Pregnancy in Military Aviation - asmameeting.orgasmameeting.org/asma2013_mp/pdfs/asma2013_present_045.pdf · Pregnancy in Military Aviation Hazards, Risks, and Controls ... • Functional

Distribution A: Approved for public release; distribution is unlimited. Case Number: 88ABW-2013-2293, 13 May 2013

Pregnancy in Military AviationPregnancy in Military AviationHazards, Risks, and ControlsHazards, Risks, and Controls

Prepared by: Michael Acromite, MD, MSPH, FACOG CDR, MC, USN

Presented by: Dr. Dan Van Syoc

2Distribution A: Approved for public release; distribution is unlimited. Case Number: 88ABW-2013-2293, 13 May 2013

Disclosure

• The views expressed are those of the author and do not necessarily reflect the views of the United States Air Force or the United States Government.

• I have no relevant financial relationships to industry.


Pregnancy in Aviation

• Pregnancy is not a disease by itself

• Pregnant women can fly safely, properly assessed

• Pregnancy is associated with often unrecognized aeromedical risk

• Uncertainty in hazards- – Variable physiology across pregnancies– Variable physiology within pregnancies– Limited research

• Understanding the risks within a collective collaboration among providers can control risk and improve safety


Aeromedical Hazards of Pregnancy

• Physiological changes

• Pregnancy-specific conditions

• Preexisting medical conditions

• Effects on medication use

• Environmental effects on mother

• Environmental effects on fetus

• Increase risk individually and in combination


Physiological ChangesOften Unrecognized or Imperceived

• Hypercoagulability• Hemodynamics• Cardiovascular• Gastrointestinal• Pulmonary• Endocrine

• Vision• Renal• Immune• Ergonomic• Sleep Pattern• Heat Exposure


Physiological Changes

• Vision– Corneal thickening affects visual acuity

• Related to corneal edema• Begins as early as first trimester• Variable within and across pregnancies

– Visual acuity checked at least every 2 weeks • when asymptomatic

– Vision checked promptly for visual symptoms

– Contact lens use is not recommended for correction



• Hypercoagulability

– Pregnancy is a hypercoagulable state• VTE 5-fold increase: #1 cause of maternal mortality (9% of deaths)• VTE: 1-2 /1000 pregnancies; 1.1 deaths/1000 pregnancies• 70-80% DVT; 15-25% PE; 50% during and 50% postpartum• Changes: Fibrinogen, vWF, Factors (V, VIII, X), plasminogen

– Preexisting thrombophilia further increases risk• Factor V Leiden- 20-25% of all VTE in pregnancy• Screening not generally recommended• Factors for screening may be identified by history

– Venous stasis• Pelvic vascular compression; Periods of inactivity



• Hemodynamics– Increased blood volume

• Increased plasma to red cell mass ratio: relative anemia

• Decreased oncotic pressure:

– favors generalized edema

– Increased susceptibility for pulmonary edema

– Iron deficiency- maternal

• Increased iron use for fetal requirements– Oxygen disassociation curve – pH change

• Respiratory alkalosis favors oxygen transfer to fetus

– May affect blood pressure, G-tolerance, vision, fatigue



• Cardiovascular– 10-fold increase in uterine blood flow

– Uterine compression of pelvic veins and vena cava• Decrease venous return and cardiac preload

– Blood pressure decrease – typical, lowest in 2nd trim• Low resistance in placenta

• Decreased systemic vascular tone

• Progesterone relaxes smooth muscle and compliance

• Decreased pressor response

– Effects on G-tolerance, hypoxia tolerance, vision, fatigue



• Pulmonary– 40% increase in tidal volume

• Hyperventilation, hypocapnia

• Respiratory alkalosis, increased pH,

– 20% decreases in these lung volumes:• Reserve volume

• Residual volume

• Functional residual capacity

– More susceptible• Infection and pulmonary edema

– Effect on hypoxia tolerance, rapid decompression



• Renal– 50% increase in renal blood flow and GFR

– 60-80% increase in renal plasma flow

– Medication clearance increased

– Increased urine production• Dehydration, urinary frequency, urgency

– Progesterone relaxes ureters – decrease motility• Ascending infections• Nephrolithiasis

– Effects on G-tolerance, fatigue, distraction, pain



• Gastrointestinal– Progesterone relaxation of smooth muscles

– Decreased motility, relaxed LES

– Increased nausea, retching, and vomiting• Hyperemesis gravidarum

– Anti-emetic: meds, OTC, non-pharm• Aviation: noncompatible (meds) vs. compatible

(effective?)

– Effects: distraction, dehydration, pain



• Endocrine– Diabetogenic state

• Placental hormones: – increase with gestational age and placenta size

• H. chorionic somatomammotrophin (H. placental lactogen):– Prepares breasts for lactation– Major contributor to insulin resistance

• Estrogen and progesterone: some insulin resistance• Favors fetal glucose availability

– Gestational diabetes or glucose intolerance– Screened at 26-28 weeks, sooner for risk– Management:

• Diet, Glyburide, Insulin, Metformin• Monitoring



• Immune System– Generalized suppression

• Tolerance to fetal antigens

• Susceptibility to infection

– Vaccinations• No live virus vaccinations

– Except if disease risk exceeds risk to pregnancy (rare)

• Other vaccines per CDC guidelines– Influenza

– Diphtheria, pertussis, tetanus

– Others



• Ergonomic– Body size, BMI

– Breast enlargement

– Weight distribution

– Generalized edema

– Cockpit and safety equipment fittings

– Egress

• Sleep– Disturbances more

common in pregnancy

– More common as pregnancy progresses

– Fatigue issue


Environmental EffectsHeat Exposure

• Mother– Pregnancy generates

more heat

– Increased maternal BMI

– Flight gear- heat retention

– Dehydration

– Heat intolerance

• FetusHeat exposure:– Increased birth

defects possible• Neural tube defects

– Increased preterm labor possible


Environmental EffectsFetus

• Noise and Vibration– Fetal hearing

developed before 20 weeks

– Newborn hearing deficits possible

– Excess noise associated with growth restriction

• Radiation– 1st trimester greatest

risk for possible effects

– <50 mSv: no effect– 10 hour civilian flight

average: 0.5 mSv

– Little effect

– May be greater for military flights


Pregnancy-Specific ConditionsCreates “High Risk” Pregnancies

• Miscarriage• Ectopic• Molar pregnancy• Uterine anomalies• Incompetent cervix• Vaginal bleeding• Unexpected pain• Congenital defects• Multiple gestation

• Preterm labor• Rupture of

membranes• Preeclampsia

– Headaches/seizure

• Thyroid dysfunction• Gestational diabetes• Oligohydramnios• Chorioamnionitis• Growth restriction


Preexisting Medical ConditionsAffected by Pregnancy

Preexisting Conditions and/or Treatments Conditions & potential pregnancy changes:

– Hypertension, thyroid, diabetes– IBD, IBS, dermatologic– Migraines, SLE, arthritis– Psychiatric/psychological– Others

Medications – Change to pregnancy-compatible medication– Adjust dose to fit distribution and clearance– May be different than what has been tolerated in flight,

or those waived for flight.


Military Training RequirementsAviation

• Aviaition Physiology and Safety Training– Pool– Egress– Hypobaric Chamber

– Hypoxia training

• Not allowed during pregnancy– Waived until after pregnancy: USAF

– Not Allowed and Not Waived: USN

– Must be considered in waiver disposition


Military Waiver to Continue Flying

• Waivers– Trained aircrew only

• Not for untrained or while in-training

• Instructor pilots – must have qualified co-pilot

– Special consideration for ATC, GBC, MOD

– Initiated by the pregnant female

– Concurrence: Flight Surgeon, OB, and Command

• General requirements: for physiological considerations– 13-24 weeks USAF; 12-28 weeks: USN, USA, USCG

– Multi-crew, pressurized, non-high performance

– Non-ejection seat


Monitoring in Pregnancy

• Ultrasound – Normal & Intrauterine

• Accurate dating– Waiver period

assignment

• Anemia• Hypotension• Hypertension• Training Qualification

• Visual acuity• Blood sugar• Infections: pulm/urine• Pregnancy-specific

conditions• Preexisting

conditions• Medication changes• Flight associated

symptoms


Postpartum

• Physiological change resolution– 6 weeks postpartum to resolve– 6 weeks for thrombosis risk, greatest in the first week

• Pregnancy-related disease resolution– Preeclampsia, diabetes, others: 6 weeks

• Preexisting condition stabilization– Reestablish medications and control

• Complications of pregnancy/delivery resolution– Depends on delivery method and complication

• Postpartum depression consideration• Breast feeding consideration• Physiology qualification status


Hazard Control – Risk Management

• Uncertainty of hazards increases calculated risk– Unknown/unrecognized risk – unmanageable

– Known risks – manageable if recognized

• Pregnancy Uncertainties:

Anxiety, inconsistency, miscommunication, misperception, misunderstanding, complacency– Variability across pregnancies

– Variability within pregnancy

– Limited human research

– Unperceived changes with strong desire to fly


Hazard Control – Risk Management

• A normal pregnancy can fly safely, with ORM– Not for high-risk pregnancy– Discontinue when risk status increases

• Requires: Coherent Collaboration of Care– Flyer, Flight Surgeon, OB Care, Command

• Different levels and areas of understanding the associated risks• Different perception of associated risks• Need a Shared Mental Model (TeamSTEPPS)

– Understanding of hazards and risks• Communicate aeromedical, medical, and operational risk

– Appropriate monitoring and assessment• Recognize variable conditions of increased risk:

– Physiological, Medical, Fetal, Enviromental


Pregnancy in Aviation

• Operational medical risk management

• Understanding policy and areas of risk

• Appropriate monitoring and reporting

• Teamwork: coherent collaboration

• Consistent application for female flyers

• Safety for pregnant pilots, aircrew, and fetus

• Appropriate return to flying postpartum


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Pregnancy in Military Aviation - asmameeting.orgasmameeting.org/asma2013_mp/pdfs/asma2013_present_045.pdf · Pregnancy in Military Aviation Hazards, Risks, and Controls ... • Functional