HBO Nuggets of the Week
A forum to discuss interesting aspects of hyperbaric medicine.
Friday, January 15, 2016
HBO Nugget 16
Hyperbaric oxygen therapy (HBOT) is usually very well tolerated. The most common risk to patients is barotrauma, typically middle ear. Other risks of prolonged exposure to oxygen include pulmonary oxygen toxicity and central nervous system seizures. Pulmonary oxygen toxicity is rarely seen since it requires long exposures at a FiO2 of greater than 50%. This is more commonly seen in ventilated patients in the ICU. Central nervous system oxygen toxicity, also known as the Paul Bert Effect, may be more of a concern since some medical conditions lower the threshold for seizures to occur.
Patients at high risk for seizures who are recommended to undergo HBOT may benefit from air breaks during their dive to reduce the total time of hyperoxic exposure. A patient will be supplied a non-rebreather mask that is connected through the chamber wall to medical air. During the dive, the hyperbaric technician will request that the patient apply the mask and breath air. A typical protocol is for the patient to breathe medical air for 5 minutes after every 30 minutes.
During the initial medical evaluation, the healthcare provider should ascertain whether the patient may be at high risk for seizures or have a seizure disorder. Air breaks should be considered for those patients that have:
· Recent brain surgery
· Brain tumors
· Recent head trauma/concussion
· Fever related seizures
· Infections such as brain abscess, meningitis, encephalitis
· Diving the patient at pressures > 2.0 ATA
Consultation with a neurologist/neurosurgeon prior to starting HBOT can be helpful as well as making sure that the patient continues any anti-convulsant medication that they are taking.
Should the patient have a seizure during his/her treatment and breathing is irregular, ascending the patient rapidly may not be prudent. Rapid ascent without regular breathing may predispose the patient to lung rupture/pneumothorax. When breathing becomes regular, ascent may be started.
Friday, June 26, 2015
Hyperbaric oxygen therapy (HBOT) is usually very well tolerated. The clear acrylic wall of the chamber allows the patient to see around the room, reducing the sensation of claustrophobia. Most chambers are fitted with speakers so that patients can listen to music or watch their favorite movie or TV show. From time to time, it does, however, become necessary to ascend your patient prior to completion of their dive.
Some common situations where you may want to consider terminating your patient’s dive include:
· Claustrophobia/confinement anxiety: gentle reassurance and a calming voice on the intercom can often assuage a patient’s anxiety. Pre-dive anti-anxiolytics may help, including agents such as benzodiazepines. Never force a patient to stay at depth if they request to come up.
· Inability to clear the ears: Avoid barotrauma. Gently “bouncing the patient” (slowly descending, ascending, descending) and using safe clearing techniques may alleviate the issue. Never force the dive. Pre-dive decongestants may be helpful. Pressure-equalization tubes are occasionally inserted by an ear, nose, and throat specialist if the indication for HBOT is urgent
· Hypoglycemia: most wound care centers do not use in-chamber glucose monitoring. If your patient is diabetic and informs you that he or she feels lightheaded, dizzy, shaky, or has tingling, you may decide to bring the patient up. Pre- and post-dive blood glucoses should always be performed and patterns analyzed. Blood glucoses may tend to drop after the initial several dives. Patients can be given glucose tablets to bring in the chamber with them.
· Any symptom concerning for a serious cardiopulmonary issue: shortness of breath, chest pain, palpitations
· Need to void: even with a pre-dive trip to the bathroom, patients on diuretics or with gastrointestinal distress may need to ascend. Urinals and incontinence briefs can be alternatives to avoid frequent dive terminations. Always ensure that anything sent into the chamber with the patient is approved by your hyperbaric safety director.
Patient comfort and safety should always be a priority during HBOT treatments. Pre- and post- dive checklists and good communication between the patient and the technician, and the technician and the physician (or supervising healthcare provider) are key to helping the dive go smoothly.
Tuesday, March 17, 2015
Collagen formation and maturation is a required step in the natural pathway to wound healing. Following injury, a wound goes through several phases in the process of healing. During the proliferation and maturation phases of wound healing, collagen is synthesized and then crosslinked by the hydroxylation of collagen by proline hydroxylase. These are oxygen-dependent steps as seen below in this simplified equation:
proline ---à proline hydroxylase---àhydroxyproline
O2, Fe2+ -----à CO2, Fe3+
Early American Indians noted that wounds that they sustained while living high up in the mountains appeared to heal more quickly in the higher pressure valleys. French divers living in submersible habitats in the 1960’s noted that their wounds healed more quickly in the moist undersea environment with higher oxygen tensions. These observations prompted T.K. Hunt in San Francisco in the early 1970s to perform studies on the effects of varying oxygen tensions on wound healing with relationship to collagen synthesis.1 He observed the rate of collagen synthesis in small cylinders implanted in rabbits with varying concentrations of oxygen. His results demonstrated collagen synthesis was accelerated in response to hyperbaric oxygen.
Hyperbaric oxygen is an adjunctive therapy in the treatment of specific nonhealing wounds; however, we must keep in mind that we should always treat the underlying cause of the wound and not just the wound itself. Peripheral arterial disease and diabetes, eg, may by underlying causes of ulceration that need to be evaluated in the initial workup of patients presenting for hyperbaric oxygen therapy consultation.
1. Hunt TK and Pai MP. The effect of varying ambient oxygen tensions on wound metabolism and collagen synthesis. Surg Gynaecol Obstet 1972;135:561-7.
Tuesday, September 16, 2014
One of the indications for treating patients with hyperbaric oxygen therapy (HBOT) is a Grade III Wagner’s diabetic foot ulcer. This classification was discussed in a previous blog. Treating a patient with diabetes in an HBO chamber requires attention to the patient’s blood glucose (BG) level.
For reasons still unclear, BG levels in patients with diabetes, either type 1 or type 2, tend to drop during HBOT. Patients with type 1 diabetes seem to be affected to a greater degree. Patients without diabetes may experience a drop in BG levels, but to a much lesser degree. Some studies have shown a mean drop in BG of nearly 50 mg/dL at 2.4 ATA. The exact mechanism needs to be understood, but it appears an increased peripheral cellular sensitivity to insulin may occur.
It is important to realize during the initial evaluation of patient candidates for HBOT that certain medications may affect glucose metabolism. These may include:
When undergoing HBOT, patients with diabetes should have their BG levels checked both pre- and post-dives. Each wound care center should establish protocols for patient BG management prior to HBOT. Clinicians may want to treat a patient prior to a dive if his or her BG level is between 110 and 140 mg/dL. During their course of therapy, falls in patients’ BG may increase after the third dive; hence, one must also be cognizant of the patient’s trend in BG levels versus any one individual number.
Wednesday, April 16, 2014
As hyperbaric medicine physicians, we may be asked to evaluate patients with compromised or failing flaps following reconstructive surgical procedures. With improved techniques in vascular and plastic surgery, there are an increasing number of these procedures being performed. Examples include:
· Breast reconstruction flaps
· Procedures to cover tissue defects after trauma
· Oral and maxillofacial procedures
One of the indications for the use of hyperbaric oxygen therapy (HBOT) is that of a failing flap or graft. HBOT can be used to promote flap survival. There are several theories describing how the flaps may benefit. One proposed theory is that there are small arteriovenous shunts that form within the flap and that HBOT may reduce these by causing vasoconstriction, thus increasing flow to more ischemic areas. The other is the well-known effect of migration of fibroblasts into hypoxic areas and induction of angiogenesis.
Typical recommended therapy is 2.0 ATA for 90 minute dives and, in some situations, the frequency could be twice a day. Treatment should always include close communication with the operating surgeon so that progress of the graft can be monitored.