- Click here for explanation of classification scheme.

To validate, in critically ill patients, an abbreviated protocol that uses five consecutive stable one-minute readings of oxygen consumption [VO₂, carbon dioxide production (VCO₂, and minute ventilation (VE) in a range of ±5%, vs. a more standard protocol that uses 30 consecutive stable one-minute readings of VO₂, VCO₂ and VE in a range of ±10%].

Definitions

• Rest: In ICU, often defined as a period when patient is left undisturbed before and during a 20- to 30-minute steady state measurement and is moving minimally or not at all during the test
• Steady state: Patient is at rest and one period of five consecutive minutes in which the coefficients of variation for VO₂, VCO₂ and VE were equal to 5% or one period of 30 consecutive minutes in which the coefficients of variation were equal to 10%
• Success group: Successfully completed both protocols; abbreviated and 30-minute protocol
• Fail group: Completed only one protocol or failed one or both protocols.

If either a five- or 30-minute steady state test was not obtained, the study was considered a failure (Fail group).

• Mechanically, ventilated patients in adult surgical and medical ICU units
• Not restless or agitated at the beginning of the indirect calorimetry
• Patients receiving continuous enteral or parenteral feedings were not excluded or had feedings interrupted for study.

• Patents restless or agitated at beginning of IC
• Patients were excluded if the fraction of inspired oxygen was greater than 0.60 or if there was an air leak via chest tubes or ventilator circuits.

Anthropometric

Height, weight, ideal body weight: Not mentioned how they were obtained.

Clinical

• Clinical data collected on all patients including:
  • Vital signs: Heart rate, respiratory rate, body temperature
  • Medications administered: 48% of patients were sedated (opiates, benzodiazapines, muscle relaxants, inotropes)
  • Nutritional intake: Data collected on nutrition support regimen including protein and non-protein calorie intake, route of administration (enteral or parenteral)
  • Ventilation parameters: Inspiratory oxygen fraction [FIO₂, positive end-expiratory pressure (PEEP)], ventilator mode
• Resting Energy Expenditure:
  • IC performed on resting, mechanically ventilated ill patients
  • IC type: Metabolic monitor
  • Equipment of calibration: Using standard gases prior to each measurement
  • Coefficient of variation using std gases: Yes
  • Rest before measure (state length of time rested if available): See definition of “rest”
  • Measurement length: 40 inches
  • Steady state: One period of five consecutive minutes in which the coefficients of variation for VO₂, VCO₂ and VE were equal to 5% and one period of 30 consecutive minutes in which the coefficients of variation were equal to 10% (Success group)
  • Fasting length: Continuous enteral and parenteral feedings
  • Exercise restrictions: Patients were bedridden; not applicable
  • Room temp: Hospital room temperature
  • Number of measures within the measurement period: Every minute; up to maximum 40 inches
  • Were some measures eliminated? Only the first successful five-minute steady state period was considered
  • Were a set of measurements averaged? IC data measured over five vs. 30 minutes for Success and Fail groups
  • Training of measurer? Not mentioned
  • Subject training of measuring process? Patients on ventilators.

Definitions

• Rest In ICU, often defined as a period when patient is left undisturbed before and during a 20- to 30-minute steady state measurement, and is moving minimally or not at all during the test
• Steady state: Patient is at rest and one period of five less than consecutive minutes in which the coefficients of variation for VO₂, VCO₂, and VE were less than 5% or one period of 30 consecutive minutes in which the coefficients of variation were less than 10%
• Success group: Successfully completed both protocols; abbreviated and 30-minutes protocol
• Fail group: Completed only one protocol or failed one or both protocols [If either a five- or 30-minute steady state test was not obtained, the study was considered a failure (“Fail group”)].

Outcome(s) and Other Measures

• Oxygen consumption (VO₂, carbon dioxide production (VCO₂, minute ventilation (VE), respiratory quotient (RQ=VCO₂ VO2 and energy expenditure were obtained with IC
• Independent variables of weight, height, age, ideal body weight (IBW), % IBW, basal metabolic rate were calculated with Harris-Benedict equation
• The mean values of oxygen consumption, carbon dioxide production, respiratory quotient, minute ventilation and resting energy expenditure obtained from five- and 30-minute protocols were calculated and compared for the Success and Fail groups
• The first five-minute period in which coefficients of variation for VO₂, VCO₂ and VE were 5% or less was compared to the first 30-minute period in which coefficients of variation for these variables were 10% or less.

Statistical Tests

• A power analysis indicated that a sample size of 23 would be necessary to detect a 10% difference between the measurement methods, alpha = 0.05 and beta = 0.8
• Data from the five-minute and 30-minute steady state were compared using student’s paired T-test. Chi-square tests and regression analysis were also utilized. Statistical significance was established at P<0.05.

Measurement Process

• Number of measurements: IC measured every minute; up to maximum of 40 minutes
• Length of measurement: For a maximum of 40 minutes
• Steady state:
  • 24 patients completed both protocols (70%)
  • 10 patients failed one or both protocols (30%)
  • Of the failures, three met the criteria for the 30-minutes steady state protocol and six met the criteria for neither steady state criteria
  • Overall, 80% of patients completed a five-minute steady state test, 74% completed a 30-minute steady state test and 18% completed neither test
  • Mean time to completion of a successful five-minute study period was 10.5+1.3 (range five to 27 minutes, median eight minutes)
  • Mean time to completion for successful 30-minute study period was 30.75+1.3 minutes (range 30 to 40 minutes, median 30 minutes)
  • Mean time savings was 20.2+1.3 minutes (range three to 26 minutes, median 23 minutes).

RQ

• There were no significant differences in VE, VO₂, VCO₂, respiratory quotient or energy expenditure between the protocols in the Success group or in the Fail group
• Success group: The mean difference between the five-minute and 30-minute protocols for VO₂ was 0±2ml per minute (range –20 to 13ml per minute), VCO₂ was –1±1ml per minute (range –13 to 17ml per minute); VE, 0.02±0.09 (range –0.9 to 1.6L per minute); RQ, –0.0004+0.0056 (range –0.03 to 0.03); and REE, –4±10kcal per day (range –122 to 74kcal per day)
• Fail group: The mean difference between the five-minute and 30-minute protocols for VO₂ was –2±5ml per minute (range –20 to 37ml per minute), VCO₂, –1±6ml per minute (range –36 to 37ml per minute); VE, 0.33±0.32L per minute (range –1.4 to 1.9L per minute); RQ, 0.0009±0.013 (range –0.06 to 0.06); REE, –15±39kcal per day (range –170 to 272kcal per day)
• Coefficients of determination (R²) for VO₂ and VCO₂ between the two methods in the Success group were 0.99
• In the Fail group, R² values ranged from 0.75 for VCO₂ to 0.91 for VO₂
• Doses of the most commonly prescribed opiate, fentanyl, was significantly higher in the subset of patients who successfully completed at least one resting steady state protocol compared to the subset of patients who failed to complete either resting steady state protocol (p<0.05). Failure to achieve steady state may have been the result of patient agitation, pain or confusion.

Measurement Timing

• Sleep or rest: Rest
• Physical activity: Not applicable as ventilated patients
• Nutritional intake: Patients receiving continuous parenteral or enteral feedings did not have those feedings interrupted for study
• Individual Characteristics:
  • Circulatory hormones: Not discussed
  • Breathing ability: On ventilators
  • Medical tests/procedures: Not mentioned
  • Chemicals: 48% of patients were sedated
• Previous studies have shown that 20- to 30-minute IC protocols for REE compare favorably to prolonged (8- to 24-hour) measurements of total energy expenditure. Shorter steady state measurements have been utilized but have not been validated.
• Our results suggest that an abbreviated resting IC protocol of five consecutive minutes at steady state (with coefficient of variation of 5% or less) is equivalent to a longer protocol of 30 minutes at steady state (with coefficient of variation of 10% or less) in most sedated or medically paralyzed, intubated critically ill patients
• A strong correlation existed between the five- and 30-minutes steady state measurements of the Success group. For instance, the standard deviation of the difference in VO₂ between the five- and 30-minute steady state tests was ±8ml per minute, two standard deviations ±16ml per minute. Not only were 96% of the measured differences within two standard deviations of the mean, but these differences were at most 3.9% different from the mean 30-minutes steady state VO₂. Agreement was similar for the calculated variables REE and RQ, respectively, 5.2% and 6.3% of the 30-minutes steady state means.
• In this study, the traditional 30-minute protocol required 30 to 40 minutes to complete. The time savings achieved using the abbreviated protocol was approximately 20 minutes per measurement. Assuming 15 minutes of transport and set up between patients, the abbreviated protocol doubles productivity of the IC and operator.
• Overall failure rate of the five-minutes steady state was 20%, compared to a failure rate for the 30-minutes steady state of 26%. It is unlikely that a meaningful five- or 30-minutes steady state measurement can be obtained in unsedated, uncooperative patients.

Actual Sample

• Total N=34 critically ill patients
• N=20 males; N=14 females
• Broken down into two groups based on success (completing both protocol) or failure (failed one or both protocol).

Success Group

• N=24
• N=14 Males
• N=10 Females
• Age: 53±4 years
• Post-operative day: 7±1.

Fail Group

• N=10
• N=six males
• N=four females
• Age: 64±2 years (P=0.03 vs. success group)
• Post-op day: 14±5.

Statistical Tests

• Power analysis indicated that a sample size of 23 would be necessary to detect a 10% difference between the measurement methods, alpha=0.05 and beta=0.8
• Student’s paired T-test. Chi-square tests and regression analysis were also utilized. Statistical significance was established at P<0.05.

Anthropometric

• Success group
  • Height (cm): 172±2
  • Weight (kg): 81±7
  • Percentage ideal body weight (IBW): 120±9
  • Basal metabolic rate (kcal per day): 1510±76
• Fail group
  • Height: 171±2
  • Weight: 77±5
  • Percentage IBW: 116±6
  • Basal metabolic rate: 1410±68.

Results

• Measurement process:
  • Number of measurements: IC measured every minute; up to maximum of 40 minutes
  • Length of measurement: For a maximum of 40 minutes
  • Steady state: 24 patients completed both protocols (70%)
  • 10 patients failed one or both protocols (30%)
  • Of the failures, three met the criteria for the 30-minute steady state protocol and six met the criteria for neither steady state criteria
  • Overall, 80% of patients completed a five-minute steady state test, 74% completed a 30-minute steady state test; and 18% completed neither test
  • Mean time to completion of a successful five-minute study period was 10.5+1.3 (range five to 27 minutes, median eight minutes)
  • Mean time to completion for successful 30-minute study period was 30.75+1.3 minute (range 30 to 40 minutes, median 30 minutes)
  • Mean time savings was 20.2+1.3 minutes (range three to 26 minutes, median 23 minutes)
• RQ: There were no significant differences in VE, VO₂, VCO₂ respiratory quotient or energy expenditure between the protocols in the Success group or in the Fail group
• Success group: The mean difference between the five-minute and 30-minute protocols for VO₂ was 0±2ml per minute (range -20 to 13ml per minute); VCO₂, -1±1ml per minute (range –13 to 17ml per minute); VE, 0.02±0.09 (range –0.9 to 1.6L per minute); RQ, -0.0004±0.0056 (range –0.03 to 0.03) and REE -4±10kcal per day (range –122 to 74kcal per day)
• Fail group
  • The mean difference between the five-minute and 30-minute protocols for VO₂ was -2±5ml per minute (range -20 to 37ml per minute); VCO₂, -1±6ml per minute (range -36 to 37ml per minute); VE 0.33±0.32L per minute (range -1.4 to 1.9L per minute); RQ, 0.0009±0.013 (range -0.06 to 0.06); REE -15±39kcal per day (range –170 to 272kcal per day)
  • Coefficients of determination (R²) for VO₂ and VCO₂ between the two methods in the Success group were 0.99
  • In the Fail group, R² values ranged from 0.75 for VCO² to 0.91 for VO²
  • Doses of the most commonly prescribed opiate, fentanyl, was significantly higher in the subset of patients who successfully completed at least one resting steady state protocol compared to the subset of patients who failed to complete either resting steady state protocol (p<0.05). Failure to achieve steady state may have been the result of patient agitation, pain, or confusion.
• Measurement timing:
  • Sleep or rest: Rest
  • Physical activity: Not applicable as ventilated patients
  • Nutritional intake: Patients receiving continuous parenteral or enteral feedings did not have those feedings interrupted for study
  • Chemicals: 48% of patients were sedated.

• Previous studies have shown that 20- to 30-minute IC protocols for REE compare favorably to prolonged (8 to 24 hours) measurements of total energy expenditure. Shorter steady state measurements have been utilized but have not been validated.
• Our results suggest that an abbreviated resting IC protocol of five consecutive minutes at steady state (with coefficient of variation of =5%) is equivalent to a longer protocol of 30 minutes at steady state (with coefficient of variation of  =10%) in most sedated or medically paralyzed, intubated critically ill patients
• A strong correlation existed between the five- and 30-minute steady state measurements of the Success group. For instance, the standard deviation of the difference in VO₂ between the five- and 30-minute steady state tests was ±8ml per minute, two standard deviations ±16ml per minute. Not only were 96% of the measured differences within two standard deviations of the mean, but these differences were at most 3.9% different from the mean 30-minute steady state VO₂ Agreement was similar for the calculated variables REE and RQ, respectively 5.2% and 6.3% of the 30-minute steady state means.
• In this study, the traditional 30-minute protocol required 30 to 40 minutes to complete. The time savings achieved using the abbreviated protocol was approximately 20 minutes per measurement. Assuming 15 minutes of transport and set up between patients, the abbreviated protocol doubles productivity of the IC and operator.
• Overall failure rate of the five-minute steady state was 20%, compared to a failure rate for the 30-minutes steady state of 26%. It is unlikely that a meaningful five- or 30-minute steady state measurement can be obtained in unsedated, uncooperative patients.

Industry:	Hershey Food Company:
University/Hospital:	Pennsylvania State

Strengths

• Because subjects were chosen based on whether agitated or not, failure rate was lower than if measured all critically ill patients
• Although small sample size, a power calculation was performed indicating that a sample size of 23 (24 were successful in this study) was necessary to detect a difference of ±10% with an alpha of 0.05 and a beta of 0.8
• A coefficient of variation of 10% is generally accepted for 20- to 30-minute steady state study periods; 5% for five consecutive one-minute steady state protocol; thus taking into account the accuracy is a strength of this study.

Limitations

• Minimally sedated, uncooperative or agitated patients are less likely to complete the resting protocol (20% failure in the present study)
• Limited generalizability to the most critically ill, sedated or medically paralyzed mechanically ventilated patients (may not be applicable for patients with assisted ventilation or spontaneous breathing)
• May not be applicable to patients with indwelling pulmonary artery catheters (VO₂ does not correlate well with that from gas exchange measurements)
• Factors such as organ dysfunction states; which may influence the test 
• Height and weight (how were they obtained).