DOES THE PATIENT NEED A CATHETER? All patients with burns of over 30% need a catheter to measure their urine output. Patients with burns of less than 10% never do. Patients with burns of between 10% and 30% only need one if their urinary output is poor. A patient also needs a catheter if his perineum has been burnt. Catheters have their risks, so observe this intermediate group of patients carefuly. It is tragic for a patient with a minor burn to die later from a urinary infection.

IS HE GETTING ENOUGH FLUID? A patient’s urine flow is the most reliable indication as to whether you have treated his shock adequately or not. But: (1) His bladder must be empty before collection starts. (2) The formula is a rough guide only, so adjust it according to how he responds. Watch his jugular venous pressure, and listen to the bases of his lungs. Adjust the rate of infusion and the volume of fluid you give him like this:

Figure 58.6: A PHYSIOLOGICAL NOMOGRAM. Don’t be defaeted by this—it is really quite easy! A patient’s blood volume, his plasma volume, his fluid requirements, and his minimum urine output are all proportional to his surface area. This in turn is proportional to his weight and height.First, align his height and weight with a ruler, this will cross Scale F, at a point which indicates his surface area. Then hold the ruler vertically at this point (hold it parallel to the thick vertical lines) and read off his blood volume etc. For further instructions, see next figure. Drawn at the suggestion of Peter Bewes using data from the Ciba–Geigy Scientific Tables.

If he is already shocked, give the initial transfusion fast over 10 or 15 minutes. A severely shocked patient may have lost a third of his blood volume, so be prepared to give him up to a third of his blood volume fast. You will need to know what his blood volume is, so consult Scale C, in Fig. 58-6. Thus a child with a blood volume of a litre may need up to 330 ml of fluid. As soon as he starts to recover, slow the drip.

If treatment starts late, give more fluid than the formula indicates.

If shock is not controlled, give more fluid than the formula indicates. Here are the signs that shock is not controlled and that he needs more fluid: restlessness, cold hands or feet, a rising pulse rate, thirst, sweating, collapsed veins, or a falling blood pressure. A common error is to give morphine instead of fluid to relieve restlessness.

Figure 58.7: HOW TO USE THE PREVIOUS FIGURE. Measure the patient’s height and weigh him. (1) Align your ruler with his height (scale A) and weight (scale H). Read off his surface area from scale E Next, (2) hold your ruler vertical at the figure for his surface area and read off his blood volume (scale C), his plasma volume (scale D), his daily fluid requirements (scale E), and his minunum urine output (scale G).For example, say he was 152 cm tall and weighed 20 kg. He would have a surface area of 1 square metre, a blood volume of 2.5 litres (scale C), and a plasma volume o£ about 1.6 litres (scale D). His fluid requirement would be about 2150 ml (scale E), and his minimum daily urine output about 600 ml (scale G). If you cannot weigh and measure him, estimate his approximate height and weight from his age. This will be much less accurate.

A patient should secrete between 0.5 to 1.0 ml/kg of urine an hour. For a 70 kg adult this is between 35 and 70 ml per hour. Scale G, in Fig. 58-6 is drawn at 0.5 ml per hour, so this is his minimum output. If he is secreting less urine than this, he usually needs more fluid, but he may need less if he has renal failure (58.10). The minimum volume of urine required to excrete the solutes produced by metabolism is about 300 ml in a normal person and 600 to 800 ml in a burns patient.

If you are not giving colloids, his urine flow is the best indication of adequate fluid replacement.

If you are giving him colloids, combine estimation of his urine output with: (1) inspection of his jugular venous pressure, (2) the filling of his peripheral veins, (3) the colour and temperature of his skin, and (4) the capillary filling of his nail beds.

If his jugular venous pressure rises and there are basal crepitations, you are over-infusing him (which is a less common error than under-infusion), so reduce his fluid intake drastically. As he loses fluid from the surface of his burn he should improve.

If you can measure his microhaematocrit, measure it 2 hourly for the first 8 hours, then 8 hourly thereafter. Fill two capillary tubes from a pin prick in his ear (in case one breaks), and plot the readings immediately on his fluid balance chart.

Provided he was not anaemic or polycythaemic before treatment began, changes in his haematocrit will be a useful guide to fluid replacement. A high haematocrit shows that he needs more fluid and vice versa. Don’t be a slave to it, and consider it with other signs.

A PATIENT SHOULD EXCRETE 0.5 TO 1 ml/kg OF URINE PER HOUR (35 to 70 ml per hour for adults)