Mali Mathru

Magnetic resonance imaging of the upper airway. Effects of propofol anesthesia and nasal continuous positive airway pressure in humans.

Background Anesthetic agents inhibit the respiratory activity of upper airway muscles more than the diaphragm, creating a potential for narrowing or complete closure of the pharyngeal airway during anesthesia. Because the underlying mechanisms leading to airway obstruction in sleep apnea and during anesthesia are similar, it was hypothesized that anesthesia-induced pharyngeal narrowing could be counteracted by applying nasal continuous positive airway pressure (CPAP). Methods Anesthesia was induced in ten healthy volunteers (aged 25-34 yr) by intravenous administration of propofol in 50-mg increments every 30-s to a maximum of 300 mg. Magnetic resonance images of the upper airway (slice thickness of 5 mm or less) were obtained in the awake state, during propofol anesthesia, and during administration of propofol plus 10 cm nasal CPAP. Results Minimum anteroposterior diameter of the pharynx at the level of the soft palate decreased from 6.6+/-2.2 mm (SD) in the awake state to 2.7+/-1.5 mm (P < 0.05) during propofol anesthesia and increased to 8.43+/-2.5 mm (P < 0.05) after nasal CPAP application. Anteroposterior diameter of the pharynx at the level of the dorsum of the tongue increased from 7.9+/-3.5 mm during propofol anesthesia to 12.9+/-3.6 mm (P < 0.05) after nasal CPAP. Pharyngeal volume (from the tip of the epiglottis to the tip of the soft palate, assuming this space to be a truncated cone) significantly increased from 2,437+/-1,008 mm3 during propofol anesthesia to 5,847+/-2,827 mm3 (P < 0.05) after nasal CPAP application. Conclusions In contrast to the traditional view that relaxation of the tongue causes airway obstruction, this study suggests that airway closure occurs at the level of the soft palate. Application of nasal CPAP can counteract an anesthesia-induced pharyngeal narrowing by functioning as a pneumatic splint. This is supported by the observed reduction in anteroposterior diameter at the level of the soft palate during propofol anesthesia and the subsequent increase in this measurement during nasal CPAP application.

Hemodynamic response to changes in ventilatory patterns in patients with normal and poor left ventricular reserve.

Hemodynamic effects of controlled mechanical ventilation (CMV), intermittent mandatory ventilation (IMV), and intermittent mandatory ventilation with 5 cm H2O PEEP (IMV5PEEP) were studied in 20 patients after aortocoronary bypass surgery. Significant increases in cardiac index (CI) and stroke volume index (SI) (p < 0.01) resulted in patients with normal left ventricular end-diastolic pressure (LVEDP) and ejection fraction (EF) changing from CMV to IMV. With a change from IMV to IMVSPEEP, the CI and SI returned to CMV values. However, in patients with increased LVEDP with an EF of less than 0.6, suggesting poor ventricular function and reserve, when the mode of ventilation was changed from CMV to IMV, right atrial pressure (RAP) and pulmonary artery occlusion pressure (PAOP) significantly increased (p < 0.01) with an associated significant decrease in mean arterial pressure (MAP), CI, SI (p < 0.01). When these patients were placed on IMV5PEEP, the hemodynamic variables returned to the values obtained during CMV. We conclude that changing from CMV to IMV has salutory effects on the patients hemodynamic values with normal left ventricular function. But in patients with failing left ventricle, volume overload of right ventricle which occurs with the institution of spontaneous respiration during IMV has deleterious effects on the hemodynamic variables. These deleterious effects can be effectively negated by the application of IMV5 PEEP.

Acute complications of pulmonary artery catheter insertion in critically ill patients

: Of 142 critically ill patients undergoing pulmonary artery catheter (PAC) insertion, 1.4% suffered pneumothorax and 7.7% experienced arterial puncture during central venous access. Catheterization was successful in all cases; however, 8.4% of patients required special maneuvers for pulmonary artery cannulation. The 52.3% incidence of cardiac arrhythmias during PAC insertion was primarily due to ventricular arrhythmia (VA), which was more common among patients with complicated myocardial infarction (p less than .01) and less common in patients with sepsis (p less than .05). The development of VA was significantly related to the duration of PAC insertion. Our study suggests that PAC placement carries certain risks and complications which should be weighed against the advantages of a PAC in each patient.

Tourniquet-induced exsanguination in patients requiring lower limb surgery. An ischemia-reperfusion model of oxidant and antioxidant metabolism.

Background Surgically induced ischemia and reperfusion is frequently accompanied by local and remote organ injury. It was hypothesized that this procedure may produce injurious oxidants such as hydrogen peroxide (H2 O2), which, if unscavenged, will generate the highly toxic hydroxyl radical (*symbol* OH). Accordingly, it was proposed that tourniquet‐induced exsanguination for limb surgery may be a useful ischemia‐reperfusion model to investigate the presence of oxidants, particularly H2 O2. Methods In ten patients undergoing knee surgery, catheters were placed in the femoral vein of the limb operated on for collection of local blood and in a vein of the arm for sampling of systemic blood. Tourniquet‐induced limb exsanguination was induced for about 2 h. After tourniquet release (reperfusion), blood samples were collected during a 2‐h period for measurement of H2 O2, xanthine oxidase activity, xanthine, uric acid (UA), glutathione, and glutathione disulfide. Results At 30 s of reperfusion, H2 O2 concentrations increased ([nearly equal] 90%) from 133+/‐5 to 248+/‐8 nmol *symbol* ml sup ‐1 (P < 0.05) in local blood samples, but no change was evident in systemic blood. However, in both local and systemic blood, xanthine oxidase activity increased [nearly equal] 90% (1.91+/‐ 0.07 to 3.93+/‐0.41 and 2.19+/‐0.07 to 3.57+/‐ 0.12 nmol UA *symbol* ml sup ‐1 *symbol* min sup ‐1, respectively) as did glutathione concentrations (1.27+/‐0.04 to 2.69+/‐0.14 and 1.27+/‐0.03 to 2.43+/‐0.13 micro mol *symbol* ml sup ‐1, respectively). At 5 min reperfusion, in local blood, H2 O2 concentrations and xanthine oxidase activity peaked at 796+/‐38 nmol *symbol* ml sup ‐1 ([nearly equal] 500%) and 11.69+/‐1.46 nmol UA *symbol* ml sup ‐1 *symbol* min sup ‐1 ([nearly equal] 520%), respectively. In local blood, xanthine and UA increased from 1.49 +/‐0.07 to 8.36+/‐0.33 nmol *symbol* ml sup ‐1 and 2.69 +/‐0.16 to 3.90+/‐0.18 micro mol *symbol* ml sup ‐1, respectively, whereas glutathione and glutathione disulfide increased to 5.13+/‐0.36 micro mol *symbol* ml sup ‐1 and 0.514+/‐ 0.092 nmol *symbol* ml sup ‐1, respectively. In systemic blood, xanthine oxidase activity peaked at 4.75+/‐0.20 UA nmol *symbol* ml sup ‐1 *symbol* min sup ‐1. At 10 min reperfusion, local blood glutathione and UA peaked at 7.08+/‐0.46 micro mol *symbol* ml sup ‐1 and 4.67 +/‐0.26 micro mol *symbol* ml sup ‐1, respectively, while the other metabolites decreased significantly toward pretourniquet levels. From 20 to 120 min, most metabolites returned to pretourniquet levels; however, local and systemic blood xanthine oxidase activity remained increased 3.76+/‐0.29 and 3.57+/‐0.37 nmol UA *symbol* ml sup ‐1 *symbol* min sup ‐1, respectively. Systemic blood H2 O2 was never increased during the study. During the burst period ([nearly equal] 5–10 min), local blood H2 O2 concentrations and xanthine oxidase activities were highly correlated (r = 0.999). Conclusions These studies suggest that tourniquet‐induced exsanguination for limb surgery is a significant source for toxic oxygen production in the form of H2 O2 and that xanthine oxidase is probably the H2 O2 ‐generating enzyme that is formed during the ischemia‐reperfusion event. In contrast to the reperfused leg, the absence of H2 O2 in arm blood demonstrated a balanced oxidant scavenging in the systemic circulation, despite the persistent increase in systemic xanthine oxidase activity.

Comparison of the sterility of long-term central venous catheterization using single lumen, triple lumen, and pulmonary artery catheters.

The incidence of thrombocytopenia and catheter-induced infection and colonization after the use of triple lumen (TLC), pulmonary artery (PA), and single lumen central venous (CVP) catheters was studied in 29 critically ill patients. Catheter-induced sepsis was documented in 7% of patients with TLC and 10% of patients with CVP and PA catheters. Thirty-three percent of TLC, 20% of PA and 10% of CVP catheters became contaminated during the study. Staphylococcus epidermidis most commonly caused catheter sepsis and contamination. Only patients with PA catheters showed significant decrease in their platelet count. We conclude that use of TLC catheters in critically ill patients does not appear to increase the risk of infectious disease and thrombocytopenia.

A Prospective Evaluation of Clinical Tests for Placement of Laryngeal Mask Airways

Background Reliable tests of correct anatomic placement of the laryngeal mask airway (LMA) may enhance safety during use and minimize the need for fiberoptic instrumentation during airway manipulation through the device. This study assessed the correlation between the outcomes of nine clinical tests to place the LMA and the anatomic position of the device as graded on a standard fiberoptic scale. Methods During 150 anesthetics, the outcome of nine clinical tests of correct placement was individually scored as satisfactory (positive) or unsatisfactory (negative) for clinical use of the LMA. Anatomic placement was assessed (by fiberoptic evaluation) by an anesthesiologist, who was blinded to the placement of the device, as grade 1, vocal cords not seen; grade 2, cords plus the anterior epiglottis seen; grade 3, cords plus the posterior epiglottis seen; and grade 4, only vocal cords seen. The outcomes of clinical tests were correlated with fiberoptic grade. Results Tests that correlated with the fiberoptic grade were the ability to generate an airway pressure of 20 cm water, the ability to ventilate manually, a black line on the LMA in midline, anterior movement of the larynx, outward movement of the LMA on inflation of the cuff, and movements of the reservoir bag with spontaneous breathing. Two tests, ability to generate airway pressure of 20 cm water and ability to ventilate manually, correlated with fiberoptic grades 4 and 3 combined (i.e., the epiglottis was supported by the LMA) and grade 2 (the epiglottis was not supported by the LMA). Tests with poor correlation with fiberoptic grade were the presence of resistance at the end of insertion, inability to advance LMA after inflation of the cuff, and presence of a capnographic trace. Conclusions The outcome of clinical tests correlates with the anatomic placement of LMAs, as judged by fiberoptic examination. Two tests that best correlated with the fiberoptic grade were the ability to generate airway pressure of 20 cm water and the ability to ventilate manually.

National survey of methods and criteria used for weaning from mechanical ventilation

A national survey of hospital-based respiratory care departments was conducted to quantitate the use of various techniques and criteria employed to facilitate weaning of patients from mechanical ventilatory support. Responses were partitioned into private, nonprivate and university/university-affiliated institutions with further subdivision into bed-size groups of not more than 50 beds, 51 to 150 beds, 151 to 300 beds, and not less than 301 beds. Intermittent mandatory ventilation (IMV) was the most frequently used weaning technique in 90.2% of the responding hospitals. IMV was also listed as the primary mode of mechanical ventilatory support (71.6%). IMV to a T-tube system was the most common weaning protocol in nonuniversity hospitals. IMV to 3 to 5 cm H2O continuous positive airway pressure and IMV to T-tube were equally utilized in university/university-affiliated centers. Paco2 was identified the most often (20.7%) and physiologic deadspace ratio the least often (2.5%) as a weaning criterion. We conclude that IMV is probably the most widely practiced weaning technique and that a variety of weaning criteria were employed.

Pulmonary hypertension and systemic vasoconstriction may offset the benefits of acellular hemoglobin blood substitutes.

OBJECTIVE We tested the hypothesis that the pharmacologic properties of a small volume of alpha alpha-cross-linked hemoglobin (alpha alpha Hb) could effectively resuscitate pigs subjected to hemorrhage. METHODS Fourteen pigs hemorrhaged to a mean arterial pressure (MAP) of 40 mm Hg for 60 minutes were treated with a 4-mL/kg 2-minute infusion of 10 g/dL alpha alpha Hb or 7 g/dL human serum albumin, an oncotically matched control solution. RESULTS The removal of blood (17 +/- 1.5 mL/kg) caused the typical physiologic responses to hemorrhagic hypovolemia. Infusion of alpha alpha Hb restored mean arterial pressure and coronary perfusion pressure, but cardiac output and mixed venous O2 saturation did not improve significantly. Pulmonary arterial pressure and pulmonary vascular resistance increased markedly and were higher than baseline levels after alpha alpha Hb. Infusion of human serum albumin produced only minor hemodynamic changes. Brain blood flow did improve to baseline values after alpha alpha Hb, but was the only tissue to do so. In the human serum albumin group, superior mesenteric artery blood flow recovered to baseline values, whereas brain blood flow did not. Blood flows to other tissues were similar in both groups. CONCLUSION Small-volume infusion of alpha alpha Hb restored mean arterial pressure and brain blood flow, but pulmonary hypertension and low peripheral perfusion may offset benefits for trauma patients.

Ventilator-induced barotrauma in controlled mechanical ventilation versus intermittent mandatory ventilation.

: Retrospective analysis of pulmonary barotrauma incidence in 292 patients ventilated greater than or equal to 24 h was conducted. From 1971-1973, 156 patients with acute respiratory insufficiency were managed with controlled mechanical ventilation (CMV) and PEEP. During 1973-1976, 136 patients were supported with IMV and CPAP. Despite higher mean peak and end-expiratory airway pressure, the IMV-CPAP group exhibited a significantly lower incidence of ventilator-induced barotrauma; 7% vs 22% (p less than 0.01). We suspect the difference is related to fewer mechanical breaths with IMV and not to the level of end-expiratory pressure employed.

Prophylactic intubation and continuous positive airway pressure in the management of inhalation injury in burn victims.

Burn mortality statistics are influenced by age and degree of total surface body burn. The addition of an inhalation injury to a cutaneous burn results in a significant increase in mortality rate. Nine hundred fourteen patients with acute thermal injury were screened for positive history of burn in a closed space, facial or oropharyngeal burn, singed nasal vibrisae, carbonacious sputum, and clinical signs of upper airway involvement. On admission, 84 patients (9.2%) had more than one of the previously mentioned factors. They were prophylactically intubated and placed on optimum level of continuous positive airway pressure (CPAP) and intermittent mandatory ventilation (IMV). The mortality rate among patients without inhalation injury was 7.1%, while 54.7% of patients with inhalation injury died. Comparison of burn patients with inhalation injury to those without pulmonary involvement at the same age group and with the same percentage of burn showed significantly higher mortality rate in patients with inhalation injury. The main cause of death in the first 72 h postburn (stage 1) in patients without inhalation injury was peripheral shock (10.1%) and in patients with inhalation injury was peripheral shock (15.2%) and cardiac failure (10.8%). No pulmonary related death occurred in this stage. In 3–10 days postburn period (stage 2), burn wound sepsis (10.1%) and cardiac failure (11.8%) were the major causes of death in patients without inhalation injury. In patients with inhalation injury, pulmonary sepsis (26%) was the major cause of death in this stage. Major causes of death after 10 days postburn (stage 3) in patients without inhalation injury were pulmonary sepsis (20%) and burn wound sepsis (22%). In patients with inhalation injury, burn wound sepsis (21.7%) was the main cause of death. These data suggest that prophylactic intubation and CPAP therapy in burn patients with suspected inhalation injury prevent pulmonary related death in early stage of burn. Irrespective of presence of inhalation injury, sepsis originating from the wound or respiratory tract is the main cause of death in the late stage of burn.