Conditions
Change during pregnancy
Normal pregnancy values
Cardiovascular
Heart rate
Increases 15–20 bpm
75–95 bpm
Cardiac output
Increases 30–50 %
6–8 l/min
Mean arterial blood pressure
Decreases 10 mmHg in mid trimester
80 mmHg
Systemic vascular resistance
Decreases 10–15 %
1200–1500 dyn/s/cm-5
ECG
Flat or inverted T waves in leads III, V1 and V2
Q waves in leads III and aVF
Hematologic
Blood volume
Increases 30–50 %
4500 mL
Erythrocyte volume
Increases 10–15 %
Hematocrit
Decreased
White blood cell count
Increased
5000–15,000/mm3
Factors I, II, V, VII, VIII, IX, X and XII
Increased
Fibrinogen
Increased
>400 mg/dL
Prothrombin time
Decreased by 20 %
Partial thromboplastin time
Decreased by 20 %
Respiratory
Tidal volume
Increased 40 %
700 mL
Minute ventilation
Increased 40 %
10.5 mL
Expiratory reserve volume
Decreased 15–20 %
550 mL
Functional residual capacity
Decreased 20–25 %
1350 mL
Upper airway
Increased oedema; capillary engorgement
Diaphragm
Displaced 4 cm cephalad
Thoracic anteroposterior diameter
Increased
Risk of aspiration
Increased
Respiratory rate
Slightly increases in the first trimester
Oxygen consumption
Increased 15–20 % at rest
Blood gas
pH
Unchanged
7.4–7.45
PCO2
Decreased
27–32 mmHg
PO2
Increased
100–108 mmHg
HCO3
Decreased
18–21 mEq/L
Abdomen and genitourinary system
Intra-abdominal organs
Compartmentalization and cephalad displacement
Gastrointestinal tract
Decreased gastric emptying; decreased motility; increased risk of aspiration
Peritoneum
Small amounts of intra-peritoneal fluid normally present; desensitized to stretching
Musculoskeletal system
Widened symphysis pubis and sacroiliac joints
Kidneys
Mild hydronephrosis (right > left)
Renal blood flow
Increased 50–60 %
700 mL/min
Glomerular filtration rate
Increased 60 %
140 mL/min
Serum creatinine
Decreased
<0.8 mg/dL
Serum urea nitrogen
Deceased
<13 mg/dL
The most obvious and dramatic change during pregnancy is the enlargement of the uterus brought about by the growth of the foetus. The uterus becomes an intra-abdominal organ at approximately 12 weeks of gestation. At 20 weeks, the vertex of the uterus can be palpated at the level of the umbilicus, and by the 36th week, the uterus reaches the costal margin. In the last few weeks of pregnancy, fundal height decreases as the foetal head engages into the pelvis in preparation for the birth.
Anatomical changes during pregnancy should be borne in mind when interpreting initial radiological assessment of the patient. The elevation of the diaphragm by approximately 4 cm and its widening by 2 cm during late pregnancy should be appreciated on the chest radiograph. This may give the appearance of widened mediastinum and an enlarged heart. Increased levels of circulating progesterone lead to the softening of the sacroiliac ligaments, hence widening the joint space. The pubic symphysis may also be widened by 4–8 mm [16].
The changes of the cardiovascular system are numerous and begin from the 8th week of gestation. Progesterone induces relaxation of the smooth muscle in the walls of the peripheral vasculature. There is a gradual decline in blood pressure from week 10 reaching its lowest point by week 28 of gestation. In the third trimester, the blood pressure gradually returns to pre-pregnancy levels. The heart rate also shows an increase by 10–15 beats per minute driving an increase in the cardiac output of 30–50 %. This gradually returns to normal over the first 2 post-partum weeks. There is a 50 % increase in the blood volume which is mostly due to an expansion of the plasma volume with only 30 % increase in the volume of red cells. This brings about a dilutional anaemia referred to as physiological anaemia of pregnancy. The hypervolaemic and hyperdynamic circulation allows the mother to tolerate blood loss of 500–1000 mL with little change in blood pressure and pulse rate. This however is achieved to the detriment of the foetus following trauma. Vasoconstriction of uterine and splanchnic blood vessels and diversion of circulatory volume masks maternal blood loss although signs of foetal distress will be apparent prior to the mother showing the expected signs of shock [17].
Almost all of the coagulation factors increase in pregnancy. This along with the expansion of blood volume and cardiac output are important adaptations for the expected blood loss at the time of delivery [11]. This hypercoagulable state predisposes the mother to thromboembolic disease.
The respiratory system also undergoes some changes. There is engorgement of the respiratory mucosa that leads to difficulties in intubation and mucosal bleeding [18, 19]. This may result in severe airway compromise. There are also adaptations related to the increased metabolic demands. The presence of the foetus necessitates an increase in oxygen consumption of 15–20 %. Progesterone stimulates the respiratory centre leading to hyperventilation, which brings about a compensated respiratory alkalosis with a concomitant drop in the PCO2. There is a 4 cm elevation of the diaphragm with a 2 cm increase in the thoracic anteroposterior diameter. This results in a 20–25 % decrease in the functional residual capacity [15]. The pregnant patient is therefore much less tolerant of hypoxia and the associated acidosis. Foetal oxygenation remains constant if maternal PaO2 is kept above 60 mmHg, because below this level there is a profound drop in foetal oxygenation [11].
Progesterone reduces gastrointestinal motility and the gravid uterus displaces the stomach cephalad. This results in the incompetence of the gastroesophageal pinchcock mechanism placing the pregnant patient at greater risk of regurgitation and aspiration [20]. Therefore, all pregnant patients should be assumed to have a full stomach and the threshold for insertion of a gastric tube lowered.
In the genitourinary system, there is gradual ascent of the uterus from the pelvis where it is well protected into the abdomen from the 12th week of gestation. Once the uterus becomes intra-abdominal, it is at greater risk of injury from blunt and penetrating trauma. The bladder is displaced anteriorly and superiorly. The renal pelvis and the ureters become dilated due to the compressive effect of the uterus as well as the effect of circulating progesterone. The increased cardiac output and blood volume increases renal perfusion by up to 60 % with a concomitant increase in the glomerular filtration rate. This leads to a significant reduction in the serum urea and creatinine levels [15].
18.3 Assessment of the Injured Pregnant Patient
18.3.1 General Assessment
The initial assessment and management of the injured pregnant patient follows the well-established routine of Advanced Trauma Life Support. The best initial treatment of the foetus is the provision of optimum resuscitation for the mother accompanied by foetal monitoring particularly when the foetus is viable. The safe and judicious assessment of the pregnant patient should be a multidisciplinary exercise with the early involvement of an obstetrician, neonatologist, radiologist and trauma surgeon [11, 15, 16, 21, 22].
Pregnant trauma patients can be divided into four groups. The first group are women, who are not aware that they are pregnant. Therefore, all female trauma patients in the reproductive age group should have a pregnancy test performed [23]. Identification of these patients is especially important because routine radiographic studies, performed in the trauma assessment, have the greatest teratogenic potential in early pregnancy. But this consideration should not interfere with life-saving investigations or interventions for the patient. Patients belonging to the second group are injured women of less than 26 weeks of gestation. In these patients, resuscitation is aimed primarily at the mother since the foetus is not yet independently viable. The third and perhaps the most challenging group consists of women with pregnancies more than 26 weeks of gestation. At this stage, there are two patients to consider during the assessment and resuscitation. Finally there are those patients, who present in the perimortem stage. In these patients, early caesarean section may facilitate maternal resuscitation and preserve the life of the foetus [16].
After 20 weeks of gestation, nursing the pregnant patient supine will induce supine hypotension syndrome as the gravid uterus compresses the vena cava, reducing the venous return and embarrassing maternal cardiac output by 30 %. This can be alleviated by either displacing the uterus to the left side or, if possible, to nursing the patient tilted left side down by 15°. Due to reduction in the mother’s respiratory reserve, supplemental oxygen should be provided. Loss of up to 2000 mL of blood is well tolerated, but this is at the expense of uterine blood supply. The use of vasopressors further compromises uterine blood flow and their use should be avoided unless it is a life-saving intervention. Monitoring of uterine activity and the assessment of the foetus is imperative and should continue for 2–6 h after an injury, even with relatively minor trauma [24, 25]. Signs of foetal distress may be the first signs of maternal hypovolaemia and haemodynamic compromise. The use of vasopressors should be avoided as they further embarrass uteroplacental perfusion. It is preferable to manage cardiac output and blood pressure by replacing volume.
In case of a positive Kleihauer-Betke test, indicating foetal blood in the maternal circulation, the rhesus-negative patients should receive anti-D antibody to prevent isoimmunization [26–28].
As part of the secondary survey, a complete medical and obstetric history should be obtained, particularly details relating to pre-existing hypertension, eclampsia and diabetes. Information about the mechanism of injury, use of drugs and alcohol should be sought. Otherwise, all limbs and body system should be examined in the usual manner. Radiological examination of all suspected fractures should be carried out with the involvement of a radiologist, as a close check needs to be kept on the cumulative dose of radiation received by the patient [22, 29–32].
Early vaginal examination is important. Ideally, this should be performed with an obstetrician in attendance to assess cervical effacement and dilation, foetal position and the presence of amniotic fluid or blood. In the presence of vaginal bleeding, it is prudent to rule out a placenta previa prior to the formal examination of the cervix [31]. The bleeding may be due to placental abruption, labour or placenta previa. Other more traumatic causes such as uterine rupture and an open pelvic fracture must also be considered.
Focused Assessment with Sonography (FAST) scan is important to assess the presence of intra-abdominal haemorrhage. An ultrasound examination of the foetus and placenta can be performed after the FAST scan or incorporated as part of the trauma scan. If a chest tube thoracostomy is needed, it has to be placed one or two intercostal spaces higher than usual to avoid diaphragmatic injury.
Tetanus prophylaxis is not contraindicated and should be administered according to standard protocols.
18.3.2 Radiological Assessment
18.3.2.1 General Considerations
Trauma in pregnancy represents a special situation as two patients are involved – the mother and the child. Radiographic and CT examinations of the pregnant patient irradiate the unborn and can cause severe harm. Intrauterine development consists of three phases and radiation sensitivity is related to gestational age.
As a general guideline, the “ALARA Principle” should be mentioned. It entails that radiation should be used “as low as reasonably achievable” [33].
18.3.2.2 Basics of Radiation Protection
The following types of radiation have to be differentiated: α-, β-, γ- and x-rays. For medical imaging, only γ-radiation (nuclear medicine) and x-rays are used.
Important Units for Radiation Benchmarking
Ion dose: measures radiation by the amount of the induced ionization – the SI unit is R.
Absorbed dose: defines the absorbed dose per kg mass, the SI unit is gray (Gy) = 1 J/kg.
Dose output: is dose/time, the SI unit is Gy/s.
Due to the inherent different properties of α-, β-, γ- and x-rays, they are converted into units that are representative of their varying biologic activity. This is achieved by multiplying the absorbed dose by a dimensionless radiation weighting factor (WR, prior Q – relative biological effectiveness). The result is the dose equivalent, which is measured in sievert (Sv):
Sievert (Sv) = Gy × WR – the corresponding values can be found in Table 18.2.
Radiation type
Radiation weighting factor
Photons
1
Electrons, muons
1
Neutrons
<10 keV
10 to 100 keV
>100 keV to 2 MeV
>2 to 20 MeV
>20 MeV
5
10
20
10
5
Protons (energy > 2 MeV)
5
α−Radiation
20
Organ dose: represents the absorbed dose output of an organ, tissue or body part, which is multiplied by the radiation weighting factor – the SI unit is again Sv.
Effective dose equivalent: considers the different radiation sensitivity for various human tissues by the so-called tissue/organ weighting factor (W t – Table 18.3). The effective dose equivalent is calculated by first multiplying the organ dose with the tissue/organ weighting factor, followed by adding all individual doses.
Table 18.3
Tissue/organ weighting factor with due consideration of the different sensitivity of tissues/organs to radiation [35]
Tissue/organ | Weighting factor (Wt) |
|---|---|
Gonads | 0.08 |
Red bone marrow | 0.12 |
Colon | 0.12 |
Lung | 0.12 |
Stomach | 0.12 |
Urinary bladder | 0.04 |
Mamma | 0.12 |
Liver | 0.04 |
Oesophagus | 0.04 |
Thyroid | 0.04 |
Skin | 0.01 |
Bone surface | 0.01 |
Brain | 0.01 |
Salivary glands | 0.01 |
Others | 0.12 |
Natural Background Radiation
The source of natural background radiation falls into two broad categories – natural (from ground and space) and artificial (medicine, radioactive fallout, nuclear waste, consumer products, etc.). The cumulative dose is approximately 4 mSv. It is interesting to note that medical diagnostic imaging and nuclear medicine are responsible for about 79 % of man-made radiation [36]. Typical radiation doses for medical imaging can be found in Table 18.4.
Table 18.4
Typical effective doses in imaging – can vary due to technical factors (e.g. additional filtration) as well as adjustment of the exposure settings to body mass/size, age and several other factors [37]
Examination | Typical effective dose (mSv) | Number of chest x-rays leading to the comparable exposure |
|---|---|---|
Chest (p.a.) | 0.02 | 1.0 |
Extremities/joints | 0.01 | 0.5 |
Skull | 0.07 | 3.5 |
Thoracic vertebra | 0.70 | 35.0 |
Hip | 0.30 | 15.0 |
Pelvis | 0.70 | 35.0 |
Mammography (bilateral, two planes) | 0.50 | 25.0 |
Intravenous urography | 2.50 | 125.0 |
Head CT | 2.30 | 115.0 |
Chest CT | 8.00 | 400.0 |
Abdomen/pelvis CT | 10.00 | 500.0 |
Renal function scintigraphy | 0.80 | 40.0 |
Thyroid scintigraphy | 0.90 | 45.0 |
Lung perfusion scintigraphy | 1.10 | 55.0 |
Skeletal scintigraphy | 4.40 | 220.0 |
Myocardial perfusion scintigraphy | 6.80 | 340.0 |
Positron emission tomography | 7.20 | 360.0 |
Myocardial scintigraphy | 17.00 | 865.0 |
Deterministic Versus Stochastic Radiation Effects
In deterministic effects, there is a classic dose–effect relationship such as the LD50/30 (the dose of whole-body irradiation where 50 % of subjects die within 30 days) [38] of ~4.0 Sv, or after a 3.0 Sv there are severe skin burns, after 3.0–4.0 Sv cataracts occur – just to name some examples.
Stochastic effects are those that occur in a random manner, including cancer and genetic defects. These events cannot be related to a single dose but the cumulative effect of multiple exposures may result in damage and for this reason, the concept of the excess lifetime risk was introduced. The risk is higher for younger people, which can be partly explained by the higher sensitivity of dividing cells to radiation. The “International Commission on Radiation Protection (ICRP)” suggests an excess rate of 5 % per Sv for lower doses and 10 % for higher ones.
An excess lifetime risk factor of 10 % means after exposing 10,000 individuals to 10 mSv dose of radiation, there will be about ten additional deaths due to leukaemia or cancer, but it is important to note that even without this radiation there would be 2,500 cancer-related deaths [37].
Radiation Effects During Intrauterine Life
The following facts are based on the report of “German Society for Medical Physics” and the “German Roentgen Society” [39]. A summary of all effects can be found in Table 18.5.
Effect | Gestational age | Lower threshold (mSv) | Risk-coefficient |
|---|---|---|---|
Death during pre-implantation phase | 0–10 days | 100 | 0.1 %/mSv* |
Malformation | 10 days–8 weeks | 100 | 0.05 %/mSv* |
Severe mental retardation | 8–15 weeks 16–25 weeks | 300 300 | 0.04 %/mSv* 0.01 %/mSv* |
IQ-reduction | 8–15 weeks 16–25 weeks | 0.03 IQ/mSv 0.01 IQ/mSv | |
Cancer/leukaemia | 0.006 %/mSv | ||
Genetic defects | 0.0003 %/mSv male 0.0001 %/mSv female |
The period of intrauterine life can be divided into three phases. These are the pre-implantation phase (until 10 days post-conception), the phase of organogenesis (10 days to 8 weeks of gestation) and the foetal period (from the 3 months of gestation to term). Exposure to radiation in each phase has characteristic effects.
Related posts:
Full access? Get Clinical Tree
