What the Stuffy-Nosed Diver needs to Know when Mixing Decongestants & HBO (Dr. Jay B. Dean, USF)
Anecdotal evidence collated by DAN, suggested that treatment with nasal decongestants predisposes divers to seizures when breathing enriched-air nitrox using SCUBA, or pure oxygen with a rebreather. In this study, five doses of a commonly used nasal decongestant, pseudoephedrine hydrochloride (PSE), were tested in freely behaving male and female lab rats to identify its effects on the time to develop neurological and visible behavioral seizures during exposure to hyperbaric oxygen (HBO). DAN researchers report that both the dose of PSE and gender influence the sensitivity of the mammalian brain to HBO.
This experimental study was completed in 2013.
Anecdotal evidence collated by DAN, suggested that use of nasal decongestants, such as pseudoephedrine salts, increased a diver’s risk for developing CNS oxygen toxicity, the primary sign of which are generalized seizures. It was postulated that high doses of pseudoephedrine hydrochloride (PSE) reduced the time it took for seizures to occur in unanesthetized, freely behaving rats exposed to 5 atmospheres absolute (ATA) oxygen in a dry dive chamber. Sixty-three male rats and 114 female rats (60 virgins and 54 retired breeders) were implanted with a radio-transmitter that recorded cortical electroencephalogram activity (EEG; increased EEG electrical spiking indicates a neurological seizure), core body temperature, and animal movements. After at least seven days of recovery from sterile surgery, each animal was given an oral dose of either saline fluid (control) or PSE (mg PSE/kg body weight): 0, 40, 80, 100, 120, 160 and 320. Rats breathed air before switching over to 100 percent O2 (1 ATA O2). After collecting baseline data, rats were dived to 5 ATA O2 until onset of neurological seizures coincident with visually detected behavioral seizures. The latency to seizure (LS) was the time elapsed between reaching 5 ATA and exhibiting onset of seizures. The LS value was used as the index of an animal’s sensitivity to HBO. The first study was done in male lab rats (Pilla et al., 2013). Based on our findings, we repeated the study in female lab rats to see if there were any differences due to gender (Held et al., 2014).
In male rats, there was no significant difference between the LS value between control animals and those dosed with 40-80 mg/kg PSE. At the higher doses of PSE, ranging from 100-320 mg/kg PSE, there was a significant dose-dependent decrease in the LS value as compared to control animals. Thus, higher doses of PSE accelerated onset of HBO-induced seizures in unanesthetized, freely behaving male rats breathing 5 ATA O2.
Female rats, unexpectedly, seized quicker than males during exposure to HBO. And treatment with PSE did not accelerate the onset of seizures at any dose including the highest dose tested.
Extrapolating our findings to humans, we conclude that the recommended daily dose of PSE should not be abused prior to diving with oxygen-enriched gas mixes or pure O2 in males (Pilla et al., 2013). And while females may not experience an increased risk for seizures when using PSE with HBO, our findings suggest that females may have a greater inborn risk for developing CNS oxygen toxicity than males (Held et al., 2013).
Additional Reading and References
- You can download the following related workshop proceedings in the DAN Publication Library:
- 2008 Technical Diving
- R. Pilla, H.E. Held, C.S. Landon and J.B. Dean (2013) High doses of Pseudoephedrine Hydrochloride accelerate onset of CNS oxygen toxicity seizures in unanesthetized rats. Neuroscience 246:391–396.
- H.E. Held, R. Pilla, G.E. Ciarlone, C.S. Landon and J.B. Dean (2014) Female rats are more susceptible to central nervous system oxygen toxicity than male rats. Physiological Reports, 2 (4), 2014, e00282, doi: 10.14814/phy2.282.