Oxygen saturation measurement
Edema can cause severe pulmonary diffusion impairment and lead to hypoxia in patients with CHF. Oxygen saturation of hemoglobin
can be measured by using arterial blood sampling or noninvasive pulse oximetry.10,11 A rule of thumb is to attempt to obtain the reading if it can be done without causing undue stress to the patient. When in
doubt, administer oxygen and gauge the patient's oxygenation status by changes in its respiratory rate and effort and the
resolution of pulmonary crackles on thoracic auscultation. Measuring oxygen saturation by arterial blood sampling or pulse
oximetry can then be attempted when the patient is clinically more stable.
The gold standard for measuring a patient's oxygenation status is arterial blood sampling.12 However, the restraint required to obtain the sample is contraindicated in unstable patients. If an arterial blood gas can
be performed without causing the patient untoward distress, samples can be obtained from the dorsal pedal or femoral arteries.
Normal partial pressure of arterial oxygen (PaO2) is greater than 80 mm Hg in patients breathing room air. If the patient's PaO2 is less than 60 mm Hg and the partial pressure of arterial carbon dioxide (PaCO2) is greater than 60 mm Hg while the patient is receiving oxygen supplementation, mechanical ventilation should be strongly
Pulse oximetry readings can be attempted on the tongue, ear pinna, toe web, prepuce, or vulva in cooperative patients. Severe
hypotension, peripheral vasoconstriction, and patient movement secondary to respiratory distress may make obtaining an accurate
pulse oximetry reading difficult in patients with CHF. Pulse oximetry readings less than 90% require intervention with supplemental
oxygen. If the pulse oximetry reading is less than 80% in a patient receiving supplemental oxygen, consider more aggressive
intervention in the form of mechanical ventilation.
Emergency treatment of patients with CHF consists of improving systemic oxygen delivery and minimizing patient stress. Oxygen
delivery is a function of oxygen uptake by the respiratory system, cardiac output, and hemoglobin concentration. The mainstays
of therapy for CHF are to provide supplemental oxygen and decrease fluid buildup within the lungs.
Administer flow-by oxygen in patients with CHF as the physical examination is taking place.13,14 Flow-by oxygen is well-tolerated and requires minimal physical restraint. Because flow-by is a relatively inefficient method
of providing an increase in the fraction of inspired oxygen, use other methods such as oxygen hoods; oxygen cages; and nasal,
nasopharyngeal, and tracheal oxygen insufflation for long-term therapy.
Oxygen hoods are available commercially or can be made in the hospital with a firm Elizabethan collar, white tape, and plastic
wrap. Most patients tolerate oxygen hoods readily. But increased condensation and iatrogenic hyperthermia can develop, so
monitor patients carefully.
Nasal or nasopharyngeal oxygen cannulae are well-tolerated for long-term oxygen supplementation.15-17 Measure a red rubber (5 to 8 F) catheter or Argyle infant feeding tube (Kendall) from the ramus of the mandible (nasopharyngeal)
or from the medial canthus of the eye (nasal). Mark the tube, and lubricate the tip with lidocaine jelly. Insert the tube
ventrally and medially, directing the nasal philtrum dorsally to facilitate passing the tube to the predetermined level. Humidified
oxygen flow rates can be administered at 50 to 100 ml/kg/min. Nonhumidified oxygen can be used if a humidification source
is unavailable, but this method is associated with dryness and irritation of the nasal mucosa and increased patient discomfort
and intolerance of the nasal cannula.
Potential complications associated with placing a nasal or nasopharyngeal cannula include increased patient distress with
restraint, epistaxis, and introduction of the tube through the cribriform plate, although this last complication is uncommon
with careful placement. Nasopharyngeal catheters can allow for higher flow rates of supplemental oxygen and are my preferred
method of oxygen supplementation.