Renal blood flow

Renal blood flow is normally 1200 ml per minute, just over 20 cardiac output. It is affected by various factors (Box 8.2). There is autoregulation of renal blood flow between a MAP of 70-170 in normal subjects (autoregulation in hypertensive patients is shifted to the right, Figure 8.1). Resistance of the renal vascular bed plays a large part in autoregulation - the smooth muscle walls of the afferent and efferent arterioles in the cortex constrict and dilate according to changes in pressure....

Pathophysiology of acute renal failure

The pathophysiology behind acute renal failure (ARF) is complex and only partly understood. Many data come from animal models where acute tubular necrosis is induced by transiently clamping a renal artery. Real patients are more complex, where renal failure is often part of a developing multisystem illness. The outer medulla is relatively hypoxic and prone to injury. When there is an ischaemic or septic insult, inflammatory mediators damage the endothelium. It is not as simple as damaged...

Treatments for respiratory failure

Any patient with acute respiratory failure should be admitted to a respiratory care unit or other level 2-3 facility. Hypoxaemia is the most life-threatening facet of respiratory failure. The goal is to ensure adequate oxygen delivery to tissues which is generally achieved with a PaO2 above 8 0 kPA (60 mmHg) or SaO2 of at least 94 . However, patients who normally have hypoxaemia, hypercapnia, and breathlessness require different therapeutic targets than patients without lung disease. One would...

Ischaemic heart disease

Major clinical predictors of perioperative cardiac complications are patients with recent (within 6 months) myocardial infarction, severe or unstable angina, and significant arrhythmias. However, many patients have Table 10.1 Risk of major perioperative cardiac event according to type of surgery Table 10.1 Risk of major perioperative cardiac event according to type of surgery Table 10.2 Risk of major perioperative cardiac event according to type of patient Table 10.2 Risk of major perioperative...

Weaning frominvasive ventilation

Weaning is the progressive reduction in respiratory support as respiratory failure improves. The respiratory muscles become deconditioned during prolonged ventilation so an abrupt withdrawal of ventilatory support is often unsuccessful. Weaning is appropriate when the underlying Pressure control (no spontaneous effort) Pressure control (no spontaneous effort) Pressure support (set to 10 and 0 cm H2O) Pressure support (set to 10 and 0 cm H2O) Spontaneous breath triggers ventilator Inspiratory...

Estimating renal function

Neither urine output nor creatinine are good estimates of renal function. Creatinine clearance is more helpful and can be estimated by the equation Normal is around 100 ml per minute but this formula was derived for use in the steady state and, if the creatinine is rising, true clearance will be lower. In oedematous patients, the GFR can be overestimated as total body weight is greater than lean body mass. However, it is useful and can provide guidance for drug adjustments. Particularly in the...

CPAP in patients with acute cardiogenic pulmonary oedema

One can think of acute cardiac failure in terms of forward failure (the inability to drive the circulation) or backward failure (the congestion caused by an inefficient pump). Backward failure causes pulmonary oedema and is often associated with a normal or high blood pressure. Treatment aims toward off-loading the heart. Medical therapy does this by sitting the patient up which reduces venous return, and giving frusemide, diamorphine and nitrates for their vasodilator properties. When medical...

Noninvasive CPAP

Non-invasive CPAP was first introduced in the 1980s as a therapy for obstructive sleep apnoea OS A . This is when a tight-fitting face or nasal mask delivers a single pressure throughout the patient's respiratory cycle. It is therefore not ventilation. In OSA, CPAP prevents pharyngeal collapse. CPAP can also be delivered through an endotracheal tube or tracheostomy tube in spontaneously breathing patients and is usually used this way during weaning. The application of a continuous pressure...

Interpreting an arterial blood gas report

Arterial blood gas analysis can be performed quickly and gives useful information about A oxygenation , B ventilation and C perfusion - which is why it is one of the first tests with bedside glucose measurement performed in critical illness. However, many clinicians fail to carry out a full analysis and benefit from information that could influence therapy. The box below describes the 6 steps in arterial blood gas analysis 2. What is the primary acid-base abnormality An abnormal pH always...

Low flow devices nasal cannulae simple face masks and reservoir bag masks

Nasal cannulae are commonly used because they are convenient and comfortable. They deliver 2-4 litres per minute of 100 oxygen in addition to the air a person is breathing. If a person is breathing slowly with 10 breaths per minute and 500 ml tidal volumes, the minute volume or inspiratory flow rate will be only 5 litres per minute. So the patient receives 2 litres per minute of 100 oxygen plus 3 litres per minute of air. Two-fifths of what the patient is breathing is 100 oxygen. However, a...