Patients circuits

Patient circuit A set of tubes connecting the patient s airway to the outlet of a respirator. 

Fortunately, the intrinsic safety associated with a host of medical devices has continued to evolve and improve. Somewhat ironically, however, not until the safety weaknesses (i.e., latent conditions) have been exposed through patient injury, death, or costly lawsuits. The development of the return electrode monitor within electrosurgical units is a prime example. By continually interrogating the impedance within the return electrode-patient circuit, this feature disables the electrosurgical unit should the impedance become too high. Burns due to compromised or failed return electrodes are now largely prevented. 

Only in patient circuits that use an exhalation valve can the baseline pressure return to ambient pressure, known as zero PEEP or ZEEP. The advantage of ZEEP requires study, although it is certainly desirable during daytime ventilation when the upper airway is stable and ventilator energy conservation to preserve battery function is more important than leak compensation. Devices using a valve circuit are indicated in the ventilator table. There are some machines that allow the use of both leak and valve circuits in which case both EPAP and ZEEP are indicated in the Tables 1 to 3. 

When using heated humiditication, water condensation can be minimized by insulating the patient circuit either by coveting or by using tubing socks. The insulation can be prepared by the patients using soft insulating material such as fleece. 

O Paroxysmal supraventricular tachycardia is caused by reentry that includes the AV node as a part of the reentrant circuit. Typically, electrical impulses travel forward (antegrade) down the AV node and then travel back up the AV node (retrograde) in a repetitive circuit. In some patients, the retrograde conduction pathway of the reentrant circuit may exist in extra-AV nodal tissue adjacent to the AV node. One of these pathways usually conducts impulses rapidly, while the other usually conducts impulses slowly. Most commonly, during PSVT the impulse conducts antegrade through the slow... 

In patients hospitalized because of asthma, patient-initiated (on-demand) therapy may result in decreased nebulized doses, decreased adverse effects, and shorter hospital stays than ther-apy given regularly at 4-hour intervals.20 In patients admitted to the intensive care unit and placed on mechanical ventilation, P2-agonists can be delivered via an MDI or nebulization through the ventilatory circuit. 

Too Much Neurotransmission. Other mental illnesses result from too much neurotransmission (i.e., overactivity) of certain brain circuits. One example may be psychosis, for example, hallucinations and delusions that have been hypothesized to result from excessive transmission of the neurotransmitter dopamine in certain pathways. In some cases, the transmission becomes so excessive that it kills the nerve cell, a phenomenon called excitotoxicity. This process is believed to occur in some patients with epilepsy and in those with Huntington s disease. 

The concept of bradyphrenia overlaps with that of apathy, defined as diminished motivation not attributable to diminished level of consciousness, cognitive impairment or emotional distress (Marin, 1990). Apathy is common in neurodegenerative disorders and is associated with orbito-frontal, medial frontal and anterior temporal dysfunction in Alzheimer s disease (Craig et al., 1996). Apathy is one of the most common neuropsychiatric symptoms in PD, and correlates with executive dysfunction (Aarsland, 1999b). However, apathy is even more common in PSP patients (Aarsland et al., 2001c), possibly related to the more marked involvement of the orbitofrontal and medial frontal circuits in PSP than in PD. 

Obsessive-compulsive disorder is a brain disorder involving the frontal-subcortical circuits. Environmental, genetic, and clinical factors interact in a complex fashion in the individual patient. This chapter will examine OCD from a neurobiological perspective. The characteristics of OCD that are of specific relevance to this topic are listed in Table 12.1. 

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