Accidental dural puncture,postdural puncture headache,intrathecal catheters,and epidural blood patch: revisiting the old nemesis

One of the controversial management options for accidental dural puncture in pregnant patients is the conversion of labor epidural analgesia to continuous spinal analgesia by threading the epidural catheter intrathecally. No clear consensus exists on how to best prevent severe headache from occurring after accidental dural puncture. To investigate whether the intrathecal placement of an epidural catheter following accidental dural puncture impacts the incidence of postdural puncture headache (PDPH) and the subsequent need for an epidural blood patch in parturients. A retrospective chart review of accidental dural puncture was performed at Hutzel Women’s Hospital in Detroit, MI, USA for the years 2002–2010. Documented cases of accidental dural punctures (N = 238) were distributed into two groups based on their management: an intrathecal catheter (ITC) group in which the epidural catheter was inserted intrathecally and a non-intrathecal catheter (non-ITC) group that received the epidural catheter inserted at different levels of lumbar interspaces. The incidence of PDPH as well as the necessity for epidural blood patch was analyzed using two-tailed Fisher’s exact test. In the non-ITC group, 99 (54 %) parturients developed PDPH in comparison to 20 (37 %) in the ITC [odds ratio (OR), 1.98; 95 % confidence interval (CI), 1.06–3.69; P = 0.03]. Fifty-seven (31 %) of 182 patients in the non-ITC group required an epidural blood patch (EBP) (data for 2 patients of 184 were missing). In contrast, 7 (13 %) of parturients in the ITC group required an EBP. The incidence of EBP was calculated in parturients who actually developed headache to be 57 of 99 (57 %) in the non-ITC group versus 7 of 20 (35 %) in the ITC group (OR, 2.52; 95 % CI, 0.92–6.68; P = 0.07). The insertion of an intrathecal catheter following accidental dural puncture decreases the incidence of PDPH but not the need for epidural blood patch in parturients.     

Decrease in the incidence of post-dural puncture headache: maintaining CSF volume

The incidence of epidural needle-induced post-dural puncture headache (PDPH) in parturients following dural puncture with a large bore (18-gauge) needle has been reported to range 76-85%. We describe seven cases in which the performance of epidural anesthesia in parturients was complicated by an unintentional dural puncture with an 18-gauge epidural needle. In all seven cases, the unintentional dural puncture was followed by (i) injection of the CSF in the glass syringe back into the subarachnoid space through the epidural needle, (ii) insertion of a epidural catheter into the subarachnoid space (now referred to as an intrathecal catheter), (iii) injection of a small amount of preservative free saline (3-5 ml) into the subarachnoid space through the intrathecal catheter, (iv) administration of bolus and then continuous intrathecal labor analgesia through the intrathecal catheter and then (v) leaving the intrathecal catheter in-situ for a total of 12-20 h. PDPH occurred in only one of these cases (14%).     

Efficacy of a prophylactic epidural blood patch in preventing post dural puncture headache in parturients after inadvertent dural puncture

BACKGROUND: Postdural puncture headache (PDPH) occurs in up to 80% of parturients who experience inadvertent dural puncture during epidural catheter placement. The authors performed a randomized double blind study to assess the effect of prophylactic epidural blood patch on the incidence of PDPH and the need for therapeutic epidural blood patch. METHODS: Sixty-four parturients who incurred inadvertent dural puncture were randomized to receive a prophylactic epidural blood patch with 20 ml autologous blood (prophylactic epidural blood patch group) or a sham patch (sham group). Subjects were evaluated daily for development of PDPH for a minimum of 5 days after dural puncture. Those who developed a PDPH were followed daily for a minimum of 3 days after resolution of the headache. Subjects with moderate headaches who reported difficulties performing childcare activities and all those with severe headaches were advised to receive a therapeutic epidural blood patch. RESULTS: Eighteen of 32 subjects in each group (56%) developed PDPH. Therapeutic blood patch was recommended in similar numbers of patients in each group. The groups had similar onset time of PDPH, median peak pain scores, and number of days spent unable to perform childcare activities as a result of postural headache. The median duration of PDPH, however, was shorter in the prophylactic epidural blood patch group. CONCLUSIONS: A decrease in the incidence of PDPH or the need for criteria-directed therapeutic epidural patch was not detected when a prophylactic epidural blood patch was administered to parturients after inadvertent dural puncture. However, prophylactic epidural blood patch did shorten the duration of PDPH symptoms.     

Efficacy of a Prophylactic Epidural Blood Patch in Preventing Post Dural Puncture Headache in Parturients after Inadvertent Dural Puncture

Background: Postdural puncture headache (PDPH) occurs in up to 80% of parturients who experience inadvertent dural puncture during epidural catheter placement. The authors performed a randomized double blind study to assess the effect of prophylactic epidural blood patch on the incidence of PDPH and the need for therapeutic epidural blood patch.

Methods: Sixty-four parturients who incurred inadvertent dural puncture were randomized to receive a prophylactic epidural blood patch with 20 ml autologous blood (prophylactic epidural blood patch group) or a sham patch (sham group). Subjects were evaluated daily for development of PDPH for a minimum of 5 days after dural puncture. Those who developed a PDPH were followed daily for a minimum of 3 days after resolution of the headache. Subjects with moderate headaches who reported difficulties performing childcare activities and all those with severe headaches were advised to receive a therapeutic epidural blood patch.

Results: Eighteen of 32 subjects in each group (56%) developed PDPH. Therapeutic blood patch was recommended in similar numbers of patients in each group. The groups had similar onset time of PDPH, median peak pain scores, and number of days spent unable to perform childcare activities as a result of postural headache. The median duration of PDPH, however, was shorter in the prophylactic epidural blood patch group.     

Management of postdural puncture headache

Postdural puncture headache (PDPH), a complication of regional anesthesia, is not infrequently seen in parturients because of their inherent risk from young age and female gender. With spinal anesthesia, the risk of PDPH is mainly dependent on the size and type of needle and can be reduced with the use of small-gauge, pencilpoint spinal needles. For unintentional dural puncture with epidural needles, a prophylactic epidural blood patch can reduce the risk of PDPH. Other potentially efficacious maneuvers include insertion of an intrathecal catheter and avoidance of second- stage pushing. Treatment of PDPH includes the use of caffeine or an epidural blood patch. Other pharmacologic interventions (eg, theophylline, sumatriptan, adrenocorticotropic hormone) and epidural administration of saline or dextran 40 await further investigation. The evidence for these interventions is discussed in this review. Copyright © 2001 by W.B. Saunders Company     

Decreased incidence of headache after accidental dural puncture in caesarean delivery patients receiving continuous postoperative intrathecal analgesia

To examine the effects of prolonged (> 24 h) intrathecal catheterization with the use of postoperative analgesia on the incidence of post–dural puncture headache (PDPH), charts of 45 obstetric patients who had accidental dural puncture following attempts at epidural block were reviewed retrospectively. Three groups were identified: Group I (n = 15) patients had a dural puncture on the first attempt at epidural block, but successful epidural block on a repeated attempt; Group II (n=17) patients had a dural puncture with immediate conversion to continuous spinal anaesthesia with catheterization lasting only for the duration of caesarean delivery; Group III (n= 13) patients had an immediate conversion to spinal anaesthesia and received post–caesarean section continuous intrathecal patient–controlled analgesia consisting of fentanyl 5 (ig'ml^-1 with bupivacaine 0.25 mg·ml^-1 and epinephrine 2 μg·ml^-1 with catheterization lasting >24 h. No parturient in group III developed a PDPH. This was substantially lower ( P < 0.009) than the 33% incidence for group I and the 47% incidence for group II. The incidence of a PDPH did not differ between group I and II. Similarly, there was no difference between group I and II with regard to requests for a blood patch. Patients receiving continuous intrathecal analgesia had excellent pain relief, could easily ambulate and none complained of pruritus, nausea, vomiting, sensory loss or weakness. In conclusion, indwelling spinal catheterization > 24 h with continuous intrathecal analgesia following accidental dural puncture in parturients may for some patients be a suitable method for providing PDPH prophylaxis and postoperative analgesia.     

Subarachnoid catheter placement after wet tap for analgesia in labor: influence on the risk of headache in obstetric patients

BACKGROUND AND OBJECTIVES: The incidence of postdural puncture headache (PDPH) after epidural wet tap for obstetric patients may be as high as 75%. We have studied how subsequent placement of a subarachnoid catheter immediately after confirmation of a wet tap, and leaving the catheter in place for 24 hours affects the incidence of PDPH. METHODS: Over a 5-year interval, 115 consecutive patients who had unintentional dural puncture were divided into 3 groups by consecutive assignment. Group A had an epidural catheter placed at another interspace. Group B had a subarachnoid catheter placed for labor analgesia that was removed immediately after delivery. Group C had a subarachnoid catheter that was left in place for 24 hours after delivery. Data were collected retrospectively. The incidence of PDPH and blood patch was compared between groups. RESULTS: The overall incidence of PDPH was 46.9% and need for blood patch 36.5%, significantly less in both subarachnoid catheter groups, 31% in B and 3% in group C, compared with group A (PDPH 81%) (P <.001). CONCLUSION: Subarachnoid catheter placement after wet tap in obstetric patients reduces the PDPH rate and does so to a greater extent if left in place for 24 hours after delivery.     

Intrathecal catheterization after unintentional dural puncture during orthopedic surgery

Purpose

We investigated whether inserting an intrathecal catheter and leaving it in place for 24 h after an unintentional dural puncture in orthopedic patients reduced the incidence of post-dural puncture headache (PDPH).

Methods

The study consisted of 427 patients in whom a total of 21 unintentional dural punctures had occurred during orthopedic surgery performed between 2002 and 2006. Seven patients (phase I; evaluated retrospectively) each underwent placement of an epidural catheter at another level after dural puncture during the period January 2002 to February 2004. Fourteen patients (phase II; evaluated prospectively) received an epidural catheter through the dural tear after an unintentional dural puncture during the period February 2004–March 2006

Results

In phase I, 5 of the 7 patients experienced PDPH, and one required an epidural blood patch. In phase II, only one of the 14 patients complained of PDPH, which resolved after 48 h of medical therapy. No patient experienced paresthesia, neurologic or hemorrhagic complication, or infection.

Conclusion

Inserting an epidural catheter through the dural tear following an unintentional dural puncture and leaving it in place for 24 h significantly reduces the incidence of PDPH.     

The effect of epidural needle type on postdural puncture headache: a randomized trial

PURPOSE: A prospective, randomized trial in labouring parturients was undertaken to assess whether the 18G Special Sprotte epidural needle is associated with a lower incidence of accidental dural puncture (ADP) in comparison with the 17G Tuohy needle. A secondary purpose was to determine if the incidence of postdural puncture headache (PDPH ) differed between groups when ADP occurred. METHODS: Following Institutional Review Board approval 1,077 parturients requesting epidural analgesia at three tertiary obstetrical units were randomized to epidural catheter insertion with a 17G Tuohy or 18G Special Sprotte needle. Patients were followed for seven days by a blinded assessor to determine the occurrence of PDPH using standardized criteria. If postural headache or neck ache presented, an ADP was diagnosed even if cerebrospinal fluid (CSF) was not observed at insertion. This subgroup was followed daily to assess headache characteristics and response to blood patch. RESULTS: Six Tuohy group patients, and two patients in the Sprotte group were excluded. One of the six excluded in the Tuohy group had an ADP. Twenty-eight ADPs occurred, nine unrecognized by CSF visualization (1.8% Tuohy, 3.4% Sprotte, P = 0.12). The incidence of unrecognized ADPs was higher in the Sprotte group (40% Sprotte vs 20% Tuohy, P < 0.05). If ADP occurred, the incidence of PDPH was lower in the Sprotte group (100% Tuohy vs 55% Sprotte, P = 0.025). The ease of use, and user satisfaction were higher in the Tuohy group (84 +/- 17.3% Tuohy vs 68.2 +/- 25.3% Sprotte, P < 0.001). CONCLUSION: The incidence of ADP was not reduced with the Special Sprotte epidural needle in comparison with the Tuohy needle, but PDPH after ADP occurred less frequently in the Sprotte group.     

Treatment of post-dural-puncture headache with intravenous cortisone

Postdural puncture headache (PDPH) is the most frequent complication of procedures involving dural penetration for spinal anesthesia or following unintentional dural puncture during attempted epidural anesthesia or analgesia. PDPH causes serious problems for women who have just given birth, as they are unable to give adequate care to their infants. The causes of PDPH are poorly understood and treatments are therefore various and symptomatic; most are empirical and not all are effective. When conservative measures fail, an alternative that may be proposed is the blood patch, an invasive technique which is not without risk and which many patients reject. We report three cases of incapacitating PDPH in women after vaginal or caesarian delivery in which symptoms resolved with intravenous hydrocortisone treatment. Hydrocortisone treatment for PDPH has never been reported in the literature, but given our results, we consider that clinical trials are warranted to establish the efficacy of this treatment and to determine if there is a chance that it might offer an alternative to the blood patch.     

The effect of placement and management of intrathecal catheters following accidental dural puncture on the incidence of postdural puncture headache and severity: a retrospective real-world study

Accidental dural puncture during an attempt to establish labour epidural analgesia can result in postdural puncture headache and long-term debilitating conditions. Epidural blood patch, the gold standard treatment for this headache, is invasive and not always successful. Inserting an intrathecal catheter after accidental dural puncture may prevent postdural puncture headache. We evaluated the effect of intrathecal catheter insertion on the incidence of postdural puncture headache and the need for epidural blood patch and whether duration of intrathecal catheterisation or injection of intrathecal saline affected outcome. Our retrospective study was conducted at two tertiary, university-affiliated medical centres between 2017 and 2022 and included 92,651 epidurals and 550 cases of accidental dural puncture (0.59%); 219 parturients (39.8%) received an intrathecal catheter and 331 (60.2%) a resited epidural. Use of an intrathecal catheter versus resiting the epidural did not decrease the odds of postdural puncture headache, adjusted odds ratio (aOR) (95%CI) 0.91 (0.81–1.01), but was associated with a lower need for epidural blood patch (aOR (95%CI) 0.82 (0.73–0.91), p < 0.001). We found no benefit in leaving in the intrathecal catheter for 24 h postpartum (postdural puncture headache, aOR (95%CI) 1.01 (1.00–1.02), p = 0.015; epidural blood patch, aOR (95%CI) 1.00 (0.99–1.01), p = 0.40). We found an added benefit of injecting intrathecal saline as it decreased the incidence of postdural puncture headache (aOR (95%CI) 0.85 (0.73–0.99), p = 0.04) and the need for epidural blood patch (aOR (95%CI) 0.75 (0.64–0.87), p < 0.001). Our study confirms the benefits of intrathecal catheterisation and provides guidance on how to best manage an intrathecal catheter.     

Post dural puncture headache following combined spinal epidural or epidural anaesthesia in obstetric patients.

A retrospective review of obstetric anaesthesia charts was performed for all parturients receiving regional anaesthesia over a 22-month period. The incidence of headache, post dural puncture headache (PDPH) and various other complications of regional anaesthesia that had been prospectively assessed were noted, as was the anaesthetic technique used (epidural or combined spinal epidural (CSE)). PDPH was rare (0.44%) and occurred with similar frequency in those managed with either epidural or CSE anaesthesia or analgesia. The pencil-point spinal needle gauge (27 or 29) did not influence the incidence of PDPH. Following a CSE technique, the epidural catheter more reliably produced effective analgesia/anaesthesia as compared with a standard epidural technique (1.49% versus 3.18% incidence of replaced catheters respectively). We conclude, based on the results of this retrospective review, that CSE is acceptable with respect to the occurrence of PDPH and that it is possible it is advantageous in relation to the correct placement of the epidural catheter     

Second stage pushing correlates with headache after unintentional dural puncture in parturients

PURPOSE: To determine the association between bearing down, postdural puncture headache (PDPH) and epidural blood patch (EBP) following single 17 gauge unintentional dural puncture (UDP) in parturients. METHODS: The charts of 60 parturients identified with UDP in our institutional database during epidural placement were independently reviewed. Patients were divided into categories based on the anesthetic record: well-documented single punctures; well-documented multiple punctures; catheter-related puncture; unclear category (not clear if more than one puncture occurred or if dural puncture had occurred at all) and no evidence of dural puncture. Patients with single 17 gauge punctures were divided into those who had pushed (Group 1) and those who had not (Group 2). Group 2 patients had undergone Cesarean section before reaching second stage labour. The incidence of PDPH, EBP, and cumulative duration to delivery after UDP were compared between groups. RESULTS: Thirty-three patients with well-documented single punctures were identified: 23 had engaged in active pushing as part of second stage labour (Group 1); 10 had not (Group 2). Seventy-four percent of Group1I developed PDPH compared with 10% in Group 2 (P < 0.002). Fifty-seven percent of Group 1 received an EBP compared with 0% in Group 2 (P < 0.002). Increasing the duration of pushing was associated with an increasing incidence of PDPH; the majority of women who pushed > 30 min developed headache. CONCLUSIONS: An increased incidence of PDPH and EBP after UDP occurs in women bearing down in 2nd stage labour when compared with those who never pushed. There was also an association between the cumulative duration of bearing down and the incidence of PDPH.     

High quality labour analgesia using small gauge epidural needles and catheters

PURPOSE: Inadvertent epidural needle punctures represent the leading cause of severe postdural puncture headache (PDPH) in parturients. Use of small gauge (G) epidural needles for continuous analgesia has received little attention despite possible important reductions in PDPH. We report the first study to examine the feasibility of using small G Tuohy needles and 23 G catheters for labour analgesia. METHODS: Healthy parturients 30 min), recognized dural puncture, PDPH, patient assessment of analgesia within 24 hr of delivery, complications and anesthesiologist satisfaction. RESULTS: Twenty-seven parturients were recruited. Successful blocks were initiated and maintained in 24/27 who rated overall analgesia from good to excellent (19/24 very good to excellent). Three block failures occurred at the initiation phase only (two unilateral, one absent). There was no evidence of catheter kinking after placement. One patient developed PDPH after unrecognized dural puncture which was self-treated with acetaminophen for four days, followed by complete symptom resolution. CONCLUSION: It is feasible to provide high quality labour analgesia using small G epidural needles and catheters. The effect of small G epidural needles on PDPH warrants future study.     

Effect of neuraxial technique after inadvertent dural puncture on obstetric outcomes and anesthetic complications

BackgroundThe aim of this study was to evaluate labor and delivery outcomes in parturients with inadvertent dural puncture managed by either insertion of an intrathecal catheter or a resited epidural catheter.MethodsThis was a retrospective cohort review of 235 parturients who had an inadvertent dural puncture during epidural placement over a six-year period. The primary outcome was the proportion of women with a delayed second stage of labor. Secondary outcomes were the proportion of cesarean deliveries, the proportion of cases resulting in post-dural puncture headache, and the incidence of failed labor analgesia.ResultsBaseline characteristics such as age, body mass index and parity were similar between the two groups. Among the 236 cases of inadvertent dural puncture, 173 women (73%) had an intrathecal catheter placed while 63 women (27%) had the epidural catheter resited. Comparing intrathecal with epidural catheters, there was no observed difference in the proportion of cases of prolonged second stage of labor (13% vs. 16%, P=0.57) and the overall rate of cesarean deliveries (17% vs. 16%, P=0.78). However, we observed a lower rate of post-dural puncture headache in women who had cesarean delivery compared to vaginal delivery (53% vs. 74%, P=0.007). A greater proportion of failed labor analgesia was observed in the intrathecal catheter group (14% vs. 2%, P=0.005).ConclusionThe choice of neuraxial technique following inadvertent dural puncture does not appear to alter the course of labor and delivery. Cesarean delivery decreased the incidence of post-dural puncture headache by 35%. Intrathecal catheters were associated with a higher rate of failed analgesia.     

Prophylactic vs therapeutic blood patch for obstetric patients with accidental dural puncture – a randomised controlled trial

Epidural blood patch is a standard treatment for obstetric patients experiencing a severe post‐dural puncture headache. Patients who sustained an accidental dural puncture during establishment of epidural analgesia during labour or at caesarean delivery were randomly assigned to receive a prophylactic epidural blood patch or conservative treatment with a therapeutic epidural blood patch if required. Eleven of 60 (18.3%) patients in the prophylactic epidural blood patch group developed a post‐dural puncture headache compared with 39 of 49 (79.6%) in the therapeutic epidural blood patch group (p < 0.0001). A blood patch was performed in 36 (73.4%) of patients in the therapeutic group. The number of patients who needed a second blood patch did not differ significantly between the two groups: 6 (10.0%) for prophylactic epidural blood patch and 4 (11.1%) for therapeutic epidural blood patch. We conclude that prophylactic epidural blood patch is an effective method to reduce the development of post‐dural puncture headache in obstetric patients.     

An audit of accidental dural puncture during epidural insertion of a Tuohy needle in obstetric patients

We report a prospective audit of 100 parturients who experienced accidental dural puncture by a Tuohy needle, while attending a tertiary referral obstetric unit during the period 1993-1999. The post dural puncture headache rate was 81% and the diagnosis of dural puncture was delayed until presentation of the headache in 27% of these cases. The incidence of unrecognised dural puncture was not influenced by the technique used for identification of the epidural space. Intraspinal opioid administration after dural puncture was associated with a significant reduction in the incidence of headache (P < 0.04). There was no association between mode of delivery and post dural puncture headache. Deliberate cannulation of the subarachnoid space with an epidural catheter at the time of dural puncture, for continuous spinal analgesia or anaesthesia, did not affect the incidence of post dural puncture headache but was associated with a significantly reduced rate of epidural blood patch (43% versus 80%, P < 0.01). Of those who developed post dural puncture headache, 48% were classified 'severe' and in 49% the headache presented within 24 h of dural puncture. There was a trend to earlier onset of headache (either immediate or within 24 h) when the epidural identification technique was loss-of-resistance to air rather than saline (54% versus 33%, P = 0.07). Twenty-eight percent of those suffering from post dural puncture headache were treated expectantly and 72% received a therapeutic blood patch. Of seven parturients who received sumatriptan, six found it ineffective and five subsequently received a blood patch.     

Post-dural puncture headache in the parturient

Post-dural puncture headache (PDPH) is one of the most common and debilitating complications of neuraxial blockade in the parturient. The obstetric population is at particular risk with up to 80% of women developing symptoms after inadvertent dural puncture during epidural insertion. PDPH typically develops 24–48 hours post-puncture and is classically described as an occipito-frontal headache with postural features. Diagnosis and assessment should include consideration of other potential causes of post-partum headache. At the time of inadvertent dural puncture (IDP) one may insert an intrathecal catheter, re-site the epidural or use alternative analgesia. Initial treatment of a PDPH includes bed rest, adequate hydration and simple analgesics. Epidural blood patch (EBP) remains the gold standard treatment of PDPH.     

Is epidural dexamethasone effective in preventing postdural puncture headache?

BackgroundPostdural puncture headache (PDPH) is one of the common complications of spinal anesthesia; it is observed in 1–40% of cases involving spinal anesthesia. It can cause considerable morbidity and 40% of cases may require invasive treatments such as epidural blood patch. With the exception of invasive treatments such as an epidural blood patch, current standard treatment modalities have not proved efficacious. There had been some research done that indicated successful prophylaxis and/or treatment of PDPH by administration of intravenous steroids. Based on those findings, we hypothesize that a direct injection of corticosteroids to the anesthesia puncture site could increase the amount of corticosteroid that accumulates in the puncture site, and will be more effective in decreasing dural inflammation and incidence of PDPH than that of parenteral steroids. We formulated our study to evaluate the effect of dexamethasone directly injected into spinal anesthesia puncture sites.MethodsA total of 268 patients undergoing spinal anesthesia were randomly allocated into two groups; one group received a prophylactic epidural injection of dexamethasone (2 mL, 8 mg) and the other group received 2 mL of normal saline. The incidence and intensity of PDPH and puncture site backache were each measured at 24 hours, 72 hours, and 7 days after spinal anesthesia. The intensity of the headache was graded according to the meningeal headache index.ResultsThe overall incidence of headache during the 7-day period was 5 patients (3.7%) in the control group and 11 patients (8.2%) in the study group, which is not statistically significant (X² = 2.393 and p = 0.122. The severity of headache also shows no statistical significance (2.2% in cases versus 6% in controls; z = 1.53, p = 0.126). The intensity of headache reported at the 24 hours (z = 0.698; p = 0.485), 72 hours (z = 0.849; p = 0.396), and 7 days (z = 0.008; p = 0.994) was not different. There also was no difference in the incidence of backache in the two groups.ConclusionIn contrast to other studies that showed the efficacy of intravenous dexamethasone in the prevention and treatment of PDPH, our study did not show any significant effect of prophylactic epidural injection of dexamethasone in prevention of PDPH. However regarding the low number of PDPH in routine cases, evaluation of this intervention in groups with a high incidence of PDPH by using of particulate steroids is recommended to confirm these preliminary findings.