ABSTRACT
A large variety of therapeutic devices is available to clinicians. We will describe some that play a major role in the management of respiratory and circulatory problems.
8.1. SYRINGES, INFUSION DRIPS AND INFUSION PUMPS
Syringes are used to rapidly provide the patient with a known volume of one of a large variety of drugs. For fast action, drugs can be injected into the bloodstream, usually intravenously. For slower drug action, intramuscular injections can be given; their disadvantage is that the rate at which the drug becomes effective will depend on where the bolus was deposited in the tissues and on usually unknown characteristics of the patient, such as muscle bulk. Although an injection can directly influence a measurement (see, e.g., Section 3.2.1), their indirect influence-through the action of the drug-is much more important. Since many drugs influence the values of the measured variables, a correct interpretation of the measurements is possible only if it is known which drugs have been applied and in what dosage. Providing this information to a monitoring system is important for reliable record keeping, but especially when “intelligent” alarms are generated. In that case, the information must be provided to the system at the time the injection is given.
Although bar codes on syringes and bar code readers are sometimes used, the requirement that no extra effort is to be demanded from the clinician makes this approach unpopular and error-prone. Infusion drips realize a slow, yet carefully controlled drug flow. A bag or bottle, usually filled with a physiological salt solution to which a known volume of the drug is added, empties itself slowly through a catheter into the patient, often into a vein. The desired flow rate is adjusted through a restriction in the catheter and can be read off as a number of drops in a drip chamber (Figure 8.1a). The following analysis will show that this method is not reliable.
