Monitor Flashcards
1
Q
- What is the purpose of intraoperative patient monitoring?
A
- The purpose of intraoperative patient monitoring is to continuously assess the patient’s physiologic status and the effects of surgery and anesthetic agents. (337)
2
Q
- What are four patient parameters that have been mandated to be continually evaluated by the American Society of Anesthesiologists? How frequently is it mandated that intraoperative blood pressure be measured?
A
- The American Society of Anesthesiologists has mandated that during all anesthetics the patient’s oxygenation, ventilation, circulation, and temperature shall be continually evaluated. With general anesthesia, the oxygen concentration of the gases administered is monitored and a quantitative measure of blood oxygenation (pulse oximetry) is used. Ventilation is evaluated qualitatively and, if possible, quantitatively by ensuring CO2 is present in the expired gases, and arterial blood pressure and heart rate are evaluated every 5 minutes. (337)
3
Q
- Do all monitors require calibration?
A
- All monitors require calibration. Some monitors need manual calibration, some are autocalibrating, and some are empirically calibrated. (337)
4
Q
- Name two kinds of oxygen sensors that are in use. What are the differences between them?
A
- Both amperometric and paramagnetic oxygen sensors are in use. Amperometric sensors require calibration and are slow to respond, whereas paramagnetic sensors are autocalibrating and respond rapidly, allowing measurement of both inspired and expired oxygen concentrations. (339)
5
Q
- What is the clinical utility of measuring the expired concentration of oxygen?
A
- Measurement of the expired oxygen concentration (FEO2) enables quantification of preoxygenation/denitrogenation before induction and allows a rough estimation of oxygen consumption. (339)
6
Q
- Which law of physics is used in pulse oximetry? Which wavelengths are used?
A
- Beer’s law is the basis of pulse oximetry. Two wavelengths are used: red at 660 nm and infrared at 940 nm. (339)
7
Q
- How is a pulse oximeter calibrated?
A
- Pulse oximeters are empirically calibrated using human volunteers, comparing absorbance ratios with known saturations via an electronic calibration table. (341)
8
Q
- When the absorption ratio of the pulse oximeter is 1.0, that is, equal in both the red and infrared, what percent O2 saturation will the pulse oximeter read?
A
- When the absorption ratio (660/940 nm) is 1.0, the pulse oximeter will read an oxygen saturation of 85%. (341)
9
Q
- How do carboxyhemoglobin, methemoglobin, dyes, and motion artifact affect the pulse oximeter readings?
A
- Carboxyhemoglobin falsely elevates the reading (closer to 100%), methemoglobin forces the reading toward 85% regardless of true saturation, dyes cause a similar trend toward 85% (transiently), and motion artifact leads the ratio to 1.0, also trending the reading to 85%. (341)
10
Q
- How can multiple types of hemoglobin (i.e., carboxyhemoglobin, methemoglobin) be measured?
A
- By adding additional wavelengths beyond the conventional two, modern multiwavelength (up to eight wavelengths) pulse oximeters can measure various hemoglobin species such as carboxyhemoglobin and methemoglobin. (341)
11
Q
- Name several ways ventilation can be assessed without using electronic monitors.
A
- Ventilation can be assessed by visual observation of chest movement, inspection of the rebreathing bag, and auscultation with a stethoscope to evaluate rate and depth, as well as to detect wheezing, unilateral breath sounds, or rales. (342)
12
Q
- What are some possible causes of increased airway pressures?
A
- Increased airway pressures can be due to increased airflow resistance or decreased chest wall compliance, with causes including bronchospasm, endobronchial intubation, pneumothorax, pulmonary edema, kinked endotracheal tube or circuit, or malfunctioning valves. (342)
13
Q
- What is the plateau pressure, and how is it measured?
A
- The plateau pressure is the pressure in the respiratory circuit when gas movement ceases, reflecting lung/chest wall compliance; it is measured by setting an end-inspiratory pause during volume-controlled ventilation. (342)
14
Q
- When is measuring the plateau pressure clinically useful?
A
- Measuring the plateau pressure is useful to differentiate between increased airway resistance and decreased lung compliance; the difference between peak inspiratory and plateau pressures reflects airway resistance. (342)
15
Q
- What are some possible causes of decreased airway pressures?
A
- Decreased airway pressures may result from circuit disconnections, leaks, accidental extubation, failure to deliver fresh gases, ventilator setting errors, or excess scavenging. (342)
16
Q
- What is the appropriate tidal volume for adults during positive-pressure ventilation?
A
- An appropriate tidal volume for adults is typically 6 to 8 mL/kg of ideal body weight, often combined with positive end-expiratory pressure to optimize pulmonary outcomes. (342)
17
Q
- Does the anesthesia machine “disconnect” alarm ensure detection of esophageal intubation and inadequate tidal volumes?
A
- No, the anesthesia machine “disconnect” alarm is usually based on airway pressure readings and may not detect esophageal intubation or inadequate tidal volumes, particularly during pressure support ventilation. (342)
18
Q
- What is the only monitor to ensure adequate ventilation?
A
- Measurement of exhaled CO2 (capnography) is the only monitor that ensures adequate ventilation by confirming the removal of CO2. (342)
19
Q
- What are the phases of a normal capnogram?
A
- A normal capnogram comprises three phases: Phase 1 represents inspired and dead space gas (no CO2), Phase 2 is the transition with rising CO2, and Phase 3 is alveolar gas reflecting the end-tidal CO2; phase 0 is the inspiratory segment. (342)
20
Q
- What physiologic patient characteristic can result in upsloping of phase 2 of the capnogram?
A
- Conditions that increase airway resistance, such as COPD and asthma, can cause upsloping of phase 2 in the capnogram. (342)
21
Q
- How would exhausted CO2 absorbent alter the capnogram?
A
- Exhausted CO2 absorbent leads to a progressive rise in inspired CO2, seen on the capnogram as an inability to return to a zero baseline between breaths. (342)
22
Q
- How does the end-tidal CO2 (ETCO2) value compare to the PaCO2 value? What is the cause of the difference between the two?
A
- ETCO2 is lower than PaCO2 due to dead space ventilation; the difference is proportional to the ratio of dead space to alveolar ventilation. (342)
23
Q
- What is the approximate difference in mm Hg between the ETCO2 and the PaCO2 during general anesthesia in healthy patients?
A
- In healthy patients under general anesthesia, the difference between ETCO2 and PaCO2 is approximately 3 to 5 mm Hg. (343)
24
Q
- What is dead space ventilation?
A
- Dead space ventilation is the portion of inspired and expired gas that does not participate in gas exchange, including apparatus, anatomic, and alveolar dead space. (343)
25
Q
- Why does the ETCO2 decrease in circulatory collapse?
A
- In circulatory collapse, reduced pulmonary blood flow increases alveolar dead space, thereby lowering ETCO2 while PaCO2 rises. (345)
26
Q
- What is the clinical utility of the capnogram during cardiopulmonary resuscitation (CPR) for cardiac arrest?
A
- The capnogram is valuable during CPR as it reflects the adequacy of chest compressions; an ETCO2 greater than 20 mm Hg is a target, and it is not affected by motion artifact. (345)
27
Q
- How reliable is the sampled ETCO2 from near the mouth in patients whose tracheas are not intubated?
A
- Sampled ETCO2 near the mouth in non-intubated patients is unreliable due to dilution by room air. (345)
28
Q
- Name characteristics of the circulation that can be monitored during anesthesia.
A
- Noninvasive monitors can assess heart rate, rhythm, systolic, diastolic, and mean blood pressure; invasive monitors can additionally measure central venous pressure, pulmonary artery pressure, cardiac output, and systolic pressure variation. (345)
29
Q
- Describe proper electrocardiogram (ECG) lead placement.
A
- In a three-lead ECG system, limb leads are placed on the shoulders and the third lead on the left abdomen below the rib cage; a five-lead system is preferred with a precordial lead (V5) in the fifth intercostal space at the anterior axillary line. (346)
30
Q
- Which ECG leads should be monitored during anesthesia?
A
- A combination of ECG leads II and V is typically monitored to detect the majority of dysrhythmias and ischemia. (346)
31
Q
- What information can be gathered from an ECG?
A
- An ECG provides information on heart rate, rhythm, conduction abnormalities, and signs of ischemia, as well as the effects of drugs, electrolytes, and temperature changes. (345)
32
Q
- What is the clinical utility of the “diagnostic mode” on the ECG?
A
- The diagnostic mode on the ECG removes filtering to reveal true electrical signals, helping to distinguish genuine changes from artifacts. (345)
33
Q
- What is the relationship between blood pressure and cardiac output?
A
- Blood pressure is directly proportional to cardiac output and vascular resistance, following Ohm’s law (BP = CO × Resistance). (346)
34
Q
- What is the perfusion pressure?
A
- Perfusion pressure is the pressure gradient across an organ, calculated as the upstream pressure minus the downstream pressure. (346)
35
Q
- How is the perfusion pressure calculated for each of the following: systemic circulation, pulmonary circulation, brain, and heart?
A
- For systemic circulation: MAP – CVP; for pulmonary circulation: MPAP – pulmonary capillary wedge pressure; for the brain: MAP – ICP; for the heart: diastolic pressure – right-sided heart pressure. (346)
36
Q
- How is mean arterial pressure (MAP) calculated?
A
- MAP = (⅔ × Diastolic BP) + (⅓ × Systolic BP). (346)
37
Q
- What is the clinical significance of the MAP?
A
- MAP is critical as it represents the upstream pressure necessary for perfusion of vital organs. (346)
38
Q
- What MAP defines intraoperative hypotension?
A
- Intraoperative hypotension is generally defined as a MAP below 55 to 60 mm Hg, with various studies correlating MAP <50 mm Hg for 5–10 minutes with adverse outcomes. (349)
39
Q
- What is the mechanism by which automatic noninvasive cuffs measure blood pressure?
A
- Automatic cuffs use the oscillometric method: the cuff is inflated above systolic pressure and then slowly deflated, detecting the point of maximal oscillations (MAP) and applying algorithms to estimate systolic and diastolic pressures. (349)
40
Q
- Of the systolic, diastolic, and mean blood pressures, which is most accurately measured by a noninvasive blood pressure cuff?
A
- The mean blood pressure is most accurately measured by a noninvasive blood pressure cuff. (352)
41
Q
- What is the appropriate size of cuff to use for noninvasive blood pressures? How is the blood pressure reading altered by a cuff that is too large or too small?
A
- The cuff width should be about 40% of the arm circumference. A cuff that is too large yields an artificially low reading, while one that is too small gives an artificially high reading. (352)
42
Q
- What is the Riva-Rocci technique for measuring blood pressure?
A
- The Riva-Rocci technique involves inflating an occlusive cuff and detecting the return of blood flow either by palpation or Doppler, with Korotkoff sounds used to determine systolic and diastolic pressures. (352)
43
Q
- What are some advantages of invasive arterial blood pressure monitoring over noninvasive blood pressure monitoring?
A
- Invasive monitoring provides continuous, real-time blood pressure measurements, allows for blood sampling, and can assess intravascular volume status. (352)
44
Q
- Which arteries can be catheterized for invasive blood pressure measurements?
A
- Commonly catheterized arteries include the radial, brachial, femoral, and dorsalis pedis arteries, with the radial artery being most frequently chosen due to ease of access and lower risk. (352)
45
Q
- How will the blood pressure measurement be altered by invasive arterial measurement increasing distances from the heart?
A
- Blood pressure measurements tend to show higher systolic pressures when taken from arteries further from the heart. (352)
46
Q
- How does increased length of tubing/amount of fluid in the fluid-filled tube transducer setup affect the systolic blood pressure and MAP measurement during invasive arterial blood pressure monitoring?
A
- Increased tubing length and fluid volume amplify systolic pressure artifacts, while MAP remains relatively accurate. (352)
47
Q
- How can arterial blood pressure waveforms be evaluated to assess the patient’s intravascular fluid volume status?
A
- Waveforms can be analyzed for systolic pressure variation, pulse pressure variation, and stroke volume variation, which help assess fluid responsiveness. (352)
48
Q
- What is systolic pressure variation (SPV)?
A
- SPV is the difference between the maximum and minimum systolic pressures during a positive-pressure ventilation cycle, reflecting the impact of ventilation on venous return. (352)
49
Q
- What is the clinical use of measuring SPV?
A
- SPV is used to predict the responsiveness of a patient’s cardiac output to an intravenous fluid challenge. (352)
50
Q
- What are some situations that limit the clinical use of measuring SPV?
A
- Limitations include the need for controlled positive-pressure ventilation, a regular sinus rhythm, and factors such as increased chest wall compliance, prone positioning, high PEEP, or an open thoracic cavity. (354)
51
Q
- What is pulse pressure variation, and what is its clinical use?
A
- Pulse pressure variation is the relative change in pulse pressure during positive-pressure ventilation and is used, like SPV, to predict fluid responsiveness. (354)
52
Q
- What is stroke volume variation, and what is its clinical use?
A
- Stroke volume variation, determined from pulse contour analysis, reflects changes in stroke volume during the respiratory cycle and helps predict fluid responsiveness. (354)
53
Q
- What physiologic aspects of the cardiac cycle are reflected by the “waves” and “descents” on the central venous pressure (CVP) waveform?
A
- The CVP waveform’s a wave (atrial contraction), c wave (tricuspid bulging), x descent (atrial relaxation), v wave (atrial filling), and y descent (atrial emptying) reflect different phases of the cardiac cycle. (354)
54
Q
- How useful is CVP monitoring in assessing intravascular fluid volume status?
A
- CVP monitoring is of limited utility for assessing fluid volume except at extreme values (eg, <2 mm Hg or >15 mm Hg). (354-355)
55
Q
- What central veins can be catheterized for CVP monitoring? What are some advantages and disadvantages of each?
A
- Common sites include the internal jugular, subclavian, and femoral veins. The internal jugular is easily accessible and compressible but risks carotid puncture; the subclavian is more comfortable but less compressible and riskier for pneumothorax; the femoral is accessible and compressible but has a higher infection risk. (356)
56
Q
- What information does a pulmonary artery (PA) catheter provide? What is the wedge pressure?
A
- A PA catheter provides measurements of right-sided pressures, cardiac output, and indirectly left atrial pressure via the pulmonary capillary wedge pressure. (356)
57
Q
- How is cardiac output measured with a PA catheter?
A
- Cardiac output is measured using the thermodilution technique, where cold fluid is injected and the resulting temperature change is recorded to calculate output. (356)
58
Q
- How would hypovolemic, cardiogenic, and septic shock affect the wedge pressure and cardiac output?
A
- Hypovolemic shock results in low wedge pressure and low cardiac output; cardiogenic shock results in high wedge pressure with low output; septic shock results in low wedge pressure with high output. (356)
59
Q
- What are the risks of PA catheterization?
A
- Risks include infection, clot formation, and pulmonary artery rupture. (356)
60
Q
- What aspects of cardiac physiology can be evaluated by transesophageal echocardiography (TEE)?
A
- TEE assesses cardiac valves, chamber size, contractility, ejection fraction, systolic/diastolic dysfunction, and pericardial pathology such as effusions or tamponade. (357)
61
Q
- What are some limitations of TEE?
A
- Limitations include the need for technical expertise, risk of esophageal injury, and reduced access to the patient’s head. (357)
62
Q
- Why are processed electroencephalograms (EEGs), such as the bispectral index (BIS) monitor, used during anesthesia?
A
- Processed EEGs like the BIS monitor are used to assess anesthetic depth and reduce the risk of intraoperative awareness and postoperative recall. (357)
63
Q
- What minimal alveolar concentration (MAC) of inhaled anesthetic is recommended to minimize the risk of intraoperative awareness and postoperative recall during general anesthesia?
A
- A MAC above 0.5 to 0.7 of the inhaled anesthetic is recommended to minimize the risk of awareness. (357)
64
Q
- In large randomized studies, how does monitoring of MAC compare to the BIS monitor in preventing awareness with postoperative recall?
A
- Monitoring MAC with alerts is equivalent to BIS monitoring in preventing awareness, although BIS may add extra protection during total intravenous anesthesia. (357)
65
Q
- When should the intracranial pressure (ICP) be monitored and how?
A
- ICP should be monitored in settings of increased CSF pressure, cerebral edema, or intracranial lesions, using methods such as a ventriculostomy catheter or a transducer-equipped catheter placed on the dura. (357)
66
Q
- When are cerebral oximeter monitors used?
A
- Cerebral oximeters are used during cardiac or vascular surgery when there is concern for poor cerebral perfusion. (357)
67
Q
- How is a cerebral oximeter different from a pulse oximeter?
A
- A cerebral oximeter uses reflected infrared light through the scalp and skull to measure regional cerebral oxygen saturation, rather than transmitted light as in pulse oximetry. (357)
68
Q
- What is the normal regional oxygen saturation (rSO2) of the cerebral cortex when using a cerebral oximeter?
A
- The normal rSO2 of the cerebral cortex is approximately 70%. (358)
69
Q
- Describe the various modes of stimulation with a neuromuscular blockade monitor, or ‘twitch’ monitor, and what depth of neuromuscular blockade is appropriately monitored by each mode.
A
- The neuromuscular monitor can use post-tetanic count (PTC) for deep blockade (with a 5-second tetanic stimulus followed by single twitches), train-of-four (TOF) stimulation for lighter blockade (4 stimuli at 2 Hz, counting twitches), double burst stimulation (DBS) to detect residual blockade even when 4/4 twitches are present, and quantitative TOF ratio measurement; each mode assesses different depths of blockade. (358)
70
Q
- What are the potential patient issues with residual postoperative neuromuscular blockade or too little intraoperative neuromuscular blockade?
A
- Residual blockade may lead to subclinical aspiration, hypoventilation, and airway obstruction, whereas insufficient blockade can result in patient movement and potential injury during surgery. (358)
71
Q
- What do somatosensory evoked potentials monitor? How are they affected by anesthetics?
A
- Somatosensory evoked potentials monitor the sensory pathways of the spinal cord by recording cortical responses to peripheral nerve stimulation; they are decreased in amplitude and increased in latency by halogenated agents and nitrous oxide. (358)
72
Q
- What do motor evoked potentials monitor? How are they affected by anesthetics?
A
- Motor evoked potentials monitor the motor pathways (ventral spinal cord); they are extremely sensitive to inhaled anesthetics, necessitating total intravenous anesthesia and avoidance of neuromuscular blockers. (358)
73
Q
- Which temperature monitoring sites best reflect the core body temperature?
A
- True core temperature is best measured via probes in the PA catheter, distal esophagus, nasopharynx, or tympanic membrane; oral, axillary, and bladder sites can approximate core temperature. (360)
74
Q
- Why is patient temperature monitored?
A
- Temperature monitoring is used to detect and manage hypothermia, assess fever, monitor responses to blood products, and detect malignant hyperthermia, among other purposes. (360)
75
Q
- What happens to core body temperature during brief anesthesia?
A
- Core body temperature drops even during brief anesthesia, primarily due to redistribution of heat from the core to the periphery. (360)
76
Q
- How does the magnetic field decrease with distance from the coil?
A
- The magnetic field in an MRI suite is nonlinear and decreases with distance from the coil; safety lines are used to demarcate safe distances. (360)
77
Q
- What are some issues related to monitoring in the magnetic resonance imaging (MRI) suite?
A
- In the MRI suite, only MRI-compatible monitors can be used; metal objects can be hazardous due to magnetic attraction, noise levels can be extremely high (up to 120 dB), and even nonmagnetic loops may heat up, posing risks. (360-361)
78
Q
- What is the largest problem with monitor alarms?
A
- The largest problem with monitor alarms is false positives and negatives, which can lead to alarm fatigue and potentially dangerous desensitization. (361)
79
Q
- What technological solutions are being proposed to deal with monitor alarm fatigue/false positives?
A
- Newer generation integrated alarming systems that consolidate multiple alarms and use time-based or multi-parameter criteria to reduce false alarms are being developed to address alarm fatigue. (361)
