A Randomized Study Comparing the Incidence of Postoperative Pain After Phrenic Nerve Infiltration Vs Nonphrenic Nerve Infiltration During Thoracotomy.

Thoracotomy is a common surgical procedure performed worldwide for lung disease. Despite major advances in analgesia, patients still experience severe shoulder, central back and surgical incision site pain in the postoperative period. This study aimed to assess whether intraoperative phrenic nerve infiltration reduces the incidence of postoperative pain and improves peak flow volume measurements during incentive spirometry. 90 patients undergoing open lobectomy were randomly assigned to have phrenic nerve infiltration (n = 46) or not (n = 44). The phrenic nerve infiltration group received 10 mL of 0.25% bupivacaine into the periphrenic fat pad. Preoperative assessments of spirometry and pain scores were recorded (at rest and with movement). Postoperative assessments included peak flow and pain measurements at intervals up to 72 hours. Less shoulder pain was experienced with phrenic nerve infiltration up to 6 hours postsurgery at rest (P = 0.005) and up to 12 hours with movement (P < 0.001). Reduced back pain was reported in the phrenic nerve infiltration group up to 6 hours after surgery both at rest (P = 0.001) and with movement (P = 0.00). Phrenic nerve infiltration reduced pain at the incision site for up to 3 hours both at rest (P < 0.001) and with movement (P = 0.001). Spirometry readings dropped in both groups with consistently lower readings at baseline and follow-up in the PNI group (P = 0.007). Lower analgesic usage of patient controlled analgesia morphine (P < 0.0001), epipleural bupivacaine (P = 0.001), and oramorph/zomorph (P = 0.0002) were recorded. Our findings indicate that the use of phrenic nerve infiltration significantly reduced patient pain scores during the early postoperative period, particularly during movement. We believe that each technique has advantages and disadvantages; however, further studies with large sample size are warranted.

Incidence and outcomes of sepsis after cardiac surgery as defined by the Sepsis-3 guidelines.

BACKGROUND: The Sepsis-3 guidelines diagnose sepsis based on organ dysfunction in patients with either proven or suspected infection. The objective of this study was to assess the incidence and outcomes of sepsis diagnosed using these guidelines in patients in a cardiac intensive care unit (CICU) after cardiac surgery. METHODS: Daily sequential organ failure assessment (SOFA) scores were calculated for 2230 consecutive adult cardiac surgery patients between January 2013 and May 2015. Patients with an increase in SOFA score of ≥2 and suspected or proven infection were identified. The length of CICU stay, 30-day mortality and 2-yr survival were compared between groups. Multivariable linear regression, multivariable logistic regression, and Cox proportional hazards regression were used to adjust for possible confounders. RESULTS: Sepsis with suspected or proven infection was diagnosed in 104 (4.7%) and 107 (4.8%) patients, respectively. After adjustment for confounding variables, sepsis with suspected infection was associated with an increased length of CICU stay of 134.1h (95% confidence interval (CI) 99.0-168.2, P<0.01) and increased 30-day mortality risk (odds ratio 3.7, 95% CI 1.1-10.2, P=0.02). Sepsis with proven infection was associated with an increased length of CICU stay of 266.1h (95% CI 231.6-300.7, P<0.01) and increased 30-day mortality risk (odds ratio 6.6, 95% CI 2.6-15.7, P<0.01). CONCLUSIONS: Approximately half of sepsis diagnoses were based on proven infection and half on suspected infection. Patients diagnosed with sepsis using the Sepsis-3 guidelines have significantly worse outcomes after cardiac surgery. The Sepsis-3 guidelines are a potentially useful tool in the management of sepsis following cardiac surgery.

Pulmonary penetration of piperacillin and tazobactam in critically ill patients.

Pulmonary infections in critically ill patients are common and are associated with high morbidity and mortality. Piperacillin-tazobactam is a frequently used therapy in critically ill patients with pulmonary infection. Antibiotic concentrations in the lung reflect target-site antibiotic concentrations in patients with pneumonia. The aim of this study was to assess the plasma and intrapulmonary pharmacokinetics (PK) of piperacillin-tazobactam in critically ill patients administered standard piperacillin-tazobactam regimens. A population PK model was developed to describe plasma and intrapulmonary piperacillin and tazobactam concentrations. The probability of piperacillin exposures reaching pharmacodynamic end points and the impact of pulmonary permeability on piperacillin and tazobactam pulmonary penetration was explored. The median piperacillin and tazobactam pulmonary penetration ratios were 49.3 and 121.2%, respectively. Pulmonary piperacillin and tazobactam concentrations were unpredictable and negatively correlated with pulmonary permeability. Current piperacillin-tazobactam regimens may be insufficient to treat pneumonia caused by piperacillin-tazobactam-susceptible organisms in some critically ill patients.

Systematic review of uncalibrated arterial pressure waveform analysis to determine cardiac output and stroke volume variation.

UNLABELLED: The FloTrac/Vigileo™, introduced in 2005, uses arterial pressure waveform analysis to calculate cardiac output (CO) and stroke volume variation (SVV) without external calibration. The aim of this systematic review is to evaluate the performance of the system. Sixty-five full manuscripts on validation of CO measurements in humans, published in English, were retrieved; these included 2234 patients and 44,592 observations. RESULTS: have been analysed according to underlying patient conditions, that is, general critical illness and surgery as normodynamic conditions, cardiac and (post)cardiac surgery as hypodynamic conditions, and liver surgery and sepsis as hyperdynamic conditions, and subsequently released software versions. Eight studies compared SVV with other dynamic indices. CO, bias, precision, %error, correlation, and concordance differed among underlying conditions, subsequent software versions, and their interactions, suggesting increasing accuracy and precision, particularly in hypo- and normodynamic conditions. The bias and the trending capacity remain dependent on (changes in) vascular tone with most recent software. The SVV only moderately agreed with other dynamic indices, although it was helpful in predicting fluid responsiveness in 85% of studies addressing this. Since its introduction, the performance of uncalibrated FloTrac/Vigileo™ has improved particularly in hypo- and normodynamic conditions. A %error at or below 30% with most recent software allows sufficiently accurate and precise CO measurements and trending for routine clinical use in normo- and hypodynamic conditions, in the absence of large changes in vascular tone. The SVV may usefully supplement these measurements.

Increased oesophageal acid exposure at the beginning of the recumbent period is primarily a recumbent-awake phenomenon.

BACKGROUND: A significant increase in oesophageal acid exposure during early recumbent period has been demonstrated. AIM: To determine if acid reflux during the early recumbent period occurs in the recumbent-asleep or recumbent-awake period using a novel integrative actigraphy and pH programme. METHOD: Thirty-nine subjects with heartburn at least three times a week were included. Subjects underwent pH testing concomitantly with actigraphy. Simultaneously recorded actigraphy and pH data were incorporated using a novel integrative technique to determine sleep and awake periods. Characteristics of acid reflux were compared between the recumbent-awake and recumbent-asleep periods. RESULTS: Seventeen (44.7%) subjects had acid reflux events during recumbent-awake period as compared to seven (18.4%) in the corresponding recumbent-asleep period (P = 0.046). The mean number of acid reflux events in recumbent-awake period was significantly higher than in the corresponding recumbent-asleep period (8.1 +/- 4.4 vs. 3.2 +/- 1.5, P < 0.001). In the recumbent-awake period, 38.4% of acid reflux events were associated with GERD-related symptoms as compared with 3.7% of acid reflux events during the corresponding recumbent-asleep period (P = 0.01). CONCLUSION: Increased acid reflux in the early recumbent period occurs primarily during the recumbent-awake and not during the recumbent-asleep period.

Riser's reflux--an eye-opening experience.

BACKGROUND: Patients with gastro-oesophageal reflux disease (GORD) commonly report waking up in the morning with a sour or bitter taste in their mouth. The aim of the study was to compare the prevalence and frequency of acid reflux events prior to and immediately after awakening from sleep in the morning between GORD patients and normal subjects. METHODS: Thirty-nine patients with heartburn at least three times a week and abnormal pH test and nine healthy controls were included. All subjects were evaluated by demographic and GORD Symptom Checklist questionnaires. Subjects underwent pH testing concomitantly with actigraphy. A novel technology that simultaneously integrates raw actigraphy and pH monitoring data was utilized to determine the presence, frequency, and characteristics of acid reflux events prior to (up to 1 h) and immediately after (10 and 20 min) awakening from sleep in the morning. KEY RESULTS: Nineteen (48.7%) of the GORD patients had an acid reflux event within the first 20 min after awakening from sleep in the morning as compared to only seven (17.9%) during the hour prior to awakening. Within the first 10 and 20 min after awakening, patients had a total of 32 and 60 acid reflux events, respectively, as compared to 14 during the 1 h prior to awakening (P < 0.05). None of the healthy control patients demonstrated any reflux events during these three studied periods (P < 0.001). CONCLUSIONS & INFERENCES: Riser's reflux is very common among GORD patients and possibly may explain reports of early-morning GORD symptoms.

Assessment of 24-h oesophageal pH monitoring should be divided to awake and asleep rather than upright and supine time periods.

Oesophageal acid exposure analysis is divided to upright and supine, based on the assumption that the supine-awake period is similar to the supine-asleep period. To determine if the principal acid-reflux characteristics of supine-awake are closer to supine-asleep or upright period. Patients with heartburn underwent an upper endoscopy and pH testing. The patients were instructed to carefully document their upright, supine-awake and supine-asleep periods. A total of 64 patients were enrolled into this study (M/F 35/29; mean age 52.4 +/- 13.3). The mean percentage total time pH <4, frequency of acid-reflux events (per h) and number of sensed reflux events was not different between upright and the supine-awake period (P = ns). In contrast, the mean percentage total time pH <4, frequency of acid-reflux events and number of sensed reflux events was significantly higher in both upright and supine-awake periods vs supine-asleep (4.3 +/- 6.9, 1.86 +/- 2.7 and 0.01 +/- 0.05, P < 0.0001, respectively). The principal characteristics of the acid-reflux events in the supine-awake period are closer to the upright period than to the supine-asleep period.

Comparisons of the distribution of oesophageal acid exposure throughout the sleep period among the different gastro-oesophageal reflux disease groups.

BACKGROUND: Nocturnal gastro-oesophageal reflux diseases (GERD) can lead to oesophageal mucosal injury and extra-oesophageal complications. AIM: To compare distribution of oesophageal acid exposure during sleep time among patients with non-erosive reflux disease and abnormal pH test (NERD-positive), erosive oesophagitis (EO) and Barrett's oesophagus (BO). METHODS: Patients underwent endoscopy followed by 24-h oesophageal pH testing. Oesophageal acid exposure was assessed every 2 h of the sleep period (0-2, 2-4, 4-6 and 6-8 h). Each period of 2 h was evaluated for acid reflux parameters. All groups were matched by age, time from last meal and duration of sleep time. RESULTS: Thirty-eight patients were enrolled (NERD-positive, 16; EO, 1.4; and BO, 8). All GERD groups demonstrated higher oesophageal acid exposure in the first vs. second half of the sleep period as determined by percent time pH <4 (BO: 34.7 vs.11.6, EO: 13.5 vs. 6.9, NERD-positive: 8.8 vs. 2.5, all P < 0.01). In general, patients with BO had a significantly higher distribution of oesophageal acid exposure than those with NERD-positive and EO. CONCLUSIONS: Oesophageal acid exposure generally declines throughout the sleep period regardless of GERD group, but BO patients demonstrated the greatest decline during the sleep period.

Effect of three different anaesthetic agents on the postoperative production of cardiac troponin T in paediatric cardiac surgery.

BACKGROUND: Paediatric cardiac surgery is associated with some degree of myocardial injury. Ischaemic preconditioning (IP) has been investigated widely in the adult population. Volatile agents have been shown to simulate IP providing extra protection to the myocardium during adult cardiopulmonary bypass (CPB) while propofol seems to act through different mechanisms. IP has not been investigated in the paediatric population to the same extent. Cardiac troponin T (cTnT) is a reliable marker of myocardial injury in neonates and children. We have investigated the relationship between three anaesthetic agents, midazolam, propofol, and sevoflurane, and postoperative production of cTnT. METHODS: Ninety patients undergoing repair of congenital heart defect with CPB were investigated in a prospective randomized study. cTnT was measured four times during the first 24 h following admission to the paediatric intensive care unit. Other variables measured included arterial blood gases, lactate, fluid balance, use of inotropic drugs, PaO2/FiO2 ratio and ventilator hours. RESULTS: cTnT was elevated in all three groups throughout the study period. The differences between the three groups were not statistically significant. Eight hours after admission to the intensive care unit cTnT concentrations tended to be higher in the midazolam group [mean (95% confidence intervals)]; 2.7 (1.9-3.5) ng ml(-1). Patients receiving a propofol-based anaesthesia had similar concentrations 2.6 (1.7-3.5) ng ml(-1) while those receiving sevoflurane tended to have a lower cTnT production 1.7 (1.3-2.2) ng ml(-1). CONCLUSIONS: Midazolam, propofol, and sevoflurane appear to provide equal myocardial protection in paediatric cardiac surgery when using cTnT as a marker of myocardial damage.

Feasibility and tolerability of transnasal/per-oral placement of the wireless pH capsule vs. traditional 24-h oesophageal pH monitoring--a randomized trial.

BACKGROUND: The wireless pH is a new technique to monitor oesophageal acid exposure. AIM: To compare the feasibility and tolerability of the wireless pH capsule vs. the traditional pH probe. METHODS: Consecutive patients referred for a pH test were enrolled into the study. Patients were randomized to traditional pH probe, or wireless pH capsule. Patients recorded their activities, food consumption, symptoms, satisfaction with the test and completed a quality of life questionnaire. RESULTS: Of the 50 patients recruited, 25 patients underwent placement of the traditional pH probe, and 25 the wireless pH capsule. Patients with the wireless pH capsule had less nose pain, runny nose, throat pain, throat discomfort and headache as compared with those with the traditional pH probe (P = 0.047, P = 0.001, P = 0.032, P = 0.001, P = 0.009, respectively). Patients in the wireless pH capsule group had more chest discomfort during the pH test (P = 0.037). Patients in the wireless pH capsule group perceived the test as interfering less with their overall daily activities, eating and sleep (P =0.001, P = 0.003, P = 0.025, respectively), and had overall satisfaction with the test (P = 0.023). CONCLUSIONS: Transnasal/per-oral placement of the wireless pH capsule is significantly better tolerated then the traditional pH probe.

Gut permeability in paediatric cardiac surgery.

BACKGROUND: Intestinal mucosal ischaemia can occur in infants and children during and after cardiac surgery. Severe decreases in mucosal perfusion may cause complications such as necrotizing enterocolitis and postoperative mortality. We investigated gut permeability in paediatric patients undergoing cardiac surgery using the dual sugar permeability test and absorption of two other saccharides. METHODS: Thirty-four patients undergoing palliative or corrective surgical procedures with and without cardiopulmonary bypass were investigated. Intestinal permeability was measured using 3-O-methyl-D-glucose, D-xylose, L-rhamnose and lactulose, given orally after induction of anaesthesia and 12 and 24 h later. RESULTS: Lactulose/rhamnose ratios were raised from the outset [median 0.39 (confidence interval 0.07-1.8 for patients undergoing operations without cardiopulmonary bypass and 0.30 (0.02-2.6) with cardiopulmonary bypass]. The highest lactulose/rhamnose ratios were recorded 12 h after surgery 0.32 (0.07-6.9), when cardiopulmonary bypass was used. This is approximately seven times the value expected in healthy children. There was an improvement in patients not undergoing cardiopulmonary bypass: 0.22 (0.03-0.85) 12 h and 0.11 (0-0.48) 24 h after induction of anaesthesia. Patients undergoing repair of aortic coarctation showed the fastest recovery: 0.09 (0.03-0.31) 12 h and 0.07 (0.04-0.35) 24 h after induction of anaesthesia. CONCLUSIONS: Patients with congenital heart defects have abnormal gut permeability when compared with healthy children of similar age. Cardiopulmonary bypass seems to affect the intestinal barrier morphologically (lactulose and rhamnose absorption) and functionally (3-O-methyl-D-glucose and D-xylose absorption).

Non-erosive reflux disease (NERD)--acid reflux and symptom patterns.

BACKGROUND: Recent reports suggest that patients with non-erosive reflux disease (NERD) treated with anti-reflux medications show lower symptom improvement rates than patients with erosive oesophagitis treated with the same medications. AIM: To determine the acid reflux and symptom patterns of patients with NERD in comparison with those with erosive oesophagitis and Barrett's oesophagus, and to identify different NERD subgroups. METHODS: One hundred and forty-nine consecutive patients seen for classic heartburn symptoms were evaluated for the study. Oesophageal mucosal injury was assessed by upper endoscopy and classified by Hetzel-Dent criteria. Patients with Hetzel-Dent grades 0-1 were considered to have NERD. The extent of oesophageal acid exposure was determined by ambulatory 24-h oesophageal pH monitoring. RESULTS: Seventy-one patients were found to have NERD, 36 erosive oesophagitis and 42 Barrett's oesophagus. Compared with patients with erosive oesophagitis (75%) and Barrett's oesophagus (93%), those with NERD (45%) were significantly less likely to have an abnormal pH test (P = 0.0001). Patients with Barrett's oesophagus had the highest mean number of acid reflux events (210 +/- 17.7), compared with those with erosive oesophagitis (139.7 +/- 15.2) and NERD (95.3 +/- 9.4) (P = 0.0001); however, the rate of perceived acid reflux events was similar and very low in all groups (NERD, 3.6%; erosive oesophagitis, 2.9%; Barrett's oesophagus, 2.17%). NERD-positive patients (abnormal pH test) had a similar extent of oesophageal acid exposure to those with erosive oesophagitis. NERD-positive patients were more likely to demonstrate a symptom index greater than 75% than NERD-negative patients (normal pH test) (61.9% vs. 10.5%; P = 0.0001). In the NERD-negative group, those with a negative symptom index reported having heartburn at pH < 4 only 12.7% of the time, compared with 70.7% of the time in those with a positive symptom index, despite a similar mean number of heartburn episodes. CONCLUSIONS: Patients with NERD commonly demonstrate a negative pH test. Acid reflux characteristics and symptom patterns suggest a heterogeneous group of patients.

Impact of a formulary change in proton pump inhibitors on health care costs and patients' symptoms.

Patients may fail to successfully undergo a switch in therapy associated with a formulary change. The aim of this study was to measure health care costs and outcomes among patients who failed a formulary change in proton pump inhibitors in a VA medical center. Patients who failed a switch from omeprazole to lansoprazole (N = 51) were matched with patients who were successfully switched (N = 51). Health care utilization data was gathered from VA electronic databases and medical records for six months before and after the switch and, for failure patients, during the lansoprazole trial period. Statistical comparisons between failure and success patients were performed on changes in health care costs between these time periods. Health outcome data for the lansoprazole trial period and subsequent omeprazole reinstatement period were obtained through a telephone questionnaire of failure patients. Changes in total health care utilization costs did not differ significantly between failure and success groups for any of the time periods. Failure patients had significantly poorer health outcomes during their lansoprazole trial periods with significantly greater severity of heartburn and severity and frequency of acid regurgitation (P < 0.001). In conclusion, the formulary change had a negative impact upon health outcomes among failure patients but did not significantly affect their health care utilization costs. Identification of failure patients early in their lansoprazole trial periods could improved their health outcomes and satisfaction with medical care.

Chest pain of esophageal origin.

Chest pain of esophageal origin or noncardiac chest pain is reported by at least a fifth of the general population. Recent literature focused on further understanding mechanisms of chest pain in subset of patients with functional chest pain of presumed esophageal origin. Studies have demonstrated concurrent visceral and somatic pain hypersensitivity, and amplified secondary allodynia, in patients with noncardiac chest pain (NCCP), suggesting central sensitization. Other studies have demonstrated abnormal cerebral processing of intraesophageal stimuli. However, gastroesophageal reflux disease (GERD) has remained the most common esophageal cause of NCCP. The introduction of the proton pump inhibitor test, a highly sensitive and cost-effective diagnostic strategy, simplified our diagnostic approach toward patients with GERD-related NCCP. For patients with positive proton-pump-inhibitor test results, long-term treatment with antireflux medication is warranted. For patients with non-GERD-related NCCP, pain modulators remain the cornerstone of therapy.

Omeprazole 40 mg once a day is equally effective as lansoprazole 30 mg twice a day in symptom control of patients with gastro-oesophageal reflux disease (GERD) who are resistant to conventional-dose lansoprazole therapy-a prospective, randomized, multi-centre study.

BACKGROUND: Comparative studies of omeprazole and lansoprazole are scarce and even scarcer are comparisons of higher doses. Most of the comparative studies have assessed the effect of the two proton pump inhibitors (PPIs) on gastric acid secretion or gastric pH. Few studies have compared clinical end-points such as oesophageal healing and symptom control. AIM: To determine the clinical efficacy of omeprazole 40 mg daily as compared to lansoprazole 30 mg twice a day in symptom control of patients with severe symptomatic GERD. METHODS: Ninety-six patients who failed a standard dose of lansoprazole (30 mg once daily), were enrolled in a prospective fashion from three VA medical centres and were randomized to receive 6 weeks of either omeprazole 40 mg daily or lansoprazole 30 mg twice daily. Patients reported daily on symptom severity and frequency, antacid consumption and side-effects. RESULTS: Forty-six patients received omeprazole and 44 lansoprazole. Although not statistically significant, there was a consistent trend of better symptom control in the omeprazole group for daytime and night-time heartburn and acid regurgitation. There was no statistical difference between the two groups in mean antacid consumption overall and at the end of each of the 6 weeks of the study. In addition, there was no significant difference in the overall frequency of side-effects between the two groups nor for each individual side-effect. CONCLUSION: Omeprazole 40 mg once daily is equally effective and tolerated as lansoprazole 30 mg twice daily in symptom control of patients with GERD.

Failure of oesophageal acid control in candidates for Barrett's oesophagus reversal on a very high dose of proton pump inhibitor.

BACKGROUND: Normalization of oesophageal acid exposure using high dose proton pump inhibitors in patients who are candidates for ablation therapy has been suggested to be essential for successful Barrett's reversal. However, the success rate for achieving pH normalization has not been determined. METHODS: Patients with Barrett's oesophagus (2-6 cm in length) who were found to be eligible for ablation therapy using multipolar electrocoagulation were included in this prospective study. Patients underwent an upper endoscopy to determine Barrett's length and other anatomic characteristics. Biopsies were obtained to rule out dysplasia. Subsequently, patients were treated with omeprazole 40 mg b.d. Twenty-four hour oesophageal pH monitoring was performed after a mean period of 8.4 +/- 0.6 days of therapy. RESULTS: Twenty-five patients were enrolled into the study. The pH test was abnormal in four (16%) of the study subjects. An additional two (8%) patients had abnormal supine percentage time with pH less than 4. There was no significant difference in oesophageal acid control between patients with long vs. short segment Barrett's oesophagus. Elderly (> 60 years) patients tended to have less acid control than younger (

A prospective study of the use of a dobutamine stress test to identify outcome in patients with sepsis, severe sepsis, or septic shock.

OBJECTIVE: To more clearly define the relationship between an oxygen flux test, oxygen supply dependency, and outcome in patients with sepsis, severe sepsis, or septic shock. DESIGN: Prospective, interventional clinical trial. SETTING: A teaching hospital general intensive care unit in London, UK. PATIENTS: A total of 36 patients with sepsis, severe sepsis, or septic shock were studied during a 10-month period. INTERVENTIONS: After resuscitation, patients were given an intravenous infusion of dobutamine at 10 microg/kg/min for 1 hr. Cardiac and respiratory variables were measured before the infusion and then while the infusion was in progress. Any patient who was able to increase his or her oxygen consumption by >15% was designated a responder to the test. MEASUREMENTS AND MAIN RESULTS: Hemodynamic, oxygen transport, and lactate measurements were made at baseline and after 1 hr of the dobutamine infusion. All patients were then followed up until hospital discharge. Responders to this test had a hospital mortality of 14%, whereas nonresponders had a mortality of 91% (p<.01). The responders were characterized by being younger (p<.05), having higher Acute Physiology and Chronic Health Evaluation III scores (p<.05), and having a greater requirement for inotropic support (p<.05). After the test, the responders had significantly higher oxygen delivery (p<.01) and oxygen consumption (p<.05) than the nonresponders, as well as a significantly greater temperature increase as a result of the infusion (p<.05). The nonresponders were unable to increase either oxygen delivery or oxygen consumption to the dobutamine. This test was highly predictive of outcome (p<.0001). The identification of an increase in both oxygen delivery and oxygen consumption (oxygen supply dependency) was not associated with a poor outcome. CONCLUSION: A dobutamine oxygen flux test provides evidence of the intrinsic function of cells. The inability of these cells to increase oxidative metabolism during sepsis, as indicated by the dobutamine test, is associated with a high mortality.

Evaluation of a mathematical model to predict intrapulmonary shunt non-invasively.

PURPOSE: We have previously published a mathematical model of oxygen transport. Using several physiological assumptions, the model provides a non-invasive estimate of intrapulmonary shunt. During a larger study of lung injury in a pig model, we had the opportunity to check the validity of our assumptions and the accuracy of the model's predictions. METHODS: We used six female pigs, average weight 12.8 kg. Following general anesthesia, tracheostomy and insertion of pulmonary venous and arterial lines, lung injury was induced by repeated saline lung lavage. Using hemodynamic measurements made at different levels of inspired oxygen, intrapulmonary shunt was calculated both by the traditional shunt equation and also by our mathematical model based on non-invasive measurements of FIO2 and SaO2. RESULTS: There was good agreement between the two methods of shunt calculation. Using linear regression the correlation coefficient was 0.95. Bland and Altman analysis showed a bias of -0.8 and precision of 12%. CONCLUSION: In a controlled setting, intrapulmonary shunt can be estimated from non-invasive measurements to a reasonable degree of accuracy. However, the calculation requires too many assumptions to be of general clinical value. The equations used provide a validated physiological model that acts as a useful tool for teaching cardiorespiratory physiology.

Changes in cardiac output during air ambulance repatriation.

OBJECTIVES: To measure, with the use of suprasternal Doppler ultrasound, the hemodynamic changes in patients and volunteers during air ambulance repatriation. DESIGN: Unblinded prospective observational study. SETTING: Chartered air ambulances for the international repatriation of patients. PATIENTS AND PARTICIPANTS: Six medical crew members and seven patients transported back to hospitals in the UK. INTERVENTIONS: The measurement of non-invasive blood pressure, ECG, heart rate, oxygen saturation and hemodynamic variables with suprasternal Doppler. MEASUREMENTS AND RESULTS: There was a drop in systolic and mean arterial blood pressure in the patient's group once in the air. Oxygen saturation dropped in both groups once at cruising altitude. Heart rate remained unchanged. Stroke distance and minute distance increased significantly in the patient's group and non-significantly in the volunteers. Peak velocity increased significantly in the patient's group. There was an overall reduction of systemic vascular resistance during take off and once at cruising altitude. CONCLUSIONS: Hemodynamic changes happen during air ambulance transportation in fit and healthy volunteers and patients alike. These may be due to a combination of hypobaric hypoxia and gravitational forces. It is necessary to establish if these changes have short- or long-term effects in the critically ill.