Which of the following is a characteristic of aneroid sphygmomanometers

BLOOD PRESSURE MEASUREMENT TECHNIQUE

Aneroid sphygmomanometers are most commonly used to measure blood pressures, but mercury sphygmomanometers seem to be the most accurate.46 An appropriate cuff size is essential to an accurate reading: the bladder length should be at least 75% to 80% of the circumference of the upper arm, and the width should be 40% of the arm circumference.2 Too small a cuff may produce an artificially elevated systolic blood pressure.

Blood pressure should be measured with the patient comfortably seated for at least 5 minutes, and with the arm at heart level. Talking should be avoided as that may raise blood pressure transiently. More than one reading should be done, and each should be separated by at least 1 to 2 minutes.2,40,41,46,47 If two values in the same arm differ by more than 5 mmHg, subsequent readings should be taken until a reasonable average is achieved. The cuff should be inflated to 30 mmHg greater than the palpable systolic pressure, to avoid underestimating systolic blood pressure if an auscultatory gap is present.46 Auscultatory gaps involve disappearance of the Korotkoff sounds transiently as the cuff is deflated below the true systolic blood pressure; these gaps can be found in elderly patients, may be associated with increase risk of cardiovascular disease, and can lead to underestimation of systolic blood pressures.48 During deflation, the cuff should not be deflated faster than 2 to 3 mmHg per heartbeat.26,41,49

The blood pressure should also be measured in both arms, and in the event of a discrepancy, the arm with the higher pressure should be used for treatment decisions and for follow-up measurements.41,46,47

Smoking, ingesting caffeine, and exercising before blood pressure checks may affect the readings, so this should be considered when interpreting the readings.

Blood Pressure

Blood pressure is measured in millimeters of mercury (mmHg) and comprises two components: (1) systolic blood pressure and (2) diastolic blood pressure. The systolic blood pressure is the highest pressure that is felt in the arteries, and it occurs when the ventricles contract.18 The diastolic blood pressure is the lowest or resting pressure that occurs when the ventricles relax. A blood pressure reading can be obtained using an oscillometric (electronic) automated monitoring, or an auscultatory (manual) reading with a mercury or aneroid sphygmomanometer. An ideal oscillometric blood pressure device takes six consecutive readings at one- to two-min intervals.35 The clinician would attend the first reading to ensure the patient is in the proper position and that the monitor is operating properly. The patient is then left alone for the subsequent readings. The device then discards the first reading and averages the next five measurements to obtain the blood pressure reading. If necessary, an ambulatory (out-of-office) blood pressure device can be worn by the patient to record blood pressure readings over a 24-h period at half-hour to one-hour intervals.36,37 This allows the blood pressure to be monitored for fluctuations throughout the day based on activity and medications. It also helps rule-out white coat hypertension in clinical settings.

An automated home blood pressure machine can be purchased for patients to use at home. Although these machines are typically easy and convenient to use, the accuracy of the measurement depends on the proper positioning of the patient and placement of the cuff. Moreover, readings can be inaccurate if the heart rate is irregular and if there is physical movement (e.g., shivering).

It is advised to use an automated blood pressure device that has been validated and endorsed by a regulating body.38 The aneroid and mercury sphygmomanometers have traditionally been used in practice to obtain a manual blood pressure reading. Accuracy depends on the proper standardized technique and calibration of the device.

To obtain an accurate blood pressure measurement, it is important that the patient be seated and comfortable. Ideally, the patient should be well rested for at least 5 min before the blood pressure measurement. As such, the pharmacists could conduct a medication history with the patient during this period. The patient should also not have smoked at least 30 minutes before getting their blood pressure monitored. The patient should subsequently be seated with back supported, feet flat on the floor, and arm slightly bent, palm up, and supported at heart level.31,39 Next, the appropriate cuff size should be selected. The cuff size can be determined by ensuring the bladder width is approximately 40% of the arm circumference and the bladder length is approximately 80% of the arm circumference. Once an appropriate cuff size has been selected, the center of the cuff bladder can be placed over the brachial artery. The cuff should be wrapped smoothly and snuggly around the arm approximately 2.5 cm above the crease of the elbow. The patient is now ready to have a blood pressure measurement.

An automated device will typically take a measurement after being activated and display the blood pressure reading digitally. However, if using a manual cuff, the manometer should be in direct line of eye site to allow for an accurate reading.

With a manual cuff, it is recommended to estimate the systolic blood pressure first, to determine how high to raise the cuff pressure to prevent discomfort to the patient and to prevent error caused by an auscultatory gap. To estimate the systolic pressure, the clinician palpates the radial pulse and then inflates the cuff to a point at which the radial pulse can no longer be felt. The clinician then adds 30 mmHg to this reading to obtain an estimated systolic blood pressure. After the systolic blood pressure is estimated, the clinician can use the stethoscope, placing the bell of the stethoscope lightly over the brachial artery site, but in a position to make a tight seal with the patient's skin. The clinician inflates the cuff again to the estimated systolic blood pressure, and then slowly deflates the cuff at a steady rate of 2–3 mmHg/s. While the cuff is deflating, the clinician is listening for Korotkoff sounds with the stethoscope. The pressure at which the first of two consecutive beats are heard (Korotkoff Phase I), is the systolic blood pressure. The pressure at which the last beat is heard (Korotkoff Phase V), is the diastolic blood pressure.31,32 It is recommended to continue listening until 20 mmHg below the diastolic blood pressure, and then rapidly and completely deflate the cuff. The clinician should then wait 2 minutes and repeat the reading. It is recommended to take three readings on the same arm, and average only the last two readings.

Common mistakes while taking a blood pressure reading include using an incorrect cuff size (e.g., if it is too small for the patient it can overestimate the blood pressure reading) and the patient's positioning (e.g., if the patient's arm is below heart level, or if the patient is not rested or comfortable, it can overestimate the reading). Other common mistakes while using a manual device for measuring blood pressure include stopping during deflation or reinflating the cuff too soon/deflating too quickly to allow enough time to hear the Korotkoff sounds.37 A cuff deflation rate of 2 mmHg per beat is necessary for accurate blood pressure measurement.

There are also several factors that can influence blood pressure. Factors that can raise blood pressure include nicotine or caffeine consumption in the last 30 min, certain drugs (e.g., decongestants, corticosteroids, NSAIDs), exercise, anxiety, full bladder, room temperature, patient talking during a reading, or tight clothing around the forearm. Factors that can lower blood pressure include fasting or certain drugs (e.g., depressants). Some patients have an auscultatory gap, which is a silent interval between the systolic and diastolic pressures caused by arterial stiffness and atherosclerotic disease.1 It can result in an underestimation of the systolic blood pressure or an overestimation of the diastolic blood pressure.

Intraoperative Monitoring

Intraoperative monitoring must include an assessment of oxygenation, ventilation, and circulation. The depth of sedation dictates the degree and frequency of monitoring required.75

As the treatment progresses, the state of consciousness should be evaluated frequently by verbal communication with the patient. For those patients incapable of communication, either because of age or disability, some means of evoking a response should be used. Another area of assessment is the patient’s external appearance. The oral mucosa, the nail beds, and the complexion of the skin provide indications of perfusion of the patient. This should be done at intervals throughout the procedure and documented in the record. If restraining devices that cover the patient are used, a hand or foot should be exposed. These devices should be carefully applied to the sedated patient to ensure that there is no restriction of the chest.

The heart and respiratory rates can be continuously monitored with a pretracheal stethoscope (Fig. 17-13). The bell of the stethoscope is secured in the suprasternal notch, where breath and heart sounds are easily auscultated. This instrument allows for continuous monitoring of the rate and depth of breathing. These devices are manufactured with a variety of amplification schemes, including a remote earpiece and a wireless speaker that transmits the patient’s breath sounds throughout the entire operatory. Additional ventilatory monitoring should include observation of chest excursions. The common dental team habit of using the patient’s chest as an ad hoc instrument table, or completely covering the chest with towels or other barriers, interferes with the observation of chest excursions and should be avoided when possible.

Although it is acceptable to measure physiologic parameters using the basic methods of auscultation and an aneroid sphygmomanometer with a manually inflated cuff, numerous automatic, continuous-monitoring blood pressure devices are available. In all instances, the cuff should be of the appropriate size for the patient. Pulse oximetry probes are available that attach to the finger or earlobe and produce both visual and audible signals. The pulse oximeter and automatic blood pressure cuff are often bundled together in a single monitor that may also include additional physiologic monitoring devices (Fig. 17-14).

In 1981 the introduction of pulse oximetry to health care providers created a revolution in patient safety monitoring. By 1987 it had become part of the standard monitoring armamentarium for anesthesia providers and is used in many other locations where the monitoring of the effectiveness of a patient’s breathing is desired. The device measures the extent to which hemoglobin is saturated with oxygen while simultaneously monitoring the peripheral pulse rate. A probe consisting of an optical diode sensor and a second, light-emitting diode is applied to a digit on the hand or foot, or to the earlobe. The light-emitting diode emits both red and infrared wavelengths of light, and the light-detecting diode detects light transmitted through the tissue. Red wavelengths are absorbed primarily by oxygenated hemoglobin, whereas infrared wavelengths are absorbed primarily by deoxygenated hemoglobin. The ratio of deoxygenated hemoglobin to oxygenated hemoglobin is determined and displayed. One shortcoming of the pulse oximeter is a processing delay of approximately 20 to 40 seconds. This is particularly pertinent for pediatric dentists because children may begin to experience oxygen desaturation within 10 to 20 seconds after the onset of breathlessness

The correlation between the percent oxygen saturation of hemoglobin (Sao2) and oxygen tension in arterial blood (Pao2) must be appreciated when oxygen saturation is interpreted. The relationship between the two parameters is plotted on the oxyhemoglobin dissociation curve (Fig. 17-15). Unbound oxygen dissolved in blood produces the oxygen tension (Pao2) required to supply oxygen to peripheral tissues. When a patient stops breathing, hypoxemia begins when oxygen saturation drops to 95%, corresponding to an oxygen tension of 80 mm Hg. Once the arterial saturation levels drop to 90% (Pao2 = 60 mm Hg), the patient will begin to desaturate rapidly if effective ventilation is not immediately restored. Awareness of the peripheral oxygen saturation from moment to moment is important during the administration of sedation because hypoxia is almost always the initial event in morbidity and mortality related to sedation.76

Ventilation, i.e., the mechanical act of moving air throughout the respiratory system, must be evaluated independently from oxygenation. Methods used to monitor ventilation include visual monitoring for chest wall movement, listening for breath sounds with a precordial stethoscope, determination of respiratory rate, and capnography. Capnography is the most sensitive of these methods, providing direct confirmation of apnea within seconds after breathing is interrupted. When possible, the combination of capnography and precordial stethoscopy provides the optimal strategy for monitoring the adequacy of breathing during the course of pediatric sedation. The capnograph (Fig. 17-16, A) detects both the presence and the quality of ventilation by analyzing the concentration of carbon dioxide in the exhaled gases through differential infrared absorption. The end-tidal carbon dioxide concentration is the concentration of carbon dioxide measured at the terminal portion of the exhalation curve (see Fig. 17-16, B).18 The sampling line is placed either in the nostril or in close approximation to the nose or mouth and allows for sampling of exhaled air into the unit. There are limitations to the accuracy of readings, especially when the device is used in children. Head movement, mouth breathing, crying, and tube blockage by mucous all result in inaccurate readings. In 2014 the American Association of Oral and Maxillofacial Surgeons mandated the use of capnography whenever possible during moderate sedation as part of its standard of care.77

BP Measurement in Children

The primary BP measurement methods in children include manual measurements or auscultation, automated or oscillometric devices, and 24-hour ambulatory blood pressure monitoring (ABPM). Oscillometric devices are convenient and easy to use in practice, but there has been concern about replacing manual BP measurements with automated devices in children. A recent meta-analysis by Duncombe et al. compared the accuracy of manual BP measurements with oscillometric devices and found that oscillometric devices generated higher values for systolic blood pressure (SBP) than determined with mercury sphygmomanometers, with large variability between studies.10 Eliasdottir et al. compared manual aneroid BP with oscillometric BP in children and found only moderate correlation of individual measures and that mean diastolic blood pressures (DBP) were lower with the oscillometric method.11 In a pediatric chronic kidney disease population, Flynn et al. found that oscillometric devices overestimate SBP by 9 mm Hg and DBP by 6 mm Hg compared with manual methods with an aneroid sphygmomanometer.12 These various measurement discrepancies have led to similar recommendations by the AAP, ESH, and Hypertension Canada that oscillometric devices may be used to screen for BP abnormalities in children but that elevated BP readings should be confirmed by auscultation (Table 1).1-5 Improvements in oscillometric device technology with specific attention to pediatric BP challenges may be able to reduce the discrepancy between the reference method of auscultation and the more convenient automated devices.

ABPM has been shown to be the most accurate, reproducible, and cost-effective method for diagnosing hypertension in children.13-16 It is also most predictive of target-organ damage associated with sustained hypertension.17-19 ABPM also has the advantage of diagnosing white-coat hypertension in children and thus can help avoid unnecessary patient investigations and medications. Both the AAP and ESH guidelines recommend ABPM for confirmation of elevated clinic BP for the diagnosis of hypertension.1,2 Unfortunately, ABPM is not universally available in many countries and often only pediatric nephrologists and cardiologists have the technology available, so patients require subspecialty referral for access to these devices. Either less costly ABPM devices need to be developed or ABPM programs need reimbursement to support making devices more widely available. Other less expensive devices, such as wrist monitors, unattended automated office BP monitors, and home BP monitors, could also be validated and better studied in children to fix the inequality in care (Table 2).

Guidelines are also consistent in their recommendations for repeated measures of clinic BP before diagnosing a child with hypertension, although studies are still examining the necessary number of readings (Table 1). Almost all pediatric BP studies comment that first BP readings during a visit are higher than subsequent ones, and the AAP guideline recommends that an initial elevated BP reading should be repeated twice that visit and the average of the final 2 readings be used as the BP for the visit.2 Outdili et al. studied the number of necessary oscillometric BP readings at the initial screening visit to predict sustained hypertension and they found the second BP reading or the average of readings was most predictive.20 Similarly, Negroni-Balasquide et al. studied the number of oscillometric readings needed to accurately predict an auscultatory measurement and also found that either the second BP reading or the average of readings was most representative.21

In addition, multiple visits are recommended because the prevalence of elevated BP reduces from the first visit to the third visit. A recent meta-analysis determined the prevalence of elevated BP reduced from 12.1% at the first visit, to 5.6% at the second visit and 2.7% at the third visit, supporting the need for 3 clinical encounters before diagnosing hypertension.22 The previous pediatric BP guideline, the Fourth Report by the U.S. National Heart, Lung, and Blood Institute, recommended diagnosing hypertension if the BP was above the 95th percentile on 3 occasions, but it was not clear if this was based on elevated BP at each visit or the average of the 3 visits.23 Balsara et al. compared the rates of hypertension in a school screening population by different interpretations of the recommendation and found that 7% would be diagnosed hypertensive based on the average BP of the 3 visits and only 3.3% based on elevated BP at each visit.24 The recent AAP guideline clarified that to diagnose hypertension, the BP should be elevated at each of 3 visits and if it returns to normal at any visit, then the child is not hypertensive.2 All of these studies were based on clarifying definitions and not based on evidence of target-organ damage, which is the next necessary step to confirm accurate diagnosis requirements (Table 2).

2 Methods