Although pregnant women constitute<1% of the admissions to the intensive care unit they pose an entirely different challenge to the healthcare team.
The physiological changes that occur in a normal pregnancy stress and limit the compensatory response required to adapt to a superimposed acute illness. These physiological changes are unfamiliar to most Intensivists as these patients are admitted more so for obstetric indications than for related medical conditions.
Most of these women are postpartum but if these women are antepartum, resolution of the disease states is usually facilitated by delivery of the fetus. Also since these ICU admissions are young patients with acute emergencies ,unless irreversible they recover much more quickly than other patients.
The most dramatic physiological changes in pregnancy are cardiovascular. Blood volume increases by more than 50 percent in singleton pregnancies which we know compensates for most of the blood loss during delivery. Blood flow through the placenta is almost 600ml per minute at term which is 30% of the cardiac output. Hence about 1/6th of the blood volume is located in the uterus at any time. The blood pressure falls in the first trimester reaches a nadir in the second and reaches prepregnancy values in the third. Hence a term pregnant patient can lose 30% of her blood volume before showing any changes in the vital signs. Also whenever there is hypotension the placental vasculature goes into vasospasm which may compromise the fetus.
In pregnancy there is respiratory alkalosis with a compensatory metabolic acidosis. These women have increased tidal volume, minute ventilation and oxygen consumption. But they show a reduction in residual volume and functional residual capacity. So they have less reserve when respiratory decompensation occurs.If partial pressure of oxygen falls below 47mm Hg in pregnancy umbilical vein oxygen concentration reduces causing substantial reduction in fetal oxygenation.
The biochemical parameters of normalcy for other organ systems are also different in pregnancy and what may be abnormal for one patient may be normal for a pregnant patient.
Supportive ICU care for obstetric patients
These patients should always be managed with an obstetrician well versed in critical obstetric care. Simple things like the choice of a vasopressor that selectively spares the feto placental unit to choice of an anesthetic agent for emergency surgeries or ventilatory support should be made in collaboration with the critical care obstetrician.
Whether it is trauma in pregnancy, Obstetric haemorrhage, The preeclampsia –eclampsia complex syndrome, embolism or cardiomyopathy- early diagnosis, prompt referral to a centre that can manage these emergencies and careful management by the obstetric critical care team ensures good outcomes for these young otherwise healthy patients.