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WRITE UPS - CRITICAL ISSUES - Critical Care In Obstetrics

INTRODUCTION:

A critically ill obstetric patient is one who, because of abnormal pregnancy, delivery, puerperium or because of effects of pre-existing systemic disease, anesthesia and surgery and other acquired condition on a normal pregnancy, delivery or in puerperium develops complications threatening her life for which she needs intensive monitoring, therapy and/or life support system. In another definition these are defined as maternal near-miss mortality, as those women requiring critical care or transfer to an intensive care unit. Because maternal deaths are rare in developed countries, it has been suggested that a more accurate measure of the standard of maternal care is to study the near-miss cases. The problems with definition include.

Transfer to ICU may depend on health care facilities and may not be comparable from one hospital to another.

All near-miss cases do not result in admission to an ICU, e.g. a case of PPH is cared for in labour room without transfer.

Conditions requiring intensive care may not necessarily mirror causes of maternal mortality e.g. maternal mortality for PPH is lower than for amniotic fluid embolism.

Vaginal delivery following labour may be the shortest but most hazardous journey made by any individual. Hypoxia, trauma and infection are inherent risks. The mother to be faces the brunt of most of the assaults, pain, apprehension, infection, agony of having operative delivery, extensive tissue traumas, massive bleeding, long-term morbidity and even the risk of losing her life/or that of the newborn. The art of intrapartum care now, is evidence based. Medline literature review between 1987-94 revealed that percentage of obstetrics patients requiring intensive care is 0.1- 0.3

So a team consisting of obstetricians, anesthetist and an internist is required for management of labor in a critically ill patient. Trained nursing staff and neonatologists will complete the list of required personnel.

Hemorrhage, hypertensives disorders, cardiac disease, and sepsis are some of the common problems threatening life during labor. Severe anemia and jaundice in pregnancy are two important causes of maternal mortality in our country especially in the immediate post-partum period.

PRINCIPLES OF CRITICAL CARE:

The basic guidelines of critical care areas follow:

Optimum oxygen supply to tissues.

Adequate circulating blood volume, which should neither be less nor more than adequate.

Nutritional support

Prevention of complications inherent to the modalities of critical care.

New knowledge put into practice in the ICU includes concepts of prelude augmentation and reduction, oxygen delivery and consumption, and pharmacological support with an arrhythmic isotropic, vasodilators and β blocking drugs. Examples of new equipments are intra-arterial BP monitors, pulse oximeters, pulmonary artery catheters (PAC), continuous mixed venous oxygen saturation monitors, intracranial pressure monitors, ventilators, computerized tomographic (CT) scanners, USG machines, echocardiography, machine bronchoscopes and other endoscopy equipments. Emergency equipments include defibrillators, suction machine, ECG, portable fetal monitors, etc. In addition to routine, the ability to insert radial and pulmonary artery catheters, perform endotracheal intubations, manage a ventilator, direct cardio-pulmonary resuscitation and perform cesarean hysterectomy or bilateral hypo-gastric artery ligation are also a part of critical management in obstetrics. 

PRINCIPLES OF MANAGEMENT:

Clinical monitoring

Respiratory support

Cardiovascular support

Correction of cause

Clinical Monitoring:

Mental status

Pulse

Respiration

Temperature

Skin color

Capillary refill

Sweating

Urine volume

Because of increased blood volume, homodynamic instability indicating need for transfusion may not occur until blood loss approaches 1.5 to 2 liters.

Basic Investigations:

These include complete blood count, urine, coagulation profile, electrolytes, BUN, creatinine, chest X-ray, ECG, arterial blood gases, serum lactate, urine and blood culture, pulse oximetry.

The initial approach to a critically ill patient is assessment of the state of perfusion focusing on the distinction between high and low flow states (TABLE 1).

Table1: Assessment of the state of perfusion

Inadequate circulating volume or pump dysfunction or both causes low flow states; High hypo-perfusion is typical of septic shock, liver disorders, etc.

INVASIVE HEMODYNAMIC MONITORING:

Intra-arterial BP per cutaneous placement of intra-arterial canula allows continuous monitoring and repeated samplings of blood for gas and acid base analysis. This is essential when rapid hemodynamic changes are anticipated, e.g. when administering isotropic / vasoactive drugs.

CVP is a simple method for assessing circulating volume and filling status of right heart chambers. However the absolute value is often unhelpful except in extreme cases of hypervolemia, fluid overload or heart failure. Correct interpretation requires assessment of changes in CVP. CVP does not accurately reflect left ventricular filling in patients with preeclampsia, pulmonary and cardiac disease. In these situations, utilizing a pulmonary artery catheter is helpful in determining relative volume status.

Pulmonary artery catheterization: The Swan-Ganz pulmonary artery catheter introduced in 1970 has given an identity to the practice of critical care medicine. Continuous central venous and pulmonary artery pressures and intermittent capillary wedge pressure (PCWP) measurements are obtained. Cardiac output can be measured by thermo-dilution technique. As with CVP correct interpretation requires assessment of changes in response to treatment together with alterations in clinical signs and other monitored variables. Because of lack of co-relation between measurements on the right and left sides of the heart in patients with significant cardiopulmonary disease, PCWP is monitored to optimize ventricular preload to avoid pulmonary edema.

Thus in critically ill obstetric patients, discrepancies are often, seen between measurements, of PCOWP and CVP. In such situations clinical use of CVP alone would be deleterious. With rare exception, the complications seen with pulmonary artery catheterization associated with obtaining central venous access and are similar whether a CVP line or pulmonary artery catheter is used. For these reasons, in modern perinatal intensive care unit, CVP monitoring alone is seldom indicated.

Indications for Pulmonary Artery Catheterization

Refractory/unexplained pulmonary edema and heart failure

Severe PIH with persistent pulmonary edema.

Massive hemorrhage (unresponsive to volume therapy or when accompanied by high CVP).

Septic shock with refractory hypotension/ oliguria.

ARDS

Persistent shock of unknown etiology.

Some chronic conditions when in labor/operative delivery:

NYHA class III, IV, cardiac diseases

Pulmonary hypertension.

Unexplained intrapartum /intra-operative cardiovascular decompensation.

Respiratory distress of unknown cause.

Invasive monitoring is not necessary in every patient with one of these conditions, nor is this an all-inclusive list. Invasive monitoring has its own hazards therefore it is recommended only in patients where precise hemodynamic data can improve decision making and where better interventions are possible.

 Pulmonary edema:  Swan-Ganz catheter is used to measure pulmonary capillary wedge pressure to differentiate cardiogenic from non-cardiogenic pulmonary edema: cardiogenic pulmonary edema results from increased hydrostatic pressure within pulmonary capillaries whereas non-cardiogenic pulmonary edema is the result of increased capillary wall permeability.

GUIDE TO THERAPY:

Whenever necessary, manipulations of cardiac output, reduction of preload and after-load and ionotropic therapy are required, invasive monitoring is helpful.

Oliguria:

To assess volume status in hypertensives disorders, CVP is a poor guide. PAC better guides changes in wedge pressure and cardiac output in response to fluid challenge.

In Hemorrhagic Shock:

Clinical parameters like pulse, BP, urine output, respiration and temperature are commonly utilized. Invasive technique measurements are useful in some cases. An arterial canula also allows frequent measurement of blood gases and acid-base state. In patients deteriorating after initial response a pulmonary catheter may be useful. After initial resuscitation during subsequent 24 to 48 hrs, the catheter may guide fluid therapy in complex cases in which it is not clear whether internal bleeding is continuing, or oliguria, pulmonary edema, liver dysfunction, or coagulopathy are present.

In Septic Shock:

Invasive monitoring allows manipulation of cardiovascular parameters while fluid and ionotropic therapy, assessment of response to therapy may be done through parameters such as oxygen delivery (DO2) and oxygen consumption (VO2), (DO2- cardiac output X arterial oxygen content). Oxygen consumption increases many folds in critically ill patients with multi-organ dysfunction.

NYHA Class III and IV cardiac diseases:

Monitoring is required for managing fluid and drug therapy and anesthetic management.

Respiratory distress of unknown causes:

Monitoring helps to differentiate heart failure, pneumonia, pulmonary embolism, ARDS, Chronic pulmonary disorders.

 Does Swan-Ganz Catheter Improve Outcome:

Pulmonary artery catheterization improves diagnostic accuracy and provides information that often prompts changes in treatment. Nevertheless, its influence on outcome remains uncertain, in obstetrics. Some studies have suggested that the use of catheters may be associated with a worse outcome. Large prospective randomized trials would be needed for a final answer in obstetric patients.

RESPIRATORY SUPPORT:

The first priority is to secure the airway and if necessary provide mechanical ventilation. Because mechanical ventilation minimizes the work of breathing reduces oxygen consumption and improves oxygenation, early respiratory support benefits patients with severe shock and mechanical ventilation. These patients are those with:

Infective pneumonia

Aspiration pneumonia

Asthma

Pulmonary edema

Status epilepticus

Septic shock

ARDS

Post operative homodynamic instability

High spinal/epidural anesthesia

Difficult intubations

Laryngeal edema

Drug overdose

Cardiac arrest

Hypoxic encephalopathy

The arterial blood gas criteria for acute respiratory failure are arterial oxygen partial pressure (PaO2) <50 mm or an arterial CO2 partial pressure (PaCO2) = 50 mm. The blood gas analysis reveals what the patient is accomplishing. It does not reveal how hard she is working to do it. If the patient is severely dyspneic, restless, confused and fatigued, it may be wise to intubate her prophylactically.

The art of fluid administration and hemodynamic support is one of the most challenging aspects of treating critically ill patients.

Determinants of Cardiac Output:

Circulatory support involves manipulation of the three determinants of stroke volumes (preload, myocardial contractility and after load) as well as heart rate.

Preload optimization is the most efficient way of increasing cardiac output and is a pre-requisite for restoring tissue perfusion. Controversy continues about whether colloids or crystalloid are preferable. Data from 19 randomized trials involving a total of 1315 patients indicate that albumin and non-albumin colloids increased absolute of death by 4 percent.

HYPOVOLEMIC SHOCK:

Important pathophysiology in hypovolemic shock includes sodium and water entry into skeletal muscles and cellular potassium lost to extra cellular fluid. Replacement of extra cellular fluid is important. Indeed, survival appears to be reduced in acute hemorrhagic shock when blood alone compared with blood and lactated Ringer solution is administered.

Initial fluid infusion should involve about 3 times as much crystalloid as the estimated blood loss. Establish intravenous access with two wide bore drip sets. In most cases red cell replacement proves sufficient. The exception is the women with torrential bleeding.

The use transfusion in critically ill patients varies widely with different Hb, thresholds being between 7 to 12 gm/dl.  The optimal transfusion practice for various types of critically ill patients with anemia has not been established. A restrictive strategy of red blood cell transfusion is at least as effective and possibly superior to a liberal transfusion policy. Transfusion in young patients seems prudent when Hb falls below 7 gm/dl.

If signs of shock persist despite volume replacement and perfusion of vital organs is jeopardized, ionotropic or other vasoactive agents may be given to improve cardiac output and blood pressure.

Commonly used vasoactive drugs are as follows (Table 2).

Dopamine: Acts on both α and β receptors depending on dose. Ionotropic vasoconstrictor widely used in cardiogenic and septic shock, first few hours of oliguria / renal failure.

Dobutamine: Ionotropic vasodilator, used in heart failure. In low doses, it predominantly acts on β1 receptors: in high doses acts on β2 receptors.

Norepinephrine: 60% α and 40 % β agonist effect: Vasoconstrictor for life threatening hypertension (hypovolemic and septic shock) along with fluid resuscitation.

Sodium Nitroprusside: Equal arterial and venular dilator- used in acute   hypertensives emergency. Fetal cyanide toxicity is possible.

Nitroglycerine vasodilators: In low dose, it is predominantly causes arterial dilation. It may be used in hypertensions and carcinogenic pulmonary edema.

 Table 2: Homodynamic therapy for contractility preload and after load

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