End-tidal

Carbon monoxide 30 ppm carbon monoxide in end-tidal breath (HGV) Post shift... 

Initial features are mostly pulselessness, difficulty in ventilation, desaturation, and a decreased end-tidal CO2. Cutaneous symptoms are observed in 66-70% of patients in case of IgE-mediated reactions but in more than 90% in non-IgE-mediated reactions. On the contrary, cardiovascular collapse and bronchospasm are more frequent in IgE-dependent reactions (table 2). Severe anaphylaxis may be a primary cardiac arrest [9]. 

First clinical results were obtained by using a combined catheter which included both the optical fibre sensor and the Tonocap balloon (Figure 8) A typical result obtained on an intensive care patient, is shown in Figure 9. In the graph the tracing of the end-tidal CO2 (EtCC>2), i.e. the CO2 concentration in the expiration at the end of the expiratory phase, and the values of the arterial CO2 (PaC02), obtained from blood samples drawn from the patient, are also shown. As expected, a rapid CO2 peak was detected only by the optical fibre sensor, and was not seen by Tonocap (as in the measurements carried out on volunteers). Moreover, the optical fibre sensor seems to follow better the end-tidal CO2. 

End-tidal carbon dioxide monitoring is a safe and effective method to assess cardiac output during CPR and has been associated with ROSC. 

Assume a respiratory rate of 12 min-1. From zero baseline, the curve initially rises slowly owing to the exhalation of dead space gas. Subsequently, it rises steeply during expiration to a normal value and reaches a near horizontal plateau after approximately 3 s. The value just prior to inspiration is the end-tidal C02 (Petco2). Inspiration causes a near vertical decline in the curve to baseline and lasts around 2 s. 

Figure 3.1 Graph showing the ratio between inspired (FJ) and alveolar (FA) end-tidal concentrations of the agents shown. The least soluble agents approach equilibrium (FA/FI=1) the most rapidly. Also, since both inhalation and intravenous anaesthetic drugs tend to reduce cardiac output, they facilitate the uptake of volatile agents. It follows that any inhaled anaesthetic drug must be given with great caution to patients in shocked states, e.g. hypovolaemia, arrhythmias, myocardial infarction.

End-tidal C02 (peak expired C02) is measured for each breath with a microcapnometer (Microcapnometer, model 0151-003L, Columbus Instruments, Columbus, OH, USA). This microcapnometer is uniquely suited for measurement of expired C02 in rats and other animals with low minute volumes (200-400 mL/min) since it utilizes relatively low flow rates (5 or 20 cc/min) compared with the standard capnometers that require 150-200 cc/min. This capability is achieved by using a low pressure, high velocity principle for analyzing the sampled gas. Airflow to the microcapnometer is maintained at 20 mL/min and is collected through a Teflon catheter (I.D. = 0.76 mm). Carbon dioxide concentrations are measured spectrophotometrically... 

End-tidal C02 is monitored in conscious rats by using a mask that is fitted to the snout of the rat. Since rats are obligate nasal breathers, enclosure of the mouth is not necessary. The distal tip of the nasal mask has an opening (I.D. = 3.5 mm) for breathing... 

Indeed, a measurement of end-tidal CO in breath corrected for inhaled CO is used as a measure of assessing infants at risk of severe hyperbilirubinemia because CO and bilirabin are produced in equimolar amounts (Bartoletti et al, 1979). 

Pulsus altemans in association with hjrpercapnia occurred in a study of 120 patients who breathed spontaneously during halothane anesthesia (10). End-tidal... 

Manohar M, Gustafson R, Nganwa D 1987 Skeletal muscle perfusion during prolonged 2.03% end-tidal lsoflurane-02 anesthesia in isocapnic ponies. American Journal of Veterinary Research 48 946-951 Marlin D J, Young L E, McMurphy R et al 2001 Effect of two anaesthetic regimens on airway nitric oxide production in horses. British Journal of Anaesthesia 86 127-130... 

Considerable controversy surrounds the identification of patient-specific factors that affect resuscitation survival. Proposed risk factors are age, concomitant diseases, initial pH, duration of resuscitation, and end-tidal carbon dioxide. The accuracy of these predictors has not been consistent in clinical studies, however. ... 

In clinical practice, one can monitor the equilibration of a patient with anesthetic gas. Equilibrium is achieved when the partial pressure in inspired gas is equal to the partial pressure in end-tidal (alveolar) gas. This defines equilibrium because it is the point at which there is no net uptake of anesthetic from the alveoh into the blood. For inhalational agents that are not very soluble in blood or any other tissue, equilibrium is achieved quickly (e.g., nitrous oxide, Figure 13-4). If an agent is more soluble in a tissue such as fat, equilibrium may take many hours to reach. This occurs because fat represents a huge anesthetic reservoir that will be filled slowly because of the modest blood flow to fat (e.g., halothane, Figure 13 ). 

FIGURE 13-4 Uptake of inhalational general anesthetics. The rise in end-tidal alveolar (F ) anesdietic concentration toward the inspired (Fj) concentration is most rapid widi die least soluble anesdietics, nitrous oxide and desflurane, and slowest with the most soluble anesdietic, halodiane. 

CLINICAL USE Halothane is a potent, nonpungent and well-tolerated agent that usually is used for maintenance of anesthesia and is well tolerated for inhalation induction of anesthesia, most commonly in children, in whom preoperative placement of an intravenous catheter can be difficult. Anesthesia is produced by halothane at end-tidal concentrations of 0.7-1%. The use of halothane in the U.S. has diminished substantially since the introduction of newer inhalational agents with better pharmacokinetic and side-effect profiles. 

Undefined delay times and distortion of the rise time reduce the derivable information of waveform analysis but the end-tidal value and the average value can be used clinically. Figure 23-24 presents an example of a flow mismatch with distortion of the CO waveform. The inspiratory value may be used to detect system failures. During the warm-up time and the subsequent Hrst hour, (he IR sensor typically shows increased drift and reduced accuracy until temperature balance is reached. Zero-point calibration can be effected periodically by automatically aspirating ambient air. Drifts of the measuring system are calibrated manually or automatically over longer periods by use of test gases. 

This end-tidal partial pressure (EtCOj) in the gas phase corresponds to the mixed alveolar value (pACOj) which is correlated with the arterial partial pressure (paCOj), depending on perfusion, ventilation, and distribution disorder. The difference between arterial (a) and... 

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