Shock -Shock is a complex syndrome involving a reduction in blood flow to the tissues that may result in irreversible organ damage and progressive collapse of the circulatory system. -If left untreated it will result in death. Shock can be acute but prompt treatment results in recovery, with little detrimental effect on the mother-However, inadequate treatment or failure to initiate effective treatment can result in a chronic condition ending in multisystem organ failure, which may be fatal.

Shock can be classified as follows: hypovolaemic – the result of a reduction in intravascular volume such as in severe obstetric haemorrhage • cardiogenic – impaired ability of the heart to pump blood. In midwifery it may be seen following a pulmonary embolism or in women with cardiac defects. • neurogenic – results from an insult to the nervous system as in uterine inversion

• septic or toxic – occurs with a severe generalized infection. • anaphylactic – may occur as the result of a severe allergy or drug reaction. -This section deals with the principles of hypovolaemic shock and septic shock, either of which may develop as a consequence of childbirth.

Hypovolaemic shock This is caused by any loss of circulating fluid volume, as in haemorrhage, but may also occur when there is severe vomiting. The body reacts to the loss of circulating fluid in stages as follows: Initial stage -The reduction in fluid or blood decreases the venous return to the heart. -The ventricles of the heart are inadequately filled, causing a reduction in stroke volume and cardiac output.

-As cardiac output and venous return fall, the blood pressure is reduced. -The drop in blood pressure decreases the supply of oxygen to the tissues and cell function is affected.

Compensatory stage -The drop in cardiac output produces a response from the sympathetic nervous system through the activation of receptors in the aorta and carotid arteries. - Blood is redistributed to the vital organs. - Vessels in the gastrointestinal tract, kidneys, skin and lungs constrict. -This response is seen by the skin becoming pale and cool. Peristalsis slows, urinary output is reduced and exchange of gas in the lungs is impaired as blood flow diminishes.

-The heart rate increases in an attempt to improve cardiac output and blood pressure. -The pupils of the eyes dilate. - The sweat glands are stimulated and the skin becomes moist and clammy. -Adrenaline (epinephrine) is released from the adrenal medulla and aldosterone from the adrenal cortex.

- Antidiuretic hormone (ADH) is secreted from the posterior lobe of the pituitary. -Their combined effect is to cause vasoconstriction, increased cardiac output and a decrease in urinary output. -Venous return to the heart will increase but, unless the fluid loss is replaced, will not be sustained.

Progressive stage -This stage leads to multisystem failure. - Compensatory mechanisms begin to fail, with vital organs lacking adequate perfusion. -Volume depletion causes a further fall in blood pressure and cardiac output. - The coronary arteries suffer lack of supply. Peripheral circulation is poor, with weak or absent pulses. Final, irreversible stage of shock -Multisystem failure and cell destruction are irreparable. Death ensues.

Effect of shock on organs and systems -The human body is able to compensate for loss of up to 10% of blood volume, principally by vasoconstriction. -When that loss reaches 20–25%, however, the compensatory mechanisms begin to decline and fail. - In pregnancy the plasma volume increases, as does the red cell mass. - The increase is not proportionate, but allows a healthy pregnant woman to sustain significant blood loss at birth as the plasma volume is reduced with little disturbance to normal haemodynamics

- In a woman who has not had a healthy increase in plasma volume, or has sustained an antepartum haemorrhage, a much lower blood loss is required to have a pathological effect on the body and its systems. Individual organs are affected as below.

Brain -The level of consciousness deteriorates as cerebral blood flow is compromised. -The mother will become increasingly unresponsive. -She may not respond to verbal stimuli and there is a gradual reduction in the response elicited from painful stimulation.

Lungs -Gas exchange is impaired as the physiological dead space increases within the lungs. - Levels of carbon dioxide rise and arterial oxygen levels fall. - Ischaemia within the lungs alters the production of surfactant and, as a result of this, the alveoli collapse. - Oedema in the lungs, due to increased permeability, exacerbates the existing problem of diffusion of oxygen. - Atelectasis, oedema and reduced compliance impair ventilation and gaseous exchange, leading ultimately to respiratory failure. This is known as adult respiratory distress syndrome (ARDS).

Kidneys -The renal tubules become ischaemic, owing to the reduction in blood supply. -As the kidneys fail, urine output falls to less than 20 mL/hr. -The body does not excrete waste products such as urea and creatinine, so levels of these in the blood rise

Gastrointestinal tract -The gut becomes ischaemic and its ability to function as a barrier against infection wanes. -Gram-negative bacteria are able to enter the circulation. Liver -Drug and hormone metabolism ceases, as does the conjugation of bilirubin. -Unconjugated bilirubin builds up and jaundice develops

-Protection from infection is further reduced as the liver fails to act as a filter. - Metabolism of waste products does not occur, so there is a build-up of lactic acid and ammonia in the blood. - Death of hepatic cells releases liver enzymes into the circulation.