Normal is between 100/60 and 140/90. Hypertension is thus defined as either SBP greater then 140 or DBP greater than 90. It is important to recognize that blood pressure is rarely elevated to a level that causes acute symptoms. That is, while hypertension in general is common, emergencies resulting from extremely high values and subsequent acute end organ dysfunction are quite rare. Rather, it is the chronically elevated values which lead to target organ damage, though in a slow and relatively silent fashion. At the other end of the spectrum, the minimal SBP required to maintain perfusion varies with the individual. Therefore, interpretation of low values must take into account the clinical situation. Those with poorly functioning hearts, for example, can adjust to a chronically low SBP (e.g. 80-90) and live without symptoms of hypoperfusion. However others, used to higher baseline values, might become quite ill if their SBPs were suddenly decreased to these same levels.
Many things can alter the accuracy of your readings. In order to limit their impact, remember the following:
- Do not place the blood pressure cuff over a patients clothing or roll a tight fitting sleeve above their biceps when determining blood pressure as either can cause elevated readings.
- Make sure the patient has had an opportunity to rest before measuring their BP. Try the following experiment to assess the impact that this can have. Take a patient's BP after they've rested. Then repeat after they've walked briskly in place for several minutes. Patients who are not too physically active (i.e. relatively deconditioned) will develop an elevation in both their SBP and DBP. Also, see what effect raising or lowering the arm, and thus the position of the brachial artery relative to the heart, has on BP. If you have a chance, obtain measurements on the same patient with both a large and small cuff. These exercises should give you an appreciation for the magnitude of error that can be introduced when improper technique is utilized.
- If the reading is surprisingly high or low, repeat the measurement towards the end of your exam.
- Instruct your patients to avoid coffee, smoking or any other unprescribed drug with sympathomimetic activity on the day of the measurement.
- Orthostatic (a.k.a. postural) measurements of pulse and blood pressure are part of the assessment for hypovolemia. This requires first measuring these values when the patient is supine and then repeating them after they have stood for 2 minutes, which allows for equilibration. Normally, SBP does not vary by more then 20 points when a patient moves from lying to standing. In the setting of significant volume depletion, a greater then 20 point drop may be seen. Changes of lesser magnitude occur when moving from lying to sitting or sitting to standing. This is frequently associated with symptoms of cerebral hypoperfusion (e.g.. light headedness). Heart rate should increase by more then 20 points in a normal physiologic attempt to augment cardiac output by providing chronotropic compensation. In the setting of GI bleeding, for example, a drop in blood pressure and/or rise in heart rate after this maneuver is a marker of significant blood loss and has important prognostic implications. Orthostatic measurements may also be used to determine if postural dizziness, a common complaint with multiple possible explanations, is the result of a fall in blood pressure. For example, patients who suffer from diabetes frequently have autonomic nervous system dysfunction and cannot generate appropriate arteriolar vaosconstriction when changing positions. This results in postural vital sign changes and symptoms. The 20 point value is a rough guideline. In general, the greater the change, the more likely it is to cause symptoms and be of clinical relevance.
- If possible, measure the blood pressure of a patient who has an indwelling arterial catheter (these patients can be found in the ICU with the help of a preceptor). Arterial transducers are an extremely accurate tool for assessing blood pressure and therefore provide a method for checking your non-invasive technique.
Oxygen Saturation: Over the past decade, this non-invasive measurement of gas exchange and red blood cell oxygen carrying capacity has become available in all hospitals and many clinics. While imperfect, it can provide important information about cardio-pulmonary dysfunction and is considered by many to be a fifth vital sign. In particular, for those suffering from either acute or chronic cardio-pulmonary disorders, it can help quantify the degree of impairment.
Pulse Oxymeter
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