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22 Cardiovascular Physiology And Support

to-left shunting. Patients may respond to an IV fluid bolus, decreasing nitis. His tachycardia, low blood pressure, anxiety, and poor peripheral
inhalation anaesthetic, and vasoconstrictor drugs such as phenylephrine perfusion are consistent with circulatory shock. He is febrile and has
(alpha agonist) to increase systemic vascular resistance. Most cyanotic a wide pulse pressure, which would suggest that shock may be due
patients are polycythemic, which improves oxygen delivery. Therefore, to sepsis. However, patients with peritonitis lose a large amount of
consideration should be given to transfusing this patient prior to intravascular volume due to transudative and exudative losses into the
surgery. Ketamine is a good choice for induction because it tends to peritoneal cavity. Therefore, this patient likely also has a component of
maintain systemic blood pressure. Narcotics and low-dose halothane hypovolaemia contributing to his shock state.
are good choices for this particular surgery, which must be completed The first and most important step in the management of this patient
without muscle relaxants to allow nerve stimulation during surgery. The is to recognise that he is in shock. Due to the cardiodepressive effects
goal should be to extubate the patient in the immediate postoperative of most anaesthetic agents, worsening hypotension and organ dysfunc-
period to minimise airway stimulation, which can induce a “tet” spell. tion would likely result if this patient were taken directly to the oper-
Case Scenario #2 ating room without prior resuscitation. Therefore, an effort should be
made to optimise his haemodynamics prior to the induction of anaes-
Presentation thesia. Because both septic shock and hypovolaemic shock respond
You are called to see an 8-year-old, previously healthy boy with a initially to expansion of the intravascular blood volume, a large-bore
2-day history of abdominal pain and vomiting. On examination, the IV should be started and the patient should receive one or more boluses
patient is moderately distended and has diffuse abdominal tenderness of a crystalloid solution. During the period of preoperative resuscita-
with involuntary guarding. The patient seems somewhat anxious, he tion, vital signs should be monitored frequently, and a bladder catheter
is tachypneic, his temperature is 39.5°C, his heart rate is 140, and his should be inserted to monitor urine output as a measure of adequacy
blood pressure is 90 over 45. His extremities are cool to the touch. of end organ (renal) perfusion. In addition, because sepsis is suspected,
1. What is the likely aetiology of this patient’s altered vital signs? the patient should be started on a broad-spectrum antibiotic. It is likely
2. What should you do to prepare this patient for surgery? that the ultimate treatment for the cause of this patient’s shock will
require surgical intervention; therefore, resuscitation should occur as
Treatment
expeditiously as possible.
This patient presents with an acute abdomen of two days duration.
Based upon the findings on clinical examination, he has diffuse perito-

Key Summary Points

1. Alterations in venous return (preload), vascular resistance 4. Shock is the result when pathologic conditions severely alter
(afterload), heart rate, and contractility all impact one or more factors and overwhelm compensatory responses,
cardiovascular function. resulting in cellular ischaemia due to inadequate cardiac output
or a maldistribution of blood flow.
2. In the healthy patient, compensatory mechanisms allow
maintenance of adequate cardiac output and organ blood flow 5. Recognition and treatment of the cause of shock is central to
in the face of limited changes in these variables. optimising patient outcome.
3. Neonates have a limited ability to increase cardiac output
by increasing contractility and stroke volume, and thus are
dependent upon heart rate to maintain cardiac output.

Suggested Reading

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Guyton AC, Hall JE. Cardiac output, venous return and their 1865–1915.
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Physiology, 10th ed. WB Saunders, 2000; Pp 210–222. Nichols DG, Yaster M, Lappe DG, Buck JR, eds. Golden Hour: The
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