Audit of practice in Australasian hyperbaric units on the incidence of central nervous system oxygen toxicity

Hyperbaric oxygen for sudden hearing loss: Influence of international guidelines on practice in Australia and New Zealand

INTRODUCTION

Idiopathic sudden sensorineural hearing loss (ISSHL) is an otolaryngologic emergency. The Undersea and Hyperbaric Medicine Society (UHMS) revised practice guidelines in 2014 adding ISSHL to approved indications. This study investigated whether the UHMS guidelines influenced referral and practice in Australia and New Zealand.

METHODS

Retrospective review of 319 patient referrals in two time periods (five years prior to addition of ISSHL to indications (T-PRE) and three years post (T-POST)).

RESULTS

Seven of eight participating hyperbaric facilities provided data down to the level of the indication for HBOT for analysis. In T-PRE 136 patients were treated with HBOT for ISSHL, representing between 0% and 18% of the total cases to each facility. In the T-POST period 183 patients were treated for ISSHL, representing from 0.35% to 24.8% of the total patients in each facility. Comparison between the two periods shows the proportion of patients treated with ISSHL among all indications increased from 3.2% to 12.1% (P < 0.0009). One facility accounted for 74% (101/136) of ISSHL patients receiving HBOT in T-PRE and 63% (116/183) in T-POST. ISSHL case load at that facility increased from 18% to 24.8% (P = 0.009) after the UHMS guideline publication. Three of the seven units had a significant increase in referrals after the guideline change.

CONCLUSION

There remains equipoise regarding HBOT in the management of ISSHL. Only three out of seven units had a significant increase in ISSHL patients after the UHMS guidelines publication. Without well controlled RCTs to develop guidelines based on good evidence this is unlikely to change and practice variation will continue.

Benefits and harms of increased inspiratory oxygen concentrations

PURPOSE OF REVIEW

The topic of perioperative hyperoxia remains controversial, with valid arguments on both the 'pro' and 'con' side. On the 'pro' side, the prevention of surgical site infections was a strong argument, leading to the recommendation of the use of hyperoxia in the guidelines of the Center for Disease Control and the WHO. On the 'con' side, the pathophysiology of hyperoxia has increasingly been acknowledged, in particular the pulmonary side effects and aggravation of ischaemia/reperfusion injuries.

RECENT FINDINGS

Some 'pro' articles leading to the Center for Disease Control and WHO guidelines advocating perioperative hyperoxia have been retracted, and the recommendations were downgraded from 'strong' to 'conditional'. At the same time, evidence that supports a tailored, more restrictive use of oxygen, for example, in patients with myocardial infarction or following cardiac arrest, is accumulating.

SUMMARY

The change in recommendation exemplifies that despite much work performed on the field of hyperoxia recently, evidence on either side of the argument remains weak. Outcome-based research is needed for reaching a definite recommendation.

Does oxygen-enriched air better than normal air improve sympathovagal balance in recreational divers?An open-water study

Effects of the hyperbaric environment on the autonomic nervous system (ANS) in recreational divers are not firmly settled. Aim of this exploratory study was to (1) assess ANS changes during scuba diving via recordings of electrocardiograms (ECG) and to (2) study whether nitrox40 better improves sympathovagal balance over air. 13 experienced divers (~40yrs) performed two open-water dives each breathing either air or nitrox40 (25m/39min). 3-channel ECGs were recorded using a custom-made underwater Holter-monitor. The underwater Holter system proved to be safe. Air consumption exceeded nitrox40 consumption by 12% (n = 13; p < 0.05). Both air and nitrox40 dives reduced HR (10 vs 13%; p < 0.05). The overall HRV (pNN50: 82 vs 126%; p < 0.05) and its vagal proportion (RMSSD: 33 vs 50%; p < 0.05) increased during the dive. Moreover, low (LF: 61 vs 47%) and high (HF: 71 vs 140%) frequency power were increased (all p < 0.05), decreasing the ratio of LF to HF (22 vs 34%). : Conventional open-water dives distinctly affect the ANS in experienced recreational divers, with sympathetic activation less pronounced than vagal activation thereby improving the sympathovagal balance. Nitrox40 delivered two positive results: nitrox40 consumption was lower than air consumption, and nitrox40 better improved the sympathovagal balance over air.

Seizure frequency in more than 180,000 treatment sessions with hyperbaric oxygen therapy - a single centre 20-year analysis

INTRODUCTION

Hyperbaric oxygen therapy (HBOT) involves the risk of central nervous system oxygen toxicity (CNS-OT), including seizures in patients breathing oxygen at pressures ≥ 2 atmospheres absolute. This study aimed to determine the seizure frequency and assess the clinical benefit of a 5-minute air-break (5´-AIRBK).

METHODS

Twenty-year (1999-2018) retrospective analysis of all consecutive treatments with HBOT. Medical records were reviewed to determine patient demographics, comorbidities, HBOT indications, and seizure characteristics and timing. Seizure frequency was compared before and after incorporating a 5´-AIRBK in the treatment protocol. Chi-square testing was performed using SPSS (version 24.0); P < 0.05 was accepted as statistically significant.

RESULTS

We evaluated 188,335 HBOT sessions (74,255 before versus 114,080 after introducing a 5´-AIRBK). A total of 43 seizures were observed: 29 before and 14 after the 5´-AIRBK introduction (3.9 versus 1.2 per 10,000 treatments; P < 0.0001). Seizures occurred after a median of 57 (range 15-85) minutes following compression and after a median of 21 HBOT sessions (1-126). Patients experiencing seizures were undergoing treatment for: diabetic ulcer (n = 11); acute traumatic peripheral ischaemia (ATPI) (n = 6); non-diabetic ulcer (n = 5); sudden sensorineural hearing loss (n = 5); chronic refractory osteomyelitis (n = 5); radionecrosis (n = 3); necrotising fasciitis (NF) (n = 2); and haemorrhagic cystitis after allogeneic bone marrow transplantation (n = 1). ATPI and NF had a considerably higher relative frequency of seizures compared to other indications.

CONCLUSIONS

A statistically significant lower seizure frequency was achieved with a 5´-AIRBK. Assessing and defining the appropriate patient/treatment profile can be useful to minimise the risk of CNS-OT.