Question 1c

You are called to see a 39 year old female driver in the Emergency Department who has been brought in by ambulance after a motor vehicle crash (head on collision). She is eight months pregnant (first pregnancy), and is complaining of abdominal pain.

(c)        Please discuss the expected physiological changes associated with pregnancy and how they would impact on her management.

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College Answer

Multiple factors: consider the following:

Cardiovascular: vasodilated state with lower baseline BP, higher baseline HR, and higher cardiac output. Masking of initial hypovolaemia, risking foetal circulation, best monitored by foetal heart rate. Large intra-abdominal mass (uterus) puts patient at risk of supine hypotensive syndrome: need to displace uterus or position in left lateral position.

Respiratory: diagphragms pushed up, decreased FRC (need to insert ICCs higher); respiratory alkalosis (expected CO2 30, with HCO3 20): need to keep in mind when assessing blood gases and if ventilating patient. Swollen airway, larger breasts: intubation often difficult.

Gastrointestinal: decreased gastric emptying, and weakened lower oesophageal sphincter: increased risk of aspiration.

Haematological: hypercoagulable state, risk of Rh incompatibility with foetus: potential for Rhesus isoimmunisation.

Foetus: benefits from supplemental oxygen; avoid tetracyclines, quinalones, NSAIDs (premature ductal closure), etc.


The management of the pregnant poly-trauma patient is discussed elsewhere. The answer prepared for Question 3 from the first paper of 2007 is very similar: "Outline the special considerations involved in the care of a pregnant patient involved in multi-trauma.".

In summary:

Airway changes

Bag-mask ventilation becomes more difficult:

  • The nasal mucosa is engorged, which means there is greater resistance to flow
  • The upper airway mucosa is oedematous
  • There has been weight gain

Laryngoscopy becomes more difficult:

  • Upper airway oedema
  • Breast enlargement
  • The Mallampatti grade changes during pregnancy, largely because of oedema of the pharynx, and due to weight gain. It gets even worse with labour.

Less time is available for intubation:

  • Decreased FRC, less time to intubate
  • Increased oxygen consumption, less time to intubate

Intubation is more risky

  • Increased risk of aspiration, decreased stomach emptying

Respiratory changes

  • The diaphragm is pushed up by 4cm
  • Tidal volume increases by ~ 30-50%
  • Respiratory rate increases to 15-17
  • Minute volume increases by 20-50%.
  • Chest wall compliance decreases 
  • Lung compliance remains the same 
  • FRC decreases during pregnancy, due to compression of the diaphragm by the gravid uterus.
  • pH increases to 7.40-7.47
  • PaCO2 decreases to 30 mmHg
  • PaO2 increases to 105 mmHg
  • HCO3- decreases to 20 mmol/L
  • Maternal 2,3-DPG increases 
  • p50 remains the same because of alkalosis 

Circulatory changes

  • Cardiac output increases (from 5L/min to 7L/min)
    • Stroke volume increases (from 65ml to 80-90ml)
    • Heart rate increases (from 75 to 85-90)
    • Systemic vascular resistance decreases (down by as much as 40%) - in fact, the vascular system becomes fairly refractory to the effects of vasoconstrictors such as angiotensin and vasopressin
    • The IVC is compressed by the gravid uterus in the supine position, decreasing the preload
  • Blood pressure decreases (and is lowest in the second trimester)
  • Pulmonary vascular resistance decreases
  • Pulmonary artery wedge pressure remains unchanged
  • Blood volume is increased by 50%
  • CVP remains unchanged
  • Colloid oncotic pressure decreases
  • Oxygen consumption increases by 20% during pregnancy

Electrolyte and endocrine changes

  • Vasopressin release increases;
  • Thus, there is water retention
  • A hypervolemic hypoosmolar state develops
  • In response to a decreased SVR, aldosterone release is increased. This is the major contributor to the 50% circulating volume expansion
  • There is a relative iodine deficiency (the foetus is stealing it all)
  • Cortisol secretion is increased, which has implications for all those people who still do random cortisol levels on their patients

Renal changes

  • Renal blood flow increases: the renal arteries are also affected by the fall in SVRI, and this is mediated by relaxin (which influences endothelial nitric oxide production).
  • GFR increases by as much as 85%
  • Urea and creatinine decrease because of this
  • Kidneys become enlarged; the renal pelvis dilates and there is a "physiological hydronephrosis" - more so on the right because the right ureter crosses iliac and ovarian vessels at an angle. This predisposes to pyelonephritis
  • Tubular resorption of urate and glucose decreases

Gastrointestinal and nutritional changes

  • Nausea and vomiting: in 50-90%. 
  • Oesophageal sphincter tone is decreased (aspiration is more likely)
  • There is increased intragastric pressure due to upward displacement
  • Gastric emptying is delayed, and is virtually non-existant during labour
  • Thiamine supplementation is important, because prolonged hyperemesis can result in vitamin deficiency.
  • Abdominal compartment pressure measurements are going to be wildly inaccurate.
  • There is insulin resistance, particularly later in pregnancy
  • Metabolic fuel use favours lipolysis, preserving the glucose and amino acids for use by the foetus.
  • Protein catabolism is decreased
  • There is a peak of calcium demand in the third trimester


Oh's Intensive Care manual: Chapter 64   (pp. 684) General  obstetric  emergencies by Winnie  TP  Wan  and  Tony  Gin


Soar, Jasmeet, et al. "European Resuscitation Council Guidelines for Resuscitation 2010 Section 8. Cardiac arrest in special circumstances: Electrolyte abnormalities, poisoning, drowning, accidental hypothermia, hyperthermia, asthma, anaphylaxis, cardiac surgery, trauma, pregnancy, electrocution." Resuscitation 81.10 (2010): 1400-1433.


Mattox, Kenneth L., and Laura Goetzl. "Trauma in pregnancy." Critical care medicine 33.10 (2005): S385-S389.


DROST, THOMAS F., et al. "Major trauma in pregnant women: maternal/fetal outcome." Journal of Trauma-Injury, Infection, and Critical Care 30.5 (1990): 574-578.