Manage the critically ill obstetric patient, including shock and organ support

In one line

The critically ill obstetric patient is a young woman with a physiology built to compensate, so she looks stable until she is peri-arrest; managing her means a structured ABCDE, naming the shock state to direct treatment, supporting failing organs to the same standard as any ICU patient, and — uniquely — recognising that delivering the baby is sometimes the resuscitation, all delivered through a high-care/ICU system that in South Africa is scarce, geographically maldistributed and reached only by referral.

Mechanism & pathophysiology

A pregnant woman is, physiologically, an athlete primed for a single haemorrhagic event. Plasma volume rises by roughly 40–50% and red-cell mass by less, producing the physiological haemodilution of pregnancy; cardiac output climbs 30–50% through both a higher stroke volume and a resting tachycardia of 10–20 beats per minute; systemic vascular resistance falls and the diastolic blood pressure with it; minute ventilation rises so that arterial CO₂ sits around 4.0 kPa with a compensated respiratory alkalosis. Every one of these adaptations is a margin of safety for delivery — and every one is a mask. The same young woman who tolerates losing 1,000–1,500 mL with barely a change in blood pressure has spent her reserve doing so, and when she finally drops her pressure she is already 30–40% volume-deplete and minutes from collapse. The lesson that organises all obstetric critical care is that vital signs in a young pregnant woman are a late and binary warning system: normal until they are catastrophic. This is why structured early-warning scoring and serial trend observation, not single readings, govern recognition. The groundwork — the four shock types and their first principles — is the shock-management chapter; the consultant task here is reading the obstetric distortion of each and choosing organ support.

Three further pregnancy facts reshape resuscitation. First, aortocaval compression: from the mid-second trimester the gravid uterus compresses the inferior vena cava and aorta when the woman is supine, dropping venous return by up to 30% and capping the cardiac output any resuscitation can generate. Left lateral tilt or manual uterine displacement is therefore not a nicety but a circulatory intervention — and in cardiac arrest it is the rationale for emptying the uterus by perimortem caesarean to restore maternal venous return. Second, the physiological hypercoagulability of pregnancy (rising fibrinogen and clotting factors, falling protein S, fibrinolytic shutdown) makes venous thromboembolism a leading cause of maternal collapse and tilts the differential of sudden dyspnoea and hypoxia towards pulmonary embolism and amniotic-fluid embolism. Third, the lower functional residual capacity and higher oxygen consumption mean a pregnant woman desaturates fast on apnoea and tolerates hypoxaemia poorly — the airway and the lungs have almost no reserve.

The shock states keep their classical mechanisms but wear obstetric clothing.

• Hypovolaemic (haemorrhagic) shock is the dominant obstetric shock — major obstetric haemorrhage, the detail of which is the Postpartum haemorrhage chapter. The mechanism is loss of preload and oxygen-carrying capacity, but the obstetric twist is the masking described above plus the dilutional and consumptive coagulopathy that develops early when crystalloid is poured in: the bleeding woman becomes coagulopathic, hypothermic and acidotic — the lethal triad — faster than her blood pressure admits.
• Distributive (septic) shock — vasoplegia and capillary leak from a dysregulated host response; the obstetric sources, the camouflaging physiology and the SA HIV/TB drivers are the Maternal sepsis chapter and are not re-derived here. Anaphylaxis (often to antibiotics, oxytocics or anaesthetic agents) and high neuraxial block are the other distributive causes on the labour ward.
• Cardiogenic shock — pump failure from peripartum cardiomyopathy, decompensated rheumatic or congenital heart disease (still common in SA), arrhythmia, or myocardial infarction. The fluid that rescues hypovolaemia drowns these patients, which is why the shock state must be named before the litre is given.
• Obstructive shock — mechanical impedance to filling or ejection: massive pulmonary embolism, amniotic-fluid embolism, tension pneumothorax, cardiac tamponade, and aortocaval compression itself. The unifying clue is shock with raised, not collapsed, venous pressure.

Amniotic-fluid embolism (AFE) deserves its own mechanism because it is the obstetric catastrophe that defines maternal collapse. The old picture of fetal squames mechanically plugging the pulmonary circulation has been replaced by an anaphylactoid / immune-mediated model: amniotic fluid components entering the maternal circulation around the time of delivery trigger a humoral response resembling anaphylaxis and the systemic inflammatory response, with massive pulmonary vasoconstriction. The haemodynamic course is biphasic — a brief phase of intense pulmonary hypertension and acute right-ventricular failure (the cause of the early arrests), followed, in survivors, by left-ventricular failure and a profound consumptive coagulopathy / DIC that produces torrential haemorrhage. It is rare (UK incidence about 1.7 per 100,000 maternities), unpredictable and unpreventable; it is a clinical diagnosis of sudden cardiorespiratory collapse, hypoxia and coagulopathy in labour or immediately postpartum, after excluding the treatable mimics. There is no specific therapy — management is high-quality resuscitation, early delivery if undelivered, and aggressive correction of the coagulopathy.

Acute respiratory distress syndrome (ARDS) is the common final pathway of the lungs in the critically ill mother, whether the insult is pneumonia, aspiration, sepsis, AFE, pre-eclampsia with severe features or massive transfusion. Diffuse alveolar damage from the inflammatory insult floods alveoli with protein-rich oedema, collapses surfactant function and produces the stiff, poorly-compliant, shunting lung of hypoxaemic respiratory failure (the Berlin definition: acute onset, bilateral infiltrates, hypoxaemia not explained by cardiac failure). The pregnant lung reaches it faster and tolerates it worse, and the management principle — protect the lung from the ventilator while you treat the cause — is the same as in any adult but is delivered against a fetus that also needs oxygen.

Assessment

The first decision is structural, not diagnostic: this woman is sick enough that she is managed by simultaneous assessment and resuscitation, by a team, in an area with monitoring and senior help, with the clock running. Within that, two systems carry the recognition.

• A structured obstetric early-warning system. The Modified Early Obstetric Warning Score (MEOWS) is the standard SA and international tool — a colour-banded chart of respiratory rate, oxygen saturation, temperature, heart rate, blood pressure, conscious level and urine output, calibrated to pregnancy so that the trend, not a single number, triggers escalation (a single red or two amber triggers mandate senior review). Its entire purpose is to convert the binary, late warning of obstetric vital signs into a graded, charted trend that catches the slow drift before collapse. The single most sensitive early sign is a rising respiratory rate, and it is the observation most often left unrecorded.
• ABCDE, done obstetrically. Airway — the pregnant airway is a difficult airway (oedematous, friable mucosa, full stomach, rapid desaturation), so a low threshold for senior anaesthetic help and a plan for failed intubation are part of the primary survey. Breathing — oxygen saturation, respiratory rate, work of breathing, auscultation; high-flow oxygen first, before the cause is known. Circulation — heart rate, blood pressure, capillary refill, two large-bore cannulae, and left lateral tilt / uterine displacement in any collapsed woman beyond the mid-second trimester. Disability — conscious level (AVPU/GCS), pupils, and crucially blood glucose and the possibility of eclampsia. Exposure — temperature, rashes, the abdomen, the perineum and the lochia, looking for the bleeding or infective source.

Naming the shock state is the pivot of the assessment because it directs opposite treatments, and the bedside tool that has changed obstetric critical care is point-of-care ultrasound (POCUS) and focused echocardiography. A focused echo at the bedside distinguishes the empty, hyperdynamic, collapsing ventricle of hypovolaemia (give volume and stop the bleeding) from the dilated, poorly-contracting ventricle of cardiogenic shock (do not flood; support the pump) from the small, hyperdynamic left ventricle with a dilated, pressure-loaded right ventricle of massive PE or AFE (an obstructive picture). Lung ultrasound separates the B-line pattern of pulmonary oedema/ARDS from a pneumothorax or effusion; abdominal/pelvic ultrasound finds free fluid (haemoperitoneum) and retained products. POCUS shortens the time from "she is shocked" to "she is shocked because", which is the whole game.