Intervention Scoring System. Energy expenditure was measured (MEE) by continuous on-line indirect calorimetry for 24 hrs. Predicted Energy Expenditure (PEE) was calculated using the Harris-Benedict, Caldwell-Kennedy, Schofield, Food and Agriculture/World Health Organization/United Nation Union, Maffeis, Fleisch, Kleiber, Dreyer, and Hunter equations, using the actual and ideal weight. MEE and PEE were compared using paired Student's t-test, linear correlation (r), intraclass correlation coefficient (pI), and the Bland-Altman method. Mean MEE resulted in 674 +/- 384 kcal/day. Most of the predictive equations overestimated MEE in ventilated, critically ill children during the early postinjury period. MEE and PEE differed significantly (p<.05) except when the Caldwell-Kennedy and the Fleisch equations were used. r2 ranged from 0.78 to 0.81 (p<.05), and pI was excellent (>.75) for the Caldwell-Kennedy, Schofield, Food and Agriculture/World Health Organization/United Nation Union, Fleisch, and Kleiber equations. The Bland-Altman method showed poor accuracy; the Caldwell-Kennedy equation was the best predictor of energy expenditure (bias, 38 kcal/day; precision, +/- 179 kcal/day). The accuracy in the medical group was higher (pI range,.71-.94) than in surgical patients (pI range,.18-.75).

CONCLUSIONS

Predictive equations do not accurately predict energy expenditure in ventilated, critically ill children during the early postinjury period; if available, indirect calorimetry must be performed.

Indirect calorimetry: a trend toward continuous metabolic assessment

Physiologic monitoring of the patient's metabolic response to illness and nutritional needs has been available for many decades. Traditional methods for estimating and intermittently assessing the patient's metabolic status provide incomplete and often misleading information. The measurement oxygen consumption (VO2) and carbon dioxide production (VCO2) for assessment of the critically ill patient's metabolic status has been underutilized partly because of the limitations of available technologies. Recent advances in gas exchange technologies have made VO2 and VCO2 assessment readily available at the bedside on a continuous basis. This article provides a clinical review of specific current literature related to indirect calorimetry. A synthesis of the data supports the use of gas exchange measurements of VO2 and VCO2 for serial assessment of metabolic changes and for monitoring of the patient's nutritional status. Furthermore, a multidisciplinary approach to metabolic monitoring and nutritional assessment provides a cost-efficient means of patient care, which, when properly implemented, improves patient outcomes.

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.

Quantitative analysis of the relationship between sedation and resting energy expenditure in postoperative patients

OBJECTIVE

To analyze quantitatively the relationship between sedation and resting energy expenditure or oxygen consumption in postoperative patients.

DESIGN

A prospective, clinical study.

SETTING

An eight-bed intensive care unit at a university hospital.

PATIENTS

Thirty-two postoperative patients undergoing either esophagectomy or surgery of malignant tumors of the head and neck who required mechanical ventilation and sedation for > or = 2 days postoperatively.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A total of 133 metabolic measurements were performed. Ramsay sedation scale (RSS), body temperature, and the dose of midazolam were evaluated at the time of the metabolic cart study. All patients received analgesia with buprenorphine at a fixed dose of 0.625 microg x kg(-1) x hr(-1) continuously. Midazolam was used for induction and maintenance of intravenous sedation after admission to the intensive care unit. The initial dose was 0.04 mg x kg(-1) x hr(-1) and was adjusted to achieve a desired depth of sedation at 3, 4, or 5 on the RSS every 4 hrs. The degree of sedation was classified into three states: light sedation (RSS 2-3; n = 49), moderate sedation (RSS 4; n = 39), and heavy sedation (RSS 5-6; n = 45).

RESULTS

With increasing the depth of sedation, oxygen consumption index (mL x min(-1) x m(-2)), resting energy expenditure index (REEI; kcal x day(-1) x m(-2)), and REE/basal energy expenditure (BEE) decreased significantly. Oxygen consumption index (mean +/- SD), REEI, and REE/BEE were 151 +/- 18, 1032 +/- 120, and 1.29 +/- 0.17 in the light sedation, 139 +/- 22, 947 +/- 143, and 1.20 +/- 0.16 in the moderate sedation, and 125 +/- 16, 865 +/- 105, and 1.13 +/- 0.12 in the heavy sedation, respectively.

CONCLUSION

An increase in the depth of sedation progressively decreases in oxygen consumption index and REEI in postoperative patients.

Oxygen transport and organ dysfunction in the older trauma patient

OBJECTIVES

To determine baseline values of cardiac index (CI) and oxygen transport variables in patients with multiple trauma within 24 hours of admission to a level I trauma center.

METHOD

This project was part of a larger study comparing methods of measuring oxygen consumption (VO2) in 38 severely injured patients. Measurements of CI, oxygen delivery (DO2), and VO2 were performed every 6 hours for 24 hours. Patients were monitored for multiple organ dysfunction syndrome.

RESULTS

The mean age was 59 (+/- 17) years, with 74% (n = 28) of patients 50 years or older. Patients 65 years or older had significantly lower levels of CI, DO2, and VO2. Initial age-related differences in CI (P < .001) persisted at each time period (P < .0136). Younger patients generated a higher DO2 at each time period (P < .0005). Even though there were persistent age-related differences in VO2 over time (P < .0001), no interaction between age and time was found. Survivors had lower scores for multiple organ dysfunction syndrome than did nonsurvivors (P < .0001), all of whom were 50 years or older. Mortality was 21%.

CONCLUSIONS

All patients were hypermetabolic, but older patients were much less so. Younger patients progressively had increased CI and DO2 levels, whereas older patients started with low levels that remained so. Patients in each age group appeared to lock into a level of VO2 that did not change over time. These findings underscore the vulnerability of older patients to poor outcomes. As the magnitude of the postinjury response is partly age-dependent, future research should differentiate patient characteristics associated with positive outcomes among elderly trauma patients.

The future of bedside monitoring

Today's intensivists are provided with more information than ever before, yet current monitors present data from multiple sources in a relatively raw form with virtually no intelligent data integration and processing. In the next century, technological advances in miniaturization, biosensors and computer processing, coupled with an improved understanding of critical illnesses at the molecular level, will lead to the development of a new generation of monitors. Monitoring will move from the traditional macroscopic invasive approach to a noninvasive, molecular analysis of evolving critical disease processes. It is likely that disturbances in homeostasis will become known immediately or before they would otherwise be manifest clinically. Nanotechnology will permit monitoring of critical changes in the intracellular environment or the by-products of cellular metabolism and signal messaging. This article discusses monitoring technologies that hold promise for further development in the next century and point out techniques likely to be abandoned.