Intraoperative Pulse Research Articles

Hair Splitting, Air Embolism, and Transesophageal Echocardiography

Evangelisch-Freikirchliches Krankenhaus und Herzzentrum Brandenburg in Bernau, Bernau, Germany. g.fritz@immanuel.deThe continuing medical education–accredited article “Diagnosis and Treatment of Vascular Air Embolism” by Dr. Mirski et al .1in the January 2007 issue of this journal merits some comments. The term vascular air embolism was new to me, and the PubMed search with the search term vascular air embolism yielded 7 results. The search term venous air embolism , however, with which I am more familiar, yielded 432 hits. In Dr. Mirski’s article, there are 150 references, but in only one of the cited articles, which is a radiologic article, is the term vascular air embolism used.2The Merriam-Webster Online Dictionary defines embolism as “sudden obstruction of a blood vessel.”*Therefore, by definition, there is no embolism other than vascular. The abbreviation VAE that Dr. Mirski uses for vascular air embolism in the literature is generally attributed to venous air embolism .This is no semantic hair splitting. It has rather a fundamental clinical impact as a consequence of various pathophysiologic mechanisms and distinct clinical sequelae. The term venous air embolism (VAE) describes the entrainment of air into the venous blood system leading to right ventricular constraint, elevation of pulmonary pressure and an increase in pulmonary vascular resistance, and it eventually ends in right heart failure and death. The sudden increase of right ventricular pressure might cause an reopening of the foramen ovale with consecutive transition of air bubbles from the right to left ventricle, leading to an obstruction of cerebral vessels, coronary arteries, the ophthalmic artery, or other branches of the arterial system, resulting in cerebral infarction, myocardial ischemia, blindness, or other symptoms of hypoperfusion or nonperfusion. In contrast to VAE, the entrainment of air into the arterial system, either directly or secondary through a persistent or a reopened foramen ovale, is termed arterial or paradoxical air embolism (PAE).These considerations and the fact that VAE occurs in up to 100% all of operations in the sitting position3,4lead to question which preoperative tests are necessary to identify patients with an increased risk to experience VAE and PAE intraoperatively. The persistent permanent foramen ovale, which is found in an unselected population with a prevalence of approximately 25%,5is as such a major risk factor for PAE. Transesophageal echocardiography (TEE) and transcranial Doppler ultrasound are equally effective in the detection of a permanent foramen ovale before surgery in the sitting position.6There is broad consensus that patients with a permanent foramen ovale should be excluded from surgery in the sitting position; at least the advantages of the sitting position should be carefully weighed against the risk of the potentially hazardous consequences of massive VAE and PAE in the sitting position.With respect to intraoperative monitoring, TEE is considered to be the accepted standard in detecting VAE, with an indisputable high sensitivity and specificity. Moreover, it is the only monitor to intraoperatively detect PAE, persistent foramen ovale, and pulmonary passage of air bubbles during massive VAE.7There is no intraoperative monitoring device other than TEE to reliably and quickly clarify the cause of sudden hypotension and acute hemodynamic instability, which can be due to VAE, hypovolemia, and left or right ventricular failure of any other cause.Transesophageal echocardiography requires some expertise and, for various reasons, it is not readily available everywhere. Nobody, however, would seriously have doubted the usefulness of intraoperative pulse oximetry, even in the early years after its introduction in clinical practice when it was not on hand in every operating room on the planet. Of course, anesthesiologists strongly advocate the use of pulse oximetry because it is a highly useful and an even life-saving monitoring device even if the incidence of intraoperative hypoxia is definitely not as high as VAE during operations in the sitting position. At least for procedures where one has to face potential life-threatening complications such as VAE and PAE with an incidence of up to 100%, the use of a monitor, such as TEE, with a nearly 100% specificity, sensitivity, and accuracy, has to be strongly recommended.Recently, a task force of expert neuroanesthesiologists has been entrusted by the Scientific Neuroanesthesia Subcommittee of the German Society of Anesthesiology and Intensive Care Medicine to update the recommendations regarding neurosurgical operations in the sitting and semisitting positions. Preoperative assessment and intraoperative monitoring in patients scheduled to undergo operations in the sitting or semisitting position is of paramount importance. For the task force, the usefulness of TEE in this setting is beyond any doubt, even if there are no prospective, controlled studies to answer the questions whether and how far the use of TEE has a positive impact on clinical outcome parameters such as reduction in complications and mortality.Evangelisch-Freikirchliches Krankenhaus und Herzzentrum Brandenburg in Bernau, Bernau, Germany. g.fritz@immanuel.de

Nitrous Oxide Inhalation to Improve Patient Acceptance and Reduce Procedure Related Pain of Flexible Cystoscopy for Men Younger Than 55 Years

Flexible cystoscopy in men younger than 55 years is painful despite the current best standard anesthesia (20 ml 2% lidocaine gel 15 minutes before endoscopy). The anesthetic value of lidocaine gel is debated and led us to seek an alternative. Nitrous oxide is a well established analgesic and anxiolytic agent, and it significantly reduces pain associated with transrectal ultrasound guided prostate biopsy. We studied its use in flexible cystoscopy in men younger than 55 years. A total of 61 patients were prospectively randomized to receive air (31) or Entonox (30). Both groups had 3 minutes of gas via a breath activated facemask (either Entonox or air) before endoscopy. The gel control group was comprised of 8 patients who underwent cystoscopy after instillation of lidocaine gel. The air and Entonox groups had lidocaine gel as per best standard. Vital signs were recorded before, during and after cystoscopy. Patients completed a visual analog score for gel insertion and cystoscopy. There were no statistically significant differences between the groups in terms of baseline characteristics. Pain scores for cystoscopy (p<0.001) and intraoperative pulse rate (p=0.008) were significantly less with Entonox. Side effects were transient and seen more often with Entonox (p<0.05). More of the air group would require more analgesia (p=0.001) or a general anesthetic (p=0.011) if undergoing repeat cystoscopy. Nitrous oxide inhalation significantly reduces cystoscopy related pain without significant complications. We propose that Entonox should be the anesthetic agent of choice for men younger than 55 years.

Intraoperative pulse amplitude monitoring of distal perfusion after aortic cross-clamping.

Intraoperative pulse amplitude monitoring of distal perfusion after aortic cross-clamping.

Inferior mesenteric venous sampling, pulse oximetry, and assessment of colonic perfusion during aortic aneurysm surgery.

Ischemic colitis is a serious complication of aortic surgery. The condition continues to be difficult to diagnose at an early stage. This study monitors the biochemical changes in systemic and selective inferior mesenteric vein (IMV) blood sampling during aortic surgery and compares the reproducibility of this method to intraoperative colonic pulse oximetry in a series of 18 patients undergoing infrarenal aortic aneurysm repair. Base excess, pH, pCO2, and lactate were altered by aortic cross-clamping but returned to normal within 48 hr. IMV inorganic phosphate levels were higher than systemic values, suggesting improved sensitivity with selective sampling. BB isoenzymes of creatine kinase remained normal in all patients. Pulse oximetry signals were inconsistently obtained from the colon. This study establishes the physiological changes in IMV biochemistry during aortic surgery. Unlike intraoperative pulse oximetry, selective IMV sampling provides reproducible measurements of colonic perfusion. This simple and safe technique warrants further assessment of its accuracy at diagnosing ischemic colitis.

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.

Utility of pulse oximetry in the early recognition of intraoperative hypoxaemia in tetralogy of Fallot

Undetected hypoxaemia in an anaesthetised patient can prove fatal. Pulse oximetry has been widely used to detect hypoxaemia and intracardiac shunts in congenital cyanotic heart diseases. In two patients with tetralogy of Fallot, intraoperative pulse oximetry was helpful in detecting hypoxaemia where the oxygen saturation fell to22and28 per cent with concomitant fall in PaO2. Immediate therapeutic measures were taken and patients’ oxygen saturation improved. We suggest routine use of pulse oximetry in patients undergoing corrective or palliative surgery for tetralogy of Fallot.

Failure rate of pulse oximetry in the postanesthesia care unit.

The objective of this study was to prospectively examine the incidence of patient-related failure of pulse oximetry in the postanesthesia care unit (PACU). We studied 2,937 patients who, after receiving anesthesia, were admitted to the PACU at the University of Washington Medical Center from December 1989 through May 1990. Pulse oximetry readings were recorded using a Nellcor N-200 oximeter without electrocardiographic synchronization. Failure was defined as the inability to obtain a pulse oximetry reading for 2 or more 15-minute periods after eliminating probe position or mechanical malfunctions. The overall failure rate in our study was 0.64%, with 19 patient-related pulse oximetry failures from 2,937 cases. Patients on whom the device failed were significantly older (62 +/- 18 vs 46 +/- 19 yr [mean +/- SD]; p < 0.01), had higher median American Society of Anesthesiologists status (3 vs 2), and had longer operations than nonfailure patients (328 +/- 182 vs 185 +/- 127 min; p < 0.01). There was no difference in the duration of PACU times for both groups. The failure rate and patient characteristics compare favorably with a previously published study of intraoperative pulse oximetry failure. We conclude that while the pulse oximeter is a reliable instrument for the measurement of blood oxygenation, there is a small but consistent incidence of patient-related failure with this monitoring device in the PACU.

A prospective study of intraoperative pulse oximetry failure

Since pulse oximetry is now an ASA standard for intraoperative monitoring, we sought to determine the intraoperative failure rate for this device. We prospectively evaluated the intraoperative failure rate of our pulse oximeters at the four University of Washington Hospitals (University of Washington Medical Center, Veterans Affairs Medical Center [VAMC], Children's Hospital and Medical Center, and Harborview Medical Center [HMC]) recorded from April 1989 to August 1989. We defined failure as the inability to obtain any oximetry reading for a cumulative period of more than 30 minutes during any anesthetic procedure after all equipment malfunctions had been eliminated. Our puse oximeters failed in 124 of 11,046 cases studied; this is a failure rate of 1.12%, which ranged from 0.56% at HMC to 4.24% at VAMC. The failure rate at VAMC (4.24%) was significantly higher than the other hospitals (p less than 0.001). Those cases associated with the pulse oximeter failure had the following characteristics: (1) an ASA status of 3 or higher, (2) lengthy operations, and (3) elderly patients. When the device did fail in a patient, it did not function for 32% of the mean anesthesia time. We conclude that the intraoperative use of the pulse oximetry can provide information about blood oxygen saturation in most patients. However, in approximately 1% of the patients we studied in the operating room, mechanically functioning pulse oximeters failed to provide readings of blood oxygen saturations during routine operative use.

A Case-control Study of Risk Factors for Intraoperative Suprachoroidal Expulseve Hemorrhage

The authors performed a case-control study of risk factors for suprachoroidal expulsive hemorrhage (SEH); the study involved 68 SEH cases at their institution from 1981 to 1986. The authors examined 113 variables in the study group and a procedure-matched control group of 217 patients randomly selected from the 35,459 patients who underwent intraocular surgery during this period, and subjected them to bivariate and conditional logistic regression analysis. The incidence of SEH was 0.19% overall, 0.16% for lens-related procedures, 0.15% for glaucoma surgery, 0.41% for retinal and vitreous procedures, and 0.56% for keratoplasty. Statistically significant risk factors for SEH in ageadjusted bivariate analyses included: glaucoma (P < 0.0001), increased axial length (P < 0.0001), elevated intraocular pressure (IOP) (P < 0.0001), generalized atherosclerosis (P = 0.007), and elevated intraoperative pulse (P = 0.0001). Conditional logistic regression analysis with frequency matching on age identified significant independent risks associated with a history of glaucoma, elevated IOP, increased axial length, and intraoperative tachycardia. One of the models predicts a 752-fold increased theoretical relative risk of SEH for a patient with axial length greater than or equal to 25.8 mm, a history of glaucoma, preoperative IOP greater than 18 mmHg, and intraoperative pulse greater than or equal to 85 beats per minute. The visual outcome after SEH was best in cases of extracapsular cataract extraction (ECCE), compared with other procedures. Results suggest that attention to multiple preoperative and intraoperative ocular and systemic variables may allow identification and prophylaxis of patients at risk for SEH.

Intraoperative local anesthetic injection of the carotid sinus nerve: A prospective, randomized study

One hundred patients undergoing carotid endarterectomy under general anesthesia were prospectively randomized to receive either a local anesthetic injection of their carotid sinus nerve with bupivacaine (Marcaine) or no injection. Systolic blood pressure and pulse rate were recorded before injection and at 5 and 30 minutes after injection. The need for intraoperative and postoperative use of systemic vasopressor and vasodilator medications was recorded for each group as was the incidence of arrhythmias, neurologic complications, and myocardial infarctions. Intraoperative local anesthetic injection of the carotid sinus nerve did not significantly influence the intraoperative pulse rate or incidence of hypotension. It did, however, significantly increase the incidence of intraoperative hypertension and the need for systemic vasodilator medications intraoperatively. The incidence of postoperative hypotension (6 percent of patients), hypertension (34 percent), arrhythmias (6 percent), cerebrovascular accidents (1 percent), transient ischemic attacks (3.1 percent), and myocardial infarctions (2 percent) were not significantly influenced by intraoperative local anesthetic injection of the carotid sinus nerve. Intraoperative and postoperative hypotension did not cause morbidity in this series, however, local anesthetic injection was associated with a significant incidence of perioperative hypertension. Routine prophylactic local anesthetic injection of the carotid sinus nerve cannot be recommended in view of its detrimental effects in relation to the development of hypertension.