Low Perfusion States Research Articles

Effect of Hypothermia on the Oxygen Saturation Readings with Pulse Oximeter

Although pulse oximetry is a potentially useful diagnostic tool under anesthesia. there are concerns regarding its reliability for measuring oxygen saturation (SpO2 ; arterial oxygen saturation by pulse oxymeter) in hypothermic or low perfusion states. To test pulse oximeter reliability under hypothermic condition 30 data from 14 patients were collected.Subjects were divided into group I which was as body temperature>36℃ and group 2 which was body temperature <36℃.The results were as follows:1) There were no differences between group I and group 2 in the SaO2(arterial oxygen saturation by blood gas analyzer) and SpO2.2) The SpO2 in group I was underestimated by 1.20±0.85% than SaO2 in group 1(P<0.001).3) The SpO2 in group 2 was underestimated by 0.60±1.03% than SaO2 in group 2(p<0.05).Although the SpO2 was underestimated under hypothermic condition, the pulse oximeter with expired CO2 tension monitor decreased the frequent invasive arterial blood gas analysis. And it was useful tool for the detection of the hypoxia which is most commom cause of preventable anesthesia related death.

Oximetry in children recovering from deep hypothermia for cardiac surgery

Although pulse oximetry is a potentially useful diagnostic tool in the treatment of children after major open heart surgery, there are concerns regarding its reliability for measuring oxygen saturation (SaO2) in hypothermic or low perfusion states. To test pulse oximeter reliability in children under these conditions, our study compared 187 SaO2 pulse oximeter readings (Biox 3700) with simultaneous hemoximeter (OSM2, Radiometer) readings from 56 children rewarming after open heart surgery. Ages ranged from 4 months to 18 yr; temperatures ranged from 23.5 degrees to 38 degrees C (toe) and 31.3 degrees to 40.8 degrees C (core). The mean pulse oximeter SaO2 reading was 94.90% (SD 7.18, range 54% to 100%), mean hemoximeter reading was 96.07% (SD 7.06; minimum 54%; maximum 100%). The correlation between the readings was high (r = .88, p less than .005), and was not affected by low core temperature. When oximeter and cardiac monitor pulse rates coincided, the oximeter SaO2 value was within +/- 5% (p less than .05). We conclude that the Biox 3700 oximeter is reliable for noninvasive SaO2 monitoring in mild to moderately hypothermic children after open heart surgery, particularly when oximeter and cardiac heart rates coincide. Further studies are needed to confirm our findings in children with core temperatures less than 31.3 degrees C, and when other oximeters are used.

The current status of pulse oximetry. Clinical value of continuous noninvasive oxygen saturation monitoring.

The history of the development of pulse oximetry is outlined and the principle of how the apparatus works is described. The instrument detects hypoxic hypoxia and the shape of the oxygen dissociation curve means that the minimum saturation alarm should be set at 94% in anaesthetic usage. It is accurate to within 2% and is usually unaffected by racial pigmentation, but accuracy can be affected in low perfusion states, hypothermia and in the presence of abnormal forms of haemoglobin and pigments in the blood. Its clinical evaluation in the operating theatre and intensive care unit is reported. It was found to be useful and reliable and would appear to have logistical and other advantages over current methods of detecting hypoxia. Pulse oximetry may make a significant contribution to the safety of anaesthetic practice.

987 SHOCK: NEONATAL HYPOPERFUSION SYNDROMES AND MUSCLE SURFACE

Low perfusion states are inadequately defined by standard methods in the Neonatal ICU. Using a stepwise induction of hemorrhagic shock in 7 spontaneously breathing nembutal-sedated laboratory cats, pHm was shown to vary independently of routinely monitored parameters and most strikingly, autonomous of blood pH (0-1.21 difference). In 4 critically ill human infants (760-3500 gms) pHm was shown to fall during states known to be associated with tissue underperfusion although compensatory mechanisms maintained the patient at clinically acceptable levels. During hypotensive episodes, acute volume expansion with PRBC or albumin resulted in an average transient rise in pHm of 0.18 pH units (range 0.11-0.27) with no significant change in blood pH. Trends associated with a rising mean aortic blood pressure and general improvement correlated with pHm returning to “healthy” values in HMD patients (range 6.52-7.47). There were no complications in monitoring up to 6 days. This study demonstrates (1) pHm can be used as an independent indicator of tissue perfusion at the end organ; (2) blood volume expansion temporarily increases tissue perfusion in critically ill neonates; (3) newborn and premature infants can regulate blood flow to non-vital organs (muscle); (4) this previously inaccessible information in the newborn nursery may help reduce neonatal morbidity and mortality by permitting earlier diagnosis of shock and institution of appropriate therapy.

Griffiths' point: critical anastomosis at the splenic flexure. Significance in ischemia of the colon

Griffiths' point is defined as the site of (a) communication of the ascending left colic artery with the marginal artery of Drummond, and (b) anastomotic bridging between the right and left terminal branches of the ascending left colic artery at the splenic flexure of the colon. It is upon this critical point at the splenic flexure that collateral circulation between the superior mesenteric artery and the marginal artery branch of the inferior mesenteric artery supplying the descending colon is dependent. Analysis of arteriographic studies shows that anastomosis at Griffiths' point is present in 48%, poor or tenuous in nine percent, and absent in 43%. This critical point is of significance in occlusive vascular impairment of the left colon, both in spontaneous instances and following surgical ligation of the inferior mesenteric artery, and in "nonocclusive" ischemic colitis. Its relationship to arteriosclerotic stenoses and low flow states is discussed. Individuals with absence of dependable anastomoses at Griffiths' point at the splenic flexure may be particularly vulnerable to low perfusion states and develop the syndrome of ischemic colitis. Complete arteriographic evaluation is necessary in ischemia of the colon. This includes particularly assessment of atherosclerotic changes at or near the ostia of the major visceral arteries and the vascular arrangement at Griffiths' point.

Continuous blood pH monitoring using an indwelling catheter

1.1. A pH microelectrode mounted on the tip of a cardiac catheter is described which enables continuous pH monitoring.2.2. Experimental studies in dogs demonstrate the accuracy of this in vivo pH electrode when compared to the value measured anaerobically by a conventional bench pH meter.3.3. Clinical observations indicate that the indwelling microelectrode is stable for at least seven hours and shows a rapid response to changes occurring during surgical procedures.4.4. Constant blood pH surveillance is of value in the management of low perfusion states as well as during complicated cardiovascular procedures.

Atropine, norepinephrine, and isoproterenol and the cardiac response to experimental lactic acidosis

Acute addition lactic acidosis causes marked cardiac slowing, decreased cardiac output, and a progressive rise in the central venous pressure in the dog, suggesting increased vagal activity as well as decreased myocardial function. Bilateral cervical vagotomy and atropine in large dosages were employed to evaluate the role of vagal innervation in producing bradycardia and rhythm changes during acute lactic acidosis. These experimental procedures increased cardiac rate but did not improve cardiac output after the induction of lactic acidosis. Isoproterenol was compared with norepinephrine as a therapeutic agent to improve myocardial function during acidosis. Norepinephrine administration increased arterial pressure by 16 per cent, but did not improve cardiac output or cardiac rate when infused during acidosis. By contrast, isoproterenol caused a 10 per cent fall in arterial pressure, a 93.5 per cent increase in the cardiac output, and a 32 per cent increase in cardiac rate. These experimental findings suggest that increased vagal activity is a cause for the bradycardia and rhythm changes observed during acute lactic acidosis. Isoproterenol was an effective therapeutic agent to improve cardiac output, decrease peripheral resistance, and increase cardiac rate during severe acidosis. The application of these findings to the management of low perfusion states has been discussed.