Near Infrared Spectroscopy Monitoring During Carotid Endarterectomy: Which Threshold Value is Critical?

OBJECTIVES: Retrospectively to verify which decreasing percentage in regional oxygen saturation (rSO(2)) identified patients with good collateralisation during carotid artery cross clamp. MATERIALS AND METHODS: During 594 endarterectomies under general anaesthesia the decreasing percentage from preclamp value to value detected in the first 2 min after clamping the CCA and/or ICA was calculated in real time. No temporary shunt was placed in any case. ROC analysis was performed to determine the optimal cut-off for rSO(2) decrease to identify the occurrence of neurological complications. RESULTS: A cut-off of 11.7% was identified as optimal. Sensitivity and specificity were 75% (95% CI 71-78) and 77% (95% CI 74-80), respectively. The cut-off of 20% had a lower sensitivity (30%) and a higher specificity (98%) to identify patients with complications, with positive and negative predictive value of 37 and 98%, respectively. CONCLUSIONS: The study suggest that a relative decrease in rSO(2) of <20% from preclamp to early cross clamp value has a high negative predictive value, i.e. if rSO(2) does non decrease more than 20%, ischemia by hypoperfusion is unlikely and a shunt should not be necessary. Moreover, a relative decrease >20% may not always indicate intraoperative neurological complications.     

Multiple-scattering effects in transmission oximetry

To develop an algorithm for the spectrophotometric determination of the oxygen saturation in blood, a model for the transmission of light in a scattering and absorbing medium is developed, taking into account effects of multiple scattering. The computed results obtained by a Monte Carlo simulating program agreed well with those found by experiment. The results were compared with those obtained by the commonly used algorithm of transmission oximetry (based on Lambert-Beer's law) and it was found that the calibration curves obtained by this method were strongly dependent on the haematocrit and thickness of the sample. These curves were less reliable the lower the saturation of oxygen.     

Duration of apnoea in anaesthetized children required for desaturation of haemoglobin to 95%: comparison of three different breathing gases

In this study, we compared three gas compositions to determine if the duration of apnoea for Spo₂ to decrease is proportionate to the oxygen fraction of the gas prior to apnoea. Twenty-five patients ASA physical status 1–2 aged two months to 12 years were included in the study. Anaesthesia was induced via a mask with 5% sevoflurane and 66% N₂O in oxygen. After paralysis with vecuronium (0.12 mg·kg^?1, i.v.) the trachea was intubated and anaesthesia was maintained with sevoflurane and N₂O in oxygen. When cardiovascular stability was obtained, the patient was randomly set to breathe one of three gas compositions: 1. oxygen (Fio₂ 1.0), 2. N₂O/O₂ (Fio₂ 0.4), and 3. air/O₂ (Fio₂ 0.4). All three gas compositions included 2–4% of sevoflurane to maintain anaesthesia. After more than eight min of each gas breathing, apnoea was begun by disconnecting the breathing circuit from the tracheal tube. The time from the start of apnoea (Spo₂ 100%) to Spo₂ of 95% (T₉₅) was measured. T₉₅ measured after breathing N₂O/O₂ and air/O₂ were 34.6 ± 5.7 and 28.8 ± 4.7% of that measured after oxygen breathing (P < 0.001 vs oxygen breathing, P < 0.001 vs oxygen and N₂O/O₂ breathing), respectively. Preoxygenation before intubation was validated to delay the haemoglobin desaturation brought about by apnoea. An induction technique using a low Fio₂ will allow rapid haemoglobin desaturation.     

Comparison of digital blood pressure, plethysmography, and the modified Allen''s test as means of evaluating the collateral circulation to the hand

The collateral circulation to the hand was evaluated on 70 hands of healthy volunteers. Comparisons were made between the results of the modified Allen's test alone and the Allen's test combined with either plethysmography or digital blood pressure. The modified Allen's test requires patient cooperation and the results can be subjective. Plethysmography does not require patient cooperation and produces a signal that varies directly with flow; however, this is not a quantifiable signal. Digital blood pressure (measured by the 2300 Finapres noninvasive blood pressure monitor, Ohmeda, Englewood, CO, USA) also requires no patient cooperation. The values produced are of clinical value and reproducible. Both the plethysmograph and digital blood pressure monitors were able to demonstrate the dominant arterial vessel of the hand. The digital blood pressure monitor produces an objective recordable numerical value, an accepted clinical parameter, and it does not require patient cooperation. The use of a digital blood pressure monitor may prove to be an acceptable alternative to the traditional Allen's test.     

Arterial oxygen saturation following premedication in children with cyanotic congenital heart disease

To determine the effects of premedication on arterial oxygen saturation (SaO2) and heart rate (HR), 11 children (ages three to seven years) scheduled for elective repair of cyanotic congenital heart defects were studied. Patients were premedicated with oral or rectal pentobarbitone 2 mg.kg-1 90 minutes prior to induction of anaesthesia followed by intramuscular morphine 0.2 mg.kg-1 and atropine 0.02 mg.kg-1 60 minutes prior to induction. The SaO2 and HR of each child were monitored continuously using a Nellcor pulse oximeter during two 90 minute periods: a control period commencing 25.5 hours preoperatively (day 1) and a post premedication period commencing 1.5 hours preoperatively (day 2). Data were compared at time 0 (corresponding to the time of administration of pentobarbitone on day 2), 30 (corresponding to the administration of intramuscular morphine and atropine on day 2), 60 and 90 minutes (the latter corresponding to the time of induction on day 2) after the administration of pentobarbitone. There were no significant differences in SaO2 or HR between day 1 and day 2 at time 0, 60, and 90 minutes. The SaO2 (mean +/- SD) decreased significantly immediately following intramuscular premedication at time 30 minutes on day 2 (72.7 +/- 5.9 per cent) compared to the corresponding time on day 1 (83.9 +/- 2.9 per cent) (p less than 0.05). The duration of this desaturation was 2.5 +/- 1.9 minutes. Heart rate (mean +/- SD) increased from 109.2 +/- 21.3 beats.min-1 at time 30 minutes on day 1 to 142 +/- 20.4 beats.min-1 on day 2 (p less than 0.05). We conclude that administration of intramuscular premedication preceded by oral or rectal pentobarbitone causes transient arterial desaturation and tachycardia in children with cyanotic congenital heart disease.     

The influence of local skin heating and reactive hyperaemia on skin blood flow abnormalities in patients with reflex sympathetic dystrophy (RSD)

Abstract. Skin blood flow in reflex sympathetic dystrophy (RSD) patients has been reported to develop from an increase at an early stage to a decrease at later stages. So far, it remains unclear whether these abnormalities are solely of microcirculatory origin, and result from functional vasospasm or structural vessel wall changes. Eighty-seven RSD patients were categorized as follows: stage I in case of a stationary warmth sensation; stage II in case of an intermittent warmth and cold sensation; and stage III in case of a stationary cold sensation. Laser Doppler flowmetry (LDF) was used as a measure of total skin blood flow and transcutaneous oximetry (TCPO2) as a measure of vascular reactivity in the more superficial skin layers. Local skin heating and reactive hyperaemia were used to study the relative reserve capacity of skin microvessels. Finapres was used to assess digital arterial pressures. As compared to healthy volunteers ( n =16), LDF under control conditions demonstrated an increase in skin blood flow at stage I ( P <0.01). A decrease in skin blood flow under control conditions was seen at stages II ( P <0.05) and III ( P <0.05), but the relative flow reserve capacity, as measured with LDF, was not impaired at these stages. Regression analysis did not show a relation between LDF parameters and duration of the syndrome. TCPO2 revealed no differences between patient groups and controls. Regression analysis did not demonstrate a relation between TCPO2 parameters and duration of the syndrome. Digital systolic blood pressures were increased at stages II ( P <0.05) and III ( p <0.001). These findings indicate that abnormalities in skin blood flow, as observed in RSD patients, are of microcirculatory origin. The observed decrease in skin blood flow at stages II and III most likely results from functional vasospasm rather than from structural vessel wall changes.     

Hypoxaemia during outpatient dental anaesthesia

Eighty children, ASA grade 1, who had outpatient general anaesthesia for tooth extraction were studied. An inhalational induction was performed, with patients receiving halothane, nitrous oxide and either 33% or 50% oxygen. Oxygen saturation was measured throughout the procedure using the Ohmeda Biox 3700 pulse oximeter. No significant difference in the incidence of hypoxaemia was found between the two groups. There was no association between the grade of surgeon or anaesthetist and the incidence of hypoxaemia.     

Oronasopharyngeal suction versus no suction in normal, term and vaginally born infants: a prospective randomised controlled trial

This prospective randomised controlled trial aimed to compare the effects of oronasopharyngeal suction with those of no suction in normal, term and vaginally born infants and was performed at a Turkish tertiary hospital from June 2003 to January 2004. A total of 140 newborns were enrolled in the trial (n = 70 per group). The no suction group showed lower mean heart rates through the 3rd and 6th minutes and higher SaO(2) values through the first 6 mins of life (P < 0.001). The maximum time to reach SaO2 of >or= 92% (6 vs. 11 min) and >or= 86% (5 vs. 8 min) were shorter in the no suction group (P < 0.001).     

Ketamine

Ketamine is used extensively in the developing world (DW) because of its effectiveness, availability, relatively low cost, and presumed safety. This report is a prospective, objective assessment of the efficacy and safety of ketamine when used as the sole anesthetic agent in a general medical practice hospital in the DW in children less than 16 years of age undergoing nonemergent operative procedures. Children undergoing laparotomy, thoracotomy, or craniotomy were excluded. Data analysis included serial arterial hemoglobin saturation (SpO₂) and pulse rate, amount of ketamine utilized, adequacy of anesthesia, and perioperative complications. One hundred thirty-one children undergoing a total of 210 anesthetics were studied. The level of anesthesia was adequate in all cases. The SpO₂ dropped below 90% in 40 (19%) children, below 85% in 25 (12%), and below 80% in 13 (6%). SpO₂ drops occurred significantly (P = 0.004) more often after IM than after IV injection. All drops in SpO₂ were abrupt without premonitory signs. Thirty-three (82.5%) of these 40 children responded readily to airway manipulation with a jaw thrust, and only 7 (3.3% of the total series) required face-mask O₂. None required intubation or positive-pressure ventilation. Transient laryngospasm occurred in 1 child, but there were no other complications. In particular, there was no mortality, apnea, emesis, excessive salivation, or significant early or delayed emergence phenomena. Ketamine is quite effective when used as the sole anesthetic agent in DW children. It is relatively safe, but hypoxemia may go undetected unless technologically sophisticated monitoring equipment is available. Proper suction and ventilatory support equipment should be readily available prior to ketamine injection. The first step when hypoxemia is detected is simple airway manipulation, followed by oxygen administration by face mask if needed. Rarely will intubation be indicated. Ketamine is also a good drug for the management of pediatric emergency department procedures in the United States, but all children in these more developed centers should be monitored with a pulse oximeter, since a significant number of children have a precipitous drop in SpO₂.     

Hypoxaemia during induction of anaesthesia—an audit of children who underwent general anaesthesia for routine elective surgery

Arterial oxygen saturation was measured using pulse oximetry during induction of anaesthesia in 108 children aged 10 days--14 years. No restriction was placed on the method of induction. Oxygen saturation decreased to less than 90% in 29 children (26.8%) and less than 80% in seven children (6.4%). There was a significantly increased incidence of desaturation (to less than 90%) in children under one year of age, in those who had no premedication, in those who received only atropine as a premidicant and in children who were anxious or crying before intravenous induction. Oxygen saturation did not decrease below 90% in any child who received inhalational induction.