8.1 Airway Management, Oxygen Therapy & Pulse Oximetry

8.1 Airway Management, Oxygen Therapy & Pulse Oximetry

Principles of Airway Management and Oxygen Therapy in Singapore

Under the Nurses and Midwives Act (Cap. 209) and the Singapore Nursing Board (SNB) Code for Nurses and Midwives (2023), registered nurses (RNs) bear legal and ethical accountability for maintaining airway patency, titrating prescribed oxygen therapy, and systematically monitoring patient oxygenation status. Oxygen is legally classified as a prescription drug in Singapore. Consequently, routine administration requires a valid medical prescription specifying the flow rate, delivery interface, and target arterial oxygen saturation ($SpO_2$) range.

In acute emergency clinical situations—such as sudden severe desaturation, respiratory arrest, or anaphylaxis—registered nurses are empowered under Singapore hospital standing emergency orders to initiate emergency high-flow oxygen therapy immediately while simultaneously notifying the primary medical team or activating the Medical Emergency Team (MET) / Rapid Response Team (RRT) using the standardized ISBAR framework (Identify, Situation, Background, Assessment, Recommendation).

ISBAR Clinical Escalation Framework for Acute Hypoxemia:
[I] Identify: State nurse name, ward, patient name, and NRIC.
[S] Situation: Acute drop in SpO2 < 88% with severe dyspnea.
[B] Background: 68yo COPD patient on 2L NC baseline.
[A] Assessment: RR 32/min, sternal retractions, SpO2 84% on room air.
[R] Recommendation: Immediate doctor bedside review, ABG order, and Venturi mask setup.

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Basic Airway Positioning and Airway Adjuncts

When a patient experiences airway compromise due to altered consciousness, muscle hypotonia, or soft tissue obstruction by the tongue, establishing airway patency is the immediate priority.

Airway Positioning Techniques

1. Head-Tilt Chin-Lift Maneuver: The primary maneuver used for unarousable or unresponsive patients without suspected cervical spine trauma. One hand places backward pressure on the forehead while the fingers of the other hand lift the chin forward, pulling the tongue away from the posterior pharyngeal wall.
2. Jaw-Thrust Maneuver: The mandatory maneuver for patients with suspected cervical spine trauma (e.g., road traffic accidents, falls from height). The nurse places fingers behind the angles of the mandible and lifts forward without extending or rotating the neck.

Airway Adjuncts: OPA vs. NPA

Airway adjuncts prevent upper airway obstruction by keeping the tongue off the posterior pharynx. Selection depends on the patient's level of consciousness and reflex status.

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Oxygen Delivery Systems: Flow Rates, FiO2, and Clinical Indications

Selecting the appropriate oxygen delivery device depends on the severity of hypoxemia, the patient's minute ventilation, and whether chronic hypercapnic respiratory failure is present.

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Pulse Oximetry ($SpO_2$) and Arterial Blood Gas (ABG) Monitoring

Target Saturation Guidelines in Singapore

Per Singapore Ministry of Health (MOH) clinical standards, target $SpO_2$ ranges are stratified based on patient underlying pathology:

• Standard Adult Medical/Surgical Patients: Target $SpO_2$ = 94% – 98%.
• Patients at Risk of Hypercapnic Respiratory Failure (COPD, severe obesity hypoventilation, neuromuscular weakness, kyphoscoliosis): Target $SpO_2$ = 88% – 92%. Uncontrolled oxygen delivery in hypercapnic patients abolishes the hypoxic drive, leading to acute hypercapnic coma and respiratory arrest.

Limitations and Artifacts of Pulse Oximetry

Pulse oximetry measures arterial oxygen saturation non-invasively via spectrophotometry. Nurses must recognize conditions that produce false readings:

• False Low Readings: Peripheral hypoperfusion/shock, severe hypothermia, peripheral vascular disease, dark fingernail polish, patient movement artifacts.
• False High Readings: Carbon monoxide (CO) poisoning (carboxyhemoglobin absorbs light at the same wavelength as oxyhemoglobin, yielding false $SpO_2$ readings of 98-100% despite severe tissue hypoxia).
• Severe Anemia: $SpO_2$ may read 99% while total blood oxygen content is critically reduced due to low total hemoglobin levels.

Correlation with Arterial Blood Gas (ABG)

An ABG remains the gold standard for assessing gas exchange, acid-base equilibrium, and alveolar ventilation.

Standard ABG Reference Ranges (Singapore MOH CPG):
- pH: 7.35 – 7.45
- PaCO2: 35 – 45 mmHg
- PaO2: 80 – 100 mmHg
- HCO3-: 22 – 26 mmol/L
- Base Excess (BE): -2 to +2 mmol/L

The Oxyhemoglobin Dissociation Curve illustrates the relationship between $PaO_2$ and $SpO_2$. A $PaO_2$ of 60 mmHg corresponds to an $SpO_2$ of approximately 90%. Below 90%, small drops in $PaO_2$ result in precipitous drops in oxygen saturation.

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Safety Precautions and Nursing Risk Management

• Fire Prevention: Oxygen vigorously accelerates combustion. Ensure strict "No Smoking" rules, avoid open flames, and ensure electric devices in proximity are grounded per National Centre for Infectious Diseases (NCID) and Singapore hospital safety codes.
• Avoid Oil-Based Products: Never apply petroleum jelly (e.g., Vaseline) to nostrils or lip lesions of patients receiving oxygen; use only water-soluble lubricants (e.g., K-Y Jelly).
• Oxygen Toxicity Risk: Prolonged exposure to high delivered concentrations ($FiO_2 > 50 ext{--}60%$) for longer than 24 to 48 hours damages alveolar-capillary membranes, causes nitrogen washout atelectasis, and generates toxic oxygen free radicals.