In emergencies, administer O2 empirically without a formal prescription to restore airflow. The lack of formal O2 prescription should not restrict O2 administration in a formal setting. The O2 concentration, the flow rate, the adjustment, and the patient's response should be documented. In a pre-hospital setting or for patients under ambulatory care, O2 saturation levels should be monitored until the patient's vitals are stable and a specialist does a full assessment. The concentration of O2 administered should be adjusted upwards or downwards to maintain the appropriate saturation range.
In acutely ill patients presenting for clinical intervention, O2 therapy (if indicated) should be aimed at maintaining a patent airway. In patients with cardiac arrest, respiratory distress, or respiratory arrest, administer O2 empirically. The American College of Chest Physicians and the National Heart, Lung, and Blood Institute recommend a list of conditions to classify clinical conditions requiring empirical initiation of O2 therapy. These conditions include:
- Cardiac and respiratory arrest
- Hypoxemia (PAO2<7.8 kPa, SaO2<90%)
- Hypotension (systolic blood pressure < 100 mmHg)
- Low cardiac output and metabolic acidosis (bicarbonate < 18 mmol/l)
- Respiratory distress (respiratory rate > 24/min)
Nurses are expected to recognize the clinical signs of inadequate tissue oxygenation. The pathophysiological mechanisms resulting in low tissue oxygenation are broadly categorized into two groups. The two groups include those impairing the O2-hemoglobin complex system and those causing arterial hypoxemia. Recognizing these mechanisms requires careful patient evaluation. However, more than one mechanism may contribute to poor tissue oxygenation in the same patient.
The pathophysiological mechanism grouped under the failure of the O2-hemoglobin transport system include:
- Low hemoglobin concentration
- Poor tissues perfusion rate
- Hemoglobinopathies, high carboxyhemoglobin concentration, and other conditions implicated in the abnormal O2 dissociation curve
- Histotoxic poisoning of the intracellular enzymes, including cyanide poisoning, paraquat poisoning, and septicemia.
In arterial hypoxemia, the pathophysiological mechanisms implicated include:
- Right to left shunts
- Low-inspired O2 partial pressure
- Alveolar hypoventilation in sleep apnea, opiate poisoning, etc.
- Ventilation-perfusion mismatch in asthma, atelectatic lung zones, etc.
The clinical symptoms of these pathophysiological mechanisms are nonspecific and can be challenging to recognize quickly. These symptoms include altered mental state, dyspnea, cyanosis, tachypnoea, arrhythmias, and coma. In all patients under evaluation for a possible O2 therapy regimen, arterial O2 saturation (SaO2) and partial O2 pressure (PaO2) measurements are the principal indicators for initiating, prescribing, monitoring, and modifying supplemental O2 therapy.
SaO2 and PaO2 can be normal in some patients presenting with clinical evidence of tissue hypoxemia caused by low cardiac output, anemia, and failure of tissues to use O2. In these cases, mixed venous O2 partial pressure measured in pulmonary artery blood is considered a better tissue oxygenation index because its value approximates to mean partial tissue pressure. The most widely used guidelines in assessing the patient for a possible immediate O2 intervention include the following:
- Assess the airway and optimize airflow using airway positioning as necessary in the patient. Head tilts, chin lifts, and left lateral tilts might be required.
- Perform a thorough clinical assessment and documentation at the beginning of every shift, including cardiovascular, respiratory, and neurological system assessments.
- Check and document O2 equipment setup and any change in patient positioning at the beginning of each shift.
- O2 flow rate, patency of tubing, and humidifier settings should be checked and documented hourly.
- Heart rate, respiratory rate, respiratory distress, and O2 saturation, using continuous pulse oximetry, should be checked hourly and recorded.