18.2 Measurement & Assessment of Vital Signs (BP, Pulse, Respiration, Temperature)

18.2 Measurement & Assessment of Vital Signs

Vital signs—body temperature, pulse rate, respiration, blood pressure, and pulse oximetry—are primary indicators of a patient's fundamental physiological status. Radiologic technologists must accurately measure, interpret, and monitor vital signs prior to contrast administration, during invasive interventional procedures, and when managing acutely ill, traumatized, or deteriorating patients in the radiology department.

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1. Body Temperature

Body temperature represents the physiological balance between heat produced by metabolic tissue processes and heat lost to the external environment. Temperature regulation is governed by the hypothalamus in the brain.

Normal Range & Temperature Scale Conversion

• Normal Adult Temperature Range: 36.5°C to 37.5°C (97.7°F to 99.5°F).
• Pyrexia (Fever): Body temperature exceeding 38.0°C (100.4°F).
• Hyperthermia: Severely elevated body temperature above 40.0°C (104.0°F).
• Hypothermia: Core body temperature dropping below 35.0°C (95.0°F).
• Conversion Formulas:
  • Fahrenheit to Celsius: $°\ ext{C} = (°\ ext{F} - 32) \div 1.8$
  • Celsius to Fahrenheit: $°\ ext{F} = (°\ ext{C} \ imes 1.8) + 32$

Measurement Sites & Clinical Considerations

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2. Pulse / Heart Rate

The pulse is the rhythmic expansion and recoil of an artery created by the left ventricle contracting and pumping blood into the arterial vascular system.

Normal Reference Values & Clinical Definitions

• Normal Adult Pulse Rate: 60 to 100 beats per minute (bpm).
• Tachycardia: Heart rate exceeding 100 bpm. Common causes include acute anxiety, pain, hypovolemia, fever, hemorrhage, hypoxia, and early shock.
• Bradycardia: Heart rate below 60 bpm. Common causes include physical athletic conditioning, vagal nerve stimulation, hypothermia, cardiac conduction blockages, and medications (e.g., beta-blockers).

Palpation Sites & Anatomical Locations

                  [Temporal Artery] ── (Anterior to ear)
                  [Carotid Artery]  ── (Neck, CPR site)
                  [Apical Pulse]    ── (5th ICS, MCL - Stethoscope)
                  [Brachial Artery] ── (Antecubital fossa, BP site)
                  [Radial Artery]   ── (Thumb side of wrist, Routine)
                  [Femoral Artery]  ── (Groin, Catheter access)
                  [Popliteal Artery]── (Behind knee)
                  [Dorsalis Pedis]  ── (Top of foot)

1. Radial Artery: Located on the anterior wrist at the base of the thumb. The primary and most convenient site for routine pulse assessment in conscious adults. Palpate using the tips of the index and middle fingers (never the thumb, as it has its own pulse).
2. Carotid Artery: Located in the neck lateral to the trachea, anterior to the sternocleidomastoid muscle. Used during emergency resuscitation (CPR) and severe hypotension, as it remains palpable when peripheral pulses fade.
3. Brachial Artery: Located in the antecubital fossa of the inner elbow, medial to the biceps tendon. Used for blood pressure auscultation and pulse assessment in infants.
4. Femoral Artery: Located in the groin fold. Used during cardiac catheterization, interventional vascular procedures, and assessment of lower extremity circulation.
5. Apical Pulse: Measured over the apex of the heart using a stethoscope placed at the 5th intercostal space at the left midclavicular line (MCL). Counted for 1 full minute. This is the most accurate pulse measurement and is mandatory before administering cardiac medications or when peripheral pulses are irregular.
6. Dorsalis Pedis & Posterior Tibial: Located on the dorsal aspect of the foot and behind the medial malleolus, respectively. Used to evaluate peripheral arterial patency post-angiography or lower extremity trauma.

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3. Respiration

Respiration is the physiological mechanism of gas exchange, supplying oxygen to tissues and eliminating carbon dioxide. One complete respiration consists of one inspiration (inhalation) and one expiration (exhalation).

Normal Parameters & Terminology

• Normal Adult Respiratory Rate: 12 to 20 breaths per minute (rpm).
• Tachypnea: Respiratory rate exceeding 20 breaths/min. Indicates respiratory distress, fever, hypoxia, metabolic acidosis, or severe pain.
• Bradypnea: Respiratory rate below 12 breaths/min. Caused by central nervous system depression, opioid analgesic administration, head trauma, or hypothermia.
• Dyspnea: Difficulty, labor, or pain during breathing.
• Apnea: Total cessation of breathing.
• Orthopnea: Difficulty breathing when lying flat; patient must sit erect to breathe comfortably.
• Cheyne-Stokes Respiration: A pattern of breathing characterized by alternating periods of hyperpnea (deep rapid breathing) and apnea. Often observed in terminal illness, severe heart failure, or brain stem injuries.

Assessment Technique

To obtain an accurate respiratory rate, count chest rises unobtrusively for 30 to 60 seconds immediately after taking the radial pulse, while keeping fingers on the patient's wrist. If patients realize their breathing is being observed, they involuntarily alter their natural rate and depth.

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4. Blood Pressure (BP)

Blood pressure is the lateral force exerted by circulating blood against the internal walls of the systemic arterial vessels. It is expressed in millimeters of mercury (mmHg) as two distinct numbers: Systolic over Diastolic.

• Systolic Pressure: The peak arterial pressure created during ventricular contraction (systole).
• Diastolic Pressure: The minimum resting arterial pressure maintained during ventricular relaxation (diastole).
• Pulse Pressure: The numerical difference between systolic and diastolic pressure (Normal range: 30 to 50 mmHg).

AHA / ACC Blood Pressure Classification for Adults

Equipment & Auscultation Technique

• Equipment Required: Sphygmomanometer (mercury, aneroid, or digital manometer) and a Stethoscope.
• Korotkoff Sounds: Five distinct phases of vascular sounds heard over the brachial artery as the cuff deflates:
  • Phase I: The first clear, tapping sound (indicates Systolic Pressure).
  • Phase II: A soft swishing or murmuring sound.
  • Phase III: A crisp, louder tapping sound.
  • Phase IV: A distinct, abrupt muffling sound.
  • Phase V: The complete disappearance of sound (indicates Diastolic Pressure in adults).

Critical Technical Errors in BP Measurement

• Incomplete/Improper Cuff Size: The inflatable bladder width must cover 40% of arm circumference, and bladder length must encircle 80% of arm circumference.
  • Cuff Too Small / Narrow: Produces falsely high blood pressure readings.
  • Cuff Too Large / Wide: Produces falsely low blood pressure readings.
• Arm Position: Arm must be supported at heart level. Arm held above heart level yields falsely low readings; arm hanging below heart level yields falsely high readings.

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5. Pulse Oximetry (${\ ext{SpO}}_2$)

Pulse oximetry is a non-invasive photo-electric monitoring technique used to measure the arterial blood oxygen saturation (${\ ext{SpO}}_2$) and pulse rate. The sensor clip emits two wavelengths of light (red light at 660 nm and infrared light at 940 nm) through a vascular bed (finger, toe, or earlobe) to differentiate oxygenated hemoglobin (${\ ext{HbO}}_2$) from deoxygenated hemoglobin (${\ ext{Hb}}$).

Clinical Thresholds & Limitations

• Normal Range: 95% to 100% at sea level.
• Significant Hypoxemia: ${\ ext{SpO}}_2 < 90%$. Requires immediate administration of supplemental oxygen and rapid clinical assessment.
• Factors Affecting Accuracy:
  • Poor Peripheral Perfusion / Vasoconstriction: Cold extremities, hypovolemic shock, or severe cardiac failure impair optical signal reception.
  • Nail Polish or Artificial Acrylic Nails: Metallic polish pigments (especially dark blue, black, or green) absorb light wavelengths, yielding false readings.
  • Carbon Monoxide Poisoning (Carboxyhemoglobin): Oximeters cannot distinguish carboxyhemoglobin from oxyhemoglobin, producing falsely high saturation readings in smoke inhalation victims.
  • Excessive Patient Motion: Tremors or shivering create optical noise artifacts.

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Vital Signs Normal Reference Values & Clinical Thresholds Summary