You are called to assess a 38 year old female with respiratory failure in the Emergency  Department.  This  is  her  first  pregnancy  and  she  is  28  weeks pregnant   after  several   attempts   at  IVF.  She  is  positive  for  Swine-Origin Influenza Virus (H1N1).

Arterial blood gas on a FiO2 of 0.8 shows:

  • pH  7.31 
  • pCO2  48 mm Hg
  • pO55 mm Hg
  • Bicarbonate 18 mmol/L

Evaluation of the foetal heart reveals significant bradycardia.

a)  Outline the specific challenges in this case that distinguish it from a similar illness in a previously healthy 38 year old male.

b)  Outline your specific approach to the management of this case.

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College Answer

a)  Outline the specific challenges in this case that distinguish it from a similar illness in a previously healthy 38 year old male.

•    Precious pregnancy in older, primiparous patient.
•    Known high incidence of morbidity and mortality in mother and foetus with H1N1
Influenza infection with severe CAP.
•    Requirement to work closely with specialist obstetric team and rationalising potentially conflicting priorities eg. timing of delivery of foetus.

•    Anatomical and Physiological considerations during pregnancy- elevated diaphragm and decreased FRC, decreased chest wall compliance, increased risk of aspiration during intubation, pressure of gravid uterus on IVC (and aorta) decreasing venous return (and increasing afterload) in the supine position.

•    Maintaining effective foeto-placental circulation while optimising maternal outcome.
•    Safety of various drugs in pregnancy eg. anti-virals, sedatives.
•    History of severe asthma complicating current episode of severe CAP likely to make ventilatory strategy more complex.

•    Importance of keeping family members well informed of considerations and likelihood of poor foetal outcome as priority will be given to mother’s survival.

b)  Outline your specific approach to the management of this case.

Immediate- 
•    Clinical scenario described requires rapid resuscitation.
•    Airway- Secure early, rapid sequence induction. Anticipate difficult airway (ensure help and difficult airway equipment available.
•    Breathing- Ventilate with protective lung strategy.  Example of Settings – SIMV/PC, FiO2-1.0 PC to achieve Tidal Volumes of 6-8ml/kg, Low rate- 6-8/min I:E ratio 1:3-4 to allow adequate expiratory time, PEEP 10-15cm titrated to oxygenation. Close monitoring with regular blood gas evaluation. Tolerate hypercapnia (although not ideal for foetus) if poorly compliant lungs. Position at least 30 degrees head-up to optimise respiratory mechanics. Sedate heavily to minimise oxygen consumption. Neuromuscular blockade if required to facilitate ventilation.

•    Circulation-. Fluid resuscitate (likely to be volume depleted) to clinical endpoints, vasoconstrictors to maintain perfusion pressure (eg MAP>60mmHg). Assessment of cardiac output if unstable haemodynamics with these measures (eg. echocardiogram, PiCCO, PA catheter, ScVO2)- High cardiac output expected due to
pregnancy and infection. Inotropes if cardiac output low. Position slightly left lateral to relieve IVC compression.

•    Early specialist obstetric evaluation to determine foetal condition, position of placenta and risk versus benefit of delivery of foetus may need to be considered carefully taking into consideration maternal and foetal factors.

Discussion

If we trim the psychosocial fat away from the lean physiology, there are several considerations in the management of this ARDS patient

Specific challenges:

  • Decreased FRC and chest wall compliance
  • ARDS management cannot use "permissive hypercapnea" as the fetal hemoglobin will decrease in its affinity for oxygen, thus CO2 should be kept no higher than 45mmHg. The second part of the college answer mentions this. An article commenting on one author's experience suggests that the intensivist should ignore this, as making attempts to increase minute ventilation will overload the right heart.
  • Must avoid hypoxia in order to maintain foetal wellbeing (already bradycardic, thus likely already hypoxic)
  • Need to monitor foetus closely, deliver when permissible by foetal survival
  • Safety of various drugs in pregnancy

Major pregnancy-related limiting factors which complicate the management of ARDS are as follows:

  • Intubation will be difficult, for well-known reasons.
  • Need to maintain normoxia to maintain a satisfactory foetal oxygen transfer gradient
  • Cannot tolerate permissive hypercapnea as this runs the risk of foetal acidosis. Foetal hemoglobin will decrease in its affinity for oxygen, thus CO2 should be kept no higher than 45mmHg. The second part of the college answer to Question 26 from the second paper of 2010 mentions this. An article commenting on one author's experience suggests that the intensivist should ignore this, as making attempts to increase minute ventilation will overload the right heart.
  • Pressures will be high: the gravid uterus contributes to decreased respiratory compliance
  • Prone ventilation will be difficult,  because of the belly.  However it is not completely off the table:  see this case report by Samanta et al (2014) who safely ventilated a third-trimester patient with H1N1.
  • Sustained paralysis is out of the question because of the risks to the foetus (arthrogryposis)
  • Pulmonary vasodilators are still available, including nitric oxide - though there is no experience in pregnant ARDS,  only in pulmonary hypertension as in Robinson et al (1999).

Thus, a management strategy mentioning all the important points would resemble the following list:

Airway:

  • Prepare for intubation with optimal senior ICU/anaesthetic expertise 
  • Expect a difficult airway and greatly decreased reserve

Ventilation:

  • Ensure normoxia by using a higher FiO2 target (minimum saturation 95%)
  • Aim for normocapnea,  CO2  no higher than 45mmHg
  • Rely on sedation to relax the respiratory muscles; sustained NMJ blockade is out of the question
  • Consider inhaled nitric oxide or prostacycline to improve V/Q matching
  • If these measures fail, the next option will be determined by local level of experience in prone ventilation or ECMO. Both will be risky and difficult to manage.

Circulation:

  • Ensure good central venous filling; high ventilator pressures may give rise to haemodynamic instability in the volume-depleted woman
  • Nurse the patient in alternating left and right recovery position (this may also improve V-Q matching)

Sedation

  • Avoid long-acting opiates and benzodiazepines to protect the foetal respiratoryt drive

Foetal wellbeing:

  • Continuous CTG monitoring
  • Early O&G/neonatology involvement
  • Preparation of the foetal lung for delivery with steroids

Social issues:

  • Maternal in-hospital mortality may be in the realm of 45%. Foetal mortality is more difficult to estimate. Family need to be aware of this.

References

Langenegger, Eduard, et al. "Severe acute respiratory infection with influenza A (H1N1) during pregnancy." SAMJ: South African Medical Journal 99.10 (2009): 713-716.

Oh's Intensive Care manual:

Chapter 64   (pp. 684) General  obstetric  emergencies by Winnie  TP  Wan  and  Tony  Gin

Chapter 65   (pp. 692) Severe  pre-existing  disease  in  pregnancy by Jeremy  P  Campbell  and  Steve  M  Yentis

Lapinsky, Stephen E. "Acute respiratory failure in pregnancy." Obstetric Medicine: The Medicine of Pregnancy 8.3 (2015): 126-132.

Samanta, Sukhen, J. Wig, and A. K. Baronia. "How safe is the prone position in acute respiratory distress syndrome at late pregnancy?." (2014).

Rubal, Bernard J., et al. "The'mill-wheel'murmur and computed tomography of intracardiac air emboli." Journal of the American Association for Laboratory Animal Science 48.3 (2009): 300-302.

Lifschultz, Barry D., and Edmund R. Donoghue. "Air embolism during intercourse in pregnancy." Journal of Forensic Science 28.4 (1983): 1021-1022.

Balkan, M. Erkan, and Göknur Alver. "Spontaneous pneumomediastinum in 3rd trimester of pregnancy." Annals of thoracic and cardiovascular surgery 12.5 (2006): 362.

Jain, Vikyath. "Acute respiratory distress syndrome, Respiratory failure, Pregnancy." ACUTE RESPIRATORY DISTRESS SYNDROME IN PREGNANCY 7540 (2015).

Robinson, Julian N., et al. "Inhaled nitric oxide therapy in pregnancy complicated by pulmonary hypertension." American journal of obstetrics and gynecology 180.4 (1999): 1045-1046.