Anesthesia Monitoring: EKG Rhythms and BP Monitoring

Monitoring Standards

• For every anesthetic monitor, the following parameters should be monitored: BP, HR, EKG, RR, Pulse Ox, and ETCO2 when using moderate sedation or higher (deep or GA)
• HR and RR should be monitored continuously, while BP should be monitored continually every 5 minutes

BP Monitoring

Arterial Blood Pressure Monitoring

• Accuracy is optimized by using stiff catheters and tubing, a small amount of fluid in the system, shorter length of tubing, and minimizing stopcocks
• Transducers must be zeroed and positioned at the level of the RA (typically), or at the circle of Willis (in neurosurgery for cerebral perfusion)
• Complications can be mitigated by using small catheters, minimizing attempts, and monitoring sites
• Arterial waveform analysis can be used to assess for damping, with:
  • Fast flush to assess for damping
  • Underdamping: multiple artifacts present in waveform, overestimates SBP, underestimates DBP, and MAP is accurate
  • Overdamping: dicrotic notch is lost, underestimates SBP, overestimates DBP, and MAP is accurate

Noninvasive Blood Pressure Monitoring

• Cuff size should be 40% of the extremity circumference and encircle 80% of the extremity
• If the cuff is too small, readings obtained are falsely high
• Position the cuff opposite to the IV if possible, and change position for longer cases
• Frequent measurements can cause nerve damage or IV extravasation

Pulse Oximetry and Co-Oximetry

Pulse Oximetry

• Arterial O2 sat is typically 95-100%
• Numbers should correlate but not exactly match PaO2
• Works through absorption spectrometry, measuring light absorption of a chemical substance as it passes through a solution
• Based on Beer-Lambert Law, where light absorbed by a solution is related to its concentration
• SPO2 is the ratio of oxyhemoglobin to hemoglobin
• Pulse ox sensor contains 2 LEDs and a photodetector, measuring the ratio of infrared and red light, and averaging data over a time period to calculate SPO2

Co-Oximetry

• Fractional saturation and co-oximetry measure the ratio of oxyhemoglobin to Hgb, carboxyhemoglobin, methemoglobin, and other forms of hemoglobin
• Carboxyhemoglobin:
  • Has a higher affinity for Hgb than O2 (250x)
  • Hgb binding sites occupied by CO cannot carry O2
  • SPO2 will read falsely high
  • Treatment is 100% FiO2
  • Signs and symptoms: cherry red lips
• Methemoglobin:
  • Results from the presence of iron in an oxidized form
  • Normally 1%
  • Falsely high for sats 40%, pulse ox will read 80-85%
  • Treatment is methylene blue 1-2 mg/kg as 1% solution over 3-5 minutes
• Sulfahemoglobin:
  • Results from irreversible binding of sulfur to Hgb
  • Normally 0.9%
  • May be caused by certain medications, such as migraine medication and certain antibiotics

Monitoring Standards

• For every anesthetic monitor, the following parameters should be monitored: BP, HR, EKG, RR, Pulse Ox, and ETCO2 when using moderate sedation or higher (deep or GA)
• HR and RR should be monitored continuously, while BP should be monitored continually every 5 minutes

BP Monitoring

Arterial Blood Pressure Monitoring

• Accuracy is optimized by using stiff catheters and tubing, a small amount of fluid in the system, shorter length of tubing, and minimizing stopcocks
• Transducers must be zeroed and positioned at the level of the RA (typically), or at the circle of Willis (in neurosurgery for cerebral perfusion)
• Complications can be mitigated by using small catheters, minimizing attempts, and monitoring sites
• Arterial waveform analysis can be used to assess for damping, with:
  • Fast flush to assess for damping
  • Underdamping: multiple artifacts present in waveform, overestimates SBP, underestimates DBP, and MAP is accurate
  • Overdamping: dicrotic notch is lost, underestimates SBP, overestimates DBP, and MAP is accurate

Noninvasive Blood Pressure Monitoring

• Cuff size should be 40% of the extremity circumference and encircle 80% of the extremity
• If the cuff is too small, readings obtained are falsely high
• Position the cuff opposite to the IV if possible, and change position for longer cases
• Frequent measurements can cause nerve damage or IV extravasation

Pulse Oximetry and Co-Oximetry

Pulse Oximetry

• Arterial O2 sat is typically 95-100%
• Numbers should correlate but not exactly match PaO2
• Works through absorption spectrometry, measuring light absorption of a chemical substance as it passes through a solution
• Based on Beer-Lambert Law, where light absorbed by a solution is related to its concentration
• SPO2 is the ratio of oxyhemoglobin to hemoglobin
• Pulse ox sensor contains 2 LEDs and a photodetector, measuring the ratio of infrared and red light, and averaging data over a time period to calculate SPO2

Co-Oximetry

• Fractional saturation and co-oximetry measure the ratio of oxyhemoglobin to Hgb, carboxyhemoglobin, methemoglobin, and other forms of hemoglobin
• Carboxyhemoglobin:
  • Has a higher affinity for Hgb than O2 (250x)
  • Hgb binding sites occupied by CO cannot carry O2
  • SPO2 will read falsely high
  • Treatment is 100% FiO2
  • Signs and symptoms: cherry red lips
• Methemoglobin:
  • Results from the presence of iron in an oxidized form
  • Normally 1%
  • Falsely high for sats 40%, pulse ox will read 80-85%
  • Treatment is methylene blue 1-2 mg/kg as 1% solution over 3-5 minutes
• Sulfahemoglobin:
  • Results from irreversible binding of sulfur to Hgb
  • Normally 0.9%
  • May be caused by certain medications, such as migraine medication and certain antibiotics

Monitoring Standards

• For every anesthetic monitor, the following parameters should be monitored: BP, HR, EKG, RR, Pulse Ox, and ETCO2 when using moderate sedation or higher (deep or GA)
• HR and RR should be monitored continuously, while BP should be monitored continually every 5 minutes

BP Monitoring

Arterial Blood Pressure Monitoring

• Accuracy is optimized by using stiff catheters and tubing, a small amount of fluid in the system, shorter length of tubing, and minimizing stopcocks
• Transducers must be zeroed and positioned at the level of the RA (typically), or at the circle of Willis (in neurosurgery for cerebral perfusion)
• Complications can be mitigated by using small catheters, minimizing attempts, and monitoring sites
• Arterial waveform analysis can be used to assess for damping, with:
  • Fast flush to assess for damping
  • Underdamping: multiple artifacts present in waveform, overestimates SBP, underestimates DBP, and MAP is accurate
  • Overdamping: dicrotic notch is lost, underestimates SBP, overestimates DBP, and MAP is accurate

Noninvasive Blood Pressure Monitoring

• Cuff size should be 40% of the extremity circumference and encircle 80% of the extremity
• If the cuff is too small, readings obtained are falsely high
• Position the cuff opposite to the IV if possible, and change position for longer cases
• Frequent measurements can cause nerve damage or IV extravasation

Pulse Oximetry and Co-Oximetry

Pulse Oximetry

• Arterial O2 sat is typically 95-100%
• Numbers should correlate but not exactly match PaO2
• Works through absorption spectrometry, measuring light absorption of a chemical substance as it passes through a solution
• Based on Beer-Lambert Law, where light absorbed by a solution is related to its concentration
• SPO2 is the ratio of oxyhemoglobin to hemoglobin
• Pulse ox sensor contains 2 LEDs and a photodetector, measuring the ratio of infrared and red light, and averaging data over a time period to calculate SPO2

Co-Oximetry

• Fractional saturation and co-oximetry measure the ratio of oxyhemoglobin to Hgb, carboxyhemoglobin, methemoglobin, and other forms of hemoglobin
• Carboxyhemoglobin:
  • Has a higher affinity for Hgb than O2 (250x)
  • Hgb binding sites occupied by CO cannot carry O2
  • SPO2 will read falsely high
  • Treatment is 100% FiO2
  • Signs and symptoms: cherry red lips
• Methemoglobin:
  • Results from the presence of iron in an oxidized form
  • Normally 1%
  • Falsely high for sats 40%, pulse ox will read 80-85%
  • Treatment is methylene blue 1-2 mg/kg as 1% solution over 3-5 minutes
• Sulfahemoglobin:
  • Results from irreversible binding of sulfur to Hgb
  • Normally 0.9%
  • May be caused by certain medications, such as migraine medication and certain antibiotics

Learn about the standards for monitoring patients under anesthesia, including EKG rhythms, blood pressure monitoring, and other vital signs. Understand how to optimize arterial blood pressure monitoring and transducer usage.