Other Monitors

Other Monitors

Monitoring Urine Output

Urinary bladder catheterization is the only reliable method of monitoring urinary output. Insertion of a urinary catheter is indicated in patients with congestive heart failure, renal failure, advanced hepatic disease, or shock. Catheterization is routine in some surgical procedures in which large fluid shifts are expected. Lengthy surgeries and intraoperative diuretic administration are other possible indications. Occasionally, postoperative bladder catheterization is indicated in patients having difficulty voiding in the recovery room after general or regional anesthesia. Urinary output is a reflection of kidney perfusion and function and an indicator of renal, cardiovascular, and fluid volume status. Inadequate urinary output (oliguria) is often arbitrarily defined as urinary output of less than 0.5 mL/kg/h.

Monitoring of Anesthesia Equipment

Regular evaluation of the anesthetic machine should become part of standard monitoring routine. Equipment problems, either as a result of malfunction or human error are the cause of many common anesthetic complications. It is crucial that you are thoroughly comfortable with the setup and operation of the machine you will be using before you anesthetize a patient. This is discussed in detail in the module 2 of session 2 and 3

Monitoring the Depth Anesthesia

During the course of anesthesia, the anesthetist should monitor the level of anesthesia required for the procedure. Each patient has a unique individual response to surgical stress and administered anesthetics. When we induce a state of general anesthesia, the onset of anesthesia is signaled by the lack of response to verbal commands and the loss of a 'blink' reflex when the eyelash is lightly touched. Inadequate anesthesia may be signaled by facial grimacing to a painful stimulus or by movement of an arm or leg. In the case of full paralysis with muscle relaxants, inadequate anesthesia is suggested by hypertension, tachycardia, tearing or sweating. Excessive anesthetic depth may be signaled by cardiac depression manifesting as bradycardia and hypotension. In the patient who has not been given muscle relaxants and is breathing spontaneously, excessive anesthetic depth may result in hypoventilation with hypercapnia and hypoxia.

Monitoring Neuromuscular Blockade

Neuromuscular blockade can be assessed using clinical signs and a peripheral nerve stimulator. The use of clinical signs may not be as accurate as the peripheral nerve stimulator. Commonly a head lift or hand grip is used. The patient must have recovered from anesthesia enough to cooperate and follow verbal commands. If the patient is able to lift their head off the bed for 5 seconds, then this may indicate that 33% or less of the receptors are occupied. Alternatively, a strong, sustained hand grasp will indicate that 33% or less of the receptors is occupied. Clinical signs should be used with a peripheral nerve stimulator to help determine the degree of recovery from neuromuscular blockade.

Monitoring the patient with a peripheral nerve stimulator will help to determine the following:

• When to intubate the patient
• Degree of neuromuscular blockade induced by a muscle relaxant during surgery
• Degree of recovery from neuromuscular blockade during emergence from anesthesia

There are several methods of monitoring the patient with a peripheral nerve stimulator. Two of the most common tests are train of four (TOF) and tetanus. TOF monitoring consists of 4 pulses of stimulation, delivered at a low frequency for 2 seconds at 0.5 second intervals. TOF monitoring consists of comparing the first response of simulation to the fourth response. For clinical purposes, simply counting the number of twitches is sufficient to determine the extent of neuromuscular blockade. Attempts to reverse neuromuscular blockade should not occur until there is at least one twitch available, however it is safer to wait until there are 3 or more twitches visible (Figure 2:13 and Table 2:6).

Anatomically, two common areas are used to assess neuromuscular blockade with a peripheral nerve stimulator: the ulnar nerve and the facial nerve. The ulnar nerve can be stimulated at the elbow or the wrist. Stimulation of the ulnar nerve will result in thumb movement. The muscle that is responsible for movement is called the adductor pollicis (Figure 2.13).

Table 2.6: Neuromuscular Twitches

Tetanus is a second test performed with a peripheral nerve stimulator (Figure 2:15). Tetanus is an intense stimulation that lasts for 5 seconds, resulting in muscle contraction. If the contraction of the muscle does not fade, it should be understood that up to 70% of the receptors may still be blocked. If tetanus fades, it indicates that greater than 70% of the receptors may be blocked.

TOF should be performed before tetanus. At the end of tetanic stimulation there is an immediate and temporary increase in acetylcholine, enhancing TOF response.

Alternatively, the facial nerve can be stimulated. The peripheral nerve stimulator is placed along the facial nerve, found inferior and lateral to the eye. Stimulation of the facial nerve will cause stimulation of the orbicularis oculi muscle. This results in movement of the eye brow and muscles that surround the orbit of the eye. Make sure before application of this monitor patient should well anesthetized.