1 Respiratory Assessment and Oxygenation

Assessing respiratory status

Assess respiratory status using the whole clinical picture and changes over time. Relevant findings include respiratory rate and pattern, work of breathing, mental status, speech, skin color, breath sounds, oxygen saturation, and trends—not a single measurement alone.

Restlessness or confusion, tachypnea, accessory-muscle use, and falling oxygen saturation are warning signs of worsening respiratory compromise. For example, a patient with pneumonia who becomes restless and confused, has a respiratory rate of $32\ \text{breaths/min}$, uses accessory muscles, and has falling oxygen saturation despite supplemental oxygen needs prompt assessment of airway and breathing, urgent assistance, and preparation to escalate respiratory support. Do not delay urgent action to obtain a complete history.

Oxygenation and ventilation

Oxygenation and ventilation are related but distinct. Oxygenation is the transfer of oxygen into the blood; ventilation is movement of air in and out and supports carbon dioxide removal. Pulse oximetry estimates oxygen saturation, but it does not directly measure $\text{PaCO}_2$ or ventilation.

A low $\text{PaO}_2$ indicates hypoxemia. For example, a $\text{PaO}_2$ of $54\ \text{mm Hg}$ on room air indicates hypoxemia. Hypercapnia is assessed with $\text{PaCO}_2$; an oxygen value alone does not establish carbon dioxide retention or identify its cause.

Interpreting arterial blood gases

Interpret an arterial blood gas (ABG) systematically: assess pH, identify whether $\text{PaCO}_2$ or $\text{HCO}_3^-$ explains the pH change, then consider compensation and oxygenation. Reference ranges vary slightly by laboratory, so interpret results alongside the patient’s condition and prescribed oxygen target.

Typical adult reference ranges are:

• pH: $7.35$–$7.45$

• $\text{PaCO}_2$: $35$–$45\ \text{mm Hg}$

• $\text{HCO}_3^-$: about $22$–$26\ \text{mEq/L}$

For an ABG with pH $7.29$, $\text{PaCO}_2$ $58\ \text{mm Hg}$, and $\text{HCO}_3^-$ $25\ \text{mEq/L}$, the low pH indicates acidemia and the elevated $\text{PaCO}_2$ identifies a respiratory cause. The near-normal bicarbonate suggests little or no substantial metabolic compensation.

Recognizing airway emergencies

When a patient is unresponsive, has gurgling respirations, and cannot clear secretions, prioritize opening and assessing the airway, summoning emergency help, and preparing suction and ventilation support. An obstructed or secretion-filled airway may be present. Do not delay airway interventions to obtain an ABG, and do not offer water or apply oxygen without first assessing the airway.

Stridor with increasing work of breathing and difficulty speaking can signal critical upper-airway obstruction and requires immediate assessment and emergency escalation. In prioritization, this patient takes precedence over a patient with chronic COPD who is speaking comfortably at their prescribed oxygen target, a patient requesting routine inhaler teaching, or a stable patient awaiting discharge instructions.

Escalating respiratory support

A patient receiving noninvasive ventilation who becomes increasingly drowsy, cannot protect the airway, and has worsening respiratory distress may be experiencing failure of noninvasive support. Aspiration or respiratory arrest may be imminent. Escalate immediately and prepare for advanced airway management as directed by the emergency team; the clinical picture and airway protection matter, not an ABG value alone.

Give oxygen and respiratory support according to the patient’s condition, prescribed target, and clinical protocol. Oxygen alone does not correct inadequate ventilation when ventilatory support is needed.

Responding to ventilator alarms

When a mechanically ventilated patient’s high-pressure alarm sounds, assess the patient’s breathing and airway first. Then inspect for causes such as secretions, a kinked tube, coughing, or biting, and follow local emergency procedures. Do not silence the alarm without investigating, increase its limit, routinely disconnect the ventilator, or leave the patient unattended.

• Respiratory acidosis