Hyperbaric oxygen therapy (HBOT) is defined as placement of the entire body in an increased pressure environment of a minimum 1.4 atmospheres (atm) absolute, with 100% oxygen inspiration.[1] Many factors are involved when choosing a course of therapy for a patient. The best choice for the patient balances the risks and rewards. HBOT is generally well tolerated by most patients, although there are a few clinical scenarios that must be screened before starting HBOT.

Absolute Contraindications

There is currently only one absolute contraindication to hyperbaric oxygen therapy, which is untreated pneumothorax. Placing a patient in a chamber and changing the pressure around them can result in a tension pneumothorax occurring on ascent, which could quickly become life-threatening. Any patient with pneumothorax should have it treated (likely with some form of thoracostomy tube) before hyperbaric oxygen therapy.

Relative Contraindications

These were previously thought to be absolute contraindications:

• Concurrent doxorubicin use and hyperbaric oxygen therapy (HBOT) can increase risk of doxorubicin mediated cardiotoxicity. Doxorubicin should be stopped at least 24 hours before HBOT.
• Bleomycin is known to cause interstitial pneumonitis and fibrosis and was thought to be an absolute contraindication for HBOT as previous studies had shown an increased risk of side effects when used with supplemental home oxygen. Although more recent papers have shown, many of these patients can be safely treated with HBOT, particularly if the bleomycin exposure was distant (greater than 6 months). Pretreatment evaluation with an exam, radiography, blood gas and spirometry is necessary to determine if HBOT is safe.
• Disulfiram, through blocking of superoxide dismutase, can increase the risk of oxygen toxicity (seizures and pulmonary toxicity) and should not be used concurrently.
• Cisplatin, in conjunction with HBOT, is a relative contraindication due to the fact that this agent can impair wound healing and make the treatment futile. The medication is not an absolute contraindication as there is no increased risk or severity of side effects.
• Mafenide can cause local carbon dioxide production leading to acidosis and can be simply wiped off for safety.  Evidence of significant ill effects is lacking.[2]

These have long been held to be relative contraindications, and risks versus benefit should be addressed accordingly:

• Chronic obstructive pulmonary disease is a relative contraindication due to the risk of hypercarbia. The high fraction of oxygen increasing blood oxygen saturation levels can lead to oxygen-induced hypoventilation and increased ventilation/perfusion (V/Q) mismatch.
• Asthma can result in air trapping and the development of pulmonary barotrauma. In the same manner, asymptomatic pulmonary blebs and bullae found on plain chest radiographs also serve as a relative contraindication due to the potential air trapping progressing to a pneumothorax.
• Implanted devices should be pressure tested to determine their safety and ability to function in a high-pressure environment. Most have been pressure tested to withstand 100 FSW (4 ATA). However, it is always advisable to check with the manufacturer. While there have not been any case reports of an internal cardiac defibrillator triggering a fire in a patient in the hyperbaric chamber, it is possible to turn them off during treatment (if there is an acceptable risk of dysrhythmia). 
• Patients with epidural pain pumps are at risk of device malfunction or deformation under pressure. Contact the manufacturer to verify the device’s pressure limitations.
• Pregnancy has traditionally been qualified as a relative contraindication because of unknown effects on the fetus. Recent studies have moved pregnancy from a contraindication to an indication in certain circumstances. Pregnant women can benefit from HBOT in the setting of carbon monoxide (CO) poisoning. Due to the high affinity of fetal hemoglobin to oxygen and CO, HBOT improves fetal outcomes in CO poisoning.
• High fever or epilepsy can decrease the seizure threshold, making oxygen toxicity more likely. The risk of HBOT induced oxygen toxicity resulting in seizures in patients at increased risk of seizures due to history or recent brain surgery is not known. Antiepileptics and fever control can help alleviate this risk.
• The inability to equalize ears/sinuses, perhaps from previous surgery, radiation, or acute upper respiratory tract infection, could cause pain or barotrauma. History of certain ear conditions requiring surgery, such as otosclerosis, can be problematic. Acutely congested patients or those with minor difficulty clearing their ears can be treated with phenylephrine nasal spray. If ineffective or if the patient’s history of ear disease indicates, tympanostomy tubes should be placed before the initiation of HBOT.  
• Eustachian tube dysfunction can increase the risk of barotrauma to the tympanic membrane. It is recommended that patients undergo pressure equalization training or receive tympanostomy tubes before HBOT.
• Claustrophobia is possibly a contraindication, depending on severity, adequacy of control with anxiolytics, and size of the chamber. In severe cases, it could even represent an absolute contraindication for the patient if they are a danger to themselves or the tender in a chamber.
• Eye surgeries could be problematic if there is any air or gas trapped in the eye, as expansion/contraction of gas could damage the eye.
• History of thoracic surgery can increase the risk of atelectasis and pneumothorax. A thorough assessment should be performed before proceeding.
• A history of spontaneous pneumothorax is a relative contraindication and may require further evaluation before starting HBOT.
• Upper respiratory infections and severe sinus infections increase the risk of sinus and inner ear barotrauma, leading to further complications and severe patient discomfort. Related, uncontrollably high fevers (>39C) are a relative contraindication before beginning therapy and warrants a clinical evaluation to determine the source infection.
• Asymptomatic pulmonary lesions on chest x-ray should be evaluated before proceeding to determine the underlying etiology.
• History of optic neuritis or sudden blindness has traditionally been a relative contraindication to undergoing HBOT. Although there have been limited studies on these patients. Additionally, HOBT has been shown to provide therapeutic benefit to patients with radiation-induced optic neuritis, central retinal artery occlusion, retinal vein occlusion, macular edema, and others. Therefore, patients with a history of ophthalmologic pathology should be clinically evaluated to determine the potential risks and benefits.
• Diabetes mellitus dependent on insulin therapy / acute hypoglycemia is a relative contraindication for HBOT due to therapy-induced hypoglycemia. Point of care glucose monitoring and frequent nursing interaction is often sufficient to safely perform HBOT on diabetic patients.
• Nicotine use/addiction and caffeine use are contraindications before HBOT. The vasoconstriction caused by these agents reduces the effectiveness of therapy. For the same reasons, illicit vasoconstricting agents such as cocaine or amphetamines are also contraindicated.
• Congenital spherocytosis has been thought to be dangerous, as the increased partial pressure of oxygen could cause hemolysis. However, there have been reports of patients being treated without issue.
• Perilymph fistulas, which occur from inner ear barotrauma, cause vertigo and other vestibular symptoms and can be aggravated by HBOT with gas being forced into the cochlea.[3]

Not a Contraindication

It had been hypothesized that active cancer would be a contraindication to hyperbaric oxygen therapy. The proposed mechanism was that hyperbaric oxygen causes the release of vascular endothelial growth factor (VEGF) and could cause increased tumor growth. However, given the difference in tumor growth cycles versus wound healing and review of the literature, the evidence shows a net neutral effect on gene expression related to tumor growth.

HBOT can be used for emergent or elective interventions. The primary emergent indication for HBOT is decompression sickness from gas embolism and decompression illness. It is also used for acute management of carbon monoxide toxicity, chronic refractory osteomyelitis, radiation injuries to soft tissue, and clostridial myonecrosis, although evidence for HBOT use is less clear. It has also been used in necrotizing wounds, retinal artery occlusion, and acute trauma, though clear evidence of efficacy for these conditions is somewhat lacking.[1] In some of these conditions, HBOT is an adjuvant for patients unresponsive to traditional treatment methods alone.[4] Additional research indicates that patients who have recovered from head and neck tumors after radiation and surgical intervention may experience progressive fibrosis of soft tissues within the jaw. Studies have shown that patients who receive coadministered HBOT experience better outcomes than those without, and conclude that patients who are irradiated for head and neck tumors should be referred to HBOT centers and physicians should coordinate this effort with planned surgeries to optimize tissue healing.[5] Delayed radiation sequelae for the treatment of neurologic, gynecologic, urologic, and colorectal cancers have all shown responsiveness to concurrent HBOT.[6][7] There is also evidence that HBOT for treatment of severe anemia where transfusions are refused (observant Jehovah’s Witnesses) or are unable to be safely performed.[8] Evidence for this has been established at the basic science level and has been corroborated in healthy patients. One of the main drawbacks of this treatment method is the relative lack of access. There is a national shortage of HBOT centers in the United States, limiting its use and study as a mainstay treatment.[1]

Indications for HBOT use should be carefully weighed against the patients' potential contraindications for treatment to ensure that patients’ benefit outweighs associated risks. Interprofessional collaboration is crucial to ensure that patients’ contraindications are considered and ruled out while ensuring that HBOT is used with a reasonable indication of benefit. As HBOT can be used emergently or electively, interprofessional roles vary considerably for each use. In emergent situations, earlier HBOT initiation is correlated with improved outcomes.[9] While emergency department (ED) physicians may have the final say in recommending emergent HBOT, nurses, radiologists, emergency medical service personnel, and pharmacists play a critical role in ruling out contraindications for HBOT use.

Emergency medical service personnel is responsible for producing the initial history which may include indications that emergency HBOT is needed, such as a diving injury or evidence of carbon monoxide toxicity. Radiology staff must evaluate past radiographs for evidence of pulmonary nodules or other pulmonary abnormalities that may contraindicate elective HBOT. In addition, radiology will have a critical role in emergent situations to rule out tension pneumothorax, the single absolute contraindication to HBOT.  Pharmacists and pharmacy staff have an important role in considering the patient’s current medications and medication schedules so that patients undergoing chemotherapy can also utilize elective HBOT safely and without risk of medication effects. Nurses play an important role in monitoring patients undergoing HBOT for an adverse reaction and are essential to the maintenance of patient safety and wellbeing during HBOT treatment. For elective HBOT, primary care providers must carefully note medical conditions that may relatively contraindicate HBOT, including claustrophobia, upper respiratory infections (URIs), diabetes, eustachian tube malformations, and chronic respiratory diseases. When considering HBOT, the primary care staff must continuously review potential comorbidities that may introduce additional risk to the patient.[1][2]

Oxford CEBM Evidence Levels for HBOT by Condition

• Gas embolus: Level II[10]
• Radiation injury treatment: Level II[11]
• Refractory osteomyelitis: Level III[12]