Rectal Temperature Measurement

Accuracy & Status as Gold Standard

• Reflects core body temperature accurately when the probe is placed at least 8 cm from the anus with an indwelling thermistor, and when body temperature is relatively constant.
• In the ICU, rectal probe temperatures demonstrate limited variability or bias compared to pulmonary artery (PA) catheter temperatures — the true gold standard for core temp.
• Neither tympanic membrane (TM) nor skin thermometers can reliably predict rectal temperature, confirming its primacy for detecting fever, especially in pediatrics.

Procedure

1. Position: Place the patient in the left or right lateral decubitus position.
2. Insertion depth: Advance the probe gently to 3–5 cm for routine clinical use; for suspected exertional heat stroke, insertion to 15 cm (6 in) is the most valid depth.
3. Allow the probe to equilibrate with local tissue temperature.
4. For continuous monitoring (e.g., heat stroke cooling), use a thermistor probe connected to a potentiometer.

Contraindications / Relative Contraindications

• Neutropenia — theoretical risk of bacterial translocation with rectal stimulation (use oral route instead)
• Recent rectal surgery

Complications

• Rectal perforation
• Pneumoperitoneum
• Bacteremia
• Dysrhythmias
• Syncope

Limitations & Caveats

Normal Values & Fever Thresholds

• Normal core temp: 37.0°C ± 0.6°C (98.6°F ± ~1°F)
• Fever in neonates (< 1 month): rectal temp ≥ 38°C (100.4°F)
• Hypothermia in neonates: rectal temp < 36.5°C (97.7°F)
• Temporal artery fever can be excluded if readings are < 37.7°C (corresponding to a rectal temp > 38.3°C defining fever)

Comparison with Other Sites

Equipment

Evaluation of the Rectal Temperature Procedure

✅ Point 1 — Separating the buttocks / hand positioning

⚠️ Point 2 — Insertion depth of 2–3 cm

❌ Point 3 — Subtract 0.5°C from the reading

• Fever = rectal temperature ≥ 38.0°C (100.4°F) — Roberts & Hedges; Tintinalli's Emergency Medicine
• Normal rectal temp ≈ 37.0–37.5°C (slightly higher than oral by ~0.3–0.5°C, which is already accounted for in the site-specific fever threshold)

Summary

Methods of Counting the Pulse

Physiology (What You Are Feeling)

1. Palpation (Manual Method)

• Use the tips of the index and middle fingers (first and second fingers)
• Never use the thumb — you may feel your own pulse and miscount
• Apply gentle but firm pressure over the artery
• Count beats against a clock/watch

Carotid caution: Never palpate both carotids simultaneously — could theoretically compromise cerebral blood flow. Palpate at or below the thyroid cartilage to avoid inadvertent carotid sinus massage (which can cause reflex bradycardia). If a bruit is heard, use Doppler instead of vigorous palpation.

2. Cardiac Auscultation (Apical Method)

• Place a stethoscope over the cardiac apex
• Count apical heart sounds for 1 full minute
• The apical pulse is frequently greater than the peripheral pulse in arrhythmias (e.g., atrial fibrillation) because not every contraction generates enough stroke volume to transmit a peripheral pulse
• The difference = pulse deficit — a greater deficit reflects more severe disease
• In neonates and infants, auscultation at the cardiac apex is more accurate than palpation at the brachial, carotid, or femoral arteries

3. Pulse Oximetry (Plethysmographic Method)

• Pulse oximeters detect photoplethysmographic waveforms and derive heart rate electronically
• Simultaneous readout of SpO₂ and pulse rate
• Useful for continuous monitoring but can be inaccurate in poor perfusion states, motion artifact, hypothermia, or dysrhythmias
• Does not replace palpation or auscultation for rhythm assessment

4. Electronic / Continuous Monitoring

• ECG-based cardiac monitors display heart rate from electrical depolarization — this is heart rate, not always the same as pulse rate
• Pulse deficit = heart rate (electrical) minus pulse rate (mechanical) — seen in AF, PVCs, and poor cardiac output states
• Automated BP devices detect oscillometric pulses during cuff deflation

5. Doppler Ultrasound

• Handheld Doppler probes detect arterial flow by the Doppler shift of reflected ultrasound
• Used when pulses are too faint to palpate (shock, peripheral vascular disease)
• More sensitive and specific than palpation alone
• Can detect perfusion where manual palpation fails (e.g., dorsalis pedis in critical ischemia)

Special Populations

Normal Pulse Rate Reference

Pulse Terminology

Rate Terms

Rhythm Terms

Amplitude / Volume Terms

Contour / Waveform Terms

Location / Context Terms

• < 60 bpm = the widely accepted clinical threshold used in most textbooks and guidelines
• Some researchers have proposed redefining it as < 45 bpm, because many healthy adults (especially well-trained athletes) naturally have resting heart rates of 40–59 bpm and are completely normal. A marathon runner with a pulse of 48 bpm is not bradycardic in a pathological sense.

How to Count the Radial Pulse — Simply Explained

Step 1 — Find the right position

• Ask the patient to relax their hand, palm facing upward
• You examine the right hand with your left hand, and the left hand with your right hand
• This is so your fingers are naturally positioned correctly over the artery

Step 2 — Place your fingers

• Use the soft pads (not the tips) of your index finger (2nd) and middle finger (3rd)
• Place them on the inner side of the wrist, just below the base of the thumb
• Press gently but firmly until you feel the strongest pulsation
• Never use your thumb — it has its own pulse and will confuse the count

Step 3 — Count

The reason you count for a full minute when the pulse is abnormal is that irregular beats are not evenly distributed — a short count would give an inaccurate estimate.

Step 4 — Interpret

Step 5 — Record and communicate

• Write the result clearly (e.g., "Pulse: 78 bpm, regular")
• Tell the patient the result in simple terms

Key Points to Remember

• Pads, not tips of fingers — more sensitive to subtle pulsations
• Two fingers (index + middle) — better contact with the artery
• No thumb — has its own pulse
• Cross hands — right hand checks left wrist, left hand checks right wrist
• 1 minute for abnormal, 15–30 seconds for normal

Apex of the Heart — Position

Exact Anatomical Location

5th intercostal space, midclavicular line (MCL), left side — approximately 2 cm medial to the midclavicular line

How to Find It on the Chest

Collar bone (clavicle)
        |
Count down 5 rib spaces  ←  5th intercostal space
        |
Draw an imaginary vertical line down from the middle of the clavicle  ←  Midclavicular line
        |
Where they meet = Apex of heart (slightly medial to that line)

Why It Matters Clinically

Quick Memory Trick

"5th space, midclavicular, LEFT" — Count 5 ribs down from the clavicle on the left side of the chest

Base of the Heart — Position

Simple Answer

It is directed posteriorly (backward) and upward, located at the level of the 2nd to 3rd intercostal spaces, behind the sternum.

Formed By

Vertebral Level

Apex vs Base — Side-by-Side Comparison

Memory Trick

Apex = bottom-left tip (points toward left armpit/nipple) Base = top-back (where the "plumbing" — great vessels — connects)

Stenosis — Simply Explained

Simple Analogy

Where Stenosis Occurs in the Body

What Happens Because of Stenosis

Narrowing
    ↓
Resistance increases
    ↓
Upstream pressure builds up (the structure behind it works harder)
    ↓
Downstream flow decreases (less blood/fluid gets through)
    ↓
Symptoms of reduced supply + increased workload

Example — Aortic Stenosis

• Aortic valve narrows → left ventricle must pump harder to push blood out
• Left ventricle thickens (hypertrophy) over time from overwork
• Eventually fails → symptoms: chest pain, fainting, shortness of breath
• Classic pulse finding: pulsus parvus et tardus — small and slow-rising pulse

Stenosis vs Regurgitation (the two valve problems)

Key Point