Department of Anesthesia

DEPARTMENT OF ANESTHESIA UNIVERSITY OF MANITOBA

Monitoring Training Module for Para Professional Personnel

Preamble The Department of Anesthesia at the University of Manitoba is committed to the promotion of patient safety and quality of care. Education of providers of airway and resuscitation support from all disciplines is a fundamental part of that mission. For this educational effort to be effective, it is important to consider and incorporate the particular needs of each group for whom skills development is contemplated. This document outlines the structure, and goals and objectives of a program designed to meet the developmental needs of paramedical personnel providing care for patients with respect to monitoring physiologic well-being. Program Outline Each trainee will be provided with a program outline, including a reference manual, orientation and contact information, and evaluation logs. At the end of the rotation, the trainee will be expected to keep evaluation logs and provide them to the Coordinator of the sponsoring program as proof of completion of the educational program.

The trainee will present to the assigned hospital OR suite on the first day of the rotation, at the time and place indicated in the orientation manual. The senior resident or site coordinator will direct the trainee to a primary staff person. This primary staffperson shall  Review the educational material with the trainee  Provide resource discussion  Evaluate the degree to which the trainee has met the knowledge objectives  Record the results of that evaluation on the evaluation log  Coordinate access to monitoring procedures with him/herself, enlisting other staff as necessary and available

Each individual staff physician or resident who supervises airway management techniques will  Observe the trainee and provide formative feedback  Evaluate the trainee’s competence with the technique  Record the evaluation on the provided log  As applicable review and evaluate elements of the curriculum as discussed with the primary mentor Goals and Objectives

By the end of this module, the trainee will be able to:  Assess the presence and degree of cardiovascular instability by physical examination  Apply routine non-invasive monitors of cardiovascular integrity, including EKG and non-invasive blood pressure monitoring  Interpret the information from these monitors identifying o The relevance of this information in context of information from other sources o The potential sources of error, and how to correct or allow for them  Suggest appropriate additional monitoring of cardiovascular integrity including urinary output and invasive arterial blood pressure monitoring, describing o The relative advantages and disadvantages of adding that monitor o The potential risks and complications  Interpret the information from these monitors identifying o The relevance of this information in context of information from other sources o The potential sources of error  Assess the presence and degree of respiratory instability by physical examination  Apply additional monitors of respiratory well-being, including Pulse oximetry, airway pressure and flow measurement  Describe the basic principles upon which each of the following monitors functions o EKG o Non-invasive Blood pressure o Oxygen saturation Evaluation Log for Paramedical Monitoring Training Module

Major Minor No Complete Outstanding Cognitive Objectives Omissions Omissions Omissions Discussion EKG monitoring  Describes indications, contrainidications      and complications  Correctly applies and sets up monitor       Interprets for ischemia       Identifies sources of error      NIBP monitoring       Describes indications, contrainidications      and complications  Correctly applies and sets up monitor       Interprets for ischemia       Identifies sources of error      Pulse Oximetry       Describes indications, contrainidications      and complications  Correctly applies and sets up monitor       Interprets for ischemia       Identifies sources of error                                                   Major Minor Competent Efficient Outstanding Technical Skills Objectives Errors Errors technique technique Arterial line #1      Arterial line #1      Arterial line #1      Arterial line #1      Arterial line #1      CARDIO-RESPIRATORY MONITORING IN ANESTHESIA

Roland DeBrouwere, MD, FRCPC

Of all the duties performed by the anesthesiologist perioperatively, none is more important and more time consuming than monitoring of the cardio-respiratory system. When anesthetics were first given 150 years ago, our professional ancestors had little to go by but their own ability to observe the patient's colour and breathing while palpating the pulse for rate and strength. Only in the twentieth century did devices to measure blood pressure and to view the electrocardiogram come into existence. The new millennium should bring even more exciting and exotic devices.

CARDIO-RESPIRATORY MONITORING – THE BASICS

Monitoring can be broadly broken down into two major categories: non-invasive and invasive. As a general rule the more sophisticated monitors are more invasive and often more expensive, require special skills and impose more risk to the patient. We therefore use the less expensive and less risky monitoring routinely and save the more invasive monitors for selected procedures and patients.

NON–INVASIVE MONITORS

1) THE ANESTHESIOLOGIST

Anesthesiologists are trained to evaluate the cardio-respiratory system. Simple techniques are used on every patient. These may seem like common sense but are very important. These include: 1) Patient overall appearance. 2) Respiratory rate and depth – patency of the airway. 3) Skin colour – evidence of cyanosis, anaemia, poor peripheral perfusion. 4) Cerebral perfusion – alert, appropriate, confused, combative, comatose (this modality is obviously lost under general anesthesia but is assessed preoperatively in all patients).

These may sound like the ABC’s of resuscitation and in fact they are the simplest and fastest way to assess the cardio-respiratory function of a patient. Next comes a more detailed assessment and follows the traditional approach of inspection, palpation, percussion and auscultation. 1) Peripheral pulses – presence/absence, rate, rhythm, quality 2) Cardiac auscultation - can be performed continuously with either a precordial or esophageal stethoscope. 3) Respiratory auscultation – can also be performed continuously

One simple, yet highly valuable tool is the stethoscope. It can either be a precordial head, taped to the left side of the patient's chest, or part of an esophageal probe positioned so heart and breath sounds are well heard. By listening to the stethoscope, frequency and effectiveness of ventilation can be determined, obstruction or dislodgement of the airway or endotracheal tube can be detected and adventitial sounds indicative of bronchospasm or pulmonary edema may be heard. Heart rate and rhythm can be followed without constantly watching the ECG. A well position, constantly monitored stethoscope is especially useful in pediatric, head and neck or thoracic surgery where access to the patient may be very limited.

2) THE BASIC NON-INVASIVE MONITORS

BLOOD PRESSURE:

Blood pressure is monitored in every patient in the operating room and is used along with other monitors to assess overall cardiac function. Since PRESSURE = FLOW X RESISTANCE, the presence of pressure indicates some flow and resistance is present however it does not tell you the quantity of either. Flow, or cardiac output and resistance (usually referred to as systemic vascular resistance) must be assessed by other means. Blood pressure can be assessed manually with a cuff and stethoscope or more commonly with an automatic machine set to cycle usually every three to five minutes. Automated blood pressure devices free the anesthetist’s hands by measuring systolic, diastolic and mean blood pressures at regular, pre-set intervals, displaying a digital readout and many record the data. Patient movement (e.g. shivering) affects them and awake patients often find them uncomfortable. Because of a longer inflation time, nerve injury and limb ischemia has occasionally been implicated with these devices.

ELECTROCARDIOGRAM:

Continuous monitoring of the electrical activity of the heart allows for ongoing assessment of heart rate, rhythm and allows for real-time assessment of ST segments to monitor for myocardial ischemia. Arrhythmias are extremely common during anesthesia. Premature atrial or ventricular contractions or episodes of nodal rhythm are frequent, but usually benign and self-limiting. Rarely, more serious arrhythmias such as rapid supraventricular tachycardia or complex ventricular dysrhythmias may require intervention. Any persistent arrhythmia should prompt a search for underlying, life threatening problems such as hypoxemia, hypercarbia, acidosis or ischemia. Coronary artery disease is often present in patients having non – cardiac surgery. An imbalance between myocardial oxygen supply and demand may lead to myocardial ischemia. The ECG is the best non-invasive perioperative monitor we have available. Most electrocardiograms used in the O.R. utilize three limb leads (positive, negative, and ground) which allow viewing one lead at a time in the screen along with a digital display of the heart rate. Lead I, II or III can be continuously monitored. Often Lead II is chosen as it gives the best visualization of p waves and therefore rhythm assessment. The problem with only monitoring one lead at a time, is that some problems may go undetected. PVC’s, which may look very abnormal on one lead, may look almost normal on another. Ischemic changes are best seen on a modified chest lead (CM5) but still if only this one lead is viewed a large percent of such episodes may be missed. Simultaneous monitoring of more than one lead allows better pick-up of abnormalities. Most monitors allow 5-lead capability with two different leads viewed simultaneously. Also some machines continuously monitor ST-segments for depression or elevation and can give a record of change over time. PULSE OXIMETRY:

Adequate oxygenation and the ability to detect changes are critical during anesthesia. Although direct observation of skin colour is helpful, it is quite subjective. Cyanosis may be difficult to assess in anemic or dark skinned individuals. Pulse oximeters provide an accurate, continuous non-invasive method of determining 02 saturation. The pulse oximeter consists of a peripheral probe that can be clipped onto any finger, toe or the ear lobe. One side of the probe shines two wavelengths of light through the tissue. One wavelength corresponds to saturated, and the other to desaturated hemoglobin. The other part of the probe picks up the light on the other side and, by calculating the relative degree of absorption of the light, is able to quantify the percent of saturated hemoglobin. Pulsatile flow is required. The oximeter will also measure pulse rate. Though not quite instantaneous (a delay of a few seconds occurs before changes are registered) the monitor rapidly shows changes in saturation. In many units the tone of the signal corresponds to the saturation (a lower note equals lower saturation) so it is possible to listen for changes without constantly viewing the screen. The readout may be rendered inaccurate because of low flow states, movement, electrocautery and the presence of abnormal hemoglobins.

VENTILATORY MONITORING:

End Tidal CO2 and Agent Monitors

A major cause of anesthetic morbidity and mortality is due to misplaced, displaced, or disconnected endotracheal tubes. Methods for checking proper positioning of the tube (seeing the tube pass between the cords, observing chest and abdominal movement, auscultation) are very important, but not infallible, especially in obese patients. The only definitive proof that a tube is endotracheal and not in the oesophagus is to detect the presence of sustained CO2 in the expired gas, since of course only the lungs produce CO2 - the stomach does not.

Though end tidal CO2 (ETCO2) units have been available for some time, only recently have they become widely available. Most machines record inspired and expired CO2, display the waveform on a screen, and measure respiratory rate. Using this device it is possible to obtain a great deal of information.

There are basically two sources of information in the readout from a capnometer, the number representing ETCO2, and the tracing, which is a continuous readout of the CO2 at the level of the sampler over time. To derive useful information, one must understand first where these signals come from.

The capnometer measures the CO2 at the aspiration point continuously. This is usually placed at the end of an endotracheal tube. The capnograph is the resultant trace, and is usually shaped as shown in Fig. 1. 40 mmHg 3 4 2 1 0 mmHg Fig. 1 Phase 1, is comprised of inspiration, and early expiration. During inspiration, unless the system is malfunctioning, the CO2 should be 0. During early expiration, the patient is breathing out the anatomic dead space gas, which should be the same as inspired (i.e. 0). Phase 2 begins when the mixed alveolar gas reaches the sampling port later in expiration. Normal lungs empty at a relatively homogenous rate, and so all the alveolar gas arrives as one front. As a result, the transition of Phase 1 to Phase 2 is abrupt, going from baseline to the alveolar plateau in an almost vertical step. Phase 3 is the alveolar plateau, which represents the mixed alveolar gas. This should be constant, or very nearly so, and so Phase 3 is generally a straight line with a slight upslope. Inspiration should bring another step change , which is phase 4, back to Phase 1, to resume the cycle.

Abnormalities of the shape of any of these components can yield information, independent of the actual ETCO2. If phase 1 is not flat, or not 0, there is a system malfunction. If Phase 2 is a gentle upslope, instead of a rapid upstroke, there is likely expiratory obstruction at some level. An upsloping Phase 3 is a somewhat more sensitive indicator of expiratory obstruction. If Phase 3 is not flat, it likely represents inspiratory efforts, or chest compressions. Finally, a slow descent in Phase 4 suggests, expiratory obstruction.

The actual number means little in the absence of an understanding of what it is. The ETCO2 is the last level of Phase 3 measured by the machine prior to the onset of Phase 4. This should represent the mixed alveolar concentration (PACO2), which should , in turn approximate the arterial concentration (PaCO2).

PaCO2  PACO2  ETCO2 (actual)  ETCO2 (measured)

There are several sources of error in this relationship. First of all, in the normal patient, there is a small gradient between the PaCO2 and the PACO2. An increased gradient will thus lower the ETCO2 reading relative to the PaCO2. This gradient will increase with an elevated dead space (PE), severe V/Q mismatch (obstruction), or increased Zone 1. Zone 1 increases when there is an increase in airway pressure (obstruction tension pneumothorax, peep), or decreased pulmonary perfusion pressure(cardiac output).

There can also be a difference between the PACO2 and the ETCO2. This would occur when there is an upward slope to Phase 3 as in expiratory obstruction (see Fig 2). The upward slope occurs because lung units that empty and fill rapidly are better ventilated and thus have a lower CO2. Progressively slower units have a progressively higher CO2. The uppermost limit of this progression is the PaCO2, since no alveolus can exceed this, even if completely unventilated. So the upward slope one sees is actually the beginning of a hyperbolic curve with an asymptote at CO2 = PaCO2. If the expiratory time were sufficient, the ETCO2 would be accurate, but with significant obstruction and normal respiratory rates, the next inspiration will intervene before the ETCO2 has had a chance to reach the top if its curve, and a gap will result, with the ETCO2 therefore being measured too low. PaCO2

The final source of error is between the actual ETCO2 and that measured by the machine. If there is introduction of a leak in the circuit anywhere from the sample port to the measuring chamber, the sample will be diluted with air, and show a falsely low ETCO2.

You will note that all these sources of error show the ETCO2 too low. That is because the only CO2 in the equation should be coming form the patient. The only way the ETCO2 can read falsely high is to either be inhaling CO2.

INVASIVE MONITORING

1) ARTERIAL LINES

Placing a catheter directly into a peripheral artery and transducing the pressure to an electrical signal displayed on a monitor allows for continuous accurate beat-to-beat observation of the blood pressure, assessment of the pressure wave form, and can be used for periodic removal of blood samples for blood gas analysis or other laboratory tests. However, the procedure is invasive, painful to the patient and associated with complications such as damage to the artery. Therefore, arterial lines are limited to higher risk patients in whom continuous blood pressure determination is vital, or in which frequent arterial sampling will be necessary.

2) CVP AND SWAN GANZ CATHETER MONITORING

The patient who has an uncertain intravascular volume status, or in whom major fluid shifts are expected, or when close monitoring of myocardial function is required; a more invasive approach is required.

The purpose of central pressure measurement is to estimate the preload on the heart. When we say “preload”, what we generally mean is left ventricular preload, since we are usually trying to assess the state of the systemic vasculature, rather than the pulmonary system. Strictly speaking, the preload is the length of the ventricular muscle fibres prior to contraction. The volume of the ventricle is a much more practical clinical measurement of preload, and is directly related to length. Single measurements of volume can be readily obtained using echocardiography, but the only useful continuous form of this is transesophageal (see below). It has not gained widespread use outside of the OR because it requires considerable expertise and cost, and is of little use in conscious patients. It is much easier to continuously measure pressures than volumes, and thus it is the mainstay of invasive monitoring. Using pressures to estimate the volume of the heart involves several assumptions. The first, and most basic, is that the volume and pressure within the heart will be directly proportional. This would be true if the compliance of the ventricle were constant. Unfortunately, in real life, compliance differs not only between people, but within the same heart over time. So, although there are normal ranges, pressures are much more meaningful trended over time, and when correlated with clinical observation.

The second set of assumptions has to do with which pressure is measured. The pressure we are ultimately trying to estimate is the left ventricular end diastolic pressure (LVEDP). To actually insert a catheter into the left ventricle is a very invasive procedure, and upstream pressures are used, which generally correlate well with it. Several other pressures may be chosen, but the further upstream, the more potential there is for intervening pathology to alter the relationship. A more exhaustive discussion of these pressures and their physiologic meaning is covered in your basic cardiovascular series, but generally, it can be assumed that CVP  RAP  PADP  PCWP  LAP  LVEPD

The easiest of these to measure is the CVP. A central venous pressure line (CVP) can be inserted via a large peripheral vein (e.g. internal jugular, subclavian, femoral) into the vena cava or right atrium and right heart filling pressures can be measured. A low CVP indicates a relative hypovolemic state either due to hemorrhage, dehydration or systemic vasodilatation. A high CVP may indicate fluid overload or a failing heart.

For more specific estimation of cardiac function a balloon flotation pulmonary artery (Swan Ganz) catheter is useful. A "Swan" is a long catheter with a small balloon at the distal tip which is inserted through a large bore CVP catheter, through the right atrium, tricuspid valve, and right ventricle until the tip comes to lie in a branch of the pulmonary artery. A proximal orifice located in the right atrium measures the RAP and a distal orifice measures pulmonary artery pressure. When the distal balloon is inflated the artery is blocked temporarily creating a static column of blood between the catheter tip and the left atrium, allowing left sided pressures to be measured. The resulting pressure is called the pulmonary capillary wedge pressure (PCWP) which equals the left atrial end diastolic pressure (LAP pressure) which, if the mitral valve is normal, equals left ventricular end diastolic pressure (LVEDP). A rising LVEDP suggests myocardial dysfunction.

By injecting cool saline through the catheter, thermistors measure temperature change as the fluid bolus circulates and cardiac output is calculated. From this, cardiac index, systemic and pulmonary vascular resistance, and portions of the right and left ventricular function curves can be deduced.

These invasive techniques are not free of complications and the risk/benefit ratio must be considered before subjecting a patient to them. When inserting a CVP, damage to the vein or adjacent artery can occur. Attempts to cannulate the subclavian or internal jugular veins may lead to a pneumothorax if the pleura are punctured. Inflation of the balloon on a Swan Ganz may rupture the pulmonary artery, and passage often causes arrhythmias.

TRANSESOPHAGEAL ECHOCARDIOGRAPHY

This modality is not only used for diagnosis but can also be used for real-time monitoring of cardiac function. An ultrasound transducer is passed through the oropharynx into the esophagus and stomach and the pericardium, cardiac chambers and valves and great vessels can be visualized. This monitor was once isolated to patients undergoing cardiac procedures. More and more it is being utilized in the perioperative period in high-risk patients having a variety of non-cardiac procedures. There is a remote risk of esophageal or gastric trauma or perforation with insertion of the probe and expertise is required in positioning and interpretation of the ultrasound images.

CONCLUSION

In conclusion from the "finger on the pulse" days, anesthesia has evolved into a technologically very advanced specialty allowing us to monitor continually many physiologic parameters. The rewards of this has been increased patient safety when the equipment is used properly and conscientiously and when appropriate action is taken when a problem is detected.