I&M: Monitoring of Pulse Oximetry, NIBP, and Temperature Flashcards Preview

MSA S2015 > I&M: Monitoring of Pulse Oximetry, NIBP, and Temperature > Flashcards

Flashcards in I&M: Monitoring of Pulse Oximetry, NIBP, and Temperature Deck (18):
1

Pulse Oximetry

Pulse oximeter can be placed on fingers, toes, nose, ear. The more peripherally the pulse oximeter is placed on patient, the longer the delay in detecting an event causing oxygenation change. For example, if placed on finger or toe, delay may be between 30-60s.

The LEDs alternate on and off at 400Hz and has a measurable off phase to detect ambient lighting (artifact).

Photodetector measures absorption of both pulsatile (arterial) and non-pulsatile (venous) components at both wavelengths. Pulsatile portion is only 1-2% of total.

Accuracy of monitor decreases as saturation falls below 70%. Meanwhile, when PaO2 values exceed 90mmHg, small changes in saturation are associated with large changes in PaO2. This makes it hard distinguish between high but safe levels of arterial O2 from excessively elevated levels. (see Hg-O2 dissociation graph)

2

Two components of pulse oximetry

- Pulse plethysmography = detects change in cylindrical volume of artery and displays a graphic representation of waveform on monitor.
- Infrared spectroscopy = detects absorption of light by oxyhemoglobin and deoxyhemoglobin. Oxyhemoglobin absorbs 940nm infrared light while deoxyhemoglobin absorbs 660nm red light.

3

Factors that limit accuracy of pulse oximeter

1. Movement or vibration
2. Electromagnetic interference (cell phone)
3. Hypertension, vasoconstriction
4. Hypotension, hypovolemia
5. Hyperdynamic venous circulation (tricuspid valve regurgitation)
6. IV dyes (e.g. methylene blue)
7. Dark nail polish
8. Ambient light **one of biggest factors

4

Factors that causes failure to determine oxygen saturation

Pulse oximeter requires adequate pulsations in order to distinguish arterial blood from venous blood and tissue light.

1. Hypotention
2. Hypovolemia
3. Hypothermia
4. Low CO
5. Peripheral vascular disease
6. Raynaud's phenomenon
7. External pressure
8. Proximal BP cuff
9. Improper positioning
10. Valsalva maneuver often seen in laboring patients
11. Cardiopulmonary bypass

5

Factors that causes delayed detection of hypoxic events

1. Lag time increased with low perfusion
2. Device algorithms used to prevent false alarms may increase delay in detecting hypoxic events
3. Pulse oximeter may respond to weak/noisy signal by holding onto old values
4. Increasing time over which pulse signals are averaged (signal processing) may increase delay time
5. Pulse oximeter may not detect other species of hemoglobin like carboxyhemoglobin, sulfhemoglobin, fetal hemoglobin, and methemoglobin

6

Carboxyhemoglobin

Formed when Hb is exposed to CO and has similar absorption spectrum to oxyhemoglobin --> over-readSpO2 by percentage of COHb present

7

Patient complications caused by pulse oximeter

1. Corneal abrasions (don't use dominant fingers/hand)
2. Pressure and ischemic injuries (frequent examination of site and moving probe to different sites)
3. Burns
4. Bruns associated with MRI
5. Electric shock

8

Body temperature

Core body temperature is ~37'C. Temperature decreases as move away from core. Value is not so much important as temperature trend--> warmer, cooler, staying the same? Most common measurements are on skin, esophageal, nasal, and rectal.

9

Classic
Devices to measure temperature

Glass tube filled with fluid that expands as temperature rises (mercury)

10

Thermistor
Devices to measure temperature

Consists of semiconductor whose resistance changes as temperature changes

11

Thermocouple
Devices to measure temperature

Consists of two dissimilar metals connected at both ends. One metal is kept at known reference temperature while the other is exposed to temperature to be measured. A potential difference is generated proportional to temperature difference.

12

Liquid crystal displays
Devices to measure temperature

Made of material that changes color as temperature changes and can be placed on skin.

13

Infrared
Devices to measure temperature

Consists of a series of thermocouples (thermopile) that detect the infrared radiation emitted. Thermopile generates a potential difference proportional to temperature difference.

14

Noninvasive blood pressure

NIBP involves inflating an occlusive cuff around a limb until cuff pressure is greater than systolic pressure and then letting cuff deflate until flow returns to limb.

There are four measurement techniques: auscultation, oscillotonometer, oscillometer, volume clamp

15

Blood pressure cuff size

Cuff size is imperative: cuff width should be 40% of mid circumference of limb; length should be 2x this width.

If a cuff is too narrow --> falsely high BP
If cuff is too wide --> falsely low BP

16

Sphygmomanometer

Uses a combination of pneumatic cuff, inflating bulb, release valve, and mercury manometer.

17

Auscultation

Cuff is placed on upper arm and Korotkoff sounds are listened to over brachial artery. When pulse is first heard (turbulent flow) is systolic pressure. When pulse sound disappears is diastolic pressure.

Disadvantages: poor correlation to invasive BP measurement; overestimates low BP and underestimates high BP

18

Complications of intermittent NIBP monitors

1. Damage to underlying tissues
2. Neuropathies (damage to nerves)
3. Compartment syndrome (excessive pressure build up in an enclosed space of the body)
4. Mechanical problems such as leaking cuff, hose, or connector
5. Artifacts (intrinsic and extrinsic motion)
6. Air embolism (gas bubble in vascular system)
7. Iatrogenic harm