Transesophageal echocardiography and transcutaneous O2 and CO2 monitoring for detection of venous air embolism

The sensitivities of current monitoring methods for detection of air embolism were compared in eight anesthetized dogs. Air was infused at controlled rates of 0.001 and 0.005 ml X kg-1 X min-1 for 1 min; 0.01, 0.05, 0.1, 0.2, and 0.4 ml X kg-1 X min-1 for 6 min; and 5 ml X kg-1 bolus injection. Based on the mean quantity of air infused to elicit a positive response, the monitors could be placed into three significantly different sensitivity groups. Transesophageal echocardiography (TEE) and precordial Doppler ultrasound were the most sensitive monitoring methods detecting 0.19 and 0.24 ml X kg-1 of air, respectively. TEE detected air during six infusions in which the Doppler failed to do so. The next most sensitive group of monitoring methods included pulmonary artery pressure (PAP), end-tidal CO2 (PETCO2), arterial oxygen tension (PaO2), and transcutaneous oxygen tension (PtcO2). The mean quantity of air infused to elicit a positive response in this group of monitors ranged from 0.61 to 0.76 ml X kg-1. The response of PtcO2, PaO2, PETCO2, and PAP equally reflected the quantity of air infused. The least-sensitive group of methods included arterial and transcutaneous carbon dioxide tension and systemic arterial blood pressure. These data indicate that TEE is more sensitive than Doppler ultrasound and that PAP, PETCO2, and PtcO2 are equally sensitive in detecting venous air embolism in the dog.     

Transcutaneous CO2/O2 and CO2/air suction in patients undergoing cataract surgery with retrobulbar anaesthesia

We investigated transcutaneous partial CO2 and O2 pressures and respiratory rate in unpremedicated elderly patients of ASA physical status 1 to 3 who underwent cataract surgery under retrobulbar anaesthesia. In group A no air suction was used. In group B suction was applied under the sterile drapes to avoid rebreathing of CO2. In group A transcutaneous partial CO2 pressure and respiratory rate significantly increased compared with baseline, whereas in group B they remained constant. In both groups transcutaneous partial O2 pressure and oxygen saturation as measured by pulse oximetry significantly rose after insufflating oxygen 31.min-1. Heart rate and mean arterial blood pressure remained constant. Our results demonstrate that the application of suction near the patient's head prevents CO2 rebreathing and subsequent hypercapnia associated with an elevated respiratory rate. The use of suction makes it unnecessary to raise oxygen administration. Suction combined with monitoring of partial CO2 pressure using transcutaneous sensors should be used in all ophthalmological operations under retrobulbar anaesthesia.     

Pulmonary embolism in neurosurgical patients: diagnosis and treatment

Pulmonary embolism was suspected in 45 neurosurgical patients who were treated between January, 1980, and December, 1981. Hypoxemia with respiratory alkalosis and sudden tachycardia gave rise to this suspicion more often than any other sign or symptom. Perfusion lung scanning confirmed the presence of pulmonary embolism in 23 of these cases. A retrospective analysis of the clinical course of these 23 patients suggested that one or more previous episodes of pulmonary embolism had occurred in 16 cases (69.6%), and had been either overlooked or misdiagnosed. Treatment was started immediately after diagnosis. Twenty-one patients were given heparin; however, two could not be treated because of contraindication to using anticoagulant drugs. Two patients died during treatment. The 21 surviving patients were assessed and 11 of them submitted again to perfusion lung scanning 1 week after diagnosis: 14 had improved, but seven did not show significant changes either clinically or on perfusion lung scanning. Nine treated patients developed hemorrhage, but it was readily controlled. In two of the nine patients, hemorrhage involved the surgical area. It is stressed that pulmonary embolism may be suspected and diagnosed in neurosurgical patients at an early stage. Heparin may be given and the survival rate appears to be better than previously reported figures.     

Transcutaneous blood gas CO2 monitoring of induced ventilatory depression in mice

We assessed a simple, noninvasive method of monitoring transcutaneous partial pressure of CO2 (Ptcco2) in mice to determine whether it would provide an accurate and reproducible method to assess ventilatory depression in mice. To this end, Ptcco2 and Paco2 (partial pressure of arterial CO2) measurements were performed on isoflurane-anesthetized male C57Bl/6 mice breathing differing percentages of CO2 or fentanyl, a known ventilatory depressive drug. All doses of fentanyl produced a sharp increase in Ptcco2 values within 20 min with difference in Ptcco2 values between saline and all fentanyl groups being statistically significant (P < 0.0001). A good correlation between Paco2 and Ptcco2 values was established (r2 = 0.91). A Bland-Altman analysis likewise found that Ptcco2 measurements in the mice reliably and accurately reflected their Paco2 values. Therefore, under controlled conditions, Ptcco2 measurements were found to reliably reflect Paco2 values in mice. Consequently, the Ptcco2 method can be used as a means to rapidly and quantitatively assess the ventilatory depressive properties of a wide spectrum of drugs, under varying conditions in numerous mouse models.     

Incidence of venous and paradoxical air embolism in neurosurgical patients in the sitting position: Detection by transesophageal echocardiography

Background: Venous air embolism (VAE) and paradoxical air embolism (PAE) are serious complications associated with the sitting position for neurosurgery. Although PAE is the result of VAE, the incidence of PAE according to the severity of VAE has not been investigated systematically in humans.
Methods: Twenty-one patients scheduled for neurosurgery in the sitting position were investigated prospectively. VAE and PAE were continuously monitored by cardiac two-dimensional 4-chamber view using transesophageal echocardiography (TEE) and the severity of VAE and PAE was quantitatively graded from 0 to 3 by the microbubbles score. Haemodynamic parameters and end-tidal CO₂ concentration (P_ETCO₂) during VAE and PAE were also recorded.
Results: Microbubbles in the right atrium appeared in all patients and the number of patients involved in grades 0, 1, 2 and 3 of VAE was 0, 10, 3 and 8, respectively. PAE occurred in 3 patients and only followed grade 3 of VAE. PAE always appeared from 20 to 30 s after the most severe VAE. A reduction of P_ETCO₂ and an increase of pulmonary artery pressure were noted during all episodes of grades 2 and 3 VAE. In contrast, a significant reduction of systemic blood pressure occurred in 1 case of grade 2 and 3 cases of grade 3.
Conclusions: VAE detected by TEE appeared in all patients undergoing neurosurgery in the sitting position and PAE only occurred following the most severe grade of VAE. To prevent growth of VAE is an important prophylactic for PAE.     

Comparison of surgical and anesthetic complications in neurosurgical patients experiencing venous air embolism in the sitting position

Because venous air embolism (VAE) has been considered to be a major deterrent to use of the sitting position, records of 255 patients undergoing neurosurgery in the sitting position from 1975 to 1982 were reviewed to determine the nature of morbidity and mortality in relation to the surgical procedure as well as to the occurrence of VAE. Complications were classified as surgical or anesthetic during joint review by a neurosurgeon and two neuroanesthesiologists. Outcome was classified on the basis of postoperative hospital course and discharge examination. The incidence of VAE was 30%. Although there was a variety of perioperative complications in patients with and without VAE, most of the complications were related to the operative procedure, not the sitting position or VAE. The episodes of VAE did not seem to be significant factors in the perioperative morbidity and mortality in our series of patients operated upon in the sitting position. Two case reports are discussed in detail.     

Echocardiographic detection and treatment of intraoperative air embolism

A real-time two-dimensional echocardiogram was used to detect the presence of an air embolism in patients undergoing neurosurgical procedures in the sitting position. The technique could with good sensitivity detect the appearance of a single air bubble intraoperatively, thus allowing early intervention to prevent development of further air emboli. Two types of air embolism could be differentiated; the single-bubble type and the "stormy-bubble" type. The single-bubble type was observed during skin and muscle incisions, craniotomy, and brain lesion excision. Further embolism development was prevented by electrocoagulation and application of bone wax. The stormy-bubble type occurred during dura and muscle incisions and was prevented by electrocoagulation, reflection of the dura, or suturing the affected muscle. The routine use of a Swan-Ganz catheter for removal of air embolism by suction proved effective for the treatment of the stormy-bubble type of air embolism. Masking the operative field with saline-soaked cotton strips was of moderate benefit in the stabilization of the single-bubble type of air influx, but proved to be of little value in controlling the entrance of the stormy-bubble type.     

Transcutaneous oxygen monitoring of emergency department patients

Transcutaneous oxygen sensor values reflect peripheral oxygen tensions. During shock and resuscitation, transcutaneous oxygen sensor values depend on peripheral blood flow, and, therefore, reflect cardiac output and oxygen delivery. Transcutaneous oxygen sensor monitoring, therefore, should be quite useful when caring for acutely ill patients; data from 20 surgical emergency department patients support this hypothesis. A normal initial transcutaneous oxygen sensor value of greater than 60 torr, as found in 11 of our patients, implied relatively normal oxygenation and circulation. A low initial transcutaneous oxygen sensor value of less than 60 torr implied deficits of either arterial oxygenation or of perfusion (these can be distinguished by an arterial blood gas determination). In addition, transcutaneous oxygen sensor was useful for continuous monitoring during resuscitation. Successful correction of hypoxia and perfusion deficits results in increased transcutaneous oxygen sensor values. Failure of the transcutaneous oxygen sensor value to increase during resuscitation implies ongoing deficits of tissue oxygenation.     

Swan-Ganz catheter monitoring in neurosurgical patients: theoretical and practical aspects

Theoretical and practical aspects of monitoring cardiac and blood volume status in neurosurgery patients are discussed. Groups of patients unique to neurosurgeons who might benefit from this approach include the following: those with intracranial hypertension; those undergoing blood volume expansion as a treatment for a variety of cerebrovascular disorders; and those with significant cardiovascular-respiratory problems undergoing high-risk or prolonged neurosurgical procedures. In addition, the generation of Starling-type ventrical function curves to be used in fluid management for blood volume expansion in the treatment of neurologic deficits associated with vasospasm is discussed.     

CO2 embolism during hysteroscopy

During CO2 hysteroscopy the intracavitary pressure increases up to 80 mmHg. This can result in a CO2 embolism, especially after injury/lesion of the endometrium. A 49-year-old female Caucasian patient underwent curettage, and the following day while a hysteroscopy was being performed in general anesthesia a CO2 embolism occurred, with bradyarrhythmia, drop of arterial blood pressure, superior vena cava syndrome, metallic heartsound and hypercapnia. It was possible to achieve recompensation of the right heart failure with drug therapy. Other causes (lung embolism, hypoventilation, increased CO2 production, cardiac causes) could be excluded.