Studies show all patients undergoing hyperbaric oxygen therapy (HBOT) experience a reduction in blood glucose levels compared to prehyperbaric oxygen treatment levels. This expected physiological reaction may result in a range of challenges for both patients and treatment centers, including hypoglycemic events, liability, schedule changes, cancellations, and ultimately delayed healing and a loss of revenue. Reduction in blood glucose level tends to be more pronounced in patients with diabetes when compared to patients without diabetes.1 For example, one observational study2 of patients with diabetes (including insulin-dependent and noninsulin-dependent participants) showed a mean drop of 36 mg/dL in blood glucose during HBOT. Insulin-dependent patients experienced an even more severe drop — 19% had a drop of 72 mg/dL or more, requiring intervention before HBOT.   This article describes the mechanisms of HBOT, its effects on glucose levels, and how to address related concerns.

The Basics of Hyperbaric Oxygen
Hyperbaric oxygen is a treatment in which a patient breathes 100% oxygen intermittently while inside a treatment chamber at a pressure higher than sea level pressure (ie, >1 atmosphere absolute or 1 ATM). In other words, during HBOT, the air pressure is raised up to three times higher than normal air pressure. Under these conditions, the patient’s lungs can gather up to three times more oxygen than would be possible breathing pure oxygen at normal air pressure. The patient’s blood then carries this oxygen throughout his body, stimulating the release of growth factors and stem cells. Administration of 100% oxygen at ambient pressure causes a five-fold increase in the amount of dissolved oxygen in blood. In HBOT, administration of 100% oxygen at 2 to 3 ATM increases the dissolved oxygen in blood and tissues up to 20-fold, a level high enough to sustain life without any contribution from oxygen bound to hemoglobin.3

HBOT Chambers and Indications
Hyperbaric chambers are classified by the National Fire Protection Association as Class A (multi-occupant) or Class B (single occupant). Both generally use compressed 100% oxygen as both the pressurization gas and the hyperbaric treatment gas. Class A chambers are usually hard-shelled structures made of steel and aluminum with acrylic view ports. Larger Class A chambers that accommodate multiple patients and medical staff operate at absolute pressures up to 6 ATM, and patients typically breathe from individual masks that supply pure oxygen and remove the exhaled gas.   Class B hyperbaric chambers accommodate a single patient; the entire chamber is pressurized with 100% oxygen, and the patient breathes the ambient chamber oxygen directly. Table 1 lists commonly approved indications for HBOT. Wounds, including diabetic foot ulcers, are a common treatment indication, which is why the issue of glycemic control is of particular importance.

Mechanism of Hypoglycemia in HBOT
The complex changes in glucose metabolism during HBOT have not been fully elucidated. However, studies have shown an increase in activity of insulin-receptor sites and changes in insulin sensitivity due to upregulation of PPAR-γ signaling associated with hyperbaric oxygen. In one study,5 insulin sensitivity increased within 3 days of hyperbaric oxygen treatment, and this was maintained for 30 sessions. Animal studies6 also have shown HBOT has a direct effect on the enhancement of glucose metabolic capacity and uptake in the skeletal muscle.

Common Practices for Addressing Low Glucose Levels in HBOT
Low blood glucose levels in patients undergoing HBOT present significant clinical and logistic challenges. Patients with low glucose levels during HBOT are at higher risk of seizures and seizure complications, among other adverse clinical events. Persistent low finger-stick blood glucose levels in an HBOT patient lead to treatment delays and/or cancellations, which in turn leads to operational challenges for the hyperbaric facility along with financial losses if multiple treatments are cancelled.   Currently, general guidelines and recommendations for blood glucose levels in patients undergoing HBOT are unclear; presently, no specific uniform recommendation exists on what interventions should be initiated in diabetic and nondiabetic patients with low glucose levels before hyperbaric oxygen treatments. Hyperbaric centers have created individual treatment approaches to address this often-encountered problem. Common interventions for patients with lower-than-optimal blood glucose range from providing orange juice, soda, cookies, or candy to ordering a full meal from the facility cafeteria before treatment sessions. These practices raise the question of whether healthcare professionals (HCPs) should be causing significant spikes in glucose in patients undergoing HBOT for the short-term purpose of pushing those levels high enough to initiate HBOT sessions. This practice may lose sight of the longer-term consequences of poorly controlled levels and negate patient education, which typically discourages consumption of many of the foods offered to quickly raise glucose levels.

Decisions on the cut-off number for blood glucose that warrants an intervention and appropriate interventions are highly individualized. Issues taken into consideration before any decision is made include:
    • Whether the patient is diabetic and, if so, what type and what antidiabetic treatment is on board;
    • The anticipated drop in blood glucose level while in the HBO chamber. Although this may not be easy to predict with certainty, knowledge of the patient’s previous glycemic control and blood glucose pattern will help in making an educated clinical judgment;
    • How long the patient is going to be in the chamber. The duration of HBOT varies from 90 minutes for refractory osteomyelitis to approximately 5 hours in some cases of decompression sickness.

A Protocol Example
As an example, this protocol7 may be followed for making intervention decisions for low glucose levels before administering HBOT.
    • All patients are instructed to consume their usual meal and diabetic medications before HBOT.
    • All medications that potentially impact blood glucose levels are placed on automatic alert in the electronic health record.
    • Blood glucose via finger stick is checked on all patients before and after HBOT. Patients with finger-stick blood glucose levels <120 mg/dL are evaluated and considered for intervention before HBOT sessions as follows:
      - Glucerna® (Abbott Nutrition, Columbus, OH) — 1 can/bottle (237 mL) — is given to patients with diabetes.
      - Ensure® (Abbott Nutrition) — 1 can/bottle (237 mL) — is given to patients without diabetes.
      - Nepro® (Abbott Nutrition) — 1 can (237 mL) is given to nondiabetic renal patients (chronic renal failure or end stage renal disease).
      - Hypoglycemic patients (with symptoms) receive Instaglucose in addition to the above.
      - The quantity of oral nutrition supplement (ONS) or Instaglucose is individualized to each patient and based on the physician’s assessment.
      - Finger-stick glucose level is rechecked 15 to 30 minutes afterwards (or longer) depending on the intervention provided.   ONSs provide a mix of protein, carbohydrate, fat, vitamins, and minerals that promotes a slower rise in glucose levels as well as a slower decline than candy bars or high-sugar foods and beverages. In other words, a balanced blend of the macronutrients leads to less fluctuation in glucose levels. For patients undergoing longer HBOT sessions, this is important because glucose levels can fall while the patient is in the chamber, leading to other serious consequences. ONSs are also convenient and ready to serve. Ordering a meal tray can take considerable time, and food choices may be limited depending on the time of day.

Nutrition Guidelines for Diabetes
Nutrition education may be provided to patients at the time of HBOT to improve overall glucose control. Self-management of diabetes is often a daunting prospect for patients, particularly when newly diagnosed. Hearing they must test blood sugar, follow a new diet, engage in physical activity, take medications appropriately, and be concerned with comorbidity complications is often overwhelming for patients. Although HCPs are aware of the dangers of uncontrolled diabetes, patients often are not concerned until detrimental symptoms such as a wound occur, and then it may be too late. Table 2 lists some easy tips that can quickly be discussed with patients to reinforce good eating habits. If more detailed education is needed, referral to a registered dietitian (RD) is warranted.

Practice Points
HBOT is indicated for a variety of diagnoses but comes with the risk of hypoglycemia, particularly for patients with diabetes. Patients who arrive at their appointment with lower-than-desired blood glucose levels often are given high-sugar, high-carbohydrate foods in order to quickly raise blood glucose and avoid costly delays or even treatment cancellations. Although no clear guidance exists, giving patients with diabetes soda or candy promotes a mixed message and negates the teachings of diabetic educators and RDs. It would be better to provide nutrition education and follow a protocol utilizing ONS that contain a balanced mix of macronutrients as well as vitamins and minerals.

Prof. T. Samuel Nwafor, MD, FACP, FAPWCA, is the Wound Care Medical Director and Chief of Staff, Promise Hospital, Phoenix, AZ; and a wound and hyperbaric medicine physician, Tempe St. Luke’s Hospital, Tempe, AZ. He is also President, Hannah Medical Institute AZ. Nancy Collins, PhD, RD, LD/N, FAPWCA, FAND, is founder and executive director of and For the past 20 years, she has served as a consultant to healthcare institutions and as a medico-legal expert to law firms involved in healthcare litigation.

Correspondence may be sent to Dr. Collins at

This article was not subject to the Ostomy Wound Management peer-review process.