A 36 week pregnant woman is involved in a car crash and suffers fractures to her left femur and tibia and left ribs 4-8. What are the cardiorespiratory changes in normal pregnancy?
How do they effect her response to these injuries?
This question had two parts. Lists would suffice. For example: (a) Cardiorespiratory changes include:
• Increased blood, plasma and Rd cell volume from 6 weeks. maximal at 28 to 32 weeks
• Increased cardiac output (33% by 10 weeks.to 40-50'/o by 28 to 32 weeks)
• Decreased blood pressure due to low SVR
• Susceptibility to aorto-caval compression develops during second trimester (maximal at 36-
• Cardiac hypertrophy with increased wall thickness and chamber volume.
• Left axis deviation, horizontal heart
• Hb decreased due to relative haemodilution
• Upper respiratory tract oedema and capillary engorgement
• Increased minute volume, respiratory rate, V, lV, RR. Chronic respiratory allcalosis
• Decreased FRC, RV, TLC, AWR
(b) The clinical effects on her response to the injury include:
• Larger blood volume allows blood loss to be relatively better tolerated
• Susceptible to supine hypotension
• Susceptible to basal atelectasis and hypoxia
• Difficult intubation
• High Vand low FRC means that hypoxia and hypercarbia develop rapidly with airway
obstruction. apnoea etc
This question forms a part of the "manage this pregnant trauma patient" spectrum of fellowship questions. For a general reference, one is directed to Question 3 from the first paper of 2007 (Outline the special considerations involved in the care of a pregnant patient involved in multi-trauma.). That answer also covers section (b) of the current question ("How do they effect her response to these injuries?")
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.".
Bag-mask ventilation becomes more difficult:
Laryngoscopy becomes more difficult:
Less time is available for intubation:
Intubation is more risky
Electrolyte and endocrine changes
Gastrointestinal and nutritional changes
Specific features of the cardiorespiratory changes in pregnancy can be found on the page dedicated to this topic. In brief summary, they are as follows:
|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|
|pH increases||to 740-7.47|
|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|
|Heart rate||Increased (from 75 to 85-90)|
|Stroke volume||Increased (from 65ml to 80-90ml)|
|Cardiac output||Increased (from 5L/min to 7L/min)|
|Systemic vascular resistance||Decreased|
|Pulmonary vascular resistance||Decreased|
|Pulmonary artery wedge pressure||Unchanged|
|Blood volume||Increased by 50%|
|Renal blood flow||Increased by 30-80%|
|Resting oxygen consumption||Increased by 20-30%|
|Colloid oncotic pressure||Decreased|
Critical Care Medicine has dedicated an entire supplement to the influence of pregnancy in critical care: Volume 33 Supplement 10 October 2005 - pg. S247-S397
Additionally, UpToDate has an excellent summary for the paying customer.
Hunter, Stewart, and Stephen C. Robson. "Adaptation of the maternal heart in pregnancy." British heart journal 68.6 (1992): 540.
Metcalfe, James, and Kent Ueland. "Maternal cardiovascular adjustments to pregnancy." Progress in cardiovascular diseases 16.4 (1974): 363-374.