Module 2: Metabolic Demand

Question 1

what does metabolic and oxygen demand refer to?

Answer 1

the amount of oxygen required by the body’s tissues in order to perform metabolic processes

Question 2

metabolic demand assessment

Answer 2

• cells require oxygen to produce energy required to maintain cellular function
• if O2 supply cannot meet O2 demand then cellular fx will be disrupted
• main determinants = temp, physical activity, and stress (physiological and perceived)

Question 3

what happens in aerobic cellular metabolism?

Answer 3

cells use O2 and nutrients from dietary intake to produce energy in the form of adenosine triphosphate (ATP)

Question 4

what happens if cells are required to function harder or faster, grow larger, or more cells are required to function?

Answer 4

cellular metabolism will increase their production of ATP to meet this need, increasing the cells’ need for both O2 (demand) and fuel

Question 5

what is internal body temp controlled by?

Answer 5

thermoregulatory centre in the hypothalamus

Question 6

when do fevers occur?

Answer 6

when immunological mediators act on the hypothalamus to increase its set point

Question 7

how does the body increase temp to meet an increased set point?

Answer 7

by peripheral vasoconstriction (shunt blood to internal organs, decreases heat loss from skin, pt feels cold) and shivering (increases heat production from muscles)

Question 8

what happens when set point is reduced?

Answer 8

the body speeds heat loss through vasodilation and sweating

Question 9

what is the average body temp?

Answer 9

36.7

Question 10

what happens with metabolic demand when temp increases above normal?

Answer 10

there is a 10% increase in metabolic demand for each degree above normal

Question 11

what is the most accurate way to measure temp?

Answer 11

centrally:
- esophageal
- rectal (generally 0.6 degrees higher than oral)
- urinary bladder
- pulmonary artery catheter

Question 12

what are other ways to measure temp?

Answer 12

peripherally:
- oral
- tympanic
- temporal artery
- axillary

Question 13

physical activity

Answer 13

includes activity generated by the individual (increased work of breathing, restlessness, and coughing) and activity generated by providing care to the patient (comprehensive assessments, mobilizing/re-positioning, tests, procedures)

Question 14

what % of increase in O2 demand does WOB cause?

Answer 14

40%

Question 15

what % of increase in O2 demand does shivering cause?

Answer 15

50-100%

Question 16

what % of increase in O2 demand does seizures cause?

Answer 16

> 60%

Question 17

what % of increase in O2 demand does restlessness/agitation cause?

Answer 17

> 20%

Question 18

what % of increase in O2 demand does increased HR cause?

Answer 18

increases myocardial O2 demand

Question 19

what % of increase in O2 demand does endotracheal suctioning cause?

Answer 19

27%

Question 20

what % of increase in O2 demand does doing a CXR cause?

Answer 20

25%

Question 21

what can stress arise from?

Answer 21

• physiological and emotional sources
• actual situations (critical illness) or an individual’s perception of a situation as threatening (emotional response to hospital admission)

Question 22

what happens when the body experiences a real or perceived threat?

Answer 22

SNS is activated; increase O2 supply in order to support the increase in cellular metabolism associated with the extra work the body requires to respond to the threat

Question 23

what else will contribute to stress and alterations in O2 demand?

Answer 23

Pain, anxiety, sleep disturbances, and delirium; personal experience of critical illness

Question 24

what are some examples of associated conditions that affect stress and increase O2 demand?

Answer 24

• head injury with or without sedation
• chest trauma, burns
• sepsis
• MODS
• skeletal injuries
• critical illness in ER
• anesthesia