The intrinsic state of the patient (sleeping, resting, moving, etc) as well as routine daily therapeutic and diagnostic interventions can affect IC measurements used to plan nutritional regimens, as well as to evaluate metabolic state.

The objectives of this study were:

1. To examine the alterations in metabolic (oxygen consumption (VO₂) and carbon dioxide production (VCO₂) and hemodynamic (heart rate and blood pressure) parameters caused by various common intensive care unit (ICU) activities in a group of mechanically-ventilated critically ill patients.
2. These data can be used to define a baseline metabolic state for use in the calculation of caloric requirements and
3. For use in both intrapatient and interpatient comparisons

To do this, 23 post-operative, mechanically-ventilated patients were studied on 36 occasions.

Definitions

• “Sleeping”—state where the patient was not aroused by surrounding events
• “Resting”—lying motionless with eyes open responding to surrounding events
• “Activity”—Movement of body and limbs, chest physical therapy, a physical examination, having a bath, having visitors, having medical procedures.

1. Postoperative patients
2. Mechanically ventilated
3. Hemodynamically stable
4. Not comatose
5. Located in the Surgical-Anesthesiology Intensive Care Unit
6. Diseases in subjects that were allowed: not clear; just states patients were postoperative and critically ill
7. Medications allowed: only states that one patient was heavily sedated (morphine) during part of the study period

1. Comatose patients
2. Not meeting inclusion criteria
3. Diseases in subjects that were excluded:
4. Medications excluded:

Metabolic and hemodynamic measurements were performed every 15 minutes during the 4-8 hours of each study.

If warranted, measurements were performed more often.

These measurements were correlated with observations of the patient and his/her environment.

ANTHROPOMETRIC

• Ht measured? not discussed
• Wt measured? not discussed
• Fat-free mass measured? not discussed

CLINICAL

• Monitored heart rate? Yes; continuously
• Blood pressure (BP)? Yes, continuously
• Body temperature? Not discussed
• Medications administered? Mentioned that one patient was heavily sedated at one point with morphine; affected VO₂ and VCO₂ than when unsedated
• Ventilator? Constant FIO₂ and patients were ventilated with inspired oxygen concentrations between 0.35 and 0.45

OBSERVATIONAL

• Activity state? Monitored continuously

Metabolic Rate

The VO₂, VCO₂ and respiratory quotient (RQ) were measured using:

• IC type: Beckman Metabolic Measurement Cart I; accuracy of cart was validated by Darnask et al.
• Calibration: the O₂ and CO₂ analyzers, as well as the volume tranducers, were calibrated before each measurement
• Rest before measure (state length of time rested if available): n/a
• Measurement length: 3 minutes
• Fasting length: n/a
• Room temp: not mentioned
• No. of measures within the measurement period: every 15 minutes during 4 – 8 hour period; overall each patient was studied on 36 occasions
• Were some measures eliminated? Not discussed
• Were a set of measurements averaged? Mean values for VO₂, VCO₂, heart rate, systolic blood pressure, and rate-pressure product calculated for lowest, resting and peak oxygen consumption periods
• Training of measurer? Not discussed
• Subject training of measuring

DIETARY: patients not receiving any nutritional support

Outcome(s) and other measures

1. Measured metabolic rate [(VO₂, ml/min), VCO₂ (ml/min), RQ] using metabolic cart.
2. The lowest VO₂ and VCO₂ observed, the mean resting VO₂ and VCO₂ and the peak VO₂ and VCO₂ for each study were calculated and examined along with the corresponding mean heart rate, systolic blood pressure, and rate-pressure-product (calculated from the systolic blood pressure and heart rate).

Blinding used: No

N=23 post-operative mechanically-ventilated supported patients studied on 36 occasions; mean age 68 y

Genders and anthropometrics not provided

Statistical tests: Statistical analysis included analysis of variance and Student’s T-test
Statistical significance was set at p <0.05.

ANTHROPOMETRIC

• Not provided

MEASUREMENT PROCESS

• Number of measurements: 36 occasions.

Length of measurements

• Metabolic and hemodynamic measurements were performed every 15 minutes during the 4-8 hours of each study.
• If warranted, measurements were performed more often.
• Steady state—not discussed

RQ

Throughout the study, the mean respiratory quotients (RQ) were well within the physiologic ranges between 0.75 and 0.85.

METABOLIC RATE

Metabolic and Hemodynamic Values for Lowest, Resting and Peak Metabolic State (N = 36; Values are Means + Std. Dev) as follows:

Lowest:

• VO₂ (ml/min) = 204 ± 57
• VCO₂ (ml/min) = 156 ± 32
• Heart rate (min) = 95 ± 15
• Systolic BP (mm Hg) = 129 ± 22
• Heart Rate/BP Product = 12266 ± 2958

Resting:

• VO₂ = 222 ± 53
• VCO₂ = 168± 30
• Heart Rate = 96 ± 16
• Systolic BP = 129 ± 25
• Heart Rate/BP Product =11806 ± 2776

Peak:

• VO₂ = 285 ± 72
• VCO₂ = 217 ± 55
• Heart Rate = 104 ± 18
• Systolic BP = 139 ± 29
• Heart Rate/BP Product =14252 ± 3802
• The peak VCO₂ values were 32 ± 17% above the lowest values (p <0.001).

MEASUREMENT TIMING

Sleep or rest

• The lowest VO₂ and VCO₂ production values for each study occurred primarily (83%) during sleep.
• Resting values were significantly greater than the lowest values (p <0.05)
• Mean resting VO₂ and VCO₂ averaged 9.1 ± 7.5% (SD), (p <0.05) and 7.5 ± 7.3% (p <0.001).

Physical activity

• Routine daily activities (although not particularly painful) such as dressing changes, visitors, the taking of a chest roentgenogram, etc result in significant (~20%) increase in both VO₂ and VCO₂ above both the lowest and resting levels.

Food intake—na

Various times of the day-Measurements were collected at various times of the day

INDIVIDUAL CHARACTERISTICS

• Circulatory hormones—not discussed
• Breathing ability—on mechanical ventilation
• Medical tests/procedures included:
  • Chest physical therapy, a physical examination, having a bath, having visitors, having medical procedures.
  • Chest physical therapy caused an average of 38 ± 18% increase in VO₂ and a 35 ± 18% increase in VCO₂ above lowest levels.
  • During chest physical therapy, heart rate and rate-pressure-product were significantly greater than both resting and lowest levels.
• Blood pressure, heart rate-- Hemodynamic values revealed no differences in either heart rate or systolic blood pressure between lowest and resting values.

During peak oxygen consumption, heart rate, systolic blood pressure, and the rate-pressure-product were significantly greater than both lowest and resting values. (p <0.05)

Significant changes in systolic blood pressure were noted only during “moving body or limb,” “visitors” and “physical examination.”

Chemicals—Mentioned that one patient was heavily sedated at one point with morphine; affected VO₂ and VCO₂ than when unsedated.

This study demonstrates that routine daily ICU activities can cause arousal from the resting state and significantly alter metabolic rate. Thus, it is important to couple measurements of metabolic rate with astute observations of the patent’s activity state.

The results of this study indicate that the observed variations in metabolic rate can be classified into the 4 following categories:

1. The lowest energy expenditure was found to be associated in the majority (83%) of situations; with sleep. The VO₂ averaged 9.1 ± 7.5% below resting values, while VCO₂ averaged 7.5 ± 7.3% below resting values. This is consistent with observations made in healthy individuals that sleep results in an 8 – 12% decrease in energy expenditure.
2. Resting—Responsiveness to surrounding events was gauged as eye movements tracking the movements of hospital staff. A strict definition of lying motionless was necessary since movement of limbs caused significant increases in both VO₂ and VCO₂.
3. Routine daily activities that, although not painful, involved arousal from the resting state, external stimulation, and both active and passive limb movement.
4. Chest physical therapy—this patient care activity was associated with the greatest metabolic stimulus and was associated with significant increases in heart rate as well as rate-pressure-product. The increases in VO₂ and VCO₂ observed were probably due to pain, movement and muscular tension in both the chest and abdomen.

These results allow for the definition of “resting” state. Measurement of energy expenditure are traditionally performed in the “basal” state; defined as the minimal energy expenditure of a subject lying down and resting in a thermoneutral environment having fasted for the previous 12 hours. Such conditions are rare in the critically ill patient since such a patient is receiving some form of continuous nutrition, whether it be 5% dextrose or enteral or parenteral nutrition. Measurements made during rest in patients receiving total parenteral nutrition are described as measurements of resting energy expenditure (REE) and are usually about 10 percent about basal because they include the specific dynamic action of foods.

Measuring energy expenditure in critically ill patients receiving mechanical ventilation poses a variety of problems. The initial problem is defining a reference state from which to calculate energy expenditure for use in the formation of caloric intake. This is especially crucial since these patients may be comatose, may have receiive narcotics or muscle relaxants (both of which can alter metabolic rate), or may be disoriented, and thus, be unable to follow verbal commands to remain at rest, no sleep and thrash about.

In this study, we have defined such a reference state and have named it “resting” since it appears to correspond to the resting state found in spontaneously breathing patients.

However, it is important to remember that, due to the oxygen cost of breathing, REE is greater during spontaneous breathing than during mechanical ventilation. Further investigation is needed to define a reference state for comatose patients.

While performing this study, a number of practical observations were made:

1. VO₂ and VCO₂ were lower in a patient when heavily sedated with narcotics than when unsedated.
2. After stimulation, even a routine bath or connecting the instrumentation to measure VO₂ and VCO₂ , metabolic rate may be elevated for up to 45 min. Thus, it is important to wait a while before attempting to measure a RMR.
3. Multiple and frequent measurements should be made to ensure that the patient is truly resting. The mere observation of a motionless patient with his/her eves open is insufficient to be labeled resting, but coupled with stable measurements over a 15 to 30 min period can be considered resting. Confirmation is most reliably obtained by repeating at some later time.

It must be emphasized that measurements of resting energy expenditure is a complex and exacting task that requires an astute observer and much patience.

[Not used in Conclusion Statement Summary and Grade due to inability to determine "rest time" following activities].

Strengths

• With ventilated patients, frequent measurements of gas exchange can be performed without interfering with the patient’s respiratory system. In spontaneously breathing patients, long-terms measurements are difficult since they must be performed with either a mask or mouthpiece plus nose-clip or by placing the patient in a canopy.
• Use of the combination of visual observation, monitoring of heart rate and blood pressure along with metabolic measurements for increased accuracy

Limitations

• Only hemodynamically stable, noncomatose mechanically-ventilated surgical ICU patients were studied
• This is only a subset of ICU patients who require mechanical ventilation for a moderate-to-long period of time so limited generalizability
• Disease states not discussed
• Population not described other than they were ventilated, postop surgical patients with a mean age of 68; no gender or anthropometric information provided
• Older population (mean age 68); most likely had a number of preexisting medical conditions along with advanced age
• Since patients were hemodynamically stable; alterations in VO₂ and VCO₂ may have been due to the observed events rather than to a pathophysiologic phenomenon
• Does not give information on whether patients were sedated or any other medications that might alter metabolic rate (in discussion only indicates one patient was receiving morphine during part of the study)