5.3 Oxygen Therapy & Ventilation Support

Hypoxemia vs Hypoxia, and Oxygen Delivery Devices

Hypoxemia is a low partial pressure of oxygen in arterial blood — PaO2 below 80 mmHg or SpO2 below roughly 90%. Hypoxia is inadequate oxygen at the tissue level. A patient can be hypoxemic without tissue hypoxia (early compensation) or hypoxic without hypoxemia — as in carbon monoxide poisoning, severe anemia, or cyanide toxicity, where blood oxygen content or utilization fails despite a normal PaO2. Signs of hypoxia include restlessness and confusion (early), tachycardia, tachypnea, and eventually bradycardia, hypotension, and cyanosis (late).

Oxygen delivery devices are chosen by required FiO2, precision, and patient tolerance:

Clinical pearls: a face mask (not a cannula) is required for FiO2 above about 40%; never let reservoir bags collapse during inspiration; and for a tracheostomy patient, apply oxygen over the trach — the nose is no longer in the circuit. Oxygen toxicity (absorption atelectasis and free-radical lung injury) becomes a concern with FiO2 above 60% for more than 24-48 hours, so use the lowest FiO2 that achieves the target saturation.

Chest Tubes

A chest tube drains air, blood, or fluid from the pleural space so negative intrapleural pressure — and lung expansion — can be restored. The three-chamber system has a collection chamber, a water seal chamber, and a suction control chamber.

• Water seal and tidaling: the water seal lets air exit but not re-enter. Tidaling — water rising with inspiration and falling with expiration (the reverse in a mechanically ventilated patient) — is normal and reflects pleural pressure changes. Absent tidaling may mean full lung re-expansion or a kinked/clotted tube — assess the patient and tubing.
• Bubbling: intermittent bubbling in the water seal chamber is expected as air leaves the pleural space, especially with pneumothorax. Continuous bubbling indicates an air leak in the system or at the insertion site; locate it by momentarily clamping segments per policy, starting at the insertion site. Gentle continuous bubbling in the suction control chamber is normal when suction is on.
• Never clamp routinely. Clamping a chest tube in a patient with an active air leak can convert a simple pneumothorax into a tension pneumothorax. Clamping is reserved for brief, ordered situations (locating a leak, changing the system, or a trial before removal in selected patients).

Other essentials: keep the unit below chest level at all times and upright; coil tubing without dependent loops; maintain two padded clamps and a sterile water bottle at the bedside per policy; if the system breaks or disconnects, place the tube end in sterile water to re-create a water seal; if the tube is accidentally pulled out, immediately cover the site with a sterile occlusive dressing taped on three sides and notify the provider. Record drainage output — report more than 100-200 mL/hour of fresh blood (possible hemorrhage).

Tracheostomy Care

Tracheostomy care protects the airway and prevents infection. Key nursing actions:

• Keep a spare tracheostomy tube (same size and one size smaller), an obturator, and a tracheal dilator at the bedside for emergency reinsertion. In the first 72 hours, the tract is immature — a dislodged tube is an emergency; a fresh stoma can close within minutes.
• Clean the inner cannula (or replace it if disposable) per schedule to prevent mucus plugging; clean the stoma with half-strength hydrogen peroxide or saline and apply a split sterile dressing; change ties one side at a time, allowing one finger's width under the tie.
• Confirm cuff pressure at 20-25 cm H2O when a cuff is used to prevent tracheal stenosis while maintaining the seal.
• For accidental decannulation after the tract matures: extend the neck, insert the obturator into the spare tube, and reinsert with a downward-backward curve; if you cannot reinsert, call for help and oxygenate over the stoma.

Noninvasive Ventilation: CPAP and BiPAP

Continuous positive airway pressure (CPAP) delivers one constant pressure throughout the respiratory cycle. Its classic indication is obstructive sleep apnea; it also supports oxygenation in cardiogenic pulmonary edema by improving alveolar recruitment. Bilevel positive airway pressure (BiPAP) delivers a higher pressure on inspiration (IPAP) and a lower pressure on expiration (EPAP); the gradient augments tidal volume, so BiPAP both oxygenates and ventilates — the indication of choice for acute COPD exacerbations with hypercapnia and for acute heart failure with respiratory fatigue. Contraindications include altered mental status with aspiration risk, hemodynamic instability, copious secretions, facial trauma, and active vomiting. Assess mask fit, skin integrity over the bridge of the nose, gastric distension, and the patient's tolerance; re-evaluate ABGs within 1-2 hours — failure to improve means escalation to intubation.

Mechanical Ventilation Basics

Common modes: Assist-control (AC) delivers a set tidal volume with every breath — machine-initiated or patient-triggered — guaranteeing a minimum minute ventilation. Synchronized intermittent mandatory ventilation (SIMV) delivers a set number of mandatory breaths synchronized with patient effort and allows spontaneous breathing between them. Pressure support ventilation (PSV) augments spontaneous breaths and is used for weaning. Positive end-expiratory pressure (PEEP) keeps alveoli open at end-expiration, improving oxygenation; typical starting PEEP is 5 cm H2O, with higher levels for ARDS (watch for hypotension from reduced venous return).

Alarms — always assess the patient first, then the machine:

• High-pressure alarm = increased resistance: secretions needing suction, kinked tubing, patient biting the tube, coughing/bronchospasm, water in the circuit, or pneumothorax.
• Low-pressure (low exhaled volume) alarm = disconnection or leak: loose connections, cuff leak, or tube displacement.
• If the cause is not immediately obvious, disconnect the ventilator and manually ventilate with a bag-valve mask connected to 100% oxygen while the problem is found. Never silence alarms without assessing.

Ventilator-associated pneumonia (VAP) prevention bundle:

• Keep the head of bed elevated 30-45 degrees at all times
• Perform daily sedation interruption and spontaneous breathing trials to assess extubation readiness
• Provide meticulous oral care (chlorhexidine per protocol) and subglottic secretion drainage
• Give DVT prophylaxis and peptic ulcer (stress ulcer) prophylaxis
• Maintain hand hygiene and keep the ventilator circuit free of condensed water draining toward the patient

ARDS Recognition

Acute respiratory distress syndrome (ARDS) is noncardiogenic pulmonary edema from diffuse alveolar-capillary membrane injury, triggered by sepsis, aspiration, pneumonia, trauma, or transfusion. Recognize it by the Berlin framework: acute onset within 1 week of a known insult, bilateral opacities on chest imaging not explained by heart failure, and a PaO2/FiO2 ratio of 300 or less on at least 5 cm H2O PEEP (mild 200-300, moderate 100-200, severe below 100). The hallmark is refractory hypoxemia — saturations that stay low despite escalating FiO2 — with decreased lung compliance. Management is lung-protective ventilation: low tidal volume (about 6 mL/kg predicted body weight), plateau pressure 30 cm H2O or less, higher PEEP, permissive hypercapnia, prone positioning for moderate-to-severe disease, conservative fluid management, and treatment of the underlying cause.

Suctioning Technique

Endotracheal and tracheostomy suctioning is sterile, intermittent, and as brief as possible:

1. Hyperoxygenate with 100% oxygen for 30-60 seconds (3-5 breaths) before and after each pass.
2. Use sterile technique; set suction pressure at 80-120 mmHg for adults (no more than 150).
3. Insert the catheter without suction, to no more than the tip of the artificial airway (shallow/measured-depth suctioning minimizes mucosal trauma).
4. Apply intermittent suction while withdrawing with a rotating motion, limiting each pass to 10-15 seconds.
5. Allow recovery between passes; monitor heart rate, SpO2, and rhythm — suctioning can cause vagal bradycardia, hypoxemia, and increased intracranial pressure.

Suction only when indicated (coarse crackles, visible secretions, rising peak pressures, desaturation) — never on a fixed schedule.