Blood oximetry

Earlier reports focused on the use of optical absorption properties of tissues for clinical applications (Wilson and Jacques, 1990). An example is blood oximetry, which is widely used clinically to monitor continuously blood oxygenation with the help of an optical fiber probe as described in the previous section. In this method the diffuse reflectance also collected by the fiber is analyzed based on the differences in the absorption bands of oxy and deoxyhemoglobins. Diffuse reflectance from the skin can be used to monitor changes induced, for example, by the UV radiation. Endoscopic reflectance spectroscopy from mucosa of the gastrointestinal tract has been used to determine blood content and oxygenation (Leung et al, 1989). 

In massive PE, the patient may appear cyanotic and may become hypotensive. In such cases, oxygen saturation by pulse oximetry or arterial blood gas will likely indicate that the patient is hypoxic. 

Cardiopulmonary support must be instituted and adjusted rapidly. Electrocardiogram (ECG) monitoring, continuous pulse oximetry, urine flow monitoring, and automated blood pressure recording are necessary. Peripheral or femoral arterial catheters may be used for continuous assessment of arterial pressure. 

Leukocytosis with a predominance of polymorphonuclear cells Low oxygen saturation on arterial blood gas or pulse oximetry... 

The ECT unit should be staffed by experienced professionals trained in the use of the procedure and in the care of an unconscious patient, including measures for intravenous access, monitoring of blood pressure, pulse oximetry, and EKG (Gaines and Rees, 1992). The ECT team usually includes a psychiatrist, an anesthesiologist, and a nurse. 

First, the airway should be cleared of vomitus or any other obstruction and an oral airway or endotracheal tube inserted if needed. For many patients, simple positioning in the lateral decubitus position is sufficient to move the flaccid tongue out of the airway. Breathing should be assessed by observation and oximetry and, if in doubt, by measuring arterial blood gases. Patients with respiratory insufficiency should be intubated and mechanically ventilated. The circulation should be assessed by continuous monitoring of pulse rate, blood pressure, urinary output, and evaluation of peripheral perfusion. 

Chemical sensors (i) Gases (e.g. blood oxygen electrode, carbon monoxide detector) (ii) pH and ions (e.g. pH meter, potassium-selective elecbode) and (iii) optical oximetry (e.g. pulse oximeby for non-invasive monitoring of blood oxygenation). 

Pulse oximetry may indicate low oxygen saturation (Traub et al, 2002). While arterial blood gases usually indicate hypoxemia, carbon dioxide levels have been shown to be decreased, increased, or normal (Giiloglu et al, 2002 Traub et al, 2002). A hyperchloremic metabolic acidosis may show up on blood chemistries due to systemic absorption of hydrochloric acid. 

These cases illustrate the importance of co-oximetry on grounds of clinical suspicion. Methemoglobin concentrations of 10-15% can cause dark-colored blood and cyanosis. Concentrations of 20-45% can cause lethargy. 

Intranasal midazolam 0.2 mg/kg and intravenous diazepam 0.3 mg/kg have been compared in a prospective randomized study in 47 children (aged 6 months to 5 years) with febrile seizures that lasted over 10 minutes (9). Intranasal midazolam controlled seizures significantly earlier than intravenous diazepam. None of the children had respiratory distress, bradycardia, or other adverse effects. Electrocardiography, blood pressure, and pulse oximetry were normal in all children during seizure activity and after cessation of seizures. 

In cases of respiratory overexposure, the victim should be moved to fresh air immediately and treated according to severity of irritation. The presence and severity of respiratory irritation, bronchitis, and pneumonitis should be evaluated. If respiratory tract irritation or respiratory depression is evident, arterial blood gases, chest X-ray, and pulmonary function tests should be monitored. For acute lung injury, ventilation and oxygenation should be maintained and evaluation should be done with frequent arterial blood gas or pulse oximetry monitoring. 

Boalth N, Wandrup J, Larsson L, Frischauf PA, Lundsgaard FC, Andersen WL, et al. Blood gases and oximetry calibration-free new dry-chemistry and optical technology for near-patient testing. Clin Chim Acta 2001 307 225-33. 

Figure 27-5 The optical system for measurement of PO The optica system for PO2 is based on the ability of O2 to reduce the intensity and lifetime of phosphorescence from a phosphorescent dye that is in contact with the sample. The optica system comprises a green (519-nm peak) light-emitting diode (LED, that emits light, which is reflected by a dichroic mirror onto the PO2 sensor. Because of the phosphorescence, red light (672-nm peak) is emitted back through the dichroic mirror and onto a photodetector. (From Boaith N,Wandrup J, Larsson L, et al. Blood gases and oximetry calibration-free new dry chemistry and optical technology for near-patient testing. Clin Chim Acta 2001 307 225-33.)...

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