Arterial blood gases

Blood gas analyses are an essential part of modern patient care. Although all blood gas instruments have pH, PCO2, and PO2 electrodes based on the same principles, instruments in current use vary greatly in design, operator dependence, and accuracy. For the clinician to obtain accurate and timely results there must be not only good instrumentation and laboratory techniques, but also reliable specimen collection and transport and data transmission. Dedicated personnel, duplicate instrumentation, frequent duplicate analyses of blood, blood tonometry, a good quality control system, and proficiency testing are advantageous. "Temperature correction" of the blood gas values by the laboratory to the patient's actual temperature is disadvantageous.     

Gas exchange, blood gases and acid-base status in the chick before, during and after hatching

To study the transition from chorioallantoic to pulmonary gas exchange in birds, blood gases and acid--base variables were measured in chicks of domestic fowl before, during and after hatching. Measurements were made in samples of 'venous' blood (from allantoic arteries or the right ventricle, respectively) entering the gas exchanger (chorioallantois or lungs, respectively) and arterialized blood (from allantoic veins or the left ventricle, respectively) leaving the gas exchanger. Also, O2 uptake was measured and blood flow of the gas exchanger was determined according to the Fick principle. During the last days of incubation PO2 decreased PCO2 increased in both arterialized and 'venous' blood, but the changes of pH were small due to a concomitant increase in bicarbonate concentration, in accordance with the results of previous studies. After external pipping and hatching pronounced hypocapnia developed, but the respiratory alkalosis was partiallY compensated by a transitory non-respiratory reduction of bicarbonate. In spite of arterial hypoxia at the end of incubation and some loss of blood during hatching, blood O2 transport was not seriously impaired during pipping and hatching as revealed by 'venous' blood gases. The blood gases and pH of 17-day-old chicks were close to those of adult chickens.     

Arterial blood gases after coronary artery bypass surgery.

Coronary artery bypass graft (CABG) surgery adversely affects arterial blood gas (ABG) determinations. The purposes of this study were to assess serial changes in ABGs following bypass surgery and identify factors that may influence these changes. Room air ABGs were obtained preoperatively and on days 1, 2, 4, 6, and 8 postoperatively on 125 patients undergoing bypass surgery. Fifty-five patients (saphenous vein grafting [SVG] group) had only SVG grafting while 70 (internal mammary artery [IMA] group) received one (60 patients) or two (10 patients) IMA grafts in addition to the SVG grafts and were subjected to pleurotomy. The mean preoperative values (+/- SD) were as follows: PaO2, 75.1 +/- 7.7 mm Hg, P(A-a)O2, 20.9 +/- 7.5 mm Hg; PaCO2, 33.6 +/- 4.1 mm Hg; pH, 7.43 +/- 0.04; hemoglobin, 14.8 +/- 1.4 g/dl; and hematocrit, 44.2 +/- 3.9 percent. There was a large decrease in the PaO2 postoperatively. The nadir for the PaO2 (55.7 +/- 6.6 mm Hg) occurred on the second postoperative day. Eight days postoperatively, there were still significant abnormalities; the PaO2 was 65.7 +/- 7.3 mm Hg, the P(A-a)O2 was 33.2 +/- 8.8 mm Hg; the hemoglobin was 10.5 +/- 1.4 g/dl; and the hematocrit was 31.7 +/- 4.0 percent. The decrease in the PaO2 was particularly noteworthy given the large decrease in the hemoglobin and hematocrit. The changes in the PaO2 were not significantly correlated with the age, number of grafts, pump time, length of anesthesia, or endotracheal intubation or smoking history. Immediately postoperatively, changes were similar in both groups (p > 0.05); on the second postoperative day, the PaO2 had decreased 26.9 percent in the SVG group and 25.5 percent in the IMA group. However, the postoperative abnormalities resolved more slowly in the IMA group (p < 0.05). These observations suggest that the additional trauma to the lungs and chest wall in the IMA group (pleurotomy, the placing of pleural drains, etc) will result in a longer recovery time in the IMA group than in SVG group.     

The scavenger device for nitrous oxide administration

Nitrous oxide levels of 300 to 500 ppm occur when nitrous oxide is administered in the emergency department using the Nitronox machine without use of the scavenger device, which traps expired nitrous oxide gases and vents them to the outside environment. A scavenger device that can limit nitrous oxide gas to zero ppm in the emergency department setting has been developed. We think that development of the scavenger device is a significant advance for the safe administration of nitrous oxide in the emergency department.     

Arterial blood gases and pH during sleep in chronic obstructive pulmonary disease.

Arterial blood gases were measured during 7 hours of sleep in 15 patients with severe stable chronic obstructive pulmonary discrease (COPD); 6 awake patients with COPD studies in recumbency for an average of 5 hours served as controls. Mean maximal decrease in arterial oxygen partial pressure (PaO2) (plus or minus SD) was 13.5 plus or minus 3.9 mm Hg for sleeping patients (p less than 0.005) and 5.5 plus or minus 1.7 mm Hg for controls (p less than 0.1), respectively. Changes in pH during sleep were of the magnitude expected with acute changes in arterial carbon dioxide partial pressure (PaCO2) in patients with chronic hypercapnia. Consistent changes in heart rate, respiratory frequency or cardiac rhythm were not observed during sleep. Nocturnal worsening of hypoxemia could be explained by alveolar hypoventilation in six sleeping patients and in five controls; in nine sleeping patients, further impariment of ventilation-perfusion mismatch also contributed to worsening of hypoxemia. There was no relationship between the decrease in PaO2 during sleep and the degree of airways obstruction or the PaO2 level when awake. Because of low PaO2, when awake, a fall in PaO2 during sleep brings values into the steep part of the oxyhemoglobin dissociation curve where slight changes in PaO2 result in marked changes in oxygen content. All patients with COPD whose waking PaO2 was below 60 mm Hg had PaO2 below 50 mm Hg during sleep; nocturnal oxygen therapy should be considered in such patients, particularly in the presence of polycythemia or troublesome right-sided heart failure.     

Arterial oxygen during apnea

The rate of decrease of arterial oxygen partial pressure during apnea with the glottis open was studied with the help of a mathematical model of oxygen transfer between lungs, blood and tissues. The results of computer simulations suggest: 1) that the rate is determined principally by the O₂ consumption and and by alveolar volume when PaO₂ is above 100 mm Hg; 2) that cardiac output, tissue volume, haemoglobin concentration and blood volume exert only a small influence in that range of arterial oxygen pressure; 3) that haemoglobin concentration and blood volume become increasingly important factors when arterial haemoglobin is progressively desaturated. The clinical implications of the results are discussed particularly in children.     

Factors associated with fainting: before, during and after whole blood donation

Background Whole blood (WB) donation encompasses several periods during which some donors faint. Identification of factors associated with fainting during each period should guide intervention strategies. Reducing faint reactions may reduce donor injuries and disability. Methods Blood donation was divided into three periods: Period 1 – registration; Period 2 – phlebotomy; and Period 3 – post‐phlebotomy. Period 3 consists of two sub‐periods (3A – on‐site and 3B – off‐site). For each Period, stratified rates of fainting in relation to various donor and donation characteristics were calculated and multivariable logistic regression analyses to identify factors associated with fainting were conducted. Donor injuries in each period were also analysed. Results Of the 956 766 donors registered in 2007, 554 534 (58%) donated WB. There were 43 fainting episodes and two injuries in Period 1 and 1520 faints and 73 injuries in Periods 2 and 3. Regression analyses showed that youth and donor first‐time status are associated with fainting in all periods; but most significantly in Period 1. Small estimated blood volume is notably not a factor in Period 1 but is significant in Periods 2 and 3. The highest injury rate is seen in Period 3A (0·07 and 0·09/1000 donations) for male and female donors, respectively. Conclusions Variability in factors associated with fainting across defined periods of the donation process suggest differing underlying mechanisms and the possibility that interventions for the reactions most associated with injury during each time period can be designed. The highest rate of injury per donation occurred in ambulating donors.     

Arterial blood oxygen desaturation in infants and children during upper gastrointestinal endoscopy

Arterial blood oxygen desaturation and abnormal electrocardiographic changes have been reported in adults undergoing upper gastrointestinal endoscopy. We studied 32 infants and children less than 12 years of age using pulse oximetry and continuous electrocardiography before, during, and after upper gastrointestinal endoscopy performed under intravenous sedation. Sinus tachycardia was the most common electrocardiographic change, and no clinically significant electrocardiographic abnormalities were induced by the procedure. Desaturation to less than or equal to 90% was found in 37.5% of the patients and was most commonly noted during the endoscopy procedure and in patients with cardiopulmonary disease. The desaturation was unpredictable because there was no correlation between desaturation and medication, tolerance to the procedure, weight, or age of the child. Some patients who subjectively appeared to tolerate the procedure well had significant desaturation. The use of pulse oximetry should be considered for all children undergoing upper gastrointestinal endoscopy.     

Pacemaker malfunction after nitrous oxide anesthesia

Entrapment of gas in the pacemaker pocket has been reported.^1,2 Pacemaker malfunction in those studies was a result of loss of anodal contact, and presented with small amplitude, variable amplitude or absent pacing spikes with loss of ventricular capture. We report a patient in whom pacemaker malfunction was caused by the presence of an anesthetic gas within the pacemaker pocket itself.     

Prefixed equimolar nitrous oxide and oxygen mixture reduces discomfort during flexible bronchoscopy in adult patients: a randomized, controlled, double-blind trial

STUDY OBJECTIVES: Flexible bronchoscopy (FB) is an invasive procedure associated with patient discomfort and frequent nose pain. A simple sedation procedure that does not require the intervention of an anesthetist is of interest. The aim of this prospective, randomized, double-blind study was to assess efficiency of nitrous oxide inhalation on the reduction of FB-induced discomfort in adult patients. DESIGN AND SETTINGS: Two hundred six patients were randomized to receive either a prefixed equimolar nitrous oxide/oxygen mixture (N2O) or a prefixed equimolar nitrogen and oxygen mixture (control). The primary outcome was stress as assessed by pulse rate and systemic BP during the procedure. Secondary outcomes were self-assessed pain using a visual analog scale (VAS) and patient satisfaction based on a questionnaire. Adverse events were recorded. RESULTS: A significant increase in BP was observed only in the control group (p = 0.003), while pulse rate values did not differ between the two groups. As assessed by the VAS, pain was lower in the N2O group as compared to placebo (p = 0.02). Nose pain and cough were also significantly reduced by N2O. Adverse events, mostly anxiety, were reported in 10 patients. CONCLUSION: These results indicate that equimolar N2O inhalation is efficient in reducing patient discomfort and may be an alternative to general anesthesia.     

Venous thrombosis after nitrous oxide abuse,a case report

Journal of Thrombosis and Thrombolysis - Nitrous oxide is a commonly abused inhalant by adolescents and young adults. There is limited data describing the adverse effects of nitrous oxide abuse,...     

Combined inhalation of nitric oxide and oxygen in patients with moderate to severe COPD: effect on blood gases

Inhaled nitric oxide (NO) has been reported to improve oxygenation in patients with COPD if administered in combination with oxygen (O2). Little, however, is known about the variability of these effects and the potential influence of body position. Twenty-six spontaneously breathing patients with moderate to severe COPD inhaled clean air, O2(FiO2, 0.29), 5 ppm NO, 5 ppm NO+O2, 10 ppm NO+O2, 10 ppm NO, and again clean air in an upright position. Blood gas analysis from arterialized capillary blood was performed after each inhalation. Tests were repeated on different days to assess the variability of the response. Furthermore, eight patients were studied in both upright and supine position while inhaling 5 ppm NO in the presence or absence supplemental O2. As compared to clean air, NO led to a mean decrease in PaO2 of -0.9 mmHg at 5 ppm and of -2.8 mmHg at 10 ppm NO. Similarly, NO+O2 led to a dose-dependent fall in PaO2 of -1.8 and -3.6 mmHg, respectively, as compared to O2. Average within-subject variation (SD) of the effects elicited by 5 and 10 ppm NO was 2.4 and 2.3 mmHg without additional O2, and 4.7and 5.3 mmHg with O2. The effects of 5 ppm NO+O2 differed significantly between upright and supine position; as compared to O2 alone, mean (SD) changes were -3.7 +/- 5-8 vs. +1.1 +/- 4.9 mmHg, respectively. Our findings suggest thatthe addition of NO to inhaled oxygen, when given in an upright position, does not lead to an improvement of PaO2 in patients with moderate to severe COPD. Furthermore, it turned out that it was not possible to define responders and non-responders to inhaled NO on an individual basis, since the variability ofthe responses was similar to the mean     

Arterial oxygen saturation, blood pressure, and pulse rate during upper gastrointestinal endoscopy--influence of sedation and age.

We studied the effect of sedation by I.V. meperidine on blood pressure, pulse rate, and arterial oxygen saturation during upper gastrointestinal endoscopy. Meperidine increased the tolerance of the patients and attenuated the endoscopy-induced rise in blood pressure and pulse rate. Arterial oxygen saturation was transiently depressed in the first few minutes of the endoscopic procedure even without sedation, and meperidine administration did not aggravate this oxygen desaturation. Therefore, meperidine may be a favorable sedative for upper gastrointestinal endoscopy because its treatment increases the tolerance of patients and decreases cardiac oxygen demand without decreasing arterial oxygen saturation.