[Nausea and vomiting in the postoperative phase. Expert- and evidence-based recommendations for prophylaxis and therapy]. / Ubelkeit und Erbrechen in der postoperativen Phase. Experten- und evidenzbasierte Empfehlungen zu Prophylaxe und Therapie.

There are no consensus guidelines for the management of postoperative nausea and vomiting (PONV) in German speaking countries. This meeting was intended to develop such guidelines on which individual health care facilities can derive their specific standard operating procedures (SOPs). Anesthesiologists reviewed published literature on key topics which were subsequently discussed during two meetings. It was emphasized that recommendations were based on the best available evidence. The clinical relevance of individual risk factors should be viewed with caution since even well proven risk factors, such as the history of PONV, do not allow the identification of patients at risk for PONV with a satisfactory sensitivity or specificity. A more useful approach is the use of simplified risk scores which consider the presence of several risk factors simultaneously. Most individual antiemetic interventions for the prevention of PONV have comparable efficacy with a relative risk reduction of about 30%. This appears to be true for total intravenous anesthesia (TIVA) as well as for dexamethasone and other antiemetics; assuming a sufficiently high, adequate and equipotent dosage which should be weight-adjusted in children. As the relative risk reduction is context independent and similar between the interventions, the absolute risk reduction of prophylactic interventions is mainly dependent on the patient's individual baseline risk. Prophylaxis is thus rarely warranted in patients at low risk, generally needed in patients with a moderate risk and should include a multimodal approach in patients at high risk for PONV. Therapeutic interventions of PONV should be administered promptly using an antiemetic which has not been used before. The group suggests algorithms where prophylactic interventions are mainly dependent on the patient's risk for PONV. These algorithms should provide evidence-based guidelines allowing the development of SOPs/policies which take local circumstances into account.

Perforation of the left atrium by a chest tube in a patient with cardiomegaly: management of a rare, but life-threatening complication.

Perforation of the heart is a rare, but life-threatening complication of chest tube thoracostomy. We report the very unusual case where right-sided insertion of a Matthys catheter (6 F) due to pleural effusion resulted in a left atrium perforation. Heart injury was immediately considered as a continuous flow of bright red blood emerging through the chest drain. Diagnosis was confirmed by computertomography also revealing a massive cardiomegaly due to pre-existing mitral valve regurgitation. In two consecutive thoracotomies, first the Mathys drain was removed and the heart defect closed and then the mitral valve was replaced by a bio prosthesis. The extent of the cardiomegaly and the position of the left atrium were not detected pre-operatively by chest X-ray or ultrasonic device. Despite a nosocomial pneumonia, the patient fully recovered. This case shows that extreme caution is necessary when inserting chest tubes in patients where thorax imaging by X-ray or ultrasonic device does not provide a clear anatomical site. In order to minimise complications, a blunt puncturing procedure or Seldinger technique should be used and assisted by a Doppler ultrasonic device. Also early imaging by CT and Doppler ultrasonic technique should be attempted. This may reduce incidence of severe complications as in this case.

Patients' willingness to pay for anti-emetic treatment.

BACKGROUND: Post-operative nausea and vomiting (PONV) is a common complication of anaesthesia. This study was conducted in 100 German and 100 Turkish patients scheduled for elective surgery under general anaesthesia to assess the amount patients were willing to pay for an anti-emetic that completely prevented PONV. METHODS: Post-operatively, using Dixon's up and down method, patients completed an interactive computer questionnaire with a random starting point to determine how much of their own money they were willing to pay for a totally effective anti-emetic treatment. RESULTS: On average, participants were willing to pay 65 euro in Germany and 68 euro in Turkey to avoid PONV. However, patients who actually experienced PONV were willing to pay larger amounts: 96 euro in Germany and 99 euro in Turkey. The amount patients were willing to pay was related to female sex, history of motion sickness, non-smoking status and better education. CONCLUSIONS: Despite differences in political and cultural origin, health care system and financial background, the amount patients were willing to pay for an effective anti-emetic was similar in both Germany and Turkey to that reported previously for the USA.

Does the efficacy of supplemental oxygen for the prevention of postoperative nausea and vomiting depend on the measured outcome, observational period or site of surgery?

High intra-operative oxygen concentration reportedly reduces postoperative nausea and vomiting (PONV), but recent data are conflicting. Therefore, we tested whether the effectiveness of supplemental oxygen depends on the endpoint (nausea vs. vomiting), observation interval (early vs. late) or surgical field (abdominal vs. non-abdominal). We randomly assigned 560 adult patients undergoing various elective procedures with a PONV risk of at least 40% to intra-operative 80% (supplemental) or 30% oxygen (control). Potential confounding factors were similar between groups. Incidences of nausea were similar in the groups during early (12% (supplemental) vs. 10% (control), p = 0.43) and late intervals, 26%vs. 20%, p = 0.09, as were the incidences of vomiting (early: 2%vs. 3%, p = 0.40; late: 8%vs. 9%, p = 0.75). Supplemental oxygen was no more effective at reducing PONV in abdominal (40%vs. 31%, p = 0.37) than in non-abdominal surgery (25%vs. 21%, p = 0.368). Thus, supplemental oxygen was unable to reduce PONV independent of the endpoint, observational period or site of surgery.

[Polytrauma with tension pneumothorax with inserted chest tube]. / Polytrauma mit Spannungspneumothorax bei liegender Thoraxdrainage.

The authors report a case of a 25-year-old woman with a polytrauma, caused by a free fall of 12 metres in suicidal intention. Following endotracheal intubation and mechanical ventilation by an emergency physician at the scene, the patient was delivered to the emergency room of an university hospital. An ultrasonic check of the abdomen revealed free fluid in the abdominal cavity, and a rupture of liver and spleen was suspected. Since breath sounds over the right lung were diminished, a chest tube was inserted immediately in the fifth intercostal space in the anterior axillary line. About 300 millilitres of blood were drained by the tube. Shortly thereafter, a laparotomy was performed, where spleen and liver rupture were confirmed and treated. After 60 minutes, the patient developed severe hypotension coupled with ventricular tachycardia and fibrillation, and resuscitation measures had to be initiated. Since breath sounds over the right lung were missing, a tension pneumothorax was suspected and a thoracotomy performed immediately. While huge amounts of air and blood were emerging from the thoracic cavity, a rupture of the right mainstem bronchus as well as of the right pulmonary artery and vena subclavia was identified. The chest tube was found dislocated into the subcutaneous tissue. Despite of open heart compression, application of adrenaline and noradrenaline and substitution of packed red blood cells and of crystalloid and colloid solutions, all resuscitation measures failed so that the patient died shortly after on the operation table. This case illustrates first the difficulties of an adequate thoracic trauma management, particularly, when clinical symptoms are discrete, second the problems of the insertion and control of a chest tube, and third risks associated with wrong position or secondary dislocation which may include - as in our case - "masking" of severe injury patterns and delay of life-saving measures such as an immediate thoracotomy. In order to improve prognosis of patients with poly-/thoracic trauma, establishment of spiral-CT in emergency centres, routine bronchoscopy and safe handling of chest tubes may be helpful.

[Obturator nerve block for transurethral surgery. comparing ropivacaine 0.75 % vs. prilocaine 1 %]. / Vergleich der Motorblockade zwischen Ropivacain 0,75 % und Prilocain 1 % bei der direkten Obturatoriusblockade zur transurethralen Blasentumorresektion -- ein neuer Ansatz zur Bewertung des Motorblocks mit der MRC-Skala.

OBJECTIVE: Obturator nerve block is used for transurethral resection of lateral bladder wall tumors to prevent adductor muscle spasm and associated complications. Therefore, the local anesthetic applied should provide an adequate motor blockade. Ropivacaine 0.75 % was compared to prilocaine 1 % and motor blockade assessment performed by the Medical Research Council (MRC)-scale. METHODS: 40 patients (20 per group) scheduled for transurethral resection were randomized to either receiving 10 ml ropivacaine 0.75 % or prilocaine 1 % for direct obturator nerve block in a controlled user-blinded study. Motor block was assessed with the MRC-scale 5 and 10 minutes after local anesthetic injection followed by an assessment 120 and 180 minutes after surgery. Surgery was performed in equally distributed spinal or general anesthesia, intraoperative adductor spasm intensity was evaluated by surgeon's ranking. RESULTS: Motor blockade intensity was significantly higher with ropivacaine 0.75 % at all time points of assessment. Intraoperatively, severe spasm only occurred in the prilocaine 1 %-group. CONCLUSION: Ropivacaine 0.75 % is a more appropriate agent for direct obturator nerve block than prilocaine 1 %, providing a faster onset and a more intense and longer-lasting motor blockade. This may reduce surgical complications and facilitate early surgical re-intervention. In this study, MRC-scale was appropriate for motor blockade assessment in a peripheral nerve block.

Acute respiratory failure after deep cervical plexus block for carotid endarterectomy as a result of bilateral recurrent laryngeal nerve paralysis.

We report about a case of acute respiratory distress (73-year-old female), which occurred minutes after a deep cervical plexus block (40 ml ropivacaine 0.5%) for carotid endarterectomy (CEA) and required immediate endotracheal intubation of the patient's trachea and consecutive mechanical ventilation. Subsequently, CEA was performed under general anaesthesia (TIVA) with continuous monitoring by somatosensory-evoked potentials. After a period of 14 hours, the endotracheal tube could be removed, the patient being in fair respiratory, cardiocirculatory and neurological conditions. Retrospectively, acute respiratory distress was caused by a combination of ipsilateral plexus blockade-induced and pre-existing asymptomatic contralateral recurrent laryngeal nerve (RLN) paralysis confirmed by a postoperative ENT-check and related to previous thyroid surgery more than 50 years ago. RLN paralysis, often being asymptomatic, represents a typical complication of thyroid and other neck surgery with reported incidences of 0.5-3%. Therefore, a thorough preoperative airway check is advisable in all patients scheduled for a cervical plexus block. Particularly in cases with a history of respiratory disorders or previous neck surgery a vocal cord examination is recommended, and the use of a superficial cervical plexus block may lower the risk of respiratory complications. This may prevent a possibly life-threatening coincidence of ipsilateral plexus blockade-induced and pre-existing asymptomatic contralateral RLN paralysis.

[A factorial trial of six interventions for the prevention of postoperative nausea and vomiting]. / Eine faktorielle Studie von 6 Interventionen zur Vermeidung von Ubelkeit und Erbrechen nach Narkosen Ergebnisse des "International Multicenter Protocol to assess the single and combined benefits of antiemetic strategies in a controlled clinical trial of a 2x2x2x2x2x2 factorial design" (IMPACT).

BACKGROUND: Untreated, one third of patients who undergo surgery will have postoperative nausea and vomiting. Although many trials have been conducted, the relative benefits of prophylactic antiemetic interventions given alone or in combination remain unknown. METHODS: In a randomized, controlled trial of factorial design, 5,199 patients at high risk for postoperative nausea and vomiting were randomly assigned to 1 of 64 possible combinations of 6 prophylactic interventions: 1) 4 mg of ondansetron or no ondansetron; 2) 4 mg of dexamethasone or no dexamethasone; 3) 1.25 mg of droperidol or no droperidol; 4) propofol or a volatile anesthetic; 5) nitrogen or nitrous oxide; 6) remifentanil or fentanyl. The primary aim parameter was nausea and vomiting within 24 h after surgery, which was evaluated blindly. RESULTS: Ondansetron, dexamethasone, and droperidol each reduced the risk of postoperative nausea and vomiting by about 26%, propofol reduced the risk by 19%, and nitrogen by 12%. The risk reduction with both of these agents (i.e., total intravenous anesthesia) was thus similar to that observed with each of the antiemetics alone. All the interventions acted independently of each other and independently of the patients' baseline risk. Consequently, the relative risks associated with the combined interventions could be estimated by multiplying the relative risks associated with each intervention. However, absolute risk reduction was a critical function of patients' baseline risk. CONCLUSIONS: Because antiemetic interventions are similarly effective and act independently, the safest or least expensive should be used first. Prophylaxis is rarely warranted in low-risk patients, moderate-risk patients may benefit from a single intervention, and multiple interventions should be reserved for high-risk patients.

[Twist-guided thread control: a technique for faster and atraumatic continuous sutures]. / Fortlaufende Nähte mit Fadendrill -- Eine Zeit sparende und schonende Operationstechnik.

A simple technique by twisting the thread in clockwise or counter clockwise direction before tightening the suture can help to produce a regular vascular suture line. In a blinded experiment with 60 vascular anastomosis it was proved that the time needed for suture can be reduced by 15%, and that traumatic touch with surgical instruments can be diminished by 63%.

[Anaphylactic cardiocirculatory failure after intraoperative application of dipyrone]. / Anaphylaktisches Herz-Kreislauf-Versagen nach intraoperativer Metamizolapplikation.

CASE REPORT: In our case, a 48-year-old healthy woman undergoing elective tympanoplasty under general anesthesia received an infusion of 2 g dipyrone in 100 ml 0.9% sodium chloride solution for pain prophylaxis. After receiving 1 g dipyrone within 5 min, the patient exhibited a cardiocirculatory failure and cyanosis and had to be resuscitated. After 20 min of cardiopulmonary resuscitation and administration of 3mg epinephrine and 2 mg norepinephrine, a stable circulation was reestablished. After exclusion of a fulminant pulmonary embolism and a primary cardiac event by computer tomography, electrocardiogram and enzyme diagnostics, the patient was transferred to an intensive care unit where she was mechanically ventilated for a period of 6 h. After 2 days of intensive monitoring, she was transferred to a peripheral ward,where she exhibited a normal neurological status and stable cardiocirculatory condition. A postoperatively performed allergy testing revealed a type I sensitization to dipyrone, which was responsible for the intraoperative cardiocirculatory failure due to a massive anaphylactic reaction. However, in this case, the typical symptoms of allergic reactions such as erythema, edema or bronchospasm were missing, which did not allow for an immediate diagnosis. CONCLUSION. Regarding the frequent perioperative use of dipyrone and the severity of anaphylaxis observed in this case, it should be considered that this analgesic should be applied intravenously only if adequate safety measures such as emergency therapy option and patient monitoring are guaranteed as recommended by the German drug regulation authority since 1982.

Systemic and microcirculatory effects of autologous whole blood resuscitation in severe hemorrhagic shock.

Systemic and microcirculatory effects of autologous whole blood resuscitation after 4-h hemorrhagic shock with a mean arterial pressure (MAP) level of 40 mmHg were investigated in 63 conscious Syrian golden hamsters. Microcirculation of skeletal skin muscle and subcutaneous connective tissue was visualized in a dorsal skinfold. Shed blood was retransfused within 30 min after 4 h. Animals were grouped into survivors in good (SG) and poor condition (SP) and nonsurvivors (NS) according to 24-h outcome after resuscitation and studied before shock, during shock (60, 120, and 240 min), and 30 min and 24 h after resuscitation. Microvascular and interstitial PO2 values were determined by phosphorescence decay. Shock caused a significant increase of arterial PO2 and decrease of PCO2, pH, and base excess. In the microcirculation, there was a significant decrease in blood flow (QB), functional capillary density (FCD; capillaries with red blood cell flow), and interstitial PO2 [1.8 +/- 0.8 mmHg (SG), 1.3 +/- 1.3 mmHg (SP), and 0.9 +/- 1.1 mmHg (NS) vs. 23.0 +/- 6.1 mmHg at control]. Blood resuscitation caused immediate MAP recompensation in all animals, whereas metabolic acidosis, hyperventilation, and a significant interstitial PO2 decrease (40-60% of control) persisted. In NS (44.4% of the animals), systemic and microcirculatory alterations were significantly more severe both in shock and after resuscitation than in survivors. Whereas in SG (31.8% of the animals) there was only a slight (15-30%) but still significant impairment of microscopic tissue perfusion (QB, FCD) and oxygenation at 24 h, SP (23.8% of the animals) showed severe metabolic acidosis and substantial decreases (>/=50%) of FCD and interstitial PO2. FCD, interstitial PO2, and metabolic state were the main determinants of shock outcome.

Depression of endothelial and smooth muscle cell oxygen consumption by endotoxin.

An optical method based on the oxygen-dependent quenching of a phosphorescent probe (palladium-porphyrin) was used to investigate the effect of bacterial endotoxin [lipopolysaccharide (LPS)] on oxygen consumption (VO2) by vascular cells. Endothelial (EC) and smooth muscle (SMC) cells from pig aorta were suspended in culture medium in the presence of palladium-porphyrin and transferred to glass capillary tubes that were sealed to create a hypoxic environment. Measured PO2 changed as a function of time in a highly predictable fashion when cell suspensions were exposed to agents or treatment known to affect cellular metabolism. Both EC and SMC showed a significant decrease in VO2 as cell density increased, and SMC VO2 was significantly higher than EC (1.94 +/- 0.09 vs. 1.0 +/- 0.15 nmol . min-1 . 10(6) cells-1). Exposure to LPS (1 microg/ml) caused a decrease in VO2 of 46% and 15% for EC and SMC, respectively. Pretreatment of cells with N-acetyl-L-cysteine, a substrate for glutathione synthesis with antioxidant properties, restored VO2 to normal values after exposure to LPS. These data suggest that endotoxin impairs VO2 in cells derived from the vascular wall and indicate the importance of EC and SMC respiration in maintaining vascular homeostasis under conditions of sepsis.

Microvascular and tissue oxygen gradients in the rat mesentery.

One of the most important functions of the blood circulation is O2 delivery to the tissue. This process occurs primarily in microvessels that also regulate blood flow and are the site of many metabolic processes that require O2. We measured the intraluminal and perivascular pO2 in rat mesenteric arterioles in vivo by using noninvasive phosphorescence quenching microscopy. From these measurements, we calculated the rate at which O2 diffuses out of microvessels from the blood. The rate of O2 efflux and the O2 gradients found in the immediate vicinity of arterioles indicate the presence of a large O2 sink at the interface between blood and tissue, a region that includes smooth muscle and endothelium. Mass balance analyses show that the loss of O2 from the arterioles in this vascular bed primarily is caused by O2 consumption in the microvascular wall. The high metabolic rate of the vessel wall relative to parenchymal tissue in the rat mesentery suggests that in addition to serving as a conduit for the delivery of O2 the microvasculature has other functions that require a significant amount of O2.

Subcutaneous microvascular responses to hemodilution with a red cell substitute consisting of polyethyleneglycol-modified vesicles encapsulating hemoglobin.

Phospholipid vesicles encapsulating purified hemoglobin [Hb vesicles (HbV); diameter 259 +/- 82 mm; oxygen affinity 31 mm Hg; [Hb] 5 and 10 g/dL] were developed to provide oxygen-carrying capacity to plasma expanders. Their function as a blood replacement was tested in the subcutaneous microvasculature of awake hamsters during severe hemodilution in which 80% of the red blood cell mass was substituted with suspensions of the vesicles in 5% human serum albumin (HSA) solution. Vesicles were tested with membranes that were unmodified (HbV/HSA) or conjugated with polyethyleneglycol (PEG) on the vesicular surface (PEG-HbV/HSA). The viscosity of 10 g/dL HbV/HSA was 8 cP at 358 s-1 owing to the intervesicular aggregation, while that of 10 g/dL PEG-HbV/HSA was 3.5 cP, since PEG chains inhibit aggregation. Both materials yielded normal mean arterial pressure, heart rate, and blood gas parameters at all levels of exchange, which could not be achieved with HSA alone. Subcutaneous microvascular studies showed that PEG-HbV/HSA significantly improved microhemodynamic conditions (flow rate, functional capillary density, vessel diameter, and oxygen tension) relative to unmodified HbV/HSA. Even though the enhancement of PEG modification did not achieve the functional characteristics of the blood-perfused microcirculation, PEG reduced vesicular aggregation and viscosity, improving microvascular perfusion relative to the unmodified type. These results highlight the significance of microvascular analysis in the design of red cell substitutes and the necessity of surface modification of HbV to prevent aggregation.

Microvascular oxygen delivery and interstitial oxygenation during sodium pentobarbital anesthesia.

BACKGROUND: Anesthesia may represent a considerable bias in experimental medicine, particularly in conditions of stress (such as hemorrhage). Sodium pentobarbital (PB), widely used for cardiovascular investigations, may impair oxygen delivery by hemodynamic and respiratory depression. The critical issue, however, is whether the microcirculation can still maintain tissue oxygenation during anesthesia. To answer this question, the authors studied the effect of PB anesthesia on subcutaneous microvascular oxygen delivery and interstitial oxygenation in Syrian golden hamsters. METHODS: Sodium pentobarbital anesthesia was induced by intravenous injection (30 mg/kg body weight) and maintained by a 15-min infusion (2 mg.kg-1.min-1), with animals breathing spontaneously (PB-S) or ventilated with air (PB-V). Systemic parameters evaluated were mean arterial pressure (MAP), heart rate, cardiac index (CI), arterial oxygen tension (PaO2), arterial carbon dioxide tension (PaCO2), base excess, and pH. Microvascular and interstitial oxygen tension (PO2), vessel diameter, red blood cell velocity (vRBC), and blood flow (Qb) were measured in a dorsal skinfold preparation. Microcirculatory PO2 values were determined by phosphorescence decay. RESULTS: Sodium pentobarbital anesthesia significantly decreased CI, MAP, vRBC, and Qb. During PB infusion, PaO2 values were 56 +/- 12.8 mmHg (PB-S) and 115.9 +/- 14.6 mmHg (PB-V) compared with 69.4 +/- 18.2 mmHg and 61.4 +/- 12.6 mmHg at baseline. However, microvascular PO2 was reduced by 25-55% in both groups, resulting in an interstitial PO2 decrease from 23.9 +/- 5.6 mmHg (control) to 13.1 +/- 9.1 mmHg (PB-S) and 15.2 +/- 7 mmHg (PB-V). Microcirculatory PO2 values were restored 30 min after PB infusion, even though hemodynamic depression and a light anesthetic plane were maintained. CONCLUSIONS: Sodium pentobarbital anesthesia caused impairment of microvascular oxygen delivery and interstitial oxygenation, effects that were not prevented by mechanical ventilation. Although these effects were restricted to deep anesthetic planes, prolonged hemodynamic depression suggests that caution is warranted when using PB as an anesthetic in cardiovascular investigations.

Fluid resuscitation with O2 vs. non-O2 carriers after 2 h of hemorrhagic shock in conscious hamsters.

Efficacy of a cell-free o-raffinose cross-linked and oligomerized hemoglobin (Hemo-link) solution in restoring macro- and microcirculatory conditions after 2 h of hemorrhagic shock (40 mmHg) was compared with conventional treatment with autologous whole blood, Ringer lactate (RL), and Dextran 70. Studies were conducted in the dorsal skinfold microcirculation of conscious hamsters. Initial infusion was equivalent to shed blood volume (SBV) for RL and 50% of SBV for remaining solutions. After 2 h all animals received blood at 50% of SBV. Vessel diameter, functional capillary density, microvascular red blood cell velocity, and flow were measured. Arteriolar, venular, and tissue PO2 were determined by phosphorescence decay. Systemic parameters included mean arterial blood pressure, heart rate, arterial blood gases, pH, and base excess. Autologous whole blood and Hemolink, but not Dextran 70 and RL, restored mean arterial blood pressure, systemic blood gas, and metabolic parameters. Tissue PO2 recovered to 40-50% with blood and Hemolink but remained significantly lower (10-15% of control) with Dextran 70 and RL. Initial volume replacement after shock with blood or Hemolink yields equivalent macro- and microhemodynamic improvements not attainable with non-O2-carrying plasma expanders.

pO2 measurements in arteriolar networks.

Previous studies from our laboratory have shown that the average arteriolar pO2 in the hamster skinfold preparation is lower than arterial systemic pO2. In the present work we tested the hypothesis that there is a longitudinal gradient of pO2 along precapillary vessels. Experiments were performed in Syrian golden hamsters bearing a dorsal skin chamber. The oxygen-dependent quenching of phosphorescence of palladium-porphyrin complexes was used to measure intravascular pO2 in the microcirculation. Arterioles were classified in four orders according to their position in the network, first-order vessels being the entrance points. Simultaneous determinations of diameter (D), red blood cell velocity, and systemic blood gases were also made. There was a significant fall of pO2 between vessels of different orders. First-order arterioles (mean D = 64 microns) had pO2 of 51.8 +/- 9.8 mm Hg (mean +/- SD) which was equivalent to approximately equal to 73% of the arterial systemic pO2. Within the arteriolar network, further decreases of intravascular pO2 were measured, leading to a pO2 of 34.0 +/- 7.9 mm Hg in terminal arterioles (mean D = 7.7 microns). In some vessels pO2 was measured in different positions of the same arteriole. The average longitudinal arteriolar oxygen saturation gradient was 3.4 +/- 0.4 delta %/mm (range 0.8-7.2). A significant and positive correlation was found between pO2 and microhemodynamic parameters when arterioles were grouped according to their order. This relation was not significant for venules which showed a mean pO2 of 30.8 +/- 10.8 mm Hg. Tissue pO2 averaged 24.6 +/- 5.8 mm Hg. We conclude that: (1) There is an oxygen loss in arterial vessels larger than 100 micrograms in diameter, (2) arteriolar pO2 in this preparation depends on the position of the vessel within the network, (3) a substantial portion of oxygen delivery to the hamster skin is provided by the arteriolar network, and (4) only a small pO2 gradient exists between terminal arterioles and venules, suggesting that the contribution of the capillary network to tissue oxygenation is relatively small.

Systemic and subcutaneous microvascular Po2 dissociation during 4-h hemorrhagic shock in conscious hamsters.

The relationship between systemic and microvascular Po2 in subcutaneous connective tissue and hemodynamics was investigated during 4-h hemorrhagic shock (40 mmHg) in conscious Syrian hamsters (n = 66) fitted with a dorsal skinfold window. Systemic blood gases, metabolic parameters, arteriolar, venular, and tissue Po2, microvascular red blood cell velocity, and blood flow were evaluated in survivors (S) and nonsurvivors (NS). Surviving animals were resuscitated with shed blood. Microvascular and tissue Po2 were measured by phosphorescence decay of Pd-meso-tetra (4-carboxyphenyl) porphyrin (30 mg/kg body wt iv). Shock caused a significant dissociation between systemic arterial and microvascular arteriolar Po2 levels. Arterial Po2 increased from 59.7 +/- 12.0 to 110.8 +/- 19.7 mmHg (S) and from 64.0 +/- 13.7 to 128.5 +/- 10.1 mmHg (NS), whereas Po2 in large arterioles decreased from 56.9 +/- 5.5 (control) to 29.5 +/- 20.1 (S) and 6.0 +/- 5.7 mmHg (NS). Correspondingly, tissue Po2 fell from 24.1 +/- 6.8 (control) to 0.9 +/- 0.6 (S) and 0.4 +/- 0.3 mmHg (NS). Venous Po2 decreased from 28.8 +/- 3.7 to 20.4 +/- 4.1 (S) and from 28.0 +/- 2.9 to 16.3 +/- 0.5 mmHg (NS). Shock outcome and tissue oxygenation were predicted by arterial blood gases and metabolic and microcirculatory conditions but not by central venous Po2.

Systemic and subcutaneous microvascular oxygen tension in conscious Syrian golden hamsters.

Arteriolar and venular oxygen tension distribution was studied in the subcutaneous connective tissue of the chamber window preparation in conscious Syrian golden hamsters as a function of the systemic PO2, PCO2, pH, arterial pressure and hematocrit, microvascular red blood cell (RBC) velocity, vessel diameter, and blood flow in the same microvessels. PO2 was measured with the phosphorescence decay technique using Pd-meso-tetra(4-carboxyphenyl)porphyrin (30 mg/kg body wt iv). Systemic arterial and venous PO2s were 71.6 +/- 13.1 and 28.4 +/- 5.1 mmHg, while oxygen tension was 45.1 +/- 13.3 mmHg in arterioles and 30.1 +/- 10.7 mmHg in venules. The relatively low arteriolar PO2 and the small arteriolar-venular PO2 gradient indicate that some blood oxygen exits directly to the tissue or is shunted before reaching the capillaries. RBC velocity was the strongest correlate of microvascular PO2 (arterial correlation coefficient = 0.503 and venous correlation coefficient = 0.560, P < 0.001). Microvascular PO2 was also correlated with blood flow, vessel diameter, blood pH, and PCO2 but not with systemic PO2. Arterial oxygen tension was only significantly related to PCO2, pH, and hematocrit. These findings suggest that oxygen delivery to the tissue improves with increasing blood flow velocity and that microvascular PO2 is a locally regulated parameter in the absence of major systemic perturbations.