Monitoring During anaesthesia

Prof. Abdulhamid Al-Saeed, FFARCSIAnaesthesia Department

College of MedicineKing Saud University

Lecture Objectives..Lecture Objectives..Students at the end of the lecture will be able to knows:

Monitors :

Non-invasive blood pressure , ECG , pulse oximetry capnography (CO2 monitor) and oxygen analyzer , temperature probe nerve stimulator

Specialized monitors :

arterial line (invasive blood pressure)

central venous line (cvp monitoring)

pulmonary artery flotation catheter ( monitors function of right and left side of the heart)

BIS monitor (depth of anesthesia)

Monitoring: A Definition

• interpret available clinical data to help recognize present or future mishaps or unfavorable system conditions

Monitoring in the Past

Finger on the pulse

•Visual monitoring of respiration and overall clinical appearance•Finger on pulse•Blood pressure (sometimes)

Monitoring in the Present• Standardized basic monitoring requirements

(guidelines) from the ASA (American Society of

Anesthesiologists), CAS (Canadian

Anesthesiologists’ Society) and other national

societies

• Many integrated monitors available

• Many special purpose monitors available

• Many problems with existing monitors (e.g., cost,

complexity, reliability, artifacts)

Standard

ASA monitoring for general anesthesia , monitored anesthesia care and regional anesthesia :-

Oxygenation (oxygen analyzer, pulse oximetry),

Ventilation (capnography, minute ventilation), respiratory rate (under regional anesthesia)

Circulation (electrocardiogram [ECG], arterial blood pressure, perfusion assessment),

Temperature.

High Tech Patient Monitoring

Examples of Multiparameter Patient MonitorsExamples of Multiparameter Patient Monitors

High Tech Patient Monitoring

Some Specialized Patient MonitorsSome Specialized Patient Monitors

Depth of Anesthesia Monitor

Evoked Potential Monitor

Transesophageal Echocardiography

Cardiovascular system.The circulatory system is responsible for oxygen delivery to and

removal of waste products from the organs, and this must be maintained during anesthesia.

Signs and symptoms of perfusion abnormalities

Central nervous system: mental status changes, neurologic deficits.

Cardiovascular system: chest pain, shortness of breath, ECG abnormalities, wall motion abnormalities on echocardiogram.

Renal: decreased urine output, elevated blood urea nitrogen and creatinine, decreased fractional excretion of sodium.

Gastrointestinal: abdominal pain, decreased bowel sounds, hematochezia.

Peripheral: cool limbs, poor capillary refill, diminished pulses.

ECG. The ECG monitors the conduction of electrical impulses

through the heart. Rhythm detection is best seen in lead II.

ECG

Electrocardiogram

• Displays the overall electrical activities of the myocardial cells– Heart rate & dysrhythmias– Myocardial ischaemia– Pacemaker function– Electrolyte abnormalities– Drug toxicity

• Does NOT indicate mechanical performance of the heart:– Cardiac output– Tissue perfusion

Full (12)-lead ECGStandard limb leads (bipolar)Precordial leads (unipolar)

5.lead systemUnipolar + bipolarRA, LA, RL, LL, C

3.lead systemBipolar with RA, LA, LLV5 usually used Best compromise between detecting ischaemia and

diagnosing arrhythmiaMay come with

ST-segment analysis

ECG

Standard Limb Leads

Unipolar Chest Leads

Artifacts in ECG Monitoring

• Loose electrodes or broken leads• Misplaced leads• Wrong lead system selected• Emphysema, pneumothorax,

pericardial effusion• Shivering or restlessness• Respiratory variation and

movement• Monitor Pulse Oximetry, Invasive

ABP

Arterial blood pressure. Automated noninvasive blood pressure is the most common

noninvasive method of measuring blood pressure in the operating room.

Invasive blood pressure monitoring uses an indwelling arterial catheter coupled through fluid-filled tubing to a pressure transducer. The transducer converts pressure into an electrical signal to

be displayed. Indications

– Need for tight blood pressure control (e.g., induced hyper- or hypotension).

– Hemodynamically unstable patient.– Frequent arterial blood sampling.– Inability to utilize noninvasive blood pressure

measurements.

Arterial Blood Pressure

Central venous pressure (CVP) and cardiac output

CVP is measured by coupling the intravascular space to a pressure transducer using fluid-filled tubing.

Pressure is monitored at the level of the vena cava or the right atrium.

IndicationsMeasurement of the right heart filling pressures to assess

intravascular volume and right heart function.Drug administration to the central circulation. Intravenous access for patients with poor peripheral access. Indicator injection for cardiac output determination (e.g.,

green dye cardiac output).Access for insertion of pulmonary artery catheter.

Range The CVP is normally 2 to 6 mm Hg

Central Venous Pressure

PULMONARY ARTERY CATHETER

Pulmonary Artery Catheter

Haemodynamic Profiles Obtained from PA Catheters

• SV = CO / HR (60-90 mL/beat)

• SVR = [(MAP – CVP) / CO] 80 (900-1500 dynes-sec/cm5)

• PVR = [(MPAP – PCWP) / CO] 80 (50-150 dynes-sec/cm5)

• O2 delivery (DO2)

= C.O. O2 content• Arterial O2 content (CaO2)

= ( Hb 1.38 ) (SaO2)• Mixed venous O2 content (CvO2)

= ( Hb 1.38 ) (SvO2)• O2 consumption (VO2)

= C.O. (CaO2-CvO2)

SvO2 = SaO2 – [VO2 / (Hb 13.8)(CO)]

Respiratory system. pulse oximetry, capnography, a fraction of inspired oxygen

analyzer, and a disconnect alarm.  Pulse oximeter

combines the principles of oximetry and plethysmography to noninvasively measure oxygen saturation in arterial blood.

The pulse oximeter probe contains two light emitting diodes at wavelengths of 940nm and 660 nm.

Oxygenated and reduced hemoglobin differ in light absorption (940 and 660 nm respectively).

Thus the change in light absorption during arterial pulsation is the basis of oximetry determination.

The ratio of the absorption at the two wavelengths is analyzed by a microprocessor to record the oxygen saturation.

 

 

Pulse Oximetry

Incomptencies

Critically ill with poor peripheral circulation Hypothermia & VC Dyes ( Nail varnish ) Lag Monitor Signalling 5-20 sec

PO2 Cardiac arrhythmias may interfere with the oximeter

picking up the pulsatile signal properly and with calculation of the pulse rate

Abnormal Hb ( Met., carboxy)

CapnometryWhat is Capnometry? Is the measurement of end-tidal carbon dioxide tension. This provides valuable information to the anesthesiologist. The presence of end tidal CO2 aids in confirming endotracheal

intubation. Alteration in the slope of the graph can give clues to the

presence of airway obstruction. A rapid fall in reading may signify extubation, air embolism or

low cardiac output with hypovolemia.

The Alpha angle• The angle between phases II and III, which

has• increases as the slope of phase III

increases. • The alpha angle is an indirect indication of

V/Q• status of the lung. • Airway obstruction causes an increased• slope and a larger angle. • Other factors that affect the angle are the

response time of the capnograph, sweep speed, and the respiratory cycle time.

The Beta angle• The nearly 90 degrees angle between phase

III and the descending limb in a time capnogram has been termed as the beta angle.

• This can be used to assess the extent of rebreathing. During rebreathing, there is an increase in beta angle from the normal 90 degrees.

Clinical Applications

Central nervous system (level of consciousness) monitoring

Bispectral index (BIS) assess central nervous system depression during general anesthesia.

It is based on the surface electroencephalogram (EEG), which predictably changes in amplitude and frequency as the depth of anesthesia increases.

Temperature monitoring

Indications

Infants and small children are prone to thermal lability due to their high surface area to volume ratio.

Adults subjected to large evaporative losses or low ambient temperatures (as occur with exposed body cavity, large volume transfusion of unwarmed fluids, or burns) are prone to hypothermia.

Malignant hyperthermia is always a possible complication, and temperature monitoring should always be available.

Monitoring site

Tympanic membrane temperature

Rectal temperature

Nasopharyngeal temperature,

Esophageal temperature monitoring reflects the core temperature well. The probe should be located at the lower third of the esophagus and rarely may be misplaced in the airway.

Blood temperature measurements may be obtained with the thermistor of a PAC.

Neuromuscular blockade monitoring:

Neuromuscular blockade is monitored during surgery to guide repeated doses of muscle relaxants and to differentiate between the types of block.

All techniques for assessing neuromuscular blockade use a peripheral nerve stimulator (PNS) to stimulate a motor nerve electrically.

Detecting Mishaps Using Monitors

1. Disconnection

2. Hypoventilation

3. Esophageal intubation

4. Bronchial intubation

5. Circuit hypoxia

6. Halocarbon overdose

7. Hypovolemia

8. Pneumothorax

9. Air Embolism

10. Hyperthermia

11. Aspiration

12. Acid-base imbalance

13. Cardiac dysrhythmias

14. IV drug overdose

Source: Barash Handbook

These mishaps …

Detecting Mishaps with Monitors• Pulse oximeter• Capnograph• Automatic BP• Stethoscope• Spirometer• Oxygen analyzer• ECG• Temperature

1,2,3,4,5,8,9,11,14

1,2,3,9,10,12

6,7,9,14

1,3,4,13

1,2

5

13

10 Source: Barash Handbook

… are detected using these monitors

Question NO. 8• 1- Identify the monitor Tracing?•

………………………………………

• 2- What is the Name & Cause of the Notch on the descending limb of the trace?

•………………………………………………………………………………

• 3- Name two different Clinical informations could be interpreted from this tracing?

• a) ……………………………..• b) ……………………………..

Question NO. 10

1- Identify the Rhythm in the shown ECG Strip?

------------------------------------------------------2- What is your first line of management in case of

Unstable patient …………………………………………………………

3- What is the normal QRS duration

……………………………………………………………

1- Identify the tracing

………………………………………………………………………………………

2- Name the different phases of the trace I ……………………… II …………………….. III ……………………. IV ……………………..3- What different clinical informations could

be interpreted from the trace a) ……………………………………………….. b) ………………………………………………..

Question NO. 14

1- Name the different waves on the trace?------------------------------------------------2- Define Central Venous Pressure?

……………………………………………………

……………………………………………………

3- What are the main determinants regulating CVP?

A-…………………………………. B- ………………………………...

Question NO. 15

brief the mechanism of action of this monitor :………………………………………………………………………………………

……………………………………………………………………………………………………………………………………………………………

Name 4 factors affecting the accuracy of this monitor?………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

If P50 of oxyhemoglobine dissociation curve is 40; is this curve shifted to the right or left; mention 3 possible causes?

………………………………………………………………………………………………………………………………………………………………………………………………………………………………..

Question NO. 19

36-Each of the following factors may lead to error in readings using pulse oximetry EXCEPT:A. electrocauteryB. high cardiac output statesC. infrared lights near the sensorD. intravenous dyesE. severe hemodilution