Shock Amr Mohsen

What is shock? Acute circulatory failure leading to Inadequate tissue perfusion that results in Generalized organ hypoxia

3 components The cardiovascular system is made up of three key elements (figure 1):  a pump, tubing and a fluid. The pump propels the fluid, the tubing distributes and collects it. If a patient becomes hypotensive, either the pump is not working properly, there is not enough fluid in the system, or the distribution network is malfunctioning. Under normal conditions, the various components of the cardiovascular system are interdependent, and if one element malfunctions, the others compensate to return the blood pressure to normal. An example of this is when a patient bleeds: the volume of fluid falls, and in response, the blood vessels tighten up (vasoconstrict), and the heart rate rises.

cardiovascular physiologic reserve 1. Heart Rate 2. Stroke Volume [venous return (blood volume) & myocardial contractility & peripheral resistance] 3. Peripheral Resistance All exist in dynamic equilibrium. These interactions maintain blood pressure. If one of the three becomes abnormal, the other two compensate.

Compensatory mechanisms Receptors Respond to Results Sympatho-Adrenal Response Carotid & aortic baro-receptors Reduced baroreceptor stretch ++ HR ++ SV = maintain CO VC (selective) = maintain ABP

Compensatory mechanisms Receptors Respond to Results ADH (VASOPRESSIN) Osmoreceptors Increased osmolality Water retention VC

Compensatory mechanisms Receptors Respond to Results RENIN (Angiotensin ii & AldosteronE) Juxtaglomerular apparatus Renal ischemia VC Salt & water retention

Compensatory mechanisms Sympatho-adrenal Response

Hypotension is an indication of: An abnormality of Heart Rate, Stroke Volume or Peripheral Resistance Failure of the others to compensate.

Classification of shock failure loss =hypovolemia maldistribution When there is evidence of end organ insufficiency (confusion, oliguria or lactic academia), then hypotension has caused “shock.” In shock – definitive evidence of hypotension (inadequate blood pressure to maintain tissue perfusion) – at least one element of the cardiovascular system has malfunctioned, and the others have failed to adequately compensate. The simplest way to describe shock is 1) Pump failure – “cardiogenic” shock, 2) Tubing malfunction- “distributive” shock, & 3) Fluid loss – “hypovolemic shock”. The treatment of shock depends on the cause. The commonest type – hypovolemic – is treated by replacing the fluid that is lost, blood or plasma. Cardiogenic shock is managed by using therapies that improve overall cardiac function. Distributive shock is treated by either loosening up constricted blood vessels or tightening up dilated vessels. It is important to remember that shock is failure of circulation and failure of compensation, and two separate types overlap: e.g. in anaphylaxis, there is distributive shock due to mast cell degranulation and vasodilatation. In this situation the failure is the vasodilatation, but there is failure of compensation as the volume of blood in the vasculature is inadequate to maintain pressure, and the patient becomes “relatively hypovolemic”. The treatment therefore is fluid loading and vasoconstrictors.

Classification of shock Hypovolemic shock blood loss, plasma loss (burns), fluid loss Cardiogenic shock (pump failure) Arrhythmias, MI, tamponade Maldistribution shock Septic shock Spinal shock Anaphylactic shock

Pathophysiology

ARDS Impaired ventilation Impaired perfusion Impaired diffusion Stiff lungs (surfactant def.) Alveolar oedema Impaired perfusion Shock Shunts Impaired diffusion Oedema of alveolo-capillary membrane

ARDS ARDS Late finding Normal Chest X-ray

DIC

DIC Low platelet count Low fibrinogen Prolonged PT & APTT Elevated Fibrin-degradation product Serious sign

Management of Shock & MOF In ICU

Eradicate sepsis (pus drainage) Antibiotics Treat Cause Examples Control bleeding Eradicate sepsis (pus drainage) Antibiotics

ECG Clinical parameters Pulse Temp (peripheral & core) Blood pressure Respiratory rate Monitoring Continuous ECG Pulse oxymetry

Optimum output 0.5-1ml/kg/hour. Urine output Optimum output 0.5-1ml/kg/hour. Monitoring Temperature. A simple non-invasive method of assessing cardiac output and peripheral perfusion is to measure the difference between the peripheral and core temperature. The former is measured by a sensor attached to the big toe, and the latter by a probe placed in either the rectum or the oesophagus. In a warm ambient temperature, the core is higher than peripheral temperature by a gradient that should not exceed 2°C. Any increase in this gradient is a very sensitive indicator of decreased perfusion.

(1) Arterial cannula for ABP Monitoring (invasive) Central venous pressure (CVP). The CVP is the venous pressure in the right atrium and is equal to the end-diastolic pressure in the right ventricle and is a measure of the preload to this chamber. To measure the CVP, a catheter is placed in the right atrium via the median-cubital vein, the subclavian vein or the internal jugular vein. The position of the venous catheter is checked by chest X-ray. The radiograph also serves to rule out pneumothorax due to accidental pleural injury during its insertion. The normal pressure is 5-10 cm of water. Assuming that cardiac function is normal, the CVP roughly corresponds to the blood volume. Thus, a high pressure indicates overtransfusion, while a low pressure indicates hypovolaemia. Pulmonary artery wedge pressure (PAWP). When the right side of the heart is functioning abnormally, it is highly probable that the left side of the heart is equally affected. In such a case, it is recommended to measure PAWP by the use of a Swan-Ganz catheter which is passed into a small branch of the pulmonary artery where it becomes wedged. As the balloon of the catheter occludes this small branch, the pressure measured at the catheter tip reflects that in the left side of the heart. (2) CVP N= 0-8 cmH2O (3) Swan Ganz (PAWP)

Renal function tests (Urea & elect) Arterial Bl Gases (ABGs) Lactates Monitoring Laboratory tests CBC Renal function tests (Urea & elect) Arterial Bl Gases (ABGs) Lactates Liver function tests PT, PTT & FDP

Normal Arterial Bl Gases (ABGs) ~ 7.4 pH ~ 100 PO2 ~ 40 PCO2 ~ 25 mmol/L HCO3- Monitoring Normal serum electrolytes ~ 142 mmol/L Na+ ~ 4 mmol/L K+ ~ 103 mmol/L Cl-

Respiration Support Body Systems Clear airway - Suction of secretions - Tracheal intubation or tracheostomy Oxygen (essential) - Mask for respiratory distress - Mechanical ventilation for respiratory failure PO2 < 60mm Hg RR > 35/m

Correct acidosis Support Body Systems Careful use of IV sodium bicarbonate

Circulation Support Body Systems Correction of hypovolaemia (essential) Two peripheral venous lines One central venous line Crystalloids Blood Plasma Medications (if the above fail to restore BP) Inotropes (e.g., dopamine & dobutamine) Vasopressors (noradrenaline)

Renal Support Body Systems Adequate volume replacement Dopamine improves renal blood flow Dialysis in case of acute renal failure (K+ >7mmol/L), until the kidneys recover

GIT Support Body Routine acid suppression Systems IV H2 blockers or Omeprazole

Coagulation Support Body Systems Treatment of DIC Platelet transfusion Fresh Frozen Plasma (FFP) as it contains coagulation factors

Mortality of MOF Renal failure only 8% Renal + other organ failure 70% Three failing organs 90%