CHT Oxygen Toxicity & Contraindications 1 — Questions and Answers
Question 1: What is the primary mechanism by which central nervous system (CNS) oxygen toxicity occurs during hyperbaric oxygen therapy?
- Decreased cerebral blood flow from vasoconstriction
- Formation of reactive oxygen species causing neuronal damage (Correct answer)
- Hypercapnia from CO2 retention at elevated pressures
- Nitrogen narcosis interfering with neurotransmission
Correct answer: Formation of reactive oxygen species causing neuronal damage
CNS oxygen toxicity is primarily caused by reactive oxygen species (free radicals) that overwhelm antioxidant defenses and damage neuronal membranes.
Question 2: Which of the following is the hallmark presentation of CNS oxygen toxicity during HBO therapy?
- Gradual onset of confusion and disorientation
- Sudden loss of consciousness without any warning signs
- Grand mal (tonic-clonic) convulsions (Correct answer)
- Progressive ascending peripheral numbness and tingling
Correct answer: Grand mal (tonic-clonic) convulsions
Grand mal convulsions are the hallmark of CNS oxygen toxicity; though they may be preceded by VENTID-C warning signs, they can also occur without warning.
Question 3: In the mnemonic VENTID-C used to identify early CNS oxygen toxicity symptoms, the 'V' stands for:
- Vomiting
- Vision changes such as tunnel vision (Correct answer)
- Vasodilation of cerebral vessels
- Ventricular arrhythmia
Correct answer: Vision changes such as tunnel vision
In VENTID-C, V stands for Visual disturbances (tunnel vision), which is an early warning sign of CNS oxygen toxicity preceding convulsions.
Question 4: What is the generally accepted maximum oxygen partial pressure (PO2) to minimize risk of CNS oxygen toxicity during routine HBO treatments?
- 1.2 ATA (912 mmHg)
- 1.6 ATA (1,216 mmHg) (Correct answer)
- 2.0 ATA (1,520 mmHg)
- 2.8 ATA (2,128 mmHg)
Correct answer: 1.6 ATA (1,216 mmHg)
A PO2 of 1.6 ATA (1,216 mmHg) is the generally accepted ceiling for intermittent HBO exposures to minimize CNS oxygen toxicity risk.
Question 5: Pulmonary oxygen toxicity (Lorrain Smith effect) results primarily from:
- Acute bronchospasm triggered by cold dry oxygen inhalation
- Progressive lung injury from prolonged exposure to elevated partial pressures of oxygen (Correct answer)
- Oxygen-induced vasoconstriction of the pulmonary microvasculature
- Excess surfactant production by type II pneumocytes
Correct answer: Progressive lung injury from prolonged exposure to elevated partial pressures of oxygen
The Lorrain Smith effect describes progressive pulmonary injury from prolonged high-oxygen breathing, leading to inflammation, alveolar damage, and decreased vital capacity.
Question 6: Which of the following is an ABSOLUTE contraindication to hyperbaric oxygen therapy?
- Mild claustrophobia responsive to anxiolytics
- Active treatment with bleomycin chemotherapy
- Untreated pneumothorax (Correct answer)
- Uncontrolled but stable diabetes mellitus
Correct answer: Untreated pneumothorax
Untreated pneumothorax is an absolute contraindication because increasing ambient pressure can convert it to a life-threatening tension pneumothorax.
Question 7: Air breaks during HBO treatment are administered primarily to:
- Reduce chamber pressure to prevent barotrauma to the ears
- Allow the patient to breathe room air and reduce cumulative oxygen toxicity risk (Correct answer)
- Equalize pressure across the tympanic membrane
- Flush CO2 from the chamber atmosphere
Correct answer: Allow the patient to breathe room air and reduce cumulative oxygen toxicity risk
Air breaks allow patients to breathe room air (21% O2) during treatment, reducing the cumulative oxygen dose and lowering the risk of both CNS and pulmonary oxygen toxicity.
CHT Oxygen Toxicity & Contraindications 1
What is the primary mechanism by which central nervous system (CNS) oxygen toxicity occurs during hyperbaric oxygen therapy?