test 9 Flashcards
Our continued health depends on the body’s
ability
• To deliver the appropriate amount of oxygen to
each cell
• For each cell to uptake and consume the proper
amount of oxygen
Normal Oxygen Consumption
200-250 mL O2/min
What is the final common
pathway of all causes of death
tissue hypoxia
energy production is determined by what
metabolic rate
creation of energy is supported by what
adequate amounts of glucose and oxygen delivered to the cells
similarities between aerobic and anaerobic metabolism
- both start with glucose metabolized to pyruvate
- both produce ATP
Aerobic metabolism
-O2 present
• Pyruvate converted to acetyl-CoA, which enters the Krebs cycle
which produces carbon dioxide, water and ATP
• 1 mole glucose→ 36 moles ATP
-end product= CO2 and H2O
Anaerobic metabolism
• Pyruvate converted to lactic acid and ATP
• 1 mole glucose→ 2 moles ATP
-end product= lactic acid
monitoring what can tell you a lot about what has occurred during your pump run
lactate
why measure lactic acid in blood
-if lactic acid present, we know that there are areas in our body where anaerobic metabolism has occurred
Arterial O2 content
17-20 mL/100mL blood
Venous O2 content
12-15 mL/100mL blood
A-V O2 difference
4-6 mL/100mL blood
what is one of the best ways to increase O2 content
-increase hemaglobin
O2 delivery (& normal value)
- DO2 = Arterial content × Cardiac output
- 950-1150 mL O2/min
- Indexed: 550-650 mL O2/min/m2
O2 reserve
• The amount of oxygen left AFTER consumption
has taken place
• Venous gases returning to the heart
• A built-in physiologic buffer (in case we need it)
Normal Oxygen Reserve
- 700-800 mL O2/min
- Indexed: 450 mL O2/min/m2
How long can you use your reserve
- around 32% SvO2
- then anaerobic metabolism starts to come into play
Factors That Increase Oxygen Consumption
- Patient conditions
- Medications
- Procedures
Patient Conditions that Increase Oxygen Consumption
- Minor surgery: 7% increase
- Fever (each 1 o C): 10%
- Agitation: 16%
- Increased work of breathing: 40%
- Severe infection: 60%
- Chest trauma: 60%
- Shivering: 50 to 100%
- Sepsis: 50 to 100%
Medications that Increase Oxygen Consumption
- sympathetic agonists
- causing an increase in CO and vasoconstriction
Procedures that Increase Oxygen Consumption
- Dressing change: 10% increase
- Physical examination: 20%
- Visitors: 22%
- Endotracheal suctioning: 27%
- Turning: 31%
- Chest physiotherapy: 35%
- Nasal intubation: 25 to 40%
Factors that Decrease Oxygen Consumption
- Hypothermia (7oC): 50% decrease
- Morphine sulfate IV: 21%
- Anesthesia: 25%
- Assist/control ventilation: 30%
- Neuromuscular blocking agents
Ischemic hypoxia
• Inadequate blood flow (regional or general)
• Obstructive lesions of blood vessels
-(Coronary or cerebral thrombosis or spasm or Peripheral vascular disease)
Hypoxemic hypoxia
- Inadequate transfer of oxygen from the lungs to the hemoglobin molecule
- Hypoxemia most common cause, Carbon monoxide poisoning, Methemoglobinemia
Anemic hypoxia
-Deficiency of hemoglobin molecules
Toxic hypoxia
- Inability of body cells to uptake or use oxygen
- Sepsis, cyanide toxicity, and ethanol toxicity
Excessive tissue requirements
- Oxygen demand higher than system can supply
- Hypermetabolism, Sepsis, alcohol withdrawal, extreme fever
Impaired oxygen unloading
- At the capillary level
- alkalemia, hypocarbia, and Administration of large amounts of banked blood
Compensatory Mechanisms for Impaired Tissue Oxygenation
- Increase cardiac output (primary response)
- Draw from venous reserve
- Polycythemia
Increase cardiac output (primary response)
• The tissues control the cardiac output in accordance with their
need for oxygen
• Healthy heart can increase to 15-25 L/min
-acute response
Draw from venous reserve
• Extract more oxygen from hemoglobin
• Can decrease venous sat to 32% before anaerobic metabolism starts
-acute response
Polycythemia
• Increase amount of hemoglobin and RBC mass
• Takes weeks to develop
-long term response
Monitoring Oxygen Transport
- Arterial and mixed venous blood gas (central lab)
- Point-of-care blood gas
- Noninvasive pulse oximetry
- Invasive mixed venous saturation
- Continuous indwelling arterial blood gas
- Transcutaneous measurement of local tissue saturation
Arterial and Mixed Venous Blood Gases from Central Lab
- Lag time between sampling and results
- Intermittently performed
- May not detect acute, severe hypoxemia
Point-of-Care Blood Gas Analyzers
-bedside blood gas
Point-of-Care Blood Gas Analyzers pros
• Able to measure gases, electrolytes, glucose, lactate, urea, nitrogen and hematocrit • Small and portable • Small blood volume required • Self-calibrating • Disposable cartridges
Point-of-Care Blood Gas Analyzers cons
• Can be expensive with labor intensive quality control
Noninvasive Pulse Oximetry
• 2 light emitting diodes (LED) send red and infrared
light through the arterial vascular bed
• Photodetector measures transmitted light and
detects the relative amount of color absorbed by
arterial blood and estimates the saturation
• Saturated Hb= Absorbs more infrared light
• Desaturated Hb= Absorbs more red light
-can be placed on the patient’s finger, toe, earlobe or nose bridge
• Accuracy: ± 4%
• less reliable with saturations between 50 and 70%
• no accuracy below 50%
• Adequate peripheral perfusion required
Noninvasive pulse oximetry does NOT
-guarantee that oxygen is being delivered to or used by the cells
Falsely ↓ Saturation Values for Pulse Oximetry
- Nail polish/acrylic nails
- Dark skin pigmentation
- IV dyes
- Lipid infusions
- Anemia (Hct < 10%)
- Venous pulses
- Patient movement
Falsely ↑ Saturation Values Pulse Oximetry
- Elevated carboxyhemoglobin
- Elevated methemoglobin
- Intense surgical light
SpO2 Ranges
- 96-99% : Normal
- 85-90% : Mild tissue hypoxia
- 75-85% : Significant widespread tissue hypoxia
Invasive Mixed Venous Saturation
• Measured via fiberoptic pulmonary artery
catheter
• Uses reflectance spectrophotometry
Invasive Mixed Venous Saturation: General Info
• very fragile so you don’t want to break them or bend/kink
• Manufacturer specific pre-insertion calibration
required and in vivo calibration
• Keep catheter tip away from the wall of the
pulmonary artery (reflection from the vessel will distort results)
• Not able to distinguish carboxyhemoglobin and
methemoglobin from oxyhemoglobin
Continuous Indwelling Arterial and Venous Gases
- can measure saturation through tubing of pump
- can take continuous blood gasses of samples
- calibrate with tanks of gas
Transcutaneous Measurement of Local Tissue Saturation
- near-infrared spectrometry (NIRS)
• Uses specific, calibrated wavelengths of nearinfrared
light
• light is absorbed relative to amount of oxygen attached
to the hemoglobin in the blood vessels
