MR. D, 62, has a history of prostate cancer, for which he received radiation therapy. About a year after finishing his radiation treatments, he began experiencing intermittent hematuria. He was diagnosed with radiation-induced hemorrhagic cystitis and has since required several blood transfusions. He was admitted yesterday for severe hematuria and is currently receiving the second of 2 units of packed red blood cells. He's receiving continuous bladder irrigation via a double-lumen indwelling urinary catheter. His urine is pink-tinged, and his urinary catheter required irrigation twice on the previous shift when it became obstructed by blood clots. He's scheduled for cystoscopy later on today. His care team has consulted the hyperbaric medicine team and a prescription has been written for hyperbaric oxygen (HBO2) therapy.
HBO2 therapy is used to promote tissue healing and fight infection by increasing the amount of oxygen dissolved in the patient's blood, which in turn improves oxygen delivery to tissue. Although HBO2 therapy is available in many clinical settings, it's not always well understood. This article provides an introduction to HBO2 therapy and discusses the indications, contraindications, potential adverse reactions, nursing considerations, and safety issues associated with this therapy.
Understanding the terminology
Hyperbaric literally means “over pressure.”1 In HBO2 therapy, a patient breathes 100% oxygen while resting in a chamber that's pressurized to a level greater than atmospheric pressure.1 Hyperbaric chambers vary widely in their construction, but they can be divided into two major categories. A monoplace chamber, which can accommodate one patient at a time, is typically pressurized with 100% oxygen. (See Monoplace hyperbaric chamber.) A multiplace chamber, as the name implies, can hold more than one patient. (See Multiplace hyperbaric chamber.) Multiplace chambers are normally pressurized with air, and the patients breathe oxygen through either a head tent or a mask. (See Head tent and Oxygen mask.) In either type of chamber, the patient breathes 100% oxygen while subject to increased ambient pressure.
Hyperbaric medicine has its roots in underwater construction and diving, with many parallels between the two. Most significantly, both diving and HBO2 therapy increase the pressure on the body. Although a complete description of hyperbaric physics and physiology is beyond the scope of this article, an explanation of some physical principles is helpful in understanding how HBO2 therapy works. (See Understanding pressure and volume for an explanation of basic principles.)
When a diver descends in the water, the diver's breathing apparatus responds by delivering air at a pressure that allows the diver to breathe against the increasing pressure on his or her body, or ambient pressure. Because of this, the breathing gas pressure in a diver's lungs is equivalent to the ambient pressure around him or her.2 This important point is the basis of diving and hyperbaric physiology. A patient in a hyperbaric chamber is physiologically similar to a diver in that both breathe gases while subject to pressures greater than atmospheric. However, while divers are immersed in water and typically breathe air, HBO2 patients remain dry and breathe 100% oxygen.
Now picture a container of your favorite carbonated beverage. If you take it out of the refrigerator and look at the liquid inside, you probably won't see any bubbles. When you remove the cap, though, carbon dioxide (CO2) bubbles suddenly appear in the drink. When the cap was on the drink, the CO2 was in equilibrium, with a significant amount dissolved in the liquid. The gaseous CO2 that was trapped under the cap was exerting pressure directly on the liquid, which is what kept the dissolved CO2 in solution. The physical principle behind this is Henry's Law, which states, “The amount of gas that will dissolve in a liquid at a given temperature is directly proportional to the partial pressure of that gas.”2 In other words, the more pressure that a gas exerts on a liquid, the more of that gas will dissolve in the liquid. In HBO2 therapy, breathing pressurized oxygen increases the amount of oxygen that will be dissolved in the blood.1
The alveoli in the lungs are, for all practical purposes, a gas/fluid interface. One of the beneficial effects of HBO2 is that under hyperbaric conditions, oxygen is dissolved into the plasma in quantities high enough to overcome a deficit in tissue microcirculation. Tissue capillaries can be damaged by therapeutic radiation, diabetes, burns, infection, and other insults. Damage to the microcirculation prevents erythrocytes from reaching tissues and delivering oxygen, which may result in tissue hypoxia, tissue breakdown, and impaired healing.
Unlike erythrocytes, which are solid, liquid plasma exits the tissue capillaries through normal capillary leakage. Oxygen that's dissolved in that plasma is carried along with it and can travel much farther from the capillaries under hyperbaric conditions than oxygen carried on the hemoglobin.3
The goal of HBO2 therapy is to provide a therapeutic level of oxygen while minimizing the risk of adverse reactions; however, some practitioners disagree about what constitutes a therapeutic level of oxygen.4 Most of the clinical hyperbaric patients at our facility are treated at 2 atmospheres, which is equivalent to a depth of 33 ft of seawater or fsw. Other common treatment pressures are 2.36 atmospheres, 2.45 atmospheres, and 2.82 atmospheres.1
Treatment profiles are selected based on the patient's illness, with more acute or severe disorders typically treated at higher pressures. The patient's clinical status also dictates the number of treatments needed. Acute illnesses typically require fewer treatments, and the treatment course is terminated when the disorder resolves or improves to a plateau. For example, patients with carbon monoxide poisoning typically receive one to three treatments over a 24-hour period.1 More chronic disorders require more lengthy courses of treatment, up to 60 treatments in some cases. Treatments for chronic disorders are typically done once daily with breaks on the weekends. Treatments usually last from 90 to 120 minutes.
The arterial oxygen tension (PaO2) is the amount of oxygen dissolved in the plasma, which is measured by an arterial blood gas analysis. Normal Pao2 ranges from 80 to 100 mm Hg when someone breathes room air at atmospheric pressure. According to the alveolar gas equation, a patient with normally functioning lungs who receives HBO2 therapy at 2 atmospheres would have an expected Pao2 of about 1,420 mm Hg. (See Nursing2016.com for supplemental online content, A closer look at the alveolar gas equation.) At 2.82 atmospheres, this increases to about 2,045 mm Hg.5 At these levels, enough oxygen is dissolved in the plasma that sufficient oxygen can be delivered to tissues to maintain normal metabolism. In fact, at 2.82 atmospheres and breathing 100% oxygen, the body can function normally using only dissolved oxygen, without deoxygenating hemoglobin.6
Indications and benefits
Hyperbaric chambers are considered medical devices and, as such, require FDA approval.7 An Internet search using the term hyperbaric oxygen will return a wide variety of information, not all of which is grounded in science or fact. The Undersea and Hyperbaric Medical Society, or UHMS (www.uhms.org), is a consortium of hyperbaric medicine practitioners and researchers who evaluate hyperbaric and diving medical research and make recommendations for the use of HBO2 therapy based on sound scientific evidence.8 Most hospital-based hyperbaric facilities follow the recommendations of the UHMS, which has formally approved these 14 indications for HBO2 therapy:9
- air or gas embolism
- carbon monoxide (CO) poisoning, including CO poisoning complicated by cyanide poisoning
- clostridial myositis and myonecrosis (gas gangrene)
- crush injury, compartment syndrome, and other acute traumatic ischemias
- diving decompression sickness
- arterial insufficiencies, including central retinal artery occlusion and impaired healing in selected problem wounds
- severe anemia
- intracranial abscess
- necrotizing soft-tissue infections
- refractory osteomyelitis
- delayed radiation injury, including soft-tissue and bony necrosis
- compromised grafts and flaps
- acute thermal burn injury
- idiopathic sudden sensorineural hearing loss.
In the fictional case study, the microcirculation in Mr. D's bladder was damaged by therapeutic radiation, resulting in the chronic tissue hypoxia that characterizes delayed radiation injury. Using the principles explained previously, HBO2 will help deliver oxygen to his hypoxic bladder tissue, which will trigger collagen production and capillary growth, or neovascularization. Ideally, enough capillaries will grow that Mr. D's bladder tissue will heal and remain sufficiently oxygenated once he finishes his treatment series. In cases of delayed radiation injury, this may take up to 60 treatments.10
Besides promoting neovascularization, HBO2 has several other beneficial effects. In cases of CO poisoning, it's used to help remove CO from hemoglobin, promote normal oxygen levels, and prevent delayed neurologic sequelae.1
HBO2 also helps to fight infection in several ways. It potentiates the action of certain antibiotics, which increases their effectiveness.11 In cases of clostridial gas gangrene, HBO2 blocks the production of tissue-necrosing alpha toxin by the clostridial bacteria, which effectively neutralizes the bacteria's ability to break down tissue.11
HBO2 therapy also has anti-inflammatory effects. It helps prevent leukocytes from adhering to the vascular endothelium by interfering with the beta-2 integrin protein, which interrupts the inflammatory cascade.12 The reactive oxygen species, or free radicals, produced during hyperbaric hyperoxia effectively scavenge nitric oxide, which is an endogenous vasodilator. Decreased levels of circulating nitric oxide result in net vasoconstriction, which reduces both inflammation and edema.13
Avoiding negative outcomes
Adverse reactions of HBO2 therapy are rare and largely unique to the hyperbaric environment. Pressure affects gas-filled spaces: Specifically, as the pressure around a gas-filled space increases, its volume will decrease, and vice versa. This inverse relationship between pressure and volume is known as Boyle's Law.2 The human body has several gas-filled spaces, all of which are vulnerable to barotrauma, or pressure-related injury, if these spaces fail to equalize with the changing ambient pressure in the hyperbaric chamber.
The middle ear, the area most commonly affected by barotrauma, is connected to the nasopharynx via the eustachian tube.2 The eustachian tube helps modulate pressure in the middle ear by allowing air to pass into and out of the middle ear during changes in ambient pressure. Patients may have difficulty equalizing the middle ear pressure during hyperbaric therapy if they have anatomic variations or a eustachian tube that's been narrowed by radiation-induced stenosis or inflammation of the mucosa, such as occurs during an upper respiratory tract infection. Hyperbaric personnel are trained and experienced in assisting patients with ear equalization, but if patients fail to properly equalize the pressure in their ears, the tympanic membrane or the delicate tissue lining the middle ear may be damaged. Patients who experience multiple episodes of middle ear barotrauma or have a known history of eustachian tube dysfunction may require placement of pressure equalization tubes.14
The paranasal sinuses typically equalize themselves without any effort by the patient, but as anyone who's had a sinus headache can attest, the sinuses can become obstructed. Changes in ambient pressure can cause sinus barotrauma.2 Other areas of the body where barotrauma may occur (rarely) are the lungs, if air is trapped by anatomic defects such as pulmonary blebs; the gut, if gas in the stomach or intestines expands; and the teeth, if air under an old or improperly placed filling is compressed or expands with descent or ascent.2 Untreated pneumothorax is an absolute contraindication to HBO2 therapy because a pneumothorax can become pressurized at depth and expand on ascent, resulting in tension pneumothorax.15
Most healthcare professionals are aware that high levels of inspired oxygen can cause pulmonary oxygen toxicity. Under higher-than-atmospheric pressures, oxygen also becomes toxic to the central nervous system (CNS) and can cause various signs and symptoms, including muscle twitching, visual and auditory phenomena, and seizures.2 The risk of CNS oxygen toxicity increases with the partial pressure of oxygen and the length of exposure.2 HBO2 treatments are designed to minimize the risk of CNS oxygen toxicity by staying within recommended partial pressure and exposure time parameters.
To decrease the risk of oxygen toxicity, some treatment protocols may incorporate what's known as an air break, when oxygen breathing is interrupted by periods of breathing air. One such protocol, known as “U.S. Navy Treatment Table 6,” is used for treatment of moderate-to-severe decompression illness.2 (See “U.S. Navy Treatment Table 6.”)
If the patient is in a multiplace chamber, air breaks are accomplished by removing the head tent and letting the patient breathe the ambient chamber air. In a monoplace chamber, which is pressurized with 100% oxygen, the patient is directed by the chamber operator to breathe air from a mask located inside the chamber. Air breaks may or may not be used depending on the facility and patient.
After about 20 treatments, most patients undergoing HBO2 therapy experience a transient myopic shift; patients who are nearsighted become more so, and patients who are farsighted may actually experience a vision improvement. This myopic shift typically resolves and vision returns to baseline within a few weeks after the patient finishes treatment.14
Who can't use it?
There are relatively few contraindications to HBO2 therapy. For the reasons described previously, untreated pneumothorax (air trapped in the chest cavity) is an absolute contraindication. However, patients with chest drains may be safely treated in a hyperbaric chamber.15
Several medications have demonstrated ill effects when combined with HBO2 therapy. Concurrent therapy with bleomycin can result in pulmonary complications; however, patients have been safely treated after their course of bleomycin is complete.16,17 Concurrent doxorubicin therapy may also be a contraindication due to the potential for cardiac toxicity.16 Disulfiram (used for alcohol abuse) has been shown to increase the risk of oxygen toxicity in animals when given in very large doses. Cisplatin can impede wound healing, as can topical mafenide acetate.18 Mafenide is also a carbonic anhydrase inhibitor and may cause CO2 retention with concomitant increase in cerebral blood flow, which could increase the risk of CNS oxygen toxicity.18
Patients who depend on an external medical device must be carefully evaluated and the device's compatibility checked before treatment. For example, in the authors' experience, most ventricular assist devices aren't compatible with the hyperbaric environment, so these patients aren't generally candidates for HBO2 therapy.
Relative contraindications to HBO2 therapy typically arise if a patient is at increased risk for gas trapping or seizure activity. For example, an acute asthma attack can theoretically lead to gas trapping so patients with asthma requiring HBO2 therapy may need to be monitored for exacerbations during treatment. Patients with pulmonary blebs or bullae may be at risk for gas trapping and lung expansion, but only one case report describes this occurring, and such patients are often safely treated in our facility.16
Patients with upper respiratory infection or environmental allergies who have upper respiratory congestion may be at increased risk for ear or sinus barotrauma; they may need premedication with a decongestant or topical nasal vasoconstrictive agent.15
Patients with a history of seizure disorder, or who have acute traumatic brain injury or other organic brain disease, may be at increased risk for CNS oxygen toxicity.16 They'll need careful evaluation before treatment.
Nurses caring for someone receiving HBO2 therapy in an inpatient setting need to be aware of a few important points. The following checklist can guide them in preparing their patients for treatment in either a monoplace or multiplace hyperbaric chamber.19
- Nutrition and blood glucose levels. HBO2 therapy may interfere with mealtimes. If so, ensure that the patient receives an early or off-hours meal. Patients with diabetes need special attention; blood glucose levels should be measured and documented before treatment, and antihyperglycemic agents should be given as prescribed. Timely meals are especially important for patients with diabetes because HBO2 therapy is an insulin sensitizer and can cause hypoglycemia.20,21 Insulin pumps generally aren't compatible with hyperbaric pressures and should be removed before treatment unless specifically directed by the hyperbaric staff. Additional insulin coverage may be required during the period the patient isn't receiving continuous insulin. The insulin pump infusion cannula and/or tubing may remain in place if its design permits it to be separated from the pump.
Caution patients against consuming gas-producing foods and carbonated beverages before treatment because the pressure changes in the chamber can cause painful gastric and bowel distension.2 Caffeine is a vasoconstrictor and may interfere with blood flow to tissue with compromised circulation, so patients should avoid excess caffeine. No enteral feeding pumps are currently approved for hyperbaric use, so patients won't receive continuous enteral nutrition during treatment. It may be preferable to disconnect the pump prior to transport. Patients in multiplace chambers may be able to receive bolus enteral tube feedings before or during treatment and may be permitted to eat at the discretion of the hyperbaric staff.
- Alcohol use and smoking. Alcohol consumption isn't typically a contraindication to HBO2 therapy, but chronic alcohol abuse and alcohol withdrawal can lower the patient's seizure threshold and increase the risk of seizures related to CNS oxygen toxicity.22 The care team should inform the hyperbaric team of a patient's known or suspected alcohol abuse. Nicotine causes vasoconstriction, which can interfere with the effects of HBO2, so patients should be encouraged not to use tobacco products or nicotine patches while receiving HBO2. Patients who can't refrain from smoking should be advised not to smoke an hour before or after hyperbaric treatment. Smoking materials present a fire hazard and are never allowed in the hyperbaric chamber.
- Elimination. Few hyperbaric chambers have restroom facilities inside, so patients should be encouraged to void, move their bowels, and/or empty colostomy or urinary drainage bags. Laxatives and enemas should be avoided before therapy. If required, they should be given after patients return from hyperbaric therapy if at all possible.
- Tubes, lines, and drains. Surgical drain collection devices and other drains should be emptied before the patient leaves for HBO2 therapy. If the multiplace chamber can provide suction for negative pressure wound therapy, pumps can remain in place during transport but will be disconnected when the patient arrives in the chamber. Most monoplace facilities request that negative pressure wound therapy devices be disconnected, and the hose be covered with gauze and taped in place. Chest tube drains may need to be placed to water seal (that is, discontinue suction).
- Premedication. If needed, medicate patients for pain, nausea, and/or anxiety before they leave for HBO2 therapy. This helps ensure that the medication reaches its peak at the appropriate time.
- Medication during treatment. Patients may be able to receive I.V. fluids, medication, and blood products while in the chamber. Staff at monoplace facilities can't administer oral medications during treatment. Hyperbaric staff members can provide specific details.
- Temperature. Because fever can lower a patient's seizure threshold, the hyperbaric staff should be informed if a patient has a temperature greater than 37.8° C (100° F).
- Mechanical ventilation. Some hyperbaric facilities have the staffing and resources to care for mechanically ventilated patients. Endotracheal and tracheostomy tube cuffs must be inflated with sterile 0.9% saline solution before treatment because air-filled cuffs will be reduced in volume and may loosen and migrate when the chamber is pressurized.23
- Patient safety. Although oxygen doesn't burn, it does accelerate combustion, sometimes with catastrophic results. The high concentration of oxygen in a hyperbaric chamber necessitates special safety precautions to prevent fires, especially in monoplace chambers, which are pressurized with 100% oxygen.
In monoplace facilities, patients are prohibited from bringing any personal items, including watches and jewelry, into the chamber out of an abundance of caution; some items present fire risks. Also, because patients in monoplace chambers can't be accessed during treatment, choking hazards such as dentures, food, and gum aren't typically allowed.
Patients in multiplace chambers are accompanied by trained staff during treatment, so most multiplace facilities permit patients to wear dentures, chew gum, and bring small drink containers. Due to the lower concentration of oxygen (and hence less chance of combustion) in the atmosphere of a multiplace chamber, patients are usually allowed a limited amount of reading material. (See Fire hazard safety considerations.)
Internal pacemakers and implantable cardioverter-defibrillators are typically safe, but hyperbaric staff should be made aware if a patient has such a device. The hyperbaric nurse will generally double-check with the manufacturer to ensure that the device has been tested at pressure; it's helpful to provide the model and serial number if this information is available. Internal medication pumps, such as an intrathecal drug delivery system, can be affected by pressure, so be sure to inform hyperbaric staff if the patient has one.
- Clothing. Hyperbaric patients are provided gowns or scrubs of 100% cotton, which reduces the risk of a static electrical spark. Monoplace facilities require that the patient be dressed in only a hyperbaric-approved gown. Multiplace facilities generally let patients wear their own undergarments. Street shoes aren't allowed in the hyperbaric chamber; patients may be provided with nonslip socks or footwear to wear instead.
- Dressings. Staff at monoplace chambers prefer dressings with plastic tape and generally ask that silk tape be avoided (to avoid a theoretical risk of static electrical discharge). Patient dressings will be assessed before treatment and may be changed by hyperbaric staff. Petroleum or other medicated dressings may need to be covered with damp gauze because they present a fire risk.
- Documentation. Always send the patient's medical record and current medication record with the patient.
Mr. D completed 12 hyperbaric treatments as an inpatient and was discharged home. Most (76%) of patients with hemorrhagic cystitis experience either partial or complete relief of symptoms after HBO2 therapy.20 Mr. D received an additional 48 treatments as an outpatient and his hematuria resolved completely.
HBO2 therapy is a highly effective adjunct when properly applied, and many healthcare facilities offer this treatment. Most HBO2 treatment centers are affiliated with wound-care clinics, and capability varies widely between chamber facilities. Although some can treat critically ill patients and may operate on 24/7 call, others are limited to ambulatory outpatients. The Duke University Hospital hyperbaric medical staff is available for 24-hour consultation at (919) 684-8111.
Given the clinical value of HBO2 therapy, it's important for nurses to understand the indications and implications of using this treatment modality.
Understanding pressure and volume2
Atmospheric pressure at ground level is a function of the weight of the air in the Earth's atmosphere, which is approximately 56 miles high. At sea level, this pressure is roughly 760 mm Hg.1 In hyperbaric medicine and diving, this is frequently expressed as 1 atmosphere of pressure.
Because water is much denser than air, very small depth changes will produce relatively large pressure changes. In sea water, pressure increases by 1 atmosphere for every 33 ft of depth. For example, at 66 ft of sea water (fsw), the total pressure is 3 atmospheres. The figure below shows how pressure changes with depth. The orange balloon is an air-filled space. Because pressure and volume are inversely related, if the pressure around the balloon is increased, its volume decreases. At 2 atmospheres of pressure, its volume will be half the original. At 3 atmospheres, it will be a third; at 4 atmospheres, a fourth.
Fire hazard safety considerations
All hyperbaric facilities forbid certain items that present a significant fire hazard. A partial list is included below; the hyperbaric unit at some facilities may have more specific requirements:
- personal electronic items such as cell phones, MP3 players, laptop and tablet computers, and e-readers
- spark-producing friction toys
- smoking materials
- petroleum or alcohol-based products, including makeup, perfume, freshly applied nail polish, hair spray or oil, bath oil, lotions, and ointments
- hot packs, hand warmers, and heating pads
- external insulin or infusion pumps.