The relationship between minute ventilation and end tidal CO2 in intubated and spontaneously breathing patients undergoing procedural sedation.

BACKGROUND: Monitoring respiratory status using end tidal CO2 (EtCO2), which reliably reflects arterial PaCO2 in intubated patients under general anesthesia, has often proven both inaccurate and inadequate when monitoring non-intubated and spontaneously breathing patients. This is particularly important in patients undergoing procedural sedation (e.g., endoscopy, colonoscopy). This can be undertaken in the operating theater, but is also often delivered outside the operating room by non-anesthesia providers. In this study we evaluated the ability for conventional EtCO2 monitoring to reflect changes in ventilation in non-intubated surgical patients undergoing monitored anesthesia care and compared and contrasted these findings to both intubated patients under general anesthesia and spontaneously breathing volunteers. METHODS: Minute Ventilation (MV), tidal volume (TV), and respiratory rate (RR) were continuously collected from an impedance-based Respiratory Volume Monitor (RVM) simultaneously with capnography data in 160 patients from three patient groups: non-intubated surgical patients managed using spinal anesthesia and Procedural Sedation (n = 58); intubated surgical patients under General Anesthesia (n = 54); and spontaneously breathing Awake Volunteers (n = 48). EtCO2 instrument sensitivity was calculated for each patient as the slope of a Deming regression between corresponding measurements of EtCO2 and MV and expressed as angle from the x-axis (θ). All data are presented as mean ± SD unless otherwise indicated. RESULTS: While, as expected, EtCO2 and MV measurements were negatively correlated in most patients, we found gross systematic differences across the three cohorts. In the General Anesthesia patients, small changes in MV resulted in large changes in EtCO2 (high sensitivity, θ = -83.6 ± 9.9°). In contrast, in the Awake Volunteers patients, large changes in MV resulted in insignificant changes in EtCO2 (low sensitivity, θ = -24.7 ± 19.7°, p < 0.0001 vs General Anesthesia). In the Procedural Sedation patients, EtCO2 sensitivity showed a bimodal distribution, with an approximately even split between patients showing high EtCO2 instrument sensitivity, similar to those under General Anesthesia, and patients with low EtCO2 instrument sensitivity, similar to the Awake Volunteers. CONCLUSIONS: When monitoring non-intubated patients undergoing procedural sedation, EtCO2 often provides inadequate instrument sensitivity when detecting changes in ventilation. This suggests that augmenting standard patient care with EtCO2 monitoring is a less than optimal solution for detecting changes in respiratory status in non-intubated patients. Instead, adding direct monitoring of MV with an RVM may be preferable for continuous assessment of adequacy of ventilation in non-intubated patients.

Assessment of perioperative minute ventilation in obese versus non-obese patients with a non-invasive respiratory volume monitor.

BACKGROUND: Monitoring the adequacy of spontaneous breathing is a major patient safety concern in the post-operative setting. Monitoring is particularly important for obese patients, who are at a higher risk for post-surgical respiratory complications and often have increased metabolic demand due to excess weight. Here we used a novel, noninvasive Respiratory Volume Monitor (RVM) to monitor ventilation in both obese and non-obese orthopedic patients throughout their perioperative course, in order to develop better monitoring strategies. METHODS: We collected respiratory data from 62 orthopedic patients undergoing elective joint replacement surgery under general anesthesia using a bio-impedance based RVM with an electrode PadSet placed on the thorax. Patients were stratified into obese (BMI ≥ 30) and non-obese cohorts and minute ventilation (MV) at various perioperative time points was compared against each patient's predicted minute ventilation (MVPRED) based on ideal body weight (IBW) and body surface area (BSA). The distributions of MV measurements were also compared across obese and non-obese cohorts. RESULTS: Obese patients had higher MV than the non-obese patients before, during, and after surgery. Measured MV of obese patients was significantly higher than their MVPRED from IBW formulas, with BSA-based MVPRED being a closer estimate. Obese patients also had greater variability in MV post-operatively when treated with standard opioid dosing. CONCLUSIONS: Our study demonstrated that obese patients have greater variability in ventilation post-operatively when treated with standard opioid doses, and despite overall higher ventilation, many of them are still at risk for hypoventilation. BSA-based MVPRED formulas may be more appropriate than IBW-based ones when estimating the respiratory demand of obese patients. The RVM allows for the continuous and non-invasive assessment of respiratory function in both obese and non-obese patients.

Quantification of respiratory depression during pre-operative administration of midazolam using a non-invasive respiratory volume monitor.

BACKGROUND: Pre-operative administration of benzodiazepines can cause hypoventilation-a decrease in minute ventilation (MV)-commonly referred to as "respiratory compromise or respiratory depression." Respiratory depression can lead to hypercarbia and / or hypoxemia, and may heighten the risk of other respiratory complications. Current anesthesia practice often places patients at risk for respiratory complications even before surgery, as respiratory monitoring is generally postponed until the patient is in the operating room. In the present study we examined and quantified the onset of respiratory depression following the administration of a single dose of midazolam in pre-operative patients, using a non-invasive respiratory volume monitor that reports MV, tidal volume (TV), and respiratory rate (RR). METHODS: Impedance-based Respiratory Volume Monitor (RVM) data were collected and analyzed from 30 patients prior to undergoing orthopedic or general surgical procedures. All patients received 2.0 mg of midazolam intravenously at least 20 minutes prior to the induction of anesthesia and the effects of midazolam on the patient's respiratory function were analyzed. RESULTS: Within 15 minutes of midazolam administration, we noted a significant decrease in both MV (average decrease of 14.3% ± 5.9%, p<0.05) and TV (22.3% ± 4.5%, p<0.001). Interestingly, the corresponding RR increased significantly by an average of 10.3% ± 4.7% (p<0.05). Further analysis revealed an age-dependent response, in which elderly patients (age≥65 years, n = 6) demonstrated greater reductions in MV and TV and a lack of compensatory RR increase. In fact, elderly patients experienced an average decrease in MV of 34% ± 6% (p<0.05) compared to an average decrease of 9% ± 6% (p<0.05) in younger patients. CONCLUSIONS: We were able to quantify the effects of pre-operative midazolam administration on clinically significant respiratory parameters (MV, TV and RR) using a non-invasive RVM, uncovering that the respiratory depressive effect of benzodiazepines affect primarily TV rather than RR. Such respiratory monitoring data provide the opportunity for individualizing dosing and adjustment of clinical interventions, especially important in elderly patients. With additional respiratory data, clinicians may be able to better identify and quantify respiratory depression, reduce adverse effects, and improve overall patient safety.

Intravenous Acetaminophen versus Morphine for Analgesia in Labor: A Randomized Trial.

Objective To compare the effectiveness of intravenous acetaminophen with that of morphine in reducing pain in the first stage of labor. Methods An open-label, randomized controlled trial of women ≥ 34 weeks gestation in the first stage of labor, assigned to either intravenous acetaminophen or morphine. The primary outcome was improved analgesia measured by difference of visual analog scale (VAS) score at 120 minutes from baseline. Secondary outcomes were request for rescue analgesia, maternal side effects, and fetal heart rate changes. Statistical analyses performed were chi-square, Student's t-test, and Kaplan-Meier survival analysis. Results Of 40 women randomized, 18 received acetaminophen (2 did not receive study drug), and 20 received morphine. Because of difficulties in recruitment, the sample size of 88 was not achieved. The primary outcome was similar between groups (p = 0.53). Within 120 minutes of initial treatment, more women receiving intravenous acetaminophen required rescue analgesia (acetaminophen: 52.9% vs. morphine: 17.6%, p < 0.01). Maternal and fetal side effects were similar between groups. Conclusion There was no difference in VAS scores between groups. However, as half of women receiving intravenous acetaminophen required rescue analgesia within 120 minutes of treatment, intravenous acetaminophen may be less effective for analgesia in early labor compared with intravenous morphine.

Thoracic epidural analgesia to control malignant pain until viability in a pregnant patient.

Management of nonobstetric pain in the pregnant patient presents unique challenges related to transplacental fetal exposure to opioids and the subsequent risk of neonatal withdrawal syndrome. We present the case of a pregnant patient suffering from the pain of a progressively enlarging thoracoabdominal sarcoma. Epidural analgesia (using local anesthetics with minimal opioid) was utilized over a span of weeks to manage oncologic pain, limiting fetal opioid exposure and culminating in the birth of a healthy infant. While nonobstetric abdominal pain during pregnancy is not that uncommon, neoplastic abdominal pain does appear to be rare. Combined local anesthetic and opioid continuous epidural infusion should be considered a viable option in the pain management approach to obstetric patients with nonobstetric pain associated with malignancy.

Successful treatment of Raynaud's syndrome in a lupus patient with continuous bilateral popliteal sciatic nerve blocks: a case report.

Raynaud's syndrome has been treated medically and invasively, sometimes with regional anesthesia leading up to sympathectomy. We demonstrate that regional anesthesia was in this case a useful technique that can allow some patients to find temporary but significant relief from symptoms of Raynaud's syndrome exacerbation. We present a 43-year-old woman with Raynaud's syndrome secondary to lupus who was treated with bilateral popliteal nerve block catheters for ischemic pain and necrosis of her feet; this led to almost immediate resolution of her pain and return of color and function of her feet. While medical management should continue to be a front-line treatment for Raynaud's syndrome, regional anesthesia can be useful in providing rapid dissipation of symptoms and may thus serve as a viable option for short-term management of this syndrome.

Evolution of transversus abdominis plane infiltration techniques for postsurgical analgesia following abdominal surgeries.

Transversus abdominis plane (TAP) infiltration is a regional anesthesia technique that has been demonstrated to be effective for management of postsurgical pain after abdominal surgery. There are several different clinical variations in the approaches used for achieving analgesia via TAP infiltration, and methods for identification of the TAP have evolved considerably since the landmark-guided technique was first described in 2001. There are many factors that impact the analgesic outcomes following TAP infiltration, and the various nuances of this technique have led to debate regarding procedural classification of TAP infiltration. Based on our current understanding of fascial and neuronal anatomy of the anterior abdominal wall, as well as available evidence from studies assessing local anesthetic spread and cutaneous sensory block following TAP infiltration, it is clear that TAP infiltration techniques are appropriately classified as field blocks. While the objective of peripheral nerve block and TAP infiltration are similar in that both approaches block sensory response in order to achieve analgesia, the technical components of the two procedures are different. Unlike peripheral nerve block, which involves identification or stimulation of a specific nerve or nerve plexus, followed by administration of a local anesthetic in close proximity, TAP infiltration involves administration and spread of local anesthetic within an anatomical plane of the surgical site.