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newSchoolWorks.com › VoTechWorks › Health & Personal Services › Medical Assisting › Clinical and Administrative Foundations of Medical Assisting › Lesson 4
HLT-MEDI38-02 · Lesson 4 · 12.5 clock hours · lab

Vital Signs: Blood Pressure and Oxygen Saturation

Objective. Students will accurately measure blood pressure by auscultatory method and peripheral oxygen saturation by pulse oximetry, identify readings outside normal adult ranges, and articulate the correct reporting protocol.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed clinician in the field or by a certification or approval body. It is a study draft and may contain errors. Do not use it to make decisions about any patient or medication. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

Why Blood Pressure and Oxygen Saturation Matter

Blood pressure (BP) and peripheral oxygen saturation (SpO₂) are two of the most clinically significant vital signs you will measure every day as a medical assistant. An undetected elevated BP or a dropping oxygen level can signal a life-threatening emergency. Accurate technique, correct documentation, and prompt reporting are core professional responsibilities—not optional steps.

Blood Pressure: What You Are Measuring

Blood pressure is the force exerted by circulating blood against arterial walls. It is recorded as two numbers: systolic pressure (the higher number, measured when the heart contracts) over diastolic pressure (the lower number, measured when the heart relaxes between beats). The unit is millimeters of mercury (mmHg).

Generally accepted normal adult BP is less than 120/80 mmHg. Readings consistently at or above 130/80 mmHg are classified as hypertension by current major guidelines. A single reading does not diagnose hypertension, but any reading that is significantly elevated must be reported to the provider so they can decide the next step.

The Auscultatory Method: Step by Step

The auscultatory method uses a sphygmomanometer (a BP cuff attached to a pressure gauge) and a stethoscope to detect Korotkoff sounds—the sounds produced as blood begins to flow through the compressed artery and then flows freely again.

Before you begin:

Procedure:

1. Expose the upper arm and palpate the brachial artery in the antecubital space.

2. Center the cuff's bladder over the brachial artery with the lower edge about 2–3 cm above the antecubital crease.

3. Palpate the radial pulse, inflate the cuff until the pulse disappears, then inflate 20–30 mmHg higher. This estimates systolic pressure and prevents missing an auscultatory gap.

4. Place the stethoscope bell or diaphragm lightly over the brachial artery—do not tuck it under the cuff.

5. Deflate the cuff slowly and steadily at approximately 2–3 mmHg per second.

6. Note the mmHg at which you first hear a clear tapping sound—this is the systolic reading.

7. Note the mmHg at which sounds completely disappear—this is the diastolic reading.

8. Deflate fully and remove the cuff.

9. Take a second reading at least two minutes later and average or report both, per facility policy.

Common errors to avoid: talking during measurement, deflating too fast, re-inflating mid-measurement, supporting the arm yourself (muscle tension raises reading), or crossing the patient's legs.

Pulse Oximetry: Measuring Oxygen Saturation

A pulse oximeter clips onto a peripheral site—most commonly a fingertip—and uses infrared light to estimate the percentage of hemoglobin carrying oxygen (SpO₂). The device also displays the pulse rate.

Normal SpO₂ in a healthy adult at sea level is generally 95–100%. A reading below 95% warrants close attention; most facilities require notification of the provider when SpO₂ falls below 95% or per the specific threshold defined in facility policy. A reading at or below 90% is considered a clinically urgent finding and requires immediate provider notification.

Factors that reduce accuracy:

Technique: Apply the probe to a warm, well-perfused fingertip. Wait for a stable waveform and a consistent reading for at least 30 seconds before recording.

Reporting Protocol and Patient Safety

Always compare your reading against the patient's baseline (prior readings in the chart) as well as normal ranges. Use the SBAR format when reporting to a provider:

Never tell a patient they are "fine" or interpret results for them beyond your scope of practice. You may state the numbers and let the patient know the provider will review them.

If a reading is critically elevated or SpO₂ is critically low, do not leave the patient alone. Alert the provider immediately and document the time, the reading, who you notified, and the provider's response.

Key terms9

Systolic pressureThe higher number in a blood pressure reading; represents the pressure in the arteries when the heart muscle contracts.
Diastolic pressureThe lower number in a blood pressure reading; represents the pressure in the arteries when the heart is at rest between beats.
Korotkoff soundsThe series of sounds heard through a stethoscope over the brachial artery as cuff pressure is slowly released; used to identify systolic and diastolic blood pressure values.
Auscultatory methodThe technique of measuring blood pressure by inflating a sphygmomanometer cuff and using a stethoscope to detect Korotkoff sounds.
SphygmomanometerAn instrument consisting of an inflatable cuff and a pressure gauge used to measure arterial blood pressure.
SpO₂Peripheral oxygen saturation; the estimated percentage of hemoglobin saturated with oxygen as measured by a pulse oximeter.
Pulse oximeterA non-invasive device that clips onto a fingertip or other peripheral site and uses light absorption to estimate oxygen saturation and pulse rate.
SBARA structured communication framework standing for Situation, Background, Assessment, Recommendation; used to relay clinical findings to a provider clearly and completely.
Auscultatory gapA silent interval during cuff deflation in which Korotkoff sounds disappear and then reappear; can cause underestimation of systolic pressure if the cuff is not inflated high enough.

Worked examples4

1. You inflate the cuff while palpating the radial pulse. The pulse disappears at 130 mmHg. To what pressure should you inflate the cuff before beginning auscultation?
  1. Identify the palpated systolic estimate: 130 mmHg.
  2. Add 20–30 mmHg to that estimate to ensure you start above the true systolic and do not miss an auscultatory gap.
  3. 130 + 20 = 150 mmHg (minimum); 130 + 30 = 160 mmHg (maximum acceptable starting point).
Answer: Inflate to 150–160 mmHg before beginning to deflate and listen for Korotkoff sounds.
2. A student takes a peer's BP twice, two minutes apart. Reading 1: 124/82 mmHg. Reading 2: 118/78 mmHg. What is the average of the two readings, and how should it be documented?
  1. Average systolic: (124 + 118) ÷ 2 = 242 ÷ 2 = 121 mmHg.
  2. Average diastolic: (82 + 78) ÷ 2 = 160 ÷ 2 = 80 mmHg.
  3. Document both individual readings and the average, the time, the arm used, patient position, and cuff size per facility policy.
Answer: Average BP is 121/80 mmHg. Document both readings, the average, time, position, arm, and cuff size.
3. During the competency check, a student reads BP as 138/90 mmHg and the instructor simultaneously reads 142/94 mmHg. Does the student pass?
  1. Calculate the systolic difference: 142 − 138 = 4 mmHg. The pass threshold is within ±4 mmHg, so 4 mmHg is exactly at the limit—acceptable.
  2. Calculate the diastolic difference: 94 − 90 = 4 mmHg. Again exactly at the ±4 mmHg limit—acceptable.
  3. Both differences are within ±4 mmHg, so the measurement criterion is met. The student must also have selected the correct cuff size, positioned the patient correctly, and documented accurately for a full pass.
Answer: The measurement criterion is met (both differences are ≤4 mmHg). A full pass also requires correct cuff selection, positioning, and documentation.
4. A patient's SpO₂ reads 91% on the right index finger. You notice the patient has dark nail polish. What steps should you take before deciding whether to report?
  1. Remove or reposition away from the polish: try a finger without polish, or use the earlobe.
  2. Warm the extremity if it is cold to improve peripheral perfusion.
  3. Allow the oximeter to stabilize for at least 30 seconds and obtain a new reading.
  4. If the corrected reading remains below 95%—and especially at or below 90%—notify the provider immediately per facility policy, document the original and corrected readings, site used, and time.
Answer: Retest at a site free of nail polish after warming the hand. If SpO₂ remains at or below 90% on recheck, notify the provider immediately and document all findings.

The math in this lesson1

Learners add 20-30 mmHg to a 130 mmHg palpated systolic to set cuff inflation at 150-160 mmHg.
N-Q.3
Brush up in the math halls at newSchoolWorks.com:
In class: Practice locating brachial pulse and applying a sphygmomanometer cuff at the correct height and cuff-size fit on three peers; take duplicate readings two minutes apart and compare results, discussing sources of error such as cuff size and patient position. · Use a pulse oximeter on multiple fingers and both hands of peers, note how nail polish and cold extremities affect readings, and identify the threshold at which the provider must be notified based on facility policy scenarios provided by the instructor. · Role-play the patient-notification conversation when a blood pressure reading is significantly elevated, practicing therapeutic communication; then document findings using SBAR (Situation, Background, Assessment, Recommendation) format.
Materials: Aneroid sphygmomanometers (multiple cuff sizes: adult regular, adult large, pediatric), stethoscopes, pulse oximeters, SBAR documentation template, blood-pressure error source reference guide, normal vital-sign ranges reference card
Check: Bilateral blood pressure readings taken by student and instructor simultaneously using a dual-head stethoscope; pass = systolic within ±4 mmHg and diastolic within ±4 mmHg of instructor value, correct cuff size selected, correct patient positioning, and accurate documentation; all three criteria must be met.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Clinical Medical Assisting – Vital Signs
1. A medical assistant selects an adult-regular cuff for a patient whose upper arm circumference is significantly larger than average. What effect will this have on the blood pressure reading?
Clinical Medical Assisting – Vital Signs
2. While deflating the blood pressure cuff, you first hear a clear tapping sound at 126 mmHg and the sounds disappear completely at 82 mmHg. How should you record this finding?
Clinical Medical Assisting – Patient Care
3. A patient's SpO₂ reads 88% on initial measurement. After repositioning the probe and warming the hand, the reading is 89%. What is the most appropriate next action?
Clinical Medical Assisting – Vital Signs
4. Which patient position is recommended for a routine blood pressure measurement to obtain the most accurate result?
Administrative and Communication – Documentation
5. During SBAR reporting to the provider, the medical assistant states: 'Mrs. Garcia is a 58-year-old patient here for a routine visit. Her current BP is 168/104 mmHg; her baseline last visit was 122/76 mmHg. She denies headache or visual changes.' Which component of SBAR does this statement primarily represent?
Clinical Medical Assisting – Vital Signs
6. A peer's SpO₂ reads 93% on their right index finger, which has dark nail polish. What is the best immediate action before reporting the result?
Clinical Medical Assisting – Vital Signs
7. A student inflates the blood pressure cuff but does not first estimate systolic pressure by palpation. Which error is most likely to result?
Clinical Medical Assisting – Patient Care
8. A patient's blood pressure is measured as 144/92 mmHg. The medical assistant's most appropriate response is to:
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