Evaluation of noninvasive monitoring of preoxygenation

Administration of 100% oxygen before a "rapid-sequence" induction of anesthesia is recommended to prevent hypoxemia during induction. In the present study, we used a laser scattering analyzer to study the effectiveness of nitrogen washout from the lungs with oxygen wash into the lungs under two different preoxygenation regimens; 4 times of maximal breathing of 100% oxygen in one minute and normal tidal breathing of 100% oxygen for 3 minutes. The volunteers were healthy, ASA physical status 1, 22 to 33 years of age (26 +/- 3), 167 +/- 5 cm tall, and weighing 60 +/- 5 kg. Arterial blood saturation measured by a pulse oximeter was 97 while breathing 21% oxygen, and 99% while breathing 100% oxygen. Arterial oxygen tensions were 98 mmHg while breathing 21% oxygen, and over 480 mmHg while breathing 100% oxygen. Arterial carbon dioxide and end tidal carbon dioxide concentrations indicated that 4 time of maximal breathing in a minute leads to hyperventilation. The end-tidal oxygen concentration was not significantly different between before and after oxygen administration in two different regimens. End-tidal nitrogen concentration after tidal volume ventilation was lower than that of 4 breath in a minute. These results indicate that end-tidal nitrogen and oxygen could reflect arterial nitrogen and oxygen tensions during preoxygenation.     

Gas embolism during hysteroscopy

PURPOSE: Gas embolism during hysteroscopy is rare but sometimes fatal. A fatal case of gas embolism during diagnostic hysteroscopy using carbon dioxide (CO2) is presented. CLINICAL FEATURES: A 68 yr old woman was admitted for treatment of myoma and cancer of the uterus. Hysteroscopy using CO2 was performed without monitoring or anesthesia on the ward. At the end of the examination, just after the hysteroscope was removed, she developed tonic convulsions, lost consciousness, and her pulse was impalpable. Cardiac massage was started, anesthesiologists were called and the trachea was intubated. She was transferred to the intensive care unit with continuous cardiac massage. Cardiac resuscitation was successful. A central venous line was inserted into the right ventricle under echocardiography in an attempt to aspirate gas with the patient in the Trendelenberg position, but the aspiration failed. Positive end expiratory pressure and heparin for emboli, midazolam for brain protection, and catecholamines were administered. Fifteen hours after resuscitation, the pupils were enlarged and she died 25 hr after resuscitation. CONCLUSION: Gas embolism is a rare complication of hysteroscopy. The procedure should be performed with monitoring of blood pressure, heart rate, oxygen saturation and end-tidal CO2 concentration.     

Gas embolism during laparoscopic cholecystectomy

Advancements in laparoscopic surgery have resulted in decreased length of hospitalization, reduced postoperative pain, and better cosmesis following general surgical procedures. Carbon dioxide gas embolism is a rare occurrence that can be fatal. We report the case of a patient with a venous gas embolism during laparoscopic cholecystectomy. A 63-year-old woman presented with intermittent right upper quadrant pain, and her abdominal ultrasound showed a possible gallbladder polyp. A laparoscopic cholecystectomy was planned. A Veress needle was placed in the right upper quadrant to initiate abdominal access. Shortly after carbon dioxide insufflation, the patient's hemodynamic status deteriorated, her oxygen saturation dropped, and her end-tidal CO2 decreased. Gas insufflation was immediately stopped, and the patient was resuscitated. She stabilized quickly, and the procedure was performed without further event. She did well postoperatively and was discharged home the next day. Carbon dioxide embolism during laparoscopy, albeit rare, can be a fatal complication of the procedure. Whenever sudden changes in hemodynamic stability occur, venous gas embolism should be considered. As laparoscopic techniques and applications are expanded, the general surgeon must be aware of this entity.     

Transcutaneous O2 and CO2 monitoring of neurosurgical patients: detection of air embolism

Transcutaneous oxygen tension (PtcO2) and transcutaneous carbon dioxide tension (PtcCO2) were monitored in 60 patients undergoing neurosurgical procedures. Twenty-six patients were in the sitting position and underwent routine monitoring for air embolism. Seventeen episodes of air embolism were diagnosed by precordial Doppler ultrasound or transesophageal echocardiography, and the PtcO2 decreased early during the course of each episode. The mean PtcO2 decrease was 48 +/- 35 mmHg. During ten episodes the end-tidal carbon dioxide tension (PETCO2) decreased but only after the PtcO2 had already begun to decrease. PtcCO2 increased during air embolism but PETCO2 changes preceded the change in PtcCO2 by 1-2 min. Transcutaneous values during air embolism were verified with simultaneous arterial blood gas values during six air embolism episodes. A strong positive correlation was found between transcutaneous and arterial oxygen and carbon dioxide tensions. Correcting the PtcCO2 by the patient's baseline PtcCO2/PaCO2 ratio, PtcCO2 monitoring correctly reflected hypocarbia, normocarbia, and hypercarbia in 92% of the cases. PtcO2 monitoring was useful in detecting venous air embolism and may respond sooner than PETCO2. PtcCO2 monitoring was not useful as an early detector of air embolism.     

Accumulation of carbon dioxide during eye surgery

During cataract surgery, both the surgeon and the anesthesiologist need access to the patient's face. At our institution we achieved a working compromise by using an oxygen insufflating hoop, which allowed the surgeon access to the eye and a sterile field. The patient's airway was kept free by the hoop, and the patient breathed a high inspired oxygen fraction. We measured the partial pressure of carbon dioxide (PCO2) of the gas mixture under the surgeon's drapes because they form a semiclosed breathing system for the patient. Accumulation of CO2 occurred in all patients (mean +/- SD, 6.1 +/- 3.1 mmHg), but an oxygen flow of 10 L/min through the hoop prevented an additional rise of CO2 levels during the operation. Reducing the oxygen flow below 10 L/min led to increased retention of CO2 under the drapes. Paper drapes are permeable to CO2, but plastic drapes are impermeable. We did not measure the arterial partial pressure of CO2, and so we do not know whether CO2 accumulation was accompanied by respiratory acidosis.     

Accuracy of end-tidal carbon dioxide monitoring using the NBP-75 microstream capnometer. A study in intubated ventilated and spontaneously breathing nonintubated patients

Arterial carbon dioxide partial pressure measurements using the NBP-75 microstream capnometer were compared with direct PaCO2 values in patients who were (a) not intubated and spontaneously breathing, and (b) patients receiving intermittent positive pressure ventilation of the lungs and endotracheal anaesthesia. Twenty ASA physical status I-III patients, undergoing general anaesthesia for orthopaedic or vascular surgery were included in a prospective crossover study. After a 20-min equilibration period following the induction of general anaesthesia, arterial blood was drawn from an indwelling radial catheter, while the end-tidal carbon dioxide partial pressure was measured at the angle between the tracheal tube and the ventilation circuit using a microstream capnometer (NBP-75, Nellcor Puritan Bennett, Plesanton, CA, USA) with an aspiration flow rate of 30 mL min(-1). Patients were extubated at the end of surgery and transferred to the postanaesthesia care unit, where end-tidal carbon dioxide was sampled through a nasal cannula (Nasal FilterLine, Nellcor, Plesanton, CA, USA) and measured using the same microstream capnometer. In each patient six measurements were performed, three during mechanical ventilation and three during spontaneous breathing. A good correlation between arterial and end-tidal carbon dioxide partial pressure was observed both during mechanical ventilation (r = 0.59; P = 0.0005) and spontaneous breathing (r = 0.41; P = 0.001); while no differences in the arterial to end-tidal carbon dioxide tension difference were observed when patients were intubated and mechanically ventilated (7. 3 +/- 4 mmHg; CI95: 6.3-8.4) compared to values measured during spontaneous breathing in the postanesthesia care unit, after patients had been awakened and extubated (6.5 +/- 4.8 mmHg; CI95: 5. 2-7.8) (P = 0.311). The mean difference between the arterial to end-tidal carbon dioxide tension gradient measured in intubated and non-intubated spontaneously breathing patients was 1 +/- 6 mmHg (CI95: -11-+13). We conclude that measuring the end-tidal carbon dioxide partial pressure through a nasal cannula using the NBP-75 microstream capnometer provides an estimation of arterial carbon dioxide partial pressure similar to that provided when the same patients are intubated and mechanically ventilated.     

The detection of carbon dioxide embolism during laparoscopy in pigs: a comparison of transesophageal Doppler and end-tidal carbon dioxide monitoring

Background: The aim of the study was to compare the value of transesophageal Doppler and end-tidal carbon dioxide monitoring to detect venous carbon dioxide embolism in pigs during laparoscopic cholecystectomy.
Method: Ten pigs were anesthetized under constant ventilation, and instrumented for laparoscopic cholecystectomy. CO₂ pneumoperitoneum was performed at 15 mmHg and then, successive increased intravenous gas boluses of 0.1 to 4 ml/ kg injectedthrough the femoral vein using a 55-mm long catheter. The responses indicative of embolism were defined as: 1) a change in Doppler tone placed facing the junction of the right atrium and inferior vena cava; 2)
Results: Doppler was more sensitive in detecting 0.1, 0.2 and 0.4 ml/mg of CO₂ embolism than end-tidal CO₂ ( P <0.05). Over 0.4 ml/mg no differences in sensitivity were found but the Doppler signal modifications occurred earlier than the changes in end-tidal CO₂. Moreover, these changes always consisted of a reduction of the value.
Conclusions: During laparoscopic cholecystectomy in pigs, transesophageal Doppler was a highly sensitive monitor which provided an earlier detection of CO₂ embolism and at lower doses than end-tidal CO₂ monitoring.     

Capnography in the early diagnosis of carbon dioxide embolism during laparoscopy

Venous embolism of carbon dioxide occurred during elective diagnostic laparoscopy in a healthy adult female. The diagnosis of gas embolism was made on the basis of the sudden abrupt onset of systolic and diastolic murmurs. The continuously recorded end-tidal carbon dioxide concentration (FETCO2) increased abruptly from 3.8 to 4.2 per cent and then slowly decreased to 4.0 per cent over the subsequent 30 seconds. CO2 insufflation was terminated immediately following the establishment of the diagnosis. The patient recovered uneventfully. A transient but rapid rise in FETCO2 is suggested as a useful early sign of venous CO2 embolism during laparoscopy.     

A case of suspected pulmonary air embolism in endoscopic neurosurgery

Sudden reduction in end-tidal PCO2 and SpO2 occurred during the endoscopic third ventriculostomy in a patient with hydrocephalus under general anesthesia. We suspect that it was caused by pulmonary air embolism. A 63-year-old female was scheduled for endoscopic third ventriculostomy under general anesthesia. Endoscopic manipulation caused hemorrhage from chorioid plexus 21 minutes after the procedure was begun, and intraventricular irrigation was performed to achieve hemostasis. In the subsequent 3 minutes, end-tidal PCO2 declined from 26 mmHg to 15 mmHg (PaCO2 39.6 mmHg), and SpO2 declined from 98% to 92% (PaO2 69.2 mmHg). Nitrous oxide was discontinued immediately because pulmonary air embolism was suspected and the oxygen concentration was increased to 100%. At the same time the surgical procedure was discontinued. After 15 minutes, end-tidal PCO2 recovered to 25 mmHg, and SpO2 recovered to 98% (PaO2 136.5 mmHg), and surgery was resumed. The patient recovered from anesthesia. The chest X-p at the end of operation, and pulmonary scintigraphy on the following day revealed no abnormal findings, but brain CT demonstrated a large quantity of air in both lateral ventricles.     

Pulmonary embolism induced by evacuator during transurethral resection of the prostate

A 79-year-old man was scheduled to undergo transurethral resection of the hypertrophied prostate during general anesthesia. Anesthesia was maintained with sevoflurane 0.5-1.0% and nitrous oxide 50% in oxygen mixture. Immediately after using an evacuator to remove small resected pieces of the prostate, end-tidal carbon dioxide pressure (EtCO2) decreased suddenly from 31 mmHg to 18 mmHg. Concurrently, decreases in systolic blood pressure from 110 mmHg to 60 mmHg and oxygen saturation from 100% to 95%, and an increase in arterial-alveolar carbon dioxide tension difference (a-ADCO2) were observed. We initially suspected the onset of pulmonary thrombosis as the cause of these events, ventilated the patient's lungs with 100% oxygen and administered 5,000 units of heparine and vasopressors intravenously. However, transesophageal echocardiography done subsequently revealed the presence of strongly echogenic images compatible with the air in the left cardiac atrium and the contribution of the air to those events. The EtCO2, blood pressure, and oxygen saturation improved in about 20 minutes after the initial decrease of the EtCO2 had been detected. Thereafter, surgical procedure was done uneventfully. In routine anesthetic management of transurethral surgery, it should be considered that the sudden deterioration in vital signs may have been caused by evacuator used.     

Carbon dioxide embolism during laparoscopy: effect of insufflation pressure in pigs.

Carbon dioxide embolism is a rare but potentially devastating complication of laparoscopy. To determine the effects of insufflation pressure on the mortality from carbon dioxide embolism, six swine had intravascular insufflation with carbon dioxide for 30 seconds using a Karl Storz insufflator at a flow rate of 35 mL/kg/min. The initial insufflation pressure was 15 mm Hg. Following recovery from the first embolism, intravascular insufflation using a pressure of 20 mm Hg at the same flow rate was performed in the surviving animals. Significantly less carbon dioxide (8.3 +/- 2.7 versus 16.7 +/- 3.9 mL/kg; p < 0.02) was insufflated intravascularly at 15 mm Hg than at 20 mm Hg pressure. All of the pigs insufflated at 15 mm Hg pressure with a flow rate of 35 mL/kg/min survived. In contrast, 4 of the 5 pigs insufflated at 20 mm Hg pressure died. The surviving pig died when insufflated with 25 mm Hg pressure following an embolism of 15.7 mL/kg. Intravascular injection was often associated with an initial rise in end-tidal carbon dioxide tension, followed by a rapid fall in all cases where the embolism proved fatal. Insufflation should be begun with a low pressure and a slow flow rate to limit the volume of gas embolized in the event of inadvertent venous cannulation. Insufflation should immediately be stopped if a sudden change in end-tidal carbon dioxide tension occurs.     

Air embolism during anaesthesia for shoulder arthroscopy

We report a case of venous air embolism during an elective shoulderarthroscopy in which air was used as a joint distending agent.Venous air embolism was diagnosed by the sudden decrease inthe end-tidal carbon dioxide concentration. The patient sufferedno serious complications of venous air embolism and made a fullrecovery. We present this case to make surgeons and anaesthetistsaware of the possibility of gas/air embolism during electivearthroscopy, when gas/air is used to distend the joint. Thiscase also illustrates that the end-tidal carbon dioxide monitor,which is part of the standard anaesthetic monitoring system,is very sensitive in detecting venous air embolism. Br J Anaesth 2000; 85: 925–7     

Oxygen enrichment during emergence with the laryngeal mask — the 'T-bag' versus the T-piece

We have compared the performance of a new oxygen enrichment device, the 'T-bag', with a T-piece during emergence from spontaneous breathing anaesthesia with the laryngeal mask airway. Thirty patients were randomly allocated to each group. Inspired and end-tidal gases were sampled from the proximal end of the laryngeal mask airway. Cardiorespiratory variables were recorded immediately prior to discontinuation of anaesthesia, 2 min later and then at 5-min intervals until removal of the laryngeal mask airway. The mean inspired oxygen concentration was greater than 70% and the inspired carbon dioxide was less than 2 mmHg in both groups throughout emergence. There were no episodes of hypoxia (oxygen saturation < 92%). Both devices performed well, but the 'T-bag' offered advantages in terms of respiratory monitoring and ventilatory capability.     

Efficacy of preoxygenation using tidal volume and deep breathing techniques with and without prior maximal exhalation

PURPOSE: We evaluated the influence of prior maximal exhalation on preoxygenation in 15 adult volunteers using tidal volume breathing (TVB) for five minutes and deep breathing (DB) for two minutes with and without prior maximal exhalation. METHODS: Inspired and end-tidal oxygen, nitrogen and carbon dioxide were monitored continuously and recorded during room air breathing and at 30-sec intervals during 100% oxygen TVB or DB (rate of 8 breaths.min(-1)). RESULTS: Tidal volume breathing with prior maximal exhalation resulted in an end-tidal oxygen concentration (ETO(2)) slightly higher (P = 0.028) at 0.5 and 1.0 min as compared with TVB without prior maximal exhalation at the same time periods. Regardless of whether TVB was preceded by maximal exhalation or not, 2.5 min was required to reach a mean ETO(2) value of 90% or higher. With DB, there were no differences in ETO(2) values at any time period and 1.5 min was required to reach an ETO(2) of 90% or greater, with or without prior maximal exhalation. CONCLUSIONS: Maximal exhalation prior to TVB slightly steepens the initial rise in ETO(2) during the first minute, but confers no real benefit if maximal preoxygenation is the goal. Maximal exhalation prior to DB has no added value in enhancing preoxygenation.     

The association between central venous pressure, pneumoperitoneum, and venous carbon dioxide embolism in laparoscopic hepatectomy

Background

Laparoscopic hepatectomy (LH) is increasingly used. However, the safety and outcomes of LH have yet to be elucidated. The risk of venous gas embolism is increased during liver parenchymal transection. This risk may be increased with positive pressure carbon dioxide (CO₂) pneumoperitoneum (PP). This may be exacerbated further when low central venous pressure (CVP) anesthesia is used to minimize hemorrhage during liver resection.

Methods

To determine the risk of CO₂ venous embolism, hand-assisted laparoscopic left hepatic lobectomy was performed for 26 domestic pigs. They were divided into three groups involving, respectively, positive gradient (normal-pressure PP of 12–14 mmHg and low CVP of 5–7 mmHg), negative gradient (low-pressure PP of 7–8 mmHg and normal CVP of 10–12 mmHg), and neutral gradient (normal-pressure PP and normal CVP or low-pressure PP and low CVP). Transesophageal echocardiography (TEE) was used intraoperatively to assess the presence of emboli in the suprahepatic vena cava and the right side of the heart. The TEE was recorded and analyzed by blinded observers. Carbon dioxide embolism also was monitored using end-tidal CO₂ and compared with TEE.

Results

Carbon dioxide embolism was demonstrated in 19 of the 26 cases. The majority of gas emboli were small gas bubbles associated with dissection of the major hepatic veins. No statistically significant difference in the occurrence of gas emboli was observed between the groups. Of the 19 animals, 18 experienced no significant hemodynamic changes. One pig in the positive gradient group experienced hypotension in relation to gas embolism. The effects were only transient and did not preclude safe completion of the operation.

Conclusions

Carbon dioxide embolism during LH occurs frequently. Clinically, this finding appears to be nominal, but care must be taken when dissection around large veins is performed, and awareness by the surgical and anesthesiology teams of potential venous air embolism is essential. Further evaluation of this phenomenon is required.     

Arterial oxygen tension and high intracranial pressure

Summary Arterial oxygen and carbon dioxide tension was measured in spontaneously breathing rabbits whose intracranial pressure was raised by a freeze lesion, oil embolism, or hydrostatic pressure. Reports elsewhere had stated that high intracranial pressure led to hypoxaemia.In this series of experiments, arterial oxygen tension appeared to rise and carbon dioxide tension appeared to drop. Both changes were slight and not significant statistically. There was no evidence to suggest that arterial hypoxaemia is caused by high intracranial pressure.     

The Bain anaesthetic circuit.

The Bain co-axial circuit is a recent and versatile addition to the semiclosed anaesthetic breathing systems. The relationship between the patient's arterial carbon dioxide tension (PaCO2) and fresh gas flow during intermittent positive pressure ventilation (IPPV) using this circuit has been reassessed. A mean PaCO2 of 33,4 mmHg for 64 patients was recorded using a fresh gas flow of 100 ml/kg/min and a mean PaCO2 of 37,3 mmHg for 55 patients using a fresh gas flow off 70 ml/kg/min.     

Effects of Venous Air Embolism on the Cardiovascular System and Acid Base Balance in the Presence and Absence of Nitrous Oxide

Cardiovascular responses and acid-base changes with graded volumes of intravenously injected air were measured in dogs anesthesized with pentobarbital and either 100% oxygen or 50% oxygen and nitrous oxide. Mean arterial blood pressure decreased significantly with 2.5 ml of air/kg in the oxygen group and at all volumes in the nitrous oxide group. The volume of air embolus appeared to increase more than twice in the presence of 50% nitrous oxide. Pulmonary artery wedge pressure increased significantly in both groups, while end-tidal carbon dioxide decreased significantly in both groups. The changes in pulmonary artery wedge pressure and end-tidal carbon dioxide were simultaneous, suggesting that the less invasive monitoring technique may be utilized in diagnosing significant air embolism. Right atrial pressure increased while left atrial pressure decreased significantly in both groups. With injected volumes of 2.0 and 2.5 ml or air/kg, right atrial pressure exceeded left atrial pressure creating the potential of paradoxical air embolism. The pH and PaO2 decreased while PaCO2 increased significantly during air embolization.     

Influence of Acute Pain Induced by Activation of Cutaneous Nociceptors on Ventilatory Control

Background: Although many studies show that pain increases breathing, they give little information on the mechanism by which pain interacts with ventilatory control. The authors quantified the effect of experimentally induced acute pain from activation of cutaneous nociceptors on the ventilatory control system.

Methods: In eight volunteers, the influence of pain on various stimuli was assessed: room air breathing, normoxia (end-tidal pressure of carbon dioxide (PETCO2) clamped, normoxic and hyperoxic hypercapnia, acute hypoxia, and sustained hypoxia (duration, 15-18 min; end-tidal pressure of oxygen, approximately 53 mmHg). Noxious stimulation was administered in the form of a 1-Hz electric current applied to the skin over the tibial bone.

Results: While volunteers breathed room air, pain increased ventilation (V with dotI) from 10.9 +/- 1.7 to 12.9 +/- 2.5 l/min sup -1 (P < 0.05) and reduced PETCO2 from 38.3 +/- 2.3 to 36.0 +/- 2.3 mmHg (P < 0.05). The increase in V with dotI due to pain did not differ among the different stimuli. This resulted in a parallel leftward-shift of the V with dotI -carbon dioxide response curve in normoxia and hyperoxia, and in a parallel shift to higher V with dotI levels in acute and sustained hypoxia.     

Pulsus alternans during general anesthesia with halothane: effects of permissive hypercapnia

BACKGROUND: Pulsus alternans is a classic type of abnormal pulse. It can be defined as a regular alternation of pulse amplitude in which runs of weak and strong beats follow each other alternatively without any change in cycle length. It may be a sign of severe decompensated congestive heart failure. The authors infrequently encountered some cases of pulsus alternans during halothane anesthesia with spontaneous respiration in otherwise normal subjects in association with high levels of end-tidal carbon dioxide. This study was conducted to determine if there is any relation between this phenomena and hypercapnia. METHODS: One hundred twenty patients undergoing elective lower extremity surgery were selected. Halothane was used for maintenance of anesthesia, and the patients were allowed to breath spontaneously. The occurrence of pulsus alternans was determined by plethysmographic display of pulse wave and then confirmed by palpation of the radial artery. RESULTS: Ten patients (8.3%) developed pulsus alternans together with elevated levels of end-tidal carbon dioxide (57 +/- 4 mmHg vs. 41 +/- 4 mmHg in patients without pulsus alternans [mean +/- SD]). The pulsus alternans disappeared after switching to controlled ventilation and 15-20% reduction in end-tidal carbon dioxide. During the period of pulsus alternans, vital signs and electrocardiography remained within normal limits. CONCLUSIONS: There may be some relation between occurrence of pulsus alternans and hypercapnia during halothane anesthesia. Pulsus alternans occurs in a small fraction of spontaneously breathing, halothane-anesthetized patients. Although hypercapnia is clearly a factor, the mechanism of this phenomenon is unknown.