Peter S. Colley

Propofol versus isoflurane for endoscopic sinus surgery

PURPOSE A previous retrospective study reported that propofol anesthesia decreased bleeding during endoscopic sinus surgery compared with isoflurane. We performed a prospective study to compare the effects of propofol versus isoflurane on measured blood loss and the surgeons subjective assessment of operating conditions during endoscopic sinus surgery. PATIENTS AND METHODS After receiving institutional review board approval and written informed consent, 56 patients undergoing endoscopic sinus surgery were randomly assigned to receive propofol (n = 30) or isoflurane (n = 26) supplemented with nitrous oxide-oxygen and alfentanil. Blood loss was calculated from the hemoglobin concentration in suction canisters. One surgeon, who was blinded to the anesthetic agent, performed every procedure and assessed bleeding as follows: 1, no bleeding; 2, modest bleeding; 3, bleeding interfering with operating conditions and cause for an agent switch; and 4, intolerable bleeding requiring a change in surgical plan. Results were compared in the two anesthetic groups using chi-squared test, unpaired t-test, Mann-Whitney Utest, and a permutation test. A P of .05 was considered significant. RESULTS Mean bleeding scores were less over time (P = .02) with propofol anesthesia, particularly in surgery in the ethmoid and sphenoid sinuses (P = .03), and the proportion of patients with a mean score >2 was less in the propofol group (30% v 54%; P = .033). Time until discharge to home or to a limited stay in a hospital bed was also less in the propofol group (183 v 243 minutes; P = .019). CONCLUSION In our study, surgical blood loss was the same for both anesthetic agents overall, but propofol appeared to offer an advantage in terms of subjective improvement in operating conditions, particularly in the ethmoid and sphenoid sinuses.

Sodium nitroprusside increases Qs/Qt in dogs with regional atelectasis.

This study investigated the effects of sodium nitroprusside (SNP) on arterial oxygen tension (PaO2.), pulmonary shunt (Qs/Qt), and pulmonary vascular resistance (PVR) in the presence of atelectasis of one lung. Ten dogs were anesthetized, their tracheas intubatcd with a bronchial divider, and their lungs ventilated with IPPB with pure oxygen. Atelectasis of the left lung was produced by occluding the left side of the bronchial divider and ventilating the right lung. SNP was infused to decrease mean arterial blood pressure by 25 per cent. PaO2 decreased from (mean value ± 1 SD) 134 ± 75 to 77 ± 23 torr (P < 0.05) with SNP infusion. Qs/Qt increased from 30 ± 7.0 to 39 ± 6.0 per cent (P < 0.05), while cardiac output did not change significantly. PVR of the atelectatic lung decreased, while PVR of the ventilated lung was unchanged. The decrease in PVR in the atelectatic lung suggests that SNP decreases PaO2 and increases Qs/Qt by reversing the hypoxic pulmonary vasoconstriction. As a result, during SNP infusion, perfusion of the atelectatic lung was maintained while perfusion of the ventilated lung decreased.

Ventilation-perfusion and gas exchange effects of sodium nitroprusside in dogs with normal and edematous lungs.

This study was designed to investigate the mechanism by which sodium nitroprusside (SNP) decreases oxygenation by determining its effects on venous admixture (&OV0422;VA/&OV0422;t) and ventilation— perfusion distribution (&OV0312;A/&OV0422;) in animals with normal and abnormal lungs. SNP was infused into seven dogs anesthetized with pentobarbital. Mean blood pressure was decreased by 40 per cent during normal lung function and again after the production of diffuse pulmonary edema by intravenous administration of oleic acid. Measurements of blood-gas values, &OV0422;VA/&OV0422;t and &OV0312;A/&OV0422; by the inert-gas-elimination method were taken before, during, and after SNP infusion during ventilation with air and then during ventilation with 100 per cent oxygen in each pulmonary condition. SNP caused no change in cardiac output (&OV0422;t) during normal lung function or after the production of pulmonary edema. SNP had no effect on pulmonary gas exchange during normal lung function. During pulmonary edema and ventilation with air, SNP decreased Pao2 from 71 ± 7 torr (mean ± 1 SD) to 61 ± 11 torr (P<.01), and increased &OV0422;VA/&OV0422;t (oxygen method) from 20 ± 8 to 38 ± 18 per cent (P<.01). The increase in &OV0422;VA/&OV0422;t correlated well with a 28 per cent decrease in pulmonary vascular resistance (PVR) (r =-.863). During pulmonary edema with air and ventilation SNP increased &OV0312;A/&OV0422; maldistribution, but during ventilation with oxygen, SNP caused no significant change in &OV0422;V/&OV0422;t, PVR, or &OV0312;A/&OV0422;. The increase in &OV0422;V/&OV0422;t and increases in perfusion to low &OV0312;A/&OV0422; regions seen only in animals with pulmonary edema during ventilation with air are compatible with the hypothesis that nitroprusside impairs pulmonary gas exchange by inhibiting hypoxic vasoconstriction, thus increasing &OV0312;A/&OV0422; maldistribution.

Bunegin-albin catheter improves air retrieval and resuscitation from lethal venous air embolism in dogs

Three types of catheters, the single-orifice Sorenson CVP kit catheter, the right atrial (RA) port of an American Edwards 7F Swan-Ganz catheter, and the Cook Bunegin-Albin multi-orifice CVP catheter were evaluated for their ability to retrieve venous air emboli and effect on the success rate of resuscitation from venous air emboli. The catheters were inserted in anesthetized dogs in the prone position. Swan-Ganz catheters were positioned with the RA port just above the junction of the superior vena cava (SVC) and the RA, single-orifice Sorensen catheters with the orifice tip located either just above the SVC-RA junction or in the mid-RA, and Bunegin-Albin multiorifice catheters with the proximal orifice just above the SVC-RA junction and the distal orifice near the mid-RA. Dogs were then given a predetermined lethal dose of air (5 ml/kg) over 30 sec via the femoral vein. Attempts to aspirate venous air emboli were begun with first decrease in expired CO2. The amounts of air retrieved and the incidence of successful resuscitation were compared. Significantly greater percentages of injected venous air were retrieved with the Bunegin-Albin catheter (60 ± 7%) than with the Sorenson catheter in the SVC (16 ± 6%), with the Sorenson catheter in the mid-RA (10 ± 3%) or with the Swan-Ganz RA port (4 ± 1%). Resuscitation was significantly more often successful with the Bunegin-Albin catheter (six of nine dogs) than with either Sorenson catheter (zero of seven in both groups) or the Swan-Ganz RA port (one of seven). The Cook Bunegin-Albin multi-orifice catheter appears to be superior to the Sorenson or Swan-Ganz RA port for aspiration of air after venous air embolism.

Cerebral blood flow responses to hypocapnia during hypotension.

Cerebral vascular responses to hypocapnia during hypotension to a mean arterial blood pressure (MAP) = 50 mm Hg induced with sodium nitroprusside (SNP, n = 12) or trimethaphan (TMP, n = 12) were examined in dogs. Cerebral vascular resistance (CVR) and cerebral blood flow (CBF) at PaCO2 = 40 mm Hg, and PaC0; = 20 mm Hg were examined first at normal MAP then at hypotension in six dogs in the SNP group and six dogs in the TMP group. In both the SNP group and the TMP group, CO2responsiveness, as indicated by increased CVR and decreased CBF, was intact at normal MAP, but absent during hypotension. In the remaining 6 of 12 dogs in the SNP group and 6 of 12 dogs in the TMP group, CO2responsiveness at MAP = 50 mm Hg was examined without prior determination of CO2 responsiveness at normal MAP. These additional studies were performed to rule out the possibility that absent CO2 respon- siveness during hypotension in the initial groups resulted from (1) physiologic deterioration of the prepara- tion with time, or (2) adaptation of brain extracellular fluid pH to a proceeding period of hypocapnia. Again, during both SNP- or TMP-induced hypotension CO2 responsiveness was absent. Stroke Vol 15, No 5, 1984

Regional blood flow in dogs during halothane anesthesia and controlled hypotension produced by nitroprusside or nitroglycerin

We used the radioactive microsphere method to measure and compare the effects of sodium nitroprusside (SNP) and nitroglycerin (NTG) on organ blood flow during hypotension induced by each drug. The study was done in 10 dogs anesthetized using 0.7% end-tidal halothane. Each animal received both SNP and NTG to decrease the mean arterial blood pressure (MABP) to 45 mm Hg, but the sequence in which the drugs were administered was alternated. Five of the dogs received SNP first and five received NTG first. Organ blood flow was measured after a stable period of hypotension that was brief by necessity in order to avoid cyanide toxicity due to increasing dose requirements for SNP. Measurements were made before and during hypotension induced with each drug. The mean duration of stable hypotension was shorter (P < 0.05) with NTG (5 ± 1 min) (mean ± sem) than with SNP (7 ± 1 min). During NTG-induced hypotension, blood flows to the brain, kidneys, liver, gastrointestinal tract, pancreas, and skeletal muscle were maintained at control levels. During SNP-induced hypotension, blood flows to the myocardium, liver, gastrointestinal tract, pancreas, and skeletal muscle were maintained at control levels. NTG increased myocardial blood flow (P < 0.05), while SNP decreased blood flow to brain (P < 0.05) and kidneys (P < 0.01). Both drugs decreased blood flow to the spleen (P < 0.001). Our results indicate that during the first few minutes of NTG-induced hypotension, blood flows to all organs except the spleen are well-maintained, while the first few minutes of SNP-induced hypotension are associated with decreases in blood flow to brain and kidney as well as to the spleen

Autoregulation of Cerebral Blood Flow during Normocapnia and Hypocapnia in Dogs

The effect of hypocapnia on autoregulation of cerebral blood flow (CBF) and the lower limit of autoregulation (LLA) was determined in dogs anesthetized with nitrous oxide (66%) and halothane (0.2%, end-expired concentration). CBF and cerebral vascular resistance (CVR) were determined during both normocapnia and hypocapnia (PaCO2 21-22 mmHg) at control cerebral perfusion pressure (CPP) and after reducing CPP (by hemorrhage) to 80%, 60%, 50%, and 40% of control. At control CPP hypocapnia decreased CBF from 75 +/- 5 to 48 +/- 3 ml.100 g-1.min-1 (mean +/- SEM, P less than 0.05). During both normocapnia and hypocapnia CVR decreased and CBF did not change as CPP was reduced to 60% of control. When CPP was reduced to 50% or 40% of control, CVR remained decreased and CBF fell sharply. The LLA during hypocapnia, 61 +/- 2% of control CPP, was not different than that during normocapnia, 59 +/- 3% of control CPP. Below the LLA the CBF-CPP slopes differed from zero but did not differ between hypocapnia and normocapnia. Hypocapnia does not produce a substantial shift of the LLA, and over the range of CPP values studied here, autoregulatory cerebral vasodilation only partially abolishes hypocapnia-induced cerebral vasoconstriction. The results suggest that when cerebral autoregulation is intact and in the absence of cerebrovascular disease, hypocapnia does not reduce global CBF to a level that is likely to produce ischemia and remains a useful therapeutic treatment so long as CPP remains above the LLA.

ECG-guided placement of sorenson CVP catheters via arm veins.

The success rate and the time required for placing central venous pressure (CVP) catheters via arm veins and localizing the catheter tip by using the tip as an exploring ECG lead were reported in a recent study by Cucchiara et al. (1). These authors used a 36-in polyethylene (B-D No. 7521) catheter filled with normal saline. Catheters were inserted into an arm vein via a 14-gauge Teflon Jelco needle introduced percutaneously. They reported an overall success rate of 97% with 53% of the catheters placed within 5 min and 92% placed within 15 min. The only other study reporting success rates using this technique is by Jama1 et al. (2). These authors used a Deseret Intracath inserted through a 14or 16-gauge needle placed in an arm vein and used a wire stylet for conducting ECG signals. They reported an overall success rate of 94% for intrathoracic catheter tip localization. In this latter study, however, subclavian veins were also used in an unspecified number of patients and the authors did not report how long it took them to carry out the procedure. The success rates reported by Cucchiara et al. (1) and Jamal et al. (2), did not appear to correspond with our success rate with the procedure. We, however, use a Sorenson CVP kit catheter, which might account for the perceived difference in success rate. Accordingly, we prospectively evaluated the technique as employed at our institution. We determined our success rate and analyzed factors contributing to failed attempts. We also measured the time required for the procedure and evaluated the ability of different conductive solutions to provide a usable ECG tracing.

Pulmonary Gas Exchange Effects of Nitroglycerin in Canine Edematous Lungs

The authors determined the effects of nitroglycerin on pulmonary gas exchange in 11 anesthetized dogs with diffuse pulmonary edema induced by oleic acid injury. Measurements of venous admixture (&OV0422;VA/&OV0422;t) and shunt (&OV0422;s/&OV0422;1) using both oxygen and inert-gas-elimination methods were done before, during, and after nitroglycerin infusion, first during air ventilation and then during ventilation with 100 per cent oxygen. Nitroglycerin reduced mean blood pressure (MAP) approximately 30 per cent (P < 0.01) during both air and oxygen ventilation. During air ventilation, nitroglycerin caused PVR to decrease by 29 per cent (P < 0.01) but caused no change in PVR during oxygen ventilation. Pa01 decreased from 64 ± 8 torr (mean ± SD) to 55 ± 9 torr (P < 0.01) with nitroglycerin infusion during air ventilation. The decrease in Pa01 was primarily due to an increase in QVA/Q3 which increased from 28 ± 12 per cent to 36 ± 14 per cent (oxygen method) (P < 0.05). Similarly, the inert gas QVA/Q3 increased from 31 ± 10 to 37 ± 14 per cent (P < 0.05). During oxygen ventilation, the effect of nitroglycerin on gas exchange was similar in direction but less in magnitude. These results provide evidence that nitroglycerin may cause significant impairment of pulmonary gas exchange when abnormal lung function is present and Fl01 is low. The mechanism is most likely due to inhibition of hypoxic pulmonary vasoconstriction.

The Site of Origin of the Intravascular Electrocardiogram Recorded from Multiorificed Intravascular Catheters

Successful retrieval of venous air emboli via central venous catheters requires accurate placement of the distal tip of the catheter. The distal tip of single-orificed central venous catheters can be precisely located using intravenous electrocardiography (IVECG). However, the site of origin of the IVECG complex with multiorificed central venous catheters is not well known. In this study, the site of origin of the IVECG complex deriving from the wire within a multiorificed Arrow® Antecubital Central Venous Catheterization Kit, the same Arrow® catheter type without wire, and a multiorificed Cook® Bunegin-Albin CVP Kit was determined in ten anesthetized dogs. The IVECG was found to originate from the distal portion of the Arrow® wire whether the distal tip of the wire was within the distal segment of the Arrow® multiorificed catheter, at the tip of the catheter, or protruding several cm from the tip of the catheter. When the Arrow® multiorificed catheter (without wire) was used to determine the IVECG, the mean site of origin of the IVECG was 1.7 ± 1.2 cm (mean ± SD) proximal to the distal catheter tip. When the Cook® multiorificed catheter (without wire) was used to determine the IVECG, the mean site of origin of the IVECG was 2.5 ± 0.6 cm proximal to the distal catheter tip. Knowledge of the site of origin of the IVECG with the Arrow® and Cook® multiorificed catheters should permit the distal tips of these catheters to be placed in locations where efficient retrieval of venous air emboli is likely.