Intraperitoneal and sigmoid colon tonometry in porcine hypoperfusion and endotoxin shock models

BACKGROUND: The objective of the present study was to assess the accuracy of an air tonometry device in vivo within a wide range of regional carbon dioxide tension (PrCO2) values by using saline tonometry as the standard and to investigate the possibilities to monitor perfusion of the intestine by tonometry in the intraperitoneal cavity. METHODS: Piglets were anesthetized and mechanically ventilated. A pair of tonometry catheters was placed in the sigmoid colon, while another pair was placed intraperitoneally in the right lower quadrant of the abdomen. Air tonometric regional PCO2 (aPrCO2) was measured every 15 min intraperitoneally and every 20 min in the sigmoid colon. Saline tonometric measurements were made every 30 min and steady-state values (ssPrCO2) were derived. Hypoperfusion shock was induced by graded constriction of the aorta. Endotoxin shock was induced by administration of lipopolysaccharide (LPS). RESULTS: The obtained average PrCO2 (=matched (aPrCO2+ ssPrCO2)/2) values ranged from 5.1 kPa to 14.7 kPa. Regional air PCO2 (aPrCO2) and steady-state saline PCO2 (ssPrCO2) exhibited a strong positive linear relationship (r=0.959). The 95% confidence interval of the mean of dPrCO2 (=aPrCO2-ssPrCO2) was 0.31-0.46 kPa. Intraperitoneal tonometric PrCO2 was lower than intraluminal PrCO2 in the sigmoid colon, and was also more sensitive to circulatory changes than sigmoid colon PrCO2. CONCLUSION: The regional air PCO2 (aPrCO2) showed good agreement with the steady-state saline regional PCO2 (ssPrCO2). Intraperitoneal measurements may be an alternative method of monitoring intestinal perfusion after abdominal surgery.     

体内脉搏氧饱和度的研究与应用现状

脉搏氧饱和度的监测是近20年来发展起来的新兴技术,已被临床广泛采用,成为麻醉和临床医疗不可缺少的监护手段之一.由于监测部位在外周,体表脉搏氧饱和度易受到组织低温、低灌注的影响.而体内脉搏血氧饱和度监测则是通过一种反射式脉搏氧饱和度探头借助人体的生理腔道如食道、气管、阴道等放入体内,直接获取中心部位的脉搏氧饱和度信号;从而避免了上述因素对脉搏氧饱和度信号的影响,成为了当今脉搏氧饱和度监测研究的一个热点,但仍存在着不少问题,需要进一步的研究.     

Intra-operative pulmonary embolism Detection by pulse oximetry

A case is presented of a 49-year-old patient who had a pulmonary embolism during ovarian cystectomy. The only evidence of its occurrence was a sudden, marked reduction in arterial oxygen saturation as detected by a pulse oximeter. The diagnosis was confirmed 24 hours later by a chest radiograph and a ventilation perfusion scan. Anticoagulant treatment was instituted.     

Inaccuracy of pulse oximetry in patients with severe tricuspid regurgitation

The accuracy of pulse oximetry was studied in a group of patients with severe tricuspid regurgitation. Measurements of arterial oxygen saturation from a finger and an ear probe were compared with those from a radial arterial blood sample analysed in vitro. Lower values were obtained using the pulse oximeter; the difference ranged from +2% to -11%. The discrepancies between pulse oximeter and laboratory oximeter readings were greater in this group of patients than in a control group who did not have tricuspid regurgitation. There was, however, no correlation between the magnitude of this discrepancy and either the peak central venous pressure or the venous pulse pressure.     

An audit of induction of anaesthesia in neonates and small infants using pulse oximetry

The frequency and severity of hypoxaemia during induction of anaesthesia in neonates and small infants at the Norfolk and Norwich Hospital, a district general hospital, was compared, using pulse oximetry, with that of the nearest specialist hospital, the Queen Elizabeth Hospital for Sick Children in London. There were differences in staffing and the choice of anaesthetic techniques between the hospitals. One third of the patients in both hospitals experienced desaturation of more than 5% (moderate or severe hypoxaemia) at one or more recordings during induction. The highest incidence of hypoxaemia was associated with awake intubation. There was no statistical difference in the incidence or severity of hypoxaemia between the hospitals. In the district general hospital, moderate or severe hypoxaemia of greater than 30 s duration was more likely if an anaesthetist with a regular paediatric operating list was not present at induction (p < 0.01).     

Basic studies of pulse oximetry in a rabbit model

We have developed an animal model for the evaluation of pulse oximetry during severe hypoxaemia. Twelve rabbits were anaesthetized and mechanically ventilated via a tracheostomy tube. Increasing fractions of nitrogen were added to the gas mixture they inhaled to obtain severe hypoxaemia (saturation range 26%-100%). On 412 occasions, simultaneous pulse oximeter (SpO2) and invasive haemoximeter (SaO2) measurements were compared. The regression analysis of the data gave the equation: y = 0.7 x + 26.7, r = 0.90. In the SaO2 range less than or equal to 85%, the bias (mean value of SaO2-SpO2) was higher when compared with SaO2 greater than 85%. In an in vitro study the light absorption characteristics of rabbit haemoglobin (Hb) were compared to human Hb. The millimolar extinction coefficients of both reduced and oxygenated Hb from rabbits were found to be similar to human Hb. We consider the animal model (rabbit) suitable for studies of pulse oximetry during physiological and pathophysiological conditions.     

Continuous pulse oximetry in the general surgical ward: Nellcor N-200 versus Nellcor N-3000

New measurement principles in pulse oximetry have been introduced to decrease the incidence of false movement alarms. Experimental studies have shown that the new Nellcor Symphony N-3000 may reduce the incidence of false alarms when monitoring during different activities. We compared the Nellcor Symphony N-3000 with the Nellcor N-200 pulse oximeter, when monitoring patients in the general surgical ward. Twenty-two patients were monitored during unrestricted ward activities for a total of 275 h with a N-3000 and a N-200 pulse oximeter simultaneously. Data were analysed for lack of concordance between the two pulse oximeters with respect to frequency of registered hypoxaemic episodes and thus the amount of time spent in the alarm state. The median number of desaturation episodes with the N-200 was 18 (range 0-511) compared with four (range 0-476) with the N-3000 (p < 0.0001). The median number of drop-outs (loss of signal) was 13 (range 1-46) with the N-200 compared with nine (2-41) with the N-3000 (p = 0.06). The N-200 registered saturation values of 85% or below for 23% of the observation time compared with 6% of the observation time with the N-3000 pulse oximeter (p < 0.0001). The different working principles of the two generations of oximeters were reflected in the present results derived from a clinical setting. The Nellcor Symphony N-3000 may offer an advantage compared with the Nellcor N-200, because of the reduced frequency of alarms and total time in alarm when monitoring patients in the general surgical ward.     

Intraoperative determination of intestinal viability: a comparison with transserosal pulse oximetry and histopathological examination

BACKGROUND: In this study, we aimed to measure the O2 saturation of ischemic intestinal segments and the relationship between these measures and concomitant pathological gradings. MATERIALS AND METHODS: We used 14 New Zealand White rabbits, anesthetized with a combination of 80 mg/kg (i.m.) Ketamine hydrochloride and 10 mg/kg Acepromazine (i.m.). The superior mesenteric artery (SMA) was explored, and O2 saturation was measured by pulse oximetry 5 cm proximal to the ileocecal valve at the 0th hour. At the same time a 0.5-cm full-thickness wedge biopsy was taken from the same region. Thereafter, the SMA was ligated and the abdomen was closed. All rabbits were undertaken relaparotomy at the 4th hour; O2 saturation was measured by pulse oximetry at 5 cm away from the region of the first biopsy and a 0.5-cm full-thickness wedge biopsy was taken. The abdomen was then closed. The same procedure was performed at the 8th and the 12th hour. Mucosal hemorrhage, transmural congestion, mucosal necrosis, and transmural necrosis were examined in the specimens. RESULTS: Pathologically, transmural necrosis was concomitant with 64% O2 saturation (sensitivity: 100%; specificity: 86%). Mucosal necrosis was concomitant with 76% O2 saturation values (sensitivity: 100%; specificity: 75%). Transmural congestion was concomitant with 81% O2 saturation values (sensitivity: 89%; specificity: 58%). Mucosal hemorrhage was concomitant with 91% O2 saturation (sensitivity: 100%; specificity: 31%). CONCLUSION: O2 saturation measures > 76% may indicate reversible changes as mucosal necrosis, transmural congestion, or mucosal hemorrhage, and O2 saturation measures < 64% may indicate permanent transmural necrosis. As a result, intraoperative evaluation of intestinal viability by pulse oximetry may give us an idea about the degree of pathological changes and subsequently might reduce the number of second-look operations.     

Accuracy of pulse oximetry in patients with low systemic vascular resistance

In order to assess the accuracy of pulse oximeters in patients with septic shock, we compared 80 paired readings of oxygen saturations taken from pulse oximeters and oxygen saturations obtained from co-oximetry in patients receiving intensive therapy with indwelling pulmonary artery flotation catheters. Comparison between groups with low or normal systemic vascular resistance indices showed a small (1.4%) but significant (p < 0.001) underreading of the saturation from the pulse oximeter in the presence of a low systemic vascular resistance. With normal or high systemic vascular resistance pulse oximeter readings correlated well with co-oximetry. We hypothesise that the main cause of this underreading is because the pulse oximeter is sensing pulsatile venous flow due to the opening of arteriovenous channels in the skin in septic states.     

Measurement of pulse oximetry,capnography and pH

Measurement of arterial oxygen saturation (SpO₂), end-tidal carbon dioxide (E_TCO₂) and pH are linked in this article as they all can be measured by photometric methods. The underlying physical principles, Beer–Lambert law, and other methods of measurement of pH are outlined including advantages and limitations of these techniques.     

Hemodynamic monitoring and pulse oximetry during percutaneous gastrostomy and jejunostomy: necessity or nuisance?

Summary Hemoglobin desaturation and arrhythmias have been reported during diagnostic gastroscopy and colonoscopy. During endoscopic placement of percutaneous gastrostomy tubes (PEG), the gastroscope is inserted twice and the stomach is markedly distended, thus increasing the potential risk of complications. Also, the procedure is frequently performed in patients exhibiting underlying systemic disease or little respiratory reserve. Patients undergoing PEG or percutaneous endoscopic jejunostomy (PEJ) were studied prospectively. Blood pressure, pulse, pulse oximetry, and lead II ECG tracings were obtained. Measurements were made before sedation, after sedation, at gastroscope insertion, at gastrostomy placement, at gastroscope reinsertion, and at 5 min after the procedure. In all, 50 patients (mean age, 56.8 years; 16 women, 26 men) underwent PEG only (39 cases) or PEG/PEJ (11 cases). The endoscopy suite was the site for the procedure in 38 cases and the intensive care unit was used in 12 cases. The mean time required for PEG and PEG/PEJ was 14.7± 1.1 and 18.9±2 min, respectively. Blood pressure remained stable throughout the procedure. Sinus tachycardia was observed in 72% of patients. Arterial oxygen saturation decreased after the administration of intravenous sedation but remained constant during the procedure. We reached the following conclusions: (1) desaturation occurs during sedation, (2) saturation remains constant during PEG/PEJ, (3) the mean blood pressure remains constant during PEG/PEJ, and (4) PEG/PEJ are safe procedures and monitoring should be individualized.     

Weaning with end-tidal CO2 and pulse oximetry

Study Objective: To determine whether continuous measurement of arterial oxyhemoglobin saturation (SpO₂) and end-tidal carbon dioxide (P_ETCO₂) can be used to wean patients safely and efficiently from postoperative mechanical ventilation after cardiac surgery.

Design: Prospective study comparing SpO₂ and P_ETCO₂ to calculated arterial oxygen saturation (SaO₂ and arterial carbon dioxide tension (PaCO₂) obtained from blood gas analysis.

Setting: Cardiac surgical intensive care unit at a university-affiliated hospital.

Patients: Ten patients requiring elective coronary artery bypass grafting (CABG) were studied in the postoperative period during weaning from mechanical ventilation.

Interventions: Continuous monitoring of SpO₂ and P_ETCO₂ was used to wean patients from mechanical ventilation.

Measurements and Main Results: The patients were weaned from mechanical ventilation in an average time of 6.5 ± 1.5 hours (mean ± SD). A plot of SaO₂ versus SpO₂ indicated a high correlation (r = 0.84) with sensitivity (100%) for hypoxemia (SaO₂ less than 90%). P_ETCO₂ was a good indicator of PaCO₂ (r = 0.76); its sensitivity to detect hypercarbia (PaCO₂ less than 45 mmHg) was 95%. The gradient between SpO₂ and SaO₂ was not significantly affected by the weaning process, but the PaCO₂---P_ETCO₂ gradient decreased significantly as the ventilator rate was decreased (p < 0.001). The weaning process was discontinued on four separate occasions because of metabolic acidosis. Ninety-five percent of arterial blood samples confirmed the weaning recommendations based on the continuous monitoring of SpO₂ and P_ETCO₂.

Conclusions: Continuous monitoring of SpO₂ and P_ETCO₂ can be used to wean patients safely and effectively after CABG when adjustment of minute ventilation compensates for an increased PaCO₂---P_ETCO₂ gradient during controlled ventilation.     

Improving surgical safety globally: pulse oximetry and the WHO Guidelines for Safe Surgery

Access to safe surgery should be considered as part of the basic human right for health, but unfortunately, this ideal is far from being reached in many low-income countries. Pulse oximetry is recommended as a minimum standard of monitoring by all anesthesia organizations that have set standards, yet around 78,000 operating theaters worldwide lack this essential monitor. The WHO Safe Surgery Saves Lives Program has identified evidence-based guidelines for safe surgery that are applicable in any setting, and the Global Pulse Oximetry Program will help improve access to pulse oximetry in countries where it is not available. However, these initiatives are just a start; capacity, infrastructure, trained healthcare providers and access to essential drugs, and equipment for anesthesia and surgery need to become a public health priority in many low-income countries.     

Evaluation of oesophageal pulse oximetry in patients undergoing cardiothoracic surgery

Pulse oximetry probes placed peripherally may fail to give accurate values of blood oxygen saturation when the peripheral circulation is poor. Because central blood flow may be preferentially preserved, we investigated the oesophagus as an alternative monitoring site. A reflectance blood oxygen saturation probe was developed and evaluated in 49 patients undergoing cardiothoracic surgery. The oesophageal pulse oximeter results were in good agreement with oxygen saturation measurements obtained by a blood gas analyser, a CO-oximeter and a commercial finger pulse oximeter. The median (IQR [range]) difference between the oesophageal oxygen saturation results and those from blood gas analysis were 0.00 (-0.30 to 0.30 [-4.47 to 2.60]), and between the oesophageal oxygen saturation results and those from CO-oximetry were 0.75 (0.30 to 1.20 [-1.80 to 1.80]). Bland-Altman analysis showed that the bias and the limits of agreement between the oesophageal and finger pulse oximeters were -0.3% and -3.3 to 2.7%, respectively. In five (10.2%) patients, the finger pulse oximeter failed for at least 10 min, whereas the oesophageal readings remained reliable. The results suggest that the oesophagus may be used as an alternative monitoring site for pulse oximetry even in patients with compromised peripheral perfusion.     

The influence of changes in blood flow on the accuracy of pulse oximetry in humans

Oxygen saturation (SpO2) was measured with a pulse oximeter in ten healthy, young men breathing air. A pulse oximeter probe was attached to the second toe and a laser Doppler probe to the first toe of the same foot for measurement of changes in peripheral blood flow. The pulse oximeter and laser Doppler readings were simultaneously compared when the foot was positioned 40 cm (position 1) above heart level, elevated 10 cm (position 2) above heart level and horizontally at heart level (position 3). Using this experimental human model, we achieved various blood flows. The AC and DC optical signals used for determination of oxygen saturation were recorded from the pulse oximeter and analysed. There was a significant increase (P less than 0.05) between position 1 and 3 in blood flow as measured by the laser Doppler flow meter. The corresponding pulse oximeter readings of haemoglobin saturation also increased significantly (P less than 0.05) comparing these two leg positions. Analysing the AC- and DC optical signals, the AC value of infrared light increased considerably, while the AC value of the red light decreased slightly. The DC values of red and infrared light did not change significantly. In summary, when blood flow was decreased, the ratio of red to infrared transmitted light was changed, resulting in a low SpO2 reading.     

Intraoperative pulse oximetry: Frequency and distribution of discrepant data

Study Objective: To determine the types of discrepant data during intraoperative pulse oximetry and their frequency and duration.

Design: Prospective study.

Setting: University medical center.

Patients: 46 consecutive ASA physical status I–III patients undergoing general anesthesia for elective surgical operations.

Measurements and Main Results: With an integrated computer algorithm on the pulse oximeter and another computer linked to it, data were screened and the frequency and distribution of the following oximeter signals recorded: absent; low quality or interrupted, as detected by the pulse oximeter algorithm, nonphysiologic, identified by the personal computer as a heart rate change greater than 10 beats per minute within 2 consecutive 2-second samples, with no similar abrupt change reported simultaneously on ECG. The number of episodes per hour of discrepant oximeter data and the duration of the episodes were recorded by phase of anesthesia: induction, maintenance, and emergence. Discrepant data occurred most frequently and lasted longest during emergence (p < 0.05); the majority of episodes of discrepant data during emergence lasted less than 12 seconds. Excluding discrepant data that lasted less than 12 seconds decreased the frequency of discrepant data by 63% and excluding those that lasted less than 30 seconds decreased the frequency of discrepant data by 93%.

Conclusions: Pulse oximeters frequently report discrepant data intraoperatively, most frequently during emergence from anesthesia. An alarm delay triggered by discrepant data and lasting 12 to 30 seconds would keep most discrepant data from becoming false alarms and, thus, may reduce distracting sound pollution in the operating room.     

Notes on the apparent discordance of pulse oximetry and multi-wavelength haemoglobin photometry

Multi-wavelength photometers, blood gas analysers and pulse oximeters are widely used to measure various oxygen-related quantities. The definitions of these quantities are not always correct. This paper gives insight in the various definitions for oxygen quantities. Furthermore, the possible influences of dyshaemoglobins and fetal haemoglobin on the accuracy of pulse oximetry are discussed.
As pulse oximeters are constructed for the determination of arterial oxygen saturation, they should be validated with sample oxygen saturation values and not with the oxyhaemoglobin fraction. The influence of carboxy-haemoglobin is insubstantial over an oxygen saturation range of 0% to 100%. Through the presence of methaemoglobin, pulse oximetry will give an underestimation above 70% and an overestimation below 70% oxygen saturation. The influence of fetal haemoglobin is insignificant in the neonatal use of pulse oximetry, in the range of 75% to 100% arterial oxygen saturation. However, a pulse oximeter underestimates the arterial oxygen saturation at the 25% level with 5%, if the pulse oximeter has been calibrated in human adults. Such a low level of arterial oxygen saturation can be present in the fetus during labor.     

Systemic and mesenteric hemodynamics, metabolism, and intestinal tonometry in a rat model of supraceliac aortic cross-clamping and declamping

OBJECTIVE: To describe systemic and mesenteric hemodynamics, metabolism, and intestinal tonometry in a rat model of supraceliac aortic cross-clamping and declamping. DESIGN: Prospective, randomized, experimental study. SETTING: University cardiovascular research laboratory. PARTICIPANTS: Twelve male anesthetized and ventilated Sprague-Dawley rats. INTERVENTION: Supraceliac aortic cross-clamping was performed for 30 minutes, followed by declamping and reperfusion for 180 minutes or sham clamping and sham declamping. MEASUREMENTS AND MAIN RESULTS: Mean arterial blood pressure; abdominal aortic, superior mesenteric, and carotid artery blood flow; intestinal mucosal tonometry; hemoglobin; lactate; and blood gases were measured before and after 30 minutes of aortic cross-clamping and 15, 30, 60, 120, and 180 minutes after declamping during reperfusion. Aortic cross-clamping induced an increase in mean arterial pressure (117+/-20 mm Hg to 147+/-12 mm Hg), an increase in right atrial hemoglobin saturation(66%+/-11% to 81%+/-6%), an increase in lactate levels (1.7+/-0.7 mmol/L to 4.3+/-1.3 mmol/L), and an increase in tonometric PCO2 (49.6+/-5.0 mm Hg to 75.6+/-8.6 mm Hg). Three hours of reperfusion after declamping resulted in significantly decreased mean arterial pressure (38+/-10 mm Hg); decreased aortic (101+/-12 mL/min/kg to 57+/-32 mL/min/kg), mesenteric (19+/-4 to 13+/-6 mL/min/kg), and carotid (12+/-4 mL/min/kg to 5+/-3 mL/min/ kg) blood flows; and elevated lactate levels (4.2+/-2.0 mmol/L). Tonometric PCO2 had normalized to baseline levels (51.9+/-3.8 mm Hg), but PCO2 gap was significantly higher than in sham clamped rats (17.9+/-7.8 mm Hg v. 7.0+/-2.6 mm Hg). CONCLUSIONS: Hemodynamic and metabolic effects of aortic cross-clamping and declamping known from large animal models are reproducible using a rat model. Intestinal tonometry indicated mesenteric ischemia during aortic cross-clamping, which was reversible to preclamp values within 30 minutes of reperfusion after declamping.