Comparison of methods of measurements of oxygen consumption in mechanically ventilated patients with multiple trauma: the Fick method versus indirect calorimetry

Resting Energy Expenditure Early after Cardiac Surgery and Validity of Predictive Equations: A Prospective Observational Study

OBJECTIVE

Several predictive equations have been used to estimate patients' energy expenditure. The study aimed to describe the characteristics of resting energy expenditure (REE) in patients undergoing mechanical ventilation during early postoperative stage after cardiac surgery and evaluate the validity of 9 REE predictive equations.

METHODS

This was a prospective observational study. Patients aged 18-80 years old, undergone open-heart surgery, were enrolled between January 2017 and 2018. The measured REE (mREE) was evaluated via indirect calorimetry (IC). The predictive resting energy expenditure (pREE) was suggested by 9 predictive equations, including Harris-Benedict (HB), HB coefficient method, Ireton-Jones, Owen, Mifflin, Liu, 25 × body weight (BW), 30 × BW, and 35 × BW. The association between mREE and pREE was assessed by Pearson's correlation, paired t test, Bland-Altman method, and the limits of agreement (LOA).

RESULTS

mREE was related to gender, BMI, age, and body temperature. mREE was significantly correlated with pREE, as calculated by 9 equations (all p < 0.05). There was no significant difference between pREE and mREE, as calculated by 30 × BW kcal/kg/day (t = 0.782, p = 0.435), while significant differences were noted between mREE and pREE calculated by other equations (all p < 0.05). Taking the 30 × BW equation as a suitable candidate, most of the data points were within LOA, and the percentage was 95.6% (129/135). Considering the rationality of clinical use, accurate predictions (%) were calculated, and only 40.74% was acceptable.

CONCLUSIONS

The 30 × BW equation is relatively acceptable for estimating REE in 9 predictive equations in the early stage after heart surgery. However, the IC method should be the first choice if it is feasible.

Reliability of, and Agreement Between, two Breath-by-Breath Indirect Calorimeters at Varying Levels of Inspiratory Oxygen

BACKGROUND

Indirect calorimetry (IC) is considered the accurate way of measuring energy expenditure (EE). IC devices often apply the Haldane transformation, introducing errors at inspiratory oxygen fraction (FiO₂ ) >60%. The aim was to assess measurement reliability and agreement between an unevaluated IC (device 2) (Beacon Caresystem, Mermaid Care A/S, Noerresundby, Denmark) not using Haldane transformation and an IC that does (device 1) (Ecovx, GE, Helsinki, Finland) at varying FiO₂ .

METHODS

Twenty healthy male subjects participated, with 16 completing the study (33 ± 9 years, 83.3 ± 16 kg, 1.83 ± 0.08 m). Subjects were mechanically ventilated in pressure support (3cmH₂ O; positive end-expiratory pressure: 3cmH₂ O) at FiO₂ of 21%, 50%, 85%, and 21% for 15 minutes at each FiO₂ . Mean EE, oxygen consumption (VO₂ ), and CO₂ production (VCO₂ ) were compared within and between devices across FiO₂ levels.

RESULTS

Device 2 showed within-device EE significant differences at 21% vs 50% FiO₂ and device 1 for VCO₂ at 50% vs. 85% FiO₂ . For all variables, both devices showed reliable measurements at 21% and 50% FiO₂ , but at 85%, FiO₂ bias and limits of agreement increased. Between devices, there were significant differences for EE at both 21% and 85% FiO₂ for VO₂ and for VCO₂ at 85% FiO₂ .

CONCLUSION

Both systems measured EE, VO₂ , and VCO₂ at 21%-85% FiO₂ reliably but with bias at 85% FiO₂ . The devices were in agreement at 21% and 50% FiO₂ , but further studies need to confirm accuracy at high FiO₂ .

Measurement of Oxygen Consumption Variations in Critically Ill Burns Patients: Are the Fick Method and Indirect Calorimetry Interchangeable?

OBJECTIVES

To evaluate the interchangeability of oxygen consumption variations measured with the Fick equation (ΔVO2Fick) and indirect calorimetry (ΔVO2Haldane) in critically ill burns patients.

METHODS

Prospective observational single-center study conducted in a university hospital. Twenty-two consecutive burns patients with circulatory insufficiency and hyperlactatemia (>2 mmol/L) who required a fluid challenge (FC) were included. All patients had cardiac output monitoring (transpulmonary thermodilution technique) and were ventilated and sedated. Simultaneous measurements of VO2Fick and VO2Haldane were performed before and immediately after the FC, at rest, and in hemodynamic conditions stabilized for at least 1 h. VO2Fick and VO2Haldane were measured, respectively, with the standard formulae (using arterial and central venous saturation measured with a blood gas analyzer) and with a metabolic monitor.

RESULTS

Forty-four paired measurements of VO2 were obtained. At each timepoint, the median (interquartile range, 25-75) VO2Haldane values were significantly higher than the median VO2Fick values (126 (103-192) vs. 90 (66-149) mL O2/min/m (P = 0.004) before FC and 129 (105-189) vs. 80 (54-119) mL O2/min/m (P = 0.001) after FC). Correlation between the ΔVO2Fick and the ΔVO2Haldane (%) measurements was poor, with an r = 0.06, (P = 0.77). The mean bias was 8.6% [limits of agreement (LOA): -75.7%, 92.9%].

CONCLUSIONS

Analysis of agreement showed poor concordance for the ΔVO2Haldane and the ΔVO2Fick (%) with a low mean bias but large and clinically unacceptable LOA. ΔVO2Haldane and ΔVO2Fick (%) are not interchangeable in these conditions.

Comparison of Minimally and More Invasive Methods of Determining Mixed Venous Oxygen Saturation

OBJECTIVE

To investigate the accuracy of a minimally invasive, 2-step, lookup method for determining mixed venous oxygen saturation compared with conventional techniques.

DESIGN

Single-center, prospective, nonrandomized, pilot study.

SETTING

Tertiary care hospital, university setting.

PARTICIPANTS

Thirteen elective cardiac and vascular surgery patients.

INTERVENTIONS

All participants received intra-arterial and pulmonary artery catheters. Minimally invasive oxygen consumption and cardiac output were measured using a metabolic module and lithium-calibrated arterial waveform analysis (LiDCO; LiDCO, London), respectively. For the minimally invasive method, Step 1 involved these minimally invasive measurements, and arterial oxygen content was entered into the Fick equation to calculate mixed venous oxygen content. Step 2 used an oxyhemoglobin curve spreadsheet to look up mixed venous oxygen saturation from the calculated mixed venous oxygen content. The conventional "invasive" technique used pulmonary artery intermittent thermodilution cardiac output, direct sampling of mixed venous and arterial blood, and the "reverse-Fick" method of calculating oxygen consumption.

MEASUREMENTS AND MAIN RESULTS

LiDCO overestimated thermodilution cardiac output by 26%. Pulmonary artery catheter-derived oxygen consumption underestimated metabolic module measurements by 27%. Mixed venous oxygen saturation differed between techniques; the calculated values underestimated the direct measurements by between 12% to 26.3%, this difference being statistically significant.

CONCLUSION

The magnitude of the differences between the minimally invasive and invasive techniques was too great for the former to act as a surrogate of the latter and could adversely affect clinical decision making.

Energy expenditure in patients with severe head injury: controlled normothermia with sedation and neuromuscular blockade

OBJECTIVES

Providing optimal caloric intake is important for patients with severe traumatic brain injury. Insufficient nutrition worsens prognosis, and excessive nutrition may lead to complications such as weaning delay from mechanical ventilation. However, using controlled normothermia with sedation and neuromuscular blockade for patients with anticipated severe brain edema, the optimal caloric intake is still unclear.

METHODS

Ten patients with severe traumatic brain injury were studied. All patients received midazolam and vecuronium or pancuronium to control body temperature to 36.0°C. Energy expenditure was measured using indirect calorimetry. Age, body height, body weight, heart rate, blood pressure, body temperature, and minute ventilation volume were evaluated at the time of the study. Differences between the mean measured energy expenditures (MEEs) and predicted basal energy expenditures (PEEs from the Harris-Benedict equation) were analyzed using paired t test. Furthermore, the relationships between these variables and MEEs were analyzed with multiple regression analysis.

RESULTS

The result of MEE was 1279±244 kcal/d. When compared with PEE, MEE/PEE was 87.2% ± 10%. Multiple regression analysis showed that age, body height, body weight, heart rate, and minute ventilation volume were related with MEE.

CONCLUSIONS

Energy expenditure in patients with severe traumatic brain injury who need mechanical ventilation and have received controlled normothermia with sedation and neuromuscular blockade was 13% less than predicted basal levels. Energy expenditure might be obtained from age, body height, body weight, heart rate, and minute ventilation.

[Guidelines for specialized nutritional and metabolic support in the critically-ill patient. Update. Consensus of the Spanish Society of Intensive Care Medicine and Coronary Units-Spanish Society of Parenteral and Enteral Nutrition (SEMICYUC-SENPE): macro-and micronutrient requirements]

Energy requirements are altered in critically-ill patients and are influenced by the clinical situation, treatment, and phase of the process. Therefore, the most appropriate method to calculate calorie intake is indirect calorimetry. In the absence of this technique, fixed calorie intake (between 25 and 35 kcal/kg/day) or predictive equations such as the Penn State formula can be used to obtain a more accurate evaluation of metabolic rate. Carbohydrate administration should be limited to a maximum of 4 g/kg/day and a minimum of 2g/kg/day. Plasma glycemia should be controlled to avoid hyperglycemia. Fat intake should be between 1 and 1.5 g/kg/day. The recommended protein intake is 1-1.5 g/kg/day but can vary according to the patient's clinical status. Particular attention should be paid to micronutrient intake. Consensus is lacking on micronutrient requirements. Some vitamins (A, B, C, E) are highly important in critically-ill patients, especially those undergoing continuous renal replacement techniques, patients with severe burns and alcoholics, although the specific requirements in each of these types of patient have not yet been established. Energy and protein intake in critically-ill patients is complex, since both clinical factors and the stage of the process must be taken into account. The first step is to calculate each patient's energy requirements and then proceed to distribute calorie intake among its three components: proteins, carbohydrates and fat. Micronutrient requirements must also be considered.

Immune Enteral Nutrition Can Improve Outcomes in Medical-Surgical Patients with ARDS: A Prospective Randomized Controlled Trial

Objective

To determine if early continuous enteral feeding of a diet containing eicosapentaenoic acid (EPA), gamma-linolenic acid (GLA), docosahexaenoic acid, and antioxidants in surgical-medical patients with ARDS improves Lung Injury Score (LIS), gas exchange, Multiple Organ Dysfunction (MOD) Score, ICU length of stay, and days on mechanical ventilation.

Methods

Prospective randomized 2-center double-blind controlled trial of 17 ARDS patients whom continuously tube-fed the experimental diet (n=9) or an isonitrogenous, isocaloric standard diet (n=8) at a minimum caloric delivery of 90% of basal energy expenditure.

Results

In the experimental group, there was a decrease in lung injury score (p < 0.003) and lower ventilation variables (p < 0.001). Patients in the experimental group had a statistically significant decrease in 28-day MOD score (p < 0.05). The length of ICU stay was significantly decreased in the experimental group (12.8 vs. 17.5 days; p = 0.01). The study was underpowered to detect any survival benefits between the two groups.

Conclusion

An EPA and GLA supplemented diet contributes to improved gas exchange in addition to decrease LIS, MOD scores and length of ICU stay in patients with ARDS. An EPA+GLA-enriched enteral diet may be an effective tool in the medical management of ARDS.

Controlling energetic intake based on a novel logistic regression model for the metabolic syndrome in a Chinese population

The present study was designed to develop a novel method of energy calculation for controlling energetic intake in patients with the metabolic syndrome. Demographics and dietary data were recorded for 2582 obese subjects. Nutritional education was applied to all the patients. One year later, the data on age, sex, activity intensity coefficient, waistline, environmental temperature and BMI in subjects who lost ≥ 5% body weight were entered into a multivariate logistic regression analysis model. Energy requirement was calculated from the results of multivariate logistic regression. Four hundred and thirty-four metabolic syndrome patients were then randomly divided into the treated group (216) and the control group (218). The energetic intake in the experimental group was controlled based on the new energy requirement model. The traditional energy exchange method was used in the control group. The independent factors predicting metabolic syndrome prognosis, such as age, sex, activity intensity coefficient, waistline, environmental temperature and BMI, were identified by multivariate logistic regression analysis. The energy requirement model was then constructed by logistic regression analysis. After 6 months of energetic intake control based on the new model, the parameters of the experimental group were significantly different from those of the controls (all P < 0·05): waistline, 89·65 (SD 5·54) v. 91·97 (SD 4·78) cm; BMI, 24·67 (SD 3·54) v. 25·87 (SD 2·65) kg/m2; fasting blood glucose, 6·9 (SD 3·6) v. 8·7 (SD 4·6) mmol/l; 2 h PG, 8·7 (SD 5·7) v. 10·7 (SD 4·5) mmol/l; HbA1c, 7·7 (SD 1·6) v. 8·9 (SD 2·6) %; homoeostasis model insulin resistance index, 3·14 (SD 1·62) v. 4·32 (SD 2·25). The new energy requirement model can effectively improve the clinical outcomes of controlling energetic intake in metabolic syndrome patients.

Metabolic support of the obese intensive care unit patient: a current perspective

PURPOSE OF REVIEW

Obesity is a widespread condition associated with a variety of mechanical, metabolic, and physiologic changes that affect both health outcomes and delivery of care. Nutrition support is a key element of management during critical illness known to improve outcomes favorably, but is likewise complicated in the presence of obesity. This review serves to discuss the challenges unique to management of critically ill obese patients and an evidence-based approach to nutrition support in this patient population.

RECENT FINDINGS

High-protein, hypocaloric feeding has emerged as a nutrition support strategy capable of reducing hyperglycemia and protein catabolism, while promoting favorable changes in body composition and fluid mobilization. Recent data have shown a protective effect of mild-moderate obesity (BMI 30-39.9 kg/m2), with improved morbidity and mortality outcomes in this subgroup. Therefore, it is unclear whether hypocaloric feeding represents an inferior approach in this subgroup in which weight maintenance may be preferable.

SUMMARY

There are many obstacles that limit provision of nutrition support in the obese ICU patient. Calculating energy needs accurately is extremely problematic due to a lack of reliable prediction equations and a wide variability in body composition among the obese patients. Further research is needed to determine a better approach to estimating energy needs in this population, in addition to validating hypocaloric feeding as the standard approach to nutrition support in the obese patients.

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.

Comparison of oxygen consumption calculated by Fick's principle (using a central venous catheter) and measured by indirect calorimetry

We investigated the clinical usefulness of the Fick method using central venous oxygen saturation ScvO2 and cardiac output (CO) measured by pulse dye densitometry (PDD) for monitoring oxygen consumption VO2. This prospective clinical study was performed in 28 mechanically ventilated postoperative patients after major abdominal surgery. VO2 was determined by two methods, i.e., the Fick method and indirect calorimetry. The Fick method was employed using CO measured by PDD and VO2 obtained from a central venous catheter (CVC). VO2 measured by indirect calorimetry was averaged for 15 min. Fifty-six sets of measurements were performed. VO2 values determined by the Fick method were significantly lower than those measured by indirect calorimetry (110 +/- 29 vs 148 +/- 28 ml x min(-1) x m(-2); P < 0.01). Bland and Altma analysis showed that the mean bias and precision were 33 ml x min(-1) x m(-2) and 32 ml x min(-1) x m(-2), respectively. The correlation between the two measurements of VO2 was weak (r (2) = 0.145; P = 0.0038), indicating that the Fick method using PDD and ScvO2 is not clinically acceptable for the monitoring of VO2.

Prediction of resting metabolic rate in critically ill adult patients: results of a systematic review of the evidence

Metabolic rate is generally assessed by use of equations in critically ill patients, but evidence pertaining to the validity of these equations in this population has not been systematically evaluated. This paper represents the first such systematic analysis in adult patients. A work group created by the American Dietetic Association identified pertinent peer-reviewed articles. The work group systematically evaluated these articles and formulated conclusion statements and grades based on the available evidence. Seven equations plus the Fick method were found to have validation work that met criteria for inclusion in this analysis. The Harris-Benedict equation with and without modifiers had the most validation work behind it (n=13), followed by Ireton-Jones (1992 and 1997) (n=9), Penn State (1998, 2003) (n=2), and Swinamer (n=1). Five studies pertaining to the Fick method met acceptance criteria. Based on these validation studies, the Harris-Benedict, Ireton-Jones 1997, and Fick methods can be confidently eliminated from use in assessment of energy expenditure in critically ill patients. The Penn State 2003, Swinamer, and Ireton-Jones 1992 equations may be useful in critically ill nonobese patients, whereas the Ireton-Jones 1992 and Penn State 1998 equations seem to be useful in obese patients. The strength of these conclusions is moderated because of limited and sometimes inconsistent data. More validation work is needed to confirm and increase the strength of these conclusions.

What is the meaning of standard venous admixture formula results in septic patients?

The standard venous admixture formula is widely used in the bedside assessment of intrapulmonary shunt in intensive care units. The intrapulmonary shunt fraction calculated by the standard venous admixture formula is affected by the systemic oxygen extraction ratio and thus reflects both systemic and intrapulmonary shunts, especially in septic patients with decreased oxygen extraction ratios. The standard venous admixture formula may cause misestimation of the intrapulmonary shunt fraction, especially in septic patients. Inert gas rebreathing techniques and simultaneous measurement of cardiac output by thermodilution and oxygen consumption by indirect calorimetry may be useful in septic patients.

HYPEROXIC VENTILATION REDUCES SIX-HOUR MORTALITY AFTER PARTIAL FLUID RESUSCITATION FROM HEMORRHAGIC SHOCK

Ventilation with 100% oxygen (Fio(2) 1.0; hyperoxic ventilation; HV) as an alternative to red blood cell transfusion enables survival in otherwise lethal normovolemic anemia. The aim of the present study was to investigate whether HV as a supplement to fluid infusion therapy could also restore adequate tissue oxygenation and prevent death in otherwise lethal hemorrhagic shock. In 14 anesthetized pigs ventilated on room air (Fio(2) 0.21), hemorrhagic shock was induced by controlled withdrawal of blood (target mean arterial pressure 35-40 mmHg) and maintained for 1 h. Subsequently, the animals were partially fluid-resuscitated (i.e., replacement of lost plasma volume) either with hydroxyethyl starch (6% HES, 200/0.5) alone (G 0.21) or with HES supplemented by HV (G 1.0). After completion of partial fluid resuscitation, all animals were followed up for the next 6 h. Five of seven animals of G 0.21 died within the 6-h observation period (i.e., 6-h mortality 71%). Death was preceded by a continuous increase of the serum concentrations of arterial lactate and persistent tissue hypoxia. In contrast to that, all animals of G 1.0 survived the 6-h observation period without lactic acidosis and with improved tissue oxygenation (i.e., 6-h mortality 0%; G 0.21 versus G 1.0 P < 0.05). In anesthetized pigs submitted to lethal hemorrhagic shock, the supplementation of partial fluid resuscitation with HV improved tissue oxygenation and enabled survival for 6 h.

Assessment of cerebral tissue oxygenation in patients with sickle cell disease: effect of transfusion therapy

This study used spatially resolved transcranial near-infrared spectroscopy (NIRS) to compare brain tissue oxygenation in sickle cell disease (SCD) patients with that of healthy children. In addition, NIRS was used to measure the dynamic response of cerebral oxygen balance to erythrocytapheresis. Transcranial NIRS measurements were obtained from 25 children with SCD who were not receiving transfusion or hydroxyurea therapy (NT-SCD). These patients were divided into two subgroups, those with mild (n = 10) or severe (n = 15) SCD symptoms. In addition, NIRS measurements were performed in 16 SCD patients with severe disease maintained on long-term erythrocytapheresis (T-SCD) and in 35 control children. The lowest mean brain tissue oxygen saturation occurred in the NT-SCD subgroup with severe symptoms (48 +/- 9%; P < 0.001 vs. control). NT-SCD patients with mild symptoms had higher saturation (62 +/- 8%; P < 0.001 vs. control), while the highest appeared in the control group (72 +/- 7%). In T-SCD patients, however, brain tissue oxygen saturations were higher than severely symptomatic NT-SCD children and similar to mildly symptomatic NT-SCD children (65 +/- 7%). Non-invasive measurements of brain tissue oxygenation with NIRS revealed that abnormal oxygen saturation levels in SCD patients correlated with the severity of their clinical manifestations. Additionally, cerebral oxygen balance seems to be favorably affected by erythro-cytapheresis.

Oxygen Consumption Measurement: Agreement Between the Closed-Circuit PhysioFlex Anesthesia Machine and the Deltatrac II Indirect Calorimeter

We designed this study to ascertain whether, for the purpose of clinical interpretation, the direct measurement of O(2) consumption with the PhysioFlex closed-circuit anesthesia machine and with the Deltatrac II indirect calorimeter are interchangeable. Oxygen consumption was measured using the two instruments successively in critically-ill, mechanically-ventilated patients. Measurements were recorded as the mean of 10 consecutive, minute-by-minute, stable readings. The degree of agreement between the measurements obtained with the two systems was estimated using Bland-Altman analysis and the intraclass correlation coefficient. Forty-four pairs of measurements made in 21 patients were analyzed, yielding a mean bias of 6.32 mL/min and limits of agreement of 40.28 and -27.63 mL/min. The intraclass correlation coefficient was 0.95, and the 95% confidence interval ranged from 0.91 to 0.97. The measurement of O(2) consumption obtained with the PhysioFlex anesthesia machine is interchangeable with that obtained by indirect calorimetry.

IMPLICATIONS

The PhysioFlex anesthesia machine (Dräger Inc., Lübeck, Germany) is a closed circuit anesthesia delivery device. The oxygen delivered by this device to maintain a steady-state inspired oxygen concentration is therefore a measure of the patient's oxygen consumption. This study was designed to evaluate the accuracy of the PhysioFlex for measuring oxygen consumption by comparing it with an established technology (Deltatrac II Calorimeter) for making this measurement.

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.

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.

Accuracy of feedback-controlled oxygen delivery into a closed anaesthesia circuit for measurement of oxygen consumption

BACKGROUND

Oxygen consumption (V*O2) is rarely measured during anaesthesia, probably because of technical difficulties. Theoretically, oxygen delivery into a closed anaesthesia circuit (V*O2-PF; PhysioFlex Draeger Medical Company, Germany) should measure V*O2. We aimed to measure V*O2-PF in vitro and in vivo.

METHODS

Three sets of experiments were performed. V*O2-PF was assessed with five values of V*O2 (0-300 ml min(-1)) simulated by a calibrated lung model (V*O2-Model) at five values of FIO2 (0.25-0.85). The time taken for V*O2-PF to respond to changes in V*O2-Model gave a measure of dynamic performance. In six healthy anaesthetized dogs we compared V*O2-PF with V*O2 measured by the Fick method (V*O2-Fick) during ventilation with nine values of FIO2 (0.21-1.00). V*O2-PF and V*O2-Fick were also compared in three dogs when V*O2 was changed pharmacologically [102 (SD 14), 121 (17) and 200 (57) ml min(-1)]. In patients during surgery, we measured V*O2-PF and V*O2-Fick simultaneously after induction of anaesthesia (n=21) and during surgery (n=17) (FIO2 0.3-0.5).

RESULTS

Compared with V*O2-Model, V*O2-PF values varied from time to time so that averaging over 10 min is recommended. Furthermore, at an FIO2 >0.8, V*O2-PF always overestimated V*O2. With FIO2 <0.8, averaged V*O2-PF corresponded to V*O2-Model and adapted rapidly to changes. Averaged V*O2-PF also corresponded to V*O2-Fick in dogs at FIO2 <0.8. V*O2 measured by the two methods gave similar results when V*O2 was changed pharmacologically. In contrast, V*O2-PF systematically overestimated V*O2-Fick in patients by 52 (SD 40) ml min-1 and this bias increased with smaller arteriovenous differences in oxygen content.

CONCLUSION

V*O2-PF measures V*O2 adequately within specific conditions.

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.

Red blood cell transfusion does not increase oxygen consumption in critically ill septic patients

BACKGROUND

Red blood cell (RBC) transfusion is commonly used to increase oxygen transport in patients with sepsis. However it does not consistently increase oxygen uptake at either the whole-body level, as calculated by the Fick method, or within individual organs, as assessed by gastric intra-mucosal pH.

AIM

This study evaluates the hemodynamic and oxygen utilization effects of hemoglobin infusion on critically ill septic patients.

METHODS

Fifteen septic patients undergoing mechanical ventilation whose hemoglobin was <10 g% were eligible. Ten patients (APACHE II: 25.5 +/- 7.6) received an infusion of 1 unit of packed RBC over 1 h while sedated and paralyzed. The remaining five control patients (APACHE II: 24.3 +/- 6.0) received a 5% albumin solution (500 ml) over 1 h. Hemodynamic data, gastric tonometry and calorimetry were obtained prior to and immediately after RBC transfusion or 5% albumin infusion.

RESULTS

Transfusion of RBC was associated with an improvement in left ventricular systolic work index (38.6 +/- 12.6 to 41.1 +/- 13.0 g/min/m2; P = 0.04). In the control group there was no significant change in the left ventricular systolic work index (37.2 +/- 14.3 to 42.2 +/- 18.9 g/min/m2). An increase in pulmonary vascular resistance index (203 +/- 58 to 238 +/- 49 dyne/cm5/m2; P = 0.04) was also observed, while no change was produced by colloid infusion (237 +/- 87.8 to 226.4 +/- 57.8 dyne/cm5/m2). Oxygen utilization did not increase either by Fick equation or by indirect calorimetry in either group. Gastric intramucosal pH increased only in the control group but did not reach statistical significance.

CONCLUSION

Hemoglobin increase does not improve either global or regional oxygen utilization in anemic septic patients. Furthermore, RBC transfusion may hamper right ventricular ejection by increasing the pulmonary vascular resistance index.