Hypoxia in a Patient With No Cardiac or Pulmonary History

Case Study

A rapid response event was activated by the bedside nurse for a patient who developed respiratory distress and required increasing oxygen supplementation. On arrival of the condition team, the patient was visibly dyspneic and using accessory muscles of respiration. Per the bedside nurse, the patient was a 40-year-old male with a history of hypertension and diabetes mellitus who was admitted to the hospital for treatment of community-acquired pneumonia. The patient was admitted with oxygen supplementation of 4 L via nasal cannula and treated with ceftriaxone and azithromycin.

Vital Signs

  • Temperature: 98.3 °F, axillary

  • Blood Pressure: 130/90 mmHg

  • Pulse: 120 beats per min – sinus tachycardia on telemetry

  • Respiratory Rate: 32 breaths per min

  • Pulse Oximetry: 85% on 4 L, 95% on 15 L non-rebreather

Focused Physical Examination

A quick exam showed a middle-aged male who appeared visibly dyspneic, using accessory muscles of respiration. The patient was unable to speak in complete sentences. On auscultation, significant crackles and rhonchi were present in bilateral lung fields. His cardiac exam revealed regular rhythm and tachycardia. No murmurs or added heart sounds were identified. The remaining physical examination was unremarkable.


A cardiac monitor and pads were attached to the patient. Due to hypoxemia and increased work of breathing, the patient was started on a high flow nasal cannula, which improved his work of breathing. Stat chest X-ray and arterial blood gas (ABG) were obtained. ABG showed a pH of 7.40, pCO 2 of 40, pO 2 of 70, on a 15 L non-rebreather mask, which was significant for hypoxemia. Chest X-ray revealed multi-focal pneumonia, worse than that was seen on admission imaging ( Fig. 21.1 ). The case was discussed with the intensive care specialist, and the patient was transferred to the intensive care unit for closer monitoring of respiratory status with a low threshold for intubation.

Fig. 21.1

Chest X-ray in an anteroposterior view showing bilateral infiltrates consistent with multi-focal pneumonia.

Final Diagnosis

Acute hypoxic respiratory failure from community-acquired pneumonia.


Hypoxia and hypoxemia are two interchangeably used terms in the clinical setting. Hypoxemia is defined as a low partial pressure of oxygen in arterial blood, while hypoxia is defined as insufficient global or local tissue oxygen content. See Table 21.1 for various parameters for assessing the degree of oxygenation of the blood. There is a wide range of causes of hypoxia in an acute setting, which should be narrowed down with a focused history, physical examination, and appropriate workup.

Table 21.1

Various parameters for assessing the degree of oxygenation of the blood

Measurement Features
Arterial oxygen saturation (SaO 2 )

  • Direct measurement of the percentage of oxyhemoglobin

  • Measured using arterial blood gas

Pulse oxygen saturation (SpO 2 )

  • Measurement of percent of saturated hemoglobin in the capillary bed

  • Measured with pulse oximetry

Partial pressure of oxygen (PaO 2 )

  • Represents the amount of oxygen dissolved in the plasma

  • Measured using an arterial blood gas

A-a gradient

  • This is the difference between the amount of oxygen in the alveoli (PaO 2 ) and the amount of oxygen dissolved in the plasma (PaO 2 )

  • PaO 2 can be calculated using the alveolar gas equation*

“PF ratio” or PaO 2 /FiO 2

  • This is the ratio between the amount of oxygen dissolved in the plasma (PaO 2 ) and the fraction of oxygen in inhaled air

  • Mostly in mechanically ventilated patients where FiO 2 can be calculated accurately

  • *Alveolar gas equation:

  • PaO 2 = (PB − PH 2 O) FiO 2 − (PaCO 2 ÷ R)

  • where PB = barometric pressure, PH 2 O = water vapor pressure (usually 47 mmHg), FiO 2 = fractional concentration of inspired oxygen, and R = gas exchange ratio

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Nov 19, 2022 | Posted by in CRITICAL CARE | Comments Off on Hypoxia in a Patient With No Cardiac or Pulmonary History
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