Anthony M.-H. Ho

A Critical Review of the Ability of Continuous Cardiac Output Monitors to Measure Trends in Cardiac Output

Numerous cardiac output (CO) monitors have been produced that provide continuous rather than intermittent readings. Bland and Altman has become the standard method for validating their performance against older standards. However, the Bland and Altman method only assesses precision and does not assess how well a device detects serial changes in CO (trending ability). Currently, there is no consensus on how trending ability, or trend analysis, should be performed. Therefore, we performed a literature review to identify articles published between 1997 and 2009 that compared methods of continuous CO measurement. Identified articles were grouped according to measurement technique and statistical methodology. Articles that analyzed trending ability were reviewed with the aim of finding an acceptable statistical method. Two hundred two articles were identified. The most popular methods were pulse contour (69 articles), Doppler (54), bioimpedance (38), and transpulmonary or continuous thermodilution (27). Forty-one articles addressed trending, and of these only 23 provided an in-depth analysis. Several common statistical themes were identified: time plots, regression analysis, Bland and Altman using change in CO (&Dgr;CO), and the 4-quadrant plot, which used direction of change of &Dgr;CO to determine the concordance. This plot was further refined by exclusion of data when values were small. Receiver operating characteristic curves were used to define the exclusion zone. In animal studies, a reliable reference standard such as an aortic flowprobe was frequently used, and regression or time plots could be used to show trending. Clinical studies were more problematic because data collection points were fewer (8–10 per subject). The consensus was to use the 4-quadrant plot with exclusion zones and apply concordance analysis. A concordance rate of >92% when using a 15% zone indicated good trending. A new method of presenting trend data (&Dgr;CO) on a polar plot is proposed. Agreement was shown by the angle with the horizontal axis and &Dgr;CO by the distance from the center. Trending can be assessed by the vertical limits of the data, similar to the Bland and Altman method.

Postthoracotomy pain syndrome.

Postthoracotomy pain syndrome is relatively common and is seen in approximately 50% of patients after thoracotomy. It is a chronic condition, and about 30% of patients might still experience pain 4 to 5 years after surgery. In the majority of patients pain is usually mild and only slightly or moderately interferes with normal daily living. In a small subset of patients pain can be severe and can be described as a true disability to the extent that these patients are incapacitated. The exact mechanism for the pathogenesis of PTPS is still not clear, but cumulative evidence suggests that it is a combination of neuropathic and nonneuropathic (myofascial) pain. Trauma to the intercostal nerve during thoracotomy is the most likely cause. Because pain does not cause disability in the majority of patients, management is usually conservative. If pain is causing disability then multidisciplinary pain management involving the pain specialist, social worker, physical therapist, and a psychologist is required. It is mandatory to exclude recurrence of disease or malignancy as a cause for the pain prior to initiating treatment. As with most forms of neuropathic pain, treatment of PTPS is also difficult and patients might require more than one form of therapy to control pain and reduce disability. Based on current evidence, it is not possible to draw any firm conclusion regarding whether any form of analgesic or surgical technique can influence the generation of PTPS. Preemptive analgesia initiated prior to surgery shows promise and might help reduce the incidence of PTPS. Scientific evidence is steadily growing but there is still a need for large, prospective, randomized trials evaluating PTPS. Until more is known about this condition and how to prevent the central and peripheral nervous system changes that produce long-term pain after thoracotomy, patients must be warned preoperatively about the possibility of developing PTPS and how it might affect their quality of life after surgery. In addition, measures such as selecting the least traumatic and painful surgical approach, avoiding intercostal nerve trauma, and adopting an aggressive multimodal perioperative pain management regimen commenced before the surgical incision should be performed to prevent postthoracotomy pain syndrome.

Systemic air embolism after lung trauma.

Systemic air or gas embolism has been increasingly recognized as a complication of serious chest trauma and often presents with catastrophic circulatory and cerebral events. The classic findings are hemoptysis, sudden cardiac or cerebral dysfunction after initiation of PPV, air in retinal vessels, and air in arterial aspirations. The clinician must be wary of more subtle presentations. Several diagnostic tools (TEE, Doppler, CT) can detect intracardiac and cerebral air, but they may not be necessary to confirm the diagnosis of SAE. Cessation of SAE is essential for successful resuscitation. In those with unilateral lung injury, this can theoretically be achieved by isolating and ventilating the noninjured lung. Sole reliance on immediate thoracotomy for hilar clamping to stem the flow of gas emboli is a concept that needs to be challenged. Whether airway and ventilation interventions will eliminate, delay, or decrease the need for thoracotomy and improve the prognosis of SAE remains to be seen. There is little reported in the literature regarding such interventions. Airway management of a patient at risk for SAE should include a technique that can selectively ventilate each lung. Patients with bilateral sources of SAE may benefit from the avoidance of high airway pressures. Regional anesthesia should be considered when appropriate. HBOT is useful in managing cerebral air embolism and should be incorporated as soon as possible. Clinicians involved in trauma care must be familiar with SAE. By adopting a problem-based solution through innovative airway and ventilation management, anesthesiologists may significantly alter and improve the morbidity and mortality rate of SAE resulting from chest trauma.

Prevalence of survivor bias in observational studies on fresh frozen plasma: erythrocyte ratios in trauma requiring massive transfusion

Observational studies on transfusion in trauma comparing high versus low plasma:erythrocyte ratio were prone to survivor bias because plasma administration typically started later than erythrocytes. Therefore, early deaths were categorized in the low plasma:erythrocyte group, whereas early survivors had a higher chance of receiving a higher ratio. When early deaths were excluded, however, a bias against higher ratio can be created. Survivor bias could be reduced by performing before-and-after studies or treating the plasma:erythrocyte ratio as a time-dependent covariate. We reviewed 26 studies on blood ratios in trauma. Fifteen of the studies were survivor bias-unlikely or biased against higher ratio; among them, 10 showed an association between higher ratio and improved survival, and five did not. Eleven studies that were judged survivor bias-prone favoring higher ratio suggested that a higher ratio was superior. Without randomized controlled trials controlling for survivor bias, the current available evidence supporting higher plasma:erythrocyte resuscitation is inconclusive.

Early risk stratification of patients with major trauma requiring massive blood transfusion

BACKGROUND There is limited evidence to guide the recognition of patients with massive, uncontrolled hemorrhage who require initiation of a massive transfusion (MT) protocol. OBJECTIVE To risk stratify patients with major trauma and to predict need for MT. DESIGNS Retrospective analysis of an administrative trauma database of major trauma patients. A REGIONAL TRAUMA CENTRE: A regional trauma centres in Hong Kong. PATIENTS Patients with Injury Severity Score ≥ 9 and age ≥ 12 years were included. Burn patients, patients with known severe anemia and renal failure, or died within 24h were excluded. MAIN OUTCOME MEASURES Delivery of ≥ 10 units of packed red blood cells (RBC) within 24h. RESULTS Between 01/01/2001 and 30/06/2009, 1891 patients met the inclusion criteria. 92 patients required ≥ 10 units RBC within 24h. Seven variables which were easy to be measured in the ED and significantly predicted the need for MT are heart rate ≥ 120/min; systolic blood pressure ≤ 90 mm Hg; Glasgow coma scale ≤ 8; displaced pelvic fracture; CT scan or FAST positive for fluid; base deficit >5 mmol/L; hemoglobin ≤ 7 g/dL; and hemoglobin 7.1-10 g/dL. At a cut off of ≥ 6, the overall correct classification for predicting need for MT was 96.9%, with a sensitivity of 31.5% and specificity of 99.7%, and an incidence of MT of 82.9%. The area under the curve was 0.889. CONCLUSION A prediction rule for determining an increased likelihood for the need for massive transfusion has been derived. This needs validation in an independent data set.

Acute pain management of patients with multiple fractured ribs: a focus on regional techniques.

Purpose of reviewThoracic trauma leading to multiple fractured ribs (MFR) remains very common. Good analgesia may help to improve a patients respiratory mechanics and to avoid intubation of the trachea for ventilatory support and therefore may dramatically alter the course of recovery. We herein review the analgesia options for patients with MFR. Recent findingsFor healthy patients with one to two fractured ribs, systemic analgesics may suffice. For more than three to four fractured ribs, studies and experience have reaffirmed the superior analgesia made possible with thoracic epidural, thoracic paravertebral, and intercostal blocks. From experience, interpleural block has significant drawbacks. Catheterization allows the continuation of analgesia for 2 or more days with just one block. Use of the landmark technique is usually satisfactory for accurate block placement but ultrasound and nerve stimulation are showing promise in further improving needle and catheter placement accuracy, especially in the presence of difficult anatomy. SummaryThoracic epidural, thoracic paravertebral, and intercostal blocks are the top choices for patients with MFR and they are of equivalent efficacy. Each has unique advantages and disadvantages. Our preference tends to be the thoracic paravertebral approach.

Thoracic paravertebral block and its effects on chronic pain and health-related quality of life after modified radical mastectomy.

Background and Objectives Patients undergoing breast cancer surgery frequently experience chronic postoperative pain. The primary objective of this randomized study was to determine if thoracic paravertebral block (TPVB) reduced the incidence of chronic pain after a modified radical mastectomy (MRM) when compared with general anesthesia (GA). Methods One hundred eighty women undergoing MRM were randomized to 1 of 3 study groups: group 1: standardized GA, group 2: GA with a single-injection TPVB and placebo paravertebral infusion, and group 3: GA with a continuous TPVB. Outcomes assessed postoperatively included acute postoperative pain and analgesic consumption and, at 3 and 6 months, the incidence and severity of chronic pain and physical and mental health-related quality of life (HRQOL). Results There was no significant difference in the incidence of chronic pain at 3 months (P = 0.13) and 6 months (P = 0.79) after the MRM between the study groups. The relative risk of developing chronic pain (P = 0.25) was also similar between the groups. There was no difference in acute pain (P = 0.22) or postoperative analgesic consumption (P = 0.67) between the groups. Nevertheless, differences were observed in chronic pain–related secondary outcome variables. The TPVB groups reported lower chronic pain scores (P < 0.05), exhibited fewer symptoms and signs of chronic pain (P ⩽ 0.01), and also experienced better physical and mental HRQOL than did the GA group. Chronic pain scores also decreased with time in all study groups (P < 0.05). Conclusions There is no significant difference in the incidence or relative risk of chronic pain at 3 and 6 months after an MRM when TPVB is used in conjunction with GA. Nevertheless, patients who receive a TPVB report less severe chronic pain, exhibit fewer symptoms and signs of chronic pain, and also experience better physical and mental HRQOL.

Total airway obstruction during local anesthesia in a non-sedated patient with a compromised airway

PurposeTo report a case of complete upper airway obstruction after topicalization with lidocaine in a completely conscious patient with partial upper airway obstruction.Clinical featuresA 69-yr-old man with a history of neck cancer and radiation presented for resection of recurrent neck tumour. No preoperative sedation was given. He had inspiratory and expiratory stridor but had no history of aspiration or swallowing problem. Phonation was distorted but effective. The surgeon was reluctant to perform an awake tracheostomy under local anesthesia. In preparation for a fibrescope-assisted orotracheal intubation, the non-sedated patient was given topical upper airway lidocaine during which he developed total airway obstruction and hypoxemia. He was immediately intubated with a fibrescope. His vocal cords were not edematous although the supraglottic structures appeared to be. The vocal cords were abducted and their movement was limited and not paradoxical. Tumour resection was uneventful upon successful tracheal intubation and general anesthesia. Tracheostomy at the end of the case was difficult, as expected. The patient tolerated the procedures and regained consciousness with no neurologic sequelae.ConclusionDynamic airflow limitation associated with local anesthesia of the upper airway may lead to complete upper airway obstruction in a compromised airway. The main cause may be the loss of upper airway muscle tone, exacerbated by deep inspiration during panic.RésuméObjectifPrésenter un cas d’obstruction complète des voies aériennes supérieures après pulvérisation de lidocaïne chez un patient tout à fait conscient mais souffrant déjà d’obstruction respiratoire partielle.Éléments cliniquesUn homme de 69 ans aux antécédents de cancer du cou et de radiothérapie s’est présenté pour la résection d’une tumeur récurrente au cou. Aucune sédation préopératoire n’a été administrée. Il présentait un stridor inspiratoire et expiratoire, mais n’avait pas d’antécédent de trouble d’aspiration ou de déglutition. La phonation était déformée mais efficace. Le chirurgien était réticent à réaliser une trachéotomie vigile sous anesthésie locale. Pendant la préparation de l’intubation orotrachéale fibroscopique, de la lidocaïne topique a été administrée dans les voies aériennes supérieures du patient éveillé chez qui s’est développée une obstruction totale des voies aériennes et de l’hypoxémie. Il a été immédiatement intubé avec un fibroscope. Ses cordes vocales n’étaient pas œdémateuses même si les structures supraglottiques semblaient l’être. Les cordes vocales étaient écartées et leur mouvement était limité mais non paradoxal. La résection tumorale s’est bien déroulée sous intubation trachéale réussie et anesthésie générale. Comme prévu, la trachéotomie a été difficile à réaliser à la fin de l’opération. Le patient a bien toléré les interventions et s’est réveillé sans séquelles neurologiques.ConclusionUne limitation dynamique du débit d’air associé à l’anesthésie locale des voies aériennes supérieures peut conduire à une obstruction complète des voies respiratoires supérieures en cas d’ob-struction partielle préalable. La principale cause pourrait être la perte du tonus musculaire des voies respiratoires supérieures, exacerbée par l’inspiration profonde pendant les moments de panique.

Thoracic paravertebral block for management of pain associated with multiple fractured ribs in patients with concomitant lumbar spinal trauma

Background and Objectives The need for continual neurological assessment in patients with lumbar spinal injury poses a challenge for effective management of pain associated with multiple fractured ribs. Two cases are presented to illustrate the benefits of using thoracic paravertebral block to control the pain of multiple fractured ribs without compromising the ongoing neurological assessment. Case Report Thoracic paravertebral block was used in 2 patients with concomitant multiple fractured ribs and lumbar spinal injury. Case 2 also had a head injury and there was moderate coagulopathy. The thoracic paravertebral catheter was placed in the upper thoracic region and radiological imaging was used to delineate spread before the injection of relatively small volumes (10 to 15 mL) of local anesthetic. In case 1, the thoracic paravertebral block produced ipsilateral segmental thoracic anesthesia, providing excellent pain relief for the fractured ribs. It also spared the lumbar and sacral nerve roots, preserving neurological function in the lower extremities and bladder sensation. In case 2, effective analgesia without systemic sedation and opioids resulted in the patient regaining consciousness, which allowed continuous assessment of central and peripheral neurological function. Conclusion Thoracic paravertebral block is an option for managing pain associated with multiple fractured ribs in the presence of concomitant lumbar spinal injury requiring continual neurological assessment.

Use of heliox in critical upper airway obstruction.: Physical and physiologic considerations in choosing the optimal helium:oxygen mix

Heliox has a lower density than oxygen and nitrogen, and can improve ventilation rapidly in patients with critical upper airway obstruction. The choice of the best helium:oxygen ratio depends on whether the predominant problem is hypercarbia or hypoxia. In the former situation, 80% helium should be used, and in the latter, 100% oxygen is appropriate.