Laboratory Tests for Blood Glucose Monitoring

Hemoglobin A1c (HbA1c)

Reviewing a patient’s long-term glucose control is a key step in preparing them for safe and effective HBOT, particularly when wound healing is a treatment goal. 

• The primary tool for assessing long-term glucose management is the Hemoglobin A1c (HbA1c), which reflects the patient’s average blood glucose over the preceding 2–3 months.
• In addition, HbA1c can be utilized to:
• Guide discussions with the diabetes care provider regarding optimization of glucose control if needed.
• Help determine wound healing potential: elevated HbA1c levels are correlated with poor wound healing outcomes. [12]
• Persistent hyperglycemia impairs multiple aspects of wound healing, including leukocyte function, collagen synthesis, angiogenesis, and epithelialization. [12]
• HbA1c over 8% and poorly controlled blood glucose (>180mg/dL) is associated with slower wound healing in patients with diabetes.[12][13] See Table 3.
• It is estimated that for each 1.0% point increase in HbA1c, the daily wound-area healing rate decreased by 0.028 cm2/day (p=0.027). [12]
• Estimated average glucose: the American Diabetes Association recommends the use of a new term in diabetes management, estimated average glucose, or eAG. With the use of a formula, health care providers can now help patients understand what an HbA1c result means in terms of daily glucose readings [14] 
• Table 3 below illustrates the conversion values between HbA1c and eAGE and correlates these values with wound healing impairment.
• The relationship between AHbA1c and eAG is described by the formula
• eAG (mg/dL)=(28.7×HbA1c)−46.7 [14]

Continuous Glucose Monitor (CGM)

• Continuous glucose monitoring systems are widely utilized by both patients with and without diabetes. These systems are available as a skin patch sensor or a wearable device such as a smartwatch. The basic wearable variety requires a battery, which is not safe in a hyperbaric environment.
• There are several manufacturers of CGM systems that function with a transmitter patch, wirelessly sending results to a device or smartphone.
• While some CGM transmitters have been tested in the hyperbaric environment with compressed air, to date, no published test data confirms the safe use of CGMs in a monoplace hyperbaric chamber using 100% compressed oxygen.[3]

External Insulin Pumps

• An insulin pump is a medical device that delivers insulin subcutaneously to help manage diabetes. It provides a continuous basal rate of insulin throughout the day and allows for programmable bolus doses to be administered at mealtimes or when blood glucose levels are elevated. Modern insulin pumps often work with CGMs and automated insulin dosing software to adjust insulin delivery based on real-time and predicted glucose levels.
• Insulin pumps are typically prescribed to help people with diabetes maintain better glucose control with fewer manual injections.
• Two main types of external insulin pumps exist:
• Traditional insulin pumps: small devices worn on clothing, delivering insulin subcutaneously via a long, thin catheter.
• Patch pumps: self-contained units adhering to the skin, delivering insulin subcutaneously through a short catheter covered by the pump body.[16]
• Both types can be programmed for various basal rates and deliver boluses on demand.
• Some pumps include features like: 
• Automatic adjustments to increase, decrease, or pause insulin delivery in response to changing blood sugar.
• Bolus calculators that suggest insulin doses based on factors like carbohydrate intake, current glucose, trends, and insulin already in the body.

OPERATIONAL CONSIDERATIONS

Before Patient Arrival

Chamber Inspections

• Routine chamber inspections should be conducted to confirm chamber maintenance procedures and the safe operation of all equipment utilized during HBOT.
• For resources on chamber inspections, see topic "HBO Safety Inspections".

Ground testing

• The National Fire Protection Association 99 Health Care Facilities Code (NFPA 99) requires that all hyperbaric chambers be grounded and patients inside chambers filled with 100% oxygen be likewise grounded. 

Prohibited Item(s), Assessment and Authorization

• Wound dressings, devices (e.g. continuous glucose monitor devices and insulin pumps), and other objects that go in the hyperbaric chamber with the patient may raise important safety concerns, including the production of heat, production of static electricity, production of flammable vapor, ignition temperature, and total fuel load. It is critical that clinicians understand which dressings, devices, and objects are prohibited, restricted or allowed inside a hyperbaric chamber during HBOT.
• Each hyperbaric facility should maintain an internal list of items that are approved for use, should be used with caution and should not be used in the chamber. See "Go-No-Go Lists / Prohibited Items" and "Go-No-Go: Frequently Asked Questions". 

Ancillary Equipment

• All equipment utilized by the hyperbaric medicine facility is maintained through a program of regular preventative maintenance.
•  See topic "Ancillary Equipment".

Air Breaks

• During HBOT, providing an alternative air-breathing source - commonly referred to as an air break - is often necessary. Air breaks may help reduce the risk of central nervous system (CNS) oxygen toxicity by interrupting continuous exposure to high inspired oxygen concentrations.
• While direct evidence demonstrating a reduced incidence of CNS oxygen toxicity from air breaks is limited, substantial published data support the relationship between oxygen toxicity and both the fraction of inspired oxygen (FiO₂) and duration of exposure. By limiting continuous high FiO₂ exposure, air breaks are expected to lower the overall risk of oxygen toxicity. [17]

Infection Control - Cleaning/ Disinfection of the Hyperbaric Chamber

• Adverse outcomes related to the risk of infection stands at the forefront of concern for patients treated with HBOT. Particular attention should be given to cleaning and disinfection of the hyperbaric chamber acrylic, stretcher and associated equipment, including observing the specific kill times of the solution used prior to the delivery of HBOT. 
• See topic: "Cleaning and Disinfection of Hyperbaric Oxygen Monoplace Chamber"

Barotrauma

• A thorough assessment of the patient’s medical history and current condition is essential to identify and mitigate the risk of barotrauma during HBOT.[18] 
• Middle-Ear Barotrauma (MEB): the most common type of barotrauma associated with HBOT is middle-ear barotrauma. Proper patient education on ear-clearing techniques and routine otoscopic evaluations can help prevent MEB.
• Pulmonary Barotrauma (e.g., Pneumothorax): a comprehensive pulmonary assessment is critical, especially for patients with a history of lung disease. Special attention should be given to identifying any condition that may predispose the patient to gas expansion injuries during pressurization or depressurization.
• Absolute Contraindication - Unvented Pneumothorax: an unvented pneumothorax is an absolute contraindication for HBOT due to the risk of life-threatening complications from pressure changes.

Medications in the hyperbaric environment

• The hyperbaric environment creates numerous considerations for the use of drug therapies within it. Physiologic changes to the body due to HBOT may lead to pharmacokinetic changes in drug disposition. In addition, HBOT acts as a drug and can interact, enhance or lessen the physiologic effect of the drug. Most drugs will not interact unfavorably with oxygen.
• For potential interactions of HBOT with other drugs, see topic "Medications In The Hyperbaric Environment".

Oxygen Toxicity

• The hyperbaric staff should be skilled in reducing the potential for and management of oxygen toxicity for the patient receiving HBOT. [18]
• The hyperbaric physician should be notified immediately if a patient experiences signs or symptoms of oxygen toxicity during HBOT.

Pretreatment Considerations

HBOT H&P Relevant to the CHT and CHRN

History of Present Illness (HPI)

• Presence of Type 1 or 2 diabetes or other conditions that might lead to hypoglycemia or hyperglycemia
• History of hypoglycemia or hyperglycemia   
• Unstable blood glucose can increase the likelihood of adverse effects during therapy. Any abnormal values should be reported to the HBOT provider for further patient evaluation and consideration to postpone HBOT until blood glucose is stabilized. Consultation with the diabetes care provider is recommended.
• Hypoglycemia risk: blood glucose levels below 110–150 mg/dL prior to treatment increase the risk of hypoglycemia and seizures, as HBOT can reduce glucose by up to 50 mg/dL. [13]
• Hyperglycemia risk: levels exceeding 400 mg/dL may increase the risk of seizures [19], ketoacidosis, and is at a level that impairs wound healing.  High glucose in patients with diabetes may also be a sign of wound infection.
• Symptoms of hypoglycemia [20]
• Mild Symptoms (Blood glucose level below 70 mg/dl):
• Shakiness, nervousness, anxiety
• Sweating, chills, clamminess
• Rapid heartbeat
• Palpitations
• Hunger
• Moderate Symptoms  (Blood glucose level below 55 mg/dl):
• Dizziness
• Confusion
• Sleepiness
• Weakness
• Irritability
• Difficulty speaking/slurred speech
• Severe Symptoms  (Blood glucose level below 40 mg/dl):
• Seizures
• Loss of consciousness
• Convulsions
• Coma
• Notes:
• Autonomic neuropathy may cause hypoglycemia unawareness.
• Visual observation of the patient is necessary throughout HBOT, as symptoms can develop rapidly. Be familiar with early and late signs.
• Symptoms of hyperglycemia [21]
• High blood glucose levels
• High levels of glucose in the urine
• Frequent urination
• Increased thirst

Past Medical History (PMH)

• Care Coordination
• Identify the healthcare provider responsible for managing the patient’s diabetes.
• Establish communication, as adjustments to antidiabetic medications may be necessary during the course of HBOT.
• Be prepared to educate the diabetes-managing provider about the potential for blood glucose decreases during HBOT and the importance of maintaining safe baseline glucose levels before and after each treatment.
• Nutrition screening
• Document the patient's food and calorie intake before each treatment.
• Advise patients to eat one hour prior to HBOT, focusing on protein and/or complex carbohydrates such as vegetables, whole grains, meat, cheese, and dairy.[13]
• If hypoglycemia is not mitigated by adjusting treatment times, meal times, or having the patient take juice into the chamber, consult the diabetes managing provider to reassess the patient’s diabetes medication regimen.
• Instead of asking vague questions like "Did you eat today?", inquire specifically:
• What did you eat?
• How much did you eat?
• When did you eat?
• This detailed approach offers better insight into potential blood glucose stability during treatment, particularly if recent intake was high in simple carbohydrates or insufficient to support glucose levels in conjunction with antidiabetic medications.
• General recommendation:
• All patients should avoid carbonated beverages before HBOT.
• For details, refer to the blog post "Nutritional Screening for Wound Care and HBOT".
• Daily glucose patterns 
• Assess trends in daily blood glucose readings over several weeks, if available.
• This information can help determine whether the patient is better scheduled for HBOT sessions in the morning or afternoon, based on blood glucose fluctuations.
• Historical HbA1c Documentation
• Ensure HbA1c is in the hyperbaric medical record and findings are shared with the managing provider.
• If no recent value is available, obtaining a HbA1c before starting HBOT is recommended.
• For details, refer to section ‘Laboratory Tests for Blood Glucose Monitoring’ above.
• Devices for Blood Glucose Monitoring and Insulin Delivery
• If patient uses a continuous glucose monitor or an insulin pump, consider the following items: 
• Manufacturer consultation: contact each device’s manufacturer to confirm whether the device is safe for use in the hyperbaric environment. Obtain written documentation outlining clearance, safety precautions, and recommended management during the peri-HBOT period.
• Battery-powered devices: devices with batteries are contraindicated in a 100% compressed oxygen environment due to fire risk.
• Risk of device malfunction: exposure to pressure fluctuations may impair device functionality and result in malfunction.
• External Insulin Pumps
• Pump should be disconnected prior to treatment.
• Insulin pumps with liquid reservoirs may be affected by pressure changes during compression and decompression, potentially leading to incorrect dose delivery.
• Continuous Glucose Monitor (CGM)
• Continuous glucose monitoring systems are widely utilized by both patients with and without diabetes. The basic wearable variety requires a battery, which is not safe in a hyperbaric environment.
• For further guidance, see the section 'Devices for Blood Glucose Monitoring and Insulin Delivery' above.

Medications

• Review antidiabetic medications, including timing of the last dose relative to treatment. See section 'Medications for Blood Glucose Control' above.
• Review other medications that may affect blood glucose (e.g., steroids). 

Physical Exam 

• VS/Measurements: 
• Rapid heartbeat and palpitations: may indicate mild symptoms of hypoglycemia
• PE General:
• Symptoms of hypoglycemia:
• Shakiness, nervousness, anxiety
• Sweating, chills, clamminess
• Hunger
• Symptoms of moderate hypoglycemia:
• Dizziness
• Confusion
• Sleepiness
• Weakness
• Irritability
• Difficulty speaking/slurred speech
• Severe symptoms of hypoglycemia:
• Loss of consciousness
• Coma
• Symptoms of hyperglycemia: 
• Increased thirst
• PE Genitourinary:
• Symptoms of hyperglycemia: 
• High levels of glucose in the urine
• Frequent urination
• Neurologic:
• Severe symptoms of hypoglycemia:
• Seizures
• Convulsions
• Musculoskeletal:
• Mobility
• Determine mobility limitations related to sensory or motor neuropathy.
• Determine if mobility aids or transfer assistance are needed.
• Remove prosthetic devices as part of the pre-HBOT preparation.
• Integumentary: 
• Confirm the presence of diabetic ulcers or other wounds.
• Verify that dressings are approved for hyperbaric use based on the Go/No-Go List.
• Check any wound care products (gels, ointments, creams, or skin care items) for hyperbaric safety.
• Ensure proper offloading (e.g., heels) in monoplace chambers to prevent pressure-related injuries.
• Neurologic: 
• Pain
• Document any neuropathic pain complaints.
• Plan appropriate monitoring and comfort measures during HBOT sessions.

Treatment Considerations

Management in the Monoplace Chamber

• Follow facility policy and protocol guidelines for glucose control during HBOT
• Table 4 shows a summary of suggested actions/interventions for pre- and post-treatment glucose control

Interventions 

• Consider timing of short and long-acting glycemic control medication when scheduling HBOT to avoid peak action time while at depth in the chamber. See section ‘Blood Glucose and Medication Timing in Hyperbaric Oxygen Therapy’ above. 
• Check the blood glucose levels pre-treatment 
• If blood glucose level: ≤120mg/dl, hold HBOT until further direction is given by the hyperbaric physician.
• If blood glucose level is between 120mg/dl – 130mg/dl, consider giving the patient: 
• A complex carbohydrate or nutritional supplement (i.e., Glucerna, Ensure) and,
• 4 ounces of juice to drink pre-treatment and,
• An additional 4 ounces to drink during treatment.
• Hyperbaric tender should maintain visual contact of patient at all times
• Identify signs of hypoglycemia in the patient (e.g., shakiness, nervousness, anxiety, sweating, chills, clamminess, irritability, impatience). See section ‘HBOT H&P Relevant to the CHT and CHRN’ above
• Note the time of occurrence of the symptoms.
• Consider concomitant oxygen toxicity and the need for an air break:
• Ask the patient to place their air mask to their face
• Ask the patient if they feel like these symptoms are similar to symptoms experienced with hypoglycemia
• Instruct the patient to consume juice if it was provided for use during the treatment
• Inform the patient that ascent will begin (continue to consume juice and maintain air mask to the face)
• Reduce chamber pressure to zero. Patient will ascend to surface based on the rate set (i.e., 1-2 psi/min)
• If signs of seizure activity occur, halt decompression immediately. Wait until seizure has ceased and adequate ventilation is observed before continuing ascent.
• At the surface, once the patient is removed from the chamber, immediately check the blood glucose level.[13]
• Report the reaction to the Hyperbaric Physician and proceed as ordered.[2]
• Treat per physician order and institutional policy. 

Considerations for the Multiplace Chamber

• It is possible for attendants to measure blood glucose during HBOT either by sending samples out of the chamber to be analyzed at sea level, or by compressing a glucometer inside the chamber to measure blood glucose at depth. 
• Note: the hyperbaric environment may affect the function of the glucose monitoring equipment if measurements are done in the hyperbaric chamber.

Post Treatment Considerations

Post HBOT Hypoglycemia

• For patients with post treatment blood glucose findings <120 mg/dl, consider giving 1-2 servings of carbohydrate to prevent continual drop in blood sugar. This is an important implication if the patient is driving him/herself from the appointment. 
• Note: carbohydrates convert to blood glucose within 5 minutes of ingestion and will continue to convert for up to 3 hours.
• 1 carbohydrate serving =15 grams of carbohydrates or approximately 80 calories.
• Examples of 1 carbohydrate serving (15 gm of carbohydrate): 
• 1 cup of milk
• 4 crackers
• 1 container of pudding or applesauce
• It is important to have juice (e.g orange, apple, cranberry) and 50% glucose for injection to manage hypoglycemia. For patients with renal conditions, avoid orange juice,