Patient Monitoring

Patient monitoring and the equipment to support it are vital to caring for patientsin operating rooms, intensive care units,

emergency departments, and in acute caresettings

Patient Monitoring divided into :

• Non Instrumental: clinical observation(“look, listen, feel”)Visual and auditory surveillance is central to

patient monitoring, and involves many dimensions:

• Observing the patient’s color, respiratory pattern, accessory muscle use, and looking for movements, grimaces or unsafe patient positioning

• Observing the patient’s clinical data on intraoperative monitors

• Observing bleeding and coagulation at the surgical site (e.g., are the surgeons using many sponges or are they doing a lot of suctioning?)

• Monitoring the functioning of all lines to ensure that IV catheters have not infiltrated

• Conducting an anesthesia machine and workspace checkout

• Pulse: rate, volume, rhythm------etc

• Capillary refilling

• Sweating

Instrumental patient monitoring

1. Electrocardiogram (Provides information about rate, rhythm, ischemia (ST Segments))

2. Blood pressure (manual, automatic, arterial catheter)

3. Pulse oximeter (usually on fingertip or ear lobe)

4. Capnograph (especially in patients with an LMA or ETT)

5. Oxygen analyzer (part of anesthesia machine)

6. Anesthetic agent concentration analyzer

7. Temperature (usually esophageal or axillary)8. Precordial or esophageal stethoscope (Listen to

heart sounds, breath sounds)9. Gas flows/ spirometry (part of anesthesia

machine)10. Airway pressure monitor (part of anesthesia

machine)11. Airway disconnect alarm (part of anesthesia

machine)12. Peripheral nerve stimulator (where

appropriate)13. Urometer (measure urine output where

appropriate)

Electrocardiogram ECG

This provides the clinician with three types of information: (1) heart rate, (2) cardiac rhythm (3) information about possible myocardial ischemia (via ST segment analysis) In addition, ECG monitoring can help assess the function of a cardiac pacemaker

The most common electrocardiographic system used during anesthesia is a 5-electrode lead system. This arrangement allows for the recording of any of the six limb leads plus a single precordial (V) lead

Blood Pressure

Measurement of arterial blood pressure is an important indicator of the adequacy of circulation Systemic blood pressure monitoring is commonly performed indirectly using extremity-encircling cuffs or directly by inserting a catheter into an artery and transducing the arterial pressure trace.

Variety of techniques available for measuring changes in systolic, diastolic, and mean arterial pressure (MAP).

Indirect Measurement of Arterial Blood Pressure

The simplest method of blood pressure determination estimates systolic blood pressure by palpating the return of the arterial pulse while an occluding cuff is deflated. Modifications of this technique include the observance of the return of Doppler sounds, the transduced arterial pressure trace, or a photoplethysmographic pulse wave as produced by a pulse oximeter.

• Auscultation of the Korotkoff sounds permit estimation of both systolic (SP) and diastolic (DP)

• blood pressures. MAP can be calculated using an estimating equation (MAP = DP + 1/3 [SP-DP]).

• The American Heart Association recommends that the bladder width for indirect blood pressure monitoring should approximate 40% of the circumference of the extremity.

• Bladder length should be sufficient to encircle at least 60% of the extremity.

• Falsely high estimates result when cuffs are too small, when cuffs are applied too loosely, or when the extremity is below heart level.

• Falsely low estimates result when cuffs are too large, when the extremity is above heart level, or after quick deflations.

Automated Intermittent Technique

Many limitations of manual intermittent blood pressure measurement have been overcome by automated NIBP devices, which are now used widely. In addition, automated NIBP devices provide audible alarms and can transfer data to a computerized information system. However, the greatest advantage of automated NIBP devices over manual methods of blood pressure measurement is that they provide frequent, regular blood pressure measurements and free the operator to perform other vital clinical duties.

• In a generic noninvasive oscillometric monitor (noninvasive blood pressure, or NIBP),

• Cuff pressure is sensed by a pressure transducer whose output is digitized for processing.

• After the cuff is inflated by an air pump, cuff pressure is held constant while oscillations are sampled.

Direct method (intra-arterial pressure monitoring)

Intra-arterial pressure monitoring provides an invasive, continuous measure of blood pressure by beat-to-beat reproduction of the arterial pressure waveform

The method requires the insertion of a short parallel-sided cannula into an artery.

A continuous flow of either saline or heparinised saline at rates between 1 and 4 ml per hour is used to reduce clot formation in the cannula.

The cannula is connected by a short length of narrow-bore, noncompliant

plastic tubing containing saline to a pressure

transducer

Indications for Arterial Cannulation

1. Continuous, real-time blood pressure monitoring

2. Planned pharmacologic or mechanical cardiovascular manipulation

3. Repeated blood sampling 4. Failure of indirect arterial blood pressure

measurement 5. Supplementary diagnostic information from the

arterial waveform 6. Determination of volume responsiveness from

systolic pressure or pulse pressure variation

Hazards of Arterial Cannulation

Pulse Oximetry

Pulse oximetry is a simple noninvasive method of monitoring arterial oxygen saturation (the percentage of hemoglobin (Hb) with oxygen molecules bound)

The arterial saturation obtained in this manner is usually designated as SpO2

A pulse oximeter consists of a probe attached to the patient’s finger, toe, or ear lobe, which is in turn attached to the main unit

It measures the red and infrared light wavelength transmitted through and/or reflected by a given tissue

In most units, an audible tone occurs with each heart beat which changes pitch with the saturation reading

A patient is generally said to be hypoxemic when the SpO2 falls below 90%, a point usually corresponding to an arterial PO2 of 60 mmHg

An important advantage of using a pulse oximeter is that it can detect hypoxemia well before the patient becomes clinically cyanotic.

Note that pulse oximetry is required in all patients undergoing anesthesia. However, it is important to realize that pulse oximeters give no information about the level of arterial CO2 and are therefore useless in assessing adequacy of ventilation in patients at risk of developing hypercarbic respiratory failure

Sources of error in oximetry1. Ambient light – can be minimized by using shielded probes.2. Low perfusion states – amplitude of the probe signal amplitude

depends on tissue perfusion (decreased perfusion reduces signal amplitude).

3. Motion artefact – can be reduced by increasing the signal averaging time, but only at the expense of response time

4. External dyes. Methylene blue has the most dramatic effect – as concentration increases, SaO2 values decrease. Some dark nail polishes can also interfere with oximetry.

5. Effect of additional haemoglobin species on absorbance: HbMet, HbCO and has no effect in HbF, HbS

6. Anaemia – there is a linear trend to underestimateSaO2 as the concentration falls; at haemoglobin levels of 8 g 100 ml−1 this can be 10–15%. Polycythaemia has no effect. Accuracy is less at low saturation levels in anaemic patients.

7. Diathermy – interference effect largely depends on the particular oximeter.

Capnography and Ventilation Monitoring Normal PaCO2 is 35-45 mmHg

Capnography is the continuous analysis and recording of carbon dioxide (CO2) concentrations in respiratory gases.

A capnograph uses one of two types of analyzers: mainstream or side- stream.

Mainstream units insert a sampling window into the breathing circuit for gas measurement, while the much more common sidestream units aspirate gas from the circuit and the analysis occurs away from the circuit Capnographs utilizes infrared technology (most commonly), or other techniques such as mass spectroscopy

It is useful to monitor capnography for a number of important clinical situations

1. Detecting when an anesthetic breathing circuit disconnects

2. Verification of endotracheal intubation (a sustained normal capnogram is not obtained when the endotracheal tube ends up in the esophagus)

3. Assisting in the detection of hypoventilation (raised end-tidal CO2 is often present) and hyperventilation (low end-tidal CO2 is often present)

4. Detecting rebreathing of CO2 (in which case the inspiratory CO2 level is nonzero)

5. Detecting capnograph tracings suggestive of COPD (where no plateau is present in the capnogram)

6. Monitoring CO2 elimination during cardiac arrest and CPR

Mainstream capnograph

Sidestream capnograph

Monitoring Muscle Relaxation

• Muscle relaxation, or paralysis using neuromuscular blocking agents such as vecuronium is often required during surgery. For instance, muscle relaxation

• may be needed to facilitate tracheal intubation, to allow abdominal closure, or to ensure that no movement occurs during neurosurgery

• In such settings, neuromuscular blockade monitoring or

“twitch monitoring” is employed. This usually involves electrode placement at the ulnar or facial nerve, with use of a peripheral nerve stimulator

Types Twitch Monitoring

• TWT: Single Twitch

• TET: Tetanic Stimulation

• PTC: Post Tetanic Count

• DBS: Double Burst Stimulation

• TTOF: Train Of Four

The stimulation modes allow the assessment of:

• The best time for intubation

• The block degree during the anesthesia procedure

• The need of an additional dose of the blocking agent

• The presence of the residual block

Temperature Monitoring

Normal core temperature in humans usually varies between 36.5 and 37.5°C

Heat loss is due to impairment of thermoregulatory control by anesthetic agents combined with exposure to the cold operating room environment

Hypothermia is defined as a core body temperature of less than 35°C and may be classified as mild (32–35°C), moderate (28–32°C), or severe (<28°C)

• Core temperature can be measured with sensors in the nasopharynx, esophagus, pulmonary artery, tympanic membrane, or even in the rectum or urinary bladder.

• Skin-surface temperature tends to run much lower than core temperature, but follows core temperature trends fairly well.

• The ASA standards for patient monitoring require that every patient receiving anesthesia

have temperature monitoring “when clinically significant changes in body temperature are intended, anticipated, or suspected.”

Central Venous Pressure Monitoringnormal value 3-8mmHg

Central venous cannulas are important portals for intraoperative vascular access and for the

assessment of changes in vascular volume

Central venous cannulas permit the rapid

administration of fluids, insertion of PACs, insertion of transvenous electrodes, monitoring of central venous pressure (CVP), and a site for observation and treatment of venous air embolism.

The right internal jugular vein is the preferred site for cannulation because it is accessible from

the head of the operating table, has a predictable anatomy, and has a high success rate in both

adults and children. The left-sided internal jugular vein is also available but is less desirable

because of the potential for damaging the thoracic duct or difficulty in maneuvering catheters

through the jugular–subclavian junction.

Accidental carotid artery puncture is a potential problem with either location

Pulmonary Artery Pressure Monitoring