Eupnea
Adult expected values: 12 to 20 breaths per minute, quiet, effortless, symmetric chest expansion, with an inspiration-to-expiration ratio of roughly 1 to 2. Anything that changes that ratio — prolonged expiration in obstructive disease, for example — is a finding even when the rate is normal.
Count it without changing it. Breathing is the one vital sign under voluntary control, so a patient who knows you are counting will breathe differently. Finish the radial pulse, keep your fingers on the wrist, and shift your eyes to the chest or abdomen — the patient believes you are still on the pulse. One full rise and fall is one respiration. Count 30 seconds and double if the pattern is regular; count a full 60 seconds if it is irregular, if the rate is abnormal, or if the patient is an infant.
Depth, effort and pattern
Look at
depth (shallow, normal, deep),
effort (accessory muscle use, nasal flaring, intercostal or subcostal retractions, tripod positioning, pursed-lip breathing, ability to speak in full sentences) and
pattern. Retractions and nasal flaring in a child mean respiratory distress
regardless of what the number says, and a child who becomes quiet and sleepy after a period of retractions may be tiring toward respiratory failure, not improving.
Infants and older adults
Infants breathe
diaphragmatically — watch the abdomen, not the chest — and an irregular pattern with brief pauses is normal in newborns. A pause
longer than 20 seconds, or any pause with bradycardia or cyanosis, is
apnoea and is not normal. In older adults, reduced chest wall compliance and lower vital capacity mean a slightly higher resting rate, but a rate
above 24 is abnormal at any adult age.
What the oximeter is actually telling you
Choose a patient, then decide what you make of the number.
Before you believe any saturation, check the signal. Place the probe on a warm, well-perfused digit with the light source and detector facing each other. Confirm that the displayed pulse rate matches the pulse you palpate and that the waveform or signal-strength indicator looks convincing. A saturation attached to a heart rate that does not match the patient is not data.
Why 90 percent is a cliff and not a slope
Because of the shape of the oxyhaemoglobin dissociation curve, an SpO
2 of
90 percent corresponds to a PaO2 of about 60 mm Hg, and below that point the curve falls steeply — small further drops in saturation represent large drops in dissolved oxygen. In patients with
chronic carbon dioxide retention, a target of
88 to 92 percent is deliberate, not an oversight.
Occult hypoxaemia. A true arterial saturation below 88 percent while the oximeter reads 92 to 96 percent occurs several times more often in patients with darker skin. Combine that with the fact that cyanosis is harder to appreciate on darkly pigmented skin, and the two tools most likely to catch hypoxaemia can fail together in the same patient. Assess the oral mucosa, tongue, conjunctivae, palms and soles, where cyanosis appears as a grey or ashen dullness; count the respiratory rate; listen to whether the patient can finish a sentence; and escalate on the clinical picture even when the number looks acceptable.
Your call
—enter a set and decide
Enter the rate, the saturation, the oxygen and what you can see, then press Interpret and decide.
Respiratory red flags, to the exact number. Adult respiratory rate under 10 or over 24 — and under 8 or over 30 is critical at any adult age. SpO2 under 90 percent on room air, or falling despite added oxygen: give oxygen, sit the patient upright, reassess the airway and call now. For opioid-induced depression, assess sedation, stimulate the patient, apply oxygen and prepare naloxone.
Pearl. Chart the oxygen with the saturation. “SpO2 94 percent” is meaningless. “SpO2 94 percent on 4 L/min nasal cannula, down from 97 percent on room air at 0800” is a clinical finding another nurse can act on.